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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
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
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