F5 Networks Topology Types

There are two types of topology. One-Armed and Two-Armed Routed Mode.

One-Armed

In a one-armed topology, virtual server is located at the same subnet and VLAN with pool members. There should be source address translation used to provide returning server response traffic to the client through the BIG-IP LTM.

• Advantages:
  • It doesn’t make any change at servers or network
  • BIG-IP LTM allows to use feature set exactly - No additional direct access to real servers that are required for LTM configuration is not necessary.
  • It doesn’t allow server traffic to steer asymmetrically
• Disadvantages:
  •  Servers see client IP as BIG-IP and there can be a requirement to make changes on the record mechanism. But you can add original IP address into HTTP headlines by using BIG – IP.
  • X-Forward header
  • Custom header (via iRules)

Two-Armed Routed Mode

In two-armed routed mode, virtual server is located at the different VLAN that virtual server pool members aren’t located. BIG-IP system steers traffic between each other. Depending on general network architecture, source address translation can be required or not. If network pool member traffic can be designed to steer into BIG-IP LTM, it is not required to use source address translation.

In referred mode, real servers exist on intranet and behind of LTM. It uses the LTM’s leg which belongs to that network, as a default gateway. The servers can be accessed by clients via an external network segment. LTM makes L3 - routing-channeling between the two legs at the real traffic between the server and the clients.

• Advantages:
  • Easy debugging
  • Allows BIG-IP LTM's pool members to be protected from external abuse.
  • Provides client source IP’s protection
• Disadvantages:
  • New networks and VLAN’s can be required to create
  • The server default gateways must be reconfigured for being LTM.