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abailey_1418's avatar
abailey_1418
Icon for Nimbostratus rankNimbostratus
Oct 01, 2010

iRules Disable CMP for Virtual

I know IRules and CMP compatibility is a well-documented subject, but even after a lot of reading and input from tech support, I'm stuck on a couple of things. Maybe someone has some quick answers.

 

 

I've read that if an iRule contains a Global variable, that it will "demote" the virtual server or forwarding rule. Well, we have 9.4.7 code and the iRule contains the well-known $:: problem, and the forwarding rule in question exhibits the documented trait of CMP on a virtual server being disabled: tmm0 changes the source port of the connection sometimes. And this causes a few application problems for us.

 

 

The recommendation from tech support to remove the $:: has not fixed the issue. However, my question is more basic at this point than what is wrong with the rule: how is it that we can determine that the virtual server is being "demoted?" I get the impression -- though this may be totally wrong -- that a "bp virtual (virtual_S_name) cmp mode show" should show cmp as "single" if the iRule is doing one of the well-known issues like calling a global variable that breaks CMP functionality. But it does not show this, it show CMP as working for the virtual server.

 

 

So the question is, is there any direct way to tell if an iRule is breaking CMP for the virtual server using it?

 

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  • hoolio's avatar
    hoolio
    Icon for Cirrostratus rankCirrostratus
    Oct 19, 2010
    Here is a quick test without any iRules and CMP enabled on 10.2.0:

     

     

    [root@b3900:Active] config b virtual b39_http_vs cmp show

     

    VIRTUAL b39_http_vs - CMP: enable

     

     

    [root@b3900:Active] config b virtual b39_http_vs cmp mode show

     

    VIRTUAL b39_http_vs - CMP mode: all

     

     

    And here is the output after adding an iRule which references a global variable:

     

     

    [root@b3900:Active] config b virtual b39_http_vs cmp show

     

    VIRTUAL b39_http_vs - CMP: enable

     

     

    [root@b3900:Active] config b virtual b39_http_vs cmp mode show

     

    VIRTUAL b39_http_vs - CMP mode: single

     

     

    So you should be able to use 'b virtual vs_name cmp mode show' to check whether CMP can be used for the VS. If you're not seeing this on 9.4.7, I'd guess it's due to a bug. A simple way to test whether the iRule is executing on multiple TMM instances is to add a log statement to RULE_INIT. If you see it being run by more than one TMM, then you know it's using CMP.

     

     

    If you've added functionality that isn't CMP compatible, but isn't triggering an automatic demotion, you could manually disable CMP or update the iRule/VS config to not use the CMP incompatible functions. For details on this, you can check this wiki page:

     

     

    http://devcentral.f5.com/wiki/default.aspx/iRules/CMPCompatibility.html

     

     

    Aaron