Terry, You are absolutely right. Another interesting side note is that RIP is the only IGP that does this sort of behavior. In EIGRP and OSPF we only send the metric we have and the receiver does the math to increment based on it's own link knowledge. RIP is unique in this way. You may also want to check out what happens during redistribution in relation to the metric. I think Bryan actually has a good blog on that.
On Sun, Sep 13, 2009 at 10:53 AM, Terry Vinson <[email protected]>wrote: > I like to do labs to verify things (it helps me remember more than just > reading or being told the answer) so I decided to lab up your question. I > tossed in a sniffer to look at the traffic for the following network. > > lo0 1.1.1.1 (R1)----(R2)----(R3) lo0 3.3.3.3 > > > > *The hop count for Lo0 on R1 arrives on R2 as a "metric of 1" according to > the sniffer.* > > No. Time Source Destination Protocol > Info > 4 17.200621 155.1.12.1 224.0.0.9 RIPv2 > Response > > Frame 4 (56 bytes on wire, 56 bytes captured) > Cisco HDLC > Internet Protocol, Src: 155.1.12.1 (155.1.12.1), Dst: 224.0.0.9 (224.0.0.9) > User Datagram Protocol, Src Port: router (520), Dst Port: router (520) > Routing Information Protocol > Command: Response (2) > Version: RIPv2 (2) > Routing Domain: 0 > IP Address: 1.1.1.0, *Metric: 1* > > *The Hop count of route as it leaves R2 going to R3 is 2* > > No. Time Source Destination Protocol > Info > 3 4.707069 155.1.23.2 224.0.0.9 RIPv2 > Response > > Frame 3 (76 bytes on wire, 76 bytes captured) > Cisco HDLC > Internet Protocol, Src: 155.1.23.2 (155.1.23.2), Dst: 224.0.0.9 (224.0.0.9) > User Datagram Protocol, Src Port: router (520), Dst Port: router (520) > Routing Information Protocol > Command: Response (2) > Version: RIPv2 (2) > Routing Domain: 0 > IP Address: 1.1.1.0, *Metric: 2* > IP Address: 155.1.12.0, Metric: 1 > > > > This exercise seems to verify that the hop count is incremented by the > sender. > > > > This can also be verified on the Router it's self instead of using a > sniffer (actually this way is MUCH simplier). > > R2 receives the V2 update from R1 for 1.1.1.0/24 as hop count 1 as seen > with debug ip rip > > R2#debug ip rip > RIP protocol debugging is on > R2# > *Mar 1 00:27:00.583: RIP: *received* v2 update from 155.1.12.1 on > Serial0/0 > *Mar 1 00:27:00.587: 1.1.1.0/24 via 0.0.0.0 in 1 hops > > *Mar 1 00:30:42.415: RIP: *sending* v2 update to 224.0.0.9 via Serial0/1 > (155.1.23.2) > *Mar 1 00:30:42.415: RIP: build update entries > *Mar 1 00:30:42.415: 1.1.1.0/24 via 0.0.0.0, *metric 2*, tag 0 > > I removed some the output to make it clear. We can see that the route for > 1.1.1.0/24 arrives on int s0/0 with a hop count of 1 and is sent on S0/1 > to R3 with a hop count of 2. > > If this information is incorrect please correct me. > > Hope this helped. > > Terry > > > On Sun, Sep 13, 2009 at 10:22 AM, Bryan Bartik <[email protected]>wrote: > >> Hi Solomon, >> >> The receiving router uses the metric it hears from its neighbor. It >> increments upon sending it out. >> >> -hth >> >> On Sun, Sep 13, 2009 at 7:31 AM, Solomon Ayele <[email protected]> wrote: >> >>> Dears, >>> I have a question. When RIP updates are sent from one router and received >>> by the other what does the receiving router do to the advertised metric? >>> does it increment by 1 or does the advertising router send an update with >>> metric + 1 value? My expectation was the receiving router is the one that >>> does the increment. >>> >>> This question came as I have redistributed a loopback interface to RIP >>> with metric of 10 and on the neighboring router I saw it as having metric of >>> 10. >>> >>> Best Regards >>> Solomon >>> >>> >>> _______________________________________________ >>> For more information regarding industry leading CCIE Lab training, please >>> visit www.ipexpert.com >>> >>> >> >> >> -- >> Bryan Bartik >> CCIE #23707 (R&S), CCNP >> Sr. Support Engineer - IPexpert, Inc. >> URL: http://www.IPexpert.com >> >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > -- Regards, Joe Astorino - CCIE #24347 R&S Technical Instructor - IPexpert, Inc. Cell: +1.586.212.6107 Fax: +1.810.454.0130 Mailto: [email protected]
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
