Multi-Area OSPF explained. Presentation by CoderGenie Technologies. CoderGenie Technologies provide best training on OpenStack, CCIE, CCIE SP, CCIE Security, CCIE DC

1. MULTI-AREA OSPFV2 ON
IOS XR
By Aladdin
CCIE Service Provider & Security
CoderGenie Technologies

2. AGENDA
 OSPF Packet Types
 OSPF LSA Types
 OSFP Router and Area Types
 Demonstration

3. OSPF OPERATION
 Establishing Router Adjacencies
 Electing DR and BDR
 Discovering Routes
 Choosing Routes
 Maintaining Routing information

4. OSPF PACKET HEADER

5. OSPF PACKET TYPES

6. OSPF STATES

7. OSPF STATES

8. OSPF STATES

9. OSPF HIERARCHICAL ROUTING
 OSPF requires hierarchical network
design through configuring areas where
every router must belong to at least one
area and every OSPF network must have
an area 0.
 Area 0 is our Transit (backbone) area.
Any other area is called regular (non
backbone) area. All regular areas must
touch area 0 except a few exceptions.
 Areas minimize the impact of network
events within an area and help scale the
size of the network through various area
types (stub, nssa etc) and route
summarization.

10. OSPF ROUTER TYPES
 Internal: All interfaces within the
same area.
 Backbone: At least one interface
in area 0.
 Area Border (ABR): Interfaces in
different areas.
 Autonomous System Boundary
Router (ASBR): one interface
connected to external network.

11. LSA TYPES

12. LSA TYPE 1: ROUTER LSA
 One router LSA (type 1) for
every router in an area
 Includes list of directly
attached links
 Each link identified by IP
prefix assigned to link and
link type
 Identified by the router ID of
the originating router
 Floods within its area only; does
not cross ABR

13. LSA TYPE 2: NETWORK LSA
 One network (type 2) LSA for
each transit broadcast or
NBMA network in
an area
 Includes list of attached
routers on the transit link
 Includes subnet mask of link
 Advertised by the DR of the
broadcast network
 Floods within its area only; does
not cross ABR

14. LSA TYPE 3: SUMMARY LSA
 Type 3 LSAs are used to flood
network information to areas
outside the originating area
(interarea)
 Describes network number
and mask of link.
 Advertised by the ABR of
originating area.
 Regenerated by subsequent
ABRs to flood throughout the
autonomous system.
 By default, routes are not
summarized, and type 3 LSA is
advertised for every subnet.

15. LSA TYPE 4: ASBR SUMMARY LSA
Summary (type 4) LSAs are used
to advertise an ASBR to all other
areas in the autonomous system.
They are generated by the ABR
of the originating area.
They are regenerated by all
subsequent ABRs to flood
throughout the autonomous
system.
Type 4 LSAs contain the router ID
of the ASBR.

16. LSA TYPE 5: EXTERNAL LSA
External (type 5) LSAs are used to
advertise networks from other
autonomous systems.
Type 5 LSAs are advertised and
owned by the originating ASBR.
Type 5 LSAs flood throughout the
entire autonomous system.
The advertising router ID (ASBR) is
unchanged throughout the
autonomous system.
Type 4 LSA is needed to find the
ASBR.
By default, routes are not
summarized.

17. AREA TYPES
Stub Area – as per Cisco Doc
“A stub area is an area that does not accept route advertisements
or detailed network information external to the area. Area 0
cannot be a stub area.”
Not So Stubby Area – as per Cisco Doc
“NSSA does not flood Type 5 external LSAs from the core into the
area, but can import autonomous system external routes in a
limited fashion within the area. Area 0 cannot be an NSSA.”

18. STUB AREA ON IOS XR
Default route is advertised into stub
area by the ABR1 with a default cost
of 1.
RP/0/RP0/CPU0:ABR1(config)# router ospf 1
RP/0/RP0/CPU0:ABR1(config-ospf)# area 50
RP/0/RP0/CPU0:ABR1(config-ospf-ar)# stub
RP/0/RP0/CPU0:ABR1(config-ospf-ar)#default-cost 15
no-summary keyword prevents the ABR
from sending summary link-state
advertisements (Type 3) in the stub area
making a “totally” stubby area. default-cost
specifies a cost for the default
summary route sent into stub area.

19. NOT-SO-STUBBY AREA ON IOS XR
Default route is advertised into stub
area by the ABR1 with a default cost of
1.
RP/0/RP0/CPU0:ABR1(config)# router ospf 1
RP/0/RP0/CPU0:ABR1(config-ospf)# area 50
RP/0/RP0/CPU0:ABR1(config-ospf-ar)# nssa
RP/0/RP0/CPU0:ABR1(config-ospf-ar)#default-cost 15
no-summary keyword prevents the ABR
from sending summary link-state
advertisements (Type 3) in the not-so-stubby
area making a “totally” not-so-stubby
area. default-cost specifies a cost
for the default summary route sent into
an NSSA.

20. DEMO

21. “
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