OSPF.pdf
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OSPF Ğ P
ART
1
packetlife.net
Protocol Header
Attributes
8
16
24
32
Type
Link-State
Version
Type
Length
Algorithm
Dijkstra
Router ID
Metric
Cost (Bandwidth)
Area ID
AD
110
Checksum
Instance ID
Reserved
Standard
RFC 2328, 2740
Data
Protocols
IP
Transport
IP/89
Link State Advertisements
Authentication
Plaintext, MD5
Router Link (Type 1)
Lists neighboring routers and the cost to each; flooded within an area
AllSPF Address
224.0.0.5
AllDR Address
224.0.0.6
Network Link (Type 2)
Generated by a DR; lists all routers on an adjacent segment; flooded
within an area
Metric Formula
cost =
100,000 Kbps*
link speed
Network Summary (Type 3)
Generated by an ABR and advertised among areas
ASBR Summary (Type 4)
Injected by an ABR into the backbone to advertise the presence of an
ASBR within an area
External Link (Type 5)
Generated by an ASBR and flooded throughout the AS to advertise a
route external to OSPF
NSSA External Link (Type 7)
Generated by an ASBR in a not-so-stubby area; converted into a
type 5 LSA by the ABR when leaving the area
* modifiable with
ospf auto-cost reference-bandwidth
Adjacency States
1
Down
5
Exstart
2
Attempt
6
Exchange
3
Init
7
Loading
4
2-Way
8
Full
Router Types
Area Types
DR/BDR Election
Internal Router
All interfaces reside within the
same area
Backbone Router
A router with an interface in
area 0 (the backbone)
Standard Area
Default OSPF area type
Ğ The DR serves as a common point for
all adjacencies on a multiaccess
segment
Stub Area
External link (type 5) LSAs are
replaced with a default route
Totally Stubby Area
Type 3, 4, and 5 LSAs are
replaced with a default route
Not So Stubby Area (NSSA)
A stub area containing an ASBR;
type 5 LSAs are converted to type
7 within the area
Ğ The BDR also maintains adjacencies
with all routers in case the DR fails
Area Border Router (ABR)
Connects two or more areas
Ğ Election does not occur on point-to-
point or multipoint links
AS Boundary Router (ASBR)
Connects to additional routing
domains; typically located in
the backbone
Ğ Default priority (0-255) is 1; highest
priority wins; 0 cannot be elected
Ğ DR preemption will not occur unless
the current DR is reset
External Route Types
Virtual Links
E1 Ğ Cost to the advertising ASBR plus the external cost of the route
Ğ Tunnel formed to join two areas
across an intermediate
E2 (Default) Ğ Cost of the route as seen by the ASBR
Troubleshooting
Ğ Both end routers must share a
common area
show ip [route | protocols]
show ip ospf border-routers
Ğ At least one end must reside in area 0
show ip ospf interface
show ip ospf virtual-links
Ğ Cannot traverse stub areas
show ip ospf neighbor
debug ip ospf [ڲ]
by Jeremy Stretch
v2.1
OSPF Ğ P
ART
2
packetlife.net
Network Types
Nonbroadcast
(NBMA)
Multipoint
Broadcast
Multipoint
Nonbroadcast
Broadcast
Point-to-Point
DR/BDR Elected
Yes
No
No
Yes
No
Neighbor Discovery
No
Yes
No
Yes
Yes
Hello/Dead Timers
30/120
30/120
30/120
10/40
10/40
Defined By
RFC 2328
RFC 2328
Cisco
Cisco
Cisco
Supported Topology
Full Mesh
Any
Any
Full Mesh
Point-to-Point
Configuration Example
Router A
interface Serial0/0
description WAN Link
ip address 172.16.34.2 255.255.255.252
WAN
172.16.0.0/18
Area 0
Area 9
Totally Stubby Area
Backbone
!
interface FastEthernet0/0
description Area 0
ip address 192.168.0.1 255.255.255.0
A
!
interface Loopback0
! Used as router ID
ip address 10.0.34.1 255.255.255.0
C
!
router ospf 100
! Advertising the WAN cloud to OSPF
redistribute static subnets
network 192.168.0.0 0.0.0.255 area 0
B
!
! Static route to the WAN cloud
ip route 172.16.0.0 255.255.192.0 172.16.34.1
Area 1
Stub Area
Area 2
Standard Area
Router B
Router C
interface Ethernet0/0
description Area 0
ip address 192.168.0.2 255.255.255.0
ip ospf 100 area 0
interface Ethernet0/0
description Area 9
ip address 192.168.9.1 255.255.255.0
ip ospf 100 area 9
!
interface Ethernet0/1
description Area 2
ip address 192.168.2.1 255.255.255.0
ip ospf 100 area 2
! Optional MD5 authentication configured
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 FooBar
! Give B priority in DR election
ip ospf priority 100
!
interface Ethernet0/1
description Area 2
ip address 192.168.2.2 255.255.255.0
ip ospf 100 area 2
! Optional MD5 authentication configured
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 FooBar
! Give C second priority (BDR) in election
ip ospf priority 50
!
interface Ethernet0/2
description Area 1
ip address 192.168.1.1 255.255.255.0
ip ospf 100 area 1
!
!
!
!
!
!
interface Loopback0
ip address 10.0.34.3 255.255.255.0
!
interface Loopback0
ip address 10.0.34.2 255.255.255.0
!
router ospf 100
! Define area 1 as a stub area
area 1 stub
! Virtual link from area 0 to area 9
area 2 virtual-link 10.0.34.3
!
router ospf 100
! Define area 9 as a totally stubby area
area 9 stub no-summary
! Virtual link from area 9 to area 0
area 2 virtual-link 10.0.34.2
by Jeremy Stretch
v2.1
Plik z chomika:
Caveman85
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