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On Sat, 13 Sep 2014, Martijn Grooten wrote:
At work, we have a LAN, which is connected to the Internet using a DrayTek Vigor 120 ADSL2+ Ethernet Modem(*), which I once got after someone (Gordon, I believe) recommended it. It's been giving me a lot of pleasure. (Of course, that pleasure is mostly the absense of pain the previous BT router had been giving us.) One of the boxes on the LAN is set up as the gateway and, through a second interface, is connected to the modem. The box does all the DSL stuff. All works well. At the same time, another machine also had a direct connection to the Internet, connecting to a BT router through a second interface. That's useful for maintenance purposes. But we have now replaced that router with another DrayTek modem of the same make. And things don't really work.(**) There may be hundreds of reasons for this, but I wanted to check if my reasoning is correct. (1) Having two modems connected to machines on the same LAN - although on second interfaces on each machine - shouldn't be an issue, should it?
It is an issue and not intended to work that way. The modem to router interface is PPPoE - and in this case the E part is Ethernet and really just the transport part - there is no IP at that level and it's really just intended to be a bit of wire from the modem to the router.
(The draytek modems can have an IP, but it's really for out of band access/monitoring, etc. not for carrying transit data)
What you need is a router with 3 ethernet ports - 2 on separate wires to the 2 modems and one to the office LAN. The router then runs 2 PPPoE sessions to the 2 routers and you then do some routing magic to load balance, fail-over, policy route, or whatever it is you need to do with both connections.
Or 2 routers, each with a separate physical cable to the 2 modems - but then it's harder to select the route to use for machines on the LAN - if you need to)
Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/listfaq