North American Network Operators Group

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Re: FEC (Fast Etherchannel) issues

  • From: Danny McPherson
  • Date: Thu Mar 18 18:41:40 1999

> This looks kinda like the right place for this issue, apologies if not:

Cisco NSP or the like probably would have been more appropriate.

> True or False?
> FEC (Fast EtherChannel) is not suibtable for router to router trunking
> because of the way FEC load balances


> I've heard and read in various places (although nothing conclusive) that
> since FEC uses the last portion of a MAC address and hashs it to determine
> which 100 meg link a packet goes.  This is to prevent packets from
> arriving on the other end out of order.

Only brand 'C' switches do the MAC hash thing, the routers do things with 
"microflows" (unless per-packet stuff is enabled).

> This would seem to suggest that FEC wouldn't work between routers or
> similar layouts because there is only one MAC address on either end,
> therefor packets would always go over the same link.  

Yes, between a given set of routers .. if you have brand 'C' switches in the 

> Anybody have concrete details on this issue?  Does FEC actually determine
> load balancing this say? is ther another way to configure this?  

Don't put switches in the middle?