10-19-2007 09:35 AM - edited 03-03-2019 07:15 PM
Have A customer of would like to implement EIGRP over GRE, would routers drop the Multicast routing updates.
The Multicast has a TTL of 1 but the GRE tunnel shows no hop.
thank you
10-19-2007 09:49 AM
When creating the GRE tunnel, make sure they are part of the same IP subnet.
Example,
RouterA
interface tunnel1
ip address 10.0.0.1 255.255.255.252
router eigrp 1
network 10.0.0.1 0.0.0.0
RouterB
interface tunnel2
ip address 10.0.0.2 255.255.255.252
router eigrp 1
network 10.0.0.2 0.0.0.0
it should work w/o problems (need to verify reachability beforehand).
10-19-2007 09:52 AM
thank you .
what about the Multicast TTL ?
10-19-2007 09:59 AM
I have run EIGRP over GRE tunnels many times. It works. The TTL is not an issue. The EIGRP multicast packet with TTL of 1 is encapsulated in an IP unicast header for transmission to the tunnel destination. It is the TTL of the GRE header that is decremented as the packet is forwarded through intermediate networks toward the tunnel destination. At the tunnel destination when the EIGRP packet is evaluated its TTL is valid.
HTH
Rick
10-19-2007 10:27 AM
TTL on a tunnel is not an issue as unicast/multicast traffic is treated as being on the same segment.
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