Open Shortest Path First

• Version 2 supports IPv4
• Version 3 supports IPv6

OSPF sends Hello messages introducing themselves to a neighbor. If parameters match a relationship is formed. Can dynamically discover new neighbors.

• Cost = Sum of interface cost settings for all links in a route. Cost based on interface bandwidth.
• Administrative Distance: 110 (EIGRP 90, RIP 120)

Neighbors = directly connected links. show ip ospf neighbors

Hello message contains Router ID (RID) 32-byte address. Can be configured.

Hello:

• Follows IP packet header, with IP protocol type 89
• Hello packets are sent to multicast IP address: 224.0.0.5 for all OSPF speaking routers
• OSPF routers listen for packets on 224.0.0.5 hoping to receive Hello packets and learn about new neighbors.

*** OSPF router will not neighbor another router if connected interface is in a different subnet

• Single-Area OSPF config works well in small environments.
• Multi-Area OSPF config for large network environments.

(config)# router ospf 1	# The value represents Process ID. Just use 1.
	router-id 1.1.1.1	# Set Router ID -- OPTIONAL
	
	network 10.0.0.0 0.255.255.255 area 0	# Specify network and area.

default-information originate