Router OSPF configuration 2

 

LSA1 (Router Link States)

R1 # show ip ospf database router view detailed information of Class 1 LSA in LSDB

1. Intra-Domain Routing, transmitted only in this region, does not pass through the ABR.

2. Each vro is generated.

3. including the direct connection neighbor of the vro and the information of the Direct Connection Network

Link ID: router ID

ADV router: router ID

Three types of information: Another neighbor stub network transit network (some information about the Ma network, indicating whether it is connected to the ma network !)

LSA2 (Net Link States)

R1 # show ip ospf database network

1. transfer only in this region

2. LSA2 is generated by DR only for multi-access networks.

3. Identify the routers in this network and the mask information of this network.

Link ID: IP address of the DR Interface

ADV router: DR's router ID

LSA3 (Summary Net Link States)

R1 # show ip ospf database summary

1. Inter-Domain Routing, which can flood to the entire.

2. When an API passes through an API, its ADV Router becomes the roabr-id of the API.

3. It contains all routing information in the region, including the network number and mask.

Link ID: route (network number)

ADV router: the router ID of the API (after an API, the router ID of the API is changed)

Auxiliary Function of LSA4 (Summary ASB Link States, used to inform other routers of the location of ASBR

R1 # show ip OS database asbr-summary

1. Spread the Router-id of the ASBR to other regions to let the routers in other regions know the location of the ASBR.

2. When an API is generated and sent over an API, its ADV Router becomes the Router-id of the API.

Link ID: RID of ASBR

ADV router: the router ID of the API (after an API, the router ID of the API is changed)

In the direct connection area of the ASBR, four types of LSA will not be generated, because the ASBR will issue a type of LSA, which indicates that it is an ASBR.

LSA5 (Type-5 AS External Link States)

R1 # show ip OS database external

1. An out-of-domain route does not belong to a region. Advertise external routes to the ospf region!

2. ASBR generation, flooding to the entire. It does not change the ADV Router. Because it does not change, other routers do not know how to use the ASBR. This requires the type 4LSA!

3. Type 4 LSA is needed to find the ASBR

Link ID: Route (network number)

ADV router: the router ID (unchange) of the ASBR)

R1 # sh ip OS database external

LSA7 (Type-7 AS External Link States)

R2 # show ip OS database nssa-external

Special out-of-Domain Routing exists only in the NSSA region.

Link ID: Route (network number)

ADV router: the router ID of the ASBR (only in the NSSA Region)

R2. (config-if) # bandwidth 5000

R2 (config-if) # ip ospf cost 30

OSPF has four path types:

1. Domain Routing O... 1, 2

2. Inter-Domain Routing o ia... 3, 4

3. External route O E1. .. 5 of E1

4. E2 external route O e2... 5

There are two types of external route redistribution into OSPF

· The default route for redistribution into OSPF is E2, Cost = 20, and COST is not changed during transmission.

· If it is changed to the E1 type, the cost value of each inbound interface will be accumulated during transmission.

If multiple routes destined for the same destination are redistributed to OSPF, OSPF follows the following principle when selecting an external route:

[1] O E1 is better than O E2

[2] In the same case, the smaller the Cost, the higher the priority.

[3] When the cost is the same, select the optimal path to the ASBR.

<Modify Cost reference value>

· The Cost value of ospf cost = 108/BW (bps) ring port is 1, the COST value of serial port is 64, and the Ethernet port is 10.

There are two methods to modify the COST value of a route:

First:

R1 (config) # int e0

R1 (config-if) # ip ospf cost 10 directly modifies COST value 1-65535

Second:

R1 (config) # router ospf 110

R1 (config-router) # auto-cost reference-bandwidth 1000 (the sixth power of Mbps10) modify the numerator in the COST formula. In this example, the numerator is changed to the ninth power of 10.

Summary benefits:

1. Reduce the number of Route entries

2. limits the impact of topology changes to a small scope.

3. Reduced the flood of LSA3 and LSA5

<Inter-Domain summary> (on ABR)

R2 (config) # router OS 110

R2 (config-router) # area 0 range 172.16.32.0 255.255.255.224.0

(Which region of the route is summarized)

We recommend that you perform this operation on all the BRS in the region.

Inter-Domain aggregation only applies to the LSA1 and LSA2 categories in the region.

<Summary outside China>

R4 (config) # router OS 110

R4 (config-router) # summary-address 44.0.0.0 255.0.0.0 (on ASBR)

Locally generated O 175.64.0/22 is a summary, 00:00:04, Null0

<Inject default route to OSPF domain>

R4 (config) # ip route 0.0.0.0 0.0.0.0 Serial 0 must write this default route! Do not write in RIP!

R4 (config-router) # default-information originate

O * routes other than E2 0.0.0.0/0 [110/1] are delivered

Special OSPF Area

 

<Stub>

· Setting a Stub in a region can narrow down the LSDB in the region to reduce memory consumption. Block LSA4/5 from entering the Stub Area

· In the Stub area, the ABR sends an LSA3 route to other routers in the Stub area by default.

· All routers in the Stub region must be configured with Stub.

The Stub area cannot be used as the transit area of the virtual link.

ASBR cannot appear in Stub.

Area 0 cannot be configured with Stub.

· In the hello message, a stub area flag is also called an E-bit. The flag of the STUB area is 1 by default. After the STUB area is configured, all the stub routers will set this position to 0, when a router is created as a neighbor, it will be compared and must be matched.

R2 (config-router) # area 2 stub

<Totally Stubby> Cisco private

· Reduce LSDB in the region and block LSA3 Based on Stub. (Block LSA3/4/5)

· An LSA3 route will also be sent by the ABR to other routers of Stub by default.

R2 (config-router) # area 2 stub no-summary (you only need to do this on the ABR)

<NSSA (Not-So-Stubby Areas)>

· The NSSA region breaks the rules of the Stub region and can be ASBR.

· ASBR will introduce external routes, which are introduced by LSA7. LSA7 will only appear in the NSSA region.

· Like the Stub area, The NSSA area blocks LSA4/5.

· ABR converts LSA7 to LSA5 and transmits it to other regions. At this time, the ABR also becomes an ASBR because it also introduces lsa5. The advertised router of lsa5.

R1 (config-router) # area 2 nssa (The NSSA region does not automatically generate default routes. You need to manually issue one route)

R1 (config-router) # area 2 nssa default-information-originate

Totally NSSA area

It is also a CISCO private feature --

R1 (config-router) # area 2 nssa no-summary also kills the three types of LSA and also delivers a default route, in addition, this default route replaces the default route from default-information-originate.

(Totally NSSA: blocks LSA3/4/5. The default LSA3 route generated by the ABR is transmitted to other NSSA routers)

<Authentication>

Step 1: configure the password under the interface

R1 (config-if) # ip ospf authentication-key wolf (with plaintext password)

Step 2: enable authentication under the interface

R1 (config-if) # ip ospf authentication (enable plaintext authentication)

R1 (config-if) # ip ospf message-digest-key 1 md5 wolf (with ciphertext password)

R1 (config-if) # ip ospf authentication message-digest (enable ciphertext authentication)

Note: During MD5 verification, the KEY numbers on both sides must be consistent, and KEY numbers are used for hash.

 

Area:

Step 1: configure the password under the interface

R1 (config-router) # int s0

R2 (config-if) # ip ospf message-digest-key 1 md5 wolf (with ciphertext password)

Step 2: Enable

R2 (config-router) # area 0 authentication Message-digest (enable ciphertext authentication)

Note: authentication must be enabled for all vrouters in the region.

This article is from the "T76" blog