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New Member

two DSL links redundancy/load balancing


2811 ---- DSL 1 ----- ISP

|------- DSL 2 ----- ISP

I only have two static default routes

configured on the 2811.

How can I achieve automatic redundancy/load balancing ?


Re: two DSL links redundancy/load balancing


As long as the two static routes have the same administrative distance (which is the default behaviour), the router will automatically load-balance over the two DSL lines.

The type of load balancing depends on the type of switching configured;

For process-switching—load balancing is on a per-packet basis

For fast-switching—load balancing is on a per-destination basis

For CEF-switching—load balancing is on a per-destination or a per-packet basis.

Use 'ip cef' to enable CEF which will result in per-destination load-balancing by default.

To achieve redundancy, ensure that the static routes do go down when the interface goes down. You might want to point the static route to the interface instead of the next-hop IP address in order to achieve this.

The following link has a bit more info on load-balancing:

Hope that helps - pls rate the post if it does.




Re: two DSL links redundancy/load balancing

Hi again,

Just an addition to my last post.

An example of how you could configure 2 equal static default routes is:

ip route atm0.32

ip route atm1.32

In this case, two static default routes will be entered into the routing table. Load-balancing will happen by default over these two interfaces. If one of the interfaces goes dow, all traffic will switch to the remaining traffic.

The other thing you should do is to enable OAM PVC mgmt on the PVCs as such:

int atm1/0.32 point-to-point

ip address ....

pvc 1/32

oam-pvc manage

Hope that helps,


New Member

Re: two DSL links redundancy/load balancing


the ISP provides the DSL modem and the interface is

ethernet already. So i interface with the DSL via ethernet. Problem with floating static routes for redundancy with my setup is that the ethernet interface will never go down since its always connected to the switch.

I was looking at OER but documentation and sample configs are scarce.


Re: two DSL links redundancy/load balancing


I reckon what you need to use is the following feature: Reliable Static Routing Backup Using Object Tracking.

The feature is described at:

Essentially, this feature intalls static routes depending on the status of a tracked object, such as a route etc.

Hope that helps,


Re: two DSL links redundancy/load balancing


the solution depends on the exact setup of the 2811 in this scenario.

I am assuming that you have PPPoE in place configured through two dialer interfaces and NAT overload for both?

If this is the case there are some obstacles to be aware of. If you do NAT then you have to make sure that all packets of a session flow through the same interface. Otherwise the packets arrive at the internet destination with different source IPs, which will not work (or be very slow).

So the first obstacle is to make sure that per destination load sharing occurs. As already posted earlier CEF or fast switching will do that for you outgoing. the return traffic follows your official IP and is this way taken care of.

Still you can choose to have a more random distribution of sessions to the two DSL through "pure" IP routing with two default routes. Or you prefer sorting of applications to the two DSL lines through policy based routing (PBR). In the latter case set the outgoing interface in the route-map, which falls back to normal IP routing (default route in place), when the interface specified goes down.

The other obstacle is redundancy. You need to detect that one internet connection is down to redirect the traffic to the remaining one. In case PPP is terminated on the 2811 this should be straight forward, as the dialer goes down in case there is no PPP keepalives are received any more (correct me in case your setup does not deliver this).

Did this help? Then rate the post please.