ID #1018

Some sites unreachable?

Enabling clampsing in 0.2.7 PPPoE Edition:

There is no setup provision for setting MTU and/or clampsing options in the 0.2.7 version.  Never the less, it is possible to enable that option so that boxen that don't have their MTU lowered have their packets rewritten to fit into the PPPoE pipe.

At first, when I did the ramdrive for PPPoE Edition, I had a good behaving ISP that set my MTU thrue DHCP.  When I switched ISP, I  suddenly understood why some reported their MTU still set to 1500 because this new ISP of mine did not set it thrue DHCP.

So the following will assure you have Freesco's ppp link MTU set properly AND rewrites the packets of those boxen that don't have their MTU lowered to 1492.

Everything can be done by modifying the single line of rc_net that calls the pppoe client:

pppd defaultroute mru 1492 mtu 1492 pty "pppoe -m 1452 -I $INTNAME0"

Rule of thumb: the pppoe -m option must always be 40 bytes less than the pppd MTU/MRU options which in turn should be at least 8 bytes less than the MTU of the Nic's interface (usually is 1500).

This takes care of all possibilities.  If your clients don't have their MTU lowered, the packets will get rewritten.  The side effect is a lost of performance since this rewritting process is CPU intensive.  No need to say that setting the clients MTU will give the best results, but with clampsing on, your sure everyone will access the web properly regardless hot their MTU is set.

Last update: 2004-10-07 10:13
Author: Technojunky
Revision: 1.0

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