Re: More on Bake-Off results ...

From: Henrik Nordstrom <>
Date: Sun, 17 Oct 1999 00:30:14 +0200

Alex Rousskov wrote:

> As far as I understand, L4 load balancing does not require any cache
> cooperation to maintain ideal hit ratio. For example, many switches
> balance on the origin server IP address, and such hashing (when it
> works) splits the load without hit ratio degradation.


When setting up L4 load balancing you basically have two options (with
some extra bells and wistles in some switches/distributors):

a) Load balance based on the destination IP
b) Load balance on the client IP

Load balancing on the destination IP is simpler to perform, but is
sensitive to hot spots (will be uneven if many of your clients visits
the same server).

Load balancing on the client IP can make an more even work load on the
caches, but does not maintain ideal hit ratio.

There are also other methods of load balancing where you load balance
based on the URL, but these operate above L4. One well known example is
CARP from Microsoft, commonly implemented as a PAC script. Yes, Squid
can act as an CARP array to the clients (all you need is to make a CARP
array membership table and publish it on a HTTP server, and a PAC script
which should be available in the MS Proxy documentation on Microsoft web
site. For details CARP tables see draft-vinod-carp)

Henrik Nordstrom
Squid hacker
Received on Sat Oct 16 1999 - 17:14:45 MDT

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