Serial line protocol keeps dropping

[smaber]

I've set up a test rig for CCNA practice and keep coming up against the same problem.

I have a 3845 with a 4-serial module added then 4 2501 routers in a rack. The issue is, I keep getting interfaces going from up-up to up-down..and I have no idea why.

After realising the slow notification of interface up when plugging in the serial cable (on either end) I started to check the cables. Bit confusing but they all appear to work when they want to.

I've done exactly the same configuration on a software package and all statuses are up-up and remain that way. So I know my config is ok. Plus, before I added more than one 2501, all individual links were up-up.

First, when I had the 3845 connected to one 2501, the line was up-up then when another 2501 was added the new line would remain up-up for 30s before getting the message line down. Now, with just one connected 2501, I have to shut-no shut to get the router to recognise an added cable before that will go up-down 30s later.

I don't know where the issue could lie. Anyone had this problem before?

 

[t0mm0]

I had similar experience on a test lab, unfortunately not the same routers.

Anyway, The scenario was between two 2600 series routers. Where r1 was providing clocking to r2, it seemed to give the same scenario you described.

Admittedly r1, had a 'router to a stick' layout configured to it whilst r2 had a simple network, behind it. But simply swapping the clocking source seemed to work..