Odd One very odd (am i missing something silly?)

[Fuzznuts]

I have a bit of problem we have just got 2nd Internet connection into our offices at work we have ranges of 29 address on both connections (entirely different subnets) now isp1 i have simply uplink the router (cisco 1721) into our core switch and can go about the network slapping ip adress's on to the servers and it all works fine and dandy.

however the same can not be said for ISP2 i have again uplinked the router into our core switch put a couple of ips on a couple of machines but they are unreachable from the internet or internally to each other the default gateway's etc are all correct and they all have link lights.

The only way it seems to work is if i use a crossover from the router to a switch and then plug a machine direclty to that switch. surely if this works uplinking form there into the core should have same effect i am totally baffled

the router is managed i have no telnet access btw

i have tried numerous cables even made my own there is no VLAN config other than that i am not sure what else would stand in the way

working config
--------------

ISP2 Router----Switch----PC

non working config
-------------------

ISP2 Router------Coreswitch------networkswitch----PC


Please help i am going mad wibble wibbleee

 

[Fuzznuts]

turns out i was missing something silly

one of the edge swithes near the server room had a vlan's enabled but no vlans defined, how on earth it work i have no idea i simply disabled the vlans and rebooted odd that i work for one router and not the other though?