a simple question of EIGRP.

Answered Question
Aug 4th, 2009
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Hi. everyone..


I have a problem related EIGRP on running at Cisco.


The most I wonder is that Does EIGRP use a Layer 4 Port as tcp/udp?, It is not definitly Right?


It just a Layer 3 Protocol for update to its neighbor EIGRP router. So It's not use tcp / udp to update routing update.


If my opinion is wrong, please fix it for me


Thank in advance.

Correct Answer by Peter Paluch about 7 years 11 months ago

Hello,


The EIGRP does not use ports. The reason is that EIGRP uses its own transport protocol called Reliable Transport Protocol (protocol number 88) which does not use ports. This protocol was designed because of two reasons:


1.) To make EIGRP independent of the actual Layer3 protocol. As you know, the EIGRP exists for IPX, IPv4 and IPv6 but the transport protocol remains the same.


2.) Perhaps even more importantly, EIGRP needs a transport protocol that provides reliable services and multicast delivery at the same time. The TCP is reliable but does not support multicasts. The UDP does provide multicast capability but does not provide reliability. The Reliable Transport Protocol provides both.


Because the Reliable Transport Protocol was designed specifically with EIGRP in mind, it does not need to use ports, which are so or so specific to the TCP/IP stack.


Best regards,

Peter


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chinkevi_2 Tue, 08/04/2009 - 22:55
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short answer is no.

a bit longer answer is it use RTP.

Correct Answer
Peter Paluch Tue, 08/04/2009 - 23:06
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  • Cisco Employee,

Hello,


The EIGRP does not use ports. The reason is that EIGRP uses its own transport protocol called Reliable Transport Protocol (protocol number 88) which does not use ports. This protocol was designed because of two reasons:


1.) To make EIGRP independent of the actual Layer3 protocol. As you know, the EIGRP exists for IPX, IPv4 and IPv6 but the transport protocol remains the same.


2.) Perhaps even more importantly, EIGRP needs a transport protocol that provides reliable services and multicast delivery at the same time. The TCP is reliable but does not support multicasts. The UDP does provide multicast capability but does not provide reliability. The Reliable Transport Protocol provides both.


Because the Reliable Transport Protocol was designed specifically with EIGRP in mind, it does not need to use ports, which are so or so specific to the TCP/IP stack.


Best regards,

Peter


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