which layer does all the routing protocol comes under layer 3 or layer 4

[raja d]

i am having confusion over which layer does  the routing protocols like rip ospf eigrp is-is persists

[Federico Coto Fajardo]

Hi,

The routing is performed on layer 3.

Layer 3 is where IP resides.

Layer 4 is the transport layer where TCP/UDP take care of most of the job.

All routing protocols work with IP on layer 3.

is-is depends on a non-IP protocol, but still we refer to layer 3 when we refer to routing.

Hope it helps.

Federico.

[Jon Marshall · Accepted solution]

raja.mailtome wrote:
i am having confusion over which layer does  the routing protocols like rip ospf eigrp is-is persists

Depends on the routing protocol  -

RIP uses UDP port 520 so it needs L4 UDP to work

IGRP/EIGRP/OSPF have their own protocol numbers at the IP layer - IGRP 9, EIGRP 88, and OSFP 89

BGP uses TCP port 179

Jon

[loworderbit]

I always find this to be an interesting debate.  I argue that routing protocols are network applications, so they reside at layer 7.  Yes, they use the services of the transport layer, but they do not reside there because they provide other functions (like neighbor discovery, topology tables, loop prevention, elections (dr/bdr), etc).

For exam purposes, I believe the books say these reside at layer 3.

Later

[Mohamed Sobair]

Hi,

BGP and RIPv2 are application layer protocols and they utilize udp port 520 and tcp 170.

OSPF , ISIS and Eigrp have thier own protocol numbers 89 , 124, 88 and they reside at network layer.

HTH

Mohamed

[Ganesh Hariharan]

i am having confusion over which layer does  the routing protocols like rip ospf eigrp is-is persists

Hi,

The IP Header has a field in it called the PROTOCOL Field. This protocol field carries a Number. Which indicates the upper layer(layer 4). the packet to handle and whether it will be using any source and destination ports for Multiplexing (usually TCP and UDP).

Since this protocol field carries protocol identifier number. such as 6 for TCP, 17 for UDP and 88 and 89 for EIGRP AND OSPF, Layer 4 doesnt necessarily means that it must be UDP and TCP. Your Routing Protocol itself is handling Layer 4 Communication. OSPF and EIGRP uses their own packets at layer 4 to communicate and build adjacencies with themselves. they dont use any TCP or UDP port numbers.

RIP uses UDP, and BGP uses TCP.  RIP and BGP are each applications (in a way) whose function is to communicate with other routers for the purpose of passing routing information.  OSPF doesn't use UDP or TCP, it is it's own protocol, number 89.  EIGRP doesn't use UDP or TCP, it is it's own protocol, number 88.

Hope to Help !!

Ganesh.H

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[loworderbit]

Even though some of these protocols have their own protocol numbers (and are thus argued as being layer 4 protocols), they are not just providing transport layer services (like udp/tcp).  I contend that they are application layer protocols that use their own layer 4 services...they also emulate features of upper layers.  For example, OSPF does neighbor discovery/maintenance with its hello protocol (session layer ?), and exchanges LSA's (application layer ?).

Later

[pmetzger77]

Strictly speaking, layer 3 is considered to be where routing happens. I think there is merit to the arguement that it requires services from the other layers, but then again, you have to look at it like an oger, you need all the layers to make the whole; In the end, it's all in how you look at it which is why we have these debates anyway. However for simplicity's sake (as well as the certification exams) it's layer 3.