notes: OSPF Miscellaneous Features

- you may selectively black-hole routes on stub.

command:

Here is the command syntax for the three options of this feature. They are configured under "router ospf

1. To always originate router-LSAs with infinity metric after configuration


router(config-router)#max-metric router-lsa


Graceful removal of an OSPF router from networks (i.e. to upgrade software or to perform maintenance) and reduction in packet drop
 
2. To send router-LSAs with infinity metric after reboot in a specified time

router(config-router)#max-metric router-lsa on-startup <announce-time> 

3. To send router-LSAs after reboot until BGP is converged (or maximum timer is expired - 600sec)

router(config-router)#max-metric router-lsa on-startup wait-for-bgp

With this feature and its "wait-for-bgp" option, the router advertises its locally generated router LSAs with infinity metric until BGP is converged or after a default maximum timeout (600 sec) is expired. This action will allow the router to converge without attracting transit traffic if there are better alternate paths around this router

excerpt from cisco:  http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800ade18.shtml

Received only configuration


-  breaks the RFC
- accepts only incoming route but it will not tell routes at all (received only mode)

interface e0

ip ospf database-filter all out
  
Name lookup

works with ip host table or domain lookup.  Note be careful using domain lookup may slowdown the network lookup.


ip ospf name-lookup


Top reasons  - Routes in RIB not in routing table.


- most of the reasons is the next-hop reachability.

1.  Network type mismatch
     i.e broadcast + point-to-point (DR mismatch)

2. Wrong (unreachable next-hop) on P2P link
    - subnet mask unverified, may lead to errors


3.  One side of P2P is unnumbered
     - OSPF assumes ID of MIDB index 0 (loopback)
     - may be unreachable or recursive.


4.  Next hop unreachable @ Layer 2
    - L3 to L2 mapping, Frame Relay network.


5.  Forwarding address known via external route
   - recursive lookup known via type 5  ( its not allowed) it has to internal routes.


6.  Distribute list blocking.  not showing up in the routing table but  in the OSPF database.


7.  Flood War
     - if message come up indicating %OSPF-4-FLOOD-WAR
     - you have 2 routers with duplicate ID.
     - they will not be in direct peers but some place in the network.
     - more likely after multicast (anycast RP same ip address in one or more device) configuration is completed.

8.  prefix suppression
     in an interface with multiple IPs.  if there is  requirement that you dont need to advertise the primary ip but need advertise the secondary.
       interface - ip prefix suppression
       ospf process - ospf prefix suppression


9.  capability transit   - ospf v1 - every packet must cross area 0, but in ospf v2, it doesnt necessary need for a packet to cross area0 if there are better metrics to react the destination. so its enabled by default. otherwise if you want to behave like ospfv1 issue the command below;
      no capability transit


10. LLS - local link signalling  , interoperability problem


         no capability lls


11. graceful restart (non-stop forwarding)
        -seperate the behavior for control and data plane. os if the control plane i.e ospf is having a problem, forwarding plane is not affected.


        nsf cisco enforce global

     nsf ietf enforce global

12.  BFD Bidirectional forwarding direction - used to detect indirect neighbhor disconnections.




13.  ISPF calculation - must be configured on all routers, incremental spf calculation


       router ospf 1

       ispf

 14.  methods of limiting the DB
       router ospf 1
   max-lsa 5000
   redistribute maximum-prefix 500


15.  ignoring type6 LSA (MOSPF)
         
       ignore lsa mospf


16. 2 or more same non zero areas exist in the ospf domain - works fine since there is no reference in lsa about area numbers.


area10 ---------area0-----------area10