Have a very strange problem with a 2821 installation and wonder if anyone has seen this or something similar before?
The original symptom was when configuring an IP address on a LAN port sub-interface, BGP would flap on the WAN. Since then all hardware has been swapped, and now have a situation where plugging anything into the LAN port brings down the WAN BGP. Diconnecting all lan connections restores stability, but even bringing up the LAN port by turning off keepalives with no physical device attached causes the BGP to flap!
The IOS version is same as used at 100's of similar installations with no issues, and only major configuration difference at this particular site, is that it is running a local DHCP server.