Redundancy Question

Unanswered Question
May 5th, 2010

Here is the scenario:

- Single inbound T1 connection to my DC with two PRI's

- Network Gear = Router and Switch and a SPAM Filter

- Router locked up and brought down all of the inbound and outbound services with it

What woudl you suggest as a cost sufficient solution to allow outgoing and incoming traffic as well as PRI's to be brought up as well (although PRI's are not a major concern)

I was thinking the following:

- DSL connection in

- connect to switch create a separate VLAN port for that DSL

- add the all ports to the DSL VLAN

- some how failure over all traffic if possible from GW for the T1 Router to the DSL router

- This is if the T1 goes down, traffic will remain coming in or out

Is this this concept doable with minimum amount of programming and increasing the complexity of my environment? Can you have a floaing IP shared between the T1 router and the DSL router in more like a HSRP mode? If not, I will take any other considerations as long as they are cost efficient.

Thanks guys.

I have this problem too.
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spremkumar Thu, 05/06/2010 - 01:21


Can you revert back with the router/switch models being used or considered in this environment?

As far as i know you need to have a redundant mechanism to route the traffic via the backup adsl router when the link connected to the primary router is unavailable. Pls do correct me if my understanding is wrong.


stonnet72 Thu, 05/06/2010 - 08:56

I have an Extreme Network Switch and a Adtran Router. I would consider any product that offers a cost sufficeint solution. Your understanding is absolutely correct. I was thinking of swapping out the Extreme Network switch and using a L3 switch of some sort to route the traffic from the failed link to an ADSL. What do you think? Thanks for your help.

spremkumar Fri, 05/07/2010 - 01:50


There are multiple ways in doing this,

Possible case1 : connect both the link on a single router and configure simple static route to take care of fallback routing. when the primary is up the static default route takes care of routing via the primary and once its down the secondary static route will pass the traffic through the adsl line.

Possible case2 : Run a internal routing protocol within the devices (primary link router / switch / adsl link router) and inject default route in the routing protocol from the primary link router. configure a default static route in the primary link router so that it will advertise the default route to the switch when the link is up, when the link goes down it will stop announcing it. make sure you have one more default route with higher admin (than the routing protocol) you use pointing towards the adsl link router.This will take care of the redundancy. (Assumption : running OSPF as IGP)

Possible case3 : if you have or if your switch supports tracking facility, do track the remote end ip address of the primary link and attach the track to the default route pointing towards the primary link router. Also do make sure that you have one more static route with higher admin distance pointing towards the adsl line router.


stonnet72 Fri, 05/07/2010 - 07:34

I think that is a great idea! And it certainly solve the issue if the link from the ISP is down. However, what happens if the router goes down. So essentially what I want to do is the following:

- Router A = PLink (T1)

- Router B = SLink (ADSL)

- Switch

Traffic ---> Router A via Switch, if Router A dies, then Router B handles traffic via Switch. This failover should be seamless and transparent. So essentially, the switch will have to be smart enough to know that the advertised link from Router A is not available, then route traffic out to the ADSL. That is why I think you will some type of L3 switch that will be able to route traffic.

Am I wrong?


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