Problem
I refined my network configuration a bit, because there was a problem: When I pinged the Vodafone IPv6 address of hadante from my new, shiny Hetzner box, it wouldn’t answer, because I got the policy routing wrong.
Initially I routed everyting to Hetzner via the Vodafone interface, but that’s plain wrong. This way hadante even sent packets originating from Telekom IP’s via the Vodafone interface, with the Telekom IP as source. What I really wanted:
- answer requests to the Vodafone interface via Vodafone
- make Telekom the default route
Answer requests to the Vodafone IP
The solution was easy: create a rule to send everything from the Vodafone interface out there. Unfortunately, nothing is as easy as it seems. Because the Vodafone-IPv6-Prefix is semi-static, systemd-networkd policy routing doesn’t work. The routing table can be filled automatically:
[Match] Name=ext [Network] DHCP=yes IPv6Token=::dead:b0a1 [DHCP] RouteMetric=4096 RouteTable=199 [IPv6AcceptRA] RouteTable=199
The RouteTable directive adds the routes acquired by DHCP and Router Announcments to the routing table 199 (aka kd, see /etc/iproute2/rt_tables), but without a rule it doesn’t do anything. The IPv6Token directive sets the IPv6 address to <prefix>::dead:b0a1, by the way.
The rule is added by a perl script written by yours truly. It does something like this (pseudo perl code):
...
$old = <old IPv6 address>;
$new = <new IPv6 address>;
# match old prefix
$old =~ m#^([[:xdigit:]]{1,4}:[[:xdigit:]]{1,4}:[[:xdigit:]]{1,4}:[[:xdigit:]]{1,4}:)#;
# delete old rule
system("/usr/bin/ip -6 rule dele from $1:/64 table kd");
# match new prefix
$new =m#^([[:xdigit:]]{1,4}:[[:xdigit:]]{1,4}:[[:xdigit:]]{1,4}:[[:xdigit:]]{1,4}:)#;
# add new rule
system("/usr/bin/ip -6 rule add from $1:/64 lookup kd");
...
This way both the Telekom IP and the Vodafone IP work from anywhere. As a bonus, IPv6 requests to Hetzner from the delegated Telekom IPv6 network now work, too 🙂
Configuring the Telekom interface
During my network configuration spree I tried to configure the Telekom interface with systemd-networkd instead of dhcpcd, but that didn’t work, unfortunately. I couldn’t get the prefix delegation to the internal interface to work. Supposedly systemd-networkd can do it, but the documentation is, let’s say, sparse at best. After several attempts I gave up and reverted to dhcpcd, as described in this post.