Chapter 20 Multi Area OSPF

Why multi-area

• on change, every router must update the SPF tree (Link State Advertisement LSA)
• entire topology must be stored on each router

Words

• RID Router ID. Highest IP of interface on router.
• ASBR Autonomous System Border Router
• area 0 backbone area
• ABR Area Border Router
• DR Designated Router

Link State Advertisement (LSA) types

1. Router Link Advertisement (RLA) sent by every router to other routers in area
2. Network Link Advertisement (NLA) sent by DR to every router in area
3. Summary Link Advertisement (SLA) sent by ABRs to external networks. Advertises inter-area-routes.
4. ASBR summary LSA sent by area border routers to inform the other areas how to get to the asbr
5. Autonomous System LSA sent by ASBR to advertise external routes

Adjacencies

• Must match:
  • Hello and dead timer intervals
  • area ID
  • OSPF area type
  • subnet
  • authentication data
• Hello on MC 224.0.0.5

Neighbor states

• down no hello sent or received
• attempt on nonbroadcast multi-access (NBMA) connections, neighbors must be configured manually
• init Hello packet received, but no bidirectional communication
• 2way communication setup, election can start
• exstart DR and BDR establish adjacencies
• exchange routing info is exchanged
• loading Link State Requests (LSR)s are sent to request LSAs
• full all LSA is synchronized and OSPF routing starts

Configuring

R(config)#router ospf 1
R(config-router)#router-id 1.1.1.1
R(config-router)#network 10.10.0.0 0.0.255.255 area 0
R(config-router)#network 172.16.10.0 0.0.0.3 area 1
R(config)#clear ip ospf process   ! restart
R(config)#int s0/0
R(config-if)#ip ospf cost 10      ! lower cost for serial

IPv6 - OSPFv3

Specify interfaces instead of networks

R(config)#ipv6 router ospf 10
R(config-rtr)#router-id 1.1.1.1 
R(config-rtr)#int fa0/0
R(config-if)#ipv6 ospf 10 area 0.0.0.0

show ipv6 protocols

Verifying and troubleshooting

• show ip ospf
• show ip ospf neighbor verifies OSPF interfaces
• show ip ospf interface more info for interface
• show ip ospf database LSA info
• show ip protocols ospf protocol info