Auto Last Hop setting on Big IP

Auto Last Hop is a setting that allows the BIG-IP system from 11.x.to track the source MAC address of incoming connections and return traffic from pools to the source MAC address, regardless of the routing table.

When enabled, Auto Last Hop allows the BIG-IP system to send return traffic from pools to the MAC address that transmitted the request, even if the routing table points to a different network or interface. As a result, the BIG-IP system can send return traffic to clients even when there is no matching route. For example, if the BIG-IP system does not have a default route configured and the client is located on a remote network. Additionally, Auto Last Hop is useful when the BIG-IP system is load balancing transparent devices that do not modify the source IP address of the packet. Without the last hop option enabled, the BIG-IP system could return connections to a different transparent node, resulting in asymmetric routing. It is recommended to leave this setting enabled

You can configure the Auto Last Hop setting globally and on an object level. The objects that have the Auto Last Hop setting are VLAN, SNAT, NAT and Virtual Server

The setting & behavior of Auto Last Hop on each object:

VLAN

This enables you to configure Auto Last Hop on a per-VLAN basis. By default, the VLAN object is set to the Default option.

When you configure Auto Last Hop with a value of Default at the VLAN object, it inherits the Global setting. When you configure Auto Last Hop with a value other than Default at the VLAN object, its setting takes precedence over the Global setting.

SNAT

This enables you to configure Auto Last Hop on a per-SNAT basis. By default, the SNAT object is set to the Default option.

When you configure Auto Last Hop with a value of Default at the SNAT object, it inherits the VLAN object setting. When you configure Auto Last Hop with a value other than Default at the SNAT object, its setting takes precedence over the VLAN object setting.

NAT

This enables you to configure Auto Last Hop on a per-NAT basis.  By default, the NAT object is set to the Default option.

When you configure Auto Last Hop with a value of Default at the NAT object, it inherits the VLAN object setting. When you configure Auto Last Hop with a value other than Default at the NAT object, its setting takes precedence over the VLAN object setting.

Virtual server

This enables you to configure Auto Last Hop on a per-virtual server basis. By default, the virtual server object is set to the Default option.

When you configure Auto Last Hop with a value of Default at the Virtual Server object, it inherits the VLAN object setting. When you configure Auto Last Hop with a value other than Default at the Virtual Server object, its setting takes precedence over the VLAN object setting.

Example 1

 

Global Auto Last Hop setting: Enabled
Virtual Server Auto Last Hop setting: Default
SNAT/NAT Auto Last Hop setting: Default
VLAN Auto Last Hop setting: Default

In this example, the Auto Last Hop feature is enabled on all objects.

Example 2

 

Global Auto Last Hop setting: Disabled
Virtual Server Auto Last Hop setting: Default
SNAT/NAT Auto Last Hop setting: Default
VLAN Auto Last Hop setting: Default

In this example, the Auto Last Hop feature is disabled on all objects.

Example 3

 

Global Auto Last Hop setting: Disabled
Virtual Server Auto Last Hop setting: Enabled
SNAT/NAT Auto Last Hop setting: Disabled
VLAN Auto Last Hop setting: Disabled

In this example, the Auto Last Hop feature is enabled only on the virtual server.

Example 4

 

Global Auto Last Hop setting: Enabled
Virtual Server Auto Last Hop setting: Default
SNAT/NAT Auto Last Hop setting: Default
VLAN Auto Last Hop setting: Disabled

In this example, the Auto Last Hop feature is disabled on the specific VLAN object as well as on the virtual server and SNAT/NAT objects that reference that VLAN object.

Example 5

 

Global Auto Last Hop setting: Enabled
Virtual Server Auto Last Hop setting: Enabled
SNAT/NAT Auto Last Hop setting: Enabled
VLAN Auto Last Hop setting: Disabled

In this example, the Auto Last Hop feature is disabled on the specific VLAN object, but enabled on the virtual server and SNAT/NAT objects that reference that VLAN object.

Example 6

 

Global Auto Last Hop setting: Enabled
Virtual Server Auto Last Hop setting: Default
SNAT/NAT Auto Last Hop setting: Disabled
VLAN Auto Last Hop setting: Default

In this example, the Auto Last Hop feature is enabled on the virtual server and VLAN objects, but disabled on the SNAT/NAT object.

Example 7

 

Global Auto Last Hop setting: Enabled
Virtual Server Auto Last Hop setting: Disabled
SNAT/NAT Auto Last Hop setting: Default
VLAN Auto Last Hop setting: Default

In this example, the Auto Last Hop feature is enabled on the VLAN and SNAT object, but disabled on the virtual server object.

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