OSPF notes

Packet type:

• Hello: discover and maintain neighborhood
• DBD: LSA header information, like a dictionary of LSAs
• LSR: request LSA
• LSU: update LSA (may contain several LSA)
• LS ACK: confirmation

LSA type:

Type	advertizer	scope	content
1	all routers running ospf	local area	directly connected interfaces
2	DR	local area	mask of a MA network
3	ABR	AS	summary of LSA 1 & 2
4	ABR in which area an ASBR exist	AS	where the ASBR is
5	ASBR	AS	external routes
6			Group Membership LSA
7	ASBR of NSSA	in the NSSA	external routes
8	all routers in IPv6 (LSA 1 for ipv6)
9	DR in IPv6 (LSA 2 for ipv6)
10			MPLS TE
11			MPLS TE

Route types:

• O: LSA 1, 2
• O IA, LSA 3
• O E1, LSA 5 cost increase
• O E2, LSA 5 cost does NOT increase
• O N1, LSA 7 cost increase
• O N2, LSA 7 cost does NOT increase

Network types:

• BMA: hello timer 10s, DR will be selected
• P2P: hello timer 10s, DR will be selected
• P2MP
• P2MP NB
• NBMA: hello timer 30s
• Loopback

Area types:

Type	characteristics
stub	no LSA 4, 5. default route from ABR (LSA 3), no external routes allowed
totally stub	no LSA 3, 4, 5. default route from ABR (LSA 3), no external routes allowed
NSSA	no LSA 4, 5. no default route from ABR, external routes allowed
totally NSSA (Cisco Only)	no LSA 3, 4, 5. default route from ABR (LSA 3), external routes allowed

neighbor relationship:

Type	characteristics
down	only in frame-relay
attempt	only in frame-relay
init	send hello packet
2-way	elect DR & BDR
ex-start	send DBD packets, select master/slave (whose sequence number will be used)
exchange	exchange LSA information (LSR, LSU)
loading	respond ack, start SPF caculation
full	put best routes into routing table, neighbor connection finished

DR & BDR election:

• priority, default is 1, 0 means the router doesn’t attempt election
• Router ID, stuck in down if router ids are the same