Hcip day 8 notes

OSPF Routing control
      priority

   [r1-ospf-1]preference 50  ------ modify OSPF Routing default priority --- This command will only affect all types of fields as OSPF（ospf Routing information inside the network ） Routing information for

  

 [r1-ospf-1]preference ase 100 ------ Modify the default priority of routes imported outside the domain

The above modification , Only modify the default priority of the corresponding type of route in the local route table of the device .

   

      Cost value

COST= Reference bandwidth / Real bandwidth

1. Change the overhead value by modifying the reference bandwidth

[r1-ospf-1]bandwidth-reference1000---- Modifying the reference bandwidth requires that all OSPF The devices in the network are all changed to the same .

Once the reference bandwidth is modified , All devices in the whole network have to be modified into the same , Therefore, its essence cannot control the choice , Its significance lies in that when the real bandwidth is large , The reference bandwidth can be increased , Avoid poor routing .

2. Modify the real transmission rate of the interface to reach the modified cost value

    [r1-GigabitEthernet0/0/0]undo negotiation auto  -- Turn off auto negotiation

[r1-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 the effect of controlling route selection , however , It will affect the real transmission rate of the physical interface , And can only be reduced , Therefore, it is not recommended to use .

3. Directly modify the cost value of the interface .

[r1-GigabitEthernet0/0/0]ospf cost 1000-- Modify the interface cost value

Be careful ; Because the cost value of the loopback interface is a defined value ,Q The result will not be changed by the outside world , namely 1.2 Neither method will affect the cost value of the loopback interface , But the third method can change the cost value of the loopback interface .

Particular attention ;OSPF The cost value of the network segment reaching the target in , It should be the cumulative value of the cost value of the incoming interface in the direction of routing information transmission .

OSPF The appendix E
It mainly defines a solution in a special case .

Proposed solutions , Normal entry with short mask , And the mask is longer LS ID Use direct broadcast address

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

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 , Will load balance .
Inter domain --- If there are multiple passes to reach the same target network segment 3 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 , Will load balance .
Outside the country
[r3]display ospf lsdb ase --- You can expand all at once 5 class LSA

  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 .

[r4-ospf-1]import-route rip  1 type 1---- Modify the cost value type when republishing

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--- The purpose of this design is to make it easier to intervene in the selection of routes in some cases .

type 2: The principle of road selection ： If there are multiple passes to reach the same target network segment 5 class /7 Class LSA Learned routing information , And the cost 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 low cumulative cost .

type 1 The principle of road selection ： If there are multiple passes to reach the same target network segment 5 class /7 Class LSA Learned routing information , And the cost types are all types 1, Compare the total cost （ Seed measure + Accumulate the cost value along the way ）, Give priority to those with low total cost , If the total cost is the same , Then load balancing .

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 , Then it is preferred to pass 1/2 Class learned , Even if the cost of learning in the domain is greater .--- Intra domain is better than inter domain .
Interregional and extraterritorial --- If the same destination network segment exists, pass 3 class LSA Learned inter domain information and through 5/7 class LSA Learned foreign information , Then it is preferred to pass 3 Class learned , Even if the cost of learning abroad is greater .--- Inter domain is better than extradomain .
In the Huawei system ,5 Classes and 7 class LSA The rules of choosing the road are the same .
OSPF My guard ring

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

Reissue

effect ： In a network , If running multiple routing protocols or different processes of the same routing protocol ; 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 ：

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 .
You have to focus on seed measures ----A The protocol and B The measurement calculation logic between protocols is illogical , Cannot be used directly . So I will A Publish to B When the agreement ,ASBR Will not carry the measure of the agreement to B agreement , It's sharing to B When the agreement , from ASBR The device adds a starting metric to the route .
The rules ：

take A The protocol is imported into B When the agreement , Need to be in ASBR Of B Configure republication on the protocol .
take A Agreement release B 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

      Single point -- There is one between two protocols or two processes 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 Agreement

two-way ： A/B Routing sharing of protocols

>B; A 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

>B: One dynamic routing protocol is published to another dynamic routing protocol
[r2-rip-1]import-route ospf 1

Conclusion ：1. Through republishing technology, the routing information of other protocols is imported into RIP in , Its default seed measure is 0

How to modify the seed measure

  1. During the process, the annual Bureau will be revised ;[r2-rip-1]default-cost 2

2. Modify for this reissue ;[r2-rip-1]import-route ospf 1 cost 3

Be careful ： When the above two commands are executed at the same time , According to Article 2 , 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 protocol .

Direct connection ->B： Import direct route into dynamic routing protocol

[r2-rip-1]import-route direct

Conclusion ;1. except r1 Outside the direct network segment of , All direct network segments will be imported

2. if ASBR the A->B Re release of , And it contains 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

[r2-ospf-1]default type ?

 INTEGER<1-2> Type value