Why is EIGRP and RIP uses IP TTL of 2 (CISCO)?

[leviya]

Through my studies on CCNP ROUTE, while sniffing EIGRP packets, I noticed that packets have IP TTL of 2. I also verified this for RIP. OSPF doesn't have this property since it's link state.

Why does the EIGRP and RIP have IP TTL of 2?

I already asked one CCIE person, but he didn't know.

I came to believe that this may have something to do with frame relay hub&spoke topologies. For example hub routing EIGRP multicasts from one spoke to another (assuming subinterfaces)?

Any advice/idea/explanation would be greatly appreciated.

Thanks.

[SCOTT VOLL]

and you were expecting 1?

you don't want it to pass through a router due to how the protocol works.  I'm guessing it might have to do with maybe a unnumbered interface on the router.  But that is just my guess as to using a TTL of 2.

Scott

[#3]

Hi

EIGRP and RIP set TTL of 2 for HUB-SPOKE model.

For example, Frame Relay usually use HUB-SPOKE mode.

When 2 spoke routers want to make adjacency, the packet must go through the HUB router, If the TTL is 1, then the packet cannot arrive another spoke router.

So the TTL set to 2.