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In RIPv1 the packets are broadcasted out all ports with dest. IP 255.255.255.255. In v2 they are multicasted with dest. IP 224.0.0.9. In Packet Tracer, this v2 packet is transmitted over all interfaces at the same time which looks like broadcasting with an IP of multicasting.

When EIGRP uses multicasting it transmits packets to only one dest. at a time. It also tries to send EIGRP packets to an undesired host (PC, server, etc.) which drops it.

I have tried this only on Cisco Packet Tracer. So can someone please explain me why RIPv2 packet transmission looks like broadcasting with destination IP address as 224.0.0.9?

Thank you.

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  • Could you be more specific about what you mean when you say "looks like broadcasting"? How did you conclude it's a broadcast? – Mike Pennington Nov 11 '14 at 18:24
  • When you configure entire network with RIP v2 and no packet is being transmitted, switch to simulation in Packet Tracer. There if you click on Capture/Forward enough times, you might see a RIP v2 packet with routing table info being transmitted over all of its connected interfaces with destination address as 224.0.0.9. I think this is what broadcasting is. Transmitting packets without caring weather the other end really wants it or not. – Damon Nov 11 '14 at 18:30
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    Your criteria for broadcast is different than those used by network engineers. The reason RIP sends hello packets out all interfaces is because you enabled RIP on those interfaces – Mike Pennington Nov 11 '14 at 18:39
  • I think enabled rip might mean declaring it as adjacency. As the rfc link given by @Jordan clearly states that "an IP multicast address will be used for periodic broadcasts". So I think it is actually using broadcast to update routing tables. – Damon Nov 11 '14 at 18:57
  • You seem to be getting confused by the multiple definitions of broadcast used by the rfc. 224.0.0.9 is not used to broadcast to all stations on a segment; however RIP broadcasts (ie announces) its updates using 224.0.0.9 – Mike Pennington Nov 11 '14 at 19:12
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224.0.0.9 is a protocol standard multicast address, meaning that it is reserved for all RIPv2 speaking routers. This reduces unnecessary overhead, and only speaks to RIPv2 routers, instead of a full broadcast. Here is a portion from the RIPv2 RFC.

http://tools.ietf.org/html/rfc2453

4.5 Multicasting

In order to reduce unnecessary load on those hosts which are not
listening to RIP-2 messages, an IP multicast address will be used for periodic broadcasts. The IP multicast address is 224.0.0.9. Note
that IGMP is not needed since these are inter-router messages which
are not forwarded.

On NBMA networks, unicast addressing may be used. However, if a
response addressed to the RIP-2 multicast address is received, it
should be accepted.

In order to maintain backwards compatibility, the use of the
multicast address will be configurable, as described in section 5.1.
If multicasting is used, it should be used on all interfaces which
support it.

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    This means that RIP v2 uses broadcasting same as RIP v1. But they use the destination address as 224.0.0.9 (Multicast address) instead of usual broadcast address 255.255.255.255 so as to reduce load on hosts (like PC, servers) who are not listening to that particular address. The packet will be transmitted over interface at which the hosts are connected. Just as they are not listening to that ip address, the packet will be dropped. – Damon Nov 11 '14 at 18:08

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