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Community Member

Dual WAN Config on Cisco 1812

Hello,

I've got a problem and I can't seem to solve it. I've got 2 SDSL connection and one VLAN and I am trying to Load Balance the 2 Eth WAN connections, connected to eth0 and eth1, for the vlan, or at least configure them to act in a fail-over kind of way.

First I tried to configure the router with 1 eth wan, 1 vlan and Dynamic NAT, Firewall, routing etc. Everything works perfectly!

Then I connected the second SDSL modem to eth1, configured it with an IP and subnet. Configured Dynamic NAT on the eth1 interface. Added a default route to the IP address of the second SDSL modem.

But When I add a second default route with a metric of 1 my internet goes down, well at least there is no internet on the vlan. When I change the metric to 2 internet returns.

The second thing is that I cant even reach the admin interface of the second SDSL modem, or ping it from vlan. But when I ping it from the SDM tools ping it does work.

I can't seem to find any clear answer on this issue so I really hope you can help me out!

Thanks.

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Community Member

Re: Dual WAN Config on Cisco 1812

Refer to the last few posts in this thread:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40.1ddc93ad

I linked to the 'configuring tracking for static routing' page, and gave a sample config. Also keep your eye open for special requirements since you are using a dial interface (will need to setup dial on demand).

as far as that nat issue, i have not tested it yet, but you will probably need two NAT statements. i.e.

ip nat inside source list 102 interface fast1 overload

and

ip nat inside source list 102 interface dialer0 overload

and dual route statements,

ip route 0.0.0.0 0.0.0.0 fastethernet1 (or your static gateway) 100

and

ip route 0.0.0.0 0.0.0.0 dialer0 150

(where 100 and 150 are distance metrics to determine preference)

give that a shot and let us know.

6 REPLIES
Community Member

Re: Dual WAN Config on Cisco 1812

I have went round and round with this on a 2801 with dual isp, both with DHCP assigned address, i have determined that the router looks at the first dynamic NAT statement and if it matches a good route and connection, it works. If you shut down the interface on the first NAT statment internet dies because the first NAT statment is all it looks at.

I have not found a solution to this either.

Community Member

Re: Dual WAN Config on Cisco 1812

any updates on this issue?

I am looking at a similar setup, configuring dual WAN links, and need info on setting up the NAT overload based on egress interface, especially when there are no static IPs, or static IPs on only one of the WAN links.

Community Member

Re: Dual WAN Config on Cisco 1812

Yes it can be done using a static IP on 1 of the interfaces. Dual Dhcp does not work as far as i can tell. To achieve this you use "tracking" to ping somewhere in the internet. When the tracking fails (on the primary interface) the route for the backup interface is installed. Tracking will continue to ping the primary interface and once it is restored the primary route will be reinstalled.

Community Member

Re: Dual WAN Config on Cisco 1812

Hello,

Thanks for the info, can you please specify about the commands it should require.

I'm also having similar issue with 1811 router

We have DSL on eth1 with static ip address and backup interface as dialer 1

The NAT doesn't seems to be working.

When we have IP NAT inside source list 102 interface fastethernet1 overload

wherein access-list 102 has local ip address of 192.168.1.0

If the fastether1 link goes down the NAT translation fails for interface Dialer1

If we manually change the interface from Fastethernet1 to dialer1 in IP NAT inside source then it works.

I think we need to define the dynamic NAT and somehow I'm not able to do it.

Any help is greatly appriciated.

Thanks,

Community Member

Re: Dual WAN Config on Cisco 1812

You need to setup tracking on the on the prmary interface and than when the primary fails, have a differnet default route installed. I recommend searching on the cisco website for tracking. They describe in detail how to set it up.

Community Member

Re: Dual WAN Config on Cisco 1812

Refer to the last few posts in this thread:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40.1ddc93ad

I linked to the 'configuring tracking for static routing' page, and gave a sample config. Also keep your eye open for special requirements since you are using a dial interface (will need to setup dial on demand).

as far as that nat issue, i have not tested it yet, but you will probably need two NAT statements. i.e.

ip nat inside source list 102 interface fast1 overload

and

ip nat inside source list 102 interface dialer0 overload

and dual route statements,

ip route 0.0.0.0 0.0.0.0 fastethernet1 (or your static gateway) 100

and

ip route 0.0.0.0 0.0.0.0 dialer0 150

(where 100 and 150 are distance metrics to determine preference)

give that a shot and let us know.

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