[j-nsp] Duplicate IP addresses on interfaces

[Eric Van Tol]

> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-
> bounces at puck.nether.net] On Behalf Of Jared Mauch
> Sent: Tuesday, September 30, 2008 1:18 PM
> To: Richard A Steenbergen
> Cc: juniper-nsp at puck.nether.net
> Subject: Re: [j-nsp] Duplicate IP addresses on interfaces
>
> ...
>    If one interface is down and the other is up,
> this is an acceptable configuration on Cisco.
> ...

I have seen where this is not the case.  While it is an accepted configuration option, it can break routing and cause similar issues to what Richard is saying happens on Juniper.  Sometimes it will forward packets and sometimes it will drop them.  It probably depends on the platform and IOS, but I've seen this wacky behavior on 6509s, 3550s, ME3400s, and ME3750s.

I agree that it should not be allowed and should cause a commit failure.  When we encounter this, often because a customer is moving offices or T1 LECs, we deactivate the 'family inet' portion of the config.  Unfortunately, unless we do a 'commit check' prior to committing, we end up having to commit twice if the warning appears.

-evt