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Paco_GP's avatar
Paco_GP
Icon for Nimbostratus rankNimbostratus
May 19, 2017

SIP ALG Configuration

Hello,

 

I am trying to configura a load balancing for a SIP application, basically a Polycom device registring a Cisco CUCM. THE SIP INVITES packets are reaching without problem the end CUCM servers but the registration fails. The F5 ltm is configured to perform source NAT since the CUCM servers are not behing the F5 but in another VLAN within the DC. After troubleshooting we have seen that the SIP INVITE packet is properly NATed by the F5 but taking a look at the SIP header , the original IP still appears.

 

We have realized that we need to perform a SIP ALG NAT in the F5 but we are not able to know if it is possible to do it without enabling the CGNAT feature in the F5. Seems CGNAT feature is just for carrier class load balancing solutions and we are figuring out if there is another way to do it(applying a SIP profile to the VS for example).

 

Any hint?

 

Thanks

 

application delivery
BIG-IP
LTM
  • Nazir_52641's avatar
    Nazir_52641
    Icon for Cirrus rankCirrus
    May 19, 2017

    Hi Paco GP,

    You can insert/update/delete SIP headers using iRules.

You can write a mini-SIPProxy functionality in F5 by doing the following
a) Virtual server with SIP Profile
b) Add iRule to virtual server which does the following
   i) Add Via header on receiving request/ remove Via header during response
   ii) For REGISTER request update Contact header with F5 NAT IP and on receiving 200 OK for REGISTER you may have to change the Contact header

    Following SIP events are triggerred

    1) SIP_REQUEST

    2) SIP_REQUEST_SEND

    3) SIP_RESPONSE

    4) SIP_RESPONSE_SEND

    You can insert SIP header using command

    SIP::insert Via "actual SIP header content"

    Hopes this help. You have to understand how F5 does connection mapping for SIP and how request are routed.

    Thanks

    Syed Nazir

    • Paco_GP's avatar
      Paco_GP
      Icon for Nimbostratus rankNimbostratus
      May 23, 2017

      Hello Nazir,

       

      Thank you so much for the hint. I thought I was going to be able to make it without using irules but I will try with your proposal.

       

      Regards Paco

       

    • torzillo_89761's avatar
      torzillo_89761
      Historic F5 Account
      Oct 07, 2018

      If you configure this with CGNAT, you can apply an LSN pool and then the SDP information is modified automatically by the ALG profile without requiring any iRules.