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amitabha
18 posts
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I have encountered a question that, in any MPLS central services VPN scenario if 2 customers are advertising same network prefixes (overlapping) and want to access a central vrf then what will happen. Will the return traffic knows where to forward packets??Some people say that if the RD is unique(per VPN and per PE) then it can not be a problem. I'm little confused ....what actually will happen and how? Can any one help?? |
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bluepackets
13 posts
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The RD serves to make customer routes unique, which obviously allows for overlapping address space. This is still a problem for a central service VPN though, because nothing in traffic sourced from one of the customer VPNs indicates which VPN it actually came from. Additionally, even if it did (you could get creative with DSCP values to pull this off if you weren't using them for actual QoS, but you'd be limited in how many customers you could indicate), IP is connectionless, so return traffic, or even just traffic sourced from the central services VPN to a customer VPN, would not know which customer VPN it is supposed to go to. So quite simply, in this case, no, there is no way to know where to forward return traffic. |
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blgrnboy
11 posts
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Unfortunately, as bluepackets stated, it is not possible. It is possible with some "workarounds" such as NATing those IPs to somewhere else so that they are unique. For example: CustA - 10.0.0.0/24 NATed to either a unique interface using overload, OR natting to a pool of IP address that are in a unique range, such as 10.0.0.0/24 NATed to 10.1.0.0/24. Obviously, if you are a service provider for example that would like to monitor something on the customer network, you'd have to create static entries, such that for example: 10.0.0.5 ALWAYS gets NATed to 10.1.0.5 - this way it is unique. In conclusion - it would be best to work with the customer to get them to change their addressing in such a way, that is it unique, however, if you are unable to do so, NATing can help the situation, although it does bloat the config. |
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mwijay
33 posts
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Why not use Route Targets? It distinguishes which customers should take and know about which routes. |
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