One MPLS link and 2 WAN routers in the DC, How to make redundancy

[ATHULRAJVV4093]

I want to make redundancy in my company DC. Existing design was like this,

Access Switch >> Core Switch >> Core Router >> ISP

No redundancy , single point of failure.

So we, planned to stack 2 core switches, and 2 Core router instead of one. But the thing is only one MPLS link is terminated in DC . Is redundancy is possible with 1 MPLS and 2 Core Routers??

Please give your suggestions..

[Seb Rupik]

Hi there,

You could tweak your design slightly:

* Make the L2 switch at the top of your network a 2 switch stack. Connect each router to a different stack member. Talk to your ISP and determine how the router is configured. Can it/ does it use SVIs/ BVIs which would allow you to connect separate to Layer2 links to the L2 switch in your topology. This would place one of the links in an STP blocking state, but give you resiliency in case of a switch failure in your L2 stack. Or perhaps your ISP router supports port-channels, in which case connect a member link from each stack member and bundle them together in a port-channel. This would   give redundancy and increased bandwidth.

cheers,

Seb.

[ATHULRAJVV4093]

Thanks for your quick reply.

Only one link is coming from ISP side and its running on BGP . Is two dedicated link is required for redundancy. or its possible to achieve redundancy with two routers with the help of a switch. If yes with one link, what will be the configuration look like?

[Seb Rupik · Accepted solution]

Are your peering with the ISP router using BGP or simply using static default routes towards it?

If you need to peer via BGP then you may as well scrap the L2 switch and connect the two routers via L3 links and peer each via BGP. You will then need to create a L3 link between the your two routers and peer them via iBGP.

If you are using static default routes, then you will need to ensure that there is enough space in the subnet between you and the ISP routers to create a HSRP setup between your routers.

Either topology will give you the best possible redundancy but still leave you with a single point of failure in the ISP router.

cheers,

Seb.

[ATHULRAJVV4093]

now its fine,

I spent so much time  to find the solution. Now its clear what to do

2 routers and 1 MPLS running in BGP and a switch between CE and PE ,

It doesn't make sense right?

Two dedicated MPLS link and Two routers is the best way to form redundancy right?

Correct me if i am wrong.

[Seb Rupik]

Unless you have a physical port limitation on the PE router or need to run a FHRP between your two CE routers then adding a Layer2 switch is unnecessary.

Two CE routers connected to one PE router is acceptable. Two CE to PE pairs will provide the best redundancy but with increased cost.

cheers

Seb.

[ATHULRAJVV4093]

Please clarify.

The redundancy is possible with the above set up

1 MPLS running in BGP and 2 Core Routers with the help of switch.

Please suggest me a better solution for this.

Thanks and Regards

Athul

[Seb Rupik]

If you are going to peer both CE routers to the PE then you only need the L2 switch if the CE router has one available physical port. It would be preferential to connect the PE to both CE routers directly therefore removing the need for the switch:

                             ^
                             |
                             |
                             |
                       +----------+
                       |          |
            +----------+   PE1    +--------+
            |          +----------+        |
            |                              |
       eBGP |                              |
            |                              | eBGP
            |                              |
            |                              |
            |                              |
            |                              |
       +---------+       iBGP         +---------+
       |         |                    |         |
       | CE1     +--------------------+   CE2   |
       |         |                    |         |
       +---------+                    +---------+

cheers,

Seb.

[ATHULRAJVV4093]

Hello Seb,

Please open the attached image. If its wrong network design or not

Thanks & Regards,

Athul

[Seb Rupik]

The topology will work well.

The only way to improve it would depend on the PE router supporting the creation of a port-channel to the L2 switch. In which case create a two switch stack and connect the Po member links and CE connections across the stack.

+----------+
|          |          +------------+        Po1
| CE1      +----------+  L2|sw1    +-------------------+
|          |          +------------+                   |
+----+-----+               |                  +--------+------+
     |                     |stack             |     PE1       |
     |                     |                  |               |
+----+-----+               |                  +--------+------+
|          |          +------------+                   |
|  CE2     +----------+  L2|sw2    +-------------------+
|          |          +------------+        Po1
+----------+

This way you could suffer a partial failure of the L2 switch.

cheers,

Seb.

[ATHULRAJVV4093]

Hi Seb

But the thing is only 1 MPLS link is coming not 2.

[Seb Rupik]

In which case you would gain nothing from having a switch stack. Stick with your design of a single L2 switch.