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We know that RIP v2 uses multicast address 224.0.0.9 for periodic broadcast of routing table. So it means that every router configured with RIP V2 is monitoring for any packet with destination address of 224.0.0.9.

So now if I ping that ip address; since router si listening to that ip, I should get a reply. But when I tested it on both GNS3 and Packet Tracer, no reply came.

I would like to know what is the reason.

Thank you in advance.

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  • I know a lot of server OSs will not respond to multicast/broadcast pings. According to this link supportforums.cisco.com/discussion/9110646/mystifying-224009-ip there is some confusion as to wether a cisco router would respond, but they seem to think the cisco will. What exactly are you trying to do?
    – Tim Caiazza
    Nov 21, 2014 at 14:48
  • Well the confusion is exactly my point. Theoretically I should be able to ping if I have a configuration enabled with rip v2. But when I tried it on both Packet tracer and GNS3, the reply was "Request time out". I tried it from both host and routers. That is where my confusion lies. Why it is not replying to ping.
    – Damon
    Nov 21, 2014 at 16:47
  • Why not just do a show ip rip neighbors? While I know this isn't what you are asking for, it should show you the same thing, who is listening to that mcast address. These are both network simulators so maybe they aren't behaving the same way a physical device would, but that is just a guess.
    – Tim Caiazza
    Nov 21, 2014 at 18:53
  • The neighbor will not give it. The part "listening" means that every packet with destination as 224.0.0.9 would be unpacked by the router cpu even though it has not assigned any physical interface to that ip. If the routing table is present in data part, it will update its routing table. Hence it will never show in any configuration like RIP, EIGRP, OSPF.
    – Damon
    Nov 21, 2014 at 19:26
  • Is ip multicast-routing enabled on your routers?
    – user6423
    Dec 23, 2014 at 20:29

1 Answer 1

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Damon, I'm afraid there is something wrong with your specific implementation. I, personally, can't think of an instance where a router doesn't respond to an icmp request on any of it's interfaces. Others, please chime in if that's inaccurate.

At any rate, I mocked it up in GNS3 to make sure there weren't any funky software bugs.

GNS3 Network Diagram

Basic configurations were set up on the interfaces with each router having it's router number as the lo0 interface address (i.e. R1 - 1.1.1.1). For verification, here's the rip routing table.

R1#show ip route rip
     2.0.0.0/32 is subnetted, 1 subnets
R       2.2.2.2 [120/1] via 10.1.1.2, 00:00:07, FastEthernet0/0
     3.0.0.0/32 is subnetted, 1 subnets
R       3.3.3.3 [120/1] via 10.3.3.3, 00:00:26, FastEthernet0/1
     10.0.0.0/24 is subnetted, 3 subnets
R       10.2.2.0 [120/1] via 10.3.3.3, 00:00:26, FastEthernet0/1
                 [120/1] via 10.1.1.2, 00:00:07, FastEthernet0/0
R1#

When pinging the multicast address of 224.0.0.9, 3 replys came back; R2 sent a reply, R3 sent a reply, and R1 replied to itself because it is also listening for that address.

R1#debug ip icmp
ICMP packet debugging is on
R1#ping 224.0.0.9 source lo0 repeat 1

Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.0.0.9, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1

*Mar  1 00:15:41.163: ICMP: echo reply sent, src 1.1.1.1, dst 1.1.1.1
*Mar  1 00:15:41.163: ICMP: echo reply rcvd, src 1.1.1.1, dst 1.1.1.1   <--- R1 Response
*Mar  1 00:15:41.179: ICMP: echo reply rcvd, src 10.1.1.2, dst 1.1.1.1  <--- R2 Response
*Mar  1 00:15:41.179: ICMP: echo reply rcvd, src 10.3.3.3, dst 1.1.1.1  <--- R3 Response
Reply to request 0 from 1.1.1.1, 8 ms
Reply to request 0 from 10.3.3.3, 24 ms
Reply to request 0 from 10.1.1.2, 20 ms
R1#

Pinging a multicast address will generate a response from participants listening to that address.

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  • thank you. Yes it works when the ping is sent from Routers. But when I tried to ping from a host connected to router, it does not reply. Could you explain.
    – Damon
    Dec 28, 2014 at 14:15
  • I'm not entirely sure what you're trying to do.
    – Ryan Foley
    Dec 28, 2014 at 19:00
  • I want to understand, why routers (configured with routing protocol that use multicast ip address for periodic broadcast) can ping at multicast address while a host connected to same router can not ping.
    – Damon
    Dec 29, 2014 at 5:11
  • Without seeing your specific configurations it's hard to help you. A host would get a response on that multicast address if he pinged it.
    – Ryan Foley
    Dec 29, 2014 at 10:01

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