pppoe: T9356: do not fail commit when no Router Advertisement is received (#5504)

The Router Solicitation kicked off when an IPv6 autoconf PPPoE link comes up
is best effort - the peer may answer late or not at all. rdisc6(8) then blocks
for the duration of all retries and exits non-zero, which aborted the commit:

  FileNotFoundError: [Errno 2] failed to run command: rdisc6 --single --retry 3 pppoe1000
  returned: Soliciting ff02::2 (ff02::2) on pppoe1000...
  Timed out.
  No response.
  exit code: 2

Run rdisc6(8) detached in a transient systemd unit, so neither the delay nor
the exit code reaches the commit. The outcome is logged to the journal.

1 files changed, 12 insertions, 2 deletions

diff --git a/python/vyos/ifconfig/pppoe.py b/python/vyos/ifconfig/pppoe.py
index eb217e12d..413c75023 100644
--- a/python/vyos/ifconfig/pppoe.py
+++ b/python/vyos/ifconfig/pppoe.py
@@ -17,6 +17,8 @@ from vyos.ifconfig.interface import Interface
 from vyos.template import is_ipv6
 from vyos.utils.assertion import assert_range
 from vyos.utils.dict import dict_search
+from vyos.utils.process import cmdl
+from vyos.utils.process import get_wrapper
 from vyos.utils.network import get_interface_config
 from vyos.utils.network import mac2eui64
 
@@ -156,6 +158,14 @@ class PPPoEIf(Interface):
             if 'ipv6' in config:
                 self._cmdl(['vtysh', '-c', 'conf t'] + vrf + ['-c', f'ipv6 route ::/0 {self.ifname} tag 210 {distance}'])
 
-        # kick RS when IPv6 is up.
+        # Kick a Router Solicitation when IPv6 is up. This is best effort -
+        # the peer may answer late or not at all
         if dict_search('ipv6.address.autoconf', config) is not None:
-            self._cmdl(['rdisc6', '--single', '--retry', '3', self.ifname])
+            # systemd-run(1) only asks PID 1 to start the transient unit, so
+            # rdisc6(8) does not inherit our VRF context - it has to be entered
+            # inside the unit itself
+            wrapper = get_wrapper(config['vrf'] if 'vrf' in config else None, None)
+            description = f'VyOS IPv6 Router Solicitation on {self.ifname}'
+            cmdl(['systemd-run', '--quiet', '--collect',
+                  f'--description={description}'] + wrapper +
+                 ['rdisc6', '--single', '--retry', '3', self.ifname], self.debug)