Cisco CCNP ROUTE Router OSPF Command
ROUTER OSPF process-id:
-Enables the OSPF routing process
–Process-id identifies a specific instance of the OSPF program – locally significant only
-Multiple OSPF process instances can be running simultaneously but this is not recommended
NETWORK address wildcard-mask AREA area-id:
-Enables the OSPF routing process on an interface
-Must specify either a specific ip address of an attached interface or a network to which one or more interfaces are attached
-Every network must be associated with an area that can be specified in decimal or dotted-decimal notation. For stability, no one router should belong to more than 3 areas.
Cisco CCNP ROUTE Single-area OSPF
The example above depicts a simple single area implementation with three routers using area 0.
Cisco CCNP ROUTE Verifying OSPF operation
Lets move on and evaluate the output of each of these commands.
The show ip protocols command also gives you many of the OSPF parameters such as filters, default metric, maximum paths, and the number of areas configured on a router.
Cisco CCNP ROUTE show ip ospf interface
There are several commands that a network administrator can use to verify OSPF. The show ip ospf interface command is used to identify which interfaces are currently participating in OSPF.
- • Cost associated with OSPF interface
- • Designated Router information
- • Number of Neighbors known on your Link (Network, Interface)
- • Number of Adjacent neighbors
Cisco CCNP ROUTE show ip ospf neighbor detail
The show ip ospf neighbor command will identify:
- • Discovered Neighbors
- • Interfaces those Neighbors are located on
- • Priority of Neighbors
- • Designated Router information
Cisco CCNP ROUTE OSPF Packet Types
1 Hello – Discover/maintain neighbors
2 Database Description – Summarize database
3 Link State Request – Database download
4 Link State Update – Database update
5 Link State Ack – Flooding acknowledgment
Cisco CCNP ROUTE OSPF Operational States
DOWN – no recent information received
INIT – a hello packet has been seen
2-WAY – neighborship has been established
— election for DR/BDR may now occur —
EXSTART – first phase of adjacency establishment – DR/BDR asserts it’s authority
EXCHANGE – DR sends DBDs to client, may request LSAs from client
LOADING – DR asks for most recent LSAs
FULL – links state databases are synchronized
Cisco CCNP ROUTE OSPF Hello Packets
Each hello packet sent from an OSPF router will contain:
Router ID (RID)
****Must be unique****
Subnet Mask
Priority Number
****0 means can not participate in election****
Timer Value (Hello)
****This number must match for all neighbors, if not OSPF will not form a relationship with that peer!****
Neighboring (on same segment) Router ID’s
This is the information your OSPF router will use during the OSPF elections.
Cisco CCNP ROUTE OSPF Hello Packets
The frequency of the hello packets can be modified, however if one router modifies the timer interval, all OSPF routers in that network must modify their timers to match.
Cisco CCNP ROUTE Link State Advertisements
Type 1:Router Link Advertisement
- • Generated by each router for each area to which it belongs
- • Describes the states of the router’s links to the area.
- • Flooded within entire area
Type 2: Network Link Advertisement
- • Generated by DR in multi-access network
- • Describe the set of routers attached to a particular network
- • Flooded within entire area
Type 3 & 4:Summary Link Advertisement
- •Originated by ABRs
- •Flooded though out backbone area
- •3 describes routes to networks within the local area
- •4 describes routes to ASBRs
- •Not flooded to totally stubby areas
Type 5: AS External Link Advertisement
- •Originated by the ASBR
- •Describes routes to destinations external to the autonomous system
- •Flooded everywhere except stub and totally stubby areas
Type E1 entries add the internal OSPF cost to the seed metric as the external route propagates through the network – preferred behavior
Type E2 entries do not add internal OSPF costs – default behavior. Assumption is that routing between AS represents the major cost and that the path cost inside a single AS is trivial in comparison
Cisco CCNP ROUTE show ip route
The show ip route command shows all routes known to the router regardless of how they were learned.