Description

Cisco's EIGRP routing protocol runs with the EX Switches in transit only if IGMP-snooping is disabled

Symptoms

The Cisco EIGRP protocol will not work if connected to EX Switches in transit.

Solution

Cisco's EIGRP protocol functions similar to the OSPF (Open Shortest Path First) protocol.  EIGRP routers or switches send Hello packets to each other to form neighbors. Cisco routers or switches use Mulitcast IP (224.0.0.10) and multicast MAC (01:00:5e:00:00:0a) to send EIGRP hello packets to each other.

If the Cisco routers or switches running EIGRP routing protocol are connected to the EX Switch as shown below, EIGRP hello packets received on EX Switch interface will be flooded to all the ports in that VLAN.

If the VLAN on the EX Switch is configured for IGMP-snooping protocol, flooding of multicast hello packets will not happen. The EX Switch with IGMP-snoooping enabled will drop EIGRP hello packets and routers connected at interfaces will not be able to form adjacency.

NOTE: IGMP-snooping is enabled by default in JUNOS 9.3 software and later releases

[Cisco A] ---------- Port 1 (VLAN A)-- [EX switch] --(VLAN A) Port 2 ------------ [Cisco B]

For Cisco's EIGRP protocol to work using the EX Switch in above topology (transit mode) IGMP-Snooping protocol has to be disabled on the EX Switch

To disable IGMP-Snooping protocol on the EX switch use following command:

juniper@ex# set protocol igmp-snooping vlan <name of the vlan> disable
juniper@ex# commit

NOTE: Please see link below for additional information for how IGMP snooping regulates multicast traffic on a VLAN to avoid flooding.

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