877 default route using track command

[chepeake78]

Hi there,

I have an 877 router which has a DSL WAN interface. The DSL service at this site is unreliable, so the company have purchased a separate 3G router to be used as a backup. This device maintains 3G connectivity at all times and has a static IP on the internal subnet (for arguments sake let's say 10.0.0.253).

What I want to do with the Cisco router is to track the DSL interface and if it is up, install a default route pointing to it. If it is down, I want the default route to be the 3G router.

I am thinking the best way to do this is to set up a track and then set 2 default routes; one which is installed if the tracking is up, the other has a higher admin distance and points to the 3G router and thus should only be used if the track is down. For example:

track 10 interface Dialer0 ip routing

delay down 30 up 30

ip route 0.0.0.0 0.0.0.0 Dialer0 track 10

ip route 0.0.0.0 0.0.0.0 10.0.0.253 100

Is this likely to work or is there a better way to do it?

Thanks in advance

[Bilal Nawaz · Accepted solution]

Hello, this configuration will work in your scenario. No further config required as far as I know.
This will track the interface as well as up up state and if it has a IP address.

If it fails it will switch over to your backup route which has a higher metric.

If you want faster switch over time you might want to tweak the delays?

Apart from this, all good :)

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[johnlloyd_13]

Hi,

I'm not sure about this and seems the config is incomplete. We usually setup our backup links using an IP SLA probe.


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[chepeake78]

Hi

Thanks for you reply. I think the IP SLA only is needed if I was trying to do a ping or http operation or something like that to verify connectivity. I have used this in the past like below to divert traffic one way or another based on next hop availability, but never on a WAN interface or with DSL.

track 10 ip sla 10

delay down 10 up 30

ip sla 10

icmp-echo 10.10.10.10

threshold 1000

timeout 1000

frequency 1

ip sla schedule 10 life forever start-time now

route-map example_route_map permit 10

match ip address example_access_list

set ip next-hop verify-availability 10.10.10.10 10 track 10

As the track command has the DSL option I don't think I need the IP SLA. I'm happy to be corrected though!!

[chepeake78]

Thanks, glad to know I'm on the right track!

[paulstone80]

Hi,

Another option would be to run HSRP between the two routers and track the status of the Dialer0 interface. If the interface goes down then decrement the HSRP priority on the DSL router so that the 3G router takes over as the default gateway.

HTH

Paul


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[chepeake78]

Thanks Paul. I forgt mention that the 3G router is not a Cisco router unfortunately and doesn't have HSRP support, or anything like it. If it were a Cisco router that would be really good though!

Cheers

Ché

[paulstone80]

No worries

Depending on the model it may support VRRP, which is a non-proprietary alternative to HSRP. Cisco routers support VRRP as well, so the same can solution can be applied using VRRP instead.

HTH

Paul



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