CSS; SIP Load Balancing does not work ... Please help ?

Unanswered Question
Apr 27th, 2007
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I have a Cisco CSS11501 Content Switch.

I am attempting to Load Balance SIP traffic, (the CSS support SIP according to data sheet)

The idea being that the content switches ammend the IP headers BUT ALSO look deep into the packet and also ammend the SIP headers (to match)


TO keep things simple.

I am using Bridging Mode,

vip: 111.222.333.230

real Server 1: 111.222.333.231

real Server 2: 111.222.333.232

I use the following config :

!************************** CIRCUIT **************************

circuit VLAN1

ip address 111.222.333.237

!************************** SERVICE **************************

service Ser1

ip address 111.222.333.231

port 5060

protocol udp


sservice Ser2

ip address 111.222.333.232

port 5060

protocol udp


!*************************** OWNER ***************************

owner callserve

content LOADBAL

vip address 111.222.333.230

port 5060

protocol udp

add service OpenSer1

add service OpenSer2

application sip

advanced-balance sip-call-id


I see traffic flowing through the CSS and hitting the servers.

However, when I look at a ethereal trace on Server1, I see that the CSS has changed the IP headers as expected.

(great stuff .... we have Layer3 Load Balancing)

HOWEVER, when I look at the SIP stuff, withing the SIP REGISTER packet, the CSS has NOT changed (or masked) the IP information.

I would expect the CSS to look into the packet and change SIP IP address to the "real" address (aswell)

The Content Switches are "supposed" to be SIP aware ... ?

Is this the case ? uhhmm ...

Any help would be massively appreciated.

thanks for reading ..



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joquesada Fri, 04/27/2007 - 15:49
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Dear Matt,

The CSS would look the information of the SIP header for balancing purposes, but it would not do any type of rewrite. Thanks!


Jose Quesada.

mcroft Wed, 05/16/2007 - 06:58
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Many Thanks for the reply.

Uhhmm, I understand that the CSS will not "re-write" the SIP Headers or content. However, surelly this causes problems ?

For example, I am using CSS Routed Mode. SIP proxies sit on PRIVATE IPs behind the CSS....When subsequent signalling (such as the ACK to a 200OK) is sent from SIP Clients (SIP-UAs) to the VIRTUAL IP address (VIP), the content switch re-writes the IP header and forwards to the approcpriate SIP-SERVER......

However, the SIP SERVER looks at the ROUTE_HEADER in the packet to find the OUTSIDE/PUBLIC VIP address and NOT the Local IP ... and sais "this is not for me" ... and forwards it back to the CSS.

Therefore, LOOP !

I would expect a "SIP aware" device to rewrite this IP. I am awfully confused.

Any suggestions ?

Thank you for reading.



joquesada Wed, 05/16/2007 - 20:38
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Dear Matt,

I think you are missing a group on your configuration, which it should look like this:


vip address 111.222.333.230

add destination service OpenSer1

add destiantion service OpenSer2


reference: http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/css11500series/v7.50/configuration/content_lb/guide/Sticky.html#wp1111503

Try it and let me know how it goes. Thanks!




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