Member Avatar for troverman

Right now we use a T1 circuit which is split to provide voice bandwidth for our phones and the rest for Internet. We use several static IP addresses as well.

I am looking to add a second internet provider without disrupting any of our existing phone service OR the static IP's...possibly a cable connection or dry-loop DSL connection.

The question is how do I "tell" our computers here to use the new connection for Internet but continue to use the existing static IP address we have for VPN, etc?

Is this possible? Change the gateway?

Thanks

  • 3 Contributors
  • 7 Replies
  • 194 Views
  • 1 Day Discussion Span
  • Latest Post Latest Post by troverman

Dani AI

Generated

Short answer: handle this at the edge, not by reconfiguring every desktop. Keep the provider-owned static addresses and any voice channels where they are, add the second Internet link into the perimeter device (or put a small dual‑WAN router in front of it), then use outbound policy-based routing + source NAT so normal Internet traffic exits the new link while inbound services (your static IPs and VPN) continue to be bound to the original link. This avoids touching workstations and preserves inbound reachability.

A practical plan:

  1. Confirm whether your current firewall/router supports a second WAN and policy-based routing. If it does, plug the new modem into a spare interface; if not, add a dual‑WAN router/edge box.
  2. Create an outbound rule (policy-based route) that matches LAN traffic you want sent out the new ISP and points that traffic to the new link. Pair that with SNAT/PAT so outbound flows appear to come from the new link’s public IP. Leave your existing 1:1 / port‑forward NAT rules for the static IPs on the original link unchanged.
  3. If you run your own router (Linux example), the technique is: add a route table for the second WAN and an ip rule that selects it by source network, e.g.
    ip route add default via NEW_GW dev eth1 table 200
ip rule add from 192.168.1.0/24 table 200
  4. Test: check “what is my IP” from inside, confirm inbound VPN works from outside, and simulate failover.

Notes and gotchas: asymmetric routing will break sessions if you do not SNAT outgoing traffic, so ensure egress is source‑NATed. Services that must keep the original public IP (VPN servers, inbound mail) must keep their NAT/forwarding on the T1. As noted, changing every desktop works but does not scale; as hinted, NAT/routing at the edge is the right place. If you need provider‑independent addressing or full redundancy later, consider BGP or professional assistance.

Recommended Answers

All 7 Replies

Member Avatar for skilly

my suggestion would be just add another gateway(new connection) and then add the new network to each computer.

i wouldn't even know how to combine 2 ISPs into one network, if that's what you're trying to, but i can think of a few ways that i'd like to try.

but i think 2 networks would be much simpler. just customize each machine for where/what it needs to do.

-edit upon further thought, you ARE probably trying to support one network with two internets.
and i'll keep thinking about it

Edited by skilly because: corrections
Member Avatar for troverman

i guess i'm totally at a loss here. Right now our network is like this...T1 comes in, Adtran modem splits off data and voice channels. Data comes over to our SonicWall TZ270 into the WAN port...the SonicWall then routes the data out of a LAN port, and then over to our main backbone gigabit switch, and then off to all the subswitches and workstations. I guess my question is, in keeping all this intact, is how to add the new Internet connection into the network? Does it plug into one of the other ports on the SonicWall? Do I need a separate router?

Member Avatar for lasitha2005d

Well that is not so hard if you use IAS or ISA and/or NAT Pool.
Without them its kinda complicated. Its all about default gateways however. If you are smart enough no additional setup needed to use 2 ISPs. Routers (recent) do support redundant ISP connections. You have to NLB using either routers or edge servers (from where the traffic go out). You van use Stonegate products (not sure whether they are available now). The easiest to use a router with wan ports (Cisco or similar).

Member Avatar for skilly

there is also the possibility of using a desktop as a router(internet connection sharing)if it has 2 adapters, and put a router(LAN only) in-between the existing modem and stonewall thing(or wherever)plug one adapter to the modem, other to the router, then bridge the adapters.

kinda silly, i know, but there's many ways

-edit-3 bridged adapters & no router?maybe?

Edited by skilly because: more
Member Avatar for troverman

I can't put dual adapters in our many workstations and bridge...

We can't save any money by not paying our current company for the static IP's...our monthly bill is the same. However, it does cost more to add static IP's to a second ISP.

Member Avatar for skilly

you only need one with 2 adapters. one adapter goes to same router as the rest of the workstations, the other adapter goes to new connection, bridge adapters, set-up ICS(sharing) on this one workstation to share new connection with the others.
i am over-simplifying on purpose.

Member Avatar for troverman

Oh, I see what you're saying now. Maybe that's a possibility.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.