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Help with 1811 Dual WAN With 2 LAN subnets and failover.

Thanks for any help in advance.

I have a Cisco 1811 with -ADVENTERPRISEK9-M), Version 12.4(24)T4. ( will use any version needed to get this working if this is possible)

I have 2 WAN connections a DSL with static IP’s and a Cable that is DHCP.

Server LAN at 10.10.10.X
Client LAN at 10.10.11.X
both are NAT

I would like to have 10.10.10.X route to DSL and fail over to the Cable if the DSL is down.

Then 10.10.11.X route to Cable and fail over to the DSL if the Cable is down.

I do not need or want load-balancing just failover.

I have been looking and testing many different ways to get this up and going but even with all of the documents on the web about failover and load-balancing I cannot seem to put something together that will work for me.

Willing to change the LAN if needed, It is a small LAN so would not be much of a problem just trying to find a solution that will work. So the Servers have the DSL to them self’s and all the users can use the Cable as they see fit. Then fail over so there is little to no down time.

I can offer a config but as I have never got it to work with both connections or any documents that seem to help with the config I would like to do I don’t think it would be much help.

At this point I feel I am doing something small that I am missing or it something that cannot be done.

Most the time when I have a config that seems to be working with both connections up all host have problems getting to the internet.

EX: If I ping from any host on the network I will get the following.
Windows XP CMD

Pinging with 32 bytes of data:

Request timed out.

Reply from Destination net unreachable.

Reply from bytes=32 time=17ms TTL=56

Request timed out.

Ping statistics for

    Packets: Sent = 4, Received = 2, Lost = 2 (50% loss),

Approximate round trip times in milli-seconds:

    Minimum = 17ms, Maximum = 17ms, Average = 8ms

New Member

Re: Help with 1811 Dual WAN With 2 LAN subnets and failover.

Without going too, deep into your network. There are a few router failover protocols that come to mind (HSRP & VRRP, plus GLBP). The protocols mentioned are designed for redundant routers not so, much redundant interfaces. But the HSRP would work just the same on the same router. You may want to first check with Cisco's IOS comparison chart to see if HSRP is in the version of IOS that you have.

And if so, lab it up first, then see if it works well in your environment. HSRP will allow your LAN Gateway address to be a single IP, so to your users they won't see much of a change. HSRP does consume a bit of memory, so check the specs of your router before implementing.

Let me know if this meshes with what you have and trying to accomplish.


Re: Help with 1811 Dual WAN With 2 LAN subnets and failover.


Please check the questions below:

- Do you receive a default route on c1811 from both providers?

- Where is the L3 (gateway) for your LAN subnets? On 1811 or you have some L3 structure in the LAN?

- Some config would be nice, especially how do you accomplish the NAT part

- On the connection with cable , do you have static or dynamic IP

Depending on your responses, this can be done or not. The idea is that if you have everything static (ip routing) and natted  then it's not so easy to achieve this.



Hall of Fame Super Gold

Re: Help with 1811 Dual WAN With 2 LAN subnets and failover.


I believe the original post was pretty clear about static and dynamic IP - "I have 2 WAN connections a DSL with static IP’s and a Cable that is DHCP." So setup is partly static and partly dynamic.

To the original poster

I am not clear what you have set up and rather than trying to figure out what you have I will suggest the approach that I would use if I were in your situation. You can see how close what you are doing comes to that and can decide if you want to adopt any of my suggestions. If so we can deal with questions of how they would work.

I would start by configuring routing so that there is a primary/preferred default route using the DSL connection. When I got that working as expected I would configure a backup route using a floating static route using the cable connection. The challenge in getting the failover to work is that the traditional floating static works when the primary route interface goes protocol down. But with DSL most of the time when the connection is not working the interface is still protocol up. So you may need to configure something like IP SLA to track reachability to the DSL provider network.

Once you have it working right for primary default route and dynamic failover then your requirements for the server LAN should be satisfied. To accomplish your requirements for the client LAN I would configure Policy Based Routing. In PBR you can take all traffic from the client LAN and set its next hop address to be the cable connection. And if the cable connection goes down (and you may need more IP SLA to do this) the PBR will just use the normal. default route. This should satisfy both of your requirements.



Re: Help with 1811 Dual WAN With 2 LAN subnets and failover.

Hello Richard.

 "I have 2 WAN connections a DSL with static IP’s and a Cable that is 

Maybe I wasn't clear enough, but my question was if the IP from the Cable provider is assigned static through DCHP or it's dynamic (e.g. every time you reset the cable modem the IP is changing). Anyway, that's not the biggest question here.

Regarding the other questions with PBR. I've never tested, but is this going to work if the gateway IP address of the client and server networks are on the WAN router? I was thinking of PBR solution, that's why I've asked where is the gateway. From what I remember if you have the LAN interface on the same router as the WAN one, you cannot apply PBR on the LAN interface forcing to select the next-hop from one of the WAN interfaces on the same routers. PBR is giving an error.

Giving the overall situation, your solution is excellent, considering that it's quite hard to achieve failover in a static (routing) environment.



Hall of Fame Super Gold

Re: Help with 1811 Dual WAN With 2 LAN subnets and failover.


I am not sure what you are remembering, but it is not an issue for PBR to have the LAN gateway address on the same router with the WAN interfaces. In fact I have configured that exact scenario for a customer where the LAN interface and both WAN intefaces were on the same router and it worked fine.

I agree with you that the biggest challenge in this is how to accomplish failover when routing uses static routes on Ethernet interfaces. And that is why my original suggestion was to get the basic routing and failover working before starting to do PBR.



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