OSPF LSA,s & Special Area Types | OSPF Interview Questions & Answer Part-2
Summary Insights:
- During my last blog of OSPF Part-1, I explained about OSPF Packet types and states. Now I will explain about OSPF LSA & Special area types.
Interview Questions:
- What is the name of all LSAs in OSPF?
- Which information are sending in Router LSA?
- Which router sends the Network LSA?
- What is Summary LSA & which router sends this?
- Details, in summary, ASBR LSA? Which router sends this LSA-4?
- The routers in the same area of ASBR will receive LSA-4?
- What is an Autonomous system external LSA?
- What is the difference b/w Type-1(OE1) & Type-2(OE2) External Routes?
- By default external routes type-1 or type-2?
- What is the name of LSA-6?
- What is LSA-7? Which bit is used to determine LSA-7?
- LSA-8 is used for which purpose?
- Opaque LSAs?
- How many types of OSPF Special areas?
- What is a Stub Area? & which LSA are not allowed in this area?
- What is totally stub area & which LSAs are allowed in this?
- NSSA & Totally NSSA area?
- How eternal routes are transmitted to other areas in NSSA?
- If redistribute/import external routes in normal area ASBR, will those routes be learned in NSSA?
- If the above question’s answer is No, then how to solve this Routes issue in NSSA?
- Why ASBR not forward LSA-1 & LSA-2 to other area?
OSPF LSAs Types:
Now let me summarize the answers to the above OSPF LSA related questions.
Router LSA-1:
Router LSA of OSPF contains the connected interface information & this LSA is advertising in same area only. It will not cross to other areas means no inter-area details.
Network LSA-2:
Network LSA is also advertising in the same area of OSPF. But this OSPF LSA is advertised by a designated router (DR). All connected link information of all routers in the same Networks are distributed by DR to all DR others.
Summary LSA-3:
OSPF Summary LSA is used for inter-area communication. This OSPF LSA contains details of the local area & advertised to other areas through Area border router (ABR). By this way all nodes in the OSPF domain learn different area routes & reachable to each other.
Summary ASBR LSA-4:
Summary ASBR is used to find the location of ASBR. This LSA-4 is advertised by ABR not ASBR. The more interesting thing that I mentioned in the above Question as well that all router in the same area where ASBR located is not receiving LSA-4 but they received LSA-1 or LSA-2 to find the location of ASBR because they all are in the same area , For other area using LSA-4 to find ASBR.
External LSA-5:
External LSA is used by ASBR to advertise the redistributed/imported routes to all other areas in the same domain. For example, if some other protocol i-e RIP, BGP, static, or multiple processes of OSPF on the same router running then in this case we redistribute/import those routes to OSPF, these all routes are advertised in LSA-5.
Multicast LSA-6:
Before OSPF was tried to use for multicast traffic like nowadays PIM & other protocols are using for multicasting. In those days LSA-6 was used for multicast services but now no use.
NSSA External LSA-7
NSSA LSA-7 is an external LSA using in one special area type NSSA that I will explain in next post in detail with examples.
External attribute LSA for BGP LSA-8:
when we import/redistribute BGP into OSPF on ASBR router, then during this process BGP attributes/features are lost. To maintain & carry BGP attributes in OSPF Domain LSA-8 is used.
Opaque LSA-9/10/11:
These ospf LSAs carry some extra feature information in MPLS TE & the latest technology Segment Routing (SR) & SRV6.I will explain this in a later MPLS/SR topic.
Next post I will continue to explain Below diagram OSPF Special area types.
You can read different OSPF topic i have covered in my other articles below
Keep Reading, Learning & sharing the knowledge.