OSPF in a Single Area Notes
Chart , p. 103, 3 major types of networks
OSPF Startup
Down state - not exchanged info with other routers.
Multicasts hello to 224.0.0.5
Init - Receive hello.
Add to neighbor list.
Reply.
Two-way - receives replies.
Adds to neighbor list.
"Received" means saw its own Router ID in received hello packet
Exstart - DR and BDR elected.
DR and BDR establish adjacencies with each router in network
Master-Slave relationship between each router and DR/BDR
Exchange - Master sends DBD (database description packets)
Slave responds LSAck
Loading - But if DBD has new link info, slave send LSR (link state request)
Master responds with LSU (link state update)
Full - All LSRs satisfied
Adjacent routers synchronized; identical link-state databases
Routing of IP traffic
Page 118 PVC Requirements Formula
Page 119 3 NBMA topologies
Page 124 Table
Commands:
Show ip ospf interface - determine router ID
Ip ospf priority <number> default =1 range 0-255 determines DR/BDR election
Ip ospf cost <cost> range 1 65535 default cost is bandwidth on link
Auto-cost reference-bandwidth - change numerator of OSPF cost formula
Ip ospf network
Page 133-139 trouble shooting commands
Show ip protocols
Show ip route
Show ip route ospf
Show ip ospf interface e0
Show ip ospf
Clear ip route *
Show ip ospf neighbor
Show ip ospf neighbor detail
Show ip ospf database
Debug ip ospf adj
Page 166 Switch configuration
OSPF Configuration in Multiple Areas (Lou Rossi, Sr.)
OSPF Router Types
-internal router - all of its interfaces within the same area
-backbone router - at least one interface in area 0
-area border router(ABR) - multiple interfaces connected to multiple areas
-AS boundary router(ASBR) - at least one interface connected to an external Autonomous
System
ASBR routers are also backbone routers
OSPF Route Types
- Intra-area routes are routes in the same area (IA)
- Inter-area routes are routes in different areas (O)
- External routes are routes in another autonomous system (E1, E2)
Type 1 (E1) - uses both internal and external costs
Type 2 (E2) - (default) external cost only; facilitates load balancing
Stubby, Totally Stubby,
and Not-So-Stubby Area (Mark McGregor, p.226)
"stub area An OSPF area that does not permit the flooding of
external routing information
(Type 5 or Type 7 LSAs)."
"totally stubby area A Cisco-proprietary feature that configures a stub area that
also does not permit
summary LSAs (Type 3 and Type 4)."
"NSSA (not-so-stubby area) An OSPF area that acts like a stub but that permits
external routing
information, in the form of Type 7 LSAs, to be flooded inside the area."