Weird ISP Routing

Posted on 2011-10-10
Last Modified: 2012-05-12
Hey Guys,

We are in the process of re-subnetting our network and have found that our internet traffic gets routed through a private network address. (A range that we potentially may use.) is our gateway and as you can see traffic goes through and which are devices owned by our ISP.

I find this very strange as our traffic gets routed from public to private then to public again, is this a routing config problem on those devices or is it normal behaviour ? and what does this mean if we use the as part of our internal subnet ?

Tracing route to over a maximum of 30 hops

  1     1 ms     2 ms     5 ms
  2     1 ms     1 ms     1 ms
  3    22 ms     3 ms     5 ms
  4     4 ms     5 ms     3 ms  88.211.4xx.xx1
  5     4 ms     4 ms     3 ms  88.211.4xx.xx2
  6     5 ms     5 ms     3 ms
  7     5 ms     5 ms     5 ms []
  8     5 ms     5 ms     5 ms []
  9     5 ms     5 ms     5 ms
 10     5 ms     5 ms     7 ms
 11    89 ms    83 ms    77 ms
 12   103 ms   125 ms    97 ms
 13   151 ms   149 ms   149 ms
 14   361 ms   246 ms   251 ms
 15   250 ms   249 ms   245 ms
 16   254 ms   249 ms   277 ms
 17   414 ms   340 ms   317 ms
 18   316 ms   317 ms   317 ms
 19   322 ms   318 ms   315 ms

Trace complete.
Question by:supportemea
    LVL 21

    Accepted Solution


    It is possible that your ISP uses private address, though this is commonly only seen in closed WAN networks (e.g. in MPLS networks).

    This doesn't need to be a problem, even if you use these adresses internally. You won't be able to ping these external routers any more if your route these addresses to your internal network. But traffic should flow without any problems.

    However to avoid confusion, you may want to avoid using these addresses yourself.
    LVL 5

    Assisted Solution

    Definately exclude them.  I would also check with the ISP to see what other ranges they use to make sure you don't end up with a config change on their end down the road creating an issue.

    As robocat mentioned it SHOULDN'T create an issue - as long as you're firewalled/NATed between your net and the ISP.  If your routers are able to see or retain any sort of route path showing the ISP subnet you could have issues though.

    At the very least, you don't want to be wondering later when trying to trace packets.

    Assisted Solution

    This is not a routing configuration issue since your ISP is using private IP address after your gateway

    You can happily use within your intranet until & unless you are not advertising it to ISP.
    LVL 6

    Assisted Solution

    What ISP does it at there end is not lookout of ours.

    Technically thinking ..if ur using same subnet when packet goes out from ur router ur private IP gets
    natted to public when remote peer replies back it responds to ur public IP and not private IP.

    So u need not worry ....

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