Free Essay

Natural Gas

In:

Submitted By sorush
Words 12134
Pages 49
Learning TCP/IP

BY: Nasser-Desperado

TCP/IP ‫ﻣﻮﺿﻮع : ﺁﻣﻮزش‬ Desperado_Nasser@yahoo.com ‫ﺗﺎﻟﻴﻒ و ﮔﺮدﺁورﯼ : ﻧﺎﺻﺮ ﺑﺮﻗﻴﺎن‬ www.nasser-desperado.persiangig.com : ‫ﺳﺎﻳﺖ‬ 1383/6/6 : ‫ﺗﺎرﻳﺦ ﻧﮕﺎرش‬ 1385/9/10 : ‫ﺗﺎرﻳﺦ اﻧﺘﺸﺎر‬

-1-

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﻓﻬﺮﺳﺖ‬
‫ﻧﺤﻮۀ ﺷﺒﮑﻪ ﺑﻨﺪﯼ ﺑﺎ ‪: TCP/IP‬‬
‫ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬وﻻﻳﻪ ﺑﻨﺪﯼ ﭘﺮوﺗﮑﻞ‬ ‫ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬از هﻔﺖ ﻻﻳﮥ زﻳﺮ ﺗﺸﮑﻴﻞ ﻣﯽ ﺷﻮﻧﺪ‬ ‫‪ TCP/IP‬ﭼﮕﻮﻧﻪ ﺑﺮاﯼ اﻧﺘﻘﺎل دادﻩ هﺎ ﺑﺎ ﺳﻴﺴﺘﻢ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮﻧﺪ؟‬ ‫‪TCP/IP‬‬ ‫ﭘﺮوﺗﮑﻞ ﮐﻨﺘﺮل اﻧﺘﻘﺎل ‪TCP‬‬ ‫ﺷﻤﺎرﻩ دروازﻩ هﺎﯼ ‪TCP‬‬ ‫ﺑﻴﺘﻬﺎﯼ ﮐﻨﺘﺮل ‪، TCP‬اﺗﺼﺎل ﺳﻪ راهﻪ و ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر‬ ‫دﻳﮕﺮ زﻣﻴﻨﻪ هﺎﯼ ﻋﻨﻮان‪TCP‬‬ ‫ﭘﺮوﺗﮑﻞ )‪User Datagram Protocol (UDP‬‬ ‫ﺁﻳﺎ ‪ UDP‬اﻳﻤﻨﯽ ﮐﻤﺘﺮﯼ از ‪ TCP‬دارد؟‬ ‫ﭘﺮوﺗﮑﻞ ‪ IP‬و ﭘﺮوﺗﮑﻞ ﭘﻴﻐﺎم ﮐﻨﺘﺮل اﻳﻨﺘﺮﻧﺖ )‪(ICMP‬‬ ‫ﺷﺒﮑﻪ هﺎﯼ ﻧﺎﺣﻴﻪ ﻣﺤﻠﯽ و ﻣﺴﻴﺮﻳﺎب هﺎ‬ ‫ﺁدرﺳﻬﺎﯼ ‪IP‬‬ ‫ﻧﺖ ﻣﺴﮑﻬﺎ‬ ‫ﺗﻘﺴﻴﻢ ﺑﻨﺪﯼ ﺑﺴﺘﻪ ﻧﺮم اﻓﺰارﯼ در ‪ IP‬ﺑﻪ ﺻﻮرت ﻗﻄﻌﺎت ﻣﺴﺎوﯼ‬ ‫اﺟﺰاﯼ دﻳﮕﺮ ﻋﻨﻮان ‪IP‬‬ ‫اﻳﻤﻨﯽ در ‪ IP‬ﻗﺪﻳﻤﯽ‬ ‫‪ICMP‬‬

‫ﻋﻨﺎوﻳﻦ دﻳﮕﺮدرﺳﻄﺢ ﺷﺒﮑﻪ‬
‫ﺗﻌﻴﻴﻦ ﻣﺴﻴﺮ ﺑﺴﺘﻪ هﺎ‬ ‫ﺗﻔﺴﻴﺮ ﺁدرس ﺷﺒﮑﻪ‬ ‫دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ: ﻣﺎﻣﻮران ﮐﻨﺘﺮل ﻧﻘﻞ و اﻧﺘﻘﺎل دادﻩ هﺎ ﺷﺒﮑﻪ و دروازﻩ ﺑﺎﻧﻬﺎ‬ ‫ﻓﻴﻠﺘﺮهﺎﯼ ﻗﺪﻳﻤﯽ ﺑﺴﺘﻪ‬ ‫ﻓﻴﻠﺘﺮهﺎﯼ ﺣﺎﻟﺖ ﭘﺬﻳﺮ ﺑﺴﺘﻪ‬ ‫دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ ﭘﺮوﮐﺴﯽ دار‬ ‫ﮐﺪام ﺗﮑﻨﻮﻟﻮژﯼ ﺑﺮاﯼ ﺳﺎﺧﺖ دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ ﺑﻬﺘﺮ اﺳﺖ؟‬ ‫ﺳﻔﺎرﺷﯽ ﻧﻤﻮدن دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ‬ ‫اﺗﺼﺎل دادﻩ و ﻻﻳﻪ هﺎﯼ ﻓﻴﺰﻳﮑﯽ را ﻓﺮاﻣﻮش ﻧﻨﻤﺎﻳﻴﺪ‬ ‫اﺗﺮﻧﺖ، ﺳﻠﻄﺎن ﺑﺮﻗﺮارﯼ ارﺗﺒﺎط‬ ‫‪ARP ARP ARP‬‬ ‫ﺳﻮﻳﭻ و هﺎب‬ ‫راﻩ ﺣﻞ هﺎﯼ اﻳﻤﻨﯽ ﺷﺒﮑﻪ هﺎ‬ ‫اﻳﻤﻨﯽ ﻻﻳﻪ ‪Application‬‬ ‫)‪Secure Socket Layer (SSL‬‬ ‫اﻳﻤﻨﯽ در ﺳﻄﺢ ‪IPsec-IP‬‬ ‫)‪IPSec Authentication Header (AH‬‬ ‫)‪IPSec Encapsulating Security Payload (ESP‬‬ ‫ﺁﻳﺎ ‪ IPSe‬و 6‪ IPv‬ﻣﺎ را ﻧﺠﺎت ﺧﻮاهﻨﺪ داد؟‬

‫-2-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﻧﺤﻮۀ ﺷﺒﮑﻪ ﺑﻨﺪﯼ ﺑﺎ ‪: TCP/IP‬‬
‫ﺑﺮاﯼ اﻳﻨﮑﻪ ﺑﺪاﻧﻴﺪ هﮑﺮ هﺎ از ﭼﻪ روﺷﻬﺎﻳﯽ ﺑﺮاﯼ ﺣﻤﻠﻪ ﺑﻪ ﺳﻴﺴﺘﻤﻬﺎﯼ ﮐﺎﻣﭙﻴﻮﺗﺮﯼ از ﻃﺮﻳﻖ ﺷﺒﮑﻪ اﺳﺘﻔﺎدﻩ ﻣﯽ‬ ‫ﮐﻨﻨﺪ ﻻزم اﺳﺖ ﺷﻨﺎﺧﺖ ﮐﻠﯽ از ﺑﻴﺸﺘﺮ ﺗﮑﻨﻮﻟﻮژﯼ ﺷﺒﮑـﻪ ﻋﻤﻮﻣﯽ داﺷﺘـﻪ ﺑﺎﺷﻴﺪ. ﭘﺮوﺗﮑﻞ ﮐﻨﺘﺮل اﻧﺘﻘﺎل ﻳﺎ ﭘﺮوﺗﮑﻞ‬ ‫اﻳﻨﺘﺮﻧﺖ )‪ (TCP/IP‬ﻧﺎم ﮐﺎرﺑﺮدﯼ ﻣﻴﺒﺎﺷﺪ ﮐﻪ در ﻣﻮرد ﻳﮑـﺴﺮﯼ ﭘﺮوﺗﮑﻞ هﺎﯼ ارﺗﺒﺎﻃﯽ ﮐـﺎﻣﭙﻴﻮﺗﺮ ﺑﻪ ﮐـﺎﻣﭙﻴﻮﺗﺮ‬ ‫از ﻃﺮﻳﻖ ﺷﺒﮑـﻪ اﺳﺘﻔـﺎدﻩ ﻣﻴﺸﻮد اﻳﻦ ﺑﺤﺚ ﺧﻼﺻـﻪ اﯼ از ﻋﻤﻠﮑﺮدهـﺎﯼ اﺻـﻠﯽ ‪ TCP/IP‬ﻣﯽ ﺑـﺎﺷـﺪ.ﻗﺼـﺪ ﻣﻦ‬ ‫ﺑﻴﺸﺘﺮ ﺗﺤﻠﻴﻞ ‪ TCP/IP‬اﺳﺖ و اﻳﻨﮑـﻪ هـﮑﺮ هﺎ ﭼﮕﻮﻧـﻪ ﻣﯽ ﺗﻮاﻧﻨﺪ اﻳﻦ ﭘﺮوﺗﮑﻞ را از هﻢ ﺟﺪا ﮐﺮدﻩ و در ﺟﻬﺖ‬ ‫اهﺪاف ﺧﻮد اﺳﺘﻔﺎدﻩ ﮐﻨﻨﺪ.‬ ‫ﻳـﮏ ﺳـﻮال: ﭼﺮا در ﻋﻮض اﻳﻨﮑـﻪ ﭘﺮوﺗﮑﻞ ﻧﺴﺒﺘﺎ ﺧﻮب دﻳﮕﺮ و ﭘﺮوﺗﮑﻞ هﺎﻳﯽ ﮐﻪ ﺑﻪ ﻃﻮر ﮔﺴﺘﺮدﻩ اﺳﺘﻔﺎدﻩ‬ ‫ﻣﻴﺸﻮﻧﺪ ‪ TCP/IP‬را ﻣﻮرد ﺗﺤﻠﻴﻞ ﻓﺮار ﻣﻴﺪهﻴﻢ؟‬ ‫ﺟﻮاب : ‪ TCP/IP‬ﭘﺮوﺗﮑﻠﻬﺎﻳﯽ ﻣﻴﺒﺎﺷﺪ ﮐﻪ ﺑﻪ ﻃﻮر ﻣﺘﺪاول در دﻧﻴﺎ ﻣﻮرد اﺳﺘﻔﺎدﻩ ﻗﺮار ﻣﯽ ﮔﻴﺮد.‬

‫ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬وﻻﻳﻪ ﺑﻨﺪﯼ ﭘﺮوﺗﮑﻞ :‬
‫در ﺳﺎل 0981 ﺳﺎزﻣﺎن ﺑﻴﻦ اﻟﻤﻠﻠﯽ اﺳﺘﺎﻧﺪارد )‪ (ISO‬ﭘﻴﺸﻨﻬﺎدﯼ ﺑﺮاﯼ ارﺗﺒﺎﻃﺎت ﺑﺮﻧﺎﻣﻪ اﯼ ﻣﻨﺘﺸﺮ ﮐﺮد ﮐﻪ ﻣ ﺪل‬ ‫ﻣﺮﺟﻊ )‪ (OSI‬ﻧﺎﻣﻴﺪﻩ ﺷﺪ.اﻳﻦ ﻣﺪل ﺑﺮ اﺳﺎس ﻻﻳﻪ ﺑﻨﺪﯼ ﭘﺮوﺗﮑﻠﯽ ﻗﺮار داﺷﺖ.ﻳﻌﻨﯽ وﻗﺘﯽ دو ﮐﺎﻣﭙﻴﻮﺗﺮ ﺑﺎ ﻳﮑﺪﻳﮕﺮ‬ ‫ارﺗﺒﺎط ﺑﺮﻗ ﺮار ﻣﻴﮑﻨﻨ ﺪ ﻳﮑ ﺴﺮﯼ ﻣ ﺪﻟﻬﺎﯼ ﻧ ﺮم اﻓ ﺰارﯼ ﮐﻮﭼ ﮏ ﺑ ﺮ روﯼ ه ﺮ ﺳﻴ ﺴﺘﻢ،ﻣﺠﻤﻮﻋـﻪ اﯼ از وﻇ ﺎﻳﻒ را‬ ‫اﻧﺠﺎم ﻣﯽ دهـﺪ ﺗﺎ ارﺗﺒﺎط ﺷﮑـﻞ ﮔﻴﺮد.ﻳﮏ ﻣﺪول اﻃﻤﻴﻨﺎن ﻣﯽ دهﺪ ﮐﻪ‬ ‫دادﻩ هﺎ ﺑﻪ ﻃﻮر ﻣﻨﺎﺳﺐ ﻓﺮﻣﺖ ﺷﺪﻩ اﻧﺪ،ﻣﺪل دﻳﮕﺮ ﻣﺮاﻗﺐ اﻧﺘﻘﺎل دوﺑﺎرۀ ﺑ ﺴﺘﻪ ه ﺎﯼ ﻧ ﺮم اﻓ ﺰارﯼ از دﺳ ﺖ رﻓﺘ ﻪ‬ ‫ﻣﯽ ﺑﺎﺷﻨﺪ وﻣﺪل دﻳﮕﺮﯼ ﺑﺴﺘﻪ هﺎ را از ﮐﺎرﺗﯽ ﺑﻪ ﮐﺎرت دﻳﮕﺮ از ﻃﺮﻳﻖ اﻳﻨﺘﺮﻧ ﺖ اﻧﺘﻘ ﺎل ﻣ ﯽ ده ﺪ.ه ﺮ ﻳ ﮏ از اﻳ ﻦ‬ ‫ﻣﺪﻟﻬﺎ )ﺑﺎ ﻧﺎم ﻻﻳﻪ( وﻇﻴﻔﻪ ﺗﻌﺮﻳﻒ ﺷﺪۀ ﮐ ﻮﭼﮑﯽ در ﻗﺒ ﺎل ﺑﺮﻗ ﺮارﯼ ارﺗﺒ ﺎط دارﻧ ﺪ.ﻣ ﺪوﻟﻬﺎﯼ ارﺗﺒ ﺎﻃﯽ ﮐ ﻪ در ﮐﻨ ﺎر‬ ‫ﻳﮑﺪﻳﮕﺮ ﻗﺮار ﻣﻴﮕﻴﺮﻧﺪ ﺗﻮدۀ ﭘﺮوﺗﮑﻠﯽ ﻧﺎم ﻣﯽ ﮔﻴﺮﻧﺪﮐﻪ ﺣﺎوﯼ ﺷﺎﺧﻪ اﯼ از اﻳﻦ ﻻﻳـﻪ هﺎ )ﻳﮑﯽ در ﺑﺎﻻﯼ دﻳﮕ ﺮﯼ(‬ ‫ﻣﯽ ﺑـﺎﺷﺪ.ﻣﺪل ‪ OSI‬داراﯼ هﻔﺖ ﻻﻳﻪ از ﭼﻨﻴﻦ ﻻﻳ ـﻪ ه ﺎﻳﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ ﮐ ﮥﻩ ه ﺮ ﻳ ﮏ ﻧﻘ ﺶ ﺗﻌﺮﻳ ﻒ ﺷ ﺪﻩ اﯼ در‬ ‫ﻓﺮاﻳﻨﺪ ﻧﻘﻞ و اﻧﺘﻘﺎل دادﻩ هﺎ از ﻃﺮﻳﻖ اﻳﻨﺘﺮﻧﺖ دارﻧﺪ.‬

‫ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬از هﻔﺖ ﻻﻳﮥ زﻳﺮ ﺗﺸﮑﻴﻞ ﻣﯽ ﺷﻮﻧﺪ :‬
‫ﻻﻳـﮥ1، ﻻﻳﻪ ﻓﻴﺰﻳﮑﯽ،اﻳﻦ ﻻﻳﻪ در واﻗﻊ ﺑﻴﺖ هﺎ را از ﻃﺮﻳﻖ اﺗﺼﺎل ﻓﻴﺰﻳﮑﯽ ﻣﻨﺘﻘﻞ ﻣﯽ ﻧﻤﺎﻳﺪ ﮐﻪ ﻣﯽ ﺗﻮاﻧﺪ ﮐﺎﺑﻞ‬ ‫ﻣﺴﯽ ،ﻓﻴﺒﺮ ﻧﻮرﯼ،اﺗﺼﺎل رادﻳﻮﺋﯽ ﻳﺎ هﺮ ﻣﺤﻴﻂ ﻓﻴﺰﻳﮑﯽ دﻳﮕﺮ ﺑﺎﺷﺪ.‬ ‫ﻻﻳـﻪ 2 ،ﻻﻳﻪ اﺗﺼﺎل دادﻩ هﺎ ،اﻳﻦ ﻻﻳﻪ دادﻩ هﺎ از ﻃﺮﻳﻖ ﮐﻠﻴﺪ ﻣﺮﮐﺰﯼ ﺷﺒﮑﻪ دادﻩ هﺎ ﻣﻨﺘﻘﻞ ﻣﯽ ﻧﻤﺎﻳﺪ.‬ ‫ﻻﻳـﻪ 3 ، ﻻﻳﻪ ﺷﺒﮑﻪ، اﻳﻦ ﻻﻳﻪ ﻣﺴﺌﻮل ﺟﺎ ﺑﺠﺎﻳﯽ دادﻩ هﺎ از ﻃﺮﻳﻖ ﺷﺎﺧﻪ اﯼ از ﻣﺴﻴﺮﻳﺎﺑﻬﺎ ﺑﻪ دﺳﺘﮕﺎﻩ ﻣﻘﺼﺪ،و‬ ‫در ﻃﻮل ﺷﺒﮑﻪ ﻣﯽ ﺑﺎﺷﺪ.‬ ‫ﻻﻳـﻪ 4 ، ﻻﻳﻪ اﻧﺘﻘﺎل ،اﻳﻦ ﻻﻳـﻪ ﺑﺮاﯼ ﻓﺮاهﻢ ﺁورﯼ ﺟﺮﻳﺎن ارﺗﺒﺎﻃﺎت ﻣﻨﻄﻘﯽ ﺑﻴﻦ دو ﺳﻴﺴﺘﻢ اﺳﺘﻔـﺎدﻩ ﻣﯽ ﺷﻮد،ﮐـﻪ‬ ‫ذاﺗﺎ ﺷﺎﻣﻞ ﺑﺴﺘـﻪ هﺎﻳﯽ ﻣﯽ ﺷﻮﻧﺪ ﮐﻪ در ﺣﻴﻦ اﻧﺘﻘﺎل درﺳﺖ ﻣﻨﺘﻘﻞ ﻧﺸﺪﻩ اﻧﺪ و ﺑﺎﻳﺪ دوﺑﺎرﻩ ﻣﻨﺘﻞ ﺷﻮﻧﺪ،ﺑﺴﺘﻪ هﺎ را‬ ‫ً‬ ‫در ﻣﺮﺗﺒﻪ ﻣﻨﺎﺳﺐ ﻗﺮار ﻣﯽ دهﺪ و ﮐﻨﺘﺮل ﺧﻄﺎ را ﻓﺮاهﻢ ﻣﯽ ﺳﺎزد.‬ ‫ﻻﻳـﻪ 5 ، ﻻﻳﻪ دورﻩ ﮐﺎر،اﻳﻦ ﻻﻳﻪ ﺑﺎ دورﻩ هﺎﯼ ﮐﺎر ﺑﻴﻦ دﺳﺘﮕﺎهﻬﺎﯼ ارﺗﺒﺎﻃﯽ هﻤﺎهﻨﮕﯽ ﺑﺮﻗﺮار ﻣﻴﻨﻤﺎﻳﺪ و ﺑﻪ‬ ‫ﺁﻏﺎز ﺑﻪ ﮐﺎر ﺁﻧﻬﺎ ،ﻧﮕﻬﺪارﯼ‬ ‫و ﺑﺮﻧﺎﻣﻪ رﺑﺰﻳﺸﺎن ﮐﻤﮏ ﻣﯽ ﻧﻤﺎﻳﺪ.‬ ‫ﻻﻳـﻪ 6 ، ﻻﻳﻪ ﻧﻤﻮﻧﻪ ﺳﺎزﯼ،اﻳﻦ ﻻﻳﻪ ﺑﺎ روﺷﯽ ﺳﺮ وﮐﺎر دارد ﮐﻪ در ﺁن اﺟﺰاﯼ دادﻩ هﺎ ﺑﺮاﯼ اﻧﺘﻘﺎل ﻧﻤﻮدار‬ ‫ﺧﻮاهﻨﺪ ﺷﺪ.ﻣﺜﻞ ﻣﺮﺗﺒﻪ ﻋﺪدﯼ ﺑﻴﺖ هﺎ،ﺑﺎﻳﺖ هﺎ،ﻓﺮﻣﺖ اﻋﺪاد ﺷﻨﺎور و ﻏﻴﺮﻩ.‬ ‫ﻻﻳـﻪ 7 ، ﻻﻳﻪ ﻧﺮم اﻓﺰار ﮐـﺎر ﺑﺮدﯼ، اﻳﻦ ﻻﻳـﻪ ﺑـﻪ ﺻﻮرت ﭘﻨﺠﺮﻩ اﯼ ﻧﺴﺒﺖ ﺑـﻪ ﮐﺎﻧﺎل ارﺗﺒﺎﻃﺎت ﺑـﺮاﯼ ﺧﻮد ﻧﺮم‬ ‫اﻓﺰارهﺎﯼ ﮐـﺎرﺑـﺮدﯼ ﺑﺎ ﺗﻔﺴﻴﺮ دادﻩ هﺎ و ﺗﻐﻴﻴﺮ ﺁﻧﻬﺎ ﺑﻪ اﻃﻼﻋﺎت ﺧﻮاﻧﺎ ﺑﺮاﯼ ﻧﺮم اﻓﺰارهﺎﯼ ﮐﺎرﺑﺮدﯼ ﻋﻤﻞ ﻣﯽ‬ ‫ﻧﻤﺎﻳﺪ.‬

‫‪ TCP/IP‬ﭼﮕﻮﻧﻪ ﺑﺮاﯼ اﻧﺘﻘﺎل دادﻩ هﺎ ﺑﺎ ﺳﻴﺴﺘﻢ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮﻧﺪ؟‬
‫در ﺣﺎﻟﯽ ﮐﻪ ﺑﺴﻴﺎرﯼ از ﻣﻌﻴﺎر هﺎﯼ ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬در ﭘﺮوﺗﮑﻞ ﺷﺒﮑﻪ اﯼ ﺑﻪ ﮐﺎر ﻣﯽ روﻧﺪ،اﻣﺎ ﭘﺮوﺗﮑﻞ ﺧﺎﺻﯽ‬ ‫را در ﻣﻮرد ﺗﺠﺰﻳﻪ و ﺗﺤﻠﻴﻞ ﻗﺮار ﻣﯽ دهﻴﻢ ﮐـﻪ ‪ TCP/IP‬ﻣﯽ ﺑﺎﺷﺪ.‪ TCP/IP‬ﺑﻪ ﺷﺪت ﺑﻪ اﻧﺘﻬﺎﯼ ﭼﻬﺎر ﻻﻳـﻪ‬ ‫ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬وﺻﻞ ﻣﯽ ﺷﻮد و هﺮ ﻣﻮردﯼ ﮐﻪ ﺑﺎﻻﯼ ‪ TCP/IP‬ﻣﯽ ﺑﺎﺷﺪ ﺑﻪ ﺻﻮرت ﺑﺮﻧﺎﻣﻪ ﮐﺎرﺑﺮدﯼ دﻳﺪﻩ‬ ‫ﻣﯽ ﺷﻮد،ﺑﻨﺎﺑﺮاﻳﻦ ﻻﻳـﻪ هﺎﯼ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ،ﻧﻤﻮدار ﺳﺎزﯼ و دورﻩ ﮐﺎرﯼ ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬وﺻﻞ ﻣﯽ ﺷﻮد‬ ‫و هﺮ ﻣﻮردﯼ ﮐﻪ ﺑﺎﻻﯼ ‪ TCP/IP‬ﻣﻴﺒﺎﺷﺪ ﺑﻪ ﺻﻮرت ﺑﺮﻧﺎﻣﻪ ﮐﺎرﺑﺮدﯼ دﻳﺪﻩ ﻣﯽ ﺷﻮﻧﺪ،ﺑﻨﺎﺑﺮاﻳﻦ ﻻﺑـﻪ هﺎﯼ ﻧﺮم‬ ‫اﻓﺰار ﮐـﺎرﺑﺮدﯼ ،ﻧﻤﻮدارﺳﺎزﯼ و دورﻩ ﮐﺎرﯼ ﻣﺪل ﻣﺮﺟﻊ ‪ OSI‬ﺗﻤﺎﻣﺎ در ﭘﺮوﻧﺪﻩ هـﺎﯼ ﺑﺮﻧﺎﻣـﻪ ﮐـﺎرﺑﺮدﯼ ﺟﺎﯼ‬

‫-3-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﻣﯽ ﮔﻴﺮد.‪ TCP/IP‬روﯼ اﻧﺘﻘﺎل دادﻩ هــﺎ از ﺁن ﻧﺮم اﻓﺰار ﮐـﺎر ﺑﺮدﯼ ﻣﺘﻤﺮﮐـﺰ ﻣﯽ ﺑـﺎﺷﺪ.از ﻧﻘﻄـﻪ ﻧﻈﺮ‬ ‫‪ TCP/IP‬ﻻﻳـﻪ هــﺎﯼ زﻳﺮ ﺑﺮاﯼ ارﺗﺒﺎط اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮﻧﺪ.‬ ‫ﻻﻳﻪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ: اﻳﻦ ﻻﻳﻪ ﺧﻮدش ‪ TCP/IP‬ﻧﻤﯽ ﺑﺎﺷﺪ واز ﺑﺮﻧﺎﻣﻪ هﺎﯼ ﺧﺎﺻ ﯽ ﺳ ﺎﺧﺘﻪ ﺷ ﺪﻩ اﺳ ﺖ واز‬ ‫ﻃﺮﻳﻖ ﺷ ﺒﮑﻪ ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از ‪ TCP/IP‬ارﺗﺒ ﺎط ﺷ ﮑﻞ ﻣ ﯽ ده ﺪ.ﻣ ﺪول ارﺗﺒ ﺎﻃﯽ در اﻳ ﻦ ﻻﻳ ـﻪ ﻣﻤﮑ ﻦ اﺳ ﺖ ﺷ ﺎﻣﻞ‬ ‫ﻣﺮورﮔﺮ وب،ﺳﺮوﻳﺲ دهﻨﺪﻩ وب،دو ﺳﺮوﻳﺲ ﻣﺮﺳﻮﻟـﻪ ﭘﺴﺘﯽ ،ﺳﺮوﻳﺲ دهﻨﺪﻩ وﺳﺮوﻳﺲ ﮔﻴﺮﻧﺪﻩ ﺗﻠﻨﺖ،ﺳ ﻮﻳﺲ‬ ‫دهﻨﺪﻩ وﺳﺮوﻳﺲ ﮔﻴﺮﻧﺪﻩ ‪ FTP‬ﻳﺎ ﻧﺮم اﻓﺰارهﺎﯼ ﮐﺎرﺑﺮدﯼ دﻳﮕﺮ ﻣﯽ ﺑﺎﺷﺪ.‬ ‫ﻻﻳﻪ اﻧﺘﻘﺎل : اﻳﻦ ﻻﻳﻪ ﺷﺎﻣﻞ ﭘﺮوﺗﮑﻞ ﮐﻨﺘﺮل اﻧﺘﻘﺎل ‪ TCP‬و ﻣﺸﺎﺑﻪ ﺁن،ﭘﺮوﺗﮑﻞ دﻳ ﺎﮔﺮام ﮐ ﺎرﺑﺮ)‪، (UDP‬ﭘﺮوﺗﮑ ﻞ‬ ‫ﺳﺎدﻩ اﯼ ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ ﺑﺎ در اداﻣﻪ ﺑﺎ ﺟﺰﺋﻴﺎت ﺑﻴﺸﺘﺮﯼ ﺁن را ﺗﻮﺿﻴﺢ ﺧﻮاهﻢ داد.اﻳﻦ ﻻﻳ ـﻪ ﺗ ﻀﻤﻴﻦ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ـﻪ‬ ‫ﮐﻠﻴـﻪ ﺑﺴﺘـﻪ هﺎ ﺑﻪ ﻣﮑﺎن ﻣﻨﺎﺳﺒﯽ در دﺳﺘﮕﺎﻩ ﻣﻘﺼﺪ ارﺳﺎل ﻣﯽ ﺷﻮﻧﺪ و ﻧﻴﺰ ﻣﯽ ﺗﻮاﻧﺪ ارﺳﺎل ﻣﻨﺎﺳﺐ ﺑ ﺴﺘﻪ ه ﺎ را‬ ‫ﺑﺎ ﻣﺮاﺣﻞ درﺳﺖ ﺑﺮاﯼ ﺑﺮﻧﺎﻣﻪ هﺎﯼ ﮐﺎرﺑﺮدﯼ ﮐﻪ ﺑﻪ اﻳﻦ ﻋﻤﻠﻴﺎت ﻧﻴﺎز دارﻧﺪ را ﻓﺮاهﻢ ﻣﯽ ﺁورد.‬ ‫ﻻﻳﻪ ﺷﺒﮑﻪ : اﻳﻦ ﻻﻳﻪ ﺑﺮ ﭘﺎﻳ ﻪ ﭘﺮوﺗﮑ ﻞ اﻳﻨﺘﺮﻧ ﺖ ﻗ ﺮار دارد و ه ﺪف ﺁن ارﺳ ﺎل ﺑ ﺴﺘﻪ ه ﺎ ﺑ ـﻪ دﻧﺒ ﺎل ه ﻢ از ﻃﺮﻳ ﻖ‬ ‫ﺷﺒﮑﻪ،از ﮐﺎﻣﭙﻴﻮﺗﺮ ﻣﺒ ﺪا ﺑ ـﻪ دﺳ ﺘﮕﺎﻩ ﻣﻘ ﺼﺪ ﻣ ﯽ ﺑﺎﺷ ﺪ.ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از واژﻩ ﺷﻨﺎﺳ ﯽ ﻣ ﺪل ﻣﺮﺟ ﻊ ‪، OSI‬ﻻﻳ ﻪ ‪IP‬‬ ‫ﮔﻬﯽ اوﻗﺎت ﻻﻳﻪ 3 ﻧﻴﺰ ﻧﺎﻣﻴﺪﻩ ﻣﯽ ﺷﻮد.‬ ‫ﻻﻳـﻪ اﺗﺼﺎل دادﻩ هﺎ : اﻳﻦ ﻻﻳـﻪ ﺑﺴﺘـﻪ ﻧﺮم اﻓﺰارﯼ را از ﻃﺮﻳﻖ هﺮ ﺟﻬ ﺶ ﺷ ﺒﮑﻪ اﻧﺘﻘ ﺎل ﻣ ﯽ ده ﺪ.ﻣ ﺜﻼ اﻳ ﻦ ﻻﻳ ـﻪ‬ ‫در ﮐﺎﻣﭙﻴﻮﺗﺮ دادﻩ هﺎ را از ﮐﺎﻣﭙﻴﻮﺗﺮ ﺗﺎن ﺑﻪ ﻣﺴﻴﺮ ﻳﺎب و ﺑﺮاﯼ ﺷﺒﮑﻪ ﻧﺎﺣﻴﻪ ﻣﺤﻠﯽ ﺟﺎ ﺑﻪ ﺟﺎ ﻣﯽ ﻧﻤﺎﻳﺪ.ﻣﺴﻴﺮ ﻳ ﺎب‬ ‫ﻧﻴﺰ از اﺗﺼﺎل دادﻩ هﺎﻳﺶ ﺑﺮاﯼ ﺟﺎ ﺑﻪ ﺟﺎﻳﯽ دادﻩ هﺎ ﺑﻪ ﻣ ﺴﻴﺮ ﻳ ﺎب دﻳﮕ ﺮ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮐﻨ ﺪ.دوﺑﺎرﻩ،ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از‬ ‫زﺑﺎن ﻣﺪل ﻣﺮﺟﻊ ‪، OSI‬ﻻﻳﻪ اﺗﺼﺎل دادﻩ هﺎ ،ﻻﻳﻪ 2 ﻧﺎﻣﻴﺪﻩ ﻣﯽ ﺷﻮد.‬ ‫ﻻﻳﻪ ﻓﻴﺰﻳﮑﯽ : اﻳ ﻦ ﻻﻳ ﻪ ﻣﺤ ﻴﻂ ﻓﻴﺰﻳﮑ ﯽ ﻣﺜ ﻞ ﺳ ﻴﻢ ﮐﺎﺑ ﻞ ﻳ ﺎ ﻓﻴﺒ ﺮﯼ ﻣ ﯽ ﺑﺎﺷ ﺪ ﮐ ﻪ اﻃﻼﻋ ﺎت در واﻗ ﻊ از ﻃﺮﻳ ﻖ ﺁن‬ ‫ﻣﻨﺘﻘﻞ ﻣﯽ ﮔﺮدد.‬ ‫درﮐ ﻞ ﻻﻳ ﻪ ه ﺎﯼ ‪ Network ,Transport‬از ‪ TCP/IP‬ﺳﻴ ﺴﺘﻢ ﺗ ﺸﮑﻴﻞ ﻣﻴﮕﺮدﻧ ﺪ، واز ﻧ ﺮم اﻓ ﺰارﯼ ﺳ ﺎﺧﺘﻪ‬ ‫ﻣﻴﺸﻮﻧﺪ ﮐﻪ ﺑﺮ روﯼ ﮐﺎﻣﭙﻴﻮﺗﺮ اﺟﺮا ﻣﯽ ﮔﺮدد.ﻓﻘﻂ در ﻣﺪل ‪، OSI‬ﻳﮏ ﻻﻳـﻪ ﺑﺎ هﻤﺎن ﻻﻳـﻪ در ﻗﺴﻤﺖ دﻳﮕﺮ ارﺗﺒ ﺎط‬ ‫ﺑﺮﻗﺮار ﻣﯽ ﻧﻤﺎﻳﺪ.ﺑﻌﻼوﻩ ﻻﻳـﻪ ﭘﺎﻳﻴﻦ ﺗﺮ ﺳﺮوﻳﺴﯽ را ﺑﺮاﯼ ﻻﻳﻪ هﺎﯼ ﺑﺎﻻﺗﺮ ﻓﺮاهﻢ ﻣﯽ ﺁورد.‬ ‫ﺣﺎل ﺑﺎﻳﺪ دﻳﺪ ﮐﻪ اﻳﻦ اﻧﺘﻘﺎل دادﻩ هﺎ ﺑﻴﻦ ﻻﻳﻪ هﺎ ﺑﻪ ﭼﻪ روﺷﯽ ﮐﺎ ﻣﯽ ﮐﻨﻨﺪ؟ هﺮ ﻻﻳـﻪ ﺑـﻪ اﻃﻼﻋ ﺎﺗﯽ در ﺟﻠ ﻮﯼ دادﻩ‬ ‫هﺎ اﻟﺼﺎق ﻣﯽ ﮔﺮدد ﮐـﻪ اﻳﻦ اﻃﻼﻋـﺎت در ﺟﻠﻮﯼ دادﻩ هﺎ اﻟﺼﺎق ﻣﯽ ﮔﺮدد ﮐـﻪ اﻳﻦ اﻃﻼﻋـﺎت را از ﻻﻳـﻪ ﺑﺎﻻﺗﺮ ﺁن‬ ‫ﮐﺴﺐ ﻣﯽ ﮐﻨﺪ.اﻳﻦ اﻃﻼﻋـﺎت اﺿﺎﻓــﻪ ﺷﺪﻩ در ﺟﻠﻮﯼ دادﻩ هﺎ ﻋﻨﻮان ﻧﺎم دارد و ﺷﺎﻣﻞ اﻃﻼﻋﺎت اﺳﺎﺳﯽ در ﻣ ﻮرد‬ ‫ﻻﻳـﻪ ﻣﯽ ﺑﺎﺷﺪ.‬ ‫در هﻨﮕ ﺎم درﻳﺎﻓ ﺖ دادﻩ هﺎ،ﺳﻴ ﺴﺘﻢ ﻣﻘ ﺼﺪ ﺗﻤ ﺎم ﺑ ﺴﺘـﻪ دادﻩ ه ﺎﯼ ارﺳ ﺎﻟﯽ را ﻻﻳ ـﻪ ﺑ ﻪ ﻻﻳ ـﻪ ﺑ ﺎز ﻣ ﯽ ﮐﻨ ﺪ.ﺑ ﺴﺘـﻪ‬ ‫ﺣﺎﺻﻠﻪ ﺑﻪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ ارﺳﺎل ﻣﯽ ﮔﺮدد ﮐﻪ ﻣﯽ ﺗﻮاﻧﺪ ﺗﻘﺎﺿﺎﯼ وب را ﭘ ﺮدازش ﻧﻤﺎﻳﻨﺪ،ﭘ ﺴﺖ اﻟﮑﺘﺮوﻧﻴﮑ ﯽ‬ ‫را ﻗﺒﻮل ﮐﻨﺪ ﻳﺎ هﺮ ﺁﻧﭽﻪ ﮐﻪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ ﺑﺮاﯼ اﻧﺠﺎم ﺁن ﻃﺮاﺣﯽ ﺷﺪﻩ اﺳﺖ را اﻧﺠﺎم دهﺪ.‬ ‫ﺑﺪون ﺗﻮﺟـﻪ ﺑـﻪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ ﻣﻮرد اﺳﺘﻔﺎدﻩ در اﻳﻨﺘﺮﻧﺖ راﻳﺎﻧـﻪ دادﻩ هﺎ را ﺑﻪ ﺷﮑﻞ ﺛﺎﺑﺖ،ﺑ ـﻪ ﺑ ﺎﻻ و ﭘ ﺎﻳﻴﻦ‬ ‫ﻻﻳـﻪ هﺎﯼ ﺗﻮدﻩ ﭘﺮوﺗﮑﻞ اﻧﺘﻘﺎل ﻣﯽ دهﺪ.ﺳﺮوﻳﺲ دهﻨﺪﮔﺎن دادﻩ هﺎ را از ﻃﺮﻳﻖ ﺗﻮدﻩ ه ﺎﯼ ‪ TCP/IP‬ارﺳ ﺎل ﻣ ﯽ‬ ‫ﮐﻨﻨﺪ.‬

