EIGRP router-id importance

[mbroberson1]

Can someone please explain the importance of the EIGRP RID? I understand the importance of the RID in OSPF and was wondering if it carries as much importance in EIGRP as it does in OSPF. And what are the benefits for setting the EIGRP rid or the negatives if any for not setting the EIGRP RID.

Thanks

[lgijssel]

In a good ip network, router-id's are linked to loopbacks.

A loopback never goes down which ensures that the router-id always stays the same.

The larger your network, the more important these things become.

If you want a disadvantage as well: you will have more routes in the routing table.

regards,

Leo

[Giuseppe Larosa]

Hello Brandon,

EIGRP router id plays a key role for EIGRP external routes.

EIGRP external routes have a field EIGRP router originator that is filled with EIGRP RID.

if two routers have the same EIGRP RID they will not accept external routes originated by the other one.

see

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800949ab.shtml

Hope to help

Giuseppe

[Mohamed Sobair]

Hi,

The Eigrp router-id is used on Eigrp external routes to prevent routing loops.

HTH

Mohamed

[mudasir05]

The importance of eigrp router-id can be explained in another way apart from the fact that it is used to stop external eigrp routes.

Suppose if one of the Eigrp neighbor does not want any one route to be received from his other neighbor neighbor without applying any filtering,then the best way is to use the same subnet number as its eigrp router id.This way if earlier it was receiving that external Eigrp route,however now that same route will disappear in its routing table.

Thanks

[Boris2]

Can someone please clarify if EIGRP IDs have to be unique from routers on the same LAN? I know they should be, but will neighborships form if two IDs are the same on the LAN?

[cofee]

I did a lab in gns3 and this is what I found:

- EIGRP neighbors will form adjacency even if their router-ids are same, but they will not install each other's advertised eigrp routes in RIB if their router-ids are same.

 Local eigrp speaking router doesn't care about the router-id as long as received eigrp routes are not using same router-id as the local eigrp speaking router, because local router will forward packets based on next hop and not the eigrp router-id. Below is an example where eigrp router is receiving routes from two different eigrp neighbors, which you can tell by looking at next hop address, but you will see both neighbors are using same eigrp router-id.

R2#sh ip eigrp topology 1.1.1.1 255.255.255.255
EIGRP-IPv4 Topology Entry for AS(100)/ID(22.22.22.22) for 1.1.1.1/32
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 409600
  Descriptor Blocks:
  192.168.1.1 (Ethernet1/0), from 192.168.1.1, Send flag is 0x0
      Composite metric is (409600/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 10000 Kbit
        Total delay is 6000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 192.168.2.3

R2#
R2#sh ip eigrp topology 3.3.3.0 255.255.255.0
EIGRP-IPv4 Topology Entry for AS(100)/ID(22.22.22.22) for 3.3.3.0/24
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 409600
  Descriptor Blocks:
  192.168.2.3 (Ethernet1/1), from 192.168.2.3, Send flag is 0x0
      Composite metric is (409600/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 10000 Kbit
        Total delay is 6000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 192.168.2.3

As I mentioned earlier local eigrp speaking router will accept routes from eigrp neighbors as long as originated router field, which is eigrp router id, doesn't match to its own eigrp router id. Make sure you don't have duplicate eigrp router ids in the local eigrp AS or you will have issues for sure.

[Boris2]

I just tried this in VIRL with two routers sharing the same ID (2.2.2.2). The router was able to accept the routes from a router which has the same ID as itself and the hosts in the routes were pingable. 

This seems to be in violation of what you said. Is that a glitch in VIRL or it seems router IDs are not important with EIGRP?

[cofee]

Please share the show ip route eigrp and sh ip eigrp topology x.x.x.x for the advertised routes.

[Sam Mouseli]

Apparently, this is an IOS version related thing. I don't know where exactly the line is but older Cisco IOS were not sending "route originator" field as part of an EIGRP route update. This means, they would accept each others advertised routes even if the same Router-ID was used.

HTH

[anthonymuturi]

They will still form adjacency with neigbors even if they have same Router ID. But will not accept routes from external source.

[paul driver]

Hello
You can use the eigrp rid as a form of external route filtering without using any access or prefix lists!
External routes are tagged with the eigrp rid of the route that originated the routes so if any eigrp rtr that is receiving these routes has the same rid then it wont except the routes, so you can give two routers the same rid to filter external route from being advertised to each other.

Edited
@Giuseppe Larosa apologies just noticed you have already mentioned this feature

[Giuseppe Larosa]

Hello @paul driver ,

my rather old post should be updated with the following sentences:

the newer EIGRP implementation named EIGRP extends the use of EIGRP RID to all types allowing in theory to filter all types of routes (havent't checked this in a lab)

Last but not least EIGRP has became a non proprietary protocol as its implementation guidelines are described in RFC

https://tools.ietf.org/html/rfc7868

notably enough our Hall of Fame Peter Paluch is among the authors together with Russ White.

@Peter Paluch has described all this in his own book on cisco press

Hope to help

Giuseppe

[Vishnu Vardhan S]

EIGRP Router-ID is same as OSPF RID interms of election process. 

However, unlike OSPF the EIGRP neighborship will be up even when we have same RID on both the routers. 

RID will only come into play when you redistribute a route from other routing protocol like ospf or rip, as the "originating router-id" would be same so the routes will not be learned by the router. 

R1(RID-1.1.1.1)--------R2(RID-2.2.2.2)-----------R3(RID-2.2.2.2)
Network 10.0.0.0 is in R1

router-3#show ip eigrp topology 10.0.0.0 255.0.0.0
IP-EIGRP (AS 7): topology entry for 10.0.0.0/8
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2560000256
  Routing Descriptor Blocks:
  0.0.0.0, from Redistributed, Send flag is 0x0
      Composite metric is (2560000256/0), Route is External
      Vector metric:
        Minimum bandwidth is 1 Kbit
        Total delay is 10 microseconds
        Reliability is 1/255
        Load is 1/255
        Minimum MTU is 1
        Hop count is 0
      External data:
        Originating router is 2.2.2.2 (this system)

You can also view the issue in the event command as below.

router-1 #show ip eigrp events 
Event information for AS 7:
1    18:06:15.863 Change queue emptied, entries: 1
2    18:06:15.863 Ignored route, metric: 10.0.0.0 2560512256
3    18:06:15.863 Ignored route, neighbor info: 172.16.13.3 Serial2
4    18:06:15.863 Ignored route, dup router: 2.2.2.2