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lz1dsb
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Traceroute and NAT

Fri Aug 15, 2014 9:34 pm

I've noticed the following phenomenon. When a static 1:1 NAT is configured on a MikroTik router (source and destination NAT), after I start a traceroute to the Global IP address that is being translated to a private Local IP address, I always see the last hop being doubled! it seems like the router responds once with the Global IP address, and than once again on the behalf of the internal private IP address.
It's noticeable though that when no NAT is present, the router responds first with it's own IP address on the interface where the traffic was received and than, the last hop replies.
The question is... is this expected behavior?
 
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Re: Traceroute and NAT

Fri Aug 15, 2014 11:36 pm

Yes is normal, not worry.
The first ip appear because the TTL end at the router,
The second is equal because the TTL end on the device BUT the device by nat has the same ip of the router...
I'm Italian, not English. Sorry for my imperfect grammar.
 
lz1dsb
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Re: Traceroute and NAT

Mon Aug 18, 2014 3:35 pm

Yes is normal, not worry.
The first ip appear because the TTL end at the router,
The second is equal because the TTL end on the device BUT the device by nat has the same ip of the router...
That explains it. But why than the Cisco IOS reacts in a different way in such a scenario? I've just tested it?
What is the "standard" way of reacting in such a scenario?

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