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Kevin_Tang's avatar
Kevin_Tang
Icon for Nimbostratus rankNimbostratus
Jan 12, 2021

multiple floating self IPs for the same vlan and within the same traffic group

Hi,

Is that a valid config to give more than 1 floating self IPs for the same vlan in F5 LTM? Also with the same traffic group setting.

I saw on F5 LTM cluster configured this way and looks like still working.

for example: both floating self IPs are 10.17.16.20 and 10.17.16.21, they have the same MAC address. Back end servers 10.17.16.200 and 10.17.16.201 have 2 NICs, they are not using 10.17.16.20 or 10.17.16.21 as default gateway. The other NIC IPs are 10.20.20.200 and 10.20.20.201, the servers are using 10.20.20.1 as default gateway.

 

The traffic can reach to server 10.17.16.200 and 10.17.16.201 via both floating self IPs 10.17.16.20 and 10.17.16.21, but 10.17.16.20 and 10.17.16.21 have the same MAC address. I am not sure how the F5 LTM Layer2 forwarding table works.

 

Anyone has this type of setup in F5 LTM?

 

Regards

kevin

application delivery
devops
Floating
LTM
multiple
  • Amine_Kadimi's avatar
    Amine_Kadimi
    Icon for MVP rankMVP
    Jan 12, 2021

    Having two floating IP in the same VLAN is a working scenario and I am not aware of any problem it can cause, however since you are using SNAT and as per K7820:

     

    If multiple floating self IP addresses are configured on the VLAN, the BIG-IP system translates the address of client connections by alternating through a pool of all floating self IPs on the VLAN.

     

    Regarding MAC addresses, the BIG-IP will advertise the physical interface MAC of the active node for arp reponses for 10.17.16.20 and 10.17.16.21 unless you configure MAC Masquerade in the traffic group.