Re: [LARTC] many ways to do load balancing (or not?)

[Andreas Hasenack <andreas@conectiva.com.br>]

Em Thu, Nov 21, 2002 at 02:20:57PM -0800, William L. Thomson Jr. escreveu:
> Also I do not believe the load balancing is packet based. Usually it's
> more "connection" based. Meaning that if you request a file, more than
> likely all parts of that file will be transfered using the same route.
> If you request it again, it may take the same route or another.

If I make many connections from one IP (inside) to a web server (outside),
for example (like many simultaneous downloads, or a complex page), I think
they will all go via the same route, because the originating IP and the
destination are the same. It will hit the cache.
Hmm, not good if your users use a proxy, but then again, the proxy would
cache the page probably.

> Now if the request was generated from the inside it would still work
> some what the same. If I send two emails out at once, the first will use
> gw1 and the other will use gw2.

Unless they are sent to the same MTA in the outside, then it will get a
cache hit (supposing the 60s haven't gone by then). Or not?

> All packets for each will travel via the same route and use the same
> gateway from start to finish.

Agreed.

> If it was more on a packet level, the other end would be confused.

Sure. When I said "packet count" before I was thinking about something
along the lines of real traffic balancing, that is, the router somehow
remembering how many packets it sent to each route and choosing the
less used one.

> It would be getting responses from an IP it was not expecting response
> from. I would imagine each side to send redirects, and all sorts of
> problems. Like it receiving every other packet and dropping the packets
> in between.

And breaking stateful firewalls.

> If during a file transfer the route cache is flushed, there is the
> possibility of the rest of the packets going out a different interface.

Uh oh... It shouldn't be that simple, what about that 60s timeout for
the cache? It's very likely to occur during a file transfer.

> Neither does it perfectly or with intelligent algorithms. Neither allow
> you to use all paths for a single transfer.

Only things like MPPP I guess, for example, or channel bonding, or TQL.

> So if you have two 1.5 mbs connection, you do not end up with a 3.0 mbs
> line. You do have one internal gateway for both, and if one goes down
> the other can be used. So you do have redundancy, and both lines can be
> used to serve difference requests to different places.

So it's more like redundancy/HA with a best effort towards balancing.

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