‫‪: TCP/IP‬‬
‫ﺣﺎﻻ ﮐﻪ ﺷﻨﺎﺧﺘﯽ از ﭘﺮوﺗﮑﻞ ﻻﻳﻪ ﺑﻨﺪﯼ ﭘﻴﺪا ﮐﺮدﻳﺪ ﻣ ﯽ ﺧ ﻮاهﻢ در اﻳ ﻦ ﻗ ﺴﻤﺖ ‪ TCP/IP‬را ﺑ ﺎ ﺟﺰﺋﻴ ﺎت ﺑﻴ ﺸﺘﺮﯼ‬ ‫ﺗﻮﺿﻴﺢ دهﻢ.‬ ‫ﺧﺎﻧﻮاد ﭘﺮوﺗﮑﻞ هﺎﯼ ‪ TCP/IP‬از ﭼﻨﺪﻳﻦ ﺑﺨﺶ ﺗﺸﮑﻴﻞ ﻣﯽ ﺷﻮﻧﺪ:ﭘﺮوﺗﮑﻞ ﮐﻨﺘﺮﻻﻧﺘﻘﺎل ‪، TCP‬ﭘﺮوﺗﮑﻞ دﻳ ﺎﮔﺮام‬ ‫ﮐﺎرﺑﺮ)‪، (UDP‬ﭘﺮوﺗﮑﻞ اﻳﻨﺘﺮﻧﺖ )‪ (IP‬وﭘﺮوﺗﮑ ﻞ ﭘﻴﻐ ﺎم ﮐﻨﺘ ﺮل اﻳﻨﺘﺮﻧ ﺖ )‪ TCP/IP.(ICMP‬در ﺳ ﺮﯼ اﺳ ﻨﺎد‬ ‫اﻳﺠﺎد ﺷﺪﻩ و ﻧﮕﻬﺪارﯼ ﺷﺪﻩ ادارﻩ ﮐﺎر ﻣﻬﻨﺪﺳﯽ اﻳﻨﺘﺮﻧﺖ )‪ (IEFT‬ﺗﻌﺮﻳﻒ ﻣﯽ ﺷﻮﻧﺪ.‬ ‫‪ TCP/IP‬در اﺻﻞ ﺑﺮاﯼ ﺗﺤﻘﻴﻘﺎت و ﻋﻠﻮم ﺁﻣﻮزﺷﯽ و داﻧﺸﮕﺎهﯽ ﺑﻪ وﺟﻮد ﺁﻣﺪ و داراﯼ ﻗﺎﺑﻠﻴﺘﻬ ﺎﯼ اﻳﻤﻨ ﯽ ﻗ ﻮﯼ‬ ‫ﻧﻤ ﯽ ﺑﺎﺷ ﺪ.ﻣﺠﻤﻮﻋ ﮥ ﻗ ﺪﻳﻤﯽ ﭘﺮوﺗﮑ ﻞ ‪ TCP/IP‬ه ﻴﭻ وﺳ ﻴﻠﻪ اﯼ ﺑ ﺮاﯼ ﺗ ﻀﻤﻴﻦ ﻣﺤﺮﻣﺎﻧ ﻪ ﺳ ﺎزﯼ،ﻳﮑﭙﺎرﭼﮕﯽ و‬ ‫ﺗﺎﻳﻴﺪ دادﻩ هﺎﯼ ﻣﻨﺘﻘﻞ ﺷﺪﻩ از ﻃﺮﻳﻖ اﻳﻨﺘﺮﻧﺖ ﻧﺪارد.ﺑﺪون ﮐﻨﺘﺮل ﻣﺤﺮﻣـﺎﻧـﻪ ﺳﺎزﯼ و ﻳﮑﭙﺎرﭼﮕـﯽ،وﻗﺘﯽ ﺑ ﺴﺘـﻪ اﯼ‬ ‫را از ﻃﺮﻳﻖ اﻳﻨﺘﺮﻧﺖ ارﺳﺂال ﻣﯽ ﻧﻤـﺎﻳـﻨﺪ،‪ TCP/IP‬اﻳﻦ اﻣﮑـﺎن را ﺑﺮاﯼ دﻳـﮕﺮ ﻣﺸﺘﺮﮐﺎن ﻓﺮاهﻢ ﻣﯽ ﮐﻨﺪ ﺗﺎ دادﻩ‬ ‫هﺎ را ﺑﺒﻴﻨﻨﺪ ﻳﺎ ﺗﻐﻴﻴﺮ دهﻨﺪ.ﺑﻌﻼوﻩ ،ﺑﺪون ﺗﺎﻳﻴﺪﻳ ﻪ ،هﮑﺮه ﺎ ﻣ ﯽ ﺗﻮاﻧﻨ ﺪ دادﻩ ه ﺎﻳﯽ را ﺑﺮاﻳﺘ ﺎن ارﺳ ﺎل ﻧﻤﺎﻳﻨ ﺪ، و ﺑ ﻪ‬ ‫ﻃﺮﻳﻖ ﻣﺠﺎزﯼ ﻣﺴﺌﻮﻟﻴﺖ دادﻩ هﺎﯼ ارﺳﺎﻟﯽ از ﻃﺮف دﻳﮕﺮان ﺑﻪ ﺷﺒﮑﻪ را ﺑﻪ ﻋﻬﺪﻩ ﻣﯽ ﮔﻴﺮﻧﺪ.‬ ‫در ﮔﺬﺷ ﺘﻪ ،ﮐﻠﻴ ﻪ ﻗﺎﺑﻠﻴ ﺖ ه ﺎﯼ اﻳﻤﻨ ﯽ در ﺷ ﺒﮑﻪ ه ﺎﯼ ‪ TCP/IP‬در ﻧ ﺮم اﻓﺰاره ﺎﯼ ﮐ ﺎرﺑﺮدﯼ و ﻧ ﻪ در ﺗ ﻮدﻩ‬ ‫‪ TCP/IP‬اﺟﺮا ﻣﯽ ﮔﺮدد.ﺗﻨﻬﺎ در ﺳﺎﻟﻬﺎﯼ اﺧﻴﺮ اﻳﻤﻨﯽ در ‪ TCP/IP‬و ﺑﻪ ﺷ ﮑﻞ ﺿ ﻤﻴﻤﻪ ﭘﺮوﺗﮑ ﻞ اﺿﺎﻓ ـﻪ ﺷ ﺪﻩ‬ ‫اﺳﺖ ﮐﻪ ‪ IPSec‬ﻧﺎﻣﻴﺪﻩ ﻣﯽ ﺷﻮد.ﺑﺎ اﻳﻨﮑﻪ ‪ IPSec‬ﺗﻌﻬﺪ ﺑﺴﻴﺎر ﺑـﺎﻻﻳﯽ دارد اﻣﺎ هﻨﻮز ﺑﻪ ﻃﻮر ﮔﺴﺘﺮدﻩ اﺟﺮا ﻧﻤﯽ‬ ‫ﮔـﺮدد.ﺑﻨـﺎﺑﺮاﻳﻦ،ﺑﺪون اﻳﻦ ﻗﺎﺑﻠﻴﺘﻬـﺎﯼ اﻳﻤﻨﯽ ﻧﺼﺐ ﺷﺪﻩ در اﻳﻦ ﭘﺮوﺗـﮑﻞ،ﻧﺮم اﻓﺰارهـﺎﯼ ﮐﺎرﺑﺮدب هﻨﻮز ﺧﻮدﺷ ﺎن‬ ‫را ﺑﺎ اﻳﻤﻨﯽ اﺟﺮاﻳﯽ ﺗﺠﻬﻴﺰ ﻧﻤﯽ ﮐﻨﻨﺪ.‬

‫-4-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﺣـﺎﻻ ﻣﯽ ﺧﻮاهﻢ ﮐﻪ اﻋﻀـﺎﯼ ﺧﺎﻧﻮادﻩ ‪ TCP/IP‬را ﺗﮏ ﺗﮏ ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار دهﻢ ﺗﺎ ﺁﻧﺮا ﺑﻬﺘﺮ درﮎ ﻧﻤﺎﻳﻴﺪ و‬ ‫روش ﮐﺎر هـﮑﺮهـﺎ را ﻧﻴﺰ ﻣﻮرد ﺑﺮرﺳــــﯽ ﻗﺮار ﺧﻮاهﻴﻢ داد.‬

‫ﭘﺮوﺗﮑﻞ ﮐﻨﺘﺮل اﻧﺘﻘﺎل ‪: TCP‬‬
‫‪ TCP‬ﭘﺮ ﮐﺎرﺗﺮﻳﻦ ﭘﺮوﺗﮑﻞ اﻳﻨﺘﺮﻧﺖ ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ اﻣﺮوزﻩ ﺑﺎ ﻧﺮم اﻓﺰارهﺎﯼ ﮐﺎرﺑﺮدﯼ ﺑﺴﻴﺎرﯼ اﺳﺘﻔﺎدﻩ ﻣﯽ‬ ‫ﺷﻮد.در ﺑﻴﻦ هﺰاران ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ ﮐﻪ از ‪ TCP‬اﺳﺘﻔﺎدﻩ ﻣﯽ ﻧﻤﺎﻳﻨﺪ، ﺑﻌﻀﯽ از ﺑﺮﺟﺴﺘﻪ ﺗﺮﻳﻦ ﺁﻧﻬﺎ ﻋﺒﺎرﺗﻨﺪ‬ ‫از:‬ ‫اﺗﻘﺎل ﻓﺎﻳﻞ : ﮐﻪ از ﭘﺮوﺗﮑﻞ اﻧﺘﻘﺎل ﻓﺎﻳﻞ )‪ (FTP‬اﺳﺘﻔﺎدﻩ ﻣﯽ ﻧﻤﺎﻳﻨﺪ.‬ ‫ﺗﻠﻨﺖ : ﮐﻪ واﺳﻄﻪ دﺳﺘﻮر ﺧﻄﯽ راﻩ دور را اﺳﺘﻔﺎدﻩ ﻣﯽ ﮐﻨﺪ.‬ ‫ﭘﺴﺖ اﻟﮑﺘﺮوﻧﻴﮑﯽ : ﮐﻪ از ﭘﺮوﺗﮑﻞ هﺎﯼ ﻣﺨﺘﻠﻒ اﺳﺘﻔﺎدﻩ ﻣﯽ ﻧﻤﺎﻳﻨﺪ ﮐﻪ ﻋﺒﺎرﺗﻨﺪ از: ‪Post (Simple Mail‬‬ ‫‪Transfer Protocol (SMTP,(Office Protocol (POP‬‬ ‫ﻣﺮورﮔﺮ وب : ﮐﻪ از ﭘﺮوﺗﮑﻞ )‪ Hypertext Transfer Protocol (HTTP‬اﺳﺘﻔﺎدﻩ ﻣﯽ ﻧﻤﺎﻳﻨﺪ.‬ ‫هﺮ ﻳﮏ از اﻳﻦ ﻧﺮم اﻓﺰارهﺎﯼ ﮐﺎرﺑﺮدﯼ ﺑﺴﺘﻪ هﺎﻳﯽ را ﺗﻮﻟﻴﺪ ﻣﯽ ﻧﻤﺎﻳﻨﺪ و ﺁﻧﻬﺎ را ﺑﻪ ﺗﻮدﻩ ‪ TCP/IP‬دﺳﺘﮕﺎﻩ‬ ‫ﻣﺤﻠﯽ اﻧﺘﻘﺎل ﻣﯽ دهﻨﺪ. ﻧﺮم اﻓﺰار ﻻﻳﻪ ‪ TCP‬ﮐﻪ ﺑﺮ روﯼ ﺳﻴﺴﺘﻢ وﺟﻮد دارد، اﻳﻦ دادﻩ هﺎ را ﺑﺮﻣﯽ دارد و ﺑﺴﺘﻪ‬ ‫هﺎﯼ ‪ TCP‬ﺑﺮ روﯼ هﺮ ﺑﺴﺘﻪ ﻧﺮم اﻓﺰارﯼ ﺗﻮﻟﻴﺪ ﻣﯽ ﻧﻤﺎﻳﻨﺪ.ﺑﺮاﯼ اﻳﻨﮑﻪ ﺑﺪاﻧﻴﺪ ﮐﻪ ﺣﻤﻼت ﺑﻪ ﭼﻪ روﺷﯽ در‬ ‫ﺑﺮاﺑﺮ ‪ TCP‬ﮐﺎر ﻣﯽ ﻧﻤﺎﻳﻨﺪ، ﻻزم اﺳﺖ ﭼﻨﺪﻳﻦ زﻣﻴﻨﻪ و ﻗﺼﺪ ﺁﻧﻬﺎ را در ﻋﻨﻮان ‪ TCP‬ﺗﺤﻠﻴﻞ ﮐﻨﻢ.ﺑﻪ ﺧﺼﻮص‬ ‫ﺑﻪ ﺷﺮح ﺷﻤﺎرﻩ دروازﻩ هﺎ،اﻋﺪاد ﻣﺮاﺣﻞ ﮐﺎر و اﻋﻼم ﻣﺮاﺣﻞ ﮐﺎر،و ﺑﻴﺘﻬﺎﯼ ﮐﻨﺘﺮل ﻣﯽ ﭘﺮدازم.‬

‫ﺷﻤﺎرﻩ دروازﻩ هﺎﯼ ‪: TCP‬‬
‫ﻋﻨﻮان هﺮ ﺑﺴﺘﻪ ﺷﺎﻣﻞ ‪ TCP‬ﺷﺎﻣﻞ دو ﺷﻤﺎرﻩ دروازﻩ ﻣﯽ ﺑﺎﺷ ﺪ: دروازﻩ ﻣﺒ ﺪا و دروازﻩ ﻣﻘ ﺼﺪ.اﻳ ﻦ اﻋ ﺪاد 61‬ ‫ﺑﻴﺘﯽ ﻣﺜﻞ درهﺎﯼ ﮐﻮﭼﮑﯽ روﯼ ﺳﻴﺴﺘﻢ ﻣﯽ ﺑﺎﺷﻨﺪ ﮐﻪ از ﺁﻧﺠﺎ دادﻩ هﺎ ﻣﯽ ﺗﻮاﻧﻨﺪ ارﺳﺎل ﻳﺎ درﻳﺎﻓﺖ ﺷ ﻮﻧﺪ.دروازﻩ‬ ‫هﺎ درهﺎﯼ ﻓﻴﺰﻳﮑﯽ ﻧﻤﯽ ﺑﺎﺷﻨﺪ و وﺟﻮدﯼ ﻣﻨﻄﻘﯽ دارﻧﺪ ﮐﻪ ﺑﺎ ﻧﺮم اﻓﺰار ﺗﻮدﻩ ‪ TCP/IP‬ﺗﻌﺮﻳﻒ ﻣ ﯽ ﺷ ﻮﻧﺪ.ﺗﻌ ﺪاد‬ ‫53556 دروازﻩ ‪ TCP‬ﻣﺘﻔﺎوت ﺑ ﺮ روﯼ ه ﺮ دﺳ ﺘﮕﺎﻩ وﺟ ﻮد دارد.دروازﻩ ﺻ ﻔﺮ ‪ TCP‬دروازﻩ اﯼ ذﺧﻴ ﺮﻩ ﺷ ﺪﻩ‬ ‫ﻣ ﯽ ﺑﺎﺷ ﺪ و اﺳ ﺘﻔﺎدﻩ ﻧﻤ ﯽ ﮔ ﺮدد.ه ﺮ ﺑ ﺴﺘﻪ ‪ TCP‬از درون ﻳﮑ ﯽ از اﻳ ﻦ دره ﺎ و ﺷ ﻤﺎرﻩ دروازﻩ ‪ TCP‬ﻣﺒ ﺪا از‬ ‫دﺳﺘﮕﺎﻩ ﻣﺒ ﺪا ﺑﻴ ﺮون ﻣ ﯽ ﺁﻳ ﺪ،و ﺑ ﺮاﯼ دروازﻩ دﻳﮕ ﺮﯼ )ﺷ ﻤﺎرﻩ دروازﻩ ﻣﻘ ﺼﺪ‪ ( TCP‬ﺑ ﺮ روﯼ دﺳ ﺘﮕﺎﻩ ﻣﻘ ﺼﺪ‬ ‫رهﺴﭙﺎر ﻣﯽ ﮔﺮدد.‬ ‫وﻗﺘﯽ ﻧﺮم اﻓﺰارﻩ ﮐﺎرﺑﺮدﯼ ﺳﺮوﻳﺲ دهﻨﺪﻩ ‪ TCP‬ﺑﺮ روﯼ ﺳﻴﺴﺘﻢ اﺟﺮا ﻣﯽ ﮔﺮدد.ﺑﺮ روﯼ دروازﻩ ﺧﺎﺻ ﯽ ﺑ ﺮاﯼ‬ ‫ﺑﺴﺘﻪ هﺎﯼ ‪ TCP‬ﮐﻪ از ﺳﺮوﻳﺲ ﮔﻴﺮﻧ ﺪﻩ ﻣ ﯽ ﺁﻳ ﺪ،ﻣﻨﺘﻈﺮ ﭘﺎﺳ ﺦ ﻣ ﯽ ﻣﺎﻧ ﺪ.دروازﻩ اﯼ ﮐ ﻪ دارﯼ ﺳ ﺮوﻳﺲ اﻧﺘﻈ ﺎر‬ ‫ﭘﺎﺳﺦ ﻣﯽ ﺑﺎﺷﺪ را دروازﻩ ﺑﺎز ﻣ ﯽ ﻧ ﺎﻣﻴﻢ،در ﺣ ﺎﻟﯽ ﮐ ﻪ دروازﻩ اﯼ ﮐ ﻪ در ﺁن ﭼﻴ ﺰﯼ در ﺣ ﺎل درﻳﺎﻓ ﺖ ﭘﺎﺳ ﺦ ﻧﻤ ﯽ‬ ‫ﺑﺎﺷﻨﺪ دروازﻩ ﺑﺴﺘﻪ ﻧﺎﻣﻴﺪﻩ ﻣﯽ ﺷﻮد.ﺳﺮوﻳﺲ دهﻨﺪﮔﺎن ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ از اﻧﻮاع ﮔﻮﻧ ﺎﮔﻮن ﺑ ﻪ ﺷ ﻤﺎرﻩ در ﮔ ﺎﻩ‬ ‫هﺎﯼ ﺷﻨﺎﺧﺘﻪ ﺷﺪﻩ اﯼ ﮔﻮش ﻓﺮا ﻣﯽ دهﻨﺪ.اﻳﻦ ﺷﻤﺎرﻩ دروازﻩ هﺎﯼ ﺷﻨﺎﺧﺘﻪ ﺷ ﺪﻩ ﺑ ﻪ ﺻ ﻮرت 0071‪ RFC‬هﺠ ﯽ‬ ‫ﻣﯽ ﺷﻮد،ﮐﻪ ﺷﺎﻣﻞ اﻋﺪا ﻣﺨﺘﻠﻒ ﺑﺴﻴﺎر زﻳﺎدﯼ ﻣﯽ ﺑﺎﺷ ﻨﺪ ﮐ ﻪ ﻣﻌﻴﺎره ﺎﯼ ﻣﺘﻔ ﺎوت ‪ TCP/IP‬واﺑ ﺴﺘﻪ ﺑ ﻪ ﭘﺮوﺗﮑ ﻞ‬ ‫هﺎ اﺧﺘﺼﺎص دادﻩ ﻣﯽ ﺷﻮد.‬ ‫ﺷﻤﺎرﻩ دروازﻩ هﺎﯼ ‪ TCP‬ﮐﻪ ﻏﺎﻟﺒﺎ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮﻧﺪﻋﺒﺎرﺗﻨﺪ از:‬ ‫)‪TCP Port 21-File Transfer Protocol (FTP‬‬ ‫‪TCP Port 23-Telnet‬‬ ‫‪(TCP Port 25-Simple Mail Transfer Protocol (SMTP‬‬ ‫)‪TCP Port 80-World Wide Web (HTTP‬‬ ‫‪TCP Port 666-Doom‬‬ ‫ﺑﺮاﯼ ﺗﻤﺎس ﺑﺎ اﻳﻦ ﺳﺮوﻳﺲ دهﻨﺪﮔﺎن ﻧﺮم اﻓﺰارﯼ ﮐﺎرﺑﺮدﯼ،ﻻﻳﻪ ‪ TCP‬ﺳ ﺮوﻳﺲ ﮔﻴﺮﻧ ﺪﻩ ﺑ ﺴﺘﻪ ه ﺎﻳﯽ را دروازﻩ‬ ‫‪ TCP‬ﻣﻘﺼﺪ ﺗﻮﻟﻴﺪ ﻣﯽ ﮐﻨﺪ ﮐﻪ ﺑﻪ دروازﻩ اﯼ ﺗﻌﻠﻖ دارد ﮐﻪ در ﺁ» ﻧ ﺮم اﻓ ﺰار ﮐ ﺎرﺑﺮدﯼ ﺳ ﺮوﻳﺲ دهﻨ ﺪﻩ در ﺣ ﺎل‬ ‫در ﻳﺎﻓﺖ ﭘﺎﺳﺦ ﻣﯽ ﺑﺎﺷﺪ.دروازﻩ ﻣﺒﺪا ﺑﺮاﯼ ﺑﺴﺘﻪ در ﺧﻮاﺳﺘﯽ از ﻟﺤﺎظ دﻳﻨﺎﻣﻴﮑﯽ ﺗﻮﺳﻂ ﺳﻴﺴﺘﻢ ﻋﺎﻣﻞ ﺑ ﻪ ﺑﺮﻧﺎﻣ ﻪ‬ ‫ﺳ ﺮوﻳﺲ ﮔﻴﺮﻧ ﺪﻩ اﺧﺘ ﺼﺎص دادﻩ ﻣ ﯽ ﺷ ﻮد، و ﻳ ﺎ ﻣﻘ ﺪارﯼ ﺑﻴ ﺸﺘﺮ از 3201 ﺗﻨﻈ ﻴﻢ ﻣ ﯽ ﮔﺮدد،ﺑﻨ ﺎﺑﺮاﻳﻦ دروازﻩ‬ ‫"ﺷﻤﺎرﻩ ﺑﺎﻻﺗﺮ" ﻧﺎﻣﻴﺪﻩ ﻣ ﯽ ﺷ ﻮد.دروازﻩ ﻣﻘ ﺼﺪ درﺧﻮاﺳ ﺘﯽ ﺑ ﺎ ﻧ ﺮم اﻓ ﺰار ﮐ ﺎرﺑﺮدﯼ در ارﺗﺒ ﺎط اﺳ ﺖ،ﮐﻪ در ﺁن‬ ‫ﺳﺮوﻳﺲ دهﻨ ﺪﻩ در ﺣ ﺎل درﻳﺎﻓ ﺖ ﭘﺎﺳ ﺦ ﻣ ﯽ ﺑﺎﺷ ﺪ)ﻣ ﺜﻼ دروازﻩ 08 ‪ TCP Port‬ﺑ ﺮاﯼ ﺗﺮاﻓﻴ ﮏ ‪ .( HTTP‬در‬ ‫ﺑﻴ ﺸﺘﺮ ﻧ ﺮم اﻓﺰاره ﺎﯼ ﮐ ﺎرﺑﺮدﯼ ،ﺳ ﺮوﻳﺲ دهﻨ ﺪﻩ ﺑ ﺴﺘﻪ ه ﺎ، ﭘﺎﺳ ﺨﯽ را ارﺳ ﺎل ﺧﻮاهﻨ ﺪ ﻧﻤ ﻮد ﮐ ﻪ ﺷ ﻤﺎرﻩ ه ﺎﯼ‬ ‫دروازﻩ را ﻣﻌﮑﻮس ﻣﯽ ﮐﻨﺪ.دروازﻩ ﻣﺒﺪا ﺑﺴﺘﻪ ﭘﺎﺳﺦ،ﺷﻤﺎرﻩ دروازﻩ اﯼ ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ ﺑ ﻪ ﺳ ﺮوﻳﺲ ﮔﺒﺮﻧ ﺪﻩ ﺑ ﺴﺘﻪ‬ ‫اﯼ ارﺳ ﺎل ﻣ ﯽ ﺷ ﻮد )ﺑ ﺮاﯼ ﻣﺜ ﺎل 08 ‪ ( TCP Port‬ودروازﻩ ﻣﻘ ﺼﺪ ﺟ ﺎﻳﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ ﮐ ﻪ ﺑ ﻪ ﺳ ﺮوﻳﺲ ﮔﻴﺮﻧ ﺪﻩ‬ ‫ﺑﺴﺘﻪ اﯼ ارﺳﺎل ﻣﯽ ﺷﻮد )ﺑﺮاﯼ ﻣﺜﺎل 4321 ‪.( TCP Port‬‬ ‫ﻣﺪﻳﺮ اﺟﺮاﻳ ﯽ ﺳﻴ ﺴﺘﻢ ﻣ ﯽ ﺗﻮاﻧ ﺪ ه ﺮ ﺳ ﺮوﻳﺲ دهﻨ ﺪﻩ ﻧ ﺮم اﻓ ﺰار ﮐ ﺎرﺑﺮدﯼ را ﭘﻴﮑﺮﺑﻨ ﺪﯼ ﻧﻤﺎﻳ ﺪ ﺗ ﺎ از ه ﺮ ﺷ ﻤﺎرﻩ‬ ‫دروازﻩ اﯼ اﺳﺘﻔﺎدﻩ ﻧﻤﺎﻳﺪ،اﻣﺎ ﺑﺮﻧﺎﻣﻪ هﺎﯼ ﺳﺮ.ﻳﺲ ﮔﻴﺮﻧﺪﻩ ﻣﻨﺘﻈﺮ ﺑﺮﻧﺎﻣﻪ هﺎﯼ ﮐﺎرﺑﺮدﯼ ﻣﯽ ﻣﺎﻧﺪ ﺗﺎ دروازﻩ ه ﺎﯼ‬ ‫-5-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﺧ ﺎص ﻣﻘ ﺼﺪ ﻣﻨﺘﻈ ﺮ ﭘﺎﺳ ﺦ ﺑﻤﺎﻧ ﺪ.ﺑﻨ ﺎﺑﺮاﻳﻦ ،اﮔ ﺮ ﺳ ﺮوﻳﺲ ﮔﻴﺮﻧ ﺪﻩ و ﮐ ﺎرﺑﺮ در ﻣ ﻮرد دروازﻩ ﻣﻘ ﺼﺪ ﺳ ﺮوﻳﺲ‬ ‫ﮔﻴﺮﻧﺪﻩ ﺑﺮ روﯼ ﺳﺮوﻳﺲ دهﻨﺪﻩ ﭼﻴﺰﯼ ﻧﺪاﻧﻨﺪ،ﺷﻤﺎرﻩ دروازﻩ هﺎﯼ ﻣ ﻮرد ﺑﺮرﺳ ﯽ در 0071 ‪ RFC‬اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ‬ ‫ﺷﻮد.‬ ‫ﺑﺮاﯼ دﻳﺪن اﻳﻨﮑﻪ ﮐﺪام دروازهﺎ در ﺳﻴ ﺴﺘﻢ 0002/‪ Windows NT‬ﻳ ﺎ ‪ UNIX‬اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮﻧﺪ،ﻣﯽ ﺗﻮاﻧﻴ ﺪ‬ ‫از دﺳﺘﻮر "‪ "Netstat‬اﺳﺘﻔﺎدﻩ ﻧﻤﺎﻳﻴﺪ.ﺑﺎ ﺗﺎﻳﭗ"‪ "netstat –na‬در ﺧﻂ ﻓﺮﻣﺎن ﻣﯽ ﺗﻮاﻧﻴ ﺪ ﺗﻤ ﺎم دروازﻩ ه ﺎﯼ‬ ‫دادﻩ هﺎﯼ ارﺳﺎﻟﯽ و دروازﻩ هﺎﻳﯽ ﮐﻪ ﻣﻨﺘﻈﺮ درﻳﺎﻓﺖ دادﻩ ه ﺎﯼ ارﺳ ﺎﻟﯽ و دروازﻩ ه ﺎﻳﯽ ﮐ ﻪ ﻣﻨﺘﻈ ﺮ درﻳﺎﻓ ﺖ دادﻩ‬ ‫هﺎ ﻣﯽ ﺑﺎﺷﻨﺪ،ﻧﺸﺎن دادﻩ ﻣﯽ ﺷﻮﻧﺪ.‬

