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AhmedMS's avatar
AhmedMS
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Feb 17, 2023

F5 LTM (ADC) question

Hello Dears, I hope you're doing great. Could someone help me with the below confusing terms and cases: - What is the difference between a Service port and a Virtual port (service port of VS)? When...
application delivery
AhmedMS's avatar
AhmedMS
Icon for Altostratus rankAltostratus

Thanks, Paulius for the answers.

I am a little bit confused about VS service port. If an application owner requests VIP for his app, and he just gave me the VIP and real servers' IPs and listening ports. Now all I have is (pool members - VIP), however, I still don't know which port should the VS be listening on. Is it something that should be provided or I should consider pool members' service ports and VS itself the same ports?

For the second piece, so if the PM is listening on port 7000, and I did alias port on the health monitor to be * or 7000 there is no difference. Did I get it right? In general cases, and as a default setting, should the alias port match the PM service port?

Regards,

Mike757's avatar
Mike757
Icon for MVP rankMVP
Feb 17, 2023

Hi Ahmed,

If no one tells you otherwise, I would say keeping the VS port the same as the service port on the pool members a good initial approach. But in your place I would confirm with the application owner.

When the monitor has an alias port of *, the port used is whatever is defined in the pool member. So it's usually ok to leave the alias with its default value of *:*

Forcing the alias is useful in a couple of situations I've encountered (and probably a few more I don't remember out of the blue):

- When the pool member listens on all ports and you want to test a specific service, say http on port 80, you would need to use 80 as alias port.
- When the application owner runs a healthcheck service on a different port. Imagine a web server running on 443, and another service on 8443, which must also be running for the server to work properly. You can use a "normal" monitor with the default alias to check 443, another monitor with alias *:8443, and consider the server as "up" only when both monitors are up.

Makes sense?

/Mike