19216811.liveIP
Unconfigured interfaces
iMG/RG Software Reference Manual (IPNetwork Functions)
4-4
If the packet cannot be forwarded, an ICMP
Destination Unreachable
error will be returned to the sender.
By default, the checksum of forwarded IP packets is not checked. This is for reasons of efficiency, because calcu-
lating the checksum on all packets adds significantly to the forwarding time and reduces throughput. This default
setting is common in most IP routers. Locally terminated packets always have their checksum checked.
4.1.4
Unconfigured interfaces
An interface with an IP address of 0.0.0.0 is unconfigured. An interface is added as unconfigured when it is to be
configured at a later time, for example, by IPCP or DHCP.
No traffic will be forwarded from an unconfigured interface. However, an unconfigured interface may still
receive certain types of traffic, such as responses to DHCP requests.
An unconfigured interface should not be confused with an unnumbered interface.
4.1.5
Unnumbered interfaces
In a routed network, consider two routers that are joining two different subnets via a point-to-point link. It
would usually be necessary to allocate a whole subnet just for the link between the routers, in addition to the
other two subnets.
An unnumbered interface does not have a subnet associated with it and simply serves as one end of a point-to-
point link. An unnumbered link does not have an IP address, but a router ID
THAT
is the IP address of one of
the router’s other interfaces.
You can have multiple unnumbered interfaces as long as you have at least one normal (numbered) IP interface in
your router so that you can use its IP address as the router ID. The unnumbered interfaces can either use dif-
ferent router ID values, or use the same router ID value. Wha
TEVER
THEIR
VALUE
,
THE
ROUTER
ID(s) must match
the address of a normal interface.
Note:
Unnumbered interfaces can only be used on point-to-point links. This includes PPP. You cannot use
unnumbered interfaces with Ethernet
4.1.5.1 Unconfigured interfaces vs unnumbered interfaces
An unnumbered interface is not the same as an unconfigured interface.
An unconfigured interface is created by adding an interface without specifying an IP address (ip add interface
myinterface), or by specifying an IP address of 0.0.0.0 (ip add interface myinterface 0.0.0.0).
You would add an unconfigured interface if the interface address were to be set automatically later, for exam-
ple, by IPCP or DHCP. It cannot be used for normal traffic.
An unnumbered interface is different - it is used for normal traffic but does not have its own IP address or a
local subnet associated with it.