From: Simon Baxter (Simon.Baxter@xxxxxxxxxxxxxx)
Date: Sun Dec 03 2000 - 23:08:17 GMT-3
I've discovered Virtual Links seem to prefer a path through some networks -
against the metric of transiting links....
In the below example, a slow speed 64k serial link is preferred over a 10Meg
connection - because of the Virtual link.....
Scenario is - "BOTTOM" is in area 1 and has 2 connections to area 0: via
s0/0(toR5) and via e0/0(via R2)
Without any VLs configured, the preferred path to area 0 is via the
ethernet...
(10.0.10.3 is another device in area 0)
BOTTOM#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, 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
192.192.192.0/32 is subnetted, 1 subnets
O IA 192.192.192.192 [110/21] via 10.1.2.1, 00:05:15, Ethernet0/0
10.0.0.0/24 is subnetted, 4 subnets
O IA 10.0.10.0 [110/20] via 10.1.2.1, 00:05:15, Ethernet0/0
O IA 10.3.0.0 [110/68] via 10.1.2.1, 00:05:15, Ethernet0/0
C 10.1.2.0 is directly connected, Ethernet0/0
C 10.1.1.0 is directly connected, Serial0/0
BOTTOM#trace 10.0.10.3
Type escape sequence to abort.
Tracing the route to 10.0.10.3
1 10.1.2.1 0 msec 0 msec 4 msec
2 10.0.10.3 4 msec 0 msec *
Now I add a VL between BOTTOM and R5(which has the s0/0 connection to
BOTTOM)
R5#
BOTTOM#
00:08:04: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from
backbo
ne area must be virtual-link but not found from 10.1.1.1, Serial0/0
BOTTOM(config)#router os 10
BOTTOM(config-router)#area 1 vir 200.200.200.200
BOTTOM(config-router)#^Z
BOTTOM#
BOTTOM#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, 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
192.192.192.0/32 is subnetted, 1 subnets
O 192.192.192.192 [110/1573] via 10.1.1.1, 00:00:02, Serial0/0
10.0.0.0/8 is variably subnetted, 6 subnets, 2 masks
O 10.0.10.0/24 [110/1572] via 10.1.1.1, 00:00:02, Serial0/0 <<<Now
via the serial!!!!
O 10.2.10.10/32 [110/65] via 10.2.0.2, 00:00:02, Serial0/1
C 10.2.0.0/24 is directly connected, Serial0/1
O IA 10.3.0.0/24 [110/1620] via 10.1.1.1, 00:00:02, Serial0/0
C 10.1.2.0/24 is directly connected, Ethernet0/0
C 10.1.1.0/24 is directly connected, Serial0/0
BOTTOM#
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