lab 01 vol 1  

Monday, February 9, 2009

Feb 09 ospf v1

lab 01:

OSPF network statement uses a wildcard mask to identify which interface or interfaces
are running the protocol.

The network statement determines which link-state area an interface belong to .

The wildcard mask of the network statement works like the wildcard mask option of an
IP access-list , where '0' indicates to check the particular bit position, binary one
indicates to ignore the particular bit position

Wild card mask doesnot relate to the IP subnet mask of an interface . It is simply used to
determine which interface/interfaces belong to the area of ospf process .

When multiple network statements are configured with overlapping matches , as in the
above case , the most specific network statement determines which are the interface will
exist in .

commands used :

show ip ospf int

show ip ospf int brief

show ip ospf int | in (Loopback [0-9] | Area)

DOC CD / command reference


To define the interface on which ospf runs and to define the area id for thos
interfaces , use the "network area" command in router confi mode .

wildcard-mask :

ip-address-type mask that include "dont care" bits .

Area-id :

Area that is to be associated with ospf address range . It can be
specified as either a decimal value or an "IP ADDRESS".

if you intend to associate areas with IP subnets , you can specify
a subnet address as the value of the area-id argument.

Usage Guidelines:

Using the wildcard-mask argument allows you to define one or
multiple interfaces to be associated with a specific ospf area
using a single command

For ospf to operate on the interface , the primary address of the
interface must be covered by the network area command.

If the network area command covers only the secondary address,
it will not enable ospf over that interface

IOS evaluation sequence :

The wildcard-mask argument is logically 'OR' ed with the
interface IP address

The wildcard-mask argument is logically 'OR' ed with the
ip-address argument in the network command

The software compares the two resulting values. If they match
ospf is enabled on the associated interface and this interface
is attached to the ospf area specified

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