Cisco 1801 ATM -> Ethernet bridge issue

Question:

I recently purchased a UC520W for WS-C3560X-24T-S use at home to replace an 877W, would  like it to do all the front-end stuff, NAT, firewall, PPPoE, voice. Have  installed a 1801 in front of it to bridge ADSL to Ethernet (almost),  but having some issues.

1801 config:

-----------

no ip routing

!

interface ATM0

description OUTSIDE

no ip address

no ip route-cache

no atm ilmi-keepalive

pvc 8/3

  vc-hold-queue 1024

  encapsulation aal5snap

  exit

bridge-group 1

no shut

exit

!

interface FastEthernet0

description INSIDE

no ip address

no ip route-cache

speed 100

full-duplex

bridge-group 1

no shut

exit

!

bridge 1 protocol ieee

The UC520W is doing the PPPoE negotiation fine, so the 1801 is bridging  (I've tried an 877W as well), I can ping out from the UC520 and attached  PCs OK as well. But when it comes to email and web surfing....no joy.  Replacing the 1801 with a dumb domestic modem/router in bridge mode works without  issue.

Have tried bridge irb (both enabled/disabled) and also ip routing (both enabled/disabled), no change.

Why am I getting only a partial connection? Any thoughts welcome....and  just using the domestic modem/router is the ultimate fall back solution, but I'd like  to work out where its failing if I can.

Answer:

Please, check you MTU in all the links. I think the problem could be the MTU in some WS-C3560X-48T-L interface.