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Re: CARP and switches



* Charles Sprickman <[email protected]> [2005-09-29 22:51]:
> The design seems to assume that one MAC address can 
> only exist on one port at a time, correct?
no, not at all. There have been so-called multicast MAC addresses from 
the stone age on, and that is what carp uses.
besides, switches work exactly the other way around. they have a list 
of mac addresses, and a list of ports associated with each. look for 
the broadcast mac address entries for example:
(output from an extreme networks switch, slightly obfuscated, lots of 
other addresses and other vlans cut)
swi010:2 # show fdb
Index              Mac              Vlan       Age  Flags Port List
-------------------------------------------------------------------
0f000-fdf: ff:ff:ff:ff:ff:ff    Default(0001)  0000 s m   CPU
0f020-fd9: ff:ff:ff:ff:ff:ff   somevlan(0003)  0000 s m   CPU,29, 49, 17, 45, 14, 25, 15, 13, 16, 23, 20, 26
0f030-fd7: ff:ff:ff:ff:ff:ff    another(0002)  0000 s m   CPU,28, 29, 49, 19, 39, 37, 24, 22, 21, 46
0f040-fdd: ff:ff:ff:ff:ff:ff yetanother(0005)  0000 s m   CPU,49, 38, 18, 48
0f050-fdb: ff:ff:ff:ff:ff:ff        foo(0004)  0000 s m   CPU,29, 49, 2, 12, 7, 8, 6, 9, 4, 5, 3, 1, 11
same goes for the switch's own MAC addresses, and - yes, multicast 
addrs.
-- 
Henning Brauer, [email protected], [email protected]
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