Pinging RIP

When you ping the multicast address for RIP 224.0.0.9 from a router with RIP enabled it sends replies to every interface on the router. Also if you try pinging 255.255.255.255 it does a similar thing and sends multiple replies but to the same address.  I am just curious why this is the case. Can someone please expain how the ping traveses the network? I know it has something to do with multicast

Comments

  • babyboi,

    A "normal" ping to a unicast IPv4 or IPv6 address will use the routing table to determine which interface the ping should be transmitted through.

    Broadcast (255.255.255.255) and multicast are special cases - there is no way for the router to know which interface to send through, so it will send through all interfaces.

    During actual RIP/EIGRP/OSPF routing communications, the router knows which interfaces are enabled for each routing protocol, and will only send multicast/unicast communications through the interface(s) enabled for the protocol.

    For a broadcast or multicast ping, the router does not reference its routing protocol, but sends out all interfaces that support broadcast/multicast communication.

    The multicast addresses used by RIP, OSPF & EIGRP are from the 224.0.0.0/24 link-local multicast addresses - these addresses are not forwarded by routers, so neighboring routers must be directly connected.

    When you ping the multicast address for RIP 224.0.0.9 from a router with RIP enabled it sends replies to every interface on the router. Also if you try pinging 255.255.255.255 it does a similar thing and sends multiple replies but to the same address.  I am just curious why this is the case. Can someone please expain how the ping traveses the network? I know it has something to do with multicast


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