From: Paresh Khatri (Paresh.Khatri@aapt.com.au)
Date: Mon Oct 17 2005 - 19:39:02 GMT-3
Hi Kevin,
According to RFC2328, the metric value in type-1 (router-LSAs) LSAs is 16-bits, while the metric value in type-3, type-4 and type-5 LSAs is 24bits. Therefore, the maximum metric value for type-1 LSAs is 65535 while that for the other LSA types is 16777215.
The metric that you specify with the 'ip ospf cost' command is that for a router link, which appears in the router-LSAs and therefore it is a maximum of 65535. The metric indicated in your output is for an inter-area route, which can be up to 24 bits.
There is a good reason why the metric for the inter-area routes is 24 bits - when you add up 16-bit metric values, it is quite possible that you will get a value greater than 16 bits. Since the metric for inter-area routes is a summation of the metrics of individual links that make up the path, we need a metric greater than 16-bits. The OSPF developers chose to use 24-bits.
Hope that helps,
Paresh Khatri
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
kevin gannon
Sent: Tuesday, 18 October 2005 03:16 AM
To: Ccie Lab (E-mail)
Subject: ospf max-mteric router
Just looking at this command again and you would think that
it sets the maximum possible metric for the routes. It states
it sets them to 65535. This is not the max metric as you
can see from below:
SW2(config-if)#do sh ip rou 2.2.2.2
Routing entry for 2.2.2.2/32
Known via "ospf 1", distance 110, metric 131071, type inter area
Last update from 14.14.14.1 on FastEthernet0/14, 00:00:02 ago
Routing Descriptor Blocks:
* 14.14.14.1, from 123.123.123.2, 00:00:02 ago, via FastEthernet0/14
Route metric is 131071, traffic share count is 1
SW2(config-if)#
The metric is 131071. Any ideas why this might be the
case, I know its highly unlikey to get a cost higher that
65535 in real life. Its just someone in Cisco thought
up this value maybe its a safety mechanism just in
case the router might be able to route packets ?
Regards
Kevin
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