NST Avahi (mDNS) FAQ - Revision history

Paul Blankenbaker at 23:27, 12 February 2023

2023-02-12T23:27:16Z

← Older revision		Revision as of 19:27, 12 February 2023
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	sudo systemctl enable avahi-daemon.service		sudo systemctl enable avahi-daemon.service

	== How Do I ~~Resolve~~ Avahi (mDNS) addresses when using systemd-resolved? ==		== How Do I enable the resolving of Avahi (mDNS) addresses when using systemd-resolved? ==

	The systemd-resolved service can be used to handle the "resolve" entry in /etc/nsswitch.conf (this is typically just before dns is invoked).		The systemd-resolved service can be used to handle the "resolve" entry in /etc/nsswitch.conf (this is typically just before dns is invoked).
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	sudo systemd-resolve --set-mdns=yes --interface=enp0s3		sudo systemd-resolve --set-mdns=yes --interface=enp0s3

	You can then use the systemd-resolve command to check that addresses can be resolved to host names and that host names can be resolved to addresses. Verify DNS, file and mDNS entries:		You can then use the systemd-resolve or getent hosts command to check that addresses can be resolved to host names and that host names can be resolved to addresses. Verify DNS, file and mDNS entries:

	~~systemctl~~-resolve localhost		systemd-resolve localhost
	~~systemctl~~-resolve nas.local		systemd-resolve nas.local
	~~systemctl~~-resolve 192.168.1.201		systemd-resolve 192.168.1.201
	~~systemctl~~-resolve www.google.com		systemd-resolve www.google.com
			getent hosts www.cnn.com

	You can also use PHP or Python to make sure that the gethostbyname and gethostbyaddr functions are also able to resolve names and addresses. Here is a PHP example:		You can also use PHP or Python to make sure that the gethostbyname and gethostbyaddr functions are also able to resolve names and addresses. Here is a PHP example:
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	NOTE: In my configuration, the gethostbyname for .local names seems to work much faster for C/PHP/Python that makes use of the glibc gethostbyname function. The "getent hosts NAME.local" command also works, but appears to be very slow in comparison when mDNS resolving is enabled.		NOTE: In my configuration, the gethostbyname for .local names seems to work much faster for C/PHP/Python that makes use of the glibc gethostbyname function. The "getent hosts NAME.local" command also works, but appears to be very slow in comparison when mDNS resolving is enabled.

	== How Do I Resolve Using Avahi (mDNS)? ==		== How Do I enable the resolving of Avahi (mDNS) addresses when not using systemd-resolved? ==

			The systemd-resolved service can be used to handle the "resolve" entry in /etc/nsswitch.conf (this is typically just before dns is invoked).

			hosts: files myhostname mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns

			To be able to fully resolve MutlicastDNS names to IPv4 addresses (and vice versa), you can change the hosts line to the following to get the fully functional mDNS resolver that allows you to resolve names to addresses and vice versa:

			hosts: files myhostname mdns4 [NOTFOUND=return] dns

			Since resolve was removed, you can also disable the systemd-resolved service:

			sudo systemctl disable --now systemd-resolved

			You can then use the getent command to check that addresses can be resolved to host names and that host names can be resolved to addresses. Verify DNS, file and mDNS entries:

			getent hosts localhost
			getent hosts nas.local
			getent hosts 192.168.1.201
			getent hosts www.google.com

			You can also use PHP or Python to make sure that the gethostbyname and gethostbyaddr functions are also able to resolve names and addresses. Here is a PHP example:

			echo "<?php echo(gethostbyname('www.google.com')) ?>" \| php
			echo "<?php echo(gethostbyname('pollomocha.local')) ?>" \| php
			echo "<?php echo(gethostbyaddr('192.168.1.201')) ?>" \| php

			NOTE: Changing from mdns4_minimal to mdns4 in /etc/nsswitch.conf may come with a performance cost, see https://github.com/lathiat/nss-mdns.

			== How Do I Resolve Using Avahi (mDNS) by hand? ==

	You can use the ''avahi-resolve'' command to verify that a host name resolves to an IPv4 or IPv6 address.		You can use the ''avahi-resolve'' command to verify that a host name resolves to an IPv4 or IPv6 address.

