> Just to clarify, NLB is having multiple NICs on the same server.
It's a lot more than that! NLB is Network Load Balancing, which used
to be WLBS.
We have used WLBS and NLB with IMail and MS SMTP to good effect and
vouch for their compatibility. NLB does have some definite advantages
over round-robin DNS, but the technology can be a pain to support, as
it is sensitive at the data-link layer and requires the cooperation of
your switches and routers (the only combo I can verify is 3Com teams
and Cisco hardware).
More important, though, NLB really isn't appropriate unless you need
to spread load across boxes with a range of hardware specs while still
using all machines at all times. It's not really built for
application-level uptime, nor application-level monitoring. If you're
experiencing a prolonged attack from a particular IP, for example, the
whole attack is going to stay on one of your servers, and--unless you
have some way of detecting the attack and shutting down the network
interface completely--that server is still going to receive new
incoming connections as long as the TCP/IP stack is able to process
the cluster's heartbeat traffic. And if you did build a way of
proactively shutting down the interface, or if it were shut down by
the attack itself, that would still leave you in a situation that
round-robin DNS could handle just as well (with the exception that NLB
would eliminate the initial attempt to connect to downed servers, but
the packets conserved that way would be the least of your problems
unless you've got a huge farm that has boxes flickering on and off all
the time).
--Sandy
------------------------------------
Sanford Whiteman, Chief Technologist
Broadleaf Systems, a division of
Cypress Integrated Systems, Inc.
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