Forum Discussion

mhsnetadmins's avatar
mhsnetadmins
Icon for Nimbostratus rankNimbostratus
Oct 08, 2012

snat port address overlap on LTM

Using SNAT on http virtual server and 3 nodes. What happens when the source port on a given service is duplicated? For example:

 

[root@bigip2:Active] config b conn show all | grep 1922

 

(pkts,bits) in = (45, 11922) out = (58, 27517)

 

CLIENTSIDE 10.120.15.27:1922 <-> 10.150.87.33:https

 

CLIENTSIDE 10.150.87.207:1922 <-> 10.150.87.33:https

 

SERVERSIDE 10.120.114.7:1922 <-> 10.120.114.34:https

 

 

Two clients are using the same source port accessing a virtual server. On serverside the port is used, but which client? How does the LTM handle the collision? Does it remap to another port on serverside? Or does the client simply have to retry again?

 

config
design
  • What_Lies_Bene1's avatar
    What_Lies_Bene1
    Icon for Cirrostratus rankCirrostratus
    Oct 08, 2012
    Are you using OneConnect? This will make a difference. Also, it's likely that the second client connection isn't using a source port of 1922 but as that's what you grepped on, that's all you're seeing. What do you have set for Source Port Preservation? The default is: "LTM preserves the client source port except where it is in use by an SNAT in which case a different port is used"
  • mhsnetadmins's avatar
    mhsnetadmins
    Icon for Nimbostratus rankNimbostratus
    Oct 08, 2012
    Yes, using OneConnect.

     

    As far as source port preservation is concerned, I'm currently running 9.4.8, and I thought this was a global setting.

     

    I will be upgrading to 10.2.4 soon.