[atlas] Duplicate packet detection in traceroute results

Hello Ana,

I took a very quick look in the traceroute code, see here:
https://github.com/RIPE-NCC/ripe-atlas-probe-measurements/blob/7c03fba082e93b7a1f0f14cc3769bb31e83909e3/eperd/traceroute.c
ripe-atlas-probe-measurements/traceroute.c at 7c03fba082e93b7a1f0f14cc3769bb31e83909e3 · RIPE-NCC/ripe-atlas-probe-measurements
github.com

It seems that a sequence number in the traceroute packet is used. If this sequence number is received back it’s marked as ‘response received’. If another response is received within a certain timeframe, it’s tagged as a duplicate. Otherwise its a late packet.

Hope it helps.

Cheers,

Michel

> On 20 Jan 2023, at 11:38, Ana Custura <ana at erg.abdn.ac.uk> wrote:
> 
> Hi everyone,
> 
> Just a question on how Atlas detects duplicate ('dup') packets in a traceroute.
> 
> Is the 'dup' field added to a result when two received packets are exactly the same, regardless of whether they were received for a different initial TTL? 
> 
> Or are any packets that were unexpectedly received for a specific TTL marked as duplicates (e.g. if you receive 6 replies from 2 different IP addresses to the 3 initial packets sent with TTL 1, will 3 of these replies be marked as duplicates)?
> 
> Thanks for your help!
> 
> Regards,
> Ana
> -- 
> ripe-atlas mailing list
> ripe-atlas at ripe.net
> https://mailman.ripe.net/

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