At 04:07 PM 2/19/01, Howard C. Berkowitz wrote:
>At 11:21 AM 2/19/2001 -0800, Priscilla Oppenheimer wrote:
>>At 08:14 AM 2/19/01, AndyD wrote:
>>
>>
>> >It looks like you need to go to
>> >layer 3 switching to do any load balancing other than this. And
>> >etherchannel is another option for aggregating bandwidth. But someone said
>> >with etherchannel using 4 full duplex 100 mbp ports will not give 800 mbps
>> >of throughput? I always thought that in theory that was the case??
>>
>>It's "statistical" load balancing, according to Cisco. The operation that
>>determines which link in a Fast EtherChannel to use is quite bizarre, and
>>does not provide precise load balancing. It provides load sharing. Think of
>>it like a complex highway system. Adding new highways distributes the load,
>>but it doesn't usually balance the load very precisely.
>
>Are you saying it should provide precise load balancing?
Definitely not. I think the implementation is ingenious and well-suited to
the problem. I probably should have said that instead of bizarre (though
the XOR business is kind of strange.)
Priscilla
> That would seem to add a scary amount
>of knowledge that the FEC interface would need to know -- RMON traffic
>statistics or the like to
>figure out how to distribute flows. Intuitively, the cost of adding that
>intelligence would exceed,
>by far, the cost of throwing more bandwidth at the problem.
>
>Recovery after failure would take longer as well, IMHO.
>
>
>>The division of traffic across a Fast EtherChannel is based on
>>source/destination pairs, which is usually not very balanced. There are
>>usually some big talkers and receivers. The Ethernet Bundling Controller
>>(EBC) performs an X-OR operation on the last two bits of the source MAC
>>address and the destination MAC address. This operation yields one of four
>>results: (0 0), (0 1), (1 0), or (1 1). Each of these values points to a
>>link in the Fast EtherChannel bundle.
>>
>>Priscilla
>>
>> > Since
>> >the data is transmitted on different wire pairs, if the sender and receiver
>> >transmit at the same time, why isn't 800 mbps possible????
>> >
>
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