From: Pierre-Alex (paguanel@hotmail.com)
Date: Fri Jun 16 2006 - 15:27:33 ART
Yes, agree Petr, but your topology is different than mine and is not testing
the same thing. :)
I am evaluating inter-area routes, Type IA via an Area 0 versus inter-area
routes, Type IA via a non-Area 0 (virtual-link)
I have re-written the case study for clarity:
Area 12 (network 10.1.2.0)
|
R2---virtual-link area 23---------R3
| |
| |Area34
----Area 0----------------------------R4
The purpose is to evaluate the path to network 10.1.2.0 from R4
R4 receives information from network 10.1.2.0 from R2 and R3
I have set a really high cost on R4 interface in area 0 towards R2.
The route chosen is yet via R2. See info below
For me:
Pierre-Alex
r4#sh ip route 10.1.2.0
Routing entry for 10.1.2.0/24
Known via "ospf 100", distance 110, metric 65001, type inter area ----> LOOK
AT THE COST
Last update from 10.2.4.2 on Serial0/0.402, 00:22:18 ago
Routing Descriptor Blocks:
* 10.2.4.2, from 150.1.2.2, 00:22:18 ago, via Serial0/0.402
Route metric is 65001, traffic share count is 1
Summary Net Link States (Area 0)
Routing Bit Set on this LSA ----> LSA CHOSEN - WILL BE USED FOR ROUTING
TABLE
LS age: 858
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 10.1.2.0 (summary Network Number)
Advertising Router: 150.1.2.2
LS Seq Number: 8000000C
Checksum: 0x6B1D
Length: 28
Network Mask: /24
TOS: 0 Metric: 1
Summary Net Link States (Area 34)
LS age: 1533
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network) ---------------> THIS IS FROM R3, THE ABR
Link State ID: 10.1.2.0 (summary Network Number)
Advertising Router: 150.1.3.3
LS Seq Number: 80000001
Checksum: 0x126F
Length: 28
Network Mask: /24
TOS: 0 Metric: 782
----- Original Message -----
From: Petr Lapukhov
To: Pierre-Alex
Cc: ccielab@groupstudy.com
Sent: Friday, June 16, 2006 8:09 PM
Subject: Re: type 3 LSA from Area 0 vs. type 3 LSA from non Area 0
Pierre,
Here is a simple scenario to demostrate the idea:
Diagram
---
Lo5
|
R5
| \___R3
| /
R4
Configuration:
1) R4 and R5 are connected via link in Area 1 (with Serial 0/1 interfaces)
This path has Cost = 1.
2) R3, R4 and R5 form Area 0 (with Serial 0/0 interfaces at R4, R5).
Cost has default value.
3) R5 has Loopback5 (164.1.155.5/32) in Area 5.
The task is to evaluate how R4 routes to Lo5, with and w/o virtual-link
between R4 and R5. I want put more output, since it's easy to
simulate both cases.
--
First case: NO virtual link over Area 1.
Rack1R4#show ip route 164.1.155.5
Routing entry for 164.1.155.5/32
Known via "ospf 1", distance 110, metric 846, type inter area
Last update from 164.1.34.3 on Serial0/0, 00:07:24 ago
Routing Descriptor Blocks:
* 164.1.34.3, from 150.1.5.5, 00:07:24 ago, via Serial0/0
Route metric is 846, traffic share count is 1
Path via Area 0 is preferred regardless or cost.
---
Put a virtual link from R4 to R5 via Area 1 and check routes
again:
Rack1R4#show ip ospf virtual-links
Virtual Link OSPF_VL2 to router 150.1.5.5 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0/1, Cost of using 1
Transmit Delay is 1 sec, State POINT_TO_POINT,
.....
Rack1R4#show ip route 164.1.155.5
Routing entry for 164.1.155.5/32
Known via "ospf 1", distance 110, metric 2, type inter area
Last update from 164.1.45.5 on Serial0/1, 00:00:29 ago
Routing Descriptor Blocks:
* 164.1.45.5, from 150.1.5.5, 00:00:29 ago, via Serial0/1
Route metric is 2, traffic share count is 1
The "best" path is now chosen, because LSAs flow through "Area 0 put
over Area 1".
--
Petr Lapukhov, CCIE #16379
petr@internetworkexpert.com
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