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RE: CARP and switches

The CARP multicast adresses have been defined to avoid conflict with other
vendor MAC address. Only the carp advertisements use multicast.
Read below:
A virtual router must use 00-00-5E-00-01-XX as its Media Access Control
(MAC) address. The last byte of the address (XX) is the Virtual Router
IDentifier (VRID), which is different for each virtual router in the
network. This address is used by only one physical router at a time, and is
the only way that other physical routers can identify the master router
within a virtual router. Physical routers acting as a virtual routers must
communicate within themselves using packets with multicast IP address and IP protocol number 112.
Benjamin Constant
TI Automotive 
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] 
> On Behalf Of Henning Brauer
> Sent: vendredi 30 septembre 2005 16:40
> To: [email protected]
> Subject: 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] BS Web 
> Services, http://bsws.de OpenBSD-based Webhosting, Mail 
> Services, Managed Servers, ...
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