On Wed, 13 Dec 2023, Alexandre Petrescu via Starlink wrote:
A tunnel within 3GPP network (GTP) is used, among other reasons, to
support mobility. The 'mobility', among some interpretations, is to
maintain a constant IP address for a moving end user.
Surprisingly, the URL
https://support.starlink.com/?topic=1192f3ef-2a17-31d9-261a-a59d215629f4
explains that that kind of mobility is not supported in starlink, i.e.
the end user might get another IP address if going to some other area.
It is surprising in that in other starlink.com URLs they offer starlink
service for automobiles, and these typically move a lot. Maybe the
starlink-connected automobiles do change their IP addresses a lot, but
the end users dont care that much.
To support mobility within a starlink network - maintain constant all IP
addresses in a car - maybe one would try the DHCPv6 CONFIRM message to
try to maintain the same allocated /56 but it another area. Maybe the
starlink DHCPv6-PD server will satisfy that CONFIRM, or maybe not.
Or maybe there is a need of some other protocol in starlink, or in user
equipment connected to starlink (Dishy, third party router), to offer
that mobility. But without adding new latency, of course.
(this mobility aspect is on topic of the IP country ranges -
cross-border areas would ideally not break connectivity).
There are two types of keeping your address. One is to have the same address all
the time, the other is to keep your address during a session.
Even if you get a public address, it can change from time to time (just like
DHCP addresses could on landline ISPs), but that doesn't mean that your address
will change during a session (i.e. while you are powered up and connected) even
while moving around.
If you get a public IP, that IP will change like a DHCP address would on a
landline ISP, rarely and mostly when equipment at one end or another was
restarted, but not every time you do a new satellite handoff
David Lang
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