I'm trying to replace a Speedtouch ADSL router with a Cisco 876 in order to introduce QoS, but I'm having some weird problems which would seem to be MTU related.
Symptoms: When we're visiting certain web sites, no traffic gets through. Eventually, the connection times out. A packet trace shows SYN, SYN/ACK, ACK, and the HTTP GET request from the client. Then nothing for about 30 seconds, and finally an RST from the server. If we put the Speedtouch back, everything works fine.
I've checked and double-checked the settings, and I've also tried lowering the MTU, but to no avail. The Speedtouch uses an MTU of 1492. Here's the relevant (I believe) parts of the configuration:
----------------------- interface VLAN1 no shutdown ip address 80.203.xxx.xxx 255.255.255.240 ! interface atm0 no ip address dsl operating-mode auto pvc 1/33 pppoe-client dial-pool-number 1 ! interface dialer1 ip address negotiated mtu 1492 ppp dialer pool 1 ppp chap hostname XXXXXX ppp chap password XXXXXX ! ip route 0.0.0.0 0.0.0.0 interface dialer1
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As you can see, there's no NAT, firewall, or even access lists. What am I missing here?
KR