Can't sleep until I make some sense out of this one. After reading the
many fine replies to my original study I came to believe there was a flaw in
my methodology. Tonight's results seem to indicate this was true.
So... for testing purposes I now know another behaviour of OSPF. On loopback
interfaces, the default behavior is to treat the loopbacks as stub networks,
with a summary of /32 I followed the advice of one Mr. Clue Less, and
configured all loopbacks as point-to-point networks. ( I should note here
that it appears that one can not configure loopbacks as broadcast networks,
no matter what the circumstance )
Here are the results, using standard configurations. This first result is
with EIGRP and OSPF both configured more or less mimicking a real network.
Router#
Router#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, ia - IS-IS inter
area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C 192.168.8.0/24 is directly connected, Loopback0
C 192.168.9.0/24 is directly connected, Loopback1
C 192.168.10.0/24 is directly connected, Loopback2
C 192.168.11.0/24 is directly connected, Loopback3
D 192.168.4.0/24 [90/2297856] via 192.168.254.2, 00:07:44, Serial0
D 192.168.5.0/24 [90/2297856] via 192.168.254.2, 00:07:44, Serial0
D 192.168.6.0/24 [90/2297856] via 192.168.254.2, 00:07:44, Serial0
D 192.168.7.0/24 [90/2297856] via 192.168.254.2, 00:07:44, Serial0
D 192.168.0.0/24 [90/2809856] via 192.168.254.2, 00:06:14, Serial0
192.168.254.0/30 is subnetted, 2 subnets
D 192.168.254.4 [90/2681856] via 192.168.254.2, 00:07:45, Serial0
C 192.168.254.0 is directly connected, Serial0
D 192.168.1.0/24 [90/2809856] via 192.168.254.2, 00:06:14, Serial0
D 192.168.2.0/24 [90/2809856] via 192.168.254.2, 00:06:15, Serial0
D 192.168.3.0/24 [90/2809856] via 192.168.254.2, 00:06:15, Serial0
Router#
Router#
Router#sh ip route ospf
Router#sh ip route
Notice that there are no OSPF routes in the RIB at all.
Next, I changed the OSPF administrative distance to 85 ( a bit lower than
the EIGRP default distance )
Here is the resulting change in the routing table:
Router#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, ia - IS-IS inter
area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C 192.168.8.0/24 is directly connected, Loopback0
C 192.168.9.0/24 is directly connected, Loopback1
C 192.168.10.0/24 is directly connected, Loopback2
C 192.168.11.0/24 is directly connected, Loopback3
O IA 192.168.4.0/24 [85/65] via 192.168.254.2, 00:01:22, Serial0
O IA 192.168.5.0/24 [85/65] via 192.168.254.2, 00:01:22, Serial0
O IA 192.168.6.0/24 [85/65] via 192.168.254.2, 00:01:22, Serial0
O IA 192.168.7.0/24 [85/65] via 192.168.254.2, 00:01:22, Serial0
O IA 192.168.0.0/24 [85/129] via 192.168.254.2, 00:01:23, Serial0
192.168.254.0/30 is subnetted, 2 subnets
O 192.168.254.4 [85/128] via 192.168.254.2, 00:01:23, Serial0
C 192.168.254.0 is directly connected, Serial0
O IA 192.168.1.0/24 [85/129] via 192.168.254.2, 00:01:23, Serial0
O IA 192.168.2.0/24 [85/129] via 192.168.254.2, 00:01:24, Serial0
O IA 192.168.3.0/24 [85/129] via 192.168.254.2, 00:01:24, Serial0
Router#
This is a lot cleaner than what I was showing the other night.
So now - it looks like Mr Cthulu Not Dagon can indeed migrate his real
network from EIGRP to OSPF with very little problem. There may some issues
here and there with the way OSPF handles loopbacks, as one caveat. I sure
like the idea that, if memory serves, Brian proposed - changing the admin
distances of the protocols, but retaining the EIGRP configurations, so that
they would not have to be rebuilt should things go bad with the migration.
I also imagine that one might consider planning redistribution if the
network were large enough to have to be done in several stages over time.
Once again, configs are available. E-mail me directly and I will send a
file.
Other points of minor interest. The distance command for the three routing
protocols I looked at were a bit different - enough to be annoying. Eigrp
syntax is distance eigrp [internal route value] [external route value] while
ospf is distance [admin distance ] more protocol behavior differences to
keep in mind.
Also, I am putting the router pod on line. Telnet to 64.220.150.9 password
"hello" ( without the quotes ) for a look. User mode only
All three routers are open - you will have to daisy chain your telnets. What
you will see is the result of the routing table after raising the eigrp
default distance to 125 ( slightly higher than ospf's 110 )
Can someone test this for me? Everything looks ok from this side. But I do
not an outside account I can use to test from the internet side.
Chuck
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