EIGRP Neighbors on broadcast networks(LAN)

Answered Question

Hi Experts,

I have a question that may make me sound dumb.

We have a Cisco 7206 router connected to a Cisco 6513(switchA) switch on vlan92. The switchA is connected to switchB over an etherchannel trunk.

switchA & B both have vlan92 SVI's.

When I check on the router, I can see both the switchA & B vlan92 addresses as EIGRP neighbours to the router. I thought EIGRP neighbours are formed only between directly connected routers or routers conenyed via a GRE tunnel. Can someone explain why this behaviour?

Regards,

Imran.

Router#sh ip eigrp nei
IP-EIGRP neighbors for process 50
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
5   10.3.92.254             Fa2/0             11 1d09h       1   300  0  1506856
4   10.3.92.253             Fa2/0             13 1d09h       1   300  0  159245

10.3.92.254- switchB VLAN92 SVI

10.3.92.253- switchA VLAN92 SVI.

Router is directly connected to switchA on Gig 9/45 which is in vlan92.

I have this problem too.
0 votes
Correct Answer by Jerry Ye about 6 years 2 months ago

EIGRP uses multicast address 224.0.0.10 to communicate by default. Any EIGRP enabled router in the same network (same VLAN) will respond to this multicast address, and this is why routers in VLAN92 in your environment will establish neighbor relationship.

HTH,

jerry

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Correct Answer
Jerry Ye Fri, 10/01/2010 - 18:23

EIGRP uses multicast address 224.0.0.10 to communicate by default. Any EIGRP enabled router in the same network (same VLAN) will respond to this multicast address, and this is why routers in VLAN92 in your environment will establish neighbor relationship.

HTH,

jerry

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