bill fumerola wrote:
not all load balancers work the same.
direct server return aka one-arm load balancing does no translation or
rewrite of any headers (l3 or l4). all it does is make a switching
decision based on health check and other weighting criteria.
Just to clarify, for those who aren't familiar with the basic idea:
By leaving the IP headers unmodified, the individual servers all expect
to receive packets
that look like they came directly from the internet (and in fact, did)
unmodified.
The return packets are thus suitable for being sent straight out without
needing any rewritee, and
thus without touching the LB.
The F5 BigIP LTM models I've looked at that do that are the 6400 and
6800 series, running 9.* level code.
There's nothing secret about it - it's a generic, vanilla function they
ship with. The documentation is on-line.
Google for "l4 fast bigip". (I have no connection with F5 other than
being employed by a satisfied customer.)
It means that the servers are configured identically, are reachable
without NAT, and are,
in effect, anycast. The Load Balancer is making a stateful decision
about which individual server
to send each stream to, in the case of TCP, and stateless in the case of
UDP.
It operates in exactly the same way, as if there were two equal cost
routes to two or more routers, each
advertising the existence of one of these servers, on the other side of
a PPLB router - except that it has
the ability to handle the state issue for TCP.
Anyone who operates a network with PPLB towards *external* routes, via
BGP multipath, would
have to be an idiot or a fool, and would certainly have trouble
retaining customers with clue.
Brian
P.S. I do not respond to trolls.
P.P.S. I will not respond the troll.
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