Monday, February 14, 2011

Zero Configuration Network (ZEROCONF)

Most Linux distributions utilise the Zero Configuration Network (ZEROCONF) automation suite. This is an IETF workgroup that planned and coordinated a series of dynamic configuration protocols to allow many operating systems to automatically configure themselves and communicate on a network without the need of DHCP or DNS servers. ZEROCONF utilises the 169.254.0.0/16 network address to autoconfigure using a series of unanswered "ARP" queries and then assumes an address if the queries yield an empty result.



A route to the ZEROCONF network is added to the routing table by the network initscripts.


[bash]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.214.64.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth1      <-- ZEROCONF default IP route
0.0.0.0         10.214.64.254   0.0.0.0         UG    0      0        0 eth0

ZEROCONF can be turned off by adding the following entry to the "/etc/sysconfig/network" configuration file.

[bash]# vi /etc/sysconfig/network
NOZEROCONF=yes

Note !! The value for the "NOZEROCONF" parameter can actually be set to any value, the initscripts only check to determine whether the parameter has zero length. So setting "NOZEROCONF=no" will have the same effect as setting it to "yes". You will need to comment or remove the variable to reactive ZEROCONF.

The networking service will need to be restarted before the changes will take effect.

[bash]# /etc/init.d/network restart

Checking the network routing table again will identify the ZEROCONF route has been disabled and removed from the routing table.

[bash]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.214.64.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
0.0.0.0         10.214.64.254   0.0.0.0         UG    0      0        0 eth0

ZEROCONF is also commonly referred to as IPv4 Link-Local (IPv4LL) and Automatic Private IP Addressing (APIPA).

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