‫ﺑﻴﺘﻬﺎﯼ ﮐﻨﺘﺮل ‪، TCP‬اﺗﺼﺎل ﺳﻪ راهﻪ و ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر :‬
‫ﺑﻴﺘﻬﺎﯼ ﮐﻨﺘﺮل ‪ TCP‬ﮐﺪ ﺑﻴﺘﻬﺎ ﻗﺴﻤﺖ ﻗﺎﺑﻞ ﮐﺎرﺑﺪ . ﺧﺎﺻﯽ از ﻋﻨﻮان ‪ TCP‬ﻣ ﯽ ﺑﺎﺷ ﻨﺪ.اﻳ ﻦ ﺷ ﺶ زﻣﻴﻨ ﻪ ﮐﻮﭼ ﮏ‬ ‫)هﺮ ﮐﺪام ﻳﮏ ﺑﻴﺖ ﻃﻮل دارﻧﺪ( ﺷﺮح ﻣﻴﺪهﻨﺪ ﮐﻪ ﮐﺪام ﺑﺨﺶ از دورﻩ ﮐﺎر ﺑﺴﺘﻪ ‪ TCP‬ﺑﺎ ﭼﻪ ﭼﻴ ﺰﯼ هﻤ ﺮاﻩ اﺳ ﺖ‬ ‫)ﻣﺜﻞ ﺷﺮوع دورﻩ ﮐﺎ،ﺗﺎﻳﻴﺪﻳﻪ،ﻳﺎ دورﻩ ﮐﺎرﯼ ﮐﻪ ﮔﺴﺴﺘﻪ ﻣﯽ ﺷﻮﻧﺪ(.اﻟﺒﺘﻪ،ﺑﻴﺘﻬﺎﯼ ﮐﻨﺘ ﺮل ﻣ ﯽ ﺗﻮاﻧﻨ ﺪ دﻻﻟ ﺖ ﻧﻤﺎﻳﻨ ﺪ‬ ‫ﮐﻪ ﺁﻳﺎ ﺑﺴﺘﻪ ﻧﺮم اﻓﺰارﯼ ﺑﻪ ﮐﻨﺘﺮل ﺧﺎص و ﻧﺎﮔﻬﺎﻧﯽ ﺗﻮﺳﻂ ﻻﻳﻪ ‪ TCP‬ﻧﻴﺎز دارد.‬ ‫ﭼﻮن ﺑﻴﺸﺘﺮ اﻓﺮاد ﺑﻴﺘﻬﺎﯼ ﮐﻨﺘﺮل ‪ TCP‬را "ﮐﺪ ﺑﻴﺖ" ﻣﻴﻨﺎﻣﻨﺪ ﺑﻪ هﻤﻴﻦ ﺧﺎﻃﺮ در اداﻣﻪ ﻣﻦ از اﻳ ﻦ واژﻩ اﺳ ﺘﻔﺎدﻩ‬ ‫ﻣﯽ ﮐﻨﻢ.هﺮ ﮐﺪ ﺑﻴ ﺖ را ﻣﻴﺘ ﻮان ﺑ ﻪ ﻃ ﻮر ﻣ ﺴﺘﻘﻞ ﺗﻨﻈ ﻴﻢ ﮐﺮد،ﺑﻨ ﺎﺑﺮاﻳﻦ،ﻋﻨﻮان ﻣﺠﺰاﻳ ﯽ از ﺑ ﺴﺘﻪ ‪ TCP‬ﻣ ﯽ ﺗﻮاﻧ ﺪ‬ ‫ﺷﺎﻣﻞ ﻳﮏ ﻳﺎ ﭼﻨﺪ از ﺷﺶ ﮐﺪﺑﻴﺖ ﺑﺎﺷﺪ ﮐﻪ ﻣﻘﺪار ﺻﻔﺮ و ﻳﮏ دارﻧﺪ.ﻣﻌﻤﻮﻻ ﺗﻨﻬﺎ ﻳﮏ ﻳﺎ دو ﮐﺪ ﺑﻴﺖ ﺑﻪ ﻣﻘ ﺪار ﻳ ﮏ‬ ‫در ﺑﺴﺘﻪ دادﻩ ﺷﺪﻩ ﺗﻨﻈﻴﻢ ﻣﯽ ﺷﻮد. ﺗﮏ ﺗﮏ ﮐﺪ ﺑﻴﺘﻬﺎ داراﯼ ﻣﻔﻬﻴﻢ زﻳﺮ ﻣﯽ ﺑﺎﺷﻨﺪ:‬ ‫‪ : URG‬اﺷﺎرﻩ ﮔﺮ ﻓﻮرﯼ ﻳﺎ ‪ Urgen Pointer‬ﮐﻪ در زﻣﻴﻨﻪ ‪ TCP Header‬ﻣﻬﻢ ﻣﯽ ﺑﺎﺷﺪ.‬ ‫‪ : ACK‬در زﻣﻴﻨ ﻪ ‪ Acknowledment‬ﻣﻬ ﻢ اﺳ ﺖ. اﻳ ﻦ ﺑ ﺴﺘﻪ ﺑ ﺮاﯼ ﺗ ﺼﺪﻳﻖ ﺑ ﺴﺘﻪ ه ﺎﯼ اوﻟﻴ ﻪ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ‬ ‫ﺷﻮد.‬ ‫‪ : PSH‬اﻳ ﻦ ﻣﻔﻬ ﻮم ﺑ ﻪ ﻣﻌﻨ ﺎﯼ ‪ Push Function‬ﻣ ﯽ ﺑﺎﺷ ﺪ و ﺑ ﺮاﯼ روﺷ ﻦ ﻧﻤ ﻮدن دادﻩ ه ﺎ در ﺳﺮاﺳ ﺮ ﻻﻳ ﻪ‬ ‫‪ TCP‬ﺑﻪ ﮐﺎر ﻣﯽ رود.‬ ‫‪ : RST‬ارﺗﺒﺎﻃﯽ ﮐﻪ ﺑﺎﻳﺪ ﺑﻮاﺳﻄﻪ ﺧﻄﺎ ﻳﺎ ﻧﻘﺺ ﻓﻨﯽ دﻳﮕﺮ از ﻧﻮ ﺗﻨﻈﻴﻢ ﮔﺮدد.‬ ‫‪ : SYN‬ﺳﻴﺴﺘﻢ ﺑﺎﻳﺪ ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر را هﻤﺎهﻨﮓ ﻧﻤﺎﻳﺪ.اﻳﻦ ﮐﺪ ﺑﻴﺘﻪ در ﻃ ﻮل اﺳ ﺘﻘﺮار دورﻩ ﮐ ﺎر اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ‬ ‫ﮔﺮدد.‬ ‫‪ : FIN‬دادﻩ هﺎﯼ ﺑﻴﺸﺘﺮﯼ از ﻃﺮف ﺳﺮوﻳﺲ دهﻨﺪﻩ وﺟﻮد ﻧﺪارد.ﺑﻨﺎﺑﺮاﻳﻦ،درورﻩ ﮐﺎر ﺑﺎﻳﺪ از هﻢ ﮔﺴﺴﺘﻪ ﺷﻮد.‬ ‫اهﻤﻴﺖ ﮐﻨﺘﺮل ﺑﻴﺘﻬﺎﯼ ‪ TCP‬وﻗﺘﯽ ﻣﻌﻠﻮم ﻣﯽ ﺷﻮد ﮐ ﻪ ﻣ ﺎ روش ﺷ ﺮوع ﺑ ﻪ ﮐ ﺎر اوﻟﻴ ﻪ ‪ TCP‬را ﻣ ﻮرد ﺗﺤﻠﻴ ﻞ و‬ ‫ﺑﺮرﺳﯽ ﻗﺮار دهﻴﻢ.ﮐﻠﻴﻪ ارﺗﺒﺎﻃﺎت ﻣﻨﻄﻘ ﯽ ‪ TCP‬ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از اﺗ ﺼﺎل ﺳ ﻪ راﻩ ﺑﺮﻗ ﺮار ﻣ ﯽ ﮔ ﺮدد. و اﺑ ﺰار ﭘﺎﻳ ﻪ‬ ‫ﺑﺮاﯼ اﻧﺠﺎم ﮐﺎ ‪ TCP‬ﺻﻮرت ﻣﯽ ﮔﻴﺮد.اﺗﺼﺎل ﺳﻪ راهﻪ ﺑﻪ ﺳﻴ ﺴﺘﻢ اﺟ ﺎزﻩ ﻣ ﯽ ده ﺪ ﺗ ﺎ دورﻩ ﮐ ﺎر را ﺑ ﺎز ﻧﻤﺎﻳ ﺪ و‬ ‫ﻣﺠﻤ ﻮ ﻋ ﻪ اﯼ از اﻋ ﺪاد ﻣﺮاﺣ ﻞ ﮐ ﺎر را ﺑ ﺮاﯼ ﺑ ﺴﺘﻪ ه ﺎﻳﯽ ﺑﺮﻗ ﺮار ﻣ ﯽ ﮐﻨ ﺪ ﮐ ﻪ از ﻃﺮﻳ ﻖ دورﻩ ﮐ ﺎر اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ‬ ‫ﺷﻮﻧﺪ.‬ ‫ﻓﺰض ﮐﻨﻴﺪ ﮐﻪ دﺳﺘﮕﺎهﯽ ﻣﺜﻞ ‪ A‬داراﯼ دادﻩ هﺎﻳﯽ ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ ﺑﺎﻳﺪ ﺑﻪ ﺳﻴﺴﺘﻤﯽ ﭼ ﻮن ‪ B‬ارﺳ ﺎل ﺷ ﻮﻧﺪ ﺷ ﺎﻳﺪ ‪A‬‬ ‫در ﺣﺎل اﺟﺮاﯼ ﻣﺮورﮔﺮ وب ﺑﺎﺷﺪ و ‪ B‬ﻧﻴﺰ ﺳﺮوﻳﺲ دهﻨ ﺪﻩ وب ﺑﺎﺷ ﺪ.‪ A‬اﺗ ﺼﺎل ﺳ ﻪ راﻩ را ﺑ ﺎ ﺑﺮﻗ ﺮارﯼ ارﺗﺒ ﺎط‬ ‫‪ TCP‬و ﺑﺎ ارﺳﺎل ﺑﺴﺘﻪ اﯼ ﺑﺎ ﮐﺪ ﺑﻴ ﺖ ﻣ ﺴﺎوﯼ ﺑ ﺎ ﻳ ﮏ و ﺷ ﻤﺎرﻩ ﻣﺮاﺣ ﻞ ﮐ ﺎر ﻣ ﺴﺎوﯼ ﺑ ﺎ ﻳ ﮏ ﻣﻘ ﺪار اوﻟﻴ ﻪ )ﮐ ﻪ‬ ‫ﺷﻤﺎرﻩ ﻣﺮﺣﻠﻪ ﮐﺎر اوﻟﻴﻪ ﻧﺎﻣﻴﺪﻩ ﻣﯽ ﺷﻮد( ارﺳﺎل ﻣﯽ ﻧﻤﺎﻳﺪ )ﭼﻮن اﻳﻦ ﺷﻤﺎرﻩ ﻣﺮﺣﻠﻪ ﮐﺎر از ﻃﺮف ‪ A‬ﻣ ﯽ ﺁﻳ ﺪ و‬ ‫ﺁﻧﺮا ‪ ISNA‬ﻣﯽ ﻧﺎﻣﻴﻢ(. اﻳﻦ ﺷﻤﺎرﻩ ﻣﺮﺣﻠﻪ ﮐﺎر اوﻟﻴﻪ ﺑﻪ ﻃﻮر دﻳﻨﺎﻣﻴﮑﯽ ﺑﺎ ﻻﻳ ﻪ ‪ TCP‬ﺗﻌﻴ ﻴﻦ ﻣ ﯽ ﺷ ﻮد و ﺑ ﺮاﯼ‬ ‫اﻳﻦ ارﺗﺒﺎط ﻣﻨﺤﺼﺮ ﺑﻪ ﻓﺮد اﺳﺖ.‬ ‫‪ B‬اﻳﻦ ﺑﺴﺘﻪ ‪ TCP TYN‬را از ﻃﺮف ‪ A‬درﻳﺎﻓ ﺖ ﻣ ﯽ ﮐﻨ ﺪ.اﮔ ﺮ دروازﻩ ﻣﻘ ﺼﺪ از ﻃ ﺮف ﺑ ﺴﺘﻪ ﻧ ﺮم اﻓ ﺰارﯼ ﺑ ﺮ‬ ‫روﯼ ‪ B‬ﺑ ﺎز ﺑﺎﺷ ﺪ.‪ B‬دوﻣ ﻴﻦ ﺑﺨ ﺶ از اﺗ ﺼﺎل ﺳ ﻪ راه ﻪ را ﺑ ﺎ ‪ A‬اﻧﺠ ﺎم ﻣ ﯽ ده ﺪ. ‪ B‬ﺑ ﺴﺘﻪ ﻣﺠﺰاﻳ ﯽ را ﺑ ﺎ دو‬ ‫ﻣﺠﻤﻮﻋ ﻪ ﮐ ﺪ ﺑﻴ ﺖ ‪ ACK‬و‪ SYN‬ﺑ ﻪ ‪ A‬ارﺳ ﺎل ﻣ ﯽ ﮐﻨ ﺪ.در اﻳ ﻦ ﺗ ﮏ ﺑ ﺴﺘﻪ ﭘﺎﺳ ﺦ،‪ B‬زﻣﻴﻨ ﻪ ه ﺎﯼ‬ ‫‪ Acknowledgment Number‬و ‪ Sequence Number‬را ﻧﻴﺰ ﭘﺮ ﻣﯽ ﮐﻨﺪ.ﺑﺎ اﻳ ﻦ ﭘﺎﺳ ﺦ، ‪ B‬ﭘﻴﻐ ﺎﻣﯽ ﺑ ﺎ‬ ‫اﻳ ﻦ ﻣ ﻀﻤﻮن را ارﺳ ﺎل ﻣ ﯽ ﻧﻤﺎﻳ ﺪ.‪، A‬ﻣ ﻦ درﺧﻮاﺳ ﺖ ﺑﺮﻗ ﺮارﯼ دورﻩ ﮐﺎرﺗ ﺎن را و ‪Initial Sequence‬‬ ‫‪ Number A‬را ﺗﺼﺪﻳﻖ ﻣﯽ ﮐﻨﻢ و ﺁﻧﺮا ﺑﺎ اﺳﺘﻔﺎدﻩ از ‪ Initial Sequence Number B‬هﻤﺎهﻨﮓ )‪(SYN‬‬ ‫ﺧﻮاهﻢ ﻧﻤﻮد. ﺑﻨﺎﺑﺮاﻳﻦ ‪ B‬ﺑ ﺴﺘﻪ ‪ SYN-ACK‬را ﺑ ﺎ ‪ ، ISNB‬و هﻤ ﺮاﻩ ﺑ ﺎ ﺗﺎﻳﻴﺪﻳ ﻪ ‪ ISNA‬ارﺳ ﺎل ﺑ ﺴﺘﻪ اﯼ ﺑ ﺎ‬ ‫ﻣﺠﻤﻮﻋﻪ ﮐﺪﺑﻴﺖ ‪ ACK‬و ﻳﮏ ﺗﺎﻳﻴﺪﻳﻪ )‪ (AKC‬و ﺑﻪ ‪ ISNB‬ﮐﺎﻣﻞ ﺧﻮاهﺪ ﻧﻤﻮد.‬ ‫ﺑﺪﻳﻦ ﻃﺮﻳﻖ ،‪ A‬و ‪ B‬از ﮐﺪﺑﻴﺖ هﺎ ﺑﺮاﯼ ﺑﺮﻗﺮارﯼ دورﻩ ﮐﺎر ‪ TCP‬اﺳﺘﻔﺎدﻩ ﮐ ﺮدﻩ اﻧ ﺪ. ﻩ دو ﻃ ﺮف ﺑ ﺎ ﻣﺠﻤﻮﻋ ﻪ‬ ‫ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎرﯼ ﺗﻮاﻓﻖ ﮐﺮدﻩ اﻧﺪ ﮐﻪ در ارﺗﺒﺎط اﺳﺘﻔﺎدﻩ ﺧﻮاهﺪ ﺷﺪ.ﺗﻤﺎم ﺑﺴﺘﻪ هﺎﻳﯽ ﮐﻪ از ﻃﺮف ‪ A‬ﺑ ﻪ ﺳ ﻤﺖ‬ ‫‪ B‬ﻣﯽ روﻧﺪ ﺑﻪ ﺷﮑﻞ ﻧﻤﻮدﯼ داراﯼ ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر ﺑﺎﻻﺗﺮ ﻣﯽ ﺑﺎﺷﻨﺪ و اﻳﻦ ﺷﻤﺎرﻩ در هﺮ ه ﺸﺖ ﺑﻴ ﺖ دادﻩ ه ﺎ‬ ‫ﻳ ﮏ ﺷ ﻤﺎرﻩ زﻳ ﺎد ﻣ ﯽ ﮔ ﺮدد و اﻳ ﻦ دادﻩ ه ﺎ از ﻃ ﺮف ‪ A‬ﺑ ﻪ ﺳ ﻤﺖ ‪ B‬ﻣ ﯽ رود، واز ‪ ISNA‬ﺷ ﺮوع ﻣ ﯽ ﺷ ﻮد.‬ ‫هﻤﭽﻨﻴﻦ،ﺗﻤﺎم ﺑﺴﺘﻪ هﺎﻳﯽ ﮐﻪ از ﻃﺮف ‪ B‬ﺑ ﻪ ﺳ ﻤﺖ ‪ A‬ﺑﺮﻣ ﯽ ﮔﺮدﻧ ﺪ ﺷ ﻤﺎرﻩ ﻣﺮاﺣ ﻞ ﮐ ﺎرﯼ ﺧﻮاهﻨ ﺪ داﺷ ﺖ ﮐ ﻪ از‬

‫-6-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫‪ ISNB‬ﺷﺮوع ﻣﯽ ﺷﻮد و ﺑﺮاﯼ هﺸﺖ ﺑﻴﺖ از دادﻩ هﺎ اﻓﺰاﻳﺶ ﻣﯽ ﻳﺎﺑﺪ.ﺑﻌ ﻼوﻩ، ﺑ ﺴﺘﻪ ه ﺎ ﺷ ﻤﺎرﻩ ﺗ ﺼﺪﻳﻖ ه ﺎﻳﯽ‬ ‫ﺧﻮاهﻨﺪ داﺷﺖ ﮐﻪ ﺑﺮ ﭘﺎﻳﻪ ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر ﺑﺴﺘﻪ هﺎﻳﯽ درﻳﺎﻓﺘﯽ ﻣﯽ ﺑﺎﺷﺪ.‬ ‫ﺑﺎ اﻳﻦ ﻣﺒﺎدﻟﻪ و ﺗﻮاﻓﻖ دﻗﻴﻖ در ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر،‪ TCP‬اﮐﻨﻮن ﻣ ﯽ ﺗﻮاﻧ ﺪ اﻃﻤﻴﻨ ﺎن ده ﺪ ﮐ ﻪ ﺗﻤ ﺎم ﺑ ﺴﺘﻪ ه ﺎ در‬ ‫دورﻩ ﮐﺎر ﺑﺎ ﻣﺮﺗﺒﻪ ﻣﻨﺎﺳﺐ ﻣﯽ رﺳﻨﺪ.اﮔﺮ دو ﺑﺴﺘﻪ ﻧﺮم اﻓﺰارﯼ در اﻧﺘﻘﺎل ﻣﻌﮑ ﻮس ﮔﺮدﻧ ﺪ )ﺑ ﺮاﯼ ﻣﺜﺎل،ﺑ ﻪ ﺧ ﺎﻃﺮ‬ ‫اﻳﻨﮑﻪ ﺑﺴﺘﻪ ﺑﻌﺪﯼ ﻣﺴﻴﺮ ﮐﻮﺗﺎهﺘﺮﯼ از ﺑﺴﺘﻪ اوﻟﻴﻪ ﻣﯽ رﺳﺪ(،اﻳﻦ ﻻﯼ ‪ TCP‬ﻣﯽ ﺗﻮاﻧﺪ ﻣ ﺸﮑﻞ را ﮐ ﺸﻒ ﻧﻤﺎﻳ ﺪ و‬ ‫ﺑﺴﺘﻪ هﺎ را ﻗﺒﻞ از ﻋﺒﻮر ﺑﻪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ از ﻧﻮ ﻣﺮﺗﺐ ﻧﻤﺎﻳﺪ.ﺑﻌﻼوﻩ،اﮔﺮ ﺑﺴﺘﻪ اﯼ در ﻃﻮل اﻧﺘﻘﺎم ﮔ ﻢ ﺷ ﻮد.‬ ‫‪ TCP‬ﻣﯽ ﺗﻮاﻧﺪ ﻣﺴﺎﻟﻪ را ﺑﺎ ﻳ ﮏ ﻧﮕ ﺎﻩ در ﺷ ﻤﺎرﻩ ﻣﺮاﺣ ﻞ ﮐ ﺎر و ﺗ ﺼﺪﻳﻖ ﮐ ﺸﻒ ﮐﻨ ﺪ و ﺑ ﺴﺘﻪ ﮔ ﻢ ﺷ ﺪﻩ را از ﻧ ﻮ‬ ‫اﻧﺘﻘﺎل دهﺪ.‬ ‫ﺑﻨﺎﺑﺮاﻳﻦ اﺗﺼﺎل ﺳﻪ راهﻪ و ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر ﮐﻪ از ﺁن ﺣﺎﺻ ﻞ ﻣ ﯽ ﺷ ﻮد، اﻣﮑ ﺎن اﻧﺘﻘ ﺎل ه ﺎﯼ ﻣﻨﻄﻘ ﯽ و ﻣﺮﺗ ﺐ‬ ‫ﺷﺪﻩ ﺑﺮاﯼ ‪ TCP‬ﻓﺮاهﻢ ﻣﯽ اورد.‬ ‫در ﺣ ﺎﻟﯽ ﮐ ﻪ ﮐ ﺪﺑﻴﺘﻬﺎﯼ ‪ ACK‬و ‪ SYN‬ﺑ ﻪ ﺷ ﺪت ﺑ ﺮاﯼ ﺑﺮﻗ ﺮارﯼ دورﻩ ﮐ ﺎر اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮﻧﺪ. ﮐ ﺪﺑﻴﺖ ‪FIN‬‬ ‫ﺑﺮاﯼ ﮔﺴﺴﺘﻦ دورﻩ ﮐﺎر اﺳﺘﻔﺎدﻩ ﻣﯽ ﮔﺮدد.هﺮ ﻃﺮف ﺑﺴﺘﻪ اﯼ را ﺑﺎ ﻣﺠﻤﻮﻋﻪ ﮐﺪ ﺑﻴ ﺖ ‪ FIN‬ارﺳ ﺎل ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﺗ ﺎ‬ ‫ﻧﺸﺎن دهﺪ ﮐﻪ دورﻩ ﮐﺎر ﺑﺎﻳﺪ ﺧﺎﺗﻤﻪ ﻳﺎﺑﺪ.‬ ‫ﮐﺪ ﺑﻴﺖ ‪ RST‬ﺑﺮاﯼ ﻗﻄﻊ ارﺗﺒﺎﻃﺎت و ﺑﺎز ﻧﻤﻮدن ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮد.اﮔ ﺮ دﺳ ﺘﮕﺎهﯽ ﺑ ﺴﺘﻪ اﯼ‬ ‫در درﻳﺎﻓﺖ ﻧﻤﺎﻳﺪ ﮐﻪ اﻧﺘﻈﺎر درﻳﺎﻓﺖ ﺁن ﻧﺪارد )ﻣﺜﻞ ﺑﺴﺘﻪ اﯼ ﮐﻪ ﺷﺎﻣﻞ ﻣﺠﻤﻮﻋﻪ ﺑﻴﺖ ‪ ACK‬ﻣﯽ ﺑﺎﺷﺪ وﻗﺘﯽ هﻴﭻ‬ ‫دورﻩ ﮐﺎرﯼ ﺑﺮﻗﺮار ﻧﺸﺪﻩ اﺳﺖ(، ﺑﺎ ﺑﺴﺘﻪ اﯼ ﺑﻪ ﺁن ﭘﺎﺳﺦ ﺧﻮاهﺪ داد ﮐﻪ داراﯼ ﻣﺠﻤﻮﻋﻪ ﺑﻴﺖ ‪ RST‬ﻣﯽ ﺑﺎﺷ ﺪ و‬ ‫ﺑﻪ اﻳﻦ ﻣﻀﻨﻮن ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ اﮔﺮ ﻓﮑﺮ ﻣﯽ ﮐﻨﻴﺪ دورﻩ ﮐﺎرﯼ وﺟﻮد دارد،ﺁن را ﺑﺎز ﻧﻤﺎﻳﻴﺪ،ﺑﺮاﯼ اﻳﻨﮑﻪ ﻣﺎﺷﻴﻦ ﻧﻤ ﯽ‬ ‫ﺗﻮاﻧﺪ ﻣﺪ ﻧﻈﺮﺗﺎن ﭼﻪ ﭼﻴﺰﯼ ﻣﯽ ﺑﺎﺷﺪ.‬ ‫ﮐ ﺪ ﺑﻴ ﺖ ه ﺎﯼ ‪ URG‬و ‪ PSH‬ﮐﻤﺘ ﺮ از ﭼﻬ ﺎر ﮐ ﺪﺑﻴﺖ دﻳﮕ ﺮ ﻣ ﻮرد اﺳ ﻨﻔﺎدﻩ ﻗ ﺮار ﻣ ﯽ ﮔﻴﺮﻧ ﺪ.ﮐ ﺪ ﺑﻴ ﺖ ‪ URG‬ﺑ ﻪ‬ ‫ﻣﻌﻨﺎﯼ ﺁن ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ ﺟﺮﻳﺎن دادﻩ هﺎ ﺷﺎﻣﻞ ﻳﮑﺴﺮﯼ دادﻩ هﺎﯼ ﻓﻮرﯼ ﻣﯽ ﺑﺎﺷ ﻨﺪ.اﮔ ﺮ ﮐ ﺪﺑﻴﺖ ‪ URG‬ﻣ ﺴﺎوﯼ ﺑ ﺎ‬ ‫ﻳ ﮏ ﻗ ﺮار ﮔﻴ ﺮد، زﻣﻴﻨ ﻪ ‪ Urgent Pointer‬ﻧ ﺸﺎن ﺧﻮاه ﺪ داد ﮐ ﻪ در ﮐﺠ ﺎﯼ ﺟﺮﻳ ﺎن دادﻩ ه ﺎ، دادﻩ ه ﺎﯼ ﻓ ﻮرﯼ‬ ‫واﻗﻊ ﺷﺪﻩ اﻧﺪ.‪ TCP‬روش ﮐﻨﺘﺮل دادﻩ هﺎﯼ ﻓ ﻮرﯼ را ﺑ ﺎ ﻧ ﺮم اﻓ ﺰار ﮐ ﺎرﺑﺮدﯼ ﺑ ﺮاﯼ ﻃ ﺮف دﻳﮕ ﺮ ارﺗﺒ ﺎط ﻧ ﺸﺎﻧﻪ‬ ‫ﮔﺬارﯼ ﻧﻤﺎﻳﺪ.ﮐﺪ ﺑﻴﺖ ‪ PSH‬ﺑﻪ ﻣﻌﻨﺎﯼ ﺁن اﺳﺖ ﮐﻪ ﻻﻳﻪ ‪ TCP‬ﺑﺎﻳﺪ از درون ﺗﻮدﻩ ﻻﻳﻪ هﺎ ﺳ ﺮﻳﻌﺎ روﺷ ﻦ ﮔ ﺮدد،و‬ ‫ﻧﺒﺎﻳﺪ ﺑﺮاﯼ ارﺳﺎل ﺑﻌﺪﯼ ﻣﻨﺘﻈﺮ ﺑﻤﺎﻧﺪ.‬

