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Response received from wrong real server address for a given VIP address

astanislaus
Level 2
Level 2

See attached two files showing the problem and the config file.

=========================================

zvtllagx001>sho ip slb conn client 172.31.135.62

prot vlan source destination state

----------------------------------------------------------------------

In TCP 49 172.31.135.62:2251 172.22.49.51:80 ESTAB

Out TCP 372 172.22.72.50:80 172.31.135.62:2251 ESTAB

=========================================

Now - VIP address 172.22.49.51 uses serverfarm EDW_M_TLL which has two real servers 172.22.72.52 and 172.22.72.53 as you can see from attached config.

Why then are we seeing the response coming back from real server 172.22.72.50 to this client which initiated a connection to VIP address 172.22.49.51. The response should have come from real server 172.22.72.52 or 172.22.72.53

=========================================

Note: - 172.22.72.50 and 172.22.72.51 are real servers in serverfarm EDW_C_TLL. This serverfarm is used by VIP 172.22.49.50.

8 Replies 8

astanislaus
Level 2
Level 2

CAT 6500 is running IOS version 12.2(17d)SXB11a and CSM 3.2(1).

syediahm
Level 1
Level 1

Problem lies in using same sticky group for the two virtual servers.

You can assign a same sticky group ID to multiple policies/vservers as long as all the policies mapping to the same **serverfarm** (having 2 serverfarms with the same list of real IP addresses is a bad idea.)

remove sticky group from either of the server and assign a new group to it.

Thanks

Syed Iftekhar Ahmed

Syed,

Thanks for your reply.

What you say - Is it the same as what is refered to in CSCei50063.

Anyway, not being well conversant with Content Switching Products, I am trying to get my head around to understanding your explanation in your reply.

If you can provide additional details and pointers to understanding this sticky group configuration, I would much appreciate it. In the meantime I am reading the CSM config guide to understand this better.

Lastly, you say that this config has 2 serverfarms with the same list of real IP addresses and that this is a bad idea.

I can't see 2 serverfarms with the same list of real IP addresses.

serverfarm EDW_C_TLL has real IP addresses 172.22.72.50 and 172.22.72.51

and serverfarm EDW_M_TLL has real IP addresses 172.22.72.52 and 172.22.72.53

Can you tell me where - 2 serverfarms are having the same list of real IP addresses?

Thanks again.

Alphonse

if you use the same sticky group across Vservers, then the sticky entry will be used before the load-balancing decision.

If client A hits VserverA, and load-balanced to real serverA, a sticky entry is created matching client A to serverA.

Client A then hits VserverB this time, with same sticky group applied as in VserverA, then client will go to real server A, even if that real server is not a member of any serverfarm applied to VserverB.

Recommendation is to use different sticky groups if different serverfarms are used between vservers.

Your config is using same sticky group under two virtual servers and both these Vservers are using diff real servers.

Hope it helps.

Syed Iftekhar Ahmed

Syed,

Thanks again for your 2nd reply. Now I understand this a little better.

Now, in your 1st reply you said that this config has 2 serverfarms with the same list of real IP addresses and that this is a bad idea.

I can't see 2 serverfarms with the same list of real IP addresses.

serverfarm EDW_C_TLL has real IP addresses 172.22.72.50 and 172.22.72.51

and serverfarm EDW_M_TLL has real IP addresses 172.22.72.52 and 172.22.72.53

Can you tell me where - 2 serverfarms are having the same list of real IP addresses?

what he tried to explain is that you SHOULD NOT use the same sticky group in vserver that do NOT use the same serverfarm.

So, to solve your problem, you should create a 2nd copy of the sticky group - use another group id with the same parameter, and assigned a different sticky group to each vserver.

The reason for the problem is that the sticky function does not check if the server being used exist in the serverfarm configured for the real.

So, when a client hit vserver #1, an entry is created in the sticky table.

When the same client goes to vserver #2, the CSM will see there is an entry in the sticky table and use it to forward the traffic.

This is because the CSM does not check if the server entry exist in the serverfarm.

So, the solution is to use different sticky group for each vserver.

I hope this is more clear like this.

Gilles.

syediahm
Level 1
Level 1

Giles ~

:) Thanks

Alphonse~

Probably my first response is confusing. Just disregard it. Concentrate on my 2nd / Gilles response.

(and yes your serverfarms are using different reals :)).

Thanks

Syed Iftekhar Ahmed

Syed and Gilles,

Thanks for your responses.

Syed,

On reading it again I also understood your 1st response. I think what you meant to say is that having two different serverfarms with the same real IP addresses is a bad idea. I mis-interpretd that as if my customer has configured it that wrong way.

Now I understand what you said in your 1st reply.

Thanks for your help.

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