OSPF routing control and anti ring

OSPF Routing control

priority

The following changes , Only modify the default priority of the corresponding type of route in the device local route table
modify OSPF Routing default priority
preference 50
Modify the default priority of routes imported outside the domain
preference ase 100

Cost value

1、 Change the overhead value by modifying the reference bandwidth
Modifying the reference bandwidth requires that all OSPF The devices in the network are all changed to the same
bandwidth-reference 1000
2、 The effect of modifying the cost value is achieved by modifying the real transmission rate of the interface
Turn off auto negotiation
undo negotiation auto
speed 10
Be careful ： The command takes effect after restarting the interface
3、 Directly modify the cost value of the interface
Modify the interface cost value
ospf cost 1000
Be careful ： Because the cost value of the loopback interface is a defined value , therefore , The result will not be changed by the outside world .OSPF The cost value of reaching the target network segment in , The cumulative value of the cost value of the flow interface in the direction of routing information transmission .

OSPF The road selection principle

1、 Intra domain ---- 1 class ,2 class LSA

Intra domain
If there are multiple passes to reach the same target network segment 1 class ,2 class LSA Learned routing information , The cost value reaching the target network segment will be compared , Choose the one with low cost , If the cost value is the same , Then the load will be balanced

2、 Inter domain ---- 3 class LSA

Inter domain
If there are multiple passes to reach the same target network segment 3 class LSA Learned routing information , The cost of reaching the target network segment will be relatively large , Choose the one with low cost , If the cost value is the same , Then the load will be balanced

3、 Outside the country ---- 5 class ,7 class LSA ---- type 1, type 2

You can expand all at once 5 class LSA
display ospf lsdb ase
type 1
If the cost value type is type 1, Then the cost value of all devices in the domain to reach the target network segment outside the domain is equal to the cost value of local arrival notifier plus the seed measurement
Modify the cost value type when republishing
import-route rip 1 type 1
type 1 The road selection principle ：
If there are multiple passes to reach the same target network segment 5 class /7 class LSA Learned routing information , And the cost value types are all types 1, The total cost will be compared （ Seed measure + Accumulate the cost value along the way ）, Give priority to those with low total cost . If the total cost is the same , Load balancing

type 2
If the cost value type is type 2, Then the cost value of all devices in the domain to reach the target network segment outside the domain is equal to the seed metric
type 1 Always better than type 2
type 2 The road selection principle ：
If there are multiple passes to reach the same target network segment 5 class /7 class LSA Learned routing information , And the cost value types are all types 2, Then compare the seed metrics first , Give priority to those with small seed metrics ; If the seed measures the same , Then compare the accumulated cost value along the way , Give priority to those with small accumulated cost value along the way , If the accumulated cost along the way is the same , Load balancing

4、 Intra domain and inter domain

If the same destination network segment exists, pass 1 Classes and 2 class LSA Learned information in the domain and through 3 class LSA Learned inter domain information , Will be preferred to pass 1 class ,2 Class learned , Even if the cost is more valuable
Intra domain is better than inter domain

5、 Interregional and extraterritorial

If the same destination network segment exists, pass 3 class LSA Learned information in the domain and through 5 class /7 class LSA Learned inter domain information , Will be preferred to pass 3 class LSA Learned , Even if the cost is more valuable
Inter domain is better than extradomain

6、 In the Huawei system ,5 Classes and 7 class LSA The rules of choosing the road are the same

OSPF My guard ring

1、 Inter domain anti ring
1.OSPF Because routing information is also transmitted between regions , therefore , There is a regional level segmentation mechanism . The routing information learned from which region will not be returned to this region
2. The region division of star topology requires itself to be an anti ring mechanism
2、 In domain anti ring
OSPF Anti ring mechanism in the domain ---- SPF Algorithm ---- Shortest path first algorithm

Reissue

effect
In a network , If you run multiple routing protocols or different processes of routing protocols ; The protocols cannot directly communicate with each other, including the independent forwarding and operation between processes ; Therefore, it is necessary to republish to realize the sharing of routes

Conditions
1、 There must be ASBR equipment
Connect two protocols or two processes at the same time ; You can learn the routing information on both sides at the same time , Then complete the route sharing
2、 We must pay attention to three measures
A The protocol and B The measurement calculation logic between protocols is illogical , Cannot be used directly . So I will A Agreement release B When the agreement ,ASBR Will not carry A The protocol measures to B agreement , It's sharing to B When the agreement , from ASBR The device adds a starting metric to the route

The rules
1、 take A The protocol is imported into B When the agreement , Need to be in ASBR Of B Configure republication on the protocol
2、 take A The protocol is imported into B When the agreement , Yes, it will ASBR All the people on the pass A What the agreement learned and ASBR Announced on A All direct routes of the protocol are shared in B Agreement

spot
Single point ---- Between two protocols or two processes 1 individual ASBR equipment
Bipoint ---- Between two protocols or two processes 2 individual ASBR equipment
Multipoint ---- There are multiple... Between two protocols or two processes ASBR equipment

towards
A one-way ---- Only will A The agreement is published to B In the agreement
two-way ---- A/B All routes of the protocol are shared

To configure

A - > B：
One dynamic routing protocol is published to another dynamic routing protocol
static state - > B：
Import static routes into dynamic routing protocols
import-route static
Conclusion ：
During the republication process, the default route will not be republished to the dynamic routing protocol

Direct connection - > B：
Import direct route into dynamic routing protocol
import-route direct
Conclusion ：
1、 except R1 Outside the direct network segment of , All direct connections will be imported
2、 if ASBR the A - > B Re release and direct connection - > B Re release of , And contain the same routing information twice , Will give priority to learning direct connection - > B Re release information