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Barry_Lalor_250's avatar
Barry_Lalor_250
Icon for Nimbostratus rankNimbostratus
Nov 23, 2016

Virtual Server Precedence Question

Hi everybody,

 

I am studying for my F5 201 exam and I am trying to get my head around the virtual server processing order of precedence. Using version 11.6.1 (the VE license).

 

I have a few virtual servers setup, for example.

 

destination/source/port

 

VS1 - 192.168.119.254/32 - 192.168.119.128/32 - 22

 

VS2 - 192.168.119.254/32 - 192.168.119.128/32 - *

 

The first virtual server points to server 1, and then seconds to server 2, both and enabled and functioning with SSH.

 

I make a connection to the first virtual server and everything works as expected. Now I disable the first virtual server and make a new connection (after waiting a few minutes). I expect it to get pushed to server 2, however I receive "connection refused".

 

If however, I delete the first virtual server, the connection goes though the second virtual server fine and I can ssh to server 2.

 

My question is, why must I delete the first virtual server for the second one to take over in the order of precedence? I would have thought that simply disabling the VS would have been enough to force the F5 to look at alternate options?

 

I also wanted to check that the behaviour seen in 11.6.1 should mirror that of 11.4 (which I think is the current version of the 201 exam)?

 

Many thanks for your replies.

 

application delivery
BIG-IP
LTM

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  • nathe's avatar
    nathe
    Icon for Cirrocumulus rankCirrocumulus
    Nov 23, 2016

    Barry, i think this askf5 solution will explain it: Overview of the 'tm.continuematching' db variable.

     

    By default, if you disable a higher precedence VS then a lower one will not be used. You would need to change the above variable to True to change this behaviour.

     

    Out of interest - i recently came across a version of TMOS with a bug that meant even set as False the lower precedence VS was being used. Hotfix resolved this.

     

    Hope this helps,

     

    N