OSPF N1 and N2 Routes: Configuration Situation

Earlier than discussing OSPF N1 and N2 routes, it’s important to grasp OSPR routes.

OSPF exterior routes in a traditional space would seem as both E1 routes or E2 routes. By default once we configure the redistribution of exterior routes in an OSPF space the route sort for the exterior community is E2 which seem as OE2 within the routing desk.

• E1 are the route when the price of the interior hyperlinks is considered for SPF calculation.
• E2 are the routes which take solely the exterior hyperlink price into the SPF calculation.

OSPF N1 and N2 Routes

OE1 or OE2 each are represented by LSA sort 5 within the OSPF database. Now in a particular OSPF space, NSSA or Completely NSSA the LSA sort 5 can’t be propagated. Therefore a brand new LSA sort 7 is propagated in these areas by the respective ABR for that space. Within the routing desk of routers in NSSA OSPF areas the exterior routes as a substitute of showing as OE1 or OE2 routes would seem as OSPF N1 and N2 routes (i.e. ON1 route or ON2 route). ON1 routes are similar to OE1 routes and ON2 are just like OE2. Default metric for OE2 and ON2 routes are 20.

We’ll test all these OE1 and OE2 within the topology under –

Within the topology above the route for 9.9.0.6 will probably be redistributed from EIGRP area to OSPF space 20 which is NSSA space on router R5 performing because the ASBR. This sort 7 LSA (ON2) on reaching the router R3 is transformed to Kind 5 LSA (OE2) and is propagated to space 0 and space 10 there onwards.

Associated- Final Information on OSPF LSA Varieties

Output (OSPF N1 and N2 routes)

On R4 we see the route for exterior subnet seems as N2 route by default. If we have to modify the default behaviour and have N1 route then we have to particularly point out that because the time of redistribution of EIGRP in OSPF on router R5.

R4# sh ip route | i N2

On R1 and R2 if we see route for 9.9.0.6 seems as OE2 route as R3 has transformed the kind 7 LSA to sort 5 LSA.

R1#sh ip route | i E2

R2# sh ip route | i E2

On including the under command on R5 at time of redistribution

Now we can see the route for exterior subnets as ON1 and OE1.

R4#sh ip route | i N1

R2#sh ip route | i E1

Proceed Studying:

OSPF ABR LSA 3 Filtering

OSPF Space Varieties

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