[AusNOG] Telstra Mobile NAT64 Gateway dropping UDP?

[Andras Toth]

Hi Matthew,

As long as you use a DNS hostname instead of an IPv4 literal address,
things should work fine for both local apps or tethered/hotspot access
because Telstra's DNS servers can do DNS64. Locally on the iPhone you can
use a literal IPv4 too because iOS will do local address translation
(CLAT), but it can't translate IPv4 literals to IPv6 for connections via
the hotspot.

I don't have any problems with UDP on Telstra IPv6-only connection, I just
tried and I can send and receive UDP packets via the Telstra NAT64 gateway
when visiting https://h2o.examp1e.net/ in a browser that supports QUIC
(because that uses UDP) and since that hostname does not have an IPv6
address, Telstra converts it to IPv6 via DNS64. You can see from the packet
capture below that both src and dst addresses are Telstra (one is mine,
other side is the DNS64 gateway).

18:25:12.424022 IP6 (flowlabel 0xd0300, hlim 64, next-header UDP (17)
payload length: 1238) 2001:8004:c81:6820:f5b6:b0a:c39c:7cf.58910 >
2001:8004:11d0:4e2a::84e2:18c.443: [udp sum ok] UDP, length 1230
18:25:12.666177 IP6 (hlim 45, next-header UDP (17) payload length: 1288)
2001:8004:11d0:4e2a::84e2:18c.443 >
2001:8004:c81:6820:f5b6:b0a:c39c:7cf.58910: [udp sum ok] UDP, length 1280
18:25:12.667703 IP6 (flowlabel 0xd0300, hlim 64, next-header UDP (17)
payload length: 1238) 2001:8004:c81:6820:f5b6:b0a:c39c:7cf.58910 >
2001:8004:11d0:4e2a::84e2:18c.443: [udp sum ok] UDP, length 1230
18:25:12.668868 IP6 (hlim 45, next-header UDP (17) payload length: 1288)
2001:8004:11d0:4e2a::84e2:18c.443 >
2001:8004:c81:6820:f5b6:b0a:c39c:7cf.58910: [udp sum ok] UDP, length 1280

I would suggest trying to replicate the issue and gathering a packet
capture to see what packets go through and what gets lost. It might be MTU
related issues if too large packets can't go through but I can send 1410
bytes packets via the cellular connection successfully.

Regards,
Andras


On Tue, Jan 4, 2022 at 9:34 PM Matthew H <Matthew at marrold.co.uk> wrote:

> Hi,
>
> The app works fine on other IPv6 only networks with NAT64 in place which
> appears to satisfy Apple's requirements.
>
> We are looking into adding proxies with IPv6 support, however it's likely
> to take some time and it would be good if we can find a fix / workaround in
> the meantime
>
> Thanks
>
> On Tue, Jan 4, 2022 at 10:10 AM Troy <troy at troykelly.com> wrote:
>
>> Apologies for a non answer, but any app (at least with Apple) is required
>> to support IPv6 only networks.
>>
>> https://developer.apple.com/support/ipv6/
>>
>> Rather than work on a 6 to 4 fix, why not put some energy into supporting
>> IPv6?
>>
>> *Regards, Troy*
>> Brevity is the elixir of life.
>> Father Hector McGrath, Pixie 2020
>>
>>
>>
>>
>> -------- Original Message --------
>> On 4 Jan 2022, 9:03 pm, Matthew H < Matthew at marrold.co.uk> wrote:
>>
>>
>> Hi,
>>
>> We are developing a WebRTC mobile app that sets up a media session via
>> Web Socket and then sends the media via RTP over UDP. It's working on most
>> networks but we've had users report issues with the app when their iPhone
>> is connected to the Telstra Mobile network.
>>
>> Unfortunately our network only supports IPv4, and after examining the
>> available logs it appears their iPhone only gets an IPv6 address. The Web
>> Socket communication is able to reach us so I assume a NAT64 gateway is in
>> use, but we don't see any RTP / UDP arrive at our network edge.
>>
>> We found a couple of posts that suggest users have had similar issues
>> with UDP being dropped:
>>
>>
>> https://crowdsupport.telstra.com.au/t5/network-roaming/unable-to-stream-video-over-udp-on-ipv6-only-connection/td-p/933472
>>
>> https://crowdsupport.telstra.com.au/t5/network-roaming/ios-and-ipv6/td-p/931449
>>
>> https://crowdsupport.telstra.com.au/t5/apple-ios/nordvpn-won-t-connect-on-4g-ios/td-p/932511
>>
>> Is anyone aware of Telstra's NAT64 gateway dropping UDP?
>>
>> Thanks
>> Matthew
>>
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