New MPLS connection

[chadm1993]

First off let me say that I'm not a network engineer, network admin or anything like that.  I have a company that is in a dilema.  The customer has 3 locations connected with broadband radios.  There was a large storm that moved thru this past spring and knocked out a bunch of equipment throughout the area.  There are other broadband providers in the area and after repairing the equipment the customers broadband service appears to have interference with other providers in the area.  It would be nice if the providers in the area would play nice but that's not the case.  The company has ordered a MPLS circuit for the communication between two of the branches.  Here's the way the network was setup.

Branch A and Branch B connected via Radio

Branch A and Branch C connected via Radio

Branch B and Branch C connected via Radio

If a radio link goes down the connection backhauls thru the branch that's up to get to the third branch.  The backhaul connection speed is slower but it functions.  Each branch is on the same subnet and the network provider (guessing) has configured the radios as a bridge.  The MPLS connection has been installed between Branch A and Branch B and is ready to turn up but here's the million dollar question.  Do we need to have the network provider change the network to create a new subnet for each location or is there a way to have them configure the router to accomodate the current setup?  If it stays the same I'm not sure how the traffic is routed at Branch A to retrieve data from Branch B and for it to be routed thru the MPLS connection instead of the radio backhaul link.  ???  The only thing I can think of is to reconfigure the entire network to create a new subnet at each location.  I know it takes more brains to figure this out than I have.  I apologize for the klunky explanation but it's the best I can do to describe it.  Again......  Not a network guy.

Thanks!

Chad

[nkarpysh]

Hi Chad,

Can you please clarify few things.

• are you ordering MPLS from same provider?
  
• are you planning to connect to provider MPLS through the same interface you have now for radio or they bring you new link for it?
  
• Do you also want to use btoh radio and MPLS infuture? Or only one of those?
  
• If you want to use both - do you want to load-balance traffic between those or use on as primary and other as backup?
  

Nik

[chadm1993]

Nik,

I apologize for the delay. 

The MPLS circuit has been ordered from AT&T which is not the current network provider.  The MPLS circuit will be delivered to replace the radio link since the radios do not work between Branch A and Branch B.  I guess I should have considered saying their network administrators instead of network provider in the above post.  In the future the new MPLS connection will be the only connection between the locations.  They will not keep both and load balance the traffic.

Thanks!

Chad

[nkarpysh]

Thanks Chad,

SO you will have A---- MPLS --- B ---- radio---C----radio---- A

So you just replacing one radio between A and B with MPLS. In this case no subnet change is needed.

E.G. on site A:

Currently you have particular ip routes pointing to single provider which is then passing it either to B or C based on subnet.

Once you will replace the radia between A and B with MPLS or you will need to do is to check the default route to radio-provider. And change it that way to have only C networks to be sent to it. For B networks you will have new router pointing to AT&T. Then AT&T will do its MPLS magic receieving thos traffic from you and switch it through their network to site B.

Similar default routing change should be done on B site. C site remains unchanged.

If you have dynamic routing - then it even more simple. If you ask ATT can advertise your dynamic routing between sites A and B redistributing it to BGP, so no default routes would be needed. But I guess safer it would be just to have clear default route for each subnet to particular provider not to get routing tables from provider.

Hope it helps.

Nik

[chadm1993]

Ok.  We will turn the circuit up and see how it goes.  Let's say all workstations within the company use 192.168.100.0/24.  So regardless of the location we should still be good.  Just assign the IP address to the LAN interface on the router and it should work as before....  Provided the routing tables are set or they use dynamic routing.

Thanks!

Chad

[Jon Marshall]

Chad

Just to clarify because i may be misunderstanding.

You say there is a common subnet between each branch. If so then MPLS may or may not work depending on what you have ordered.

If it standard L3 MPLS then it won't work as far as i can see because A and B will be expected to be on different subnets and you route over the MPLS network between A & B. But you won't be able to do that if A & B are using the same subnet.

If you ordered a VPLS solution from ATT which is a L2 MPLS solution then yes you can use a common subnet at A & B.

Jon

[chadm1993]

Jon,

You are correct.  There's a common subnet between each location.  My initial response to the company was that they will more than likely have to create a new subnet for each location.  The circuit has been ordered and installed.  They are ready to turn it up.  Before I go dealing with ATT I wanted to be sure I completely understood the task at hand before starting on it.  Unfortunately I'm a third party and I'm coming in kind of late in the game.  Just trying to be resourceful for the company.  So based on the response my options to discuss with them will be to change the order to a VPLS network or they will need to create a subnet for each location.  Or at a minimum a new subnet at either location A or B.

Thanks!

Chad

[Jon Marshall]

Chad

Yes, either you need to have different subnets at Branch A & B and use a L3 MPLS solution or if you want to keep both sites A & B on the same subnet then you need a L2 solution. VPLS is a L2 solution.

It would be worth having a chat to ATT as the costings/options may well be different.

Jon

[nkarpysh]

Jon is correct. That is smth I miss-understood giving my answer. If subnet is same acrosss all 3 sites then VPLS should be used if the intent to keep it.

Other thing is, becuase the ip addresses are still uniques across all sites, NAT can be used as workaround on MPLS CE routers. So CE router on A site will receive packet with destination C and B. It will send traffic to C though L1 radio based on the ARP it got from side C. Other IPs (I guess we can define which belong to site B) statically mapped to another network and routeed to MPLS. But that would definitely harden the administration and based on your particular design may work or not thus I would count on it as kind of exception.

Nik,