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RE: OSPF advertisements [7:93237] posted 09/23/2004
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So far I've seen two conflicting answers...

>>> "Thomas Nooning"  9/23/2004 4:50:28 PM >>>
The 'network' statement in OSPF doesn't specify what networks are
advertised, but what *interfaces* will participate in what OSPF area. 
In
your example your saying "any interface with an IP in the range of
172.1.0.0/16 be in area 0 and any interface with an IP in the range of
172.1.1.0/24 be in area 1".

A quick test shows that an interface in the /24 range will superscede
the
/16 assignment and be in area 1.

HTH,
Tom

>>> "Howard C. Berkowitz"  9/23/2004 5:27:30 PM >>>

No. Like access-lists, this is strictly order-dependent. First match
wins.

This is a reason that I prefer to keep complex OSPF configurations on 
a server, and precede them with "no ospf xxx".  It's far too easy to 
get conflicting results by appending rather than inserting a network 
statement.

Also helping protect against such errors is always using the mask 
0.0.0.0 on network statements, unless it's for the very special case 
where you want to override next-hop.  Yes, it makes for more 
statements -- but I find it easier to check the configuration when 
there is a one-to-one correspondence between OSPF enabled interfaces 
and network subcommands.




Jesse McGraw wrote:
> 
> Let's say I have this OSPF config:
> 
> ROUTER OSPF 10
> network 172.1.0.0   0.0.255.255 area 0
> 
> 
> and I add:
> network 172.1.1.0   0.0.0.255 area 1
> 
> which area will 172.1.1.0 be advertised in?  Will the more
> specific
> statement override the more general one even though it comes
> later in
> the config?
> 
>
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