This has nothing to do with routing - they are on same vlan and same subnet.
The only lack is they are missing L2 connectivity.
Can you check if the switches have CDP enabled, is there some mac-address being cached (sho mac-address) ?
I think he has more than 2 vlans in each devie, so I suggested to configure dynamic routing.
here some new steps:
1- apply the trunk configuration on a differet interface and from both ends.
2- enable CDP on both devices.
3- use a different media UTP cable in this interconnection.
Ok as suggested by devils advocate I have started again with the trunk config...
I have now also changed interfaces on both the 3750 and the 4507
CDP is enabled on both by going to config t - cdp run
I have also changed the cable
I am still getting nothing in CDP neighbours and cannot ping each side of the trunk.
I have logged a call with Cisco TAC via my SmartNet contract as well now.
This config should have been really simple!
If you don't have cdp neighbors then that's a physical issue unless cdp has been turned off . If you want to try again on each side try. If it doesn't come up check logs for error . Before anything else plug the devices together and you could just make the ports access ports in vlan 21 and it should ping across . Both sides must show connected and you should see cdp . If not your you might have an issue with your cables .
vtp domain XXXX (must match)
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 21
switchport mode dynamic desirable
In this case native vlan is 1 because none is specified.
Even in case there are multiple vlans, it should work if both trunk interfaces carry the vlans.
Matti, share the complete config and interestingly the output from - sho mac-address.
I wish I could post the configs but it is a secure environment so I can't. I have changed the physical cable, ports in both devices and still can't see anything on CDP neighbors which suggests that something else is going on! I will see what the TAC say but will post any feedback I get from them here in case it helps anyone else
try to connect the two switches through two access ports and from the two end, have a check if you have any traffic between the connected ports.
the connected ports and from the two devices have to assign to the same vlan.
can you check all your security configuration like running services, access lists, port security etc. and make sure that they don't affect the communications.
If you can backup your running configurations and just for a test reset to factory default and then try to connect both switches.
I have to agree with Hardi that something is off here. Your original post showed your port configurations with the 'switchport trunk native vlan 21' command present however the ouput you posted for 'show int trunk' showed VLAN 1 as the native.
Try setting both switches to VTP transparent mode and see what happens.