On 2009-04-24, David Walker <davidianwal...@gmail.com> wrote: > From: Claudio Jeker >> The main encapsulation over ADSL is PPPoE or PPPoA only lately, with the >> spread of IPTV and VDSL, EFM (Ethernet First Mile) is used by some telcos. >> So it totaly depends on what your provider is giving you. > > Maybe I didn't explain myself or perhaps I am trying to explain > something that doesn't make sense. > I understand there are differing methods of getting the packets from > the exchange to the premises, etcetera. > Considering the existing popular method of PPPoE is there more than > one way to collect those packets at the first adapter after the modem? > > My current scenario: > DSLAM<-----PPPoE----->Modem<-----TCP/IP----->Router
so with this, the modem is terminating the PPP session, and passing the address on over DHCP. some router vendors call this "half bridge" or "dhcp spoofing". I'm not sure if it's still subject to the restriction of ethernet MTU, but if it is, the modem will usually hide this by clamping MSS, the same way "match scrub (max-mss 1400)" or whatever does. > The other scenario: > DSLAM<-----PPPoE----->Modem<-----PPPoE----->Router > In this case the relevant adapter on the router recieves PPPoE > encapsulated packets from the modem exactly as they are sent from the > exchange. that's what I normally do when the ISP and ADSL backhaul support PPPoE; the modem acts as a dumb bridge and the PPP session is terminated at the router using pppoe(4). this lets you do things like use IPv6-over-PPP where supported. (some networks allow you to use either PPPoA or PPPoE for example the standard ADSL connections in the UK with BT backhaul; I normally run these as PPPoE unless using them with carp). >> Can someone let me know if I am correct in assuming that if I want >> PPPoE in client mode only that PPPoE(4) is the way to go? usually. >> Probably a more important question is what, if any, are the advantages >> or disadvantages compared to DHCP? with one vendor implementation of this, it saves you from having a huge bunch of entries in your arp table... otherwise: control over the PPP session, maybe better logging, maybe access to ipv6 or multicast which could be a problem with some CPE modem/routers, and it puts most of the "per user" settings into the firewall, so it may make it easier to maintain spare modems/routers for a bunch of lines that you can just swap-out without reconfiguring. if you need that sort of thing.
