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Last 3 hops of a traceroute are the exact same address, why?

Posted on 2011-02-21
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Last Modified: 2013-11-13
If I do a traceroute from my office to one of my customer locations it finishes fine, but the last three hops are the exact same public IP.  This public IP is NAT'ed to a Server on the network.   Does it show up three times because thats the amount of hops from the firewall to the server? I have a complete cisco infrastucture.  Below is my traceroute:  See the last three hops:

C:\>tracert xx.124.54

Tracing route to x.x.124.54 over a maximum of 30 hops

  1     1 ms    <1 ms    <1 ms  10.0.0.2
  2     1 ms     1 ms     1 ms  hx.x.x.74.static.ip.windstream.net [x.x.x.129]
  3    25 ms    23 ms     2 ms  hx.x.x.66.static.ip.windstream.net [x.x.x.129]
  4    36 ms     2 ms     2 ms  hx.x.x.x.66.static.ip.windstream.net [x.x.x.113]
  5    19 ms    26 ms     3 ms  hx.x.x.173.static.ip.windstream.net [173.189.232.113]
  6    72 ms    34 ms    29 ms  h19.236.109.66.static.ip.windstream.net [66.109.236.19]
  7    30 ms    49 ms    53 ms  h96.254.213.151.static.ip.windstream.net [151.213.254.96]
  8    53 ms    53 ms    54 ms  h11.254.213.151.static.ip.windstream.net [151.213.254.11]
  9    47 ms    47 ms    51 ms  h13.254.213.151.static.ip.windstream.net [151.213.254.13]
 10    74 ms    88 ms    56 ms  ip65-47-204-81.z204-47-65.customer.algx.net [65.47.204.81]
 11    60 ms    70 ms    89 ms  207.88.14.238.ptr.us.xo.net [207.88.14.238]
 12    88 ms   105 ms    81 ms  vb24.rar3.washington-dc.us.xo.net [207.88.12.34]
 13    91 ms    68 ms    86 ms  ae0d0.mcr1.philadelphia-pa.us.xo.net [216.156.0.42]
 14    62 ms    63 ms   103 ms  ae1d0.mcr2.philadelphia-pa.us.xo.net [216.156.1.22]
 15    75 ms   100 ms   103 ms  x.x.8.158.ptr.us.xo.net [x.x.8.158]
 16    72 ms    82 ms   110 ms  ipx-47-x-x.z113-x-65.customer.algx.net [x.x.x.118]
 17    80 ms   108 ms   108 ms  x.x.124.54
 18    88 ms   101 ms   107 ms  x.x.124.54
 19    78 ms    96 ms    103 ms  x.x.124.54

Trace complete.
You will see that the last three hops are the exact same IP.  This IP is the public address of a Server I have Nat'ed.  I'm just looking for an explanation of why the last 3 hops are the same IP.  Thanks.

 

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Question by:denver218
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by:woolnoir
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Check the routing on the box which is natting, it may be that its bouncing between interfaces.
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by:denver218
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I have a Cisco ASA5510 doing the natting.  I have one route outside statement that goes to my router that connects to the ISP.  I also have route inside statements for my internal networks.  
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by:woolnoir
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That explains it then, its just that the route the packets are taking are being natted to the external interface address if your NAT box.. nothing to worry about.
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by:denver218
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Can you explain a little further, I'm still not completely sure why the last three hops are the same IP address.  Thanks.
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woolnoir earned 250 total points
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I'd imagine you have 3 interfaces involved

the external one (which has the IP being reported)
The internal one (which is probably being natted to the external ip, so the tracert is reporting that IP)
finally, the server itself which is configured specifically by your natting to be translated to the external IP.

Essentially each hope being reported by the traceroute is having its address reported, or translated to the external address.
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by:rfc1180
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You are seeing the same IP address as all the return echo replies are being translated due to the overload of the outside interface.

You might have something like.

ASA(config)# global (outside) 1 interface
ASA(config)# nat (inside) 1 0.0.0.0 0.0.0.0

Each router that is sending the ICMP Echo-Reply is being natted:

Hop 17 (ASA)
Hop 18 (possible an ISA, Router, additional Firewall)
Hop 19 (Server)

Billy
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by:denver218
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OK, so this is normal and nothing to worry about right?  
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by:rfc1180
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Normal is no need to worry.

Billy
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by:woolnoir
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Yep its fine.. no need to worry
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by:denver218
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Thanks
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