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Router not detecting serial line is down

a-greaves
Level 1
Level 1

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 6

kmuthukamu
Level 1
Level 1

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.

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 ?

a-greaves
Level 1
Level 1

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

m.witte
Level 1
Level 1

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.

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.

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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