What is the purpose/use of LSA Type 1 / Router LSA ? How do we find information about LSA Type 1? What is the purpose/use of LSA Type 2 / Network LSA ? What is the purpose/use of LSA Type 3 / Summary LSA ? What is the purpose/use of LSA Type 4 / Summary ASBR LSA ? What is the purpose/use of LSA Type 5 / External LSA ? What is the purpose/use of LSA Type 6 / MOSPF LSA ? What is the purpose/use of LSA Type 7 / NSSA External LSA ? Can we filter LSA Type 1? Why/Why Not? What will be the impact? Can we filter LSA Type 2? Why/Why Not? What will be the impact? Can we filter LSA Type 3? Why/Why Not? What will be the impact? Where can we filter LSA type 3? ABR/Non-ABR? Can we filter LSA Type 4? Why/Why Not? What will be the impact? Can we filter LSA Type 5? Why/Why Not? What will be the impact? Where can we filter LSA type 3? ASBR/ABR/Non-ABR? Can we summarize Intra Area LSA s (LSA 1/LSA2)? Why/Why Not? What will be the impacts? Where can we summarize Intra Area LSA s? What type of LSA is the summarized route? Can we summarize Inter Area LSA s?(LSA 3/LSA 4)? Why/Why Not? What will be the impacts? Where can we summarize Inter Area LSA s? Why? Can we summarize External LSA s?(LSA 5/ LSA 7)? Why/Why Not? What will be the impact? Where can we summarize External LSA s? Why? What type of LSA is the summarized external route? Why do we see route to Null0, when we summarize? How is the route to Null0 added? Manually / Automatic? Under what conditions, will the summary route be withdrawn? What is the minimal condition for a summary route to stay published? Explain the OSPF DR/BDR election process? What values play key role in DR/BDR election? What should we do if we want a certain device to become DR/BDR? How to ensure that a certain device never becomes Dr/BDR? What happens if there is no DR/BDR on a Multi Access segment? Why do we need DR/BDR in OSPF? Who is selected first, DR or BDR? Is DR/BDR election Pre-Emptive? What all OSPF Media types support OSPF DR/BDR selection? What all OSPF Network types support OSPF DR/BDR selection? Why happens if a Spoke Router becomes DR in a Hub-and-Spoke topology? What is the waiting period, upto which a router will wait before declaring i tself as a DR/BDR? If we enable OSPF on Ethernet interface of a single isolated router. Will it do DR/BDR election? Do we have an option to authentication OSPF routing updates? How many different form of OSPF Authentication are there? Which OSPF Authentication Type is best & why? Why use OSPF Authentication? What are the advantages provided by using OSPF authentication? What all is Authenticated? Hellos / LSA s / Everything Which command is Useful when troubleshooting OSPF Authentication? Can we deploy different authentication methods (e.g. plain text/Null/MD5) in same area? Can we configure authentication on per neighbor basis? Can we have different authentication options used over same multi access lin k? Can we configure a common OSPF Authentication key under Global Process? Can we have different keys in use over different links? Can we have different keys in use over same link?Here are some of the common questions on OSPF at operationel Level : 1. Can communication between areas take place without using backbone area 2. If same route recieved through different LSA's. what will be the order of pr eference intra-area routes, O interarea routes, O IA external routes type 1, O E1 external routes type 2, O E2 3. How route summarixation is done at ABR 4. Why LSA 7 is required, as LSA 7 got converted into LSA 5 at the ABR 5. Why the OSPF state got stuck in Exstart and Exchange state 6 Command to use if we don't LSA 7 to get converted into LSA 5 7. Why OSPF is called Link State 8. Which LSA's are allowed in different area types 9. LSA 3, LSA 4, LSA 5 are generated by which routers: ABR or ASBR 10. If no. of routes received from same LSA type for a destination. Which one is preferred 11. In case of NBMA type, DR & BDR conceptsRouting Loops: The traceroute is the best to find simple routing loops. Show ip route to a poin t will find the more complex ones. You hope to see routes coming in and out of the table very quickly. You will also see the routing processes running all the time.A simple example if you have a lab of a way to create a difficult to find loop w ould be. You can actaully do this with 2 routers it is just to make the example more clear.Router A talks to router b via OSPF Router A talks to router C via EIGRP ROuter B talks to router C via OSPF Router C is running both OSPF and EIGRP and redistributes EIGRP routes into OSPFNow say router A has a routeIP route 10.10.10.10 255.255.255.255 1.2.3.4 200 R1(OSPF)R2(OSPF) (EIGRP) | | | | | | | | | | | | | | | | | (EIGRP) | R3(OSPF)-----------------| This has a high metric of 200 to illistrate this problem.Now router A redistributes this static route into EIGRP. Router C receives it v ia EIGRP puts it in his routing table and redistributes in into OSPF.Router B gets this route via OSPF and puts it in his routing table. He also for wards this to router A.When router A gets this route via OSPF route it has a better administrative dist ance than the static so he removes the static and puts the OSPF route in the routing table.Now since the static route was just removed from the routing table router A take s it out of EIGRP which means router C stops sending the OSPF route to router B. Since router B no longer has the OSPF router he no longer tells router A about the route. Router A removes the ospf and puts the static back in since it now is the only route.And you start all over again.This type of routing loop goes so fast it is very hard to tell. Traffic will wo rk sometime and fail others. These type of loops are best just avoided by desig n.