netdev - failed to set GRE remote IP address after interface was created

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Message-ID: <389196c8-1223-f996-3309-653b56fa4386@s-terra.ru>
Date:   Mon, 20 Dec 2021 18:51:09 +0300
From:   Муравьев Александр 
        <amuravyev@...erra.ru>
To:     <netdev@...r.kernel.org>
Subject: failed to set GRE remote IP address after interface was created

It is impossible to change a remote IP address for a GRE interface if it 
was initially created without specifying a remote address.

E.g. if the interface was created by command "ip tunnel add gre1 mode 
gre key 123", it is impossible to specify a remote IP address:

"ip tunnel change gre1 remote 1.1.1.1" gives invalid argument error.

I was able to reproduce the behavior in modern Debian and Ubuntu systems.

Is it impossible to change "point-to-point" GRE interface to 
"point-to-multipoint" and vice versa? I just was unable to find this bug 
description/ticket.

Alexander Muravev