hey, Cil, I'm wondering about the TTL's. I was doing some tech review for someone, and in the course of that reviewed some sniffer traces. OSPF was showing TTL's of 255. the traces were presented to me because I had asked about virtual link TTL's, which speculatively speaking would have to be very large, because the router could never know how many links a VL packet would have to traverse before it found the router noted as the other side, In any case, all OSPF traces, virtual link or otherwise, were showing a TTL of 255. maybe that's just Cisco?
Do you have any speculation as to why the TTL would be 2 for the protocols you mention? Also, the BGP TTL can be manipulated through the use of the neighbor ebgp-multihop command Chuck -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Priscilla Oppenheimer Sent: Tuesday, September 25, 2001 5:20 PM To: [EMAIL PROTECTED] Subject: Re: which layer do the ospf bgp rip work on [7:20953] 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: http://www.groupstudy.com/form/read.php?f=7&i=21266&t=20953 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]