Hello Ana,

I took a very quick look in the traceroute code, see here:
ripe-atlas-probe-measurements.png
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@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
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