During my last blog of OSPF Part-1, I explained about
OSPF Packet types and states. Now I will explain about LSA & OSPF Special
area types Interview questions & answer summary.
- § 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 LSA-related
questions.
Router LSA-1
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
is also advertising in the same area of OSPF. But this 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
is used for inter-area communication. This LSA contains details of the local area
& advertised to other areas by 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 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 routes in the same area where ASBR is not receive LSA-4
but they received LSA-1 or LSA-2 to find the location of ASBR because they all
are in the same area.
External
LSA-5 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 in 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 used.in those days LSA-6 was used
for multicast services but now no use.
NSSA External
LSA-7 is an external LSA using in one special area type NSSA
that I will explain later in this 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 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 OSPF Special area
types.
Keep Reading, Learning & sharing the knowledge.
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