[nsp] OSPF NSSA

[John Pang]

Hi Stephen and Mustafa,

Thanks alot for your advice and info.

I tried out Mustafa's method of putting R4's loopback
into Area 1 and R1 is now able to see 2 paths to R4.
:)

Just curious but is putting the loopback into an Area
a standard procedure? Is this behaviour standard for
OSPF or is it due to the way Cisco IOSes operate?

Previously I used to do redistribute connected to
inject the loopback IP address into OSPF. How is this
different from manually specifying the loopback IP
address as a member of the area?

Once again, many thanks for the kind advice and
assistance.

--- Hani Mustafa <hani.mustafa at noorgroup.net> wrote:
> > distribute-list ?
> 
> With OSPF, distribute lists do not block actual
> LSA's. They merily prevent them from being used in
> the routing table. LSA's will still be propagated to
> other routers.
> 
> Try using "area 1 filter-list prefix <prefix-list>".
> 
> I have played around with this scenario of yours and
> have found out that if you set up area 1 as NSSA,
> and also include the loopback (assuming its your
> router-id) in your network commands, R1 will
> automatically do a recursive look-up and loadbalance
> for the external route (even though there will be
> one OSPF external type-5 LSA in R1's database, which
> conforms with what Oliver says).
> 
> R4
> interface loopback 0
>   ip address 4.4.4.4 255.255.255.255
> 
> router ospf 1
>   area 1 nssa
>   network 4.4.4.4 0.0.0.0 area 1
>   <... other network commands ...>
>   redistribute static subnets
> 
> 
> If you do a "show ip ospf database external" at this
> point on R1, you will find one LSA for the
> redistributed route, with the "Forward Address" set
> to R4's router-id. The router then looks at the 2
> Summary LSA's for R4's router-id (advertised by R2
> and R3), and loadbalances between both of them
> (provided they're equal).
> 
> ~Hani Mustafa
> 
> > > One main reason why I ran NSSA was because R1 &
> R4 are
> > > also redistributing static/connected routes and
> I
> > > would like to limit the number of external
> routes that
> > > enter R4 since R4 can basically just pass the
> traffic
> > > to either R1/R2 and doesn't need to see
> everything
> > > else that R1 redistributes.
> > > 
> > > Do you have any idea what could be done to
> achieve
> > > this effect? Maybe some filtering in normal OSPF
> area
> > > mode?


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