Hi,

I have two Asus WL-500g Premium routers, one running the original Asus firmware, the other one running OpenWRT Kamikaze 7.09.
My ISP uses PPPoE with an MTU of 1460. I noticed problem with certain websites (for instance downloading Nero for Linux from the Nero website didn't work).
I recall that this could be related to MTU problems... packets getting "too" big and both ends being unable to work it out stops the traffic between those sites altogether.

To make sure it is a problem with OpenWRT, I also tried it with an identical Asus router running the original firmware. Both routers are behind yet another router and I can easily switch the default gateway from the OpenWRT router to the router with the original firmware. The original firmware works just fine...

I tried getting as much info from the original firmware as possible and noticed the following options are being used by PPP on the original firmware (which I tried copying into the /etc/config/network file, see below). Unfortunately it makes no difference (and some options are not being recognised so I had to take them out). I also tried running PPP from the command line:

# pppd file /ppp/options

but this was unable to setup the Internet connection (it got a wrong IP address from the ISP??)

I also tried setting all interfaces to MTU 1460... to no avail.

Does anyone have any pointers how I can further research/debug this issue?

cheers,
Jan

#### isp configuration
config interface                isp
        option ifname           "eth0.1"
        option proto            'pppoe'
        option mtu              1460
        option mru              1460
        option username         '*****'
        option password         '******'
        option idle             1800 demand
        option usepeerdns
        option defaultroute
        option persist
#       option ipcp-accept-remote
#       option ipcp-accept-local
        option noipdefault
        option ktune
#       option default-asyncmap nopcomp noaccomp
#       option novj             nobsdcomp nodeflate
#       option lcp-echo-interval 10
#       option lcp-echo-failure 6
        option unit             0

#

do a ip li it will tell you the mtu used for each interface (you can use ifconfig as well)

ps -ef ww or ps ww should show you the command lines passed to ppp make sure the mtu option is sent

also check iptables, I haev something like this in mine
$IPT -t mangle $FNC FORWARD -o $WANADSL -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

Hi Alex,

MTU was all set OK. ppp attempts to set the MTU to 1500 but doesn't succeed to do so (and complains that I may have serious connection problems).
The connection comes up OK though. The clamp-mss-to-pmut fixes the MTU problem.

thanks for your help!
Jan

PS for other readers: you need to substitute "-A" for $FNC and the name of your external interface for $WANADSL (without the quotes) in Alex's example.