From: Joe A (groupstudy@xxxxxxxxxxx)
Date: Tue Aug 13 2002 - 16:30:08 GMT-3
Think of a virtual link as a real link into area 0. If you do that,
then you can see how router C now has an interface in area 0, so it
learns A's loopback, also in area 0, as a route from within the same
area, that is, an O route.
Router A learns router C's loopback, but the loopback itself is not in
area 0, it is in area 2, hence the O IA. Before creating the virtual
link, you could have put router C's loopback in area 0 and you'd then
have a partitioned area 0. You can then create the virtual link to
close the partition and you'd see all the loopbacks as O routes.
JOE
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Hunt Lee
Sent: Tuesday, August 13, 2002 7:19 AM
To: ccielab@groupstudy.com
Subject: OSPF virtual link
This is the network:
RTA ----- RTB ----- RTC
RTA's interface to RTB:- 10.1.1.1
RTB's interface back to RTA:- 10.1.1.2
RTB's interface to RTC:- 10.1.1.5
RTC's interface back to RTB:- 10.1.1.6
Each router also it's own Loopback interface, where RTA has 1.1.1.1/32,
RTB has 2.2.2.2/32 & RTC has 3.3.3.3/32
All 3 routers are running OSPF, please see configs as below:-
At RTA:-
router ospf 1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
At RTB:-
router ospf 2
log-adjacency-changes
area 1 virtual-link 3.3.3.3
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
At RTC:-
router ospf 3
log-adjacency-changes
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Since Area 2 on RTC does not have a direct connection to Area 0, I have
configured a Virtual Link for this (the transit area is Area 1).
What I don't understand is that from RTA, it sees RTC's Loopback address
via Inter-Area route (O IA), but at RTC, RTC sees RTA's Loopback address
via Intra-Area route (O). Shouldn't they be both OIA or O routes?? Why
would they be different?
RouterA#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
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 10.1.1.2, 00:40:52, Serial0
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/129] via 10.1.1.2, 00:40:52, Serial0
10.0.0.0/30 is subnetted, 2 subnets
C 10.1.1.0 is directly connected, Serial0
O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:40:52, Serial0
RouterA#
RouterC#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
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/129] via 10.1.1.5, 00:41:04, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 10.1.1.5, 00:41:04, Serial0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O 10.1.1.0 [110/128] via 10.1.1.5, 00:41:04, Serial0
C 10.1.1.4 is directly connected, Serial0
RouterC#
RouterB#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
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65] via 10.1.1.1, 00:41:42, Serial1
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/65] via 10.1.1.6, 00:41:42, Serial0
10.0.0.0/30 is subnetted, 2 subnets
C 10.1.1.0 is directly connected, Serial1
C 10.1.1.4 is directly connected, Serial0
RouterB#
Thanks
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