At work we currently have 2 separate networks, 1 for our phones (192.168.2.x) and 1 for the computers (192.168.1.x) that share 1 router (Draytek 2820) for internet access. We have a typical small business network with all of the computers connected to a switch, the DSL router connected to the switch, and the DSL router acting as DNS server and gateway. The phones are connected to a separate switch, the LAN interface on the PBX (an Epygi Quadro 6L) is connected to the switch and the WAN interface is connected to the DSL router.

Because of some minor problems we've been having I thought it might be a good idea to have a separate DSL tail for data, so in the case of the voice DSL tail going down it doesn't mean that we can't access email as well. If we go down this path it means that the voice DSL tail only gives us access to the SIP servers our calls go through.

We are currently sent emails when a voicemail is left (the PBX does this) but obviously if the PBX can't access our (external) mail server anymore then that's going to be a bit of a problem.

What would be the best way of re-arranging the networks so that we could have separate DSL tails for data and voice but still be able to receive email notification of voicemails? I'm open to anything - setting up a proper router/gateway type server, hosting mail internally, separate networks by VLAN etc.



Not an answer to your entire question, but if one of the reasons you want to get two DSL connections is for redundancy in case one network goes down, make sure that they're not both with the same provider, because if one link goes down, if the other is with the same provider, chances are it will too.

(although if it's DSL and they're both connected to the same local exchange, chances are they'll both go down anyway)

  • That's what I was thinking. We had a 24 hr outage last week that wouldn't have been so bad had we been able to access email. – Mark Jun 26 '09 at 3:44

I'm assuming by "DSL Tail" You mean you would be bringing in a second DSL line with it's own router.

The easiest way to do this would be to setup VLANing or get a second switch then put one of the routers in both networks and setup a static route from the Voice network to the data network for your external email servers.

So as an example with your data router being the one with a leg in each network:
DataRouter would have and
PhoneRouter would just have
Then setup a static route on PhoneRouter for your Mail server IP to

You could also check with your provider for thier IP scope and route the whole network to

If your sip provider and mail provider are the same you could run into connectivity issue with the whole scope approach.


Just had another thought. If you can swing the budget, you could get something like a cisco 2801 router with 2 ADSL HWIC (HWIC-1ADSL as an example)

That way you wouldn't need to reconfigure your network, you could set the data connection as your default route and then put a static route in for your SIP traffic towards your SIP trunk.

One other thought would be ... you might not need to do anything as your DSL for your sip provider is just another internet connection right? There is nothing special besides you are sending sip traffic over it. So you wouldn't really have to do anything if that is the case because you would have an internet connection for your PBX to talk to your hosting provider on.

  • Does that mean the data router will need something like a separate LAN interface so it can be connection to both networks? – Mark Jun 26 '09 at 4:06
  • Yep, on one of the two routers you will need 2 lan interfaces in my example it would be data, but you could reverse the setup and have 2 on the phone router - although the static route would stay there. – Zypher Jun 26 '09 at 4:48

I don't know if I get you correctly, but if you are going to have 2 separate DSL links, one for voice and one for data, you'll still have "half a problem" if one of them is down - either you have no data (email etc), or you have no phones.

I would go with Zypher's suggestion to get a router with 2 uplinks - either DSLs or ethernet & use DSL modems. This way, you should at least be able to use the second link as a backup (so you can have a fast link as primary and a cheap and slow one for backup) and probably also do some prioritizing/traffic shaping if you are concerned about that.

Actually, I just looked at the Draytek 2820 product page and it seems to have a second WAN port and is able to do load balancing and backup. So maybe you could just get a second DSL connection & DSL modem and that's all you need? According to that page, the box is even able to use a 3G USB stick as backup, so if you have decent coverage, you might think about that. Makes a good backup link for those cases where all cables are cut by some idiot digging the ground.

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