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Fix: add section to troubleshoot Avahi and mDNS #771

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Sep 21, 2020
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Fix: add section to troubleshoot Avahi and mDNS #771

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Docs: add Avahi troubleshooting command
mbologna Sep 15, 2020
af975ab
Docs: add mdns.allow to troubleshooting section
mbologna Sep 15, 2020
ae875ec
Fix: post PR review fixes
mbologna Sep 17, 2020
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12 changes: 11 additions & 1 deletion TROUBLESHOOTING.md
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Expand Up @@ -28,8 +28,9 @@ Could not resolve hostname server.tf.local: Name or service not known
Check that:
- your firewall is not blocking UDP port 5353
- on SUSE systems check YaST -> Security and Users -> Firewall -> Zones -> public, "mdns" should appear on the list on the right
- avahi is installed and running
- Avahi is installed and running
- typically you can check this via systemd: `systemctl status avahi-daemon`
- Avahi is capable of resolving the host you are trying to reach: `avahi-resolve -n uyuni.tf.local`
- mdns is configured in glibc's Name Server Switch configuration file

In `/etc/nsswitch.conf` you should see a `hosts:` line that looks like the following:
Expand All @@ -38,6 +39,15 @@ hosts: files mdns [NOTFOUND=return] dns
```
`mdns` (optionally suffixed with `4` for IPv4-only or `6` for IPv6-only) should be present in this line. If it is not, add it.

Starting with `nss-mdns` version 0.14.1, you also need to populate `/etc/mdns.allow` with:

```
.local
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.tf.local
```

`mdns.allow` is required to [force all multicast DNS domains to be resolved regardless of label count or unicast SOA records](https://github.com/lathiat/nss-mdns/blob/master/README.md#etcmdnsallow).

## Q: how can I work around slowness in resolution of `tf.local` mDNS/Zeroconf/Bonjour/Avahi names?

If there is a 5-second delay on any name resolution (or ping) between Avahi hosts, a likely cause is that ipv6 is enabled on the VMs (that is the default setting) but the network is blocking ipv6 traffic.
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