From: Chuck Larrieu (chuck@xxxxxxxxxxxxx)
Date: Sun Feb 04 2001 - 13:35:37 GMT-3
If I understand your question correctly, you believe you should not be able
to ping from a FLSM domain into a VLSM domain?
The ping packet carries no mask information. As long as there is a route to
the distant network, the ping packet will be routed. Your IGRP router
contains a route to the classful 192.168.10.0/24 therefore a ping to
192.168.10.9 will be routed.
Consider the internet, and the ability to ping from here to there, crossing
multiple routers, AS's, aggregations, and de-aggregations along the way. If
ping required masks to match, how would anything ever get through? The
VLSmasks are for preservation of address space at the subnet level as well
as easy aggregation at the backbone level ( in order to reduce the size of
routing tables )
BTW, another tool that is handy is the extended ping, which allows one to
use alternative source addresses. This also places the ping through the
source router's routing process. Ever had it happen that you can ping a
destination from a router, yet traffic is not routed properly through it?
Extended pi a pain to us, but it does offer quite a bit of helpful tools to
use in troubleshooting.
HTH
Chuck
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Jay
Chandradas
Sent: Sunday, February 04, 2001 2:23 AM
To: ccielab@groupstudy.com
Subject: VLSM question
Hi all,
I am trying a VLSM and classful routing prot. issue. I am little confused
when I tried in my set up. Can u help me?
set up :
R2 ------------------------------------------R1----------------------------
--------------------------R3 networks included : 192.168.10.0/20
( IGRP 192.168.1.0/24 IGRP ) ( ospf 192.168.5.0/24
ospf) 192.168.2.0/27
my aim is to ping the vlsm networks from R2, which is running only IGRP. I
thought R2 will not be able to ping 192.168.10.9 ( with a mask /29) . I was
trying to put a defalut network statement in R1 , thinking it will propagate
the default route to the down stream router R2. and it did. Then I removed
the default network statement from R1. But still I am able to ping the vlsm
networks from R2. Am I missing something here?.. I will show the routing
table for all the three routers for clarity.
i know that for IGRP, if the route is a part of same major net as the
interface but has a different mask , IGRP does not advertise the route out
the interface- why is R1 advertizing the vlsm routes to R2?
router2#sh ip route
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
I 192.168.10.0/24 [100/8576] via 192.168.1.1, 00:00:33, Serial0
I 192.168.5.0/24 [100/10476] via 192.168.1.1, 00:00:33, Serial0
I 10.0.0.0/8 [100/8576] via 192.168.1.1, 00:00:33, Serial0
C 193.168.1.0/24 is directly connected, Ethernet0
C 192.168.1.0/24 is directly connected, Serial0
I 192.168.2.0/24 [100/8576] via 192.168.1.1, 00:00:33, Serial0
router2#ping 192.168.10.9
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.9, timeout is 2
seconds: <------------------------------------ PINGS !!! I thought
wthout a default route it will not ping.
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 68/68/68 ms
router2#
router1#sh ip r
09:50:52: %SYS-5-CONFIG_I: Configured from console by consoleoute
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
192.168.10.0/29 is subnetted, 1 subnets
* 192.168.10.8 [110/65] via 192.168.5.3, 00:14:04, Serial0
<-----------------------------192.168.10.0 is having 1 /29 bit mask.
C 192.168.5.0/24 is directly connected, Serial0
O E2 10.0.0.0/8 [110/100] via 192.168.5.3, 00:14:04, Serial0
I 193.168.1.0/24 [100/8576] via 192.168.1.2, 00:00:20, Serial1
C 192.168.1.0/24 is directly connected, Serial1
192.168.2.0/27 is subnetted, 1 subnets
* 192.168.2.32 [110/74] via 192.168.5.3, 00:14:04, Serial0 router1# router3#
09:51:19: %SYS-5-CONFIG_I: Configured from console by consolesh ip route
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
192.168.10.0/29 is subnetted, 1 subnets
C 192.168.10.8 is directly connected, Loopback10
C 192.168.5.0/24 is directly connected, Serial1
C 10.0.0.0/8 is directly connected, Loopback1
O E2 193.168.1.0/24 [110/100] via 192.168.5.1, 00:14:38, Serial1
O E2 192.168.1.0/24 [110/100] via 192.168.5.1, 00:14:38, Serial1
192.168.2.0/27 is subnetted, 1 subnets
C 192.168.2.32 is directly connected, Ethernet0
router3#
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