OSPF route management

OSPF Routing control
priority
[3-0Spf-11preference 50— modify OSPF Routing default priority — This life
The command will only affect all types of fields OSPF（OSPF Routing information inside the network ）
Routing information for .
[r3-0sp-1Jpreference ase 100— Modify the default priority of routes imported outside the domain
level
The above modification , Only for the default priority of the corresponding type of route in the local route table of the device
Level .
Cost value
COST= Reference bandwidth / Direct real bandwidth
1, Change the overhead value by modifying the reference bandwidth
[r3-ospf-11bandwidth-reference 1000— Modifying the reference bandwidth requires
all OSPF The devices in the network are all changed to the same .
Because once the reference bandwidth is modified , All devices in the whole network have to be modified to -
What kind of , therefore , Its essence cannot control the choice of road . Its significance lies in when the real bandwidth
more , The reference bandwidth can be increased , Avoid poor routing .
2, The effect of modifying the cost value is achieved by modifying the real transmission rate of the interface
[r3-GigabitEtherneto/Q/OJundo negotiation auto— Turn off white action
negotiation
[r3-GigabitEthernet0/0/0]speed 10
Be careful , The command takes effect after restarting the interface
This method can indeed change the size of the cost value for the specified interface , Play a
Control the effect of route selection . however , It will affect the real transmission rate of the interface , and
And , It can only be reduced , therefore , It is not recommended to make
With this scheme .
3.
Directly modify the cost value of the interface
Ir3-GigabitEtherneto/o/0lospf cost 1000— Modify the interface cost value
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 , namely 1,2 Neither method will affect the loopback interface
Cost value of . however , The first 3 This method can change the cost value of the loopback interface
Particular attention ：OSPF The cost value of reaching the target network segment in , Routing information sender
The cumulative value of the cost value flowing into the interface .
OSPF The road selection principle
Intra domain —1 class ,2 class LSA
Inter domain —3 class LSA
Outside the country —5 class ,7 class LSA— type 1
type 2
1, Intra domain – If there are multiple passes to reach the same target network segment 1 class ,2 class LSA Learning to
When routing information for , The cost value reaching the target network segment will be compared , Choose the one with low cost . If on
Same pin value , Then the load will be balanced .
2, Inter domain — If there are multiple passing classes reaching the same target network segment 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 similar
Same as , Then the load will be balanced .
3, Outside the country
[r3Jdisplay ospf sdb ase— You can expand all at once 5 class LSA
type 1： If the cost value type is type 1, Then all devices in the domain reach the target network segment outside the domain
The cost value of is equal to the cost value of the local arrival notifier plus the seed metric .
[r4-oSpf-1Jimport-route rip 1 type 1— Modify the cost value type when republishing
type 2： If the cost value type is type 2, Then all devices in the domain reach the target network segment outside the domain
The cost value of is equal to the seed measure .
type 1 Forever Youqian type 2,
— The purpose of this design is to
More convenient to interfere with route selection .
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 , Once the cost value type is type 2, Compare species first
Sub measure , Give priority to those with small seed metrics ; If the seed measures the same , Then compare
Accumulate the cost value along the way , Give priority to those with small accumulated cost value along the way . If you accumulate expenses along the way
The same value , Load balancing .
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, Will be more general
expenses （ Seed measure ＋ Accumulate the cost value along the way ）, Give priority to those with low total cost . Such as
If the total cost is the same , Load balancing
4, Intra domain and inter domain one – If the same destination network segment exists, pass 1 Classes and 2 class LSA Study
To the domain information and through 3 class LSA Learned inter domain information , Will be preferred to pass 1 class
2 class LSA Learned , Even if the cost is more valuable .
---- Intra domain is better than inter domain .
5, Interregional and extraterritorial —- If the same target network segment is reached, there is a passing class LSA Learned domain
Information between and through 5 class /7 class LSA Learned foreign 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 routing rules are the same .
OSPF
Inter domain anti ring
,OSPF Because routing information is also transmitted between regions , therefore , There are regional horizontal scores
Cutting 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 the same routing protocol
cheng ; The protocols cannot directly communicate with each other, including the independent forwarding and operation between processes ; therefore
You need 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 ; Can be the same as
Learn the routing information on both sides , 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 The agreement is published to B When the agreement ,ASBR Will not carry A agreement
Measures to B agreement , It's sharing to B When the agreement , from ASBR The device adds
Add a starting measure ,
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 agreement is published to e When the agreement , Yes, it will ASBR All the people on the pass A Agreement learned and
ASBR Announced on A All direct routes of the protocol are shared to B Agreement .
spot
towards
Single point One – Between two protocols or two processes 1 individual ASBR equipment
Bipoint

Between two protocols or two processes 2 individual ASBR equipment
Multipoint — There are names between the two protocols ASBR equipment
One way one -- Only will A The agreement is published to B In the agreement
– A/B All routes of the protocol are shared
A->B:
One dynamic routing protocol is published to another dynamic routing protocol
static state -＞B： Import static routes into dynamic routing protocols
Direct connection -＞B： Import direct route into dynamic routing protocol
RIP
A->B:
One dynamic routing protocol is published to another dynamic routing protocol
[r2-rip-1limport-route ospf1
Conclusion ：1, Through republishing technology, the routing information of other protocols is imported into RIP in
The default seed measure assigned to it is 0.
How to modify the seed measure ：
1, Modify the overall situation in the process ：Ir2-rip-1Jdefault-cost 2
2, Modify for this reissue ：[r2-rip-1Jimport-route ospf 1
cost 3
Be careful ： When the above two commands are executed at the same time , Will be in accordance with paragraph 2 strip , Match more
Precise commands to execute .
static state -＞B： Import static routes into dynamic routing protocols
[r2-rip-1]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
[r2-rip-1limport-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 - Two B Re release of , And contain the same routing information twice , Will give priority to learning direct connection -＞
B Re release information
[r2-ospf-1]default cost ?
INTEGER<0-16777214> Cost value
Ir2-ospf-1] default type?
INTEGER<1-2> Type value