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New Member

Router not detecting serial line is down

Basically I have 2 routers connected via serial leased line using HDLC encapsulation through a CO.

If the serial cable is removed at one end, the other Router still shows the line as up/up.

The 'debug serial interface' command isn't functioning, but I'm sure I've seen this problem on another Router and the keepalives were failing, but the Router still said line was up/up.

I had the idea to add EIGRP across the link, just to get the Routers to send 'hello' messages and to

form a relationship. However this didn't work either, i.e. the serial line is still indicating up/up when the far end cable is removed.

Is this a known IOS bug ?

6 REPLIES
New Member

Re: Router not detecting serial line is down

If we experience status is up, line protocol is up too, when no cable is connected too. Then it's possible that

interface needs to be reseated. It may happen with modular devices.

New Member

Re: Router not detecting serial line is down

I have this problems too but I using the PPP encapsulation with the IOS 12.2. Do you have this experience and why you suggested to be reseated the module ?

New Member

Re: Router not detecting serial line is down

I should have added that the Router in question is a 1700 series with IOS Version 12.1(3).

New Member

Re: Router not detecting serial line is down

I am pretty sure that the CO is providing the clocking to both of the routers so if the other side is down, it shouldn't affect the other router. Only on frame-relay if you have a PVC defined from point to point will you see and thing and that will be that the PVC is down.

New Member

Re: Router not detecting serial line is down

first, be sure that you don't have the command: "no keepalive" in interface config.

i noted this problem in PPP encapsulation too.

but if i wait much enough time, the protocol will finally go down. so i think the problem is proportional to keepalive time. in fact, if i decrease the keepalive time, the time i will waiting for before the protocol goes down, decreases too.

Gold

Re: Router not detecting serial line is down

So, how long are you waiting? The keep is usually something like 5 seconds, with the hold at something like 15 seconds, I think, for hdlc. The end that loses clock should go down immediately; other than this, you're limited to the dead time.

Russ

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