Redundant Internet and MPLS link

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Jul 10th, 2009
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Hello


I have two routers 3825 both having one Internet link and MPLS link from different subscribers as shown in the attachment. Site 1 consists of RTR A and RTR B . And site 2 consists of RTR A and RTR B . Now I want to have MPLS and Internet link both to work as redundant.


Now if suppose one MPLS link of site 1 (say MPLS A) goes down. How shall the Site 2 router B will came to know that it has to send the packets to MPLS B instead of MPLS A.


Thanks


Ritesh



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Giuseppe Larosa Fri, 07/10/2009 - 04:26
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Hello Ritesh,

you need to configure an IPSEC VPN over the Internet link to be able to use it as a backup link.


I suggest to use a point-to-point GRE tunnel protected by IPSec.

In this way you can even run a routing protocol over the GRE tunnel.


Different solutions are possible:

you can use GRE keepalives and static routes with object tracking for the backup routes.

With GRE you can use a routing protocol and I would use it.


by using eBGP on the MPLS link with the SP (if it is a L3 VPN service) each edge router prefers mpls path over the GRE tunnel if over the GRE tunnel you use a different routing protocol for example OSPF.

the eBGP routes will be preferred for their lower AD (20) when compared to OSPF (110).

All this when comparing two prefixes with same prefix length. most specific route is used regardless of AD.


Hope to help

Giuseppe


Mohamed Sobair Fri, 07/10/2009 - 04:51
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Hi,


Could you please elaborate on how is SITEA and SITEB is currently connected?


1- what I meant, How RouterA and RouterB on Site A is connected to Router A and Router B on Site B?


2- Do you have IBGP running between your edge routers?


3- Do you have CSC currently implemented?


HTH

Mohamed

riteshmalpani Fri, 07/10/2009 - 05:26
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Presently I have one MPLS and internet link on router A and router B of site A respectively .The same strutcure is there at Site B . Now as the demand grew, I am going to deploy redundant MPLS and internet link from different service provider other than present Service providers.


I need that every router of each site sholud have one MPLS and one internet link from different service provider and the other from different service provider.


Now I designed OSPF from firewall to Gateway routers and BGP between PE routers and my routers with routes redistributing.


Please let me know will this work or not. As I look when one MPLS link from one Service Provider is down how the other end router came to know that it has to send the traffic to different MPLS service provider. Because for the other end router the service provider 1 is not down.



BrinksArgentina Fri, 07/10/2009 - 09:45
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It will work. If RT-A MPLS goes wrong, the BGP peer will timeout and clear these routes from the routing table.


If you setup BGP correctly, RT-A will send inter-site traffic to RT-B and RT-B have a working link to the other site.



Guido.

Please rate all the helpful comments.

Mohamed Sobair Fri, 07/10/2009 - 10:43
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Hi Ritesh,


Here is the scenario:


1- For a single site redundancy, i would implement ebgp with both providers for the MPLS links and since you are dual homed with two service providers, running IBGP between your edge routers is sufficient.


As currently you only one best path for router A and router B to both MPLS providers, and even you can influence router A to take router Bs MPlS provider instead Of A. A failure ocuurs on the provider site A, Router A removes MPLS provider A from its routing table, forward the traffic to router B, router B already forwarding traffic to MPLS provider B , and vice versa.


2- If you want to have redundancy on two sites, then you should have full IBGP mesh between you routers on both sites or having Confederation deployed.


let me know if this answers your question,


Mohamed

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