~tore Tore Anderson's technology blog

IPv6 roaming in the United Kingdom

Earlier this week I visited the United Kingdom to attend the excellent UKNOF36 meeting.

As I usually do when when going abroad, I spent some time testing to what extent IPv6 works while roaming in the various PLMNs I have access to.

The previous posts in this series are:

Those posts contain some more technical background about the testing methodology, so I suggest you skim through them in order to better interpret the test results in this post.

Test results

O2 - MCCMNC 23410

Home PLMN Tech IPV6 PDP context IPV4V6 PDP context
Tele 2 Sweden 2G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 3G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 4G N/A N/A
Telenor Norway 2G Fails (cause 33) IPv4-only connection
Telenor Norway 3G Fails (cause 33) IPv4-only connection
Telenor Norway 4G N/A N/A

I was not able to get 4G coverage with any of my SIM cards in this network, which probably means that neither Tele 2 nor Telenor have a 4G roaming agreement with O2.

While in 2G and 3G coverage Tele 2 and Telenor’s HLR/HSS blacklisting trick comes into play. (See the IPv6 roaming in Belgium and Romania post for an explanation of what that trick is.)

Vodafone - MCCMNC 23415

Home PLMN Tech IPV6 PDP context IPV4V6 PDP context
Tele 2 Sweden 2G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 3G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 4G Fails IPv4-only connection
Telenor Norway 2G Fails (cause 33) IPv4-only connection
Telenor Norway 3G Fails (cause 33) IPv4-only connection
Telenor Norway 4G Works perfectly IPv4-only connection

In 2G and 3G coverage this looks like the standard HLR/HSS blacklisting trick. However the 4G behaviour is very unusual (as the blacklisting trick is specific to 2G and 3G).

IPv6-only PDP contexts work fine with my Telenor SIM card, but not with my Tele 2 one. My phone logs this latter failure as being due to an unknown/invalid cause code so I have no idea about what’s going on here.

Dual stack IPV4V6 PDP contexts do not work in 4G coverage with any of my SIM cards, and any attempt to use them results in IPv4-only connectivity. As this is not caused by Telenor and Tele 2’s blacklisting trick, the logical conclusion is that Vodafone is deliberately blocking dual stack PDP contexts from being used in their end.

I also saw very similar IPv6-hostile behaviour in Vodafone Romania’s network. I wonder if that is a coincidence or not.

3 - MCCMNC 23420

Home PLMN Tech IPV6 PDP context IPV4V6 PDP context
Tele 2 Sweden 2G N/A N/A
Tele 2 Sweden 3G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 4G N/A N/A
Telenor Norway 2G N/A N/A
Telenor Norway 3G N/A N/A
Telenor Norway 4G N/A N/A

It appears Telenor doesn’t have a roaming agreement with this operator (my phone reported no access to network). With my Tele 2 SIM card I could not get neither 2G or 4G coverage, only 3G. In 3G coverage Tele 2’s HLR/HSS blacklisting trick comes into play.

EE - MCCMNC 23430

Home PLMN Tech IPV6 PDP context IPV4V6 PDP context
Tele 2 Sweden 2G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 3G Fails (cause 33) IPv4-only connection
Tele 2 Sweden 4G Works perfectly Works perfectly
Telenor Norway 2G Fails (cause 27) IPv4-only connection
Telenor Norway 3G Fails (cause 27) IPv4-only connection
Telenor Norway 4G Works perfectly Works perfectly

This looks pretty much as expected for an operator where the HLR/HSS blacklisting trick is being used to block IPv6 in 2G and 3G coverage. However, it’s the first time I’ve seen this result in 3GPP cause code 27 (missing or unknown APN). Usually I see code 33 (requested service option not subscribed). Not sure if this difference is significant somehow, but the outcome is the same in any case.

When in 4G coverage, both IPv6-only and dual stack PDP contexts worked just fine.

That said, I did have trouble getting dual stack to work in EE 4G coverage when I used another one of phones. Unfortunately I did not have time to investigate that further during my brief visit. Next time, perhaps.