Newbie question on ip_hash

Why does ip_hash only use the first 3 octects of the IP address?

The reason I ask is that we run we servers for a number of schools.
Each
school is going the be their own subnet, ranging from a /24 to a /20 in
size. Since ip_hash will lump everyone from a /24 in the same hash, it
will direct them to the same server, correct?

If I am correct above, is there any way to create persistent connections
based on the full IPv4 address?

William Brown
Core Hosted Application Technical Team and Messaging Team
Technology Services, WNYRIC, Erie 1 BOCES

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Hello!

On Tue, Feb 05, 2013 at 10:38:35AM -0500, [email protected] wrote:

Why does ip_hash only use the first 3 octects of the IP address?

The reason I ask is that we run we servers for a number of schools. Each
school is going the be their own subnet, ranging from a /24 to a /20 in
size. Since ip_hash will lump everyone from a /24 in the same hash, it
will direct them to the same server, correct?

Yes.

The ip_hash balancing was designed to work with internet services,
and use of /24 networks allows it to keep users from migrating
between backend servers as they get new IP address on
reconnect/reboot (typically from the same /24 network, at least at
the time ip_hash was introduced) while still providing good
distribution between backend servers. This probably isn’t very
useful nowadays, but this is how it works.

If I am correct above, is there any way to create persistent connections
based on the full IPv4 address?

There is a number of 3rd party modules available which do hash
calculation based on arbitrary variables, and these may be used if
you need a hash based on full client’s IPv4 address (there is
$remote_addr variable).


Maxim D.
http://nginx.com/support.html

Maxim wrote on 02/06/2013 11:47:22 AM:

The ip_hash balancing was designed to work with internet services,
and use of /24 networks allows it to keep users from migrating
between backend servers as they get new IP address on
reconnect/reboot (typically from the same /24 network, at least at
the time ip_hash was introduced) while still providing good
distribution between backend servers. This probably isn’t very
useful nowadays, but this is how it works.

Thank you for the explanation.

If I am correct above, is there any way to create persistent
connections

based on the full IPv4 address?

There is a number of 3rd party modules available which do hash
calculation based on arbitrary variables, and these may be used if
you need a hash based on full client’s IPv4 address (there is
$remote_addr variable).

The backend I am hoping to use nginx for works fine without persistence,
I
was just thinking it would help with troubleshooting by keeping all of a
user’s activity on one server. That way I would have one log to check.
I
will look into those modules.

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