I solved this one myself but here's the story in case it saves someone else the pain..
Had to set up a 3Com SI432 router for a remote site with only an ISDN2 for WAN connectivity to rest of the world. SO I set it up to do dial-on-demand, i.e. only bring the line up when there's traffic to send. Save call charges, stay employed etc.
However at first attempt the ISDN came up and stayed up and never went down even with nothing more than a hub plugged in to the router's LAN port. Cause of that one was OSPF needs to have the ISDN link defined as a Demand Interface, both on this router and its central partner. This prevents the routing exchanges keeping the line up.
However once I fixed that it got stranger. The lines would drop after the idle timer expired, then immediately come up again, then drop after the idle timer expired and immediately come up again, and again, and again. This one turned out to be SNMP. It shut the lines down due to no activity, and on doing so decided to send a trap to the monitoring station reporting this, and the monitoring station was of course on the central site so up came the line again to send the trap...
I think the moral of the story is to resist the temptation to set anything else up until you've got the basics working!
OK - you can stop laughing now.
I wonder if this will turn to one of those ‘my hilarious networking experience’ thread…
I know a year back we were having a 60 player LAN and one of my friends put another uplink going to a switch both not running STP. I’m sure most of you knows what happen next . Took me awhile to wonder what was going on until I found out there was two cables running to the same switches. Too bad I didn’t have the sponsorship for better switches that actually had STP so this would of never happened! I laugh at it now, but it wasn’t funny on the day when u got 60 Counter-Strike players yelling @ ya and its not even your fault!
Anyway thanks for that info Bishop I'll remember that if I setup an ISDN connection
I've seen that one too Neon, but like you it wasn't my fault either! But I think the best one of all was the time just after I joined present job when the entire country-wide WAN fell to bits. Big time. Turned out to be an engineer installing another remote site who gave the router a duplicate IP address. I swore I'd choke the guy if he ever did it again - and over the next two months he did do it again, twice more