‫دﻳﮕﺮ زﻣﻴﻨﻪ هﺎﯼ ﻋﻨﻮان‪: TCP‬‬
‫در زﻣﻴﻨﻪ هﺎﯼ ﻋﻨﻮان ‪ TCP‬ﮐﻪ ﻗﺒﻼ ﺑﺮﺳﯽ ﮐﺮدﻳﻢ،ﭼﻨﺪﻳﻦ زﻣﻴﻨﻪ دﻳﮕﺮ در ﻋﻨﻮان ‪ TCP‬وﺟﻮد دارد .اﻳﻦ زﻣﻴﻨ ﻪ‬ ‫هﺎﯼ اﺿﺎﻓﯽ ﻋﺒﺎرﺗﻨﺪ از:‬ ‫‪ : Data Offset‬اﻳﻦ زﻣﻴﻨﻪ ﺟﺎﻳﯽ را در ﺑﺴﺘﻪ ‪ TCP‬ﻧﺸﺎن ﻣﯽ دهﺪ ﮐﻪ ﻋﻨﻮان ﭘﺎﻳﺎن ﻣﯽ ﻳﺎﺑﺪ و ار ﺁﻧﺠﺎ دادﻩ ه ﺎ‬ ‫ﺷﺮوع ﻣﯽ ﺷﻮﻧﺪ و ﻣﺴﺎوﯼ ﺑﺎ ﻃﻮل ﻋﻨﻮان ‪ TCP‬ﺑﺎ واژﻩ هﺎﯼ 23 ﺑﻴﺘﯽ اﺳﺖ.‬ ‫‪ : Reserved‬اﻳﻦ زﻣﻴﻨﻪ ﺑﺮاﯼ ﻣﺼﺮف ﺑﻌﺪﯼ ذﺧﻴﺮﻩ ﻣﯽ ﺷﻮد.‬ ‫‪ : Window‬اﻳﻦ زﻣﻴﻨﻪ ﺑﺮاﯼ ﮐﻨﺘﺮل ﺷﻤﺎرﻩ هﺎﯼ ﺑﺮﺟﺴﺘﻪ ارﺳﺎل ﺷﺪﻩ ﺑﻴﻦ ﺳﻴﺴﺘﻤﻬﺎ اﺳﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮد. در ه ﺮ‬ ‫ﻃﺮف ارﺗﺒﺎط ﻃﺮﻳﻘﻪ اﯼ ﺑﺮاﯼ ﮐﻨﺘﺮل ﺟﺮﻳﺎن ﺑﺴﺘﻪ هﺎ از دﻳﮕﺮ ﻗﺴﻤﺖ اﻳﺠﺎد ﻣﯽ ﮐﻨﺪﺗﺎ اﻃﻤﻴﻨﺎن دهﺪ ﮐﻪ ﺗﻤﺎم ﺑ ﺴﺘﻪ‬ ‫هﺎ ﺑﻪ ﻃﻮر ﻣﻨﺎﺳﺐ درﻳﺎﻓﺖ ﻣ ﯽ ﺷ ﻮد و ﺑ ﻪ ﺷ ﮑﻞ دﺳﺘﺮﺳ ﯽ ﻗﺒ ﻞ از اﻳﻨﮑ ﻪ ﺑ ﺴﺘﻪ ه ﺎﯼ ﺟﺪﻳ ﺪ ارﺳ ﺎل ﺷ ﻮﻧﺪ،ﻣﻮرد‬ ‫ﺗﺼﺪﻳﻖ ﻗﺮار ﻣﯽ ﮔﻴﺮد.‬ ‫‪ : Checksum‬اﻳﻦ ﺁﺷﮑﺎر ﺳﺎزﯼ ﺧﻄﺎ ﺑﺮاﯼ ﺗﺎﻳﻴﺪ اﻳﻦ ﻣﻄﺎﻟﺐ اﺳﺘﻔﺎدﻩ ﻣﯽ ﮔﺮدد ﮐ ﻪ ﺑ ﺴﺘﻪ ‪) TCP‬ﻋﻨ ﻮان دادﻩ‬ ‫هﺎ( در ﻣﺴﻴﺮش در ﻃﻮل ﺷﺒﮑﻪ ﺧﺮاب ﻧﺸﺪﻩ اﺳﺖ.‬ ‫‪ : Urgent Pointer‬اﻳ ﻦ زﻣﻴﻨ ﻪ داراﯼ اﺷ ﺎرﻩ ﮔ ﺮﯼ در دادﻩ ه ﺎﯼ ﺑ ﺴﺘﻪ ﻣ ﯽ ﺑﺎﺷ ﺪ ﺗ ﺎ ﻧ ﺸﺎن ده ﺪ ﮐ ﻪ در ﮐﺠ ﺎ‬ ‫اﻃﻼﻋﺎﺗﯽ ﮐﻪ ﻓﻮرا ﻣﻮرد ﻧﻴﺎز ﻣﯽ ﺑﺎﺷﺪ،واﻗﻊ ﻣﯽ ﺷﻮد.‬ ‫‪ : Options‬اﻳ ﻦ ﻣﺠﻤﻮﻋ ﻪ از زﻣﻴﻨ ﻪ ه ﺎ ﺑ ﺎ ﻃ ﻮل ﻣﺘﻐﻴ ﺮ ﻣ ﯽ ﺗﻮاﻧﻨ ﺪ اﻃﻼﻋ ﺎت اﺿ ﺎﻓﯽ را در ﻣ ﻮرد ﻻﻳ ﻪ ‪TCP‬‬ ‫ﺑﺘﻮاﻧﺪ ﺗﻨﻬﺎ ﺑﺴﺘﻪ هﺎﯼ ،‪ TCP‬را ﺑﺎ ﺣﺪاﮐﺜﺮ اﻧﺪازﻩ دادﻩ ﺷﺪﻩ ﭘﺸﺘﻴﺒﺎﻧﯽ ﮐﻨﺪ،ﺳﻴﺴﺘﻢ ﻣﯽ ﺗﻮاﻧﺪ اﻳ ﻦ اﻃﻼﻋ ﺎت را در‬ ‫‪ TCP Options‬ﻧﺸﺎن دهﺪ.‬ ‫‪ : Padding‬اﻳﻦ زﻣﻴﻨﻪ ﺷﺎﻣﻞ ﻣﺠﻤﻮﻋﻪ ﺻﻔﺮ ﺑﻴﺖ هﺎﯼ ﮐﺎﻓﯽ اﺳﺖ ﺗﺎ ﻃﻮل ﻋﻨ ﻮان ‪ TCP‬را ﺑ ﻪ ﺣ ﺪﯼ ﮔ ﺴﺘﺮش‬ ‫دهﺪ ﮐﻪ ﺑﻪ ﻣﺮز 23 ﺑﻴﺘﯽ ﺧﺎﺗﻤﻪ ﻳﻠﺒﺪ و در ﻋﻨﻮان داﺧﻞ ﻣﯽ ﺷﻮد ﺗﺎ ﺧﺎﻃﺮ ﻧ ﺸﺎن ﺳ ﺎزد ﮐ ﻪ ﮐﻠﻴ ﻪ ﻣ ﻮارد ﺑ ﻪ ﻃ ﻮر‬ ‫ﻣﺴﺎوﯼ ﻣﺮﺗﺐ ﺷﺪﻩ اﻧﺪ.‬

‫ﭘﺮوﺗﮑﻞ )‪User Datagram Protocol (UDP‬‬
‫در ﺣﺎﻟﯽ ﮐﻪ ﻧﺎم ﮐﻠﯽ ﭘﺮوﺗﮑﻞ ﺑﻪ ﺻﻮرت "‪ "TCP/IP‬ﻧﺎﻣﻴﺪﻩ ﻣﯽ ﺷﻮد،اﻋﻀﺎﯼ دﻳﮕﺮﯼ از اﻳﻦ ﺧﺎﻧﻮادﻩ در ﮐﻨﺎر‬ ‫‪ TCP‬و‪ IP‬وﺟ ﻮد دارﻧ ﺪ.‪ UDP‬ﭘﺮوﺗﮑ ﻞ ﻻﻳ ﻪ ‪ Transport‬دﻳﮕ ﺮﯼ اﺳ ﺖ ﮐ ﻪ ﻣ ﯽ ﺗﻮاﻧ ﺪ ﺑ ﺮ ﺑ ﺎﻻﯼ ‪ IP‬ﻗ ﺮار‬ ‫ﮔﻴ ﺮ.‪ TCP‬و‪ UDP‬ﺑ ﻪ ﻣﺜ ﺎل دو ﭘ ﺴﺮ ﻋﻤ ﻮ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ.‪ TCP‬ﺑ ﻪ ﺗﻮﺟ ﻪ ﺑﻴ ﺸﺘﺮﯼ ﻧﻴ ﺎز دارد وﺑ ﺎ ﻧ ﺎم ﺧ ﺎﻧﻮادﮔﯽ‬

‫-7-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد.اﻣﺎ ‪ UDP‬هﻨﻮز ﭘﺎﻳ ﻪ ﺑ ﺴﻴﺎرﯼ از ﻧ ﺮم اﻓ ﺰار ه ﺎﯼ ﮐ ﺎرﺑﺮدﯼ ﻣﻬ ﻢ ﻣ ﯽ ﺑﺎﺷ ﺪ.در اﻧﺘﺨ ﺎب اﻧﺘﻘ ﺎل‬ ‫دادﻩ هﺎ ﺑﺎ اﺳﺘﻔﺎدﻩ از ‪ TCP‬ﻳﺎ ‪، UDP‬ﺗﻮﺳﻌﻪ دهﻨﺪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ ﺑﺎﻳ ﺪ در ﻧﻈ ﺮ داﺷ ﺘﻪ ﺑﺎﺷ ﺪ ﮐ ﻪ ﭼ ﻪ ﻧ ﺮم‬ ‫اﻓﺰار ﮐﺎرﺑﺮدﯼ از ﻻﻳ ﻪ ‪ Transport‬ﻣ ﻮرد ﻧﻴ ﺎز ﻣ ﯽ ﺑﺎﺷ ﺪ.ﺑ ﺴﺘﻪ دادﻩ ﺷ ﺪﻩ و ﺟﺮﻳ ﺎن ارﺗﺒ ﺎط،ﻣﻌﻤﻮﻻ ‪ TCP‬ﻳ ﺎ‬ ‫‪ UDP‬ﻣ ﯽ ﺑﺎﺷ ﺪ. و ﻧﻤ ﯽ ﺗ ﻮان ه ﺮ دو ﭘﺮوﺗﮑ ﻞ را ﺑ ﻪ ﻃ ﻮر هﻤﺰﻣ ﺎن ﺑ ﻪ ﮐ ﺎرﺑﺮد.ﺳ ﺮوﻳﺲ ه ﺎﻳﯽ ﮐ ﻪ از ‪UDP‬‬ ‫اﺳﺘﻔﺎدﻩ ﻣﯽ ﻧﻤﺎﻳﻨﺪ داراﯼ ﻧﺮم اﻓﺰارهﺎﯼ ﮐﺎرﺑﺮدﯼ ﺻﻮﺗﯽ و ﺗﺼﻮﻳﺮﯼ در ﺣﺎل ﺟﺮﻳﺎن و هﻤﻮارﻩ ﺑﺎ ﭘﺎﺳﺦ و ﭘﺮس‬ ‫ﺟﻮ هﺎ ) ‪ (Domain Name Service KNS‬ﻣﯽ ﺑﺎﺳﻨﺪ.ﺑ ﺮاﯼ اﻳﻨﮑ ﻪ ﺑﺪاﻧﻴ ﺪ ﭼ ﺮا اﻳ ﻦ ﺳ ﺮوﻳﺲ ه ﺎ ﺑ ﺮ ﻣﺒﻨ ﺎﯼ‬ ‫‪ UDP‬ﻣﯽ ﺑﺎﺷﻨﺪ،ﺧﺼﻮﺻﻴﺎت ‪ UDP‬را ﺑﺎ ﺟﺰﺋﻴﺎت ﺑﻴﺸﺘﺮ ﻣﻮرد ﺗﺤﻠﻴﻞ ﻗﺮار ﻣﯽ دهﻢ.‬ ‫‪ UDP‬ﻋﺎرﯼ از ارﺗﺒ ﺎط ﻣ ﯽ ﺑﺎﺷ ﺪ ﻳﻌﻨ ﯽ ﭘﺮوﺗﮑﻞ،ﺷ ﮑﻞ و ﻧ ﻮع ارﺗﺒ ﺎط را ﻧﻤ ﯽ داﻧ ﺪ و ه ﻴﭻ ﻣﻔﻬ ﻮﻣﯽ از ﺷ ﺮوع‬ ‫دورﻩ ﮐﺎر،ﺗﺼﺪﻳﻖ،از هﻢ ﮔﺴﻴﺨﺘﮕﯽ ﻳﺎ ﻣﻮارد ﻣﺸﺎﺑﻪ دﻳﮕﺮ ﻧﺪارد.ﺑﻌﻼوﻩ،ﺧﻮد ‪ UDP‬ﺑﺴﺘﻪ هﺎﯼ از دﺳﺖ رﻓﺘﻪ را‬ ‫اﻧﺘﻘﺎل ﻧﻤﯽ دهﺪ، و ﻳﺎ ﺁﻧﻬﺎ را در ﻣﺮﺗﺒﻪ ﻣﻨﺎﺳﺐ ﻗﺮار ﻧﻤﯽ دهﺪ.ﺑﻨﺎﺑﺮاﻳﻦ ،اﮔﺮ ﺑﺴﺘﻪ 1،ﺑﺴﺘﻪ 2 و ﺑﺴﺘﻪ 3 ﻓﺮﺳ ﺘﺎدﻩ‬ ‫ﺷﻮﻧﺪ،ﻣﻘﺼﺪ ﻣﻤﮑﻦ اﺳﺖ ﺑﺴﺘﻪ 2 ،ﺑﺴﺘﻪ 1 و ﮐﭙ ﯽ دﻳﮕ ﺮﯼ از ﺑ ﺴﺘﻪ 1 را درﻳﺎﻓ ﺖ ﮐﻨ ﺪ.ﺑ ﺴﺘﻪ 3 ﮔ ﻢ ﺷ ﺪﻩ اﺳ ﺖ،و‬ ‫ﺑﺴﺘﻪ 1 ﺑﻪ ﻃﺮﻳﻘﯽ دوﺑﺎرﻩ ﻓﺮﺳﺘﺎدﻩ ﺷﺪﻩ اﺳﺖ.‪ UDP‬ذاﺗﺎ ﻏﻴﺮ ﻗﺎﺑﻞ اﻃﻤﻴﻨﺎن اﺳﺖ و ﻣﻤﮑﻦ اﺳ ﺖ ﺑ ﺴﺘﻪ ه ﺎﻳﯽ را‬ ‫ﮔﻢ ﻧﻤﺎﻳﺪ ﻳ ﺎ ﺧ ﺮاب ﺁﻧﻬ ﺎ را ﺧ ﺮاب ﮐﻨ ﺪ.ﺑﻌ ﻀﯽ از ﻧ ﺮم اﻓﺰاره ﺎﯼ ﮐ ﺎر ﺑ ﺮدﯼ ﺑ ﺮاﯼ درﻳﺎﻓ ﺖ ﺑ ﺴﺘﻪ ه ﺎﻳﯽ از ﻃﺮﻳ ﻖ‬ ‫ﺷﺒﮑﻪ ﺑﺴﻴﺎر ﺟﺎﻟﺐ ﻣﯽ ﺑﺎﺷﺪ،و ﺑﻪ اﻃﻤﻴﻨﺎن ﺑﺴﻴﺎر زﻳﺎدﯼ ﻧﻴﺎز ﻧﺪارﻧﺪ.ﭼﻨﻴﻦ ﻧﺮم اﻓﺰارهﺎﯼ ﮐ ﺎر ﺑ ﺮدﯼ اﺗ ﺼﺎل ﺳ ﻪ‬ ‫راهﻪ،ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر در هﺮ ﺑﺴﺘﻪ،ﺗﺎﻳﻴﺪ و ﻏﻴﺮﻩ ﻧﻤ ﯽ ﺧﻮاهﻨ ﺪ.در ﻋﻮض،ﺑﻌ ﻀﯽ از ﻧ ﺮم اﻓﺰاره ﺎﯼ ﮐ ﺎرﺑﺮدﯼ‬ ‫ﺑﻪ ﺳﺎدﮔﯽ و ﺳﺮﻋﺖ ﻧﻴﺎز دارﻧﺪ.‬ ‫ﻳﻪ ﺳﻮال : ﭼﻪ ﻧﻮع ﻧﺮم اﻓﺰارهﺎﯼ ﮐﺎرﺑﺮدﯼ داراﯼ اﻳ ﻦ ﻣﻠﺰوﻣ ﺎت ﻣ ﯽ ﺑﺎﺷ ﻨﺪ؟ﻏﺎﻟﺒﺎ ﻧ ﺮم اﻓﺰاره ﺎﯼ ﮐ ﺎرﺑﺮدﯼ ﮐ ﻪ‬ ‫دادﻩ هﺎﻳﯽ را ﺑﺮاﯼ ﮔﻮش و ﭼﺸﻢ اﻧﺴﺎن اﻧﺘﻘﺎل ﻣﯽ دهﻨﺪ،ﻣﺜﻞ دادﻩ هﺎﯼ ﭘﻴﻮﺳﺘﻪ ﺻﻮﺗﯽ ﻳ ﺎ ﺗ ﺼﻮﻳﺮﯼ از اﻳ ﻦ ﻧ ﻮع‬ ‫ﻣﯽ ﺑﺎﺷﻨﺪ.درﺣﺎﻟﯽ ﮐﻪ ﭼﺸﻢ وﮔﻮﺷﺘﺎن را ﺧﻮاهﻴﺪ ﺑﺴﺖ،اﮔﺮ ﺑ ﺴﺘﻪ اﯼ ﮔ ﺎﻩ و ﺑﻴﮕ ﺎﻩ از دﺳ ﺖ ﺑﺮود،اﺣﺘﻤ ﺎﻻ ﺑﻴ ﺸﺘﺮ‬ ‫وﻓﺘﯽ ﻣﺘﻮﺟﻪ ﻣﯽ ﺷﻮﻳﺪ ﮐﻪ ﺗﻤﺎم ﺑﺴﺘﻪ اﯼ ﮔﺎﻩ و ﺑﻴﮕﺎﻩ از دﺳﺖ ﺑﺮود،اﺣﺘﻤ ﺎﻻ ﺑﻴ ﺸﺘﺮ وﻗﺘ ﯽ ﻣﺘﻮﺟ ﻪ ﻣ ﯽ ﺷ ﻮﻳﺪ ﮐ ﻪ‬ ‫ﺗﻤﺎم ﺑﺴﺘﻪ هﺎ ﺑﺎ ﭘﺮدازش ﺳﻨﮕﻴﻦ و ﺑﻪ ﮐﻨﺪﯼ ارﺳﺎل ﻣﯽ ﺷﻮﻧﺪ.ﺑﻌﻼوﻩ ﺑﻌﻀﯽ از ﻧﺮم اﻓﺰارهﺎﯼ ﭘﺎﺳﺨﯽ و ﭘﺮس و‬ ‫ﺟ ﻮﻳﯽ از ‪ ، UDP‬ﻋﻠ ﯽ اﻟﺨ ﺼﻮص ‪ DNS‬اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮐﻨﻨ ﺪ.وﻗﺘ ﯽ ﺑ ﻪ ﺁدرس ﺷ ﺒﮑﻪ ﺑ ﺮاﯼ ﻧ ﺎم ﻗﻠﻤ ﺮو ﺧﺎﺻ ﯽ‬ ‫ﻧﮕﺎهﯽ ﻣﯽ اﻧﺪازﻳ ﺪ.‪ DNS‬ﺁدرس ‪ www.skodis.com‬را ﺑ ﻪ ﺷ ﻤﺎ ﻧ ﺸﺎن ﻣ ﯽ ده ﺪ.وﺑ ﺴﺘﻪ ‪ UDP‬ﻣﺠﺰاﻳ ﯽ در‬ ‫ﭘﺎﺳﺦ درﻳﺎﻓ ﺖ ﻣ ﯽ ﮔ ﺮدد ﻣ ﺜﻼ ﺑ ﺴﺘﻪ اﯼ ﮐ ﻪ اﻇﻬ ﺎر ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﺁدرس 3.14.12.01 ﻣ ﯽ ﺑﺎﺷ ﺪ اﻳ ﻦ ﻧ ﺮم اﻓ ﺰار‬ ‫ﮐﺎرﺑﺮدﯼ ﺑﻪ ﻣﻮارد اﺿﺎﻓﯽ هﻤﺮاﻩ ﺑﺎ ﺑﺮﻗﺮارﯼ ارﺗﺒﺎط ﺑﺎ اﺳﺘﻔﺎدﻩ از اﺗﺼﺎل ﺳﻪ راه ﻪ ﺑ ﺮاﯼ ارﺳ ﺎل ﭘ ﺮس وﺟ ﻮ و‬ ‫درﻳﺎﻓﺖ ﭘﺎﺳﺦ ﻧﻴﺎز ﻧﺪارﻧﺪ.‬ ‫‪ UDP‬داراﯼ ﺷﻤﺎرﻩ دروازﻩ هﺎﯼ 61 ﺑﻴﺘﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ.ﺑﻨ ﺎﺑﺮاﻳﻦ 53556 دروازﻩ ‪ UDP‬اﺣﺘﻤ ﺎﻟﯽ وﺟ ﻮد دارد.در‬ ‫‪، TCP‬دادﻩ ه ﺎ از ﻳ ﮏ دروازﻩ ﺳﻴ ﺴﺘﻢ ﻣﺒ ﺪا ﺑﻴ ﺮون ﻣ ﯽ ﺁﻳﻨ ﺪ )دروازﻩ ﻣﺒ ﺪا‪، (UDP‬و ﺑ ﻪ دروازﻩ اﯼ ﮐ ﻪ در‬ ‫ﺳﻴﺴﺘﻢ ﻣﻘﺼﺪ ﺧﺘﻢ ﻣﯽ ﺷﻮﻧﺪ)دروازﻩ ﻣﻘﺼﺪ ‪، ( UDP‬ﻳﮑﯽ از ﻣﺘﺪاول ﺗ ﺮﻳﻦ ﺳ ﺮوﻳﺲ ه ﺎﯼ ‪ UDP‬ﮐ ﻪ ﺑ ﻪ ﻃ ﻮر‬ ‫وﺳﻴﻊ اﺳﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮد)‪ (DNS‬ﻣﻨﺘﻈ ﺮ درﻳﺎﻓ ﺖ ﭘﺎﺳ ﺦ از ﭘ ﺮس وﺟﻮه ﺎﯼ ‪ DNS‬در دروازﻩ 35 و ‪ UDP‬ﻣ ﯽ‬ ‫ﻣﺎﻧﺪ.دﻳﮕﺮ ﺳﺮوﻳﺲ هﺎﯼ ‪ UDP‬ﻋﺒﺎرﺗﻨﺪ از :‬ ‫96 ‪Trivial File Transports Protocol (TFTP),UDP Port‬‬ ‫161 ‪Simple Network Management Protocol (SNMP) ,UDP Port‬‬ ‫)‪RealPlayer (audio/video‬‬

‫ﺁﻳﺎ ‪ UDP‬اﻳﻤﻨﯽ ﮐﻤﺘﺮﯼ از ‪ TCP‬دارد؟‬
‫ﺑﺪون اﺗﺼﺎل ﺳﻪ راهﻪ،ﺁﻳﺎ ‪ UDP‬اﻳﻤﻨﯽ ﮐﻤﺘﺮﯼ از ‪ TCP‬دارد؟ ﺑ ﻪ ﻋﺒ ﺎرت دﻳﮕﺮ،ﺁﻳ ﺎ ﻧ ﺮم اﻓ ﺰار ه ﺎﯼ ﮐ ﺎرﺑﺮدﯼ‬ ‫ﮐﻪ در ‪ UDP‬اﺟﺮا ﻣﯽ ﺷﻮﻧﺪ ﺳ ﺨﺖ ﺗ ﺮ ازﺳ ﺮوﻳﺲ ه ﺎﯼ ‪ TCP‬اﻳﻤ ﻦ ﻣ ﯽ ﺷ ﻮد ﮐ ﻪ اﻟﺒﺘ ﻪ، ﺑ ﺮاﯼ اﺟ ﺰاﯼ ﺷ ﺒﮑﻪ‬ ‫درﮎ و ردﮔﻴﺮﯼ ﺁﻧﭽﻪ ﮐﻪ ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ ﺑﺎ اﺳﺘﻔﺎدﻩ از ‪ UDP‬ﺻﻮرت ﻣ ﯽ ﮔﻴ ﺮد )ﻣﺜ ﻞ دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ و‬ ‫ﻣﺴﻴﺮ ﻳﺎﺑﻬﺎ( ﺑﺮﺧﻼف ‪ TCP‬ﺳﺨﺖ ﺗﺮ و ﻣﺸﮑﻞ ﺗﺮ ﻣﯽ ﺑﺎﺷﺪ.ﺑﻪ ﺧﺼﻮص ،ﮐﺪﺑﻴﺖ ه ﺎﯼ ‪ TCP‬و ﺷ ﻤﺎرﻩ ﻣﺮاﺣ ﻞ‬ ‫اﺷﺎرﻩ هﺎﯼ ﺑﺴﻴﺎر زﻳﺎدﯼ را ﺑﻪ دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ و ﻣﺴﻴﺮ ﻳﺎﺑﻬﺎ داﻧﺪ.ﺑﻨﺎﺑﺮاﻳﻦ ﺑﺎ ﺁﻧﻬﺎ راﺣﺘﺘﺮ ﻣﯽ ﺗﻮان ارﺗﺒﺎط را‬ ‫ﮐﻨﺘﺮل ﮐﺮد.ﺟﺰﺋﯽ از ﺷﺒﮑﻪ از زﻣﺎن ﺑﺮﻗﺮارﯼ دورﻩ ﮐﺎر ‪ TCP‬اﻃﻼع ﻻزم دارد،ﺑﺮاﯼ اﻳﻨﮑﻪ ﻣﯽ ﺗﻮاﻧﺪ ﺑﻪ ﮐ ﺪﺑﻴﺖ‬ ‫‪ SYN‬رﺟﻮع ﻧﻤﺎﻳﺪ ﺑﻌﻼوﻩ ﻣﺴﻴﺮ ﻳ ﺎب ﻳ ﺎ دﻳ ﻮارﻩ ﺁﺗ ﺶ از زﻣ ﺎن ﺗ ﺼﺪﻳﻖ ﺑ ﺴﺘﻪ ﻳ ﺎ دورﻩ ﮐ ﺎرﯼ ﮐ ﻪ ﮔﺴ ﺴﺘﻪ ﺷ ﺪﻩ‬ ‫اﺳﺘﻮﺑﺎ ﺳﺎﺧﺖ ﮐﺪﺑﻴﺖ هﺎ و ﺷﻤﺎرﻩ ﻣﺮاﺣﻞ ﮐﺎر اﻃﻼع دارد.‬ ‫ﺑﺎ ﻧﺒﻮد ﮐﺪﺑﻴﺘﻬﺎ و ﻣﺮاﺣﻞ ﮐﺎر ‪ ، UDP‬ردﻳﺎﺑﯽ ﺟ ﺎﻳﯽ ﮐ ﻪ دو ﺳﻴ ﺴﺘﻢ ﺑ ﺎ ه ﻢ در ارﺗﺒ ﺎط ﻣ ﯽ ﺑﺎﺷﻨﺪ،ﺑ ﺴﻴﺎر ﻣ ﺸﮑﻠﺘﺮ‬ ‫اﺳﺖ.ﺑ ﺴﺘﻪ ه ﺎﯼ ‪ UDP‬ﮐ ﻪ از اﻳﻨﺘﺮﻧ ﺖ ﺣﺎﺻ ﻞ ﻣ ﯽ ﺷ ﻮﻧﺪ،ﻣﯽ ﺗﻮاﻧﻨ ﺪ ﭘﺎﺳ ﺦ ه ﺎﻳﯽ ﺑ ﺮاﯼ ﺳ ﺮوﻳﺲ ه ﺎﯼ ﻣﻨﻄﻘ ﯽ‬ ‫ﺑﺎﺷﻨﺪ،ﻳﺎ ﻣﯽ ﺗﻮاﻧﻨﺪ اﺳﮑﻦ هﺎﻳﯽ ﺑﺎﺷﻨﺪ ﮐﻪ از روﯼ ﺳﻮءﻧﻴﺖ ﺻﻮذت ﻣﯽ ﮔﻴﺮد.‬ ‫ﺑﺎ ﺟﺴﺘﺠﻮﯼ ﺳﺎدﻩ در ﻋﻨﻮان ‪ ،UDP‬ﻣﯽ ﺗﻮان دﻳﺪ هﻴﭻ ﻃﺮﻳﻘﯽ وﺟﻮد ﻧﺪارد ﮐﻪ ﺑﮕﻮﻳﻴﻢ ﺑﺴﺘﻪ ﻧﺮم ﻓ ﺎزارﯼ، ﻗﻄ ﻪ‬ ‫ﺷﺮوع ارﺗﺒﺎط ﻳ ﺎ ﭘﺎﺳ ﺦ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ.ﺑﻨ ﺎﺑﺮاﻳﻦ ﮐﻨﺘ ﺮل ‪ UDP‬از ﻟﺤ ﺎظ اﻳﻤﻨ ﯽ ﺑ ﺴﻴﺎر ﻣ ﺸﮑﻠﺘﺮ از ﮐﻨﺘ ﺮل ‪ TCP‬ﻣ ﯽ‬ ‫ﺑﺎﺷﺪ.‬

‫-8-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬ ‫ﺧﻮب در اداﻣﻪ درﺑﺎرﻩ دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ ﺗﻮﺿﻴﺢ ﺧﻮاهﻢ داد.‬

‫ﭘﺮوﺗﮑﻞ ‪ IP‬و ﭘﺮوﺗﮑﻞ ﭘﻴﻐﺎم ﮐﻨﺘﺮل اﻳﻨﺘﺮﻧﺖ )‪(ICMP‬‬
‫وﻓﺘ ﯽ ﻻﻳ ﻪ ‪ TCP‬ﻳ ﺎ ‪ UDP‬ﺑ ﺴﺘﻪ اﯼ را ﺗﻮﻟﻴ ﺪ ﻣ ﯽ ﻧﻤﺎﻳﻨ ﺪ،اﻳﻦ ﺑ ﺴﺘﻪ ﺑﺎﻳ ﺪ از ﻃﺮﻳ ﻖ ﺷ ﺒﮑﻪ ارﺳ ﺎل ﺷ ﻮﻧﺪﻩ ﻻﻳ ﻪ‬ ‫‪ ، (TCP or UDP) Transport‬ﺑﺴﺘﻪ را ﺑ ﻪ ﻻﻳ ﻪ ‪ Network‬ﻣ ﻮرد اﺳ ﺘﻔﺎدﻩ اﻣ ﺮوزﯼ ﻣ ﯽ ﺑﺎﺷ ﺪ، و ﺑ ﺮاﯼ‬ ‫ﺗﻤﺎم ﺗﺮاﻓﻴﮑﻬﺎﻳﯽ ﮐﻪ در ﺣﺎل ﺣﺮﮐﺘﺎز ﻃﺮﻳﻖ اﻳﻨﺘﺮﻧﺖ ﻣﯽ ﺑﺎﺷﻨﺪ.اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد. در هﻨﮕﺎم درﻳﺎﻓ ﺖ اﻃﻼﻋ ﺎت از‬ ‫ﻻﻳﻪ ‪ ، Transport‬ﻻﻳﻪ ‪ IP‬ﻋﻨﻮاﻧﯽ را ﺗﻮﻟﻴﺪ ﻣﯽ ﮐﻨﺪ ﮐ ﻪ ﺷ ﺎﻣﻞ ﺁدرس ‪ IP‬ﻣﻘ ﺼﺪ و ﻣﺒ ﺪا ﻣ ﯽ ﺑﺎﺷ ﺪ.ﻋﻨ ﻮان ﺑ ﻪ‬ ‫ﺟﻠﻮﯼ ﺑﺴﺘﻪ ‪ TCP‬اﻟﺼﺎق ﻣﯽ ﺷﻮد ﺗﺎ ﺑﺴﺘﻪ ‪ IP‬ﻓﺎﺻﻠﻪ اﯼ را اﻳﺠﺎد ﻧﻤﺎﻳﺪ،ﮐﻪ ﺑﺮاﯼ ﺣﻤﻞ ﮐﻞ ﻣﺤﺘﻮﻳﺎت از ﻃﺮﻳ ﻖ‬ ‫ﺷﺒﮑﻪ اﺳﺘﻔﺎدﻩ ﺧﻮاهﻨﺪ ﺷﺪ )ﻋﻨﻮان ‪ ، IP‬ﻋﻨﻮان ‪ ، TCP‬و دادﻩ هﺎﯼ ﺗﺮاز ﻧﺮم اﻓﺰار ﮐﺎرﺑﺮدﯼ(.‬

