Without allow/deny:

Found user 'avahi' (UID 107) and group 'avahi' (GID 1012).
Successfully dropped root privileges.
chroot.c: chroot() helper started
lt-avahi-daemon 0.6.22 starting up.
WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Successfully called chroot().
Successfully dropped remaining capabilities.
chroot.c: chroot() helper got command 02
Loading service file /services/sftp-ssh.service.
Loading service file /services/ssh.service.
socket() failed: Address family not supported by protocol
Failed to create IPv6 socket, proceeding in IPv4 only mode
Joining mDNS multicast group on interface xenbr0.IPv4 with address 85.17.131.2.
New relevant interface xenbr0.IPv4 for mDNS.
Joining mDNS multicast group on interface eth0.IPv4 with address 192.168.0.5.
New relevant interface eth0.IPv4 for mDNS.
Network interface enumeration completed.
Registering new address record for 85.17.131.2 on xenbr0.IPv4.
Registering new address record for 192.168.0.5 on eth0.IPv4.
Registering HINFO record with values 'X86_64'/'LINUX'.
Server startup complete. Host name is xen01.local. Local service cookie is 815975261.
Service "xen01" (/services/ssh.service) successfully established.
Service "SFTP File Transfer on xen01" (/services/sftp-ssh.service) successfully established.
Got SIGINT, quitting.
chroot.c: chroot() helper got command 0d
Leaving mDNS multicast group on interface xenbr0.IPv4 with address 85.17.131.2.
Leaving mDNS multicast group on interface eth0.IPv4 with address 192.168.0.5.
chroot.c: chroot() helper got command 0c
chroot.c: chroot() helper exiting with return value 0

With allow eth0:

Process 13679 died: No such process; removing PID file. (/var/run/avahi-daemon//pid)
Found user 'avahi' (UID 107) and group 'avahi' (GID 1012).
Successfully dropped root privileges.
chroot.c: chroot() helper started
lt-avahi-daemon 0.6.22 starting up.
WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Successfully called chroot().
Successfully dropped remaining capabilities.
chroot.c: chroot() helper got command 02
Loading service file /services/sftp-ssh.service.
Loading service file /services/ssh.service.
socket() failed: Address family not supported by protocol
Failed to create IPv6 socket, proceeding in IPv4 only mode
Joining mDNS multicast group on interface eth0.IPv4 with address 192.168.0.5.
New relevant interface eth0.IPv4 for mDNS.
Network interface enumeration completed.
Registering new address record for 192.168.0.5 on eth0.IPv4.
Registering HINFO record with values 'X86_64'/'LINUX'.
Server startup complete. Host name is xen01.local. Local service cookie is 3150992728.
Service "xen01" (/services/ssh.service) successfully established.
Service "SFTP File Transfer on xen01" (/services/sftp-ssh.service) successfully established.
Got SIGINT, quitting.
chroot.c: chroot() helper got command 0d
Leaving mDNS multicast group on interface eth0.IPv4 with address 192.168.0.5.
chroot.c: chroot() helper got command 0c
chroot.c: chroot() helper exiting with return value 0

With deny eth0:
Found user 'avahi' (UID 107) and group 'avahi' (GID 1012).
Successfully dropped root privileges.
chroot.c: chroot() helper started
lt-avahi-daemon 0.6.22 starting up.
WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Successfully called chroot().
Successfully dropped remaining capabilities.
chroot.c: chroot() helper got command 02
Loading service file /services/sftp-ssh.service.
Loading service file /services/ssh.service.
socket() failed: Address family not supported by protocol
Failed to create IPv6 socket, proceeding in IPv4 only mode
Joining mDNS multicast group on interface xenbr0.IPv4 with address 85.17.131.2.
New relevant interface xenbr0.IPv4 for mDNS.
Network interface enumeration completed.
Registering new address record for 85.17.131.2 on xenbr0.IPv4.
Registering HINFO record with values 'X86_64'/'LINUX'.
Server startup complete. Host name is xen01.local. Local service cookie is 2706254748.
Service "xen01" (/services/ssh.service) successfully established.
Service "SFTP File Transfer on xen01" (/services/sftp-ssh.service) successfully established.
Got SIGINT, quitting.
chroot.c: chroot() helper got command 0d
Leaving mDNS multicast group on interface xenbr0.IPv4 with address 85.17.131.2.
chroot.c: chroot() helper got command 0c
chroot.c: chroot() helper exiting with return value 0

With allow+deny eth0:
Found user 'avahi' (UID 107) and group 'avahi' (GID 1012).
Successfully dropped root privileges.
chroot.c: chroot() helper started
lt-avahi-daemon 0.6.22 starting up.
WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Successfully called chroot().
Successfully dropped remaining capabilities.
chroot.c: chroot() helper got command 02
Loading service file /services/sftp-ssh.service.
Loading service file /services/ssh.service.
socket() failed: Address family not supported by protocol
Failed to create IPv6 socket, proceeding in IPv4 only mode
Network interface enumeration completed.
Registering HINFO record with values 'X86_64'/'LINUX'.
Server startup complete. Host name is xen01.local. Local service cookie is 2072567116.
Service "xen01" (/services/ssh.service) successfully established.
Service "SFTP File Transfer on xen01" (/services/sftp-ssh.service) successfully established.
Got SIGINT, quitting.
chroot.c: chroot() helper got command 0d
chroot.c: chroot() helper got command 0c
chroot.c: chroot() helper exiting with return value 0