From: Curtis Call (curtiscall@xxxxxxx)
Date: Wed Nov 07 2001 - 14:00:28 GMT-3
In real world scenarios I think the passive interface option would be the
ideal choice in most situations. The reason for this is that passive
interface advertises the interface within the Router LSA as a stub network
thereby restricting it to within the area (ABRs will create a Network Summary
LSA for the network but this can be summarized or filtered), while
redistribute connected will advertise the networks as AS-External (Type 5)
LSAs. This will cause the networks to be advertised throughout the entire
OSPF domain (with the exception of stub areas of course). At times this might
be the desired behavior, but in most situations it is just weakening the
hierarchical structure of OSPF by placing routes in the OSPF Global Database
that have no business being there.
Just my .02
Rick Stephens <rstephens@wantec.com> wrote:
> Group,
>
> I have a question about which might be preferred or best practice when
> advertising an interface (network) without sending LSAs out the interface.
> Really, I am not sure how to even ask the question, but let me provide an
> example. Say you had two routers R1 & R2, connected by serial (or
whatever)
> and running OSPF between each other. The requirement is to advertise the
E0
> on R1, but not to advertise OSPF out that interface. I see two ways to do
> this, but wonder which would be "best" and what might be the pros and cons
> to each method.
>
> 1) Redistribute connected
> int s0
> ip address 10.1.1.1 255.255.255.0
> !
> int e0
> ip address 172.16.1.1 255.255.255.0
> !
> router ospf 1
> network 10.1.1.1 0.0.0.0 area 0
> redistribute connected metric 20 subnet route-map E0_Only
> !
> route-map E0_Only permit 10
> match ip address 1
> !
> access-list 1 permit 172.16.1.0 0.0.0.255
>
> **Note: This method will advertise 172.16.1.0 as an E2 route.
>
> 2) network statement in OSPF for that interface and the "passive-interface"
> command.
> int s0
> ip address 10.1.1.1 255.255.255.0
> !
> int e0
> ip address 172.16.1.1 255.255.255.0
> !
> router ospf 1
> network 10.1.1.1 0.0.0.0 area 0
> network 172.16.1.1 0.0.0.0 area 1
> passive-interface e0
>
> Note: This method will advertise 172.16.1.0 as an IA route.
>
>
> I suspect that it is the typical Cisco answer of "it depends". But, your
> thoughts and direction would be appreciated.
>
> Richard Stephens
> WAN Technologies, Inc.
> St. Louis, Missouri
> rstephens@wantec.com
----------
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