Re: Understanding IPv6-PD over PPPoE

On 15/06/2021 15:56, Bjørn Mork wrote:

Is my ISP behaving in a broken way, by not assigning me an address in
response to IA_NA, or is it standard behaviour for ISPs to only
respond to IA_PD requests?

There is no standard behaviour.  Both ways are fine.  There usually
isn't much need for the IA_NA address.

Well, some more related brokenness just discovered while diagnosing some network problems on a different internet connection:

- PPP link comes up and assigns IPv4 through LCP.
- I send an IPv6 router solicitation to my ISP.
- ISP responds with a router advertisement, which has the "managed address configuration" and "other configuration" flags set.
- I send DHCPv6 Solicit with IA_NA and IA_PD options.
- ISP responds with a DHCPv6 Advertise, which contains neither an IPv6 address nor prefix.

The ISP supports IPv6 but I'm guessing they haven't provisioned this connection for it - the router solicitation is working but DHCPv6 isn't giving out an address or prefix.

The result is that the machine has a default route but no public IPv6 address, which is similar to my first example. When you try to make an IPv6 connection out to the internet, instead of it just outright failing as it would without a suitable route, it tries to use the PPP interface's link local address as the source. This means that trying to connect to a dual-stack host is very very slow since you have to wait for the v6 connection to time out before it falls back to v4.

I can't see a good reason for installing a default route when DHCP hasn't allocated an address or prefix - doing so just leaves the machine with a broken network setup.

- Steve Hill
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