201 · Question #253
A BIG-IP system has the following configuration: SNAT is set to Auto Map There are two VLANs internal and external Default route is pointed to the gateway on external VLAN Self P for internal VLAN is
The correct answer is C. 192.1.1.1. When SNAT is set to Auto Map, the BIG-IP system uses the floating self-IP address of the VLAN on which the server resides to source traffic to the backend server.
Question
A BIG-IP system has the following configuration:
- SNAT is set to Auto Map
- There are two VLANs internal and external
- Default route is pointed to the gateway on external VLAN
- Self P for internal VLAN is 1921.1.2
- Self IP for external VLAN is 192.1.2.2
- Floating IP addresses for internal VLAN is 192.1.1.1
- Floating IP addresses for external VLAN is 192.1.2.1
- The Virtual Server IP address is 192.1.1.100
Which IP address does the BIG-IP system use first when traffic reaches the servers on the internal VLAN?
Options
- A192.1.1.100
- B192.1.2.2
- C192.1.1.1
- D192.1.2.1
How the community answered
(27 responses)- A7% (2)
- B4% (1)
- C85% (23)
- D4% (1)
Why each option
When SNAT is set to Auto Map, the BIG-IP system uses the floating self-IP address of the VLAN on which the server resides to source traffic to the backend server.
The Virtual Server IP address is the destination for client-side traffic, not the source IP for server-side traffic when SNAT is enabled.
192.1.2.2 is a non-floating self-IP on the external VLAN, which is not used for SNAT on the internal VLAN.
With SNAT Auto Map, the BIG-IP system uses a self-IP address on the egress VLAN to source connections to the backend server. Since the servers are on the internal VLAN, and 192.1.1.1 is the floating IP for the internal VLAN, it will be used as the source IP address for traffic going from the BIG-IP to the backend servers. The floating self-IP is preferred for SNAT Auto Map when configured.
192.1.2.1 is the floating IP on the external VLAN, which is not the egress VLAN for traffic to internal servers.
Concept tested: BIG-IP SNAT Auto Map source IP selection
Source: https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/bigip-virtual-servers-concepts-12-0-0/4.html
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