‫ﺷﺒﮑﻪ هﺎﯼ ﻧﺎﺣﻴﻪ ﻣﺤﻠﯽ و ﻣﺴﻴﺮﻳﺎب هﺎ‬
‫ﺑﺮاﯼ اﻳﻨﮑﻪ ﺑﺪاﻧﻴﻢ ‪ IP‬ﭼﻄﻮر ﮐﺎر ﻣﯽ ﮐﻨﺪ، ﻻزم اﺳ ﺖ ﮐﻤ ﯽ وﻗ ﺖ ﺑﮕ ﺬارﻳﻢ و روش ﺳ ﺎﺧﺘﻪ ﺷ ﺪن ﺷ ﺒﮑﻪ را درﮎ‬ ‫ﮐﻨﻴﻢ.هﺪف از ‪ IP‬ﻣﺤﻞ ﺑﺴﺘﻪ هﺎﯼ ﻣﺘﺪاوم اﻧﺘﻘﺎل ﻳﺎﻓﺘﻪ از ﻃﺮﻳﻖ ﺷ ﺒﮑﻪ ﻣ ﯽ ﺑﺎﺷ ﺪ.اﻣ ﺎ در واﻗ ﻊ ﺷ ﺒﮑﻪ ﭼ ﻪ ﭼﻴ ﺰﯼ‬ ‫ﻣ ﯽ ﺑﺎﺷ ﺪ؟ ﺷ ﺒﮑﻪ ه ﺎﯼ ﮐﺎﻣ ﻞ از ﺑﻠ ﻮﮎ ه ﺎﯼ ﺳ ﺎﺧﺘﺎرﯼ ﭘﺎﻳ ﻪ ﺳ ﺎﺧﺘﻪ ﻣ ﯽ ﺷ ﻮﻧﺪ ﮐ ﻪ ﺷ ﺒﮑﻪ ه ﺎﯼ ﻧﺎﺣﻴ ﻪ ﻣﺤﻠ ﯽ‬ ‫)‪ (LAN‬ﻧﺎﻣﻴﺪﻩ ﻣ ﯽ ﺷ ﻮﻧﺪ. ‪ LAN‬ﺑﻄ ﻮر ﺳ ﺎدﻩ دﺳ ﺘﻪ اﯼ از ﮐ ﺎﻣﭙﻴﻮﺗﺮ ه ﺎﯼ ﻣﺘ ﺼﻞ ﺑ ﻪ ه ﻢ ﺑ ﻪ اﺳ ﺘﻔﺎدﻩ از ﮐﻠﻴ ﺪ‬ ‫ﻣﺮﮐﺰﯼ اﺳﺖ، ﮐ ﻪ ﻣ ﺴﻴﺮ ﻳ ﺎب ه ﺎﻳﯽ ﺟ ﺪا از ﺳﻴ ﺴﺘﻢ ه ﺎ ﻧﺪارﻧ ﺪ. هﻤ ﺎﻧﻄﻮر ﮐ ﻪ ﻧ ﺎم ﺁﻧﻬ ﺎ ﺑﻴ ﺎن اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ،‬ ‫‪ LAN‬ﺑﻄ ﻮر ﻧﻤﻮﻧ ﻪ و از ﻟﺤ ﺎظ ﺟﻐﺮاﻓﻴ ﺎﻳﯽ ﮐﻮﭼ ﮏ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ،ﻣﻌﻤﻮﻻ در ﻳ ﮏ ﺳ ﺎﺧﺘﻤﺎن ﻳ ﺎ در ﻳ ﮏ ﻣﺤ ﻴﻂ‬ ‫داﻧﺸﮕﺎهﯽ ﮐﻮﭼﮏ ﻣﻮرد ﮐﺎرﺑﺮد دارﻧﺪ.‬ ‫ﺷﺒﮑﻪ هﺎﯼ ﻣﺤﻠﯽ )‪ (LANs‬ﺑﺎ ﻳﮑﺪﻳﮕﺮ ﺑﻪ اﺳﺘﻔﺎدﻩ از ﻣﺴﻴﺮﻳﺎب ه ﺎ ﻣﺘ ﺼﻞ ﻣ ﯽ ﺷ ﻮﻧﺪ.ﮐ ﺎر ﻣ ﺴﻴﺮﻳﺎب ﺟ ﺎ ﺑ ﻪ ﺟ ﺎ‬ ‫ﮐﺮدن ﺑﺴﺘﻪ هﺎ ﺑﻴﻦ ﺷﺒﮑﻪ هﺎﯼ ﻣﺤﻠﯽ اﺳﺖ، در ﻧﺘﻴﺠﻪ ﺑﺪﻳﻦ ﺗﺮﺗﻴ ﺐ ﺷ ﺒﮑﻪ ﺑﺰرﮔ ﯽ را اﻳﺠ ﺎد ﻣ ﯽ ﮐﻨ ﺪ.ﻳ ﮏ ﻳ ﺎ ﭼﻨ ﺪ‬ ‫ﭘﺮوﺗﮑﻞ ﻻﻳﻪ ‪ ،Network‬دادﻩ ه ﺎ را ﺑ ﻪ ﻃ ﻮر ﻣ ﺪاوم از ﻃﺮﻳ ﻖ ﺷ ﺒﮑﻪ، و از ﻳﺎراﻧ ﻪ ﮐ ﺎرﺑﺮ، از ﻃﺮﻳ ﻖ ﻳﮑ ﺴﺮﯼ‬ ‫ﻣﺴﻴﺮ ﻳﺎﺑﻬﺎ ، ﺑﻪ ‪ LAN‬ﻧﻬﺎﻳﯽ و ﺑﻪ ﻣﻘﺼﺪ ﻧﻬﺎﻳﯽ ﻣﻨﺘﻘﻞ ﻣﯽ ﮐﻨﺪ. اﻟﺒﺘﻪ، ﺑﺴﻴﺎرﯼ از ﺳﻴﺴﺘﻤﻬﺎ ﺑﻪ ﻃﻮر ﻣﺴﺘﻘﻴﻢ ﺑﻪ‬ ‫ﻣﺴﻴﺮﻳﺎﺑﻬﺎ ﺑﺎ ﻳﮑﺪﻳﮕﺮ ﺑﺎ اﺳﺘﻔﺎدﻩ از اﺗﺼﺎﻻت ﻧﻘﻄﻪ ﺑ ﻪ ﻧﻘﻄ ﻪ ﻣﺘ ﺼﻞ ﻣ ﯽ ﮔﺮدﻧ ﺪ.ﺧ ﻮد اﻳﻨﺘﺮﻧ ﺖ ﭼﻴ ﺰﯼ ﻧﻴ ﺴﺖ اﻣ ﺎ‬ ‫ﻣﺠﻤﻮﻋﻪ ﺣﺎﺻﻠﻪ اﯼ اﺳﺖ از ﺷﺒﮑﻪ هﺎﯼ ﻣﺤﻠﯽ و اﺗﺼﺎﻻت ﻧﻘﻄﻪ ﺑﻪ ﻧﻘﻄﻪ ﺑﺎ ﻳﮑﺪﻳﮕﺮ ﮐﻪ ﺑﺎ اﺳ ﺘﻔﺎدﻩ از دﺳ ﺘﻪ اﯼ‬ ‫از ﻣﺴﻴﺮ ﻳﺎﺑﻬﺎ ﺑﻪ هﻢ ﻣﺘﺼﻞ ﻣﯽ ﺷﻮﻧﺪ.‬

‫ﺁدرﺳﻬﺎﯼ ‪IP‬‬
‫ﺁدرس هﺎﯼ ‪ IP‬دﺳﺘﮕﺎﻩ ﺧﺎﺻﯽ را ﺑﺮ روﯼ ﺷﺒﮑﻪ ﺗﻌﺮﻳﻒ ﻣﯽ ﻧﻤﺎﻳﺪ،و 23 ﺑﻴﺖ ﻃﻮل دارﻧﺪ. هﺮ ﺳﻴ ﺴﺘﻢ ﺑ ﻪ ﻃ ﻮر‬ ‫ﻣ ﺴﺘﻘﻴﻢ ﺑ ﻪ اﻳﻨﺘﺮﻧ ﺖ ﻣﺘ ﺼﻞ ﻣ ﯽ ﮔ ﺮدد و ﺁدرس ‪ IP‬واﺣ ﺪﯼ دارد.ﺁدرس ه ﺎﯼ ‪ IP‬ﻣﻌﻤ ﻮﻻ در ﻧﻤﺎدﮔ ﺬارﯼ ﭼﻬ ﺎر‬ ‫ﻧﻘﻄ ﻪ اﯼ ﻧﻮﺷ ﺘﻪ ﻣ ﯽ ﺷ ﻮد. ﻧﻤﺎدﮔ ﺬارﯼ ﭼﻬ ﺎر ﻧﻘﻄ ﻪ اﯼ ه ﺮ ﭼﻬ ﺎر دﺳ ﺘﻪ ه ﺸﺖ ﺑﻴﺘ ﯽ از ﺁدرس ه ﺎﯼ ‪ IP‬را ﺑ ﻪ‬ ‫ﺻ ﻮرت ﻋ ﺪدﯼ ﺑ ﻴﻦ ﺻ ﻔﺮ و 552 را ﻟﻴ ﺴﺖ ﻣ ﯽ ﻧﻤﺎﻳﺪ،ﮐ ﻪ ﺣﺎﺻ ﻞ ﺁن ﺁدرس ‪ IP‬ﺑ ﻪ ﺷ ﮑﻞ ‪ W.X.Y.Z‬ﻣ ﺜﻼ‬ ‫3.14.12.01 ﻣﯽ ﺑﺎﺷﺪ. ﻣﺜﺎل ﭘﺎﻳﻴﻦ‬ ‫3.14.12.01‬ ‫=‬ ‫01010000‬ ‫10101000‬ ‫10010100‬ ‫11000000‬

‫ه ﺮ ﺑ ﺴﺘﻪ ‪ IP‬ﺣ ﺎوﯼ ﺁدرس ‪ IP‬ﻣﺒ ﺪا ﻣ ﯽ ﺑﺎﺷ ﻨﺪ، و ﺳﻴ ﺴﺘﻤﯽ را ﺗﻌ ﺮف ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ در ﺣ ﺎل ارﺳ ﺎل ﺑ ﺴﺘﻪ، و‬ ‫ﺁدرس ‪ IP‬ﻣﻘﺼﺪ ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ ﺳﻴﺴﺘﻢ را ﺑﺮاﯼ ﺑﺴﺘﻪ ﺗﻌﺮﻳﻒ ﻣﯽ ﮐﻨﺪ.‬

‫ﻧﺖ ﻣﺴﮑﻬﺎ‬
‫هﺮ ﺁدرس ‪ IP‬در واﻗﻊ ﺣﺎوﯼ دو ﻣﻮﻟﻔﻪ ﻣﯽ ﺑﺎﺷﺪ. ﺁدرس ﺷﺒﮑﻪ و ﺁدرس ﻣﻴﺰﺑ ﺎن در ﺁن ﺷ ﺒﮑﻪ ﺧ ﺎص ، ﺁدرس‬ ‫ﺷﺒﮑﻪ ‪ LAN‬ﺧﺎﺻﯽ را ﺗﻮﺿﻴﺢ ﻣﯽ دهﺪ ﮐﻪ در ﺁ» داد وﺳﺘﺪ دادﻩ هﺎ ﻣﯽ ﺗﻮاﻧﺪ ﺑ ﺮاﯼ ارﺳ ﺎل ﺗﻨﻈ ﻴﻢ ﺷ ﻮد.ﺁدرس‬ ‫ﻣﻴﺰﺑﺎن دﺳﺘﮕﺎﻩ ﺧﺎﺻﯽ را در ‪ LAN‬دادﻩ ﺷﺪﻩ ﻣﻌﺮﻓﯽ ﻣﯽ ﮐﻨﺪ.‬ ‫ﭼﻄﻮر ﮐﺎﻣﭙﻴﻮﺗﺮ ﻳﺎ ﻣﺴﻴﺮ ﻳﺎب ﻣﯽ داﻧﺪ ﮐﻪ ﮐﺪام ﺑﺨﺶ از ﺁدرس ‪ IP‬ﺑﻪ ﺷ ﺒﮑﻪ اﺷ ﺎرﻩ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ و ﮐ ﺪام ﺑﺨ ﺶ ﺑ ﻪ‬ ‫ﻣﻴﺰﺑﺎن اﺷﺎرﻩ ﻣﯽ ﮐﻨﺪ؟ اﻳﻦ اﻃﻼﻋﺎت ﺑﺮﭘﺎﻳﻪ ﭼﻴﺰﯼ ﺗﻌﻴﻴﻦ ﻣﯽ ﮔ ﺮدد ﮐ ﻪ ﻧ ﺖ ﻣ ﺴﮏ ﻧﺎﻣﻴ ﺪﻩ ﻣ ﯽ ﺷ ﻮد. ﻧ ﺖ ﻣ ﺴﮏ‬ ‫ﺗﻌﺮﻳﻒ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﮐ ﺪام ﺑﻴﺘﻬ ﺎ در ﺁدرس ﺷ ﺒﮑﻪ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ )ﮐ ﻪ ﻣ ﺎﺑﻘﯽ ﺑﻴﺘﻬ ﺎ در ﺁدرس ‪ IP‬در ﺑﺨ ﺶ ﻣﻴﺰﺑ ﺎن‬ ‫ﺁأرس وﺟ ﻮد دارﻧ ﺪ(.ﻧ ﺖ ﻣ ﺴﮏ ﺷ ﻤﺎرﻩ دوﺗ ﺎﻳﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ.وﻗﺘ ﯽ ﺑﻴ ﺖ دادﻩ ﺷ ﺪﻩ در ﺁدرس ‪ IP‬ﺑﺨ ﺸﯽ از ﺁدرس‬ ‫ﺷﺒﮑﻪ ﺑﺎﺷﺪ، داراﯼ ﻣﺠﻤﻮﻋﻪ ﺑﻴﺘﻬﺎﯼ ﻣﺴﺎوﯼ ﺑﺎ ﻳﮏ اﺳﺖ.وﻗﺘﯽ ﺑﻴﺖ ﺁدرس ‪ IP‬ﺑﺨﺸﯽ از ﺁدرس ﻣﻴﺰﺑ ﺎن ﺑﺎﺷ ﺪ،‬ ‫ﻧﺖ ﻣﺴﮏ داراﯼ ﺑﻴﺖ ﺻﻔﺮ ﻣﯽ ﺑﺎﺷﺪ.ﺑﻨﺎﺑﺮاﻳﻦ ، ﻣﯽ ﺗﻮاﻧﻴﺪ ﺁﻧﭽﻪ را ﮐﻪ ﺷﺒﮑﻪ ﺑﺎ اﺳﺘﻔﺎدﻩ از ﺗﺎﺑﻊ ‪ XOR‬در ﺣ ﺎل‬ ‫ﺗﺮﮐﻴﺐ ﮐ ﻞ ﺁدرس ‪ IP‬ﺑ ﺎ ﻧ ﺖ ﻣ ﺴﮏ اﺳ ﺖ را ﭘﻴﮑﺮﺑﻨ ﺪﯼ ﻧﻤﺎﻳﻴ ﺪ.ﻧ ﺖ ﻣ ﺴﮑﻬﺎ ﻧﻴ ﺰ ﻣﺜ ﻞ ﺁدرﺳ ﻬﺎﯼ ‪ IP‬ﺑ ﻪ ﺻ ﻮرت‬ ‫ﻧﻤﺎدﮔﺬارﯼ ﭼﻬﺎر ﻧﮑﺘﻪ اﯼ ﻧﻮﺷﺘﻪ ﻣﯽ ﺷﻮﻧﺪ.‬ ‫-9-‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫: ‪Address‬‬ ‫: ‪Netmask‬‬

‫3.14.12.01‬

‫=‬

‫01010000‬ ‫11111111‬

‫10101000‬ ‫11111111‬

‫10010100‬ ‫00000000‬

‫11000000‬ ‫00000000‬ ‫‪XOR‬‬

‫= 0.0.552.552‬

‫_______________________________________________________‬ ‫00000000 00000000 10101000 01010000‬

‫ﺗﻘﺴﻴﻢ ﺑﻨﺪﯼ ﺑﺴﺘﻪ ﻧﺮم اﻓﺰارﯼ در ‪ IP‬ﺑﻪ ﺻﻮرت ﻗﻄﻌﺎت ﻣﺴﺎوﯼ‬
‫ﻣﺤﻴﻂ هﺎﯼ ﻣﺘﻔﺎوت اﻧﺘﻘﺎل دارﯼ ﺧﺼﻮﺻﻴﺎت ﻋﻤﻠﮑﺮد ﻣﺨﺘﻠ ﻒ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ. ﺑﻌ ﻀﯽ از ﻣﺤ ﻴﻂ ه ﺎ، وﻗﺘ ﯽ ﺑ ﺴﺘﻪ ه ﺎ‬ ‫ﺑﺰرﮔﺘﺮﻧﺪ،ﮐﺎر ﺑﺴﻴﺎر ﺑﻬﺘﺮﯼ را اﻧﺠﺎم ﻣﯽ دهﻨﺪ. در ﺣﺎﻟﯽ ﮐﻪ ﻣ ﺎ ﺑﻘ ﯽ از داﺷ ﺘﻦ ﺑ ﺴﺘﻪ ه ﺎﯼ ﻧﺮﻣ ﺎﻓﺰارﯼ ﮐ ﻪ ﻃ ﻮل‬ ‫ﮐﻮﺗﺎهﺘﺮﯼ دارﻧﺪ،ﺳﻮد ﻣﯽ ﺑﺮﻧﺪ. ﺑﺮاﯼ ﻣﺜﺎل،دﺳﺘﻪ ﺑﻨﺪﯼ ﺑﺴﺘﻪ ‪ IP‬اﻧﺘﻘﺎل ﻳﺎﻓﺘﻪ از ﻃﺮﻳﻖ ﻣﺎهﻮارﻩ ﺑﺴﺒﺎر ﻣ ﺸﮑﻠﺘﺮ‬ ‫از ارﺳﺎل ﺑﺴﺘﻪ اﯼ اﺳﺖ ﮐﻪ از ﺟﻠﻮﯼ ﺷﻴ ﺸﻪ دﻓﺘﺮﺗ ﺎن ﻣ ﯽ ﮔ ﺬرد.در ﺣ ﻴﻦ ارﺳ ﺎل اﻃﻼﻋ ﺎت از ﻃﺮﻳ ﻖ ﻣ ﺎهﻮارﻩ ،‬ ‫ﺑﺴﺘﻪ هﺎﯼ ﺑﺰرﮔﺘﺮ ﮐﺎرﺁﻳﯽ ﺑﻴﺸﺘﺮﯼ دارﻧﺪ،ﺑﺮاﯼ ﺑﻬﻴﻨﻪ ﺳﺎزﯼ ﻃﻮل اﻃﻼﻋ ﺎت ﺑ ﺮاﯼ اﺗ ﺼﺎل ارﺗﺒ ﺎﻃﯽ ﻣﺨﺘﻠ ﻒ ،‪IP‬‬ ‫ﺑﺮاﯼ اﺟﺰاﯼ ﺷﺒﮑﻪ )ﻣﺜﻞ دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ ﻳ ﺎ ﻣ ﺴﻴﺮ ﻳﺎﺑﻬ ﺎ( ﺗﻮاﻧ ﺎﻳﯽ ﻻزم را ﻓ ﺮاهﻢ ﻣ ﯽ ﺁورد ﺗ ﺎ ﺑ ﺴﺘﻪ ه ﺎ را ﺑ ﻪ‬ ‫ﻗﻄﻌﺎت ﮐﻮﭼﮑﺘﺮ ﺗﻘﺴﻴﻢ ﻧﻤﺎﻳﺪ، ﻋﻤﻠﯽ ﮐﻪ ﺗﻘﺴﻴﻢ ﻧﻤﺎﻳﺪ،ﻋﻤﻠﯽ ﮐﻪ ﺗﻘﺴﻴﻢ ﺑﻨﺪﯼ ﺑﺎ ﻗﻄﻌﺎت ﻣﺴﺎوﯼ ،ﻧﺎﻣﻴ ﺪﻩ ﻣ ﯽ ﺷ ﻮد.‬ ‫ﺳﻴﺴﺘﻢ ﻣﻘﺼﺪ ﻳﺎ ﺷﺒﮑﻪ ﻣﯽ ﺗﻮاﻧﺪ ﺑﺴﺘﻪ هﺎﯼ ‪ IP‬ﺑﺰرگ را ﺑﭙﺬﻳﺮد و ﺁﻧﻬﺎ را ﺑﻪ ﻗﻄﻌﺎت ﮐﻮﭼﮑﺘﺮ و ﺑﺮاﯼ اﻧﺘﻘﺎل از‬ ‫ﻃﺮﻳﻖ ﺷﺒﮑﻪ ﺗﻘ ﺴﻴﻢ ﻧﻤﺎﻳ ﺪ.ﻻﻳ ﻪ ‪ IP‬ﺳﻴ ﺴﺘﻢ ﻣﻘ ﺼﺪ ﻣ ﺴﺌﻮل ﺳ ﺮ ه ﻢ ﺑﻨ ﺪﯼ دوﺑ ﺎرﻩ ﻗﻄﻌ ﺎت اﺳ ﺖ و ﻗﺒ ﻞ از اﻳﻨﮑ ﻪ‬ ‫اﻃﻼﻋﺎت اﻃﻼﻋﺎت ﺑﻪ ﻻﻳﻪ اﻧﺘﻘﺎل ﻋﺒﻮر ﻧﻤﺎﻳﻨﺪ.‬ ‫ﻋﻨﻮان ‪ IP‬دو زﻣﻴﻨﻪ را ﻓﺮاهﻢ ﻣﯽ ﺁورد ﺗﺎ از اﻳﻦ ﻋﻤﻞ ﺗﻘﺴﻴﻢ ﺑﻨﺪﯼ ﭘﺸﺘﻴﺒﺎﻧﯽ ﮐﻨﺪ در اﺑﺘ ﺪا زﻣﻴﻨ ﻪ ‪Fragment‬‬ ‫‪ Offset‬ﺑﻪ دوﺳﻴﺴﺘﻢ ﻣﯽ ﮔﻮﻳﺪ ﮐﻪ در ﮐﺠﺎ ﻣﻨﺪﺟﺎت اﻳﻦ ﻗﻄ ﻪ ﺑﺎﻳ ﺪ وﺟ ﻮد داﺷ ﺘﻪ ﺑﺎﺷ ﺪ،وﻗﺘﯽ ﮐ ﻪ ﮐ ﻞ ﺑ ﺴﺘﻪ از ﻧ ﻮ‬ ‫ﺳﺮ هﻢ ﺑﻨﺪﯼ ﻣﯽ ﺷﻮد.زﻣﻴﻨﻪ ‪ Identification‬ﺑﺎ ﺳﻴﺴﺘﻢ ﺗﻘﺴﻴﻢ ﺑﻨﺪﯼ ﺑﻪ ﻣﻘ ﺪار واﺣ ﺪﯼ ﺗﻨﻈ ﻴﻢ ﻣ ﯽ ﺷ ﻮد ﺗ ﺎ ﺑ ﻪ‬ ‫ﺳﻴﺴﺘﻢ ﻣﻘﺼﺪ ﮐﻤ ﮏ ﻧﻤﺎﻳ ﺪ، ﺑ ﺴﺘﻪ را ﻧ ﻮ ﺳ ﺮ ه ﻢ ﺑﻨ ﺪﯼ ﻧﻤﺎﻳ ﺪ. ﺑﻌ ﻼوﻩ، ﻧ ﺸﺎﻧﻪ ه ﺎﯼ ﻋﻨ ﻮان ‪ IP‬اﻃﻼﻋ ﺎﺗﯽ را در‬ ‫ﻣﻮرد ﺗﻘﺴﻴﻢ ﺑﻨﺪﯼ اﻃﻼﻋﺎت ﻣﺸﺨﺺ ﻣﯽ ﮐﻨﺪ. ﺳﻴ ﺴﺘﻢ ارﺳ ﺎل ﮐﻨﻨ ﺪﻩ ﻣ ﯽ ﺗﻮاﻧ ﺪ اﻳ ﻦ زﻣﻴﻨ ﻪ ه ﺎ را ﻧﺘﻈ ﻴﻢ ﻧﻤﺎﻳ ﺪ ﺗ ﺎ‬ ‫ﻧﺸﺎن دهﺪ ﮐﻪ ﺑﺴﺘﻪ ﻧﺒﺎﻳ ﺪ در هﻨﮕ ﺎم ارﺳ ﺎل از ﻃﺮﻳ ﻖ ﺷ ﺒﮑﻪ ﺗﻘ ﺴﻴﻢ ﺷ ﻮد.اﻟﺒﺘ ﻪ اﮔ ﺮ ﺑ ﺴﺘﻪ اﯼ ﺗﻘ ﺴﻴﻢ ﺷ ﻮد، اﻳ ﻦ‬ ‫ﻧﺸﺎﻧﻪ هﺎ ﻣﺸﺨﺺ ﻣﯽ ﮐﻨﻨﺪﮐﻪ ﺁﻳﺎ ﻗﻄﻌﺎت دﻳﮕﺮﯼ از ﺑﺴﺘﻪ اﺻﻠﯽ هﻨﻮز راﻩ وﺟﻮد دارﻧﺪ ﻳﺎ ﺧﻴﺮ. اﻳ ﻦ دو ﺑﻴ ﺖ ﻣ ﯽ‬ ‫ﺗﻮاﻧﻨﺪ داراﯼ ﻣﻘﺎدﻳﺮ زﻳﺮ ﺑﺎﺷﻨﺪ.‬ ‫1 ‪) Flag Bit‬ﺑﻴﺖ ‪ = 0 : (Don’t Fragment‬اﻣﮑﺎن دارد ﻗﻄﻌﻪ اﯼ وﺟﻮد داﺷﺘﻪ ﺑﺎﺷﺪ. 1 = هﻴﭻ ﻗﻄﻌﻪ اﯼ‬ ‫وﺟﻮد ﻧﺪاردد.‬ ‫1 ‪) Flag Bit‬ﺑﻴﺖ ‪ = 0 : (More Fragment‬ﻗﻄﻌﻪ ﻗﺒ ﻞ هﻨ ﻮز ﺑ ﺎﻗﯽ ﻣﺎﻧ ﺪﻩ اﺳ ﺖ. 1 = ﻗﻄﻌ ﺎت ﺑﻴ ﺸﺘﺮﯼ ﺟ ﺎ‬ ‫ﻣﺎﻧﺪﻩ اﺳﺖ.‬

‫اﺟﺰاﯼ دﻳﮕﺮ ﻋﻨﻮان ‪IP‬‬
‫ﺣﺎل ﮐﻪ ﻣﻌﻨ ﺎﯼ ﺁدرس ‪ IP‬و زﻣﻴﻨ ﻪ ه ﺎﯼ ﺗﻘ ﺴﻴﻢ ﺑﻨ ﺪﯼ را در ﻋﻨ ﻮان ‪ IP‬داﻧ ﺴﺘﻴﻢ. ﻧﮕ ﺎهﯽ ﻣ ﯽ اﻧ ﺪازﻳﻢ ﺑ ﻪ دﻳﮕ ﺮ‬ ‫زﻣﻴﻨﻪ هﺎﻳﯽ ﮐﻪ ﺑﺴﺘﻪ ‪ IP‬از ﺁﻧﻬﺎ ﺳﺎﺧﺘﻪ ﻣﯽ ﺷﻮﻧﺪ. زﻣﻴﻨﻪ هﺎﯼ ﻋﻨﻮان ‪ IP‬ﻋﺒﺎرﺗﻨﺪ از :‬ ‫‪ : Version‬اﻳﻦ ﭼﻬﺎر ﺑﻴﺖ وﺑ ﺮاﻳﺶ ﭘﺮوﺗﮑ ﻞ اﻳﻨﺘﺮﻧﺘ ﯽ ﻣ ﻮرد اﺳ ﺘﻔﺎدﻩ را ﺗﻮﺿ ﻴﺢ ﻣ ﯽ دهﻨ ﺪ. 4 ‪IP Version‬‬ ‫ﻳﮑﯽ از ﻣﺘﺪاوﻟﺘﺮﻳﻦ وﻳﺮاش هﺎﯼ ﻣﻮرد اﺳﺘﻔﺎدﻩ در اﻳﻨﺘﺮﻧﺖ اﺳﺖ.‬ ‫‪ : IHL‬اﻳﻦ زﻣﻴﻨﻪ ‪ ، Internet Header Length‬ﻃﻮل ﻧﻬﺎﻳﯽ ﻋﻨﻮان ‪ IP‬اﺳﺖ.‬ ‫‪ : Service Type‬اﻳﻦ زﻣﻴﻨﻪ ﺑﺎ ﮐﻴﻔﻴﺖ ﺳﺮوﻳﺲ هﻤﺮاﻩ ﻣﯽ ﺑﺎﺷﺪ، و ﺑ ﻪ اﺟ ﺰاﯼ ﺷ ﺒﮑﻪ ﻣﻘ ﺪار ﺣ ﺴﺎﺳﻴﺖ داد و‬ ‫ﺳﺘﺪ دادﻩ هﺎﻳﯽ را ﻧﺸﺎن ﻣﯽ دهﺪ ﮐﻪ ﻣﻤﮑﻦ اﺳﺖ در ﺗﺎﺧﻴﺮهﺎ وﺟﻮد داﺷﺘﻪ ﺑﺎﺷﺪ.‬ ‫‪ : Total Length‬اﻳﻦ زﻣﻴﻨﻪ ﻃﻮل ﻧﻬﺎﻳﯽ ﺑ ﺴﺘﻪ ‪ ، IP‬را ﺗﻌﺮﻳ ﻒ ﻣ ﯽ ﮐﻨ ﺪ ﮐ ﻪ ﺷ ﺎﻣﻞ ﻋﻨ ﻮان ‪ IP‬و دادﻩ ه ﺎﻳﺶ‬ ‫ﻣﯽ ﺑﺎﺷﺪ.‬ ‫‪ : Identification‬اﻳﻦ زﻣﻴﻨﻪ ﺑﺮاﯼ ﭘﺸﺘﻴﺒﺎﻧﯽ از ﺳﺮ هﻢ ﺑﻨﺪﯼ دوﺑﺎرﻩ ﻗﻄﻌﺎت اﺳﺘﻔﺎدﻩ ﻣﯽ ﮔﺮدد.‬ ‫‪ : Fragment Offset‬اﻳﻦ ﻋﺪد ﻧﺸﺎﻧﮕﺮ ﺟﺎﻳﯽ اﺳﺖ ﮐﻪ اﻳﻦ ﻗﻄﻌﻪ در ﮐﻞ ﺑﺴﺘﻪ ﻣﯽ ﻧﺸﻴﻨﺪ.‬ ‫‪: (TTL) Time-to-Live‬اﻳﻦ زﻣﻴﻨﻪ ﺑ ﺮاﯼ ﻧ ﺸﺎن دادن ﺣ ﺪاﮐﺜﺮ ﺗﻌ ﺪاد ﺟﻬ ﺶ ه ﺎﯼ ﻣ ﺴﻴﺮ ﻳ ﺎب ﺑ ﻪ ﻣ ﺴﻴﺮ ﻳ ﺎب‬ ‫ﺑﺴﺘﻪ اﯼ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد ﮐﻪ در هﻨﮕﺎم ﻋﺒﻮر ﺑﺴﺘﻪ از ﺷﺒﮑﻪ ﺑﺎﻳﺪ در ﻧﻈﺮ ﮔﺮﻓﺘﻪ ﺷﻮد.‬ ‫‪ : Protocol‬اﻳﻦ زﻣﻴﻨﻪ ﭘﺮوﺗﮑﻠﯽ را ﺗﻮﺿﻴﺢ ﻣﯽ دهﺪ ﮐﻪ ﺑﺎ اﻳﻦ ﺑﺴﺘﻪ ‪ IP‬ﺣﻤﻞ ﻣﯽ ﮔﺮدد و ﻏﺎﻟﺒﺎ ﺑﺮاﺑ ﺮ ﻣﻘ ﺪارﯼ‬ ‫ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ در ارﺗﺒﺎط ﺑﺎ ‪ TCP‬ﻳﺎ ‪ UDP‬ﻣﯽ ﺑﺎﺷﺪ.‬ ‫‪ : Header Checksum‬اﻳ ﻦ اﻃﻼﻋ ﺎت ﺑ ﺮاﯼ ﺣ ﺼﻮل اﻃﻤﻴﻨ ﺎن از اﻳ ﻦ ﻣ ﻮرد ﺻ ﻮرت ﻣ ﯽ ﮔﻴ ﺮد ﮐ ﻪ ﻋﻨ ﻮان‬ ‫ﺗﺨﺮﻳﺐ ﻧﺸﺪﻩ اﺳﺖ و در ﺟﻬﺶ ﻣﺴﻴﺮ ﻳﺎب از ﻧﻮ ﻣﺤﺎﺳﺒﻪ ﻣﯽ ﺷﻮد.‬ ‫- 01 -‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫‪ : Source IP Address‬اﻳﻦ زﻣﻴﻨﻪ ﺷﺒﮑﻪ و ﻣﻴﺰﺑﺎﻧﯽ را ﻧﺸﺎن ﻣﯽ دهﺪ ﮐﻪ ﺑﺴﺘﻪ ار ﺁن ﺑﻴﺮون ﻣﯽ ﺁﻳﺪ.‬ ‫‪ : Destination IP Address‬اﻳﻦ زﻣﻴﻨﻪ ﺷﺒﮑﻪ و ﻣﻴﺰﺑﺎﻧﯽ را ﻧﺸﺎن ﻣﯽ دهﺪ ﮐﻪ ﺑﺴﺘﻪ ﺑﻪ ﺁﻧﺠﺎ ﻣﯽ رود.‬ ‫‪ : Options‬اﻳﻦ زﻣﻴﻨﻪ ﻃﻮل هﺎﯼ ﻣﺘﻐﻴﻴﺮ اﻃﻼﻋﺎت ﮔﺴﺘﺮدﻩ ﻻﻳﻪ ‪ IP‬را ﻧﺸﺎن ﻣﯽ دهﻨﺪ. از اﻳﻦ زﻣﻴﻨ ﻪ ﺧ ﺼﻮﺻﺎ‬ ‫در ﻣﺴﻴﺮ ﻳﺎﺑﯽ ﻣﻨﺒﻊ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد، ﻋﻤﻠﯽ ﮐﻪ در زﻳﺮ ﺑﺎ ﺟﺰﺋﻴﺎت ﺑﻴﺸﺘﺮ ﺷﺮح دادﻩ ﻣﯽ ﺷﻮد.‬ ‫‪ : Padding‬اﻳﻦ زﻣﻴﻨﻪ ﺑﺮاﯼ ﮔﺮد ﻧﻤﻮدن ﻃﻮل ﻋﻨﻮان ‪ IP‬اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮد ﺑ ﻪ ﻃ ﻮرﯼ ﮐ ﻪ در ﻣ ﺮز ﺧﻄ ﯽ 23‬ ‫ﺑﻴﺘﯽ ﻗﺮار ﺑﮕﻴﺮد.‬

