Why EIGRP needs RID?

[schmidtjoe]

hello,

can someone elaborate why EIGRP needs a RID? Does it just help to avoid a loop? Thanks

[MHM Cisco World]

any routing protocol except static need RID 
it prevent the routing Loop 

[schmidtjoe]

Hi Mentor,

EIGRP is using split horizon to avoid a routing loop. Is RID the check point of split horizon?

[MHM Cisco World]

not even split horizon that use RID, even OSPF routers in same Area use RID to prevent Loop. 
but sure Split horizon in EIGRP is mandatory use RID. 

[MHM Cisco World]

this from one slide, it show that even if the EIGRP not require unique RID for establish neighbour but the note below show that it can cause problem. 

Understanding EIGRP Part 6 (Router ID and Neighborship Requirements) (kwtrain.com)

[MHM Cisco World]

OSPF (link state protocol) routers in same area detect the RID duplicate. 

[MHM Cisco World · Accepted solution]

split horizon with and without unique RID 
case1 
R1 see R2 and R3 same Ruoter and hence not advertise the Lo 2.2.2.2/32 receive from R2 to R3 

Case2
I change the R3 to new RID and you can see the now R1 advertise the LO 2.2.2.2/32 to R3.

[M02@rt37 · Accepted solution]

Hello @schmidtjoe

EIGRP uses a RID to uniquely identify each router in the network, and the RID plays an important role in the operation of the protocol.

Here are some reasons why EIGRP needs a RID:

- The RID is used to uniquely identify each router in the network. This is important because EIGRP routers need to be able to distinguish between each other in order to exchange routing information and build a topology database.

- The RID is used in EIGRP's loop prevention mechanism. When a router sends an EIGRP update to its neighbors, it includes its RID in the update. If a router receives an update with its own RID, it knows that there is a loop and will discard the update.

- EIGRP routers use the RID to break ties in the best path selection process. If two routes have the same metric, the router with the lowest RID is chosen as the successor.

- In EIGRP named mode, the RID is used to uniquely identify a named instance of the protocol on a router. This is important when a router is running multiple instances of EIGRP, such as when it is connected to multiple autonomous systems.