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CSS Newbie - Modules required for One-Legged topology

Hi all,

I'm looking to setup a system to load balance 12 http web application servers which talk to a backend database cluster. The servers are connected to top of rack 4948 switches which are dual homed to a pair of 6500 chassis for resilience.

Looking through the application networking pages on CSS's I think that a one-legged pair of CSS11503 switches (possibly in an Active-Active standby mode) connected one to each of the 6500's should do the trick. My question is does this sound sensible and would I need any other module in the CSS11503 other than the SCM?

Thanks in advance,

Zac

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: CSS Newbie - Modules required for One-Legged topology

Zac,

be aware that the CSS is splitting the traffic accross all the modules [no matter where the traffic came in]. So the more modules you have, the more connections the CSS can handle.

For this purpose we sell SAM module that have no interfaces and their only purpose is to perform loadbalancing decision.

Also, regarding one-armed solution.

At first glance it is easy deploy.

However, the CSS is a stateful device, so it requires to see for a single connection all the packets from the client and all the packets from the server.

In a one-armed scenario, this is not automatic. You need to set the CSS to be the default gateway of the server, or use client nat or policy routing.

If you go for client nat, the servers will see connections from one ip address only and you won't be able to perform stats about the clients.

Gilles.

2 REPLIES
Cisco Employee

Re: CSS Newbie - Modules required for One-Legged topology

Zac,

be aware that the CSS is splitting the traffic accross all the modules [no matter where the traffic came in]. So the more modules you have, the more connections the CSS can handle.

For this purpose we sell SAM module that have no interfaces and their only purpose is to perform loadbalancing decision.

Also, regarding one-armed solution.

At first glance it is easy deploy.

However, the CSS is a stateful device, so it requires to see for a single connection all the packets from the client and all the packets from the server.

In a one-armed scenario, this is not automatic. You need to set the CSS to be the default gateway of the server, or use client nat or policy routing.

If you go for client nat, the servers will see connections from one ip address only and you won't be able to perform stats about the clients.

Gilles.

New Member

Re: CSS Newbie - Modules required for One-Legged topology

Many thanks Gilles. Looks like I'll be better off connecting servers direct to CSS11503's. I've been asked to look at the ACE module for the 6500's as well as I may be able to solve some other issues with some old CSS1100's by going down that route especially as the 6500's are about to get upgraded to SUP720 supervisor.

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