From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Oct 13 2004 - 08:32:41 GMT-3
Hi Guys,
SW2 is learning all it's routes both from R1 on subnet 163.3.38.0/24 and R3 on
subnet 163.3.18.0/24 via RIP v2.
Except for the 2 ethernet links connecting R1 and R3 to SW2, R1 and R2 are
running ISIS on all their other interfaces including the link that connects R1
directly to R3. Both R1 and R3 have all the same subnets listed in their
respective route tables and both are redistributing all their isis routes into
rip with a metric of 1.
Here's the config on R1 and R3
router rip
version 2
redistribute connected metric 1
redistribute isis level-2 metric 1
passive-interface default
no passive-interface Ethernet0/0
network 163.3.0.0
no auto-summary
SW2
/ \
/ \
isis network R1 <--isis ---> R3 isis network
^
|
163.3.13.0/24
This is a copy of SW2's route table. Notice that for all the 163.3 routes,
sw2 learns them from both R1 and R3 and has them listed twice.
The 150.3.0.0 subnets represent the loopback interfaces on each router where
the number in the 3rd octet is the router number.
After I first configured the above and looked at SW2's route table, I got the
table shown below. Notice that routes redist into rip on R1 and R3 are listed
twice which is what I expected.
However, for most of the 150.3 routes, those are only listed once. Why is
that?
Gateway of last resort is not set
R 204.12.3.0/24 [120/1] via 163.3.38.3, 00:00:20, FastEthernet0/14
163.3.0.0/16 is variably subnetted, 12 subnets, 2 masks
R 163.3.35.0/24 [120/1] via 163.3.38.3, 00:00:20, FastEthernet0/14
[120/1] via 163.3.18.1, 00:01:54, FastEthernet0/15
C 163.3.38.0/24 is directly connected, FastEthernet0/14
R 163.3.45.0/29 [120/1] via 163.3.18.1, 00:01:54, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:20, FastEthernet0/14
R 163.3.54.0/24 [120/1] via 163.3.18.1, 00:01:55, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:20, FastEthernet0/14
R 163.3.57.0/24 [120/1] via 163.3.18.1, 00:01:55, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:20, FastEthernet0/14
R 163.3.4.0/24 [120/1] via 163.3.18.1, 00:01:55, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:20, FastEthernet0/14
R 163.3.5.0/24 [120/1] via 163.3.18.1, 00:01:55, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:21, FastEthernet0/14
R 163.3.6.0/24 [120/1] via 163.3.18.1, 00:01:55, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:21, FastEthernet0/14
R 163.3.7.0/24 [120/1] via 163.3.18.1, 00:01:55, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:21, FastEthernet0/14
R 163.3.12.0/24 [120/1] via 163.3.18.1, 00:00:05, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 163.3.13.0/24 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
[120/1] via 163.3.18.1, 00:00:05, FastEthernet0/15
C 163.3.18.0/24 is directly connected, FastEthernet0/15
R 192.10.3.0/24 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
150.3.0.0/24 is subnetted, 8 subnets
R 150.3.5.0 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 150.3.4.0 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 150.3.7.0 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 150.3.6.0 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 150.3.1.0 [120/1] via 163.3.18.1, 00:00:06, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 150.3.3.0 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
R 150.3.2.0 [120/1] via 163.3.38.3, 00:00:22, FastEthernet0/14
C 150.3.8.0 is directly connected, Loopback0
Rack1SW2#
After a few minutes, however, without changing any configuration, I looked at
the SW2's route table again. But, this time SW2 only had 1 path for each
route with just 2 exceptions.
R 204.12.3.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
163.3.0.0/16 is variably subnetted, 12 subnets, 2 masks
R 163.3.35.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
C 163.3.38.0/24 is directly connected, FastEthernet0/14
R 163.3.45.0/29 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.54.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.57.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.4.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.5.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.6.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.7.0/24 [120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.12.0/24 [120/1] via 163.3.18.1, 00:00:09, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:08, FastEthernet0/14
R 163.3.13.0/24 [120/1] via 163.3.18.1, 00:00:12, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
C 163.3.18.0/24 is directly connected, FastEthernet0/15
R 192.10.3.0/24 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
150.3.0.0/24 is subnetted, 8 subnets
R 150.3.5.0 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
R 150.3.4.0 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
R 150.3.7.0 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
R 150.3.6.0 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
R 150.3.1.0 [120/1] via 163.3.18.1, 00:00:12, FastEthernet0/15
[120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
R 150.3.3.0 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
R 150.3.2.0 [120/1] via 163.3.38.3, 00:00:11, FastEthernet0/14
C 150.3.8.0 is directly connected, Loopback0
Rack1SW2#
So, I'm confused. Why did sw2 originally show 2 paths for all the isis routes
redist into rip except the loopback interfaces but shortly afterwards show
just one path for most of the subnets?
Also, what is the reason that a few subnets eg 150.3.1.0, 163.3.12.0, and
163.3.13.0, are listed twice while all the other subnets are just listed once?
(Note that 163.3.13.0/24 directly connects R1 to R3 via isis while
163.3.12.0/24 and 150.3.1.0/24 are directly connected to R1.)
Does this example show that routing is working as expected or is something
very screwy going on here?
Thanks, Tim
This archive was generated by hypermail 2.1.4 : Sat Nov 06 2004 - 17:11:47 GMT-3