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EIGRP packets are not sent across an ATM PVC due to missing broadcast keyword in the PVC configuration

Core Issue

A router uses the multicast address 224.0.0.10 when it sends any Enhanced Interior Gateway Routing Protocol (EIGRP) packet to multiple routers. The multicast address is used for sending hello packets to discover neighbors, sending routing updates to neighbors and sending query messages to find alternate paths to a particular network.

When a router is configured to run EIGRP over an ATM network, the router looks for the broadcast keyword in the ATM Permanent Virtual Circuit (PVC) configuration to send the multicast packets over the PVC. The multicast packets are sent only if the broadcast keyword is present in the PVC configuration, which indicates that broadcast and multicast packets are allowed to be carried over the PVC. Otherwise, it results in an encapsulation error and the EIGRP multicast packets are dropped by the router. This results in the loss of neighbors and routes, which leads to routing failure.

Routers configured for ATM using a physical ATM interface or multipoint sub-interface can use either static mapping or Inverse Address Resolution Protocol (InARP) on a PVC to map the remote IP address to the local Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI) PVC value. The broadcast keyword is automatically added to the PVC when InARP is used, but it must be manually added when static mapping is configured.

Resolution

To send EIGRP packets over a PVC configured with static mapping, add the broadcast keyword to the existing map statement by issuing the protocol ip {protocol-address} broadcast command in PVC configuration mode. This applies to any other non-broadcast, multi-access network, such as Frame Relay.

For more information on configuring the ATM PVC to send routing protocol updates, refer to the Broadcast or Multicast Mapping Problem section of Troubleshooting Encapsulation Failures with the debug atm errors Command.

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Last update:
‎06-18-2009 04:02 PM
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