reformat and refer to trac for routing issue

tsa/howto/upgrades/buster.mdwn

@@ -105,21 +105,24 @@ Issues
 Pending
 -------
 
- * Warning: upgrading (restarting) openvswitch will mean all guests lose network.
-
- * At least on kvm5, brpub was having issues.  Either ipv4 or ipv6 address was missing,
-   or the v6 route to the guests was missing.  Probably because the ipv6 route
-   setting failed since we set a prefsrc and that was only brought up later?
-
-
-   Rewrote network/interfaces to set things up more manually.
-   On your host, check if brpub has both ipv4 and ipv6 addresses after boot before
-   launching VMs, and that is has an ipv6 route into brpub with the configured
-   prefsrc addr.  If not, fiddle likewise.
+ * upgrading restarts openvswitch will mean all guests lose network
+
+ * At least on `kvm5`, `brpub` was having issues.  Either ipv4 or ipv6
+   address was missing, or the v6 route to the guests was missing.
+   Probably because the ipv6 route setting failed since we set a
+   prefsrc and that was only brought up later?
+
+   Rewrote `/etc/network/interfaces` to set things up more manually.
+   On your host, check if `brpub` has both ipv4 and ipv6 addresses after
+   boot before launching VMs, and that is has an ipv6 route into `brpub`
+   with the configured `prefsrc` address.  If not, fiddle
+   likewise.
+   
+   See [ticket #31083](https://trac.torproject.org/projects/tor/ticket/31083) for followup on possible routing issues.
 
- * On physical hosts witch /etc/sysfs.d/local-io-schedulers.conf, note that 'deadline' no
-   longer existsts.  Probably it is also not necessary as Linux might pick the right
-   scheduler anyhow.
+ * On physical hosts witch `/etc/sysfs.d/local-io-schedulers.conf`,
+   note that `deadline` no longer existsts. Probably it is also not
+   necessary as Linux might pick the right scheduler anyhow.
 
  * the following config files had conflicts but were managed by Puppet
    so those changes were ignored for now. eventually they should be