Getting listener error "This listener cannot use the same frontend port as an existing listener" even though there is only one listener present on Azure Portal

Question

Error "This listener cannot use the same frontend port as an existing listener" is displayed under port no. even though there is only one listener currently present in application gateway. I think it is a bug because we can have two listener using same frontend port. And as a proof, I have other application gateway which is using same front end port for two listener and there such error is not observed.

Error screenshot

Answer 1

Hello @Manali Santosh Jahagirdar ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand that you are trying to create a listener in your Application gateway with port 443 and getting following error "This listener cannot use the same frontend port as an existing listener".

You mentioned that there is only one listener present on Azure Portal with this port. If the existing listener is a public basic listener with port 443, then you cannot create another public basic listener with port 443. The same applies if the existing listener is private basic listener with port 443, then you cannot create another private basic listener with port 443.

As you rightly mentioned you can have two listener using same frontend port but there is a condition for this: You can use the same port for both public-facing and private-facing listeners.

You can use public-facing and private-facing listeners with the same port number to simultaneously support both public and private clients (feature in Preview).

Refer: https://learn.microsoft.com/en-us/azure/application-gateway/application-gateway-faq#can-i-use-the-same-port-for-both-public-facing-and-private-facing-listeners

If you already have an existing public basic listener with port 443, then you cannot create another public basic listener with port 443. You can however create a private basic listener with port 443.

You can also create a multi-site listener with port 443.

Kindly let us know if the above helps or you need further assistance on this issue.

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Answer 2

Hi

I had a similar issue and it seems that contrary to what is said in the documentation, it is in fact not possible.

https://learn.microsoft.com/fr-fr/answers/questions/1692569/application-gateway-cannot-give-the-same-port-numb

Is there a reason why I have this message (see picture)?

thank you