OSPF Notes Part 5


OSPF Network Topology Options
OSPF assumes a subnet is broadcast-capable by default.
OSPF Network Types
Broadcast multiaccess
Point-to-point
Point-to-multipoint broadcast
Point-to-multipoint nonbroadcast
Nonbroadcast multiaccess (NBMA)

NBMA and point-to-multipoint are standards-compliant (RFC 2328), whereas point-to-multipoint
nonbroadcast, broadcast, and point-to-point implementations are Cisco proprietary.
NBMA networks utilize DRs like broadcast networks, however neighbors must be manually defined instead of being automatically discovered.

Find here the table of OSPF Network types


Source

Other categories

Cisco Jokes Photos Tutorials Voip Goa


Bookmark this on Delicious

Home

OSPF Notes Part 4

OSPF cost can be manually specified per interface:
Router(config-if)#ip ospf cost <cost>

An alternative to defining static costs per interface is to change the numerator bandwidth (default 100Mbps):
Router(config-router)ospf auto-cost reference-bandwidth <reference speed>

Reference speed is a 32-bit value (1 - 4294967). If reference speed is modified, the same modification should be performed on all routers within the area.


Router Priority
Default DR election priority is 1, and a router with a priority of 0 will not become a DR. Priority range is 0 - 255.

Router(config-if)#ip opsf priority <priority>

Verifying OSPF Configuration
show ip ospf - OSPF process details

show ip ospf database - Contents of the topology database

show ip ospf interface - Interfaces participating in OSPF

show ip ospf neighbor - Neighbor information

show ip protocols - Displays all active routing protocols

show ip route

debug ip ospf events

debug ip packet


Source

Other categories

Cisco Jokes Photos Tutorials Voip Goa


Bookmark this on Delicious

Home

OSPF Notes Part 3

Packet Types
OSPF is IP protocol 89.
Hello - Used to establish communication with directly connected neighbors
Database Descriptor (DBD) - Lists router IDs from which the router has an LSA and its
current sequence number
Link State Request (LSR) - Request for an LSA
Link State Update (LSU) - Reply to an LSR with the requested information
Link State Acknowledgment (LSAck) - Used to confirm receipt of link-state information

Packet Fields
Version - Version of OSPF being run
Type
Length
Router ID
Area ID
Checksum
Authentication type (none/plaintext/md5)
Authentication data
Data

Configuring OSPF in a Single Area
Necessary information:
OSPF process ID (locally significant)
Participating interfaces
Area ID
Router ID

Enable OSPF
Router(config-router)# router ospf <process number>

Configure Included Networks
Router(config-router)# network <network> <wildcard mask> area <area ID>

A single interface can be specified by supplying its IP address and a null wildcard mask: network
192.168.0.1 0.0.0.0 area 0

Router ID
If no router ID has been administratively declared, a router will choose the highest loopback IP address.
If no loopback addresses are present, the highest IP address of the first active interface will be used.

A router ID can be manually specified:
Router(config-router)# router-id <IP address>

Best practice dictates the creation of a loopback address to be used as the router ID for stability and continuity:
Router(config)# interface loopback 0
Router(config-if)# ip address <IP address> <subnet mask>


Default Cost
Link cost is a 16-bit value (0-65535); default cost is calculated as 100Mbps/interface bandwidth.(Interfaces 100Mbps and faster are assigned a cost of 1.)

Source

Other categories

Cisco Jokes Photos Tutorials Voip Goa


Bookmark this on Delicious

Home