Pipex > Tiscali >TalkTalk

I've been with Pipex for years. Tiscali took over in March. A couple of weeks ago my internet service went crazy.

Some sites worked: for example, Google seemed OK.

Some sites didn't: Facebook wouldn't load.

Others were erratic. The Guardian front page loaded fine — but none of the links. FirstDirect almost worked — I could look at my balances, and set up a transfer, but the final step of confirmation would hang, and hang, and never complete.

The solution: the MTU (Maximum Transmission Unit) on my Speedtouch 510 was set to 1500. Tiscali (or maybe its already TalkTalk) don't do 1500 — they do 1492 (familiar as the year Columbus set sail).

My configuration file now says (in ip.ini)

ifconfig intf=loop mtu=1492 group=local
ifconfig intf=eth0 mtu=1492 group=lan
ifconfig intf=pppoa mtu=16384 group=wan

and everything appears to be back in working order.

There's a lot of discussion of different values on the web. The 16384 above is 16K, the actual MTU used by the pppoa interface (which links me to my ISP) is negotiated down from this value by the Speedtouch 510. The ip iflist command (use this via the telnet interface to the Speedtouch 510) tells you this negotiated MTU value for the pppoa interface (and also the values you have specified for the loop and eth0 interfaces). The MTU for loop and eth0 should be set to the same value as is negotiated for pppoa.

=>ip iflist
Interface       GRP MTU   RX        TX        TX-DROP  STATUS
0  loop         1   1492  2147      0         0        UP   
1  eth0         2   1492  12453866  234402217 0        UP   
2  pppoa        0   1492  234257958 12256628  0        UP