Unanswered Question
Feb 28th, 2007

Recently Tiscali upgraded their service and changed from aa5snap to aal5mux. there was no notification of this and I had to figure this out when things fell apart. see:

About 5 days later, problems started again.

While surfing, I only get partial pages downloaded before page freezes. Speeds on downloads at about 4Kbps!. Funny thing though, is that Google search is same speed as always.

Again tiscali insists nothing has changed. I know for CERTAIN I did not change my config.

I plugged in a USRobotics router and another Cisco 827 and I encounter the exact same problems so it is not unique to my hardware. With tiscali supplied speedtouch modem, things are full speed.

speedtouch modem default mtu is same as cisco default - 1500. Anyhow, I played around with mtu settings. but made no difference, also pppoa which I am on, is not susceptible to mtu it seems. However, I do not want to rule this out.

do I need to set max receive unit on cisco to 1500? if so how? it is set to 1500 on speedtouch modem.

Can somebody please advise on where I would start to debug this problem.

Kind regards. attached is config

Building configuration...

Current configuration : 911 bytes


version 12.2

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption


hostname Router



ip subnet-zero

ip name-server





interface Ethernet0

ip address

ip nat inside

hold-queue 100 out


interface ATM0

no ip address

no atm ilmi-keepalive

pvc 0/38

encapsulation aal5mux ppp dialer

dialer pool-member 1


dsl operating-mode auto


interface Dialer0

ip address negotiated

ip nat outside

encapsulation ppp

dialer pool 1

dialer-group 1

ppp authentication chap callin

ppp chap hostname [email protected]

ppp chap password 0 123456789abc


ip nat inside source list 1 interface Dialer0 overload

ip classless

ip route Dialer0

no ip http server



access-list 1 permit


line con 0

stopbits 1

line vty 0 4



scheduler max-task-time 5000


I have this problem too.
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andrew.butterworth Sat, 03/03/2007 - 04:36

It's an MTU issue. My mum has a SOHO ADSL router I put in for her ages ago. The week before last she started having problems with only partial pages showing and loads of timeouts. Strangely worked every time.... I assume the google servers have a small MTU configured on them.

I also assume Tiscali made some changes to either block ICMP messages or some other filtering. Anyway I fixed it by reducing the MTU on the PC to 1458 (download DrTCP) and everything sprang into life. I could have reduced the MTU on the router but since this is a single PC either way solves the issue.




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