Is it possible to have a virtual local L3 loopback interface

Hi everyone,

Is it possible to have a local virutal IP address similar to what cisco calls loopback interface ?

I am trying to achieve a network topology as follows:

[Internet]----[router]----subnetX-----[F5]

The subnet between the router and F5 is a /30 RFC 1918 subnet used for routing. F5 has a Self IP 10.0.0.X/30 on this subnet and a default route pointing to 10.0.0.Y

In F5 I have DNS service listening on a public IP, e.g 1.2.3.4. This IP is also configured as a Self IP 1.2.3.4/32.

Incoming traffic is OK: traffic from internet is reaching 1.2.3.4 by the mean of a route configured on the router, and return traffic from F5 has 1.2.3.4 as a source IP.

However, traffic originating from F5 is not working because its source IP is always 10.0.0.X, so packets get lost. I would like to source the outgoing traffic from 1.2.3.4. SNAT didn't help here.

Also, when I test with a ping request and manually source the traffic from 1.2.3.4 using the -I argument, outbound traffic is OK. I would like to have this exact behavior for data traffic (iquery, monitoring ...etc).

The customer has requirements to not use public IPs for interconnection links.

Any help is appreciated