Multiple Gateways on same subnet

[robmurphy]

I need to split the traffic from 24 SIP endpoints using G711A over multiple ADSL links.

G711A is used as at present G729 is not available on the SIP server used. The SIP server used cannot be changed.

At present the VoIP traffic goes over a leased line delivered over multiple copper pairs (in the UK this is called EFM), but I want a fall back so if that link goes down service to the customer can be restored.

The SIP endpoints are on a 192.168.x.x private network connected to the internet through NAT.

For a backup solution I have looked at:

A second leased line from the same provider as the first. This would likely suffer from the same problems, so is not really a backup.

A leased line over copper pairs from another provider. I have checked and the other providers cannot do leased line over copper pairs in the area so it would have to be over fibre, and this means the cost would be too high.

A backup connection using an ADSL WAN connection. The customer is quite far from the exchange so the DSL links will have limited up link bandwidth. To use ADSL there would have to be multiple (3 or 4) ADSL links

I am considering using the multiple ADSL WAN connections, but I will need to share the load across them simply. I need to get something workable in place ASAP. I was think of limiting the DHCP pool on each router to 8 IP addresses as each router should be able to handle that many phones. Each router would give its IP address as the default gateway in the when it sends a DHCP reply. I know at first there will be 3 routers replying to each DHCP request, but I know networks can cope with multiple DHCP servers

I have a few questions I would appreciate your views on.

Are there any problems with having multiple gateways on the same subnet?

Is it a workable idea to use DHCP as a simple form of load sharing?

Any ideas on how to use a router, or PC with at least 5 ports, to fail over automatically from the leased line to the 3 ADSL connections. The ADSL routers can be put in Bridge mode so the router is dealing with a single primary Ethernet link, and 3 secondary Ethernet links which would need to be load shared. As the traffic is SIP and RTP, the solution would need to avoid double NAT.

How do routers with multiple Ethernet connection detect the WAN link has failed? The physical link will still be up. The router does not have a remote endpoint it can setup a VPN to. It can ping the SIP server used, but this is owned and managed by a separate company so no changes can be made to it.

The ideal solution would be that the SIP endpoint keeps its IP address on the private network, and the router/PC just routes the traffic out over the ADSL links if the leased line fails. As the endpoints re-resister with the SIP server every few minutes the change in the public IP used for the connection picked up by the SIP when it gets the re-register message.

Thanks in advance for any help.

 

[spidey07]

This is exactly what Cisco's GLBP is for. Gateway Load Balancing Protocol. You even set it up to where it will track your WAN connections and remove itself from being a gateway for clients.

 

[Emulex]

why not just use a cheap dual/multi-wan router. pfsense can do this too if you want to use a powerful pentium-2 router from your scrap-pile.

 

[theevilsharpie]

Are there any problems with having multiple gateways on the same subnet?

Not really, although I don't think it's the best way to achieve what you want.

Is it a workable idea to use DHCP as a simple form of load sharing?

Unless you can specify the IP address of the gateway, probably not. Even if you could, it would be a very inefficient method of load balancing traffic.

Any ideas on how to use a router, or PC with at least 5 ports, to fail over automatically from the leased line to the 3 ADSL connections. The ADSL routers can be put in Bridge mode so the router is dealing with a single primary Ethernet link, and 3 secondary Ethernet links which would need to be load shared. As the traffic is SIP and RTP, the solution would need to avoid double NAT.

Most respectable business routers have the ability to load balance multiple WAN connections.

How do routers with multiple Ethernet connection detect the WAN link has failed? The physical link will still be up. The router does not have a remote endpoint it can setup a VPN to. It can ping the SIP server used, but this is owned and managed by a separate company so no changes can be made to it.

The router will have some sort of functionality to detect a dead gateway. The simplest method is to ping an address on the Internet (for DSL connections, I usually use the default gateway). If the router is unable unable to reach your defined destination using a particular interface, it will assume that the interface is down and fail over to another one. For your application, pinging the SIP server would be a nearly perfect method of detecting interface availability.

 

[Emulex]

dns lookup
http get /
ping
internet up/down
(combo of all of the above).


google xincom dual wan/edimaxusa dual wan/hotbrock dual wan (all the same). works great. you have to bind ssl connections to a specific router.

PFSENSE can do the same thing on a pc mind you.

 

[drebo]

A Cisco router with IP SLA can do it no problem. There are many ways to accomplish what you want.

 

[Emulex]

which cisco router for $150 or less will do dual WAN with more than ping and port checks?

 

[drebo]

One that will last a shit ton longer than some Korean-made piece of crap.

How much is downtime worth to your business?

 

[theevilsharpie]

which cisco router for $150 or less will do dual WAN with more than ping and port checks?

You won't get a real Cisco (as opposed to Cisco Small Business) firewall that can do dual WAN for $150 unless you buy used. Also, Cisco's product offerings for the low-end market are lacking compared to competitors. If you're that budget constrained, don't even think about Cisco.

If you budget is limited to $150, you're not going to find a whole lot. For about $300, you'll find some Cisco Small Business and Netgear ProSafe firewalls with dual-wan capability.