What does it mean to “plumb” an IP address?

Question

Plumbing an IP address means what? What are some examples of it?

Answer 1

Essentially, it’s just another word for multi-homing a device (such as a server), with the caveat that it’s done on the same link rather than separate links. It’s generally a bad practice because multi-homing mostly accomplishes 2 things:

1. It wastes IP addresses needlessly (in most cases)
2. It creates a layer 2 security risk because you now have direct paths on multiple networks with typically no filtering (because most environments filter layer 3 but not layer 2), and because if anyone breaches that host they can now easily move laterally across the rest of the hosts on the same networks.