From: Eric Hauptman (ehauptma@xxxxxxxx)
Date: Sat Apr 14 2001 - 15:44:35 GMT-3
Dan,
Thanks for the info. However, even though I didn't have the command on either
serial interface, one side was up/down while the other was up/up. Are you
saying that if, for example, router 1 detects a loop, that same loop will be
detected by router 2? It seems to me that if the telco sends a loop pointing
towards router 1 the "down-when-looped" command will do its job and detect the
serial being down and drop the route from the routing table. However, how will
router 2 know about the loop pointing to router 1? Won't router 2 think
everything is just great and leave the serial in its normal up/up state? Or
will router 2 notice that there is a loop somewhere in the network and change
it's status to up/down, just like router 1?
Eric
Dan wrote:
> Eric,
>
> The "down-when-looped" command was introduced to avoid this problem.
> Both sides of the serial link should have the "down-when-looped" command
> added to the Serial interface.
> When either router detects a loop, it usually stays up/up, but when you have
> the "down-when-looped" command, the interface goes to "up/down (looped)" so
> that you can still see the loop but the router will remove any routes
> referencing this interface from the routing table.
>
> Dan Pontrelli
> Customer Installation Engineer - Verio NYC
> CCNP, MCSE, CNA
>
> ----- Original Message -----
> From: "Eric Hauptman" <ehauptma@home.com>
> To: "Groupstudy" <ccielab@groupstudy.com>
> Sent: Saturday, April 14, 2001 3:51 AM
> Subject: Re: Point to Point Serial link
>
> > I would like to thank all those who responded to my point-to-point serial
> link
> > problem. I was informed tonight that our provider, AT&T, had a loop
> somewhere
> > in the telco pointing back to
> > one end of the site, thus leaving one side up/down & the other side up/up.
> >
> > However, going forward, I'm perplexed about the best way to back this
> circuit
> > up using my current ISDN B-channels on the 2610 router. I had it setup to
> use
> > floating static routes with higher AD for the BRI channels, which works
> fine as
> > long as the serial drops on BOTH sides. What happened yesterday is that
> when
> > one side went down the floating static kicked in and the BRI was dialed.
> > However, the other side's serial was still up/up, meaning the return
> traffic
> > was still being sent to the serial line, not the ISDN line, hence traffic
> > couldn't pass. We manaully solved the problem by removing the floating
> statics
> > and putting all static routes on both sides pointing to the BRI lines.
> >
> > Does anyone have any ideas on the best way to deal with the situation in
> the
> > future? I assume some sort of dynamic routing protocal might be the
> answer,
> > but I was hoping to run this link without the added overhead of a routing
> > protocol. Thanks.
> >
> > Eric H.
> >
> > Bob Dixon wrote:
> >
> > > Maybe a stupid question, but are you sure that your physical wiring is
> in
> > > place as it should be? In other words, maybe routerA's serial0 is cabled
> to
> > > a live circuit terminating on an unknown device that is exchanging
> > > keepalives as it should. This would mean serial0 on routerA shows up/up.
> Of
> > > course, it is highly unlikely that you could ping across the wan link in
> > > this scenario. routerB's serial 0 could be cabled to a cicuit that is
> open
> > > on the other end. That means serial 0 on routerB shows up/down. Just a
> > > thought.
> > >
> > > >From a perspective that may sound more like PC troubleshooting than
> router
> > > troubleshooting, you could try powering down the router that shows
> up/down,
> > > re-seat the WIC card, and then boot the router. I just turned up some
> t1's
> > > and t3's the other day. We had a weird problem where the t1 wic showed
> > > up/down (keepalive was set) and the ILEC could not loop the built-in csu
> on
> > > the WIC. After re-seating the WIC, the ILEC could latch the WIC and
> after
> > > dropping the loop, the circuit came up/up and ran clean.
> > >
> > > Bob
> > >
> > > ----- Original Message -----
> > > From: Prashanth <prashanthcm@yahoo.com>
> > > To: Curtis Call <curtiscall@home.com>; <ccielab@groupstudy.com>
> > > Sent: Saturday, April 14, 2001 2:26 AM
> > > Subject: RE: Point to Point Serial link
> > >
> > > > possible to send us the config?
> > > >
> > > >
> > > > --- Curtis Call <curtiscall@home.com> wrote:
> > > > > It might be that one side is expecting keepalives
> > > > > and the other is not
> > > > > expecting nor sending them.
> > > > >
> > > > >
> > > > > >-----Original Message-----
> > > > > >From: Eric Hauptman [mailto:ehauptma@home.com]
> > > > > >Sent: Friday, April 13, 2001 2:25 AM
> > > > > >To: Groupstudy
> > > > > >Subject: OT: Point to Point Serial link
> > > > > >
> > > > > >
> > > > > >I have a production network where one side of a
> > > > > point to point serial
> > > > > >link is showing up/down and the other side is
> > > > > showing up/up. I thought
> > > > > >that if one side went down they would both go down.
> > > > > I know on frame
> > > > > >relay one can be up/up and the other down, but I
> > > > > thought on a point to
> > > > > >point this would not be the case. Am I missing
> > > > > something basic here? I
> > > > > >am running the T1s into 2610 routers with built in
> > > > > WIC-T1-CSUs.
> > > > > >
> > > > > >Thanks.
> > > > > >
> > > > > >Eric
> > > > >
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