[j-nsp] PtP link over FR

Scott Morris swm at emanon.com
Thu Jul 17 07:49:09 EDT 2008

There is no ARP in frame-relay.  More specifically, on a P2P subinterface,
there's no mapping either.  The assumption is that if it's not MY address it
must be yours.  So as long as you believe the other side is within the
defined subnet, then you're good.

If you have on one side, and on the other, they will
still talk to each other just fine.  At least until you try to run ospf or
something that cares about the netmask!


-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net
[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Jesper Skriver
Sent: Thursday, July 17, 2008 7:24 AM
To: Farhan Jaffer
Cc: Juniper Puck; cisco-nsp at puck.nether.net
Subject: Re: [j-nsp] PtP link over FR

Let me guess, on Cisco Router A you got an ARP entry for Cisco Router B's
address when you put a Cisco router in the middle, as the Cisco router has
proxy-arp enabled by default.

Or to put it more clearly the IP addresses used FR p2p pvc is a subset of
the IP addresses used on the link between Cisco Router A and Juniper Router.

Or on Cisco router A you have a static route without a next-hop address to
the IP subnet used on the FR link

In either case it's a mis configuration, that gets 'saved'/'hidden' by the
fact proxy-arp is enabled by default on the Cisco router.


On Thu, Jul 17, 2008 at 04:06:31PM +0500, Farhan Jaffer wrote:
> Hi,
> There is an interesting situation, let me discuss the scenario first,
> Cisco Router A ----(same n/w) ---- Juniper Router -----(FR 
> point-to-point pvc) ------- Cisco Router B.
> PVC is Active & point to point connectivity is OK. But the ping 
> response from cisco router A to B via FR is unreachable & vice versa.
> however if i replace Juniper router with Cisco Router, it works fine.
> Is there any IP forwarding like thing? or any other problem.
> Thanks very much in advance.
> -FJ
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net 
> https://puck.nether.net/mailman/listinfo/juniper-nsp


Jesper Skriver, jesper(at)skriver(dot)dk  -  CCIE #5456

One Unix to rule them all, One Resolver to find them, One IP to bring them
all and in the zone to bind them.
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