Zhasper wrote: > On 12/12/06, Oliver Hookins <[EMAIL PROTECTED]> wrote: > >> >> Not quite right, you still have layer 2 frames which are disassembled >> and reassembled. However your device is operating as a simple ethernet >> (or ATM if your ISP supports it) bridge rather than also encapsulating >> the traffic in PPP which is the norm, hence less overheads. > > IIRC (and I'm sure someone will correct me if I don't), the famous > 1492-byte MTU on DSL connections is caused by the 8 bytes of PPPoE > headers taking up part of the 1500-byte ethernet frame. > > Switching to L2 removes that overhead, which has a few benefits: > avoids mysterious MTU issues, means that 1500-byte packets on the > ethernet segment don't have to be re-packaged as 1492-byte packets to > go over the DSL segment (I think this is what O was talking about), > etc. >
There's more to it that that. If it's telstra DSL, there's also L2TP overhead - that's the tunnel that takes a load of aggregated PPP sessions and dumps them onto your ISPs ppp termination box. The actual telstra-recommended MTU that ISPs generally force is more like 1452. BB -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
