[c-nsp] wisdom of switchport block ...

Tarko Tikan tarko at lanparty.ee
Mon Feb 10 14:30:58 EST 2014


>      I am looking at tightening up my subscriber access network and, if
> I understand the documentation correctly, 'switchport block unicast'
> will prevent a cisco switch (3560g in this case) from flooding unicast
> frames out any port so configured, unless the destination mac address
> was learned from that port.

Blocking unknown unicast is very typical for access networks using 
service-vlans (or N:1, whatever you like to call it).

MAC aging and DHCP lease timers will have to be tuned accordingly, make 
sure DHCP < aging. This way DHCP renewals will keep active addresses in 
the MAC table.


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