Check your IOS versions and upgrade if needed. I ran into this exact
problem using frame relay encapsulation when one side was running 12.1(6)
and the other was 11.1(something). As soon as I upgraded the second one to
a 12 release, all was well.
HTH,
John
> Hi All,
>
> I've got a problem with the serial port of a 2500 of mine.
>
> I used a serial back to back cable, in order to connect 2 2500s. I know
what
> a normal response the 2500 should give, it should normally detect that
the
> interface is up (I've used no shutdown already), and then set the line
> protocol to up.
>
> For one of the serial port, the interface and the line protocol changes
to
> up when I connect the two routers together. But after awhile, this is
what I
> get:
>
> 01:30:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to up
> 01:31:08: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to down
> 01:31:18: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to up
> 01:31:38: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to down
> 01:31:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to up
> 01:32:08: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to down
> 01:32:18: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to up
> 01:32:38: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed
> state
> to down
>
> It keeps continuing. From what I can see, the line protocol keeps going
up
> and down periodically, however the interface is still up.
>
> This is what I've tried:
> - Different cables.
> - Different serial ports
> - Changing clock rate and bandwidth
> - Rebooting the router
>
> Could someone give me some suggestions?
>
>
> Thanks
>
> Albert
>
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