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Re: [LUG] Two DrayTek Vigor modems on the same LAN

 

On 13 Sep 2014, at 22:29, Martijn Grooten <martijn@xxxxxxxxxxxxxxxxxx> 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?

yes and no - see other posts 

> 
> (2) The modem creates its own mini-LAN for maintenance. So it assigns
> the machine IP address 192.168.2.10 through DHCP and assigns itself IPO
> address 192.168.2.1. This allows you to connect to its web interface. Is
> it a problem if both modems use the same IP addresses?

Turn off DHCP on the one you don’t want to be a default route. and configure 
manually without setting a GW. 

This way the machine will use both lans (dual homed) but the default route will be 
the one using DHCP.  - ( FYI they need to be on there own subnets! other wise all it 
will all bork - you’ve just set them as different hosts ) 

i.e. host nics 10.0.2.127 and 10.0.3.127  with a 255.0.0.0 mask  - the router should 
be 10.0.2.1 



> 
> I don't think either should be a problem - assuming one doesn't do funny
> things with the routing - but I have a tendency to make daft mistakes
> when designing a network.
> 

if your plan is a resilient network - you need to do more complex stuff and working 
in a 192.168 sublan isn’t going to be useful  use 10.0.0.x range. or you’ll run into 
issues later with VPN’s etc. 



> Thanks
> 
> Martijn
> 
> (*) http://www.broadbandbuyer.co.uk/products/7898-draytek-v120/
> 
> (**) The current issue is that we can't reach the modem, even though it
> has assigned an IP address to the machine connecting to it.
> 
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