Rip v2

[aconticisco]

what does it mean via 0.0.0.0 when receiving a route update of rip v2 for example: 10.1.10.0/24 via 0.0.0.0, metric 1, tag 0 instead of the 0.0.0.0 should not be the next hop ip address ? thank You

[Richard Burts]

Andrea

I am not sure that I fully understand your question. Frequently indicating a next hop of 0.0.0.0 is a way of indicating that a route is reachable through a connected interface of the local router.

Perhaps you could post the exact message that contains this and could clarify where it comes from? Is this some output from debug rip?

If we could see the exact message and know more about its context then perhaps we would have a better explanation of it.

HTH

Rick

[Edison Ortiz]

Rick,

I believe the OP is referring to an output like this:

______

*Mar 2 21:05:51.164: RIP: received v2 update from 10.0.0.21 on FastEthernet0/0

*Mar 2 21:05:51.164: 10.1.1.0/24 via 0.0.0.0 in 1 hops

*Mar 2 21:05:51.164: 99.9.9.0/24 via 0.0.0.0 in 2 hops

________

and I also believe the reason there isn't any IP address on the via portion is that RIP doesn't have the concept of neighbors as other routing protocols. The source of the route is unknown.

__

Edison.

[shrikar.dange]

hi,

Usually that field is the next hop address,if one exits,than the address of the advertising router.That is it indicates a next hop router on the same subnet metrically closer to the destination than advertising router is.

If the field is set to all zeros (0.0.0.0) the address of the advertising router is "THE BEST" next hop router.

For example on a broadcast interface you are running another protocol along with the RIP & redistributing those routes in to RIP.And on one side you have only rip speking routers.This router is in between rip speaking and other protocol speking routers & advertising those redistributed routes to its Rip neighbours.Then in the advertisement for those redistributing towards rip neighbout the next hop will be 0.0.0.0.

Telling the rip neighbours that I am the best nest hop for these networks.

HTH,

regards,

shri :)

[LvSrikanthLakshman]

the best route is selected by AD and metric. I cant see any documentation that 0.0.0.0 means the best route. 0.0.0.0 0.0.0.0 means all unknown route.

Even in case if 0.0.0.0 means the best route why it doesnt appear like that in show ip route? It appears only during the time of debug ip rip.

[LvSrikanthLakshman]

thats not the fact! It knows the next hop address. The next hop address arrives from the updates sent by the next hop! Infact, this via 0.0.0.0 only appears in debug message. Show ip route shows only the next hop address and not 0.0.0.0

[Giuseppe Larosa]

Hello,

>> this via 0.0.0.0 only appears in debug message

I think Edison Ortiz's post can be an explanation of why the debug shows this via 0.0.0.0 the root cause is that RIPv2 has no neighbor state machine and misses the router-id concept.

I have rated Edison's answer as deserved.

Hope to help

Giuseppe

[jorgenolla]

The "Next Hop" field of the RIPv2 datagram is used to redirect a RIP neighbor to a better path to the destination network. This field was added on v2 of RIP.

Usually the RIP process looks at the IP address of the source of the packet to determine the next hop for the networks advertised on the update.

In RIPv2 if the "Next Hop" field of the "Route Entry" its (0.0.0.0), the router will set the next hop to the IP address of the source of the packet.

If the "Next Hop" field of the "Route Entry" is not all 0s, then it will set the next hop to the address the "Next Hop" field specifies.

When you look at the composition of the update packet between RIP v1 vs v2 you will notice the change on the fields:

v1:

Address family identifier

ip address

metric

v2:

Address family identifier

Route Tag

ip address

subnet prefix

next hop

metric

When you look at the output from the debug command, all it is saying is that it will set the next hop address to the ip address of the source of the update, unless the update tells me there is a better path (which is specified by the ip address in the "Next Hop" field.)

It's kind of like an ICMP Redirect.

Best Regards

[aconticisco]

thank you for all the replies, yes an example would be with the debug ip rip command;

RIP: sending v2 update to 224.0.0.9 via Ethernet0 (10.0.0.200)

00:40:10: RIP: build update entries

00:40:10: 172.0.0.0/16 via 0.0.0.0, metric 2, tag 0

00:40:10: 192.168.2.0/24 via 0.0.0.0, metric 1, tag 0

00:40:10: RIP: sending v2 update to 224.0.0.9 via Serial0 (192.168.2.250)

00:40:10: RIP: build update entries

00:40:10: 10.0.0.0/8 via 0.0.0.0, metric 1, tag 0

instead of via 0.0.0.0 would it not be more clear if there was the ip address of the outgoing interface