Does router support layer 4 protocol?

elvantelvant Member Posts: 56 ■■□□□□□□□□
in CCNA & CCENT
I read about UDP 520 is use by router to advertise the RIP routing info.
Does it mean router support layer 4 protocol and has PORT?
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  • HumperHumper Member Posts: 647
    RIP resides at the application layer (along with BGP). RIP uses UDP port 520 for transport. Routing tables are broadcasted periodically (every 30seconds by default) unreliably.

    By the way updates are broadcasted in RIPv1 and multicasted in RIPv2 (224.0.0.9)
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  • mikej412mikej412 Member Posts: 10,086 ■■■■■■■■■■
    Someone is opening up a can of whoop-ass with their question.... icon_lol.gif

    For the CCNA, remember that a router is "layer 3" according to the OSI model.

    But with extended access lists, you can go to layer 4.... and up to layer 7 (remembering that the OSI model squishes 3 layers into one TCP/IP model layer).
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  • elvantelvant Member Posts: 56 ■■□□□□□□□□
    I thought the RIP is take place at router exclusively, I mean the routers exchange info between each other and they keep the routing table inside the router. Is it wrong?

    How about others, like OSPF (neighbor tables, topology DB, routing table)keeps in router?
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  • elvantelvant Member Posts: 56 ■■□□□□□□□□
    Sorry, probably my question not clear enough. I try to put more words on it.
    First of all, this is my understanding: router is layer 3, so its function only up to layer 3 protocol, and it wont border anything about layer 4 and above. So, routers exchange routing info/update among each other without involve any host(PC), only layer 3 device (router) 'talk' with each other without layer 4 device(PC port).

    My question is, if exchanging routing info only happens between routers, how can it use UDP (port 520, layer 4) to send routing info?

    Thanks
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  • EdTheLadEdTheLad Member Posts: 2,111 ■■■■□□□□□□
    As stated before, RIP is an protocol that is used to exchange layer 3 routing information,it uses udp port 520 to communicate with another RIP process on a neighboring router.
    The application RIP creates a routing table that is used to forward packets at layer 3.A routers main function is to route packets at layer 3, this does not mean that the only function of a router is to build routing tables and forward packets.If you cant understand this basic concept i think you should go back and learn about the OSI stack etc, before reading about routing protocols.
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