Cisco OSPF

Open Shortest Path First kommunicerar med multicast som alltid har ttl satt till 1. OSPF använder IP protokoll #89. RFC 2328

Type: Link State

Algorithm: Dijkstra

AD: 110

Metric: Cost (Bandwidth)

Protocols: IP

Grannskap

Neighbors måste komma överens om:

• Subnät/Mask
• Area
• Timers
• Olika router-ID
• Flaggor: Stub, NSSA
• MTU
• Authentication type
• Kompatibla nätverkstyper, DR-election eller ej

Graceful shutdown, en OSPF router skickar ett HELLO utan grannar då tas grannskapet ner.

Rekommendationer

• Set your maximum LSA settings to keep from killing weak boxes
• Baseline your network so you know how many LSAs normally float around
• Configure LSA warnings to alert of problems
• Crash each type of box on your network in a lab environment so you know what it will do under stress.

Konfiguration

router ospf [process-id]

router-id for this OSPF process (in IPv4 address format)

router-id [OSPF router-id] 
log-adjacency-changes

Uppdatera reference bandwidth till 100G

router ospf 1
auto-cost reference-bandwidth 100000
exit

Enable routing on an IP network

network [network-number] [wildcard-mask] area [area-id]

Slå på routing för alla nät och styr grannskap/uppdateringar med passive-interface

passive-interface default
network 0.0.0.0 0.0.0.0 area 0
no passive-interface [interface]

Enable MD5 authentication in Area 0

area 0 authentication message-digest

Enable OSPF authentication on an interface

interface [interface]
ip ospf message-digest-key 10 md5 [password]
exit

Default route

default-information originate

AD

router ospf 1
 distance 80

DR/BDR election, multiaccess network

interface [interface]
ip ospf priority [number]  #default 1
exit

Summarization

ABR

router ospf 1
area 10 range 10.10.0.0 255.255.252.0
exit

ASBR

router ospf 1
summary-address 10.10.0.0 255.255.252.0
exit

Tuning protocol parameters

ip ospf hello-interval seconds
ip ospf dead-interval seconds
ip ospf retransmission-interval seconds
ip ospf transmit-delay seconds

Stub

No LSA type 5

area 1 stub

Stub bit is sent in hello packets

Totally Stubby

No LSA type 3,4,5. Default route only.
ABR

area 1 stub no-summary

Others

area 1 stub

NSSA

LSA type 7

area 1 nssa

NSSA Totally Stubby

LSA type 7. No LSA type 3,4.

area 1 nssa no-summary

Virtual Link

Virtual link är rekommenderat som backup- eller temporär anslutning.

R1

router ospf 1
network 10.0.1.0 0.0.0.255 area 1
network 1.1.1.0 0.0.0.255 area 0
area 1 virtual-link 3.3.3.3  #Router-ID

R3

router ospf 1
network 10.0.1.0 0.0.0.255 area 1
network 10.0.2.0 0.0.0.255 area 2
network 3.3.3.0 0.0.0.255 area 2
area 1 virtual-link 1.1.1.1  #Router-ID

Show

show ip ospf virtual-links

Diverse

Loopback

ip ospf network point-to-point
exit

MTU mismatch

ip ospf mtu-ignore

Redistribution

Default seed metric: 20 (except BGP)

Static

redistribute static

RIP

redistribute rip subnets

EIGRP

redistribute eigrp 1 subnets 

Troubleshoot

show ip ospf neighbor
ping 224.0.0.5
show ip ospf interface brief
show ip protocols
show ip ospf events
show ip ospf border-routers

Reset database and neighbors

clear ip ospf process