Is there any data on packet duplication?

Sabri Berisha sabri at cluecentral.net
Tue Jun 23 06:14:45 UTC 2020


----- On Jun 22, 2020, at 10:21 PM, Saku Ytti saku at ytti.fi wrote:

Hi,

> Metro: S1-S2-S3-S1
> PE1: S1
> PE2: S2
> Customer: S3
> STP blocking: ANY
> 
> S3 sends frame, it is unknown unicast flooded, S1+S2 both get it
> (regardless of which metro port blocks), which will send it via PE to
> Internet.
> 
> STP doesn't help, at all. Hope this helps.

Yeah, except that unless you use static ARP entries, I can't come up
with a plausible scenario in which this would happen for NTP. Assuming
we're talking about a non-local NTP server, S3 will not send an NTP
packet without first sending an ARP. Yes, your ARP will be flooded, 
but your NTP packet won't be transmitted until there is an ARP reply.
By that time MACs have been learned, and the NTP packet will not be
considered BUM traffic, right? 

That said, I have seen packet duplication in L2 onlu networks that
I've worked on myself, but that was because I disregarded a lot of
rules from the imaginary networking handbook.

Thanks,

Sabri


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