alteon hash metric

[cconn...@lycos.com]

hello
could someone explain how the alteon uses the 'hash' metric to load
balance. if using filters to redirect traffic to a real server group
and specifiyng thash 'sip' this tells the alteon to keep the same
source ip to the same real server, how does the alteon do this?
thanks

[Dophi]

There are 2 different kinds "hash" functions on Alteon. One for SLB and
another one for Filter.

1. /cfg/slb/group <group number>/metric hash

a. For Application Redirection, the client destination IP address is
used. All requests for a
specific IP destination address will be sent to the same server. This
is particularly useful
for maximizing successful cache hits.

b. For SLB, the client source IP address is used. All requests from a
specific client will be
sent to the same server. This option is useful for applications where
client information
must be retained between sessions.

2. /cfg/slb/filt <filter number>/adv/thash

Allows you to choose hash parameter to use for filter redirection.
The Default is auto. The sip
option allows you to perform tunable hash on source IP address for this
filter. The option dip
allows you to perform tunable hash on destination IP address for this
filter. The option both
allows you to perform tunable hash on both source IP address and the
destination IP address at the same time. The option sip+sport allows
you to perform tunable hash on both source IP address and source port
at the same time.

So, Alteon uses source IP to calculate each session and redirects it to
a real server. We can't know which sever will be assigned by Alteon on
the first session from a client but can control every session from the
same 24-bit source IP address will be redirected to the same real
server as the first session.

[cconn...@lycos.com]

thanku, what is exactly tunable hash? does the alteon pass the sip
value of the client to the group if you have metric 'hash' specified?
is the purpose so the alteon can create an index for the session (based
on sip) to speed up subsuqent requests from the client with the same
source ip?
thanks

[Dophi]

As I mentioned above, tunable hash for Alteon is a hash algorithm which
we can change parameters in order to achieve a purpose of redirections
of filters. Compare with the hash function of a real group, the
parameters of tunable hash can be changed. So, it is tunable.

Alteon always keeps source IP of every packets unless you enable proxy
IP function or NAT. No matter what metric you choose, Alteon never
changes the source IP of every packets. It only uses source IP,
destination IP, or source port to make a load balance or redirecting
decision.

Yes, in your case, Alteon uses source IP to make and maintain a session
table to keep load balance function properly.

[divya]

replying to Dophi, divya wrote:

Hello All ,

I am new to the world of load Balancing .Kindly help me with my doubt
regarding Alteon
Load Balancing using hash metric.By referring the Real Server Group
configuration ,
I could see that the load balancing metric used is persistent hash.
And by referring virtual Services Configuration, I came to know that the hash
parameter used is sip.

Below is some details I got regarding Hash metric.

*The hash value is computed as follows:

The load balancer computes two hash values using:
The back-end server IP Address and Port (X).
One of the incoming URL, Domain name, Destination IP, Source IP,
Source
& Destination IP, Source IP & Source Port, Call ID, Token (Y).
The load balancer computes a new hash value (Z) based on (X) and (Y).
The hash value (Z) is stored in cache.

The load balancer forwards the request to the server with highest hash value,
by
using the value (Z) from the computed hash values. Subsequent requests
with the same hash value (cached) are sent to the same server.
*

Can anyone just explain the end to end data flow once a new request comes???


Thanks in Advance

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