----- On Jun 22, 2020, at 10:21 PM, Saku Ytti saku@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