I need some serious help with a complex routing setup I am doing.

Lets I have a /24 IPv4 .I am announcing the same /24 at two different locations. One is a ISP exchange center where all the ISPs peer each other locally.To make it simple just understand that this network does not has internet connectivity but yes the /24 is being publicly announced.So except the users on ISPs peering each other cant connect through this pool.Lets say this is NETWORK A.Lets call the server on NETWORK A be ALPHA.

Now I am announcing this same /24 at server outside the above network.The routes are announced on internet so every user on internet is connecting to me through this server.Lets say this is NETWORK B and Server on this network is BITA.Now I am routing all this traffic through a GRE Tunnel to the APHA Server located in my above network.Keep in mind, as I stated the users on the NETWORK A would be connecting directly to my APLHA Server in NETWORK A as due to short routes defined. My basic aim is to route all the traffic to the server in NETWORK A.Now this happens :-

A user connected on NETWORK A connects me through NETWORK A.He has no issues with connectivity. Now we have NETWORK B on other side.Let me tell you NETWORK B is routing traffic to server in NETWORK A through a GRE Tunnel.Now traffic is being forwarded to a IP which is Internet Enabled in the server.So in the server there are two lines NETWORK A connection line and Internet Line.Its receiving traffic of NETWORK B through GRE Tunnel through this Internet Line.So we have this scenario here :-

NETWORK A Users - NETWORK A - APLHA SERVER NETWORK B Users - Server Routing Traffic Through GRE Tunnel - Internet Line - APLHA SERVER

Now there is no problem with NETWORK A Users.I need to learn that once i receive the routed traffic coming from GRE how to connect it with traffic of NETWORK A.Like combining two networks through a single gateway and then sending it to the server or what should I do ? Also i need that the TCP or UDP Packet coming from NETWORK B should go back through GRE Tunnel back to NETWORK B Network and then return the packets from there so I need this thing to be done exactly.

Lets say I have a /24 - 103.XX.XX.XX

/24 103.XX.XX.XX is being announced at NETWORK A

USER SENDS TCP/UDP Packet to 103.XX.XX.12:27015 - NETWORK A - APLHA Server - Packet back to NETWORK A - USER

/24 103.XX.XX.XX is being announced at NETWORK B ( Same /24 of NETWORK A)


Please help me with this.This looks really complex but it reading it once or twice will make it more clear.Also i need help step by step as I am not very well versed with Networking.Also I need to do this complex setup and cant avoid it.If i need to be more clear let me know.Let me know if i need to setup a gateway or router in between or whatever.I have added a very basic small picture of what I want and i am not a expert and dont know perfect symbols so just a basic paint picture.Thanks for helping :)

I cannot post images so here is the link - http://s2.postimg.org/abr4idx6x/Solution.png

Let me know if its not allowed here.

  • 1
    You are mixing the terms, like pool, network and prefix - these are totally different entities. Sentences like network is announcing are total nonsense in general. Plus, your post is overwhelmed with words, thus its extremely hardly to understand it. One decent scheme, even in paint would do way more that the entire post. Don't forget to mention what protocol your routers are announcing your prefixes with.
    – drookie
    Feb 4 '15 at 16:45
  • Done as requested.Please help me if you can now. Feb 4 '15 at 17:36
  • Do I understand your scheme correctly ? tech.hq.norma.perm.ru/files/scheme.png If yes - are the network prefixes behind alpha and beta actually identical ? Like and ? If they are - WHY ?
    – drookie
    Feb 4 '15 at 18:35
  • Yes you are correct the scheme is right and both /24 are same.This is because I need some specific ISPs to connect to me directly and rest other via the network B.Actually NETWORK A is a Internet Exchange Point in my country through which just domestic traffic of the country is routed and no international traffic can enter in this network.Its sort of a complex setup. Feb 5 '15 at 1:58

From what I understand you are trying to build an anycast scheme, and then you are experiencing problems with network connectivity. Well, prior to create complex things you should really understand the simple ones. There's muptiple ways to ensure connectivity won't be lost, some of these that come to my mind are:

  • Use RFC 1918 addressing in A and B as the primary adressing, add public LAN as aliases, use gre tunnel as the connectivity bridge between A and B.
  • Use public WAN addressing in a and B, but use unique addressing. Then add anycast addressing as aliases. This way you don't need the gre tunnel.

The root cause of your problems is that, according to my scheme, you really don't have a network connectivity between subnets.

  • I did not get what you explained me but I am doing this.I would be creating a GRE Tunnel between Network A and Network B.With the help of static routing I will route the traffic for particular destination IP through this GRE Tunnel. Feb 8 '15 at 11:38

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