[j-nsp] ISIS metric of redistributed directly connected routes

[Mark Tinka]

On Monday 02 March 2009 01:53:24 am Richard A Steenbergen 
wrote:

> But the observed metric value from router A on all of the
> routes being "redistributed" in this way from router B is
> 20, even though the interface metric between routers is
> only 10. The loopback route (which isn't redistributed)
> has a correct value of 10. A show isis database detail
> confirms that the other routers are receiving the
> "redistributed" route with a metric of 10 before adding
> interface costs. After playing around with it for a bit,
> I was able to reset this to 0...

This is the behaviour we have also seen in JunOS.

We use 'passive' rather than 'redistribute' for interfaces 
we need to do this on.

In JunOS, we have seen that Loopback interfaces passively 
introduced into the IS-IS topology have a correct metric of 
0. So there is no ambiguity from another router's point of 
view in the network, that reachability to the Loopback 
address has a metric similar to that of the router's 
physical interface(s) itself.

This is the same behaviour in IOS.

However, we've noticed that passively introducing physical 
interfaces into the IS-IS topology always adds a cost of 10 
to routes associated with that interface, which creates the 
behaviour you're seeing.

Conversely, IOS will maintain routes whose physical 
interfaces have been passively introduced into IS-IS with a 
metric of 0.

We don't use the 'reference-bandwidth' command in our IS-IS 
domain, so we default to the little documentation Juniper 
have about this that, with the exception of the Loopback 
interface - which inherits a metric of 0 - all other 
interfaces default to a metric of 10 if the 'reference-
bandwidth' command is not used.

Perhaps Juniper folk on this list can elaborate further.

Cheers,

Mark.
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