‫اﻳﻤﻨﯽ در ‪ IP‬ﻗﺪﻳﻤﯽ‬
‫ﺑﻬﺘﺮ اﺳﺖ اﺷﺎرﻩ ﮐﻨﻢ ﮐﻪ ﭘﺮوﺗﮑﻞ ﻗﺪﻳﻤﯽ ﻣﻮرد اﺳﺘﻔﺎدﻩ در اﻳﻨﺘﺮﻧﺖ ، 4 ‪ IP Version‬داراﯼ ﻗﺎﺑﻠﻴﺘﻬﺎﯼ اﺳﺎﺳ ﯽ‬ ‫اﻣ ﺮوزﯼ ﻧﻤ ﯽ ﺑﺎﺷ ﺪ.ﺗﻤ ﺎم اﺟ ﺰاﯼ ﺑ ﺴﺘﻪ در ﻣ ﺘﻦ واﺿ ﺤﯽ ﻗ ﺮار دارﻧ ﺪ، ه ﻴﭻ ﭼﻴ ﺰ رﻣ ﺰﯼ ﻧﻴ ﺴﺖ. ه ﺮ ﭼﻴ ﺰﯼ در‬ ‫ﻋﻨﻮان، ﺣﺘﯽ در ﻗﻄﻌﻪ دادﻩ هﺎ ﺑ ﻪ وﺳ ﻴﻠﻪ هﮑ ﺮ دﻳ ﺪﻩ ﻳ ﺎ اﺻ ﻼح ﺷ ﻮد. ﺑﻌ ﻼوﻩ ﭘﺮوﺗﮑ ﻞ داراﯼ ه ﻴﭻ ﺗﺎﻳﻴﺪﻳ ﻪ ﻧﻤ ﯽ‬ ‫ﺑﺎﺷﺪ. ﺑﻨﺎﺑﺮاﻳﻦ ، هﮑﺮ ﻣﯽ ﺗﻮاﻧﺪ ﺑﺴﺘﻪ هﺎﻳﯽ را ﺑﺎ ﺁدرس ‪ IP‬ﻣﺒﺪا اﻳﺠﺎد ﮐﻨﺪ.‬

‫‪ICMP‬‬
‫ﻋﻨ ﺼﺮ اﺻ ﻠﯽ و ﺑ ﺴﻴﺎر ﻣﻬ ﻢ دﻳﮕ ﺮ ﺧ ﺎﻧﻮادﻩ ‪ TCP/IP‬ﭘﺮوﺗﮑ ﻞ ﭘﻴﻐ ﺎم ﮐﻨﺘ ﺮل اﻳﻨﺘﺮﻧ ﺖ )‪ (ICMP‬ﻣ ﯽ ﺑﺎﺷ ﺪ.‬ ‫‪ ICMP‬ﻣﺜﻞ ﻟﻮﻟﻪ ﮐ ﺶ ﺷ ﺒﮑﻪ ﺁﺑﺮﺳ ﺎﻧﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ. ﮐ ﺎرش اﻧﺘﻘ ﺎل دﺳ ﺘﻮر و ﮐﻨﺘ ﺮل اﻃﻼﻋ ﺎت ﺑ ﻴﻦ ﺳﻴ ﺴﺘﻢ ه ﺎ و‬ ‫اﺟﺰاﯼ ﺷﺒﮑﻪ اﺳﺖ ﺗﺎ اﻧﺘﻘ ﺎل دادﻩ ه ﺎﯼ واﻗﻌ ﯽ را رواج ده ﺪ وﺧﻄﺎه ﺎ را ﮔ ﺰارش ﮐﻨ ﺪ.ﻳ ﮏ ﺳﻴ ﺴﺘﻢ ﻣ ﯽ ﺗﻮاﻧ ﺪ از‬ ‫‪ ICMP‬اﺳﺘﻔﺎدﻩ ﻧﻤﺎﻳﺪ ﺗﺎ ﺗﻌﻴﻴﻦ ﮐﻨﺪ ﮐﻪ ﺁﻳﺎ ﺳﻴﺴﺘﻢ دﻳﮕﺮ ﺑﺎ ارﺳﺎل ﭘﻴﻨ ﮓ هﻮﺷ ﻴﺎر اﺳ ﺖ ﻳ ﺎ ﺧﻴ ﺮ ﮐ ﻪ ﭘﻴﻨ ﮓ ﭘﻴﻐ ﺎم‬ ‫‪ ICMP Echo Reply‬را ارﺳﺎل ﺧﻮاهﺪ ﺧﻮاهﺪ ﮐ ﺮد. ﻣ ﺴﻴﺮ ﻳ ﺎب ﻣ ﯽ ﺗﻮاﻧ ﺪ از ‪ ICMP‬اﺳ ﺘﻔﺎدﻩ ﻧﻤﺎﻳ ﺪ ﺗ ﺎ ﺑ ﻪ‬ ‫ﺳﻴ ﺴﺘﻢ ﻣﺒ ﺪا اﻃ ﻼع ده ﺪ ﮐ ﻪ ﻣ ﺴﻴﺮﯼ ﺑ ﺮاﯼ ﻣﻘ ﺼﺪ ﻣ ﻮرد ﻧﻴ ﺎز ﻧ ﺪارد )ﭘﻴﻐ ﺎﻣﻢ ه ﺎﯼ ‪ICMP Destinat‬‬ ‫‪ . (Unreachable‬ﻣﻴﺰﺑﺎن ﻣﯽ ﺗﻮاﻧﺪ ﺑﻪ ﺳﻴﺴﺘﻢ دﻳﮕ ﺮ اﻃ ﻼع ده ﺪ ﮐ ﻪ ﺗﻌ ﺪاد ﺑ ﺴﺘﻪ ه ﺎﻳﯽ ﮐ ﻪ در ﺣ ﺎل ارﺳ ﺎل را‬ ‫ﮐﺎهﺶ دهﺪ وا ﻳﻦ ﻋﻤﻞ را ﺑﺎ ﻓﺮﺳﺘﺎدن ﭘﻴﻐﺎم ‪ ICMP Source Quench‬اﻧﺠ ﺎم ﻣ ﯽ ده ﺪ. ﺑﻨ ﺎﺑﺮاﻳﻦ، ‪ICMP‬‬ ‫در ﺳﻴ ﺴﺘﻢ ه ﺎ ﺑ ﺮاﯼ ﺗﺒ ﺎدل اﻃﻼﻋ ﺎت در ﻣ ﻮرد روش ﺟﺮﻳ ﺎن ﺳ ﺎزﯼ داده ﺎ )ﻳ ﺎ ﻗﻄ ﻊ ﺟﺮﻳ ﺎن دادﻩ ه ﺎ( از ﻃﺮﻳ ﻖ‬ ‫اﻳﻨﺘﺮﻧﺖ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد.‬ ‫‪ ICMP‬از هﻤﺎن ﻓﺮﻣﺖ ﻋﻨﻮان، ﺑﻪ ﺷﮑﻞ ‪ IP‬ﺑﺮاﯼ ﺁدرﺳﻬﺎﯼ ‪ IP‬ﻣﻘ ﺼﺪ و ﻣﺒ ﺪا، ﺗﻘ ﺴﻢ ﺑﻨ ﺪﯼ ﺑ ﺴﺘﻪ ﺑ ﻪ ﻗﻄﻌ ﺎت‬ ‫ﻣﺴﺎوﯼ، و دﻳﮕﺮ ﻋﻤﻠﮑﺮدهﺎ اﺳﺘﻔﺪﻩ ﻣﯽ ﮐﻨﺪ. زﻣﻴﻨﻪ ﭘﺮوﺗﮑ ﻞ ﻋﻨ ﻮان ‪ IP‬ﺑ ﺎ ﻣﻘ ﺪارﯼ ﻣﺘﻨﺎﺳ ﺐ ﺑ ﺎ ‪ ICMP‬ﻧ ﺼﺐ‬ ‫ﻣﯽ ﮔﺮدد. ﭘﺲ از ﻋﻨ ﻮان ‪ ، IP‬در ﺗﺮﮐﻴ ﺐ دادﻩ ه ﺎﯼ ﺑ ﺴﺘﻪ ‪ ICMP،IP‬زﻣﻴﻨ ﻪ اﯼ را اﺿ ﺎﻓﻪ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﺑ ﻪ‬ ‫ﺷﮑﻞ ﻧﻮع ‪ ICMP‬ﺷﻨﺎﺧﺘﻪ ﻣﯽ ﺷﻮد. ﻓﺮﻣﺖ ﺑﺎﻗﻴﻤﺎﻧﺪﻩ ﺑﺴﺘﻪ ‪ ICMP‬ﺑﺴﺘﮕﯽ ﺑﻪ اﻳ ﻦ ﻧ ﻮع ‪ ICMP‬دارد. ﭘﻴﻐ ﺎم‬ ‫هﺎﯼ ‪ ICMP‬ﻋﻨﺎوﻳﻦ زﻳﺎدﯼ دادﻧﺪ.‬

‫هﺪف ار اﻳﻦ ﻧﻮع ﭘﻴﻐﺎم‬
‫اﻳﻦ ﭘﻴﻐﺎم ﺑﺮاﯼ ﭘﺎﺳﺦ ﺑﻪ ﭘﻴﻨﮓ اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد‬ ‫وﻗﺘﯽ ﺳﻴﺴﺘﻢ هﻮﺷﻴﺎر ﻣﯽ ﺑﺎﺷﺪ‬ ‫اﻳ ﻦ ﭘﻴﻐ ﺎم ﻧ ﺸﺎن ﻣ ﯽ ده ﺪ ﮐ ﻪ ﭘﻴﻐ ﺎم اول ‪ IP‬ﻧﻤ ﯽ‬ ‫ﺗﻮاﻧ ﺴﺘﻪ ﺑ ﻪ ﻣﻘ ﺼﺪش ارﺳ ﺎل ﺷ ﺪﻩ ﺑﺎﺷ ﺪ و اﻳ ﻦ‬ ‫اﺣﺘﻤﺎل وﺟﻮد دارد ﮐﻪ ﻣﺴﻴﺮ ﻳﺎﺑﯽ در ﻃﻮل راﻩ.‬ ‫ﻣ ﺴﻴﺮ ﺗﻌﺮﻳ ﻒ ﺷ ﺪﻩ اﯼ ﺑ ﻪ ﻣﻘ ﺼﺪ ﻧﺪاﺷ ﺘﻪ ﺑﺎﺷ ﺪ.‬ ‫اﻟﺒﺘﻪ، اﮔﺮ دﺳﺘﮕﺎﻩ ﻣﻘﺼﺪ ﻧﺘﻮاﻧﺪ ﺑﺎ ﭘﺮوﺗﮑﻞ ﻣﻨﺎﺳﺐ‬ ‫ﺻ ﺤﺖ ﻧﻤﺎﻳ ﺪ، اﻳ ﻦ ﻧ ﻮع ﭘﻴﻐ ﺎم ﺑ ﺎز ﺧﻮاه ﺪ ﮔ ﺸﺖ.‬ ‫ﺑﺪﻳﻦ ﺷﮑﻞ ﻣﻴﺰﺑ ﺎن ﻣﻘ ﺼﺪ ﻣ ﯽ ﺗﻮاﻧ ﺴﺖ اﻳ ﻦ ﭘﻴﻐ ﺎم‬ ‫را ﺑﺮﮔﺮداﻧ ﺪ اﮔ ﺮ دروازﻩ ‪ TCP‬ﻳ ﺎ ‪ UDP‬ﻣﻘ ﺼﺪ‬ ‫ﺑﺴﺘﻪ ﺑﺎﺷﺪ.‬ ‫ﺳﻴﺴﺘﻢ در ﺣﺎل درﻳﺎﻓﺖ ﺑﺴﻴﺎر ﺳﺮﻳﻊ ﺑ ﺴﺘﻪ ه ﺎ ﻣ ﯽ‬ ‫ﺑﺎﺷﺪ ﺗﺎ ﺁﻧ ﻪ را در ﺻ ﻒ ورودﻳ ﺶ ﭘ ﺮدازش ﮐﻨ ﺪ و‬ ‫ﻣﻤﮑ ﻦ اﺳ ﺖ ﭘﻴﻐ ﺎم اﺳ ﺖ ﭘﻴﻐ ﺎم ‪Source‬‬ ‫‪ Quench‬را ارﺳ ﺎل ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﺑ ﻪ ارﺳ ﺎل اﻃ ﻼع‬ ‫ﻣﯽ دهﺪ ﺳﺮﻋﺖ اﻧﺘﻘﺎل را ﮐﺎهﺶ دهﺪ.‬

‫ﻣﻘﺪار در زﻣﻴﻨﻪ ﻧﻮع‬ ‫‪ICMP‬‬
‫0‬ ‫3‬

‫ﻧﻮع ﭘﻴﻐﺎم‬
‫‪Echo Reply‬‬ ‫‪Destination‬‬ ‫‪Unreachable‬‬

‫4‬

‫‪Source‬‬ ‫‪Quench‬‬

‫- 11 -‬

‫‪Learning TCP/IP‬‬ ‫اﻳﻦ ﭘﻴﻐﺎم ﺑﻮﺳﻴﻠﻪ ﻣﺴﻴﺮ ﻳﺎب ﻓﺮﺳ ﺘﺎدﻩ ﻣ ﯽ ﺷ ﻮد ﺗ ﺎ‬ ‫ﻧ ﺸﺎن ده ﺪ ﮐ ﻪ ﺗﺮاﻓﻴ ﮏ ﺑﺎﻳ ﺪ در ﻣ ﺴﻴﺮ ﻳ ﺎب دﻳﮕ ﺮ‬ ‫ﺑﺎﺷﺪ ﮐﻪ ﻣﯽ ﺗﻮاﻧ ﺪ ﺗﺮاﻓﻴ ﮏ را ﺑ ﻪ ﻣﻘ ﺼﺪﯼ ارﺳ ﺎل‬ ‫ﻧﻤﺎﻳﺪ ﺗﺎ راﻧﺪﻣﺎن ﺑﺎﻻﺗﺮﯼ دارد.‬ ‫اﻳ ﻦ ﻧ ﻮع ﭘﻴﻐ ﺎم ﺑ ﺮاﯼ ارﺳ ﺎل ﭘﻴﻨ ﮓ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ‬ ‫ﺷﻮد ﺗﺎ اﺟﺮاﯼ ﺳﻴﺴﺘﻢ را ﺗﻌﻴﻴﻦ ﻧﻤﺎﻳﺪ.‬ ‫اﻳﻦ ﭘﻴﻐﺎم ﻧﺸﺎن ﻣﯽ دهﺪ ﮐﻪ ﺣﺪاﮐﺜﺮ ﺗﻌﺪاد ﭘ ﺮش ه ﺎ‬ ‫در زﻣﻴﻨ ﻪ ‪ Time-to-Live‬ﻋﻨ ﻮان ‪ IP‬از ﺣ ﺪ‬ ‫ﺗﺠﺎوز ﮐﺮدﻩ اﺳﺖ.‬ ‫اﻳﻦ ﻧﻮع ﭘﻴﻐﺎم ﺑﺎ ﺳﻴﺴﺘﻤﯽ در ﭘﺎﺳﺦ ﺑ ﻪ ﺑ ﺴﺘﻪ ‪،IP‬‬ ‫ﺑ ﺎ ﭘ ﺎراﻣﺘﺮ ﺑ ﺪﯼ در ﻳﮑ ﯽ از زﻣﻴﻨ ﻪ ه ﺎﯼ ﻋﻨ ﻮاﻧﺶ‬ ‫ارﺳﺎل ﻣﯽ ﺷﻮد.‬ ‫اﻳ ﻦ ﻧ ﻮع ﭘﻴﻐ ﺎم ﺷ ﺎﻣﻞ زﻣ ﺎن در دﺳ ﺘﮕﺎﻩ ارﺳ ﺎل‬ ‫ﮐﻨﻨ ﺪﻩ ﻣ ﯽ ﺑﺎﺷ ﺪ؛ و زﻣ ﺎن دﺳ ﺘﮕﺎﻩ ﻣﻘ ﺼﺪ را‬ ‫درﺧﻮاﺳﺖ ﻣﯽ ﮐﻨﺪ.‬ ‫در درﻳﺎﻓ ﺖ ﭘﻴﻐ ﺎم ‪، ICMP Timestamp‬‬ ‫ﺳﻴﺴﺘﻢ در زﻣﺎن ﺧﻮدش ﺑﺎ ﺟ ﻮاب ‪Timestamp‬‬ ‫ﭘﺎﺳﺦ ﺧﻮاهﺪ داد‬ ‫اﻳ ﻦ ﭘﻴﻐ ﺎم ﻣ ﯽ ﺗﻮاﻧ ﺪ ﺑ ﻪ وﺳ ﻴﻠﻪ ﻣﻴﺰﺑ ﺎﻧﯽ اﺳ ﺘﻔﺎدﻩ‬ ‫ﮔ ﺮدد ﺗ ﺎ ﺗﻌﻴ ﻴﻦ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﺷ ﺒﮑﻪ در ﺣ ﺎل ﮐ ﺎر ﻣ ﯽ‬ ‫ﺑﺎﺷﺪ.‬ ‫اﻳﻦ ﭘﻴﻐﺎم ﺣﺎوﯼ ﭘﺎﺳﺨﯽ ﺑﻪ ﭘﻴﻐ ﺎم ‪Information‬‬ ‫‪ Request‬در ﻣﻮرد ﺁدرس ‪ IP‬ﺷﺒﮑﻪ ﺑﺎﺷﺪ.‬ ‫5‬

‫‪BY: Nasser-Desperado‬‬ ‫‪Redirect‬‬

‫8‬ ‫11‬

‫‪Echo‬‬ ‫‪Time‬‬ ‫‪Exeeedad‬‬ ‫‪Para meter‬‬ ‫‪Problem‬‬ ‫‪Time Stamp‬‬

‫21‬

‫31‬

‫41‬

‫‪Times‬‬ ‫‪Tamp Reply‬‬ ‫‪Information‬‬ ‫‪Request‬‬ ‫‪Information‬‬ ‫‪Replay‬‬

‫51‬

‫61‬

‫ﻋﻨﺎوﻳﻦ دﻳﮕﺮدرﺳﻄﺢ ﺷﺒﮑﻪ‬
‫ﺗﻌﻴﻴﻦ ﻣﺴﻴﺮ ﺑﺴﺘﻪ هﺎ‬
‫ﺑ ﺮاﯼ اﻧﺘﻘ ﺎل ﭘ ﯽ درﭘ ﯽ دادﻩ ه ﺎ ﺑ ﻪ دﻧﺒ ﺎل ه ﻢ از ﻃﺮﻳ ﻖ ﺷ ﺒﮑﻪ ﺑ ﺴﺘﻪ ه ﺎ ﺑﺎﻳ ﺪ از ﻣﺒﺪاءﺷ ﺎن ﺑ ﻪ ﻣﻘ ﺼﺪﺷﺎن‬ ‫ﺣﻤ ﻞ ﺷ ﻮﻧﺪ ﺗﻌﻴ ﻴﻦ ﻣ ﺴﻴﺮ ﻓﺮاﻳﻨ ﺪ اﻧﺘﻘ ﺎل ﺑ ﺴﺘﻪ اﯼ از ﻳ ﮏ ﺷ ﺒﮑﻪ ﺑ ﻪ ﺷ ﺒﮑﻪ دﻳﮕ ﺮ ﺑ ﺎ ه ﺪف ﭘ ﻴﺶ ﺑ ﺮدن‬ ‫ﺑ ﺴﺘﻪ ﺑ ﻪ ﺳ ﻤﺖ ﻣﻘ ﺼﺪش در ﻣ ﺴﻴﺮﯼ ﺑ ﺎ راﻧ ﺪﻣﺎن ﻧ ﺴﺒﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ ﺗﻌﻴ ﻴﻦ ﻣ ﺴﻴﺮ ﺑ ﺎ ﻣ ﺴﻴﺮﻳﺎب ه ﺎ اﺟ ﺮا ﻣ ﯽ‬ ‫ﮔﺮدد ﻣﺴﻴﺮﻳﺎﺑﻬﺎ ﻣﺴﻴﺮﯼ راﺗﻌﻴﻴﻦ‬ ‫ﻣ ﯽ ﻧﻤﺎﻳﻨ ﺪ ﮐ ﻪ ﺑ ﺴﺘﻪ ﺑﺎﻳ ﺪ از ﻃﺮﻳ ﻖ ﺷ ﺒﮑﻪ اﻧﺘﺨ ﺎب ﻧﻤﺎﻳ ﺪ و اﻳ ﻦ ﻣ ﺴﻴﺮ از ﭘﺮﺷ ﯽ ﺑ ﻪ ﭘ ﺮش دﻳﮕ ﺮ ﺗﻌﻴ ﻴﻦ‬ ‫ﻣﯽ ﺷﻮد و‬ ‫ﺑﺴﺘﻪ هﺎ را دﺳﺘﻪ ﺑﻨﺪﯼ و ﺑﺮاﯼ اﻧﺘﻘﺎل از ﻃﺮﻳﻖ ﺷﺒﮑﻪ ﺑﻪ ﻗﻄﻌﺎت ﻣﻨﻈﻢ ﺗﻘﺴﻴﻢ ﻣﯽ ﻧﻤﺎﻳﺪ‬ ‫ﺑﻴ ﺸﺘﺮ ﺷ ﺒﮑﻪ ه ﺎﯼ اﻣ ﺮوزﯼ از ﻣ ﺴﻴﺮﻳﺎﺑﯽ دﻳﻨ ﺎﻣﻴﮑﯽ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮐﻨﻨ ﺪ ﮐ ﻪ ﻣ ﺴﺮﻳﺎﺑﻬﺎ ﺧ ﻮد ﻣ ﺴﻴﺮﯼ را‬ ‫ﮐ ﻪ ﺑ ﺴﺘﻪ ه ﺎ اﺳ ﺘﻔﺎدﻩ ﺧﻮاهﻨ ﺪ راﻧﻤ ﻮد را ﺗﻌﻴ ﻴﻦ ﻣ ﯽ ﻧﻤﺎﻳﻨ ﺪ .ﻣ ﺴﻴﺮﻳﺎب ه ﺎ در ﺑ ﻴﻦ ﺧﻮدﺷ ﺎن ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از‬ ‫ﻣ ﺴﻴﺮﻳﺎﺑﯽ ﺗﺒ ﺎدل اﻃﻼﻋ ﺎت ﻣ ﯽ ﻧﻤﺎﻳﻨ ﺪ و ﺑﻬﺘ ﺮﻳﻦ ﻣ ﺴﻴﺮهﺎ را ﻳ ﺮاﯼ اﻧﺘﻘ ﺎل ﺑ ﺴﺘﻪ ه ﺎ ﺗﻌﻴ ﻴﻦ ﻣ ﯽ ﮐﻨﻨ ﺪ ﺗﻌ ﺪاد‬ ‫زﻳﺎدﯼ از ﭘﺮوﺗﮑﻞ هﺎﯼ ﻣﺴﻴﺮﻳﺎﺑﯽ ﺑﺎ ﭘﻴﭽﻴﺪﮔﯽ هﺎﯼ ﻣﺨﺘﻠﻒ اﺧﺘﺮاع ﺷﺪﻩ اﻧﺪ ﮐﻪ ﻋﺒﺎرﺗﻨﺪ از:‬ ‫‪Border Gateway (BGP),Open Shortest Path First (OSP),Routing‬‬ ‫.)‪Information Protocol (RIP‬‬ ‫ﮔﺰﻳﻨ ﻪ ﻣ ﺴﻴﺮ ﻳ ﺎﺑﯽ دﻳﮕ ﺮ داراﯼ ﻣ ﺴﻴﺮ ه ﺎﯼ ﺛﺎﺑ ﺖ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ. در ﻣ ﺴﻴﺮ ﺛﺎﺑ ﺖ، ﺗﻤ ﺎم داد و ﺳ ﺘﺪ دادﻩ ه ﺎ ﺑ ﺎ‬ ‫هﻤ ﺎن ﺁدرس ﻣﻘ ﺼﺪ هﻤﻴ ﺸﻪ در ﻳ ﮏ ﺟﻬ ﺖ ارﺳ ﺎل ﻣ ﯽ ﮔﺮدﻧ ﺪ )ﺑ ﺪون ﺗﻮﺟ ﻪ ﺑ ﻪ ﺻ ﺪﻣﻪ اﺟﺘﻨ ﺎب ﻧﺎﭘ ﺬﻳﺮ در‬ ‫ارﺗﺒ ﺎط ﺑ ﺎ ه ﺮ ﻣ ﻮرد ﻇﺮﻓﻴ ﺖ دﻳﮕ ﺮ( از ﻣ ﺴﻴﺮهﺎﯼ ﺛﺎﻟ ﺚ ﻏﺎﻟﺒ ﺎ ﺑ ﺮاﯼ ﻣ ﺴﻴﺮ ﻳﺎﺑﻬ ﺎﻳﯽ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮد ﮐ ﻪ‬ ‫در ﺁن ﺑ ﻪ ﻧ ﺪرت ﻣ ﺴﻴﺮ ﻳﺎﺑﻬ ﺎﻳﯽ ﺗﻐﻴﻴ ﺮ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ، و ﻧ ﺴﺒﺖ ﺑ ﻪ ﻣ ﻮارد اﻳﻤﻨ ﯽ ، دﻳﻨ ﺎﻣﻴﮑﯽ ، ﻣ ﺴﻴﺮ ه ﺎﻳﯽ‬

‫- 21 -‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﻣﻄﻠ ﻮب و دﻟﺨ ﻮاﻩ ﻧﻤ ﯽ ﺑﺎﺷ ﻨﺪ . ﻣ ﺴﻴﺮ ه ﺎﯼ ﺛﺎﻟ ﺚ ﻏﺎﻟﺒ ﺎ در دروازﻩ اﻳﻨﺘﺮﻧﺘ ﯽ را ﻣ ﯽ ﺳ ﺎزﻧﺪ ، ﺑ ﻪ ﺷ ﺪت‬ ‫ﻣﺮزﺑﻨﺪﯼ ﻣﯽ ﺷﻮﻧﺪ.‬ ‫‪ IP‬ﮔﺰﻳﻨ ﻪ ﻣ ﺴﻴﺮ ﻳ ﺎﺑﯽ دﻳﮕ ﺮﯼ را اراﻳ ﻪ ﻣ ﯽ ﻧﻤﺎﻳﺪﮐ ﻪ ﻣ ﺴﻴﺮ ﻳ ﺎﺑﯽ ﻣﺒ ﺪا دﺳ ﺘﮕﺎﻩ ﻣﺒ ﺪا ﺑ ﺴﺘﻪ اﯼ را اﻳﺠ ﺎد‬ ‫ﻣ ﯽ ﻧﻤﺎﻳ ﺪ و ﻣ ﺴﻴﺮﯼ را ﺗﻌﻴ ﻴﻦ ﺧﻮاه ﺪ ﻧﻤ ﻮد ﮐ ﻪ ﺑ ﺴﺘﻪ ه ﺎ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ ﮐ ﻪ ﺑ ﺴﺘﻪ از ﻃﺮﻳ ﻖ ﺁن از درون‬ ‫ﺷﺒﮑﻪ ﻋﺒﻮر ﺧﻮاهﺪ ﻧﻤﻮد.‬