Paul Blankenbaker at 23:11, 12 February 2023

2023-02-12T23:11:12Z

← Older revision		Revision as of 19:11, 12 February 2023
Line 54:		Line 54:
	echo "<?php echo(gethostbyname('pollomocha.local')) ?>" \| php		echo "<?php echo(gethostbyname('pollomocha.local')) ?>" \| php
	echo "<?php echo(gethostbyaddr('192.168.1.201')) ?>" \| php		echo "<?php echo(gethostbyaddr('192.168.1.201')) ?>" \| php

			NOTE: In my configuration, the gethostbyname for .local names seems to work much faster for C/PHP/Python that makes use of the glibc gethostbyname function. The "getent hosts NAME.local" command also works, but appears to be very slow in comparison when mDNS resolving is enabled.

	== How Do I Resolve Using Avahi (mDNS)? ==		== How Do I Resolve Using Avahi (mDNS)? ==

Paul Blankenbaker: Added section on how to configure systemd-resolved to handle mDNS addresses

2023-02-12T21:43:38Z

Added section on how to configure systemd-resolved to handle mDNS addresses

← Older revision		Revision as of 17:43, 12 February 2023
Line 15:		Line 15:

	sudo systemctl enable avahi-daemon.service		sudo systemctl enable avahi-daemon.service

			== How Do I Resolve Avahi (mDNS) addresses when using systemd-resolved? ==

			The systemd-resolved service can be used to handle the "resolve" entry in /etc/nsswitch.conf (this is typically just before dns is invoked).

			hosts: files myhostname mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns

			If you choose to enabled systemd-resolved, you can leave /etc/nsswitch.conf alone. However, if you'd like to reduce it, you can simplify the hosts entry to:

			hosts: myhostname resolve

			To enable and start the systemd-resolved service:

			sudo systemctl enable --now systemd-resolved

			The default configuration for systemd-resolved has the MulticastDNS option disabled. So, you won't be able to resolve Avahi (mDNS) entries by default. To enable, uncomment or add the following line to /etc/systemd/resolved.conf:

			MulticastDNS=yes

			Then restart the systemd-resolved service:

			sudo systemctl restart systemd-resolved

			Finally, you can use the systemd-resolve command to configure how systemd-resolved should resolve mDNS addresses, in particular what interfaces it should resolve (resolvectl can probably be used as well):

			sudo systemd-resolve --set-mdns=yes --interface=enp0s3

			You can then use the systemd-resolve command to check that addresses can be resolved to host names and that host names can be resolved to addresses. Verify DNS, file and mDNS entries:

			systemctl-resolve localhost
			systemctl-resolve nas.local
			systemctl-resolve 192.168.1.201
			systemctl-resolve www.google.com

			You can also use PHP or Python to make sure that the gethostbyname and gethostbyaddr functions are also able to resolve names and addresses. Here is a PHP example:

			echo "<?php echo(gethostbyname('www.google.com')) ?>" \| php
			echo "<?php echo(gethostbyname('pollomocha.local')) ?>" \| php
			echo "<?php echo(gethostbyaddr('192.168.1.201')) ?>" \| php

	== How Do I Resolve Using Avahi (mDNS)? ==		== How Do I Resolve Using Avahi (mDNS)? ==

Paul Blankenbaker: Cleaned up how to fix AT&T router issue

2019-04-22T21:22:01Z

Cleaned up how to fix AT&T router issue

← Older revision		Revision as of 17:22, 22 April 2019
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	I have run into AT&T WIFI access points that resolve .local domains under the normal DNS protocol. This breaks normal Avahi lookups and was driving me crazy for several weeks. I finally came across an answer to this issue at [https://bugzilla.redhat.com/show_bug.cgi?id=1690078 Red Hat Bugzilla – Bug 1690078]. Basically on an NST system, you need to:		I have run into AT&T WIFI access points that resolve .local domains under the normal DNS protocol. This breaks normal Avahi lookups and was driving me crazy for several weeks. I finally came across an answer to this issue at [https://bugzilla.redhat.com/show_bug.cgi?id=1690078 Red Hat Bugzilla – Bug 1690078]. Basically on an NST system, you need to:

	# Change the ''/etc/nsswitch.conf'' file to use the ''mdns4'' library instead of the ''mdns4_minimal'' library:		* Change the ''/etc/nsswitch.conf'' file to use the ''mdns4'' library instead of the ''mdns4_minimal'' library:

