This is how many MAC addresses the switch can hold in its cache
DUCK
----- Original Message -----
From: Howard C. Berkowitz <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, July 24, 2000 3:25 PM
Subject: Re: MAC Addresses
> >What does it mean to say that the Catalyst 1912 has 1024 MAC Addresses,
> >while the Catalyst 2828 has 8192 MAC Addresses.
> >Can anyone please explain?
> >Thanks in advance.
> >Reply to,
> >[EMAIL PROTECTED]
> >
>
> You touch on what is an interesting problem in product design, which
> shows why products differentiate.
>
> Specifically, this refers to the size of the MAC address lookup table
> on the bridge. It doesn't mean that there can only be 1024 or 8192
> MAC addresses defined, only that many that the switch will handle
> quickly by knowing immediately whether to block or forward the frame.
>
> Cisco and Bay(Nortel) have taken different approaches to MAC tables.
> Neither one is best under all circumstances. Cisco defines a table
> for the entire switch, which is used by all broadcast domains.
> Nortel defines a separate 1K table to each port.
>
> Let's say you are brought in to fix a horribly performing campus
> network that has 1000 active hosts in a broadcast domain. Fits easily
> into 1K. In a calm, rational way, you split that single domain into
> four subnets. 250 each. No problem.
>
> But each subnet then goes through 20% growth, giving 300 hosts per
> domain. Weird and unpredictable performance starts occurring, as the
> four subnets compete for slots in the cache. In this case, if you
> know the subnets will individually have no more than 1K MAC
> addresses, the guaranteed 1K of the Bay switch is much more
> predictable. Do you have a sane, managed policy about growth? To
> coin a phrase, It Depends.
>
> Return to the problem of a horribly performing campus network, but
> assume this time that it has 4000 hosts -- quite possible with FDDI.
> Connect a Bay switch to this, and it will be in immediate trouble. So
> will a Cat 1912. But a 2828 will handle the total number of hosts in
> a reasonably predictable manner.
>
> "What Problem are you trying to solve?"
> ***send Cisco questions to the list, so all can benefit -- not
> directly to me***
>
> Howard C. Berkowitz [EMAIL PROTECTED]
> Technical Director, CertificationZone.com
> Senior Product Manager, Carrier Packet Solutions, NortelNetworks (for ID
only)
> but Cisco stockholder!
> "retired" Certified Cisco Systems Instructor (CID) #93005
>
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