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Re: OSPF external type-2 route load balance posted 08/31/2007
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Thanks for that Scott.

Looks like this demonstrates this rather well, at least how I read it.

From OSPF Design Guide on CCO.

sic 'External routes fall under two categories, external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.'


Rgds
Gary
----- Original Message ----- From: "Scott Smith" <hioctane@xxxxxxxxx>
To: "Sadiq Yakasai" <sadiqtanko@xxxxxxxxx>
Cc: "Joseph Brunner" <joe@xxxxxxxxxxxxxxxxxxx>; "Herbert Maosa" <asawilunda@xxxxxxxxxxxxxx>; "ISolveSystems" <support@xxxxxxxxxxxxxxxxx>; "Cisco certification" <ccielab@xxxxxxxxxxxxxx>
Sent: Friday, August 31, 2007 7:49 PM
Subject: Re: OSPF external type-2 route load balance



Bingo!

A1 learns 100.100.100.0 from both 10.43.1.61 & 10.43.1.73.

Before - BW 1536 to both ASBRs

A1(config-router)#do sh ip route ospf
100.0.0.0/24 is subnetted, 1 subnets
O E2 100.100.100.0 [110/20] via 10.43.1.61, 00:00:36, Serial1/0.1
[110/20] via 10.43.1.73, 00:00:36, Serial1/0.2



After - Dropped BW to 512 on s1/0.1


A1(config-subif)#do sh ip route ospf
    100.0.0.0/24 is subnetted, 1 subnets
O E2    100.100.100.0 [110/20] via 10.43.1.73, 00:00:06, Serial1/0.2


Then changed BW back to 1536 on s1/0.1 (now both are equal again)


A1(config-subif)#do sh ip route ospf
100.0.0.0/24 is subnetted, 1 subnets
O E2 100.100.100.0 [110/20] via 10.43.1.73, 00:00:02, Serial1/0.2
[110/20] via 10.43.1.61, 00:00:02, Serial1/0.1


The metric is a constant 20, however, for the externals OSPF also uses
the cost to the ASBR.

--
Scott
CCIE #17040 (R&S)


On 8/31/07, Sadiq Yakasai <sadiqtanko@xxxxxxxxx> wrote:
Can you show the Type 4 LSA database as well?

I think the cost to the ASBR has a role to play in selecting 2 Type 5
LSA's reporting the same prefix.

I am not quite sure about this though.

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