	# Work around to dang AT&T Access Point resolving .local domains		# Work around to dang AT&T Access Point resolving .local domains
	hosts: files ~~mdns4_minimal~~ [NOTFOUND=return] dns myhostname		hosts: files mdns4 [NOTFOUND=return] dns myhostname

	# Create a /etc/mdns.allow file with the following entries:		* Create a /etc/mdns.allow file with the following entries:

	# Work around to dang AT&T Access Point resolving .local domains		# Work around to dang AT&T Access Point resolving .local domains

Paul Blankenbaker: Created page with "TOC = Avahi/mDNS General = == What Services Need to Be Running? == The ''avahi-daemon.service'' needs to be running. You can check its status via: systemctl status av..."

2019-04-22T21:20:14Z

Created page with "__TOC__ = Avahi/mDNS General = == What Services Need to Be Running? == The ''avahi-daemon.service'' needs to be running. You can check its status via: systemctl status av..."

New page

__TOC__
= Avahi/mDNS General =

== What Services Need to Be Running? ==

The ''avahi-daemon.service'' needs to be running. You can check its status via:

systemctl status avahi-daemon.service

You can start it via:

sudo systemctl start avahi-daemon.service

You can enable it so it is started at boot time via:

sudo systemctl enable avahi-daemon.service

== How Do I Resolve Using Avahi (mDNS)? ==

You can use the ''avahi-resolve'' command to verify that a host name resolves to an IPv4 or IPv6 address.

[root@nst-test ~]# avahi-resolve -4 -n nst-test.local
nst-test.local 192.168.1.221
[root@nst-test ~]# avahi-resolve -6 -n nst-test.local
nst-test.local 2600:1700:1850:e820:56a0:f48:d01f:86bd
[root@nst-test ~]#

== How Do I Add Avahi Resolving to nsswitch.conf? ==

You need to have the following packages installed:

sudo dnf install avahi-daemon nss-mdns

You need to have the ''avahi-daemon'' service running:

sudo systemctl start avahi-daemon.service
sudo systemctl enable avahi-daemon.service

In order for normal commands (like ''ping'', ''ssh'', etc) to resolve Avahi host names, you need to have the following configuration line in your ''/etc/nsswitch.conf'' file:

hosts: files mdns4_minimal [NOTFOUND=return] dns myhostname

This line is typically added automatically when you add the nss-mdns package.

== What Happens If My Router Resolves .local Domains? ==

I have run into AT&T WIFI access points that resolve .local domains under the normal DNS protocol. This breaks normal Avahi lookups and was driving me crazy for several weeks. I finally came across an answer to this issue at [https://bugzilla.redhat.com/show_bug.cgi?id=1690078 Red Hat Bugzilla – Bug 1690078]. Basically on an NST system, you need to:

# Change the ''/etc/nsswitch.conf'' file to use the ''mdns4'' library instead of the ''mdns4_minimal'' library:

# Work around to dang AT&T Access Point resolving .local domains
hosts: files mdns4_minimal [NOTFOUND=return] dns myhostname

# Create a /etc/mdns.allow file with the following entries:

# Work around to dang AT&T Access Point resolving .local domains
.local.
.local

== How Do I Scan My Network For Avahi Service? ==

The easy was is to use the NST Web Interface. From the menu bar, select ''Security'' -> ''Active Scanners'' -> ''NST Avahi (mDNS) Discovery''. This will generate a table of available services and hosts with active links that allow further inspection.

Alternatively, you can run the following from the command line:

sudo avahi-browse --all

NST Avahi (mDNS) FAQ - Revision history

Paul Blankenbaker at 23:27, 12 February 2023

Paul Blankenbaker at 23:11, 12 February 2023

Paul Blankenbaker: Added section on how to configure systemd-resolved to handle mDNS addresses

Paul Blankenbaker: Cleaned up how to fix AT&T router issue

Paul Blankenbaker: Created page with "__TOC__ = Avahi/mDNS General = == What Services Need to Be Running? == The ''avahi-daemon.service'' needs to be running. You can check its status via: systemctl status av..."

Paul Blankenbaker: Created page with "TOC = Avahi/mDNS General = == What Services Need to Be Running? == The ''avahi-daemon.service'' needs to be running. You can check its status via: systemctl status av..."