I spent this weekend in Czechia. 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

T-Mobile - MCCMNC 23001

Home PLMN	Tech	IPV6 PDP context	IPV4V6 PDP context
Telenor Norway	2G	Fails	IPv4-only connection
Telenor Norway	3G	Fails	IPv4-only connection
Telenor Norway	4G	Works perfectly	Works perfectly

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

These results do not necessarily mean that T-Mobile has a problem with supporting IPv6 on 2G and/or 3G. It could very well be that it is entirely due to Telenor’s HLR/HSS blacklisting, and that it would start working immediately if Telenor were to move T-Mobile to their IPv6 whitelist.

When in 4G coverage, IPv6-only and dual stack work perfectly. This is as expected, because the HLR/HSS blacklisting trick does not work on 4G.

O2 - MCCMNC 23002

Home PLMN	Tech	IPV6 PDP context	IPV4V6 PDP context
Telenor Norway	2G	Fails	IPv4-only connection
Telenor Norway	3G	Fails	IPv4-only connection
Telenor Norway	4G	Works perfectly	Works perfectly

Exactly the same results as T-Mobile. Telenor’s HLR/HSS IPv6 blacklisting in action.

Vodafone - MCCMNC 23003

Home PLMN	Tech	IPV6 PDP context	IPV4V6 PDP context
Telenor Norway	2G	Works perfectly	Works perfectly
Telenor Norway	3G	Works perfectly	Works perfectly
Telenor Norway	4G	Works perfectly	Works perfectly

Vodafone is the only Czech operator to get a perfect score. IPv6-only and dual stack connectivity always works, regardless of the technology used.