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I set up L2TP tunnels between FreeBSD4.2 and Redback through VLAN interfaces. Then ADSL clients connect to our FreeBSD server through PPP tunnel directly. Actually, the PPPd is caused by L2tpd (http://sourceforge.net/projects/l2tpd/) to genarate a PPP tunnel.
Now I met some weird problems about the MTU value on PPP interfaces. Here is the values I set for all the interfaces, Ethernet:1500 Vlan:1496 PPP:1496-16(L2tp header)-20(ip-ip tunnel header)-4(ppp header)=1456 So I set mtu 1456 and mru 1456 for ppp interfaces I am not sure it is the right value. Any suggestion? On the PPPoE client the default value is 1492 for mru and 1454 for mtu. During the test, I found I can hit websites but can't download files from some websites. So I droped the PPP mtu and mru to 1452 and I can download but can't hit some websites. Does anybody have such experience as above? Any help will be appreciated. Thanks! Jack
