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New Member

2503 Back2Back configuration

I am trying to configure two 2503's in a back2back configuration but cannot get them to see each other properly . I have connected with the obligetary DCE and DTE cables. I have set int ser0 on R1 to dce-terminal-timing-enable, set clock rate, bw, encap, etc. On my R2 I have checked speed, encap, IP and all the usual etc but I get continuios interface up down events.

I cant find a decent link on the cisco webby either.

Can anyone paease advise what I am doing wrong!?!


Re: 2503 Back2Back configuration

Your relevant interface configs and "debug serial interface" will shed some light on whats going on.

New Member

Re: 2503 Back2Back configuration

Hi .... check on which router u have your clocking set ... Must be on DCE side of config (DCE cable attached here).

New Member

Re: 2503 Back2Back configuration

You only need 2 commands (at each end of a link) to get a serial interface working in a back to back situation:

int s0

clock rate 64000

no shut

Get rid of all other commands so you minimise the chance of an error. When you put the 'clock rate' command on the wrong (DTE) end of the link it will give you an error message but that is harmless and saves mucking about with the 'sh controller' command (which sometimes does not report which end of the cable you have anyway).

Attempting to run a serial line faster than the media supports (E.g. >128Kb/s with an X21 cable) will cause constant up/down/up/down messages in a similar fashion to not having a clock rate set at all - always start from 64Kb/s.

New Member

Re: 2503 Back2Back configuration

Thanks all, I had the DTE/DCE cables around the wrong way!!! I even double checked this first!!!

Sorry and thanks for your help.