‫ﺗﻔﺴﻴﺮ ﺁدرس ﺷﺒﮑﻪ‬
‫ﺑﻠ ﻮﮎ ﺁدرﺳ ﻬﺎﯼ ‪ IP‬ﺑ ﻪ ﺳ ﺎزﻣﺎﻧﻬﺎﯼ ﻣﺨﺘﻠ ﻒ و ﻓ ﺮاهﻢ ﮐﻨﻨ ﺪﮔﺎن ﺳ ﺮوﻳﺲ اﻳﻨﺘﺮﻧﺘ ﯽ ﮔﻮﻧ ﺎﮔﻮن اﺧﺘ ﺼﺎص‬ ‫دادﻩ ﻣ ﯽ ﺷ ﻮد . ﺳ ﺎﻟﻬﺎ ﻗﺒ ﻞ زﻣ ﺎﻧﯽ ﮐ ﻪ ﭘ ﻴﺶ ﺑﻴﻨ ﯽ اﺗ ﺼﺎل ﺑ ﻪ اﻳﻨﺘﺮﻧ ﺖ ﻧﻴ ﺰ ﻗﺎﺑ ﻞ ﭘ ﻴﺶ ﺑﻴﻨ ﯽ ﺑ ﻮد ، ﻳﮑ ﺴﺮﯼ‬ ‫ﺳ ﺎزﻣﺎﻧﻬﺎ ﺷ ﻤﺎرﻩ ﺁدرس ه ﺎﯼ اﻳﻨﺘﺮﻧﺘ ﯽ ﺗ ﺼﺎدﻓﯽ را اﻧﺘﺨ ﺎب ﮐﺮدﻧ ﺪ و ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از اﻳ ﻦ ﺁدرس ه ﺎﯼ‬ ‫ﺗ ﺼﺎدﻓﯽ ‪ ، IP‬ﺳ ﺎﺧﺖ ﺷ ﻴﮑﻪ ه ﺎﯼ ‪ IP‬ﺧ ﻮد را ﺁﻏ ﺎز ﻧﻤﻮدﻧ ﺪ و ﺑﻨﻴﺎﻧﮕ ﺬاران ﺷ ﺒﮑﻪ اﯼ را ﺧﻮاهﻴ ﺪ دﻳ ﺪ‬ ‫ﮐ ﻪ از ﺷ ﻤﺎرﻩ دﻟﺨ ﻮاﻩ ﺧ ﻮد اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮐﻨﻨ ﺪ )ﻣ ﺜﻼ ﻣ ﻦ ﺧ ﻮدم 4 را دوﺳ ﺖ دارم( و ﺷ ﺒﮑﻪ ﮐﻠ ﯽ را ﺑ ﺮ‬ ‫اﺳ ﺎس ﺁن ﺷ ﻤﺎرﻩ ﻣ ﯽ ﺳ ﺎزﻧﺪ ) ﺑ ﻪ ه ﺮ ﻣ ﻮردﯼ ﺁدرس ‪ IP‬ﺑ ﻪ ﺷ ﮑﻞ 4.‪ x.y.z‬ﻣ ﯽ ده ﺪ(. اﻳ ﻦ ﺁدرﺳ ﻬﺎ‬ ‫ﻏﺎﻟﺒ ﺎ ﺑ ﻪ ﺻ ﻮرت ﺁدرﺳ ﻬﺎﯼ ﻣﻨﻄﻘ ﯽ ﻧﺎﻣﮕ ﺬارﯼ ﻣ ﯽ ﮔﺮدﻧ ﺪ ﺑ ﺮاﯼ اﻳﻨﮑ ﻪ ﺑﻄ ﻮر رﺳ ﻤﯽ ﺑ ﻪ ﺳ ﺎزﻣﺎن‬ ‫دﻳﮕ ﺮﯼ اﺧﺘ ﺼﺎص دادﻩ ﻣ ﯽ ﺷ ﻮد. ﻣﺘﺎﺳ ﻔﺎﻧﻪ، اﮔ ﺮ ﮐ ﺴﯽ ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از ﺁدرﺳ ﻬﺎﯼ ﻣﻨﻄﻘ ﯽ ﺑﺨﻮاه ﺪ ﺑ ﻪ‬ ‫اﻳﻨﺘﺮﻧ ﺖ ﻣﺘ ﺼﻞ ﮔ ﺮدد ، ﺑﺎﻳ ﺪ از دو ﺷ ﺒﮑﻪ در اﻳﻨﺘﺮﻧ ﺖ ﺑ ﺎ ﺁدرﺳ ﻬﺎﯼ ‪ IP‬ﻳﮑ ﺴﺎن اﺳ ﺘﻔﺎدﻩ ﻧﻤﺎﻳ ﺪ. اﻳ ﻦ‬ ‫وﺿ ﻌﻴﺖ ﺑ ﻪ ﻃ ﻮر ﺟ ﺪﯼ در ﻣ ﺴﻴﺮﻳﺎﺑﯽ ﺗﻮﻟﻴ ﺪ اﺷ ﮑﺎل ﻣ ﯽ ﻧﻤﺎﻳ ﺪ. ﺑ ﺮاﯼ اﻳﻨﮑ ﻪ ﻣ ﺴﻴﺮﻳﺎﺑﻬﺎﯼ اﻳﻨﺮﻧﺘ ﯽ ﻧﻤ ﯽ‬ ‫داﻧﻨﺪ ﮐﻪ داد و ﺳﺘﺪ دادﻩ هﺎﯼ اﻳﻦ ﺁدرس دوﺑﻞ ﻣﻘﺼﺪ را ﺑﻪ ﮐﺠﺎ ارﺳﺎل ﻧﻤﺎﻳﻨﺪ.‬ ‫ﺑﻌ ﻼوﻩ ، در ﺗ ﻼش ﺑ ﻪ اﺗ ﺼﺎل ﺑ ﺎ اﻳﻨﺘﺮﻧ ﺖ ، ﻓ ﻀﺎﯼ ﺁدرس ‪ IP‬ﺑ ﺎ ﺑ ﺮاﯼ ه ﺮ ﻓ ﺮد وﺟ ﻮد دارﻧ ﺪ. ﺑﻨ ﺎﺑﺮاﻳﻦ ،‬ ‫‪ IETF‬ﻳﮑ ﺴﺮﯼ ﺷ ﻤﺎرﻩ ﺁدرﺳ ﻬﺎ را ﺑ ﺮاﯼ اﻳﺠ ﺎد ﺷ ﺒﮑﻪ ه ﺎﯼ ﺧ ﺼﻮﺻﯽ ‪ IP‬در ﻣ ﻮرد 9181 ‪RFC‬‬ ‫ﺗﻨﻈ ﻴﻢ ﻧﻤ ﻮد ﻣ ﯽ ﺗﻮاﻧﻴ ﺪ ﺷ ﺒﮑﻪ ‪ IP‬ﺧ ﻮد را ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ از ﺁدرﺳ ﻬﺎﯼ ﺗﻨﻈ ﻴﻢ ﺷ ﺪﻩ ‪ IP‬ﻣﺜ ﻞ‬ ‫‪ 192.168.y.z‬و‪ 10x.y.z‬و‪ yz‬ﻳ ﺎ ، ‪ 172.16.y.z‬در اﻳ ﻦ ﻣﺤ ﻞ ﺑ ﺴﺎزﻳﺪ . اﮔ ﺮ داده ﺎﻳﯽ را ﺑ ﻪ ﻳﮑ ﯽ‬ ‫از ﺁﻳ ﻦ ﺁدرﺳ ﻬﺎ در اﻳﻨﺘﺮﻧ ﺖ ارﺳ ﺎل ﮐﻨﻴ ﺪ ، ﺁن داد ه ﻪ از دﺳ ﺖ ﺧﻮاهﻨ ﺪ رﻓ ﺖ ، ﺑ ﺮاﯼ اﻳﻨﮑ ﻪ اﻳ ﻦ‬ ‫ﺗﻨﻈﻴﻤ ﺎت ﻣﻨﺤ ﺼﺮ ﺑ ﻪ ﻓ ﺮد ﻧﻤ ﯽ ﺑﺎﺷ ﺪ و ﻏﻴﺮﻗﺎﺑ ﻞ ﻣ ﺴﻴﺮ ﻧﺎﻣﻴ ﺪﻩ ﻣ ﯽ ﺷ ﻮﻧﺪ ﺑ ﺮاﯼ اﻳﻨﮑ ﻪ ه ﻴﭻ ﻣ ﺴﻴﺮ ﻳ ﺎﺑﯽ‬ ‫در اﻳﻨﺘﺮﻧﺖ ﻧﺨﻮاهﺪ داﻧﺴﺖ ﮐﻪ ﺑﻪ ﭼﻪ روﺷﯽ ﺑﻪ اﻳﻦ ﺁدرﺳﻬﺎﯼ ﻏﻴﺮ واﺣﺪ دﺳﺖ ﭘﻴﺪا ﻧﻤﺎﻳﻴﺪ.‬ ‫ﭼﻄ ﻮر دﺳﺘﺮﺳ ﯽ ﺑ ﻪ ﺷ ﺒﮑﻪ ﺷ ﺒﮑﻪ را ﭘ ﺸﺘﻴﺒﺎﻧﯽ ﻧﻤ ﺎﻳﻴﻢ ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ ار ﺁدرﺳ ﻬﺎﯼ ﻣﻨﻄﻘ ﯽ ﻳ ﺎ ﺗﻨﻈﻴﻤ ﺎت‬ ‫ﺗﻮﺿﻴﺢ دادﻩ ﺷﺪﻩ در ?8191 ‪RFC‬‬ ‫ﺟ ﻮاب ﺗﺮﺳ ﻢ اﻳ ﻦ ﺁدرﺳ ﻬﺎﯼ ﻣ ﺴﺎﻟﻪ ﺳ ﺎز ﺑ ﻪ ﺁدرﺳ ﻬﺎﯼ ﻣﻌﺘﺒ ﺮ ‪ IP‬در ﻣ ﺴﻴﺮ ﻳ ﺎب ﺷ ﺒﮑﻪ ﻳ ﺎ دﻳ ﻮارﻩ ﺁﺗ ﺶ‬ ‫ﺑ ﺎ اﺳ ﺘﻔﺎدﻩ ازﺗﮑﻨﻴﮑ ﯽ ﻣ ﯽ ﺑﺎﺷ ﺪ ﮐ ﻪ ﺗﻔ ﺴﻴﺮ ﺁأرس ﺷ ﺒﮑﻪ )‪ (NAT‬ﻧ ﺎم دارد. ﺑ ﺮاﯼ اﻧﺠ ﺎم ‪، NAT‬‬ ‫دروازﻩ اﯼ ﺑ ﻴﻦ ﺷ ﺒﮑﻪ ﺑ ﺎ ﺁدرس ﻣﻨﻄﻘ ﯽ ﻳ ﺎ ﺗﻨﻈ ﻴﻢ ﺷ ﺪﻩ و اﻳﻨﺘﺮﻧ ﺖ ﻗ ﺮار ﻣ ﯽ ﮔﻴ ﺮد. وﻗﺘ ﯽ ه ﺮ ﺑ ﺴﺘﻪ از‬ ‫ﺷ ﺒﮑﻪ داﺧﻠ ﯽ ﺑ ﻪ اﻳﻨﺘﺮﻧ ﺖ ﻣ ﯽ رود ، اﻳ ﻦ دروازﻩ ﺁدرس ﻣﻨﻄﻘ ﯽ ﻳ ﺎ ﻏﻴ ﺮ ﻗﺎﺑ ﻞ ﻣ ﺴﻴﺮ ﻳ ﺎﺑﯽ ﺷ ﺒﮑﻪ داﺧﻠ ﯽ‬ ‫در ﻋﻨ ﻮان ﺑ ﺴﺘﻪ را ﺑ ﺎ ﺁدرس ‪ IP‬واﺣ ﺪ و ﻗﺎﺑ ﻞ ﻣ ﺴﻴﺮﻳﺎﺑﯽ ﺗ ﻮﻳﺾ ﻣ ﯽ ﮐﻨ ﺪ. وﻗﺘ ﯽ ﭘﺎﺳ ﺨﻬﺎ ﺑﺮﻣ ﯽ ﮔﺮدﻧ ﺪ‬ ‫، دروازﻩ اﻳ ﻦ ﺑ ﺴﺘﻪ ه ﺎ را درﻳﺎﻓ ﺖ ﺧﻮاه ﺪ ﻧﻤ ﻮد ، و ﺁدرﺳ ﻬﺎﯼ ﻣﻘ ﺼﺪ ‪ IP‬را ﻗﺒ ﻞ از ارﺳ ﺎل از ﻃﺮﻳ ﻖ‬ ‫ﺷﺒﮑﻪ داﺧﻠﯽ ، از ﻧﻮ ﺑﺎزﻧﻮﻳﺴﯽ ﻣﯽ ﮐﻨﺪ.‬ ‫دروازﻩ ﻣﯽ ﺗﻮاﻧﺪ ﺁدرﺳﻬﺎﻳﯽ را ﺑﺮاﯼ ‪ NAT‬ﺑﻄﺮﻳﻖ ﻣﺨﺘﻠﻒ ﻃﺮح رﻳﺰﯼ ﻧﻤﺎﻳﺪ ﮐﻪ ﻋﺒﺎرﺗﻨﺪ از:‬ ‫ﻃ ﺮح رﻳ ﺰﯼ ﺑ ﺮاﯼ ﺁدرس ﻣﺠ ﺰاﯼ ‪ IP‬ﺧ ﺎرﺟﯽ : ﺑ ﺮاﯼ اﻳ ﻦ ﻧ ﻮع ‪ ،NAT‬ه ﺮ ﺑ ﺴﺘﻪ اﯼ ﮐ ﻪ از ﺷ ﺒﮑﻪ‬ ‫داﺧﻠ ﯽ ﺑﻴ ﺮون ﻣ ﯽ ﺁﻳ ﺪ ﺑ ﺮاﯼ ﺁدرس ‪ IP‬ﻣﺠﺰاﻳ ﯽ ﻃ ﺮح ﻣ ﯽ ﺷ ﻮد. در اﻳﻨﺘﺮﻧ ﺖ، ﺗﻤ ﺎم داد وﺳ ﺘﺪهﺎ دادﻩ‬ ‫ه ﺎ از ﺁدرس ‪ IP‬دﺳ ﺘﮕﺎﻩ ‪ NAT‬ﺣﺎﺻ ﻞ ﻣ ﯽ ﮔ ﺮدد. اﻳ ﻦ ﺗﮑﻨﻴ ﮏ ﺁدرس ده ﯽ ﮐ ﻪ راﻧ ﺪﻣﺎن ﺑ ﺎﻻﻳﯽ دارد و‬ ‫ﺑﻄ ﻮر ﻣﺘ ﺪاول ﺑ ﺮاﯼ اﺗ ﺼﺎل ﻳ ﮏ ﺷ ﺒﮑﻪ ﺑ ﺰرگ ﺑ ﻪ اﻳﻨﺘﺮﻧ ﺖ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﺷ ﻮد، ﭼ ﻮن ﺗﻌ ﺪاد ﻣﺤ ﺪودﯼ از‬ ‫ﺁدرﺳﻬﺎﯼ ‪ IP‬در دﺳﺘﺮس ﻣﯽ ﺑﺎﺷﻨﺪ.‬ ‫ﻃ ﺮح رﻳ ﺰﯼ ﺗ ﮏ ﺑ ﻪ ﺗ ﮏ : دروازﻩ ﻣ ﯽ ﺗﻮاﻧ ﺪ ه ﺮ دﺳ ﺘﮕﺎﻩ روﯼ ﺷ ﺒﮑﻪ داﺧﻠ ﯽ را ﺑ ﻪ ﺁدرس ‪ IP‬ﻣﻌﺘﺒ ﺮ و‬ ‫واﺣ ﺪ هﻤ ﺮاﻩ ﺑ ﺎ ه ﺮ دﺳ ﺘﮕﺎﻩ ﻃ ﺮح رﻳ ﺰﯼ ﻧﻤﺎﻳ ﺪ. ﺑﻨ ﺎﺑﺮاﻳﻦ ، ﺑ ﻪ ﻧﻈ ﺮ ﻣ ﯽ رﺳ ﺪ داد و ﺳ ﺘﺪ دادﻩ ه ﺎ از ﻳ ﮏ‬ ‫ﮔ ﺮوﻩ ﺁدرس ‪ IP‬ﺑ ﻪ وﺟ ﻮد ﻣ ﯽ ﺁﻳ ﺪ. اﻳ ﻦ ﺗﮑﻨﻴ ﮏ ﻏﺎﻟﺒ ﺎ ﺑ ﺮاﯼ ﻃ ﺮح رﻳ ﺰﯼ درﺧﻮاﺳ ﺘﻬﺎﯼ ﮐ ﺎرﺑﺮ از ﻃﺮﻳ ﻖ‬ ‫اﻳﻨﺘﺮﻧﺖ ﺑﻪ ﺳﺮوﻳﺲ هﻨﺪﻩ هﺎﯼ ﺷﺒﮑﻪ ﺟﺎﻧﺒﯽ ﻣﺜﻞ ﺳﺮوﻳﺲ دهﻨﺪﻩ وب اﺳﺘﻔﺎدﻩ ﻣﯽ ﺷﻮد.‬ ‫ﺁدرس اﺧﺘ ﺼﺎﺻﯽ از ﻟﺤ ﺎظ دﻳﻨ ﺎﻣﻴﮑﯽ : دروازﻩ ﻣ ﯽ ﺗﻮاﻧ ﺪ ﺗﻘ ﺴﻴﻢ ﮐﻨﻨ ﺪﻩ ﺗﻌ ﺪاد زﻳ ﺎدﯼ از ﺁدرس ﻏﻴ ﺮ‬ ‫ﻗﺎﺑ ﻞ ﻣ ﺴﻴﺮ ﻳ ﺎﺑﯽ ‪ IP‬ﺑ ﻪ ﺗﻌ ﺪاد ﮐﻤﺘ ﺮﯼ از ﺁدرﺳ ﻬﺎﯼ ﻣﻌﺘﺒ ﺮ ‪ IP‬ﺑﺎﺷ ﺪ. اﻳ ﻦ روش ﺗﮑﻨﻴ ﮏ ه ﺎﯼ دﻳﮕ ﺮ‬ ‫ﻣﺘﺪاول ﺗﺮ اﺳﺖ.‬ ‫ﺑ ﺮاﯼ ﺣﻔ ﻆ ﺁدرﺳ ﻬﺎﯼ ‪ IP,NAT‬اﻣ ﺮوزﻩ در اﻳﻨﺘﺮﻧ ﺖ ﺑ ﺴﻴﺎر ﻣ ﻮرد اﺳ ﺘﻔﺎدﻩ ﻗ ﺮار ﻣ ﯽ ﮔﻴ ﺮد. ﺁﻳ ﺎ ‪NAT‬‬ ‫اﻳﻤﻨ ﯽ را ﺑﻬﺘ ﺮ ﻣ ﯽ ﺳ ﺎزد؟ ﺑ ﻪ ﻣﺨﻔ ﯽ ﺳ ﺎزﯼ ﮐ ﺎرﺑﺮد ﺁدرس داﺧﻠ ﯽ ‪ IP‬ﺷ ﺒﮑﻪ ﮐﻤ ﮏ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ. ﮐ ﻪ ه ﺮﻩ‬ ‫ﻣ ﯽ ﺗﻮاﻧ ﺪ اﺳ ﺘﻔﺎدﻩ ﮐﻨ ﺪ ﺗ ﺎ ﻧﻘ ﺸﻪ ﺗﻮﭘﻮﻟ ﻮژﯼ ﺷ ﺒﮑﻪ را ﺑ ﻪ وﺟ ﻮد ﺁورد. اﻟﺒﺘ ﻪ ، ﺧ ﻮد ‪ NAT‬اﻳﻤﻨ ﯽ‬

‫- 31 -‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﺑ ﺴﻴﺎرﯼ ﭘﻴ ﺸﻨﻬﺎد ﻣ ﯽ ﮐﻨ ﺪ. در ﺣ ﺎﻟﯽ ﮐ ﻪ هﮑﺮه ﺎ ﻧﻤ ﯽ ﺗﻮاﻧﻨ ﺪ ﺑﻄ ﻮر ﻣ ﺴﺘﻘﻴﻢ ﺑ ﺴﺘﻪ ه ﺎﻳﯽ را از ﻃﺮﻳ ﻖ‬ ‫دروازﻩ ‪ NAT‬ارﺳ ﺎل ﻧﻤﺎﻳﻨ ﺪ. دروازﻩ ‪ NAT‬ﺁدرﺳ ﻬﺎﻳﯽ را از ﺳ ﻮﯼ هﮑ ﺮ ﺗﺮﺳ ﻴﻢ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ. ﺑ ﺪﻳﻦ‬ ‫دﻟﻴﻞ ، اﮔﺮ اﻳﻤﻨﯽ ﻻزم ﺑﺎﺷﺪ ﺗﮑﻨﻴﮑﻬﺎﯼ ‪ NAT‬ﺑﺎﻳﺪ ﺑﺎ اﺟﺮاﯼ دﻳﻮارﻩ ﺁﺗﺶ اﻳﻤﻦ ﺗﺮﮐﻴﺐ ﺷﻮد.‬

‫دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ: ﻣﺎﻣﻮران ﮐﻨﺘﺮل ﻧﻘﻞ و اﻧﺘﻘﺎل دادﻩ هﺎ ﺷﺒﮑﻪ و دروازﻩ ﺑﺎﻧﻬﺎ‬
‫دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ ، اﺑ ﺰارﯼ ﻣ ﯽ ﺑﺎﺷ ﻨﺪ ﮐ ﻪ ﺟﺮﻳ ﺎن ﻧﻘ ﻞ و اﻧﺘﻘ ﺎل دادﻩ ه ﺎﯼ ﻋﺒ ﻮرﯼ ﺑ ﻴﻦ ﺷ ﺒﮑﻪ ه ﺎ را‬ ‫ﮐﻨﺘ ﺮل ﻣ ﯽ ﻧﻤﺎﻳ ﺪ. اﻳ ﻦ اﺑ ﺰار در ﻣ ﺮز ﺑ ﻴﻦ ﺷ ﺒﮑﻪ ه ﺎ ﻗ ﺮار ﻣ ﯽ ﮔﻴ ﺮ ، و ﺑ ﻪ ﺻ ﻮرت دروازﻩ ه ﺎﯼ ﻋﻤ ﻞ ﻣ ﯽ‬ ‫ﮐﻨ ﺪ ﮐ ﻪ ﺗ ﺼﻤﻴﻢ ﻣ ﯽ ﮔﻴﺮﻧ ﺪ ﭼ ﻪ ﻧ ﻮع ارﺗﺒ ﺎﻃﯽ ﺑﺎﻳ ﺪ ﻣﺠ ﺎز و از ﭼ ﻪ ارﺗﺒ ﺎﻃﯽ ﺑﺎﻳ ﺪ ﻣﺠ ﺎز ﺑﺎﺷ ﺪ و از ارﺗﺒ ﺎﻃﯽ‬ ‫ﺑﺎﻳ ﺪ اﻣﺘﻨ ﺎع ﺷ ﻮد. ﺑ ﺎ ﻧﮕ ﺎﻩ ﺑ ﻪ ﺳ ﺮوﻳﺲ ه ﺎ ، ﺁدرﺳ ﻬﺎ ، و اﺣﺘﻤ ﺎﻻ ﺣﺘ ﯽ ﮐ ﺎرﺑﺮان ﻣ ﺎﻣﻮر ﻧﻘ ﻞ و اﻧﺘﻘ ﺎل‬ ‫دادﻩ ه ﺎ ، دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ ﺗﻌﻴ ﻴﻦ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ اﺗ ﺼﺎﻻت ﺑﺎﻳ ﺪ از ﻃﺮﻳ ﻖ ﺷ ﺒﮑﻪ دﻳﮕ ﺮ ﻣﻨﻘ ﻞ ﮔ ﺮدد. ﺑ ﺪﻳﻦ‬ ‫ﺻﻮرت ، دﻳﻮارﻩ هﺎﯼ ﺁﺗﺶ ﺑﻴﺸﺘﺮ ﻣﯽ ﺗﻮاﻧﺪ ﺑﻪ ﺻﻮرت ﻣﺎﻣﻮران ﺗﺮاﻓﻴﮑﯽ ﺷﺒﮑﻪ ﻋﻤﻞ ﻧﻤﺎﻳﺪ.‬ ‫اﮔ ﺮ دﻳ ﻮار ه ﺎﯼ ﺁﺗ ﺶ ﺑﻄ ﻮر ﺻ ﺤﻴﺢ ﭘﻴﮑﺮﺑﻨ ﺪﯼ ﺷ ﻮﻧﺪ، ﺳﻴ ﺴﺘﻤﻬﺎﯼ ﻳ ﮏ ﺳ ﻤﺖ ﺁن از ﺣﻤﻠ ﻪ هﮑﺮه ﺎ از‬ ‫ﺳ ﻤﺖ دﻳﮕ ﺮ دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ ﺟﻠ ﻮﮔﻴﺮﯼ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ. هﮑﺮه ﺎ ﺗﻨﻬ ﺎ ﻣ ﯽ ﺗﻮاﻧﻨ ﺪ ﺑ ﻪ ﺳﻴ ﺴﺘﻢ ه ﺎﯼ ﺧﻔﺎﻇ ﺖ‬ ‫ﺷ ﺪﻩ ﺑ ﻪ ﻃﺮﻳﻘ ﯽ دﺳﺘﺮﺳ ﯽ ﭘﻴ ﺪا ﻧﻤﺎﻳﻨ ﺪ ﮐ ﻪ دﻳ ﻮارﻩ ﺁﺗ ﺶ ﺑ ﻪ ﺁﻧﻬ ﺎ اﺟ ﺎزﻩ ﻣ ﯽ دهﻨ ﺪ. ﺳ ﺎزﻣﺎﻧﻬﺎ و ﺷ ﺮﮐﺘﻬﺎ‬ ‫ﺑﻄ ﻮر ﻣﺘ ﺪاول از دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ ﺑ ﺮاﯼ ﺣﻔﺎﻇ ﺖ ﻓﺮاﺳ ﺎﺧﺘﺎر ﺧ ﻮد از اﻳﻨﺘﺮﻧ ﺖ و از ﺣﻤ ﻼت ارﺗﺒﺎﻃ ﺎت‬ ‫ﺣﺮﻳ ﻒ ﺗﺠ ﺎرﯼ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮐﻨﻨ ﺪ. ﺑﻌ ﻼوﻩ، دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ ﺷ ﺒﮑﻪ داﺧﻠ ﯽ، در ﺣ ﺎل اﻓ ﺰاﻳﺶ و ﺣﻔﺎﻇ ﺖ‬ ‫ﺷﺒﮑﻪ هﺎﯼ ﺣﺴﺎس داﺧﻠﯽ از دﻳﮕﺮ ﺷﺒﮑﻪ هﺎﯼ ﺳﺎزﻣﺎن ﻣﯽ ﺑﺎﺷﻨﺪ.‬ ‫ﻣﻘﺎﻳ ﺴﻪ دﻳﮕ ﺮ ﺑ ﺮاﯼ ﺗﺠ ﺴﻢ دﻳ ﻮارﻩ ﺁﺗ ﺶ، دروازﺑ ﺎن ﺑ ﺎزﯼ ﻓﻮﺗﺒ ﺎل ﻣ ﯽ ﺑﺎﺷ ﺪ. ﮐ ﺎر دروازﺑ ﺎن ﺟﻠ ﻮﮔﺒﺮﯼ‬ ‫از ﮔ ﻞ زدن ﺗ ﻴﻢ ﻣﺨ ﺎﻟﻒ ﻣ ﯽ ﺑﺎﺷ ﺪ. ﺗ ﻮپ ﻓﻮﺗﺒ ﺎل ﭼﻴ ﺰﯼ ﺷ ﺒﻴﻪ ﺑ ﻪ ﺑ ﺴﺘﻪ ﻣ ﯽ ﺳﺎﺷ ﺪ. ﮐ ﺎر دﻳ ﻮارﻩ ﺁﺗ ﺶ‬ ‫ﺟﻠ ﻮﮔﻴﺮﯼ از ارﺳ ﺎل ﺑ ﺴﺘﻪ ه ﺎﯼ ﻧﺎﺧﻮاﺳ ﺘﻪ ﺑ ﻪ داﺧ ﻞ ﺷ ﺒﮑﻪ ﻣ ﯽ ﺑﺎﺷ ﺪ. اﻟﺒﺘ ﻪ ، دروازﺑ ﺎن ﺑﺎﻳ ﺪ اﺟ ﺎزﻩ ده ﺪ‬ ‫ﮐ ﻪ ﺗ ﻮپ از داﺧ ﻞ دروازﻩ ﺑﻴ ﺮون ﮐ ﺸﻴﺪﻩ ﺷ ﻮد ، در ﻧﻬﺎﻳ ﺖ ﻧﻴ ﺰ ﺑ ﺎزﯼ ﭘﺎﻳ ﺎن ﺧﻮاه ﺪ ﻳﺎﻓ ﺖ. دﻳﻮاره ﺎﯼ‬ ‫ﺁﺗ ﺶ ﺑﺎﻳ ﺪ ﻳﮑ ﺴﺮﯼ از ارﺗﺒﺎﻃ ﺎت از ﮐ ﺎر اﻓﺘ ﺎدﻩ ﻧﻴ ﺰ اﺟ ﺎزﻩ ﻋﺒ ﻮر ده ﺪ، ﺑﻨ ﺎﺑﺮاﻳﻦ ﮐ ﺎرﺑﺮان داﺧﻠ ﯽ ﻣ ﯽ‬ ‫ﺗﻮاﻧﻨ ﺪ ﺑ ﻪ ﺷ ﺒﮑﻪ ﺧ ﺎرﺟﯽ دﺳﺘﺮﺳ ﯽ ﭘﻴ ﺪا ﻧﻤﺎﻳﻨ ﺪ ،در ﺣ ﺎﻟﯽ ﮐ ﻪ ﺑﻴ ﺸﺘﺮ ارﺗﺒﺎﻃ ﺎت ورودﯼ رد ﻣ ﯽ ﺷ ﻮﻧﺪ )‬ ‫ﺑﺠﺰ ﺑﺮاﯼ ﺳﺮوﻳﺴﻬﺎﯼ ﺧﺎص(.‬

