How LTM process traffic for a VIP

How the traffic gets to the BIG-IP depends on whether the virtual servers are on the same IP network that is on the Self-IP/VLAN, or a completely different IP network.

Option 1: Virtual Server is on the same IP network as Self-IP and next-hop router. In this scenario the BIG-IP and router are directly connected on the same IP network as the Self-IP and virtual servers, so it will ARP out on that IP network/VLAN at which point the BIG-IP will respond with it's MAC address on that VLAN. That is the MAC address that the router will use to forward the traffic to the LTM on that IP network. (This changes when using MAC masquerade which I talk about a little later)

Option 2: Virtual servers are on a different IP network than the Self-IP and the router. In this scenario the a static route has to be configured on the router that has the IP network of the virtual servers and the next-hop will be the self-ip on the BIG-IP that is on the same IP network.

The MAC addresses are part of the VLAN, if you have a High Availability configuration with multiple units and configure MAC masquerade. If your network configuration is like option 1 the MAC masquerade address will be the one used for all floating-Self-IP's and the virtual servers.

More details on MAC masquerade: https://support.f5.com/kb/en-us/solutions/public/13000/500/sol13502.html

For matching virtual servers it attempts to find the most specific match in the following order destination address, source address and then port.

More details on how it will match the virtual servers can be found here:

https://support.f5.com/kb/en-us/solutions/public/14000/800/sol14800.html

When the LTM fails over it will send out a GARP for all IP addresses that are on the same IP network as Self-IP addresses that it has configured. If the network configuration is Option 2, the router or next hop devices don't have ARP entries for the virtual servers and we will not send a GARP for virtual servers. If the network configuration is like Option 2 then it will send a GARP for all the virtual servers too.