Open Shortest Path Forward is included in Link-State Advertisement (鏈路狀態通告)
- main part:
Single Area & Mulitple Area & Stub Area (omit)
ROUTER ID cmd
Default GW Route
Link-state DB
- LB
- virtual part:
Connection to Remote Area
- NBMA, fully meshed
- cmd part:
show ip ospf interface
show ip ospf neibor
show ip ospf border-routers
show ip ospf database
show ip ospf vitual-links
---------------------------
| |
Internet -- (R) ---- (R) Backbone(area0) |
| |
|------(R)----------(R)-----
| | |
| area1 | area2 R --- Internet
| | |
-----------------------------
Cisco IOS provides a method for assigning an OSPF ID equal to the desirable OSPF ID.
$router-id <OSPF ID>
# OSPF id ranging from 0-255
(to be continued)
https://github.com/QueenieCplusplus/GW
to see router's link-state db by entering cmd without param
r3$show ip ospf database
> output
OSPF Router wiht ID (10.0.0.3) (PID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq$ Checksum LinkCount
10.0.0.2 10.0.0.2 6
10.0.0.3
"10.0.0.4"
...(omit)
192.168.255.5 192.168.255.5 2
Net Link States (Area 0)
Link ID ADV Router Age Seq$ Checksum
"10.0.5.2" 10.0.0.4 173 bits_val hex_val
"10.2.0.2" 10.0.0.3
to see cmd output with param 10.0.0.4
r3$show ip ospf database 10.0.0.4
> output
OSPF Router wiht ID (10.0.0.3) (PID 1)
"Router" Link States (Area 0)
link state id: 10.0.0.4
Advertising router: 10.0.0.4
Num of links: 6
Link connected to : another Router (PPP)
(Link ID) Neibouring Router ID : 10.0.0.6
(Link Data) Router Interface address: 172.16.0.9
...
Link connected to : a Stub Network
(Link ID) Network/Subnet number : 172.16.0.8
(Link Data) Network Mask: 255.255.255.252
...
Link connected to : a Transit Network
(Link ID) Designated Router Addr : "10.0.5.2"
(Link Data) Router Interface address: "10.0.5.2"
...
to see cmd output with param 10.2.0.2
r3$show ip ospf database 10.2.0.2
> output
OSPF Router wiht ID (10.0.0.3) (PID 1)
"Net" Link States (Area 0)
Link state id: 10.2.0.2 (addr of designated router)
Advertising router: 10.0.0.3
Network Mask: /22
Attached Router: 10.0.0.3
Attached Router: 10.0.0.2
OSPF, like all other routing protocol (sources) available on Cisco Rputers, can install multi-routes for the same mask.
This feature enable LB of traffic destined for the same mask (network prefix).
$maximum paths <# of paths>
# of paths, shall be under OSPF config
# max num is 4
# if param is 1 in value, then it means no LB is enable.
Vitual Links are established on a PPP basis between 2 Routers there are connected to common area, one of which shall be connected to OSPF Area0.
---------Area 0--------
| BackBone |
| |
| segment1 |
| 10.0.1.0/24 |
| |
| | | |
| e0 e0 |
----(R)-------(R)------
-------------------| Area10 |------------------
| s0 s0 |
| |
| | | |
| | | |
| |
| s0 s0 |
| | | |
| (R) (R) |
| | | |
| e0 e0 |
| |
| Segment10 |
| 10.10.4.0/24 |
| |
| | | |
| | | |
| |
| e0 e0 |
| | | |
-------------------(R)------ (R)-----------------
| |
--------- to0---- --- to0 --------
| | | | | |
| segement100 | | segement200 |
| 10.100.1.0/24 | | 10.200.1.0/24 |
| | | |
| Area 100 | | Area 200 |
| | | |
---------------- -----------------
Router N's config
Each Router must under OSPF cmd config, like
Rn$ area <area> virtual-link <router ID>
area, these 2 routers connected to, and the virtual-link is establish thru.
router ID, the OSPF ID of the counterpart router.
lo == loopback
e == thernet
s == serial
ip subnet-zero
> interface lo0
> ip address 10.0.0.1 255.255.255.0
> interface e0
> ip address 10.0.1.1 255.255.255.0
> interface s0
> ip address 10.10.255.5 255.255.255.252
bandwidth 64
router ospf 1
> network 10.0.0.0. 0.0.255.255 area0
> network 10.10.0.0 0.0.255.255 area10
> area0 range 10.0.0.0. 255.255.0.0
> area0 range 10.10.0.0 255.255.0.0
> area10 virtual-link 10.0.0.5
ip classless