From: Jack Heney (jheneyccie@xxxxxxxxxxx)
Date: Thu Oct 12 2000 - 17:24:46 GMT-3
The reason it won't route to 192.17.59.193 is related to longest match, but
not in the way you are implying. Longest match states that a router must
choose the route that has the longest prefix that matches ENTIRELY....Since
your router know about 192.17.59.0/26, only destinations that start with
192.17.59.00xxxxxx area considered a match...Since 192.17.59.193 starts with
192.17.59.11xxxxxx, it isn't a match at all....Longest match still applies,
what you have is no match. (Your other option is 192.17.59.64, which is
192.17.59.01xxxxxx, which also doesn't match)
hth,
Jack
>From: "Cheung, Tom [JJMI-AR]" <TCHEUNG@MEDUS.JNJ.com>
>Reply-To: "Cheung, Tom [JJMI-AR]" <TCHEUNG@MEDUS.JNJ.com>
>To: "'ccielab@groupstudy.com'" <ccielab@groupstudy.com>
>Subject: FW: routing problem
>Date: Thu, 12 Oct 2000 15:47:50 -0400
>
>
> > All,
> >
> > I have a general routing question. Here's the scenario:
> >
> > serial serial
> > r5 ---------------------- R1 ------------------> frame cloud
> > 172.17.59.64/26 (IGRP) 172.17.59.x (OSPF, VLSM)
> >
> > On OSPF side 172.17.59.x is variable subnetted into /28, /29 and /30.
> > I injected the OSPF routes into IGRP by "summary-address 172.17.59.0
> > 255.255.255.192"
> >
> > From R5, I'm able to ping 172.17.59.5, 59.9, 59.17 etc. but was unable
>to
> > ping 59.193. It is "unroutable".
> >
> > My explanation to why 192.17.59.193 is "not routable" is that R5 knows
> > only 172.17.59.0/26 and 172.16.59.64/26. 192.17.59.192 is not a
> > 192.17.59.0 subnet. Therefore R5 drops packets for 192.17.59.193. But
> > then, shouldn't "ip classless" force the router to do longest match and
> > find 182.17.59.0 for 59.193?
> >
> > R5's show ip route, debug IP packet output during the ping fail are
> > attached for your reference.
>[r5#
>r5#sh ip ro
>Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
> D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
> i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate
>default
> U - per-user static route, o - ODR
>
>Gateway of last resort is not set
>
> 172.17.0.0/26 is subnetted, 2 subnets
>I 172.17.59.0 [100/159250] via 172.17.59.65, 00:00:17, Serial0
>C 172.17.59.64 is directly connected, Serial0
> 10.0.0.0/24 is subnetted, 1 subnets
>C 10.1.2.0 is directly connected, Ethernet0
>r5#
>r5#
>r5#deb ip packet
>IP packet debugging is on
>r5#ping 172.17.59.193
>
>Type escape sequence to abort.
>Sending 5, 100-byte ICMP Echos to 172.17.59.193, timeout is 2 seconds:
>
>00:11:20: IP: s=172.17.59.66 (local), d=172.17.59.193, len 100, unroutable.
>00:11:21: IP: s=10.1.2.1 (local), d=255.255.255.255 (Ethernet0), len 52,
>sending
> broad/multicast
>00:11:22: IP: s=172.17.59.66 (local), d=172.17.59.193, len 100, unroutable.
>00:11:24: IP: s=172.17.59.66 (local), d=172.17.59.193, len 100, unroutable.
>00:11:26: IP: s=172.17.59.66 (local), d=172.17.59.193, len 100, unroutable.
>00:11:28: IP: s=172.17.59.66 (local), d=172.17.59.193, len 100, unroutable.
>Success rate is 0 percent (0/5)
>
>
>
>
>
> > Tom
> >
> >
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