‫ﻓﻴﻠﺘﺮهﺎﯼ ﻗﺪﻳﻤﯽ ﺑﺴﺘﻪ‬
‫ﻓﻴﻠﺘﺮه ﺎﯼ ﻗ ﺪﻳﻤﯽ ﺑ ﺴﺘﻪ ﺑ ﺮاﯼ ﺑ ﻴﺶ از ﻳ ﮏ ده ﻪ ﻣ ﻮرد اﺳ ﺘﻔﺎدﻩ ﻗ ﺮار ﮔﺮﻗﺘﻨ ﺪ، و ﻣ ﯽ ﺗﻮاﻧﻨ ﺪ روﯼ‬ ‫ﻣ ﺴﻴﺮﻳﺎب ﻳ ﺎ دﻳ ﻮارﻩ ﺁﺗ ﺶ اﺟ ﺮا ﺷ ﻮﻧﺪ. ﺑ ﺮ اﺳ ﺎس ﻧ ﺎم ﺁﻧﻬ ﺎ، ﻓﻴﻠﺘﺮه ﺎﯼ ﺑ ﺴﺘﻪ روﯼ ﺗ ﮏ ﺗ ﮏ ﺑ ﺴﺘﻪ ه ﺎ،‬ ‫ﺗﺤﻠﻴ ﻞ اﻃﻼﻋ ﺎت و ﺟﻬ ﺖ ﻋﻨ ﻮان ﺁﻧﻬ ﺎ ﺗﺎﮐﻴ ﺪ دارد. دﺳ ﺘﮕﺎﻩ ﻗ ﺪﻳﻤﯽ ﻓﻴﻠﺘ ﺮ ﺑ ﺴﺘﻪ ه ﺮ ﺑ ﺴﺘﻪ ﻋﺒ ﻮرﯼ از ﺁﻧ ﺮا‬ ‫ﺗﺤﻠﻴ ﻞ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﺗ ﺎ ﺗ ﺼﻤﻴﻢ ﺑﮕﻴ ﺮد ﺁﻳ ﺎ ﺑ ﺴﺘﻪ ﺑﺎﻳ ﺪ از اﻧﺘﻘ ﺎل ﺁن ﺟﻠ ﻮﮔﻴﺮﯼ ﮔ ﺮدد. ﻓﻴﻠﺘﺮه ﺎﯼ ﻗ ﺪﻳﻤﯽ ﺑ ﺴﺘﻪ‬ ‫اﻳﻦ ﺗﺼﻤﻴﻢ را ﺑﺎ اﺳﺘﻔﺎدﻩ از اﻃﻼﻋﺎت زﻳﺮ اﻧﺠﺎم ﻣﯽ دهﺪ.‬ ‫ﺁدرس ‪ IP‬ﻣﺒ ﺪا : ﺁﻳ ﺎ ﺑ ﺴﺘﻪ ﮐ ﻪ از ﺁدرس ‪ IP‬ﻣ ﯽ ﺁﻳ ﺪ، ﺑﺎﻳ ﺪ در هﻨﮕ ﺎم ورود ﺑ ﻪ ﺷ ﺒﮑﻪ ﻣﺠﻮزداﺷ ﺘﻪ‬ ‫ﺑﺎﺷ ﺪ؟ اﻳ ﻦ اﻃﻼﻋ ﺎت از ﻋﻨ ﻮان ‪ HP‬ﺑ ﺴﺘﻪ ﺟﻤ ﻊ ﺁورﯼ ﻣ ﯽ ﺷ ﻮد، دﺳ ﺘﮕﺎﻩ ﻣﺒ ﺪا ﻳ ﺎ ﺷ ﺒﮑﻪ ارﺳ ﺎل ﮐﻨﻨ ﺪﻩ‬ ‫را ﻧﺸﺎن ﻣﯽ دهﺪ.‬ ‫ﺁدرس ‪ IP‬ﻣﻘ ﺼﺪ : ﺁﻳ ﺎ ﺑ ﺴﺘﻪ ﺑ ﻪ ﺳ ﻤﺖ ﺳ ﺮوﻳﺲ ﮐﻨﻨ ﺪﻩ اﯼ ﮐ ﻪ ﺑﺎﻳ ﺪ اﻳ ﻦ ﻧ ﻮع ﻧﻘ ﻞ و اﻧﺘﻘ ﺎل دادﻩ ه ﺎ را‬ ‫درﻳﺎﻓ ﺖ ﻧﻤﺎﻳ ﺪ، ارﺳ ﺎل ﻣ ﯽ ﮔ ﺮدد؟ اﻳ ﻦ زﻣﻴﻨ ﻪ، از ﻋﻨ ﻮان ‪ IP‬ﺑ ﺴﺘﻪ ﻧﻴ ﺰ دﺳ ﺘﮕﺎﻩ ﻣ ﻮرد ﻧﻈ ﺮ ﻣﻘ ﺼﺪ ﻳ ﺎ‬ ‫ﺷﺒﮑﻪ ﺑﺴﺘﻪ را ﻧﺸﺎن ﻣﯽ دهﺪ.‬ ‫دروازﻩ‪ TCP/UDP‬ﻣﺒ ﺪا : درﮔ ﺎﻩ ﻣﺒ ﺪ ﺑ ﺴﺘﻪ ﭼﻴ ﺴﺖ و ﺁﻳ ﺎ ﻧ ﺮم اﻓ ﺰار ﮐ ﺎرﺑﺮدﯼ ﺧﺎﺻ ﯽ دﻻﻟ ﺖ ﻣ ﯽ‬ ‫ﻧﻤﺎﻳﺪ؟ اﻳﻦ اﻃﻼﻋﺎت از ﻋﻨﻮان ‪ TCP‬ﻳﺎ ‪ UDP‬ﺟﻤﻊ ﺁورﯼ ﻣﯽ ﮔﺮدد.‬ ‫ﺁدرس دروازﻩ/‪TCP‬ﻣﻘ ﺼﺪ : دروازﻩ ﻣﻘ ﺼﺪ ؟ ﭼ ﻮن ﺳﺮوﻳ ﺴﻬﺎﯼ ﻣﺘ ﺪاول ﻏﺎﻟﺒ ﺎ از دروازﻩ ه ﺎﯼ‬ ‫ﺷ ﻨﺎﺧﺖ ﺷ ﺪﻩ اﯼ از 0071‪ RFC‬اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﻧﻤﺎﻳﻨ ﺪ، از دروازﻩ ﻣﻘ ﺼﺪ ﺑ ﺮاﯼ ﻓ ﺮاهﻢ ﺁورﯼ اﻣﮑ ﺎن‬ ‫ﮐ ﺎرﺑﺮدﯼ ﺑﻌ ﻀﯽ از ﺳﺮوﻳ ﺴﻬﺎ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮔ ﺮدد، در ﺣﺎﻟﻴﮑ ﻪ از ﻣ ﺎﺑﻘﯽ ﺻ ﺮف ﻧﻈ ﺮ ﻣ ﯽ ﮔ ﺮدد. اﻳ ﻦ‬ ‫اﻃﻼﻋﺎت ﻧﻴﺰ از ﻋﻨﻮان ‪ TCP‬ﻳﺎ ‪ UDP‬ﺑﺴﺘﻪ ﺟﻤﻊ ﺁورﯼ ﻣﯽ ﮔﺮدد.‬ ‫ﮐ ﺪ ﺑﻴ ﺖ ‪ : TCP‬ﺁﻳ ﺎ ﺑ ﺴﺘﻪ داراﯼ ﻣﺠﻤﻮﻋ ﻪ ﺑﻴ ﺖ ‪ SYN‬ﻣ ﯽ ﺑﺎﺷ ﺪ. ﺑ ﻪ اﻳ ﻦ ﻣﻌﻨ ﺎ ﮐ ﻪ ﺑﺨ ﺸﯽ از ﺷ ﺮوع‬ ‫ارﺗﺒ ﺎط ﻣ ﯽ ﺑﺎﺷ ﺪ، ﻳ ﺎ داراﯼ ﻣﺠﻤﻮﻋ ﻪ ﺑﻴ ﺖ ‪ ACK‬ﻣ ﯽ ﺑﺎﺷ ﺪ ﮐ ﻪ ﺑﻴ ﺎﻧﮕﺮ ﺑﺨ ﺸﯽ از ارﺗﺒ ﺎﻃﯽ اﺳ ﺖ ﮐ ﻪ‬ ‫ﻗ ﺒﻼ ﺑﺮﻗ ﺮار ﺷ ﺪﻩ اﺳ ﺖ؟ از اﻳ ﻦ اﻃﻼﻋ ﺎت ﻣ ﯽ ﺗ ﻮان در اﻧﺘﺨ ﺎب اﻳﻨﮑ ﻪ ﺑ ﻪ ﺑ ﺴﺘﻪ ه ﺎ ﺑﺎﻳ ﺪ ﻣﺠ ﻮز ﻋﺒ ﻮر‬ ‫دادﻩ ﺷ ﻮد ﻳ ﺎ ﺗ ﺎﺧﻴﺮ اﺳ ﺘﻔﺎدﻩ ﻣ ﯽ ﮔ ﺮدد. اﻟﺒﺘ ﻪ، اﻳ ﻦ دادﻩ ه ﺎ در ﺑ ﺴﺘﻪ ه ﺎﯼ ‪ ، UDP‬ﮐ ﻪ ﻣﻔﻬ ﻮﻣﯽ از‬ ‫ﮐﺪﺑﻴﺖ هﺖ ﻧﺪارد، ﺣﻀﻮر ﻧﺪارﻧﺪ.‬

‫- 41 -‬

‫‪Learning TCP/IP‬‬

‫‪BY: Nasser-Desperado‬‬

‫ﭘﺮوﺗﮑ ﻞ ﻣ ﻮرد اﺳ ﺘﻔﺎدﻩ : ﺁﻳ ﺎ ﺑﺎﻳ ﺪ در ﺷ ﺒﮑﻪ ﺑ ﻪ اﻳ ﻦ ﭘﺮوﺗﮑ ﻞ ﻣﺠ ﻮز ﺑﻬ ﺮﻩ ﺑ ﺮدارﯼ دادﻩ ﺷ ﻮد، ﻓﻴﻠﺘ ﺮ‬ ‫ﺑ ﺴﺘﻪ ﻧ ﺮم اﻓ ﺰارﯼ ﻣﻤﮑ ﻦ اﺳ ﺖ در ﺣ ﺎﻟﯽ ﮐ ﻪ از ﺑﮑ ﺎر رﻓ ﺘﻦ ‪ UDP‬اﺟﺘﻨ ﺎب ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﺑ ﻪ ﺑ ﺴﺘﻪ ه ﺎﯼ‬ ‫‪ TCP‬اﺟﺎزﻩ اﺳﺘﻔﺎدﻩ دهﺪ ﻳﺎ ﺑﺎﻟﻌﮑﺲ.‬ ‫ﺟﻬ ﺖ : ﺁﻳ ﺎ ﺑ ﺴﺘﻪ ﺑ ﺪاﺧﻞ دﺳ ﺘﮕﺎﻩ ﻓﻴﻠﺘ ﺮ ﺑ ﺴﺘﻪ ﻣ ﯽ اﻳ ﺪ ﻳ ﺎ از ﺁن ﺟ ﺪا ﻣ ﯽ ﺷ ﻮد ﺑ ﻪ دﺳ ﺘﮕﺎﻩ ﻓﻴﻠﺘ ﺮ ﺑ ﺴﺘﻪ ﻣ ﯽ‬ ‫ﺗﻮاﻧﺪ ﺑﺮ اﺳﺎس ﮔﺰﻳﻨﺶ، ﻓﻴﻠﺘﺮ ﻋﺒﻮرﯼ ﺑﺴﺘﻪ و ﺑﺮ ﻣﺒﻨﺎﯼ ﺟﻬﺖ ﺟﺮﻳﺎن ﺑﺴﺘﻪ ﺗﺼﻤﻴﻢ ﺑﮕﻴﺮد.‬ ‫واﺳ ﻄﻪ : ﺁﻳ ﺎاز ﺷ ﺒﮑﻪ ﻣﻄﻤ ﺌﻦ ﻳ ﺎ ﻏﻴ ﺮ ﻣﻄﻤﺌﻨ ﯽ ارﺳ ﺎل ﻣ ﯽ ﺷ ﻮد؟ دﺳ ﺘﮕﺎﻩ ﻓﻴﻠﺘ ﺮ ﺑ ﺴﺘﻪ، ﺑ ﺮ ﻣﺒﻨ ﺎﯼ‬ ‫واﺳ ﻄﻪ اﯼ ﮐ ﻪ ﺑ ﺴﺘﻪ را ﻣﻨﺘﻘ ﻞ ﻣ ﯽ ﮐﻨ ﺪ، ﻣ ﯽ ﺗﻮاﻧ ﺪ ﺑ ﺴﺘﻪ ه ﺎﻳﯽ را ارﺳ ﺎل ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﺟﻠ ﻮﯼ اﻧﺘﻘ ﺎل دادﻩ ه ﺎ‬ ‫را ﺑﮕﻴ ﺮد. ﻓﻴﻠﺘﺮه ﺎﯼ ﺑ ﺴﺘﻪ )ﻣ ﺴﻴﺮﻳﺎﺑﻬﺎ ﻳ ﺎ دﻳ ﻮارﻩ ه ﺎﯼ ﺁﺗ ﺶ( ﺑ ﺎ ﻳﮑ ﺴﺮﯼ ﻗﻮاﻋ ﺪ ﻓﻴﻠﺘ ﺮ ﮔﻴ ﺮﯼ، ﺑ ﺎ ه ﺮ‬ ‫ﺧ ﻂ در ﻣﺠﻤﻮﻋ ﻪ ﻗﻮاﻋ ﺪ ﭘﻴﮑﺮﺑﻨ ﺪﯼ ﻣ ﯽ ﺷ ﻮﻧﺪ ﮐ ﻪ ﻣ ﺸﺨﺺ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﺁﻳ ﺎ ﻧ ﻮع دادﻩ ﺷ ﺪﻩ ﺑ ﺴﺘﻪ ﺑﺎﻳ ﺪ ﻣ ﻮرد‬ ‫ﻗﺒ ﻮل ﻗ ﺮار ﮔﻴ ﺮد ﻳ ﺎ ﺑﺎﻳ ﺪ ﺣ ﺬف ﺷ ﻮد. اﻳ ﻦ ﻗﻮاﻋ ﺪ ﻏﺎﻟﺒ ﺎ ﻟﻴ ﺴﺘﻬﺎﯼ ﮐﻨﺘ ﺮل دﺳﺘﺮﺳ ﯽ )‪ (ACLs‬ﻓﻴﻠﺘ ﺮ ﮔﻴ ﺮﯼ‬ ‫ﺑ ﺴﺘﻪ ﻧﺎﻣﻴ ﺪﻩ ﻣ ﯽ ﺷ ﻮن، ﺑﺨ ﺼﻮص وﻗﺘ ﯽ ﮐ ﻪ ﺑ ﺮ روﯼ ﻣ ﺴﻴﺮﻳﺎﺑﻬﺎ اﺟ ﺮا ﻣ ﯽ ﮔ ﺮدد. ﺷ ﺮﮐﺘﻬﺎ ﺗﻮﻟﻴ ﺪ ﮐﻨﻨ ﺪﻩ‬ ‫ﻧ ﺮم اﻓ ﺰار ه ﺮ ﮐ ﺪام از ﻳ ﮏ ﻧ ﻮع ﻓﻴﻠﺘ ﺮ ﮔﻴ ﺮﯼ ﭘ ﺸﺘﻴﺒﺎﻧﯽ ﻣ ﯽ ﻧﻤﺎﻳ ﺪ ﮐ ﻪ ﺑ ﺮاﯼ اﻳ ﻦ ﻗﻮاﻋ ﺪ، داراﯼ دﺳ ﺘﻮر‬ ‫زﺑ ﺎن ﻣﺨ ﺘﺺ ﺑﺨ ﻮد ﻣ ﯽ ﺑﺎﺷ ﻨﺪ، ﺑ ﺎ ﻳﮑ ﺴﺮﯼ ﺗﻮﻟﻴ ﺪات ﮐ ﻪ زﺑ ﺎن ﺳﻔﺎرﺷ ﯽ را ﻓﺮاهﻤﻤ ﯽ ﺁورﻧ ﺪ و ﻣ ﺎﺑﻘﯽ ﮐ ﻪ‬ ‫‪ GUI‬را ﺑ ﺮاﯼ ﺗﻌﺮﻳ ﻒ ﻗﻮاﻋ ﺪ ﻓﻴﻠﺘﺮﮔﻴ ﺮﯼ ﺑ ﺴﺘﻪ ﻓ ﺮاهﻢ ﻣ ﯽ ﺁورﻧ ﺪ. ﺑﻌ ﻀﯽ از ﻗﻮاﻋ ﺪ ﻣﺘ ﺪاول ﻓﻴﻠﺘﺮﮔﻴ ﺮﯼ‬ ‫ﺑﺴﻪ ﺑﺎ اﺳﺘﻔﺎدﻩ از زﺑﺎن ﺗﻌﺮﻳﻒ ﻗﺎﺑﻞ درﮎ ﻃﺒﻴﻌﯽ ﺷﺮﮐﺖ ﺳﺎزﻧﺪﻩ را ﺗﻮ ﺟﺪول ﻧﻮﺷﺘﻢ.‬ ‫ﮐﺪ ﺑﻴﺖ‬ ‫هﻴﭻ‬ ‫‪ACK‬‬ ‫‪All‬‬ ‫دروازﻩ ﻣﻘﺼﺪ‬ ‫08‬ ‫22

Similar Documents

Premium Essay

Natural Gas

...The demand for natural gas has increased in the past decade and that has lead to exploration into unexplored areas of the United States. These explorations lead to the Fernow Experimental Forest in West Virginia. The Fernow is well known for long-term Silviculture, watershed, and ecological research (Kochenderfer 2006). As the preparation drilling a total of over 700 hundred trees were removed. During hydraulic fracturing which is a process in which fractures in rocks below the earth's surface are opened and widened by injecting chemicals and liquids at high pressure to extract natural gas ("hydraulic fracturing," 2012). During this process many of the trees and shrubs showed signs of being affected by the process. The trees started to brown early, they stared weltering and fell to the ground earlier then they should have. One would think that due to drilling and the release of natural gases that you wouldn’t find signs of wildlife. That’s not the case with the white tail deer. The white tail deer require the intake of salt and other minirals especially during the summer and spring months. The water coming from the gas site had a high concentration of minerals that the deer liked. That’s the one unqie thing about deer is they are an adaptive species. The black bear population did see a slight decrease in activity around the drill site. According to the CIA world fact book the U.S. has the highest demand for natural gas with 683,300,000,000 cubic meters of gas in 2010, with...

Words: 465 - Pages: 2

Premium Essay

Natural Gas

...Natural Gas Name Course Instructor’s Name Date Submitted Natural gas is classified as a fossils fuel and is abundant in most parts of the world. It is referred to as ‘natural gas’ because it occurs naturally as a hydrocarbon that is an element from carbon and hydrogen atoms. It consists mainly of methane and is colorless. It is known to be the simplest type of hydrocarbon (Originenergy.com.au, 2015). Natural gas is a very efficient energy source apart from being environmental friendly. It is known to be the cleanest-burning conventional fuel because it emits smaller amounts of greenhouse gases as compared to the heavier hydrocarbon fuels like coal. The primary compositions of natural gas are methane (CH4), ethane and propane. Natural gas is mainly used to fuel electric power generators, the raw material for making consumer products from plastics and heats buildings. This paper explores the advantages and problems associated with extraction, processing, transportation and use of natural gas. Advantages of natural gas Natural gas is available worldwide in abundance. In the US only, there are over a trillion barrels of gas reserves that are yet to be harvested. Just like other sources of fuel like coal and oil, natural gas is a viable power source that has to be conserved. It is estimated in the coming years more sites with natural gas will be discovered. The US department of energy predicts there will be a rise...

Words: 1042 - Pages: 5

Premium Essay

Natural Gas Pipelines

...Natural gas is the energy of the future. It provides cleaner energy, at a more efficient rate. The northeast corner of our nation is always in need of energy. Pipeline projects are claimed to be harmful to the environment, yet studies have shown no value in property is lost due to pipelines. This nation needs to add funding and focus towards natural gas production and sale due to the many positive benefits shown. Countries like Taiwan, South Korea, and Japan are all major users of Natural Gas. They import an amazing amount of LNG (Liquefied Natural Gas) every year. They account for one third of the world's natural gas importation. The dense populations and lack of resources causes them to need to pull in millions of barrels of LNG. Their usage of natural gas has far surpassed the use of coal and oil in their country. Japan spent $63.28 Billion dollars on it last year. These asian countries have seen the benefits in this cheap, and clean energy. (NaturalGas.org) Japan is nearly balanced with energy now, where it once was a complete disaster....

Words: 489 - Pages: 2

Premium Essay

Natural Gas Outlook

...and $3.67 in 2013. Currency issues also have an effect on natural gas prices in the US. For example, should the value of the US dollar weaken against the Canadian dollar, the costs of Canadian natural gas could rise, which would put upward pressure on prices. This could increase the attractiveness of regions where production is more expensive, thus allowing additional supplies to enter the market and potentially limiting how high prices could go. Higher consumption seen in 2012 and in 2013 In its Short-Term Energy Outlook published June 12, 2012, the Energy Information Administration (EIA) projected that total natural gas consumption would increase by 4.3% in 2012 and 2.4% in 2013. Despite the warmer-than-usual winter and the slowdown in withdrawals, the EIA believes that the increase in electric power consumption of natural gas will dwarf the declines that it expects in the residential and commercial sectors. As a result, these people ask whether limited natural gas resources should be squandered on generating electricity when other inexpensive methods of generating power exist The EIA projected, in its Annual Energy Outlook 2012 Early Release, that total dry natural gas production would rise 3.0% in 2012, then fall 3.0% in 2013 before starting a relatively steady trend upward. The 3.0% drop in dry gas production in 2013 is unlikely, in our opinion, as oil and gas shale-drilling efforts continue However, gas production from oil shale wells is picking up in a big way....

Words: 1437 - Pages: 6

Premium Essay

Natural Gas Exploration

...1. Natural gas should be the product that BP should invest in. It is no longer a new source of energy as its publicity has been increasing as a possible best alternative to oil which still is by far a dominating resource. Now, there is no doubt that the amount of oil available is decreasing and in fact using oil as heavily as it has been used is not welcomed, especially by individuals or groups who advocate countless number of anti-CO2 emission campaign. Natural gas also emits CO2 just like oil because they are just the same in that both are fossil fuels, although the emission of CO2 by natural gas is said to be almost a half. Plus, if this is to be used for generating electricity, it is capable of generating the same or even higher amount of electricity. It is said to be cheaper to access to. According to the article, it is around 75% cheaper than oil at the moment. (probably a citation as evidence is more persuasive) and it’d be best to include the exact price of the current oil supply. Many alternatives have been invented and tried out, but none of them still has proven enough to meet the demand for energy. Taking the balance between the ability to generate electricity and the emission of greenhouse effect gas, natural gas is ahead of the others. I personally think that the points you’ve written above should be included in my part in section A – product/ services. That’s because I’ll be explaining why we would wanna replace nuclear power by natural gas. (Nclear...

Words: 701 - Pages: 3

Premium Essay

Convert to Natural Gas

...Convert to Natural Gas Currently in America there are two main items that are always on the minds of the people. The first of which is the state of the economy, and how long will it take to get out of this recession. The second is finding an alternate source of energy besides oil. This can be seen in the rate at which hybrid cars are popping up on the market. Natural gas, which is abundant in America, may very well be the answer to both. The law of demand states that as the price of the good increases the quantity demanded of the good decreases. The law of supply states that as the price of the good increases, the quantity supplied of the good increases. Energy however is one of the exceptions to both of these rules. Oil and fossil fuels have a relatively high demand worldwide yet the prices are still at all-time highs. Natural gas on the other hand is at a low is cost with a high supply. While the amount of oil produced has had a slight increase recently, thanks to new technologies, it has only been enough to keep up with the rise in demand. The fact that the oil market is a global one, along with the political control over most of the world’s oil pockets continues to have the price of oil at a fairly high price. Unfortunately it will most likely stay this way. A gain made in improving the supply production of oil takes years of research. Just like oil, natural gas shows itself to be an exception to the laws of supply and demand. Unlike oil, natural gas is a...

Words: 548 - Pages: 3

Premium Essay

Natural Gas Paper

...Natural Gas Paper Natural Gas Natural gas is a flammable gas that consists of methane and other hydrocarbons. This gas is found underground and is also used as fuel. Natural gas is produced when trapped gas is released above ground. That release creates unusual spouts of heat and fire. Scientists realized that under the ground lay an energy producing gas waiting to be extracted. Today when a company is looking for natural gas, they seek out a particular type of rock formation above ground. Tests are run that can measure sound waves and gravitational pulls in a particular area. If the tests appear promising, the drilling begins. Drilling only returns natural gas half of the time. In order to tap into the underground reserve, the drilling team must dig about 6000 feet into the ground. Once the gas is extracted from the ground it is sent to power plants and processing plants. It is then cleaned, separated and converted into fuel that is usable for homes and businesses. There are times that the gas is compressed, then transported to various rural areas where pipeline aren’t available. It is then placed in small metal tanks. The USA produces about a quarter of the earth’s natural gas. The five best sources for fossil fuel are Louisiana, Wyoming, New Mexico, Oklahoma and Texas. Natural gas can be found in several other places within the Northern Hemisphere. Qatar is the world’s largest natural gas field. The Persian Gulf is the second largest. Natural gas impacts the quality...

Words: 340 - Pages: 2

Premium Essay

Natural Gas Fracking

...I was neutral on the subject of natural gas fracking, I had never heard of it and had no idea how destructive this process of extraction was. The further I got on this report, the more furious I became that this was happening on US soil, and not only that but people in the highest levels of government were not only sanctioning it, but using their power in public office to advance the agenda of companies that they were either running before they cae into office, or companies that friends were running, or were just giving them kickbacks, which would be the only reason that anyone would let this go on. After doing just a small amount of research you realize rather quickly how detrimental this process is, not only to the environment, but to the helpless animals who had had wells built in their migration patterns. Not to mention the helpless children whos parents had no idea what the were getting themselves and their families into when they signed what appeared to be a harmless contract allowing a drilling company to put up a small rig on their property. Who didn’t realize that in a short amount of time they would be able to light the water coming out of their faucet on fire, that their animals would loose their hair, have problems eating and die. The fact that any human being would allow this to be done to other human beings all in the name of money is beyond me, but I’ll get into that later. What is hydraulic fracturing anyway? The U.S. contains gas fields that rival the oil fields...

Words: 2245 - Pages: 9

Premium Essay

Natural Gas

...Natural gas is a vital component of the world’s supply of energy. It is one of the cleanest, safest, and most useful of all energy sources. Natural gas is a fossil fuel. Like oil and coal, this means that it is, essentially, the remains of plants and animals and microorganisms that lived millions and millions of years ago. In the 19th and early 20th centuries, natural gas was used primarily for street and building lighting, providing what was known as gaslight. Today, improved distribution of gas has made possible a wide variety of uses in homes, businesses, factories, and power plants. The U.S. Energy Information Administration projects a 50 percent rise in global natural gas consumption between 2010 and 2035, with growth in Brazil and China driving increased demand. One of the main reasons for this increase is due to electric power. Natural gas power plants usually generate electricity in gas turbines, directly using the hot exhaust gases of fuel combustion. There are numerous reasons why natural gas is becoming more reliant for generating electricity than other fossil fuels. While coal is the cheapest fossil fuel for generating electricity, it is also produces more pollution. The electric generation industry, in fact, has traditionally been one of the most polluting industries in the United States. Regulations surrounding the emissions of power plants have forced these electric generators to come up with new methods of generating power, while lessening environmental damage...

Words: 463 - Pages: 2

Premium Essay

Liquefied Natural Gas

...Liquefied natural gas or LNG is natural gas (predominantly methane, CH4) that has been converted to liquid form for ease of storage or transport. Liquefied natural gas takes up about 1/600th the volume of natural gas in the gaseous state. It is odorless, colorless, non-toxic and non-corrosive. Hazards include flammability after vaporization into a gaseous state, freezing and asphyxia. A typical LNG process. The gas is first extracted and transported to a processing plant where it is purified by removing any condensates such as water, oil, mud, as well as other gases such as CO2 and H2S. An LNG process train will also typically be designed to remove trace amounts of mercury from the gas stream to prevent mercury amalgamizing with aluminium in the cryogenic heat exchangers. The gas is then cooled down in stages until it is liquefied. LNG is finally stored in storage tanks and can be loaded and shipped. The liquefaction process involves removal of certain components, such as dust, acid gases, helium, water, and heavy hydrocarbons, which could cause difficulty downstream. The natural gas is then condensed into a liquid at close to atmospheric pressure (maximum transport pressure set at around 25 kPa (3.6 psi)) by cooling it to approximately −162 °C (−260 °F). LNG achieves a higher reduction in volume than compressed natural gas (CNG) so that the energy density of LNG is 2.4 times greater than that of CNG or 60% of that of diesel fuel.[1] This makes LNG cost efficient to...

Words: 342 - Pages: 2

Premium Essay

Compressed Natural Gas

...KEY ISSUES IN PAKISTAN INDUSTRY Key Issues in Industry in Pakistan The previous two chapters have given a chronological account of developments in the industrial sector in Pakistan, showing how perspectives of different regimes have influenced industrial and economic growth. This chapter looks at contemporary issues in the industrial sector, including privatization, the textile sector and a host of others. Many of the issues in the industrial sector today have their roots in policies adopted many years ago; so much so, that some analysts and experts blame the problems of today on key decisions of yesteryear. 8.1 Numbers and Trends in Industry The phenomenal growth rate experienced in the industrial sector in Pakistan in the early 1950s took place, from an almost non-existent base, where the growth rate of the industrial sector was doubling itself every few years. The extraordinary growth rates of over 20 per cent between 1950 and 1955 in large-scale manufacturing were achieved primarily because very little existed to start with and, hence, any investment and production, no matter how little, would register impressive gains. Only in the early 1960s did largescale manufacturing come close to the extraordinary period of the early and mid-1950s. Nevertheless, overall manufacturing did manage to produce a growth rate of close to 10 per cent on average throughout the 1960s (Table 8.1), followed by a substantial reduction in the 1970s, the reasons for which ...

Words: 330 - Pages: 2

Premium Essay

Natural Gas Consumtion Patterns

...Natural Gas Consumption Patterns Natural gas, one of the cleanest, safest, and most useful of all energy sources, is a mixture of hydrocarbon gases that occurs with petroleum deposits that is used as a fuel and in the manufacture of organic compounds. Between 1997 and 2011, total natural gas consumption in the United States rose 7%. This is modest growth in and of itself but it masks bigger changes in individual sectors. Electric power was the second lowest user of natural gas in 1997 but is now the largest user. This sector also shows the greatest sensitivity to price change than any other sector. As of 2009, natural gas consumption for power surpassed the consumption in the industrial sector. With coal prices rising and natural gas prices declining, dispatching natural gas generators in some parts of the country has become increasingly competitive with operating coal generators. The competition between natural gas and coal fired generators first appeared in the Southeast where it was more expensive to use coal-fired generators due to the higher cost of transporting the coal over long distances. The industrial sector uses natural gas for processing heat, steam generation, onsite electricity generation, space heating and petrochemical processing. In 1997, the industrial sector was the largest user of natural gas. This sector’s use has steadily declined from 1997 until 2010 where there was an upturn in...

Words: 784 - Pages: 4

Premium Essay

Natural Gas Hedging Strategy

...UNDERSTANDING NATURAL GAS MARKETS Table of Contents PREVIEW Overview ...................................................................... 2 The North American Natural Gas Marketplace ............... 4 Natural Gas Supply ....................................................... 8 Natural Gas Demand ................................................... 12 Natural Gas Exports .................................................... 15 How Natural Gas is Traded .......................................... 16 Conclusion: A New Era For U.S. Natural Gas Markets ... 20 Glossary ..................................................................... 20 References ................................................................. 23 Understanding Natural Gas Markets Overview Natural Gas is an Important Source of Energy for the United States. Natural gas is an attractive fuel because it is clean burning and efficient, and ample supplies of natural gas are available from domestic resources. Recently, natural gas production in the U.S. has increased substantially due to technological advancements in natural gas extraction methods. This increased production has displaced traditional supply sources and resulted in reduced prices for natural gas consumers. The prospect of ample natural gas supplies, continued low prices, and the favorable environmental and economic position of natural gas-fired electric generation plants are leading to expectations of growing U.S. demand for natural gas, especially...

Words: 9155 - Pages: 37

Premium Essay

American’s Natural Gas Highway

...American’s Natural Gas Highway Costumers are facing serious problems if they want to “go green” and economical. For example, there are a few opportunities on the market to choose from economical and environment-friendly cars, but there are not many places to refuel them, which make people change their desires, go buying the ecofriendly cars. There is no benefit of having a car if you cannot drive it everywhere. This makes the manufacturers to suffer, and being stuck with inventory and no opportunity to sell or extend their productions. In order to solve the problem, Clean Energy Fuels Corp. and Navistar International partnered up with the plan to create America’s Natural Gas Highway. This would be the first network of natural gas fueling stations across the United States. The first steps to accomplished this goal is to coordinate relationships between a truck maker, fuel supplier, a truck stop chain, and natural gas driller. Clean Energy Fuels Corp. and Navistar International shared the plan with the Pilot Flying J Travel Centers, which is the largest network of truck and travel shops. The company will provide the service locations where the trucks could be refueled. America’s Natural Gas Highway also includes Chesapeake, the gas drilling company that would provide fuel to Clean Energy. Navistar will sell the best in-class natural gas (LNG) truck fleets to the consumer that are in contract with the Clean Energy; providing the fuel. Pilot Flying J Travel Centers will provide...

Words: 1432 - Pages: 6

Premium Essay

Natural Gas Case Study

...Natural Gas Case Study University of Phoenix Natural Gas Case Study The convention on Contracts for the International Sale of Goods (hereafter CISG) was an agreement to reduce the hassle of international trade and provide a universal way to handle disputes. The benefit of international trade was unmistakable to companies across the globe; however, the complications associated with the different laws and regulations of each sovereign nation often discouraged companies from partaking in this fruitful venture. Thus, the CISG helped companies minimize the risks of international trade, by providing a uniformed code that could be applied to all international transactions. In the natural gas case, the plaintiff a German company agreed to purchase propane from the defendant, an Austrian partnership. The fact the contract was never fulfilled properly led to the German company bring forth a breach of contract lawsuit, the courts applied the CISG to determine their findings. The natural gas case, as previously stated, was between a German buyer and an Austrian seller. The buyer or plaintiff agreed to purchase propane from the seller. The seller was to have the propane shipped from its supplier in the United States to Belgium where the buyer would receive it. Due to the fact that the two parties had never done business before, the seller required the buyer to secure a letter of credit for the transaction. However, the buyer’s bank required details about the transactions, specifically...

Words: 919 - Pages: 4