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This is the support site for Andrews & Arnold Ltd, a UK Internet provider. Information on these pages is generally for our customers but may be useful to others, enjoy!
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=== MTU ===
The payload size (MTU) of traffic going through the L2TP tunnel will be lower than that of the underlying ISP - this is due to the extra 'headers' that are appliued to make the tunnel.
Some L2TP clients may auto discover the MTU, but you may want to specify it in your L2TP client configuration so as to obtain the optimum size.
You'd first want to find out what the maximum MTU is of your underlying ISP. you can do this with some pings, see our [[MTU|MTU Page]]. Once you know your MTU, you can calculate what the L2TP MTU should be.
* Generally, the L2TP MTU would be 38 bytes less than the MTU you have on the underlying internet connection.▼
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* To find out the MTU of your underlying internet connection, see
▲* Generally, the L2TP MTU would be 38 bytes less than the MTU you have on the underlying internet connection.
* In theory fragments will work to allow 1500 MTU on our service, but fragments are inefficient, and if everyone sends fragmented packets that could degrade the service.
Ethernet 1500 1500
802.11Q* - 4* 1500
PPPoE - 6 1494
PPP - 2 1492 <--
IPv4 - 20 1472
UDP - 8 1464
L2TP - 6 1458
(HDLC) - 2 1456
PPP - 2 1454 <--
=== Port forwarding on some 'Mobile Broadband' routers ===
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