Archive for the ‘OSPF’ Category


Dienstag, Mai 23rd, 2006

Also important to know are the LSA Types OSPF speaks to other routers

The type indicates and tells something about the area type. The following exist:

  • Type 1  is an info about routers and directly connected links
  • Type 2 info about LAN and routers connected
  • Type 3 Networks reachable outside the area
  • Type 4 reachability info to the autonomous system board from the ABR
  • Type 5 info about destinations outside the OSPF domain from an ASBR
  • Type 6 multicast info
  • Type 7 NSSA area

OSPF Areas

Dienstag, Mai 23rd, 2006

When you start with OSPF, everything seems to be simple. But later on you learn about many differnent types of OSPF areas.

  • Stub area – has no connection to external networks, it does not contain any external routes, relieys mostly on default routes, does not have AS-external routes (Type 5 LSAs)
  • Totaly Stub area – is an extension to the stub area and includes external routes and routes to other area over a default route, get these by Typ 3LSAs, does not support summary routes
  • Backbone area – is always area zero
  • NSSA, Not so stubby area – the same as SA, but can import external routes and send them to the backbone or other areas, type 3 and type 4 summary routes are not advertised into NSSA


ospf – summarize areas

Dienstag, Mai 23rd, 2006

If you want to summarize areas in the routing table of router behind an ABR you could use the following command in OSPF Router configuration mode.
area 1 range

With this command, als subnets belonging to are not showing up in the routing table of routers behind the ABR.

Stub area

Dienstag, Mai 23rd, 2006

If you don’t want to show up all your routes in a routing table of a stub router, use the „no-summary“ command at the router next to the stub router.

If you have one router configured with the „area 1 stub“ command use the „area 1 stub no-summary“ command on the other router to just let a default router show up in the stub router.