Shulou(Shulou.com)06/03 Report--

OSPF Multi-region principle and Virtual Link

I. the generation of OSPF multi-regions

Reason: improve network scalability (multi-area), fast convergence (control the number of routers in the domain)

1. Three kinds of traffic

1. Intra-domain traffic-traffic formed by the exchange of packets between routers in a single area

two。 Inter-domain traffic-traffic formed by exchanging packets between routers in different areas

3. External traffic-traffic formed by the exchange of packets between a router in an OSPF domain and a router in an OSPF area or another autonomous system

Second, the router type of OSPF

Four types: DR | BDR | ABR | ASBR

Area type of OSPF

(1) backbone area

(2) non-backbone areas-distinguished by the types of routes that can be learned

1. Standard area

two。 Stub area-no LSA4, 5, 7 advertisements

3. Full stub area-there are no LSA3, 4, 5, 7 advertisements except for an unattended route advertisement for LSA3

4. Impure terminal region

Stub area and complete stub area

Meet the conditions

1. There is only one default route as the exit of its area

two。 A region cannot be used as a traversing area of a virtual link.

No Autonomous system Boundary Router ASBR in 3.Stub area

4. Not the backbone area Area 0

There are no LSA4, 5, 7 advertisements in the stub area; in the full stub area, except for a default route advertisement for LSA3, no LSA3, 4, 5, 7 advertise the no-summary to make it a full stub area-- only supplement this command on ABR, because only ABR will summarize

3. Composition of OSPF link-state database (seven LSA types)

Each router creates a database of each interface, corresponding neighboring nodes, and interface speed

Each entry in the link-state database is called LSA (link-state advertisement), and there are six common LSA types

Type 1 router LSA issued by routers in the area

Type 2 network LSA issued by DR in the area

Type 3 network summary link advertisements sent by LSA ABR in other areas

Sent by Type 4 ASBR Summary LSA ABR to advertise ASBR information

Issued by Type 5 AS external LSA ASBR to advertise external rout

Sent by ASBR within the external LSA NSSA area of Type 7 NSSA to advertise external routes for local area connections

Where Type 4 and Type 5 appear at the same time, 4 is sent by ABR to advertise ASBR location information, and 5 is sent by ASBR to advertise external routes. If there is no ASBR in the area, there will be no 4 and 5.

Fourth, the router's selection of routing entries

1. The router only adds the optimal routing entries to the routing table

2. The basis for selecting routing entries

(1) Administrative distance

(2) Measurement

5. Route redistribution

1. A single IP routing protocol is the preferred scheme for managing IP routing in a network.

2. CiscoIOS can execute multiple routing protocols, each of which belongs to the same autonomous system as the network served by the routing protocol.

3. CiscoIOS uses the route retransmission and distribution feature to exchange routing information created by different protocols (the process numbers of different protocols are different)

Type of path redistributed to the route in the OSPF domain

1. External path of type 1 (Type1 externalpath,E1)

two。 External path of type 2 (Type2 externalpath,E2)

The NSSA area is an addendum to OSPF RFC

A special LSA type 7 is defined

Provide features similar to stub area and totally stubby area

Can provide include ASBR

VI. Virtual links in OSPF

In OSPF, a virtual link refers to a link that connects to a backbone area through a non-backbone area. (virtual links exist to solve the problem that routers in other areas cannot be connected in the backbone area, but this requires that the network segment network as a virtual link is stable enough.)

The purpose of the virtual link

1. Connect a region to a backbone area through a non-backbone area

two。 Connect a segmented backbone area through a non-backbone area

Rules and characteristics of configuring virtual links

(1) the virtual link must be configured between two ABR routers

(2) the transmission area cannot be a stub area.

(3) the stability of the virtual link depends on the stability of the area it passes through.

(4) Virtual links help to provide logical redundancy.

OSPF virtual link: a link that connects to a backbone area through a non-backbone area.

Purpose of virtual link:

1. Connect a region to a backbone area through a non-backbone area.

two。 Connect a segmented backbone area through a non-backbone area.

Configuration command for virtual link: area area-id virtual-link router-id

Virtual-link: virtual link router-id: the router-id of the other party

Experimental environment:

1.GNS3 software

2.2 initialized PC hosts + 4 routers

3. If the host is using a virtual machine, then all the firewalls of the virtual machine need to be turned off, otherwise the data transmission will be affected later.

The process of the experiment:

1.GNS3 software, 2 PC hosts + 4 routers ready

two。 We connect them all with a network cable, define each IP address according to our personal preference, and write it next to the port, so that we can enter the IP address and check it. .

3. Let's configure the IP address of R1~R4, router-id, and declare the R1~R4 network segment. I will not repeat it here because of my previous experiment.

4. After all configuration, you will find that R1 has only 10 and 20 routing tables and nothing else, R2 is 10-50 complete, R3 has no 10 and 20, R4 only has its own 40 and 50.

So if we want to interconnect PC1 and PC2, we have to make virtual links on area 1 before we can communicate with each other.

R2

R3

5. After doing the virtual link to check the route, you will find that the R1~R4 route is full.

6. We use PC1 to link to PC2

It is realized that a non-backbone area is connected to a backbone area through a virtual link.

Summary

First of all, we should have a clear understanding of dynamic routing and static routing. According to the introduction of the basic principles of the previous part, we should understand several parts of OSPF protocol, especially the related concepts of DR, BDR router, backbone area and standard area, as well as the establishment of OSPF adjacency (7 states), the understanding of route redistribution, the two construction methods of virtual link and so on, including a simple virtual link configuration experiment.

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