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Draytek Vigor 120 with Linux problem

driveconsultant
Grafter
Posts: 164
Registered: ‎03-08-2007

Draytek Vigor 120 with Linux problem

I have just installed a new Draytek Vigor 120 modem which I have connected to a Gentoo Linux box. This is mostly working without too much of a problem, but there are a few web sites that I am now unable to connect to and I a little baffled.
The story is as follows: I had a Netgear DG834G which was pretty unreliable. It would drop the connection fairly often, needing a reset. I have had a lot pf problems with Netgear - many of my family and friends have had failures. So I started using a cheap and nasty Huawei HC520B that had previously been supplied to someone by TalkTalk. This connected OK but left something to be desired in other features such as DHCP. I built a fanless Gentoo Linux box based on an Alix to replace this, but initially continued to use the Huawei just for the ADSL connection. I have now bought the Vigor 120 and set it up with pppoe on the Linux box.
So now, although I can connect to most sites, a few just sit there hanging. As an example, one of the first sites I connected to was www.speedtest.net, and it does not connect at all. A traceroute to this site succeeds, and so does a telnet to port 80. Another example of a site that doesn't work is the BBC for streaming radio. When I connect the Huawei up again it works - I've switched between them a few times to prove this.
I have the MTU on the ppp connection set to 1492 as recommended by most places, I don't know what else I could usefully change. I don't know whether the problem is in my config or whether it could be a PlusNet issue. I thought that the Vigor 120 would be a neat and efficient solution because it is less IP hops, less NAT etc. Now I'm wondering whether I've wasted my money.
Any ideas anyone?
2 REPLIES 2
ian007jen
Rising Star
Posts: 392
Thanks: 4
Fixes: 2
Registered: ‎06-09-2007

Re: Draytek Vigor 120 with Linux problem

Try MTU =1500, my asus router doing pppoe with a modem is set to 1500.

my asus is set to 1492 in the gui. (pppoe to a modem), but when i run a ifconfig it reports the mtu as 1500.
the modem's mtu is also 1500 (ifconfig)
....so ensure the modems MTU is 1500, and the linux box 1492.
Ian
Highlighted
driveconsultant
Grafter
Posts: 164
Registered: ‎03-08-2007

Re: Draytek Vigor 120 with Linux problem

Thanks for that but my MTU was already 1492. ifconfig shows it as 1492. There is no MTU setting on the modem.
After a lot of hunting I think I have found the solution. The fix comes in iptables:
iptables -A OUTPUT -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu