Couple additions (corrections).
I just discovered that RIP, IGRP and EIGRP actually use a TTL of 2! (I had
said that all routing protocol packets use a TTL of 1. OSPF and BGP do.) I
stick to my main point that routing protocol packets go to
directly-connected routers and could use just a data-link layer like IS-IS
does. (Some routing protocols propagate messages to neighbors on the other
side, but they don't simply forward packets at the IP layer).
Also, I want to say that I should have been more precise, as Howard was:
Routing protocols are layer management protocols at the network layer.
Also, I liked this that he said: Just because a protocol is transmitted
using a protocol at layer (N) doesn't make the payload protocol layer (N+1).
If we think about it, there are other examples of this being true besides
management protocols. It's pretty common to see the session-layer NetBIOS
protocol running on top of LLC, for example. (It's sometimes called NetBEUI
in this case, but it still has session-layer behavior.)
Priscilla
At 12:56 PM 9/25/01, Priscilla Oppenheimer wrote:
>At 07:05 AM 9/25/01, you wrote:
> >hmm..
> >that's tricky, as I remember BGP used TCP for the routing update.
>
>RIP runs on top of UDP, so you would have to make the same argument for
>RIP, but it's not a good argument. Characterizing what layer they are at by
>what layer they reside on doesn't work.
>
>We could claim that all the routing protocols except IS-IS (which runs
>directly on top of LLC) are upper-layer protocols since they run on top of
>IP, but that doesn't work either. Theoretically they don't have to run on
>top of IP. They don't use IP's method for forwarding traffic across an
>internetwork. Every routing protocol packet I have ever seen has a TTL of
>1. EIGRP can propagate queries, but that's not forwarding based on
>network-layer addresses. OSPF propagates Link State Updates, but that's not
>forwarding based on network-layer addresses either. Routing protocol
>packets are send to other routers on the same segment as either unicasts,
>broadcasts, or multicasts.
>
>Obviously, I have heard the argument before about routing protocols running
>at the application layer and there's some logic to it, as there is logic to
>characterizing the layer by what layers are below it, but it's just not
>based on reality regarding the definitions by ISO for their OSI reference
>model.
>
>The function of the network layer is forwarding packets across an
>internetwork and learning how to reach networks in the internetwork
>(routing protocols). The function of the application layer is providing
>services to end-user applications, such as e-mail, Telnet, Web browsing.
>
>By the way, with 7-layer bean dip, if you put the beans on top and the
>lettuce on the bottom, do the beans become lettuce and vice versa? ;-)
>
>Priscilla
>
> >The only thing I can think of functionaly perhaps it's on layer 3, but
> >interm of BGP itself, perhaps it's an application residing most certainly
> >not in network layer.
> >
> >donny
> >
> >
> >>From: "Priscilla Oppenheimer"
> >>Reply-To: "Priscilla Oppenheimer"
> >>To: [EMAIL PROTECTED]
> >>Subject: Re: which layer do the ospf bgp rip work on [7:20953]
> >>Date: Mon, 24 Sep 2001 23:27:16 -0400
> >>
> >>Network layer. Routing is a fundamental component of the network layer.
> >>
> >>At 10:14 PM 9/24/01, lhill peng wrote:
> >> >which layer do the routing protocol such as ospf rip bgp eigrp work on?
> >> >sb said that they are on application, others on network
> >> >what is the right answer??
> >>________________________
> >>
> >>Priscilla Oppenheimer
> >>http://www.priscilla.com
> >_________________________________________________________________
> >Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
> >
>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
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