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F5 Default Route


Hi All,


Hope you all are doing great.


I have requirement where my old IP range (SUBNET) is fully exhausted. Now we got new range of ip (Subnet).


So can we configure two subnet (one for old default route (already exist) and one for new subnet) in F5 for same partition. Doing so will have an impact on existing default route ?








No, if Auto Last Hop is still enable on you F5 BIG-IP.

K13876: Overview of the Auto Last Hop setting (11.x - 16.x)

Auto Last Hop is a setting that allows the BIG-IP system to track the source MAC address of incoming connections and return traffic from pools to the source MAC address, regardless of the routing table.



Hi Lidev,


Thanks for replying. Can you please elaborate your answer "No". Like for it means we can configure two default routes ?





No need, please read K article and you see that Auto Last Hop feature allows packets to be routed without interrogating routing table.

If this answer was helpful, please don't forget to mark the answer as "Select as Best" in order to pass your post as resolved and help other people to find it 😉

As of now i am not seeing any traffic on new range VIP. From Network end all routes are in place and rules are in place in firewall. What check or configuration required at F5 end ?



Have you added a new self-ip (new subnet) on BIG-IP (Network ›› Self IPs) ?

Nope. At present we have self IP for old subnet only. Haven't configured self ip for new subnet.

You have to do this new Self IP declaration to ensure that the routing works.

Thanks for that information. So in that case need to create VLAN also ? which is define for new subnet. Old subnet and new subnet are in different VLAN.

Yes and tagged the new VLAN on the F5 interface.

Thanks Lidev for your help and support.Let me try this and i ll update the thread accordingly.

Hi Lidev,


We created NEW VLAN, and defined new self IP, but still its not working. What can we try ? Or do i miss anything?


  • Global Auto Last Hop setting is enable ? (System > Configuration > Local Traffic > General)
  • Ping is ok on new self ip ?


If everything seems OK on BIG-IP configuration, you can do a tcpdump on the F5 BIG-IP to identify root cause of the routing issue.


Hey RAQS ,

Did that work? Did you do any additional steps? I am also looking for a similar solution, your feedback would help me implement better.

Do you have any article/doc that sums up all the steps to do so?

Thanks in advance.