Re: [Starlink] Info on IP country ranges

[Alexandre Petrescu <alexandre.petrescu@gmail.com>]

Le 13/12/2023 à 19:27, David Lang a écrit :
> 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.
Fair enough.
>
> Even if you get a public address, it can change from time to time 
> (just like DHCP addresses could on landline ISPs), 

Well, it depends on ISP.  Indeed some wireline ISPs change the address 
of home customers relatively often - on DHCP lease expiry, MAC-less or 
NAI-less DHCP during reboots, etc.  But other landline ISPs do provide 
always the same IP address to customers.  Some times it is even part of 
the signed contract.


> 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.

Do you mean that the /56 I'd get from starlink with DHCPv6-PD would stay 
the same if I had ongoing sessions, and moved in and out the hexagon 
cells,or even in-out of a teleport coverage? (driving a car on a longer 
distance).

Remark that /56 can not be equated simply to the behaviour of an IPv4 
address.  That /56 means more than just one address and, additionally, 
it is bound to an IPv6 address to which it is routed (either a GUA or a 
LL, a 'next-hop' address).

The maintenance of that /56 constant can happen with or without 
maintenance of the 'next-hop' address constant.

If starlink keeps constant both the 'next-hop' address and the allocated 
/56 during movements to very wide distances (cell-to-cell, 
teleport-to-teleport) then it could some options.

If starlink keeps constant just the /56 allocated to end user, and 
varies the 'next-hop' address attached to it then it would other options.

There are design options.

>
> 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

satellite handoff: do you mean the handoff provoked by the movement of 
satellites to a ground-fixed user, or do you mean the movement of end 
user in and out of hexagon cells covered by satellites?

IMHO, I think it can mean either of the two.  For the latter (movement 
of end user between cells) there'd probably be another /56 delegated to 
an end user, regardless of having ongoing sessions - DHCP does not check 
the status of apps.

Further, a very wide area movement might provoke a change in teleport, 
not just a change in hexagon cells.  A change in teleport certainly 
provokes a change in the allocated /56 of the end user, again regardless 
of her having running sessions.  In order to keep a same /56 allocated 
to a same end user handed over from one teleport to another there would 
be a need of some teleport-to-teleport protocol, maybe a tunnelled BGP, 
or other.

Alex


>
> David Lang