Shulou(Shulou.com)06/02 Report--

* * Agreement * *

OSPF (Open Shortest Path First Open shortest path first) is an internal gateway protocol (Interior Gateway Protocol, referred to as IGP), which is used to make routing decisions within a single autonomous system (autonomous system,AS). Is an implementation of the link-state routing protocol, which belongs to the Internal Gateway Protocol (IGP), so it operates within the autonomous system.

* * AD value * *

The protocol management distance of Cisco OSPF is 110,

The protocol management distance of Huawei OSPF is 150.

* * Link status * *

Another term for the interface of a linked router, so OSPF is also called an interface state routing protocol; OSPF establishes a link-state database by advertising the status of network interfaces between routers to generate the shortest path tree, and each OSPF router uses these shortest paths to construct routing tables

* * principle * *

# create adjacency list

# synchronizing the database

# calculate the routing table

* * region classification * *

Backbone: area 0

Non-backbone: not in area 0

* * purpose of Hello protocol * *

1. Used to discover neighbors

two。 Some parameters in the Hello package must be negotiated successfully before becoming a neighbor

The 3.Hello package acts as a keepalive between neighbors

4. Allow two-way communication between neighbors

5. It elects DR and BDR on the NBMA (Nonbroadcast Multi-access (non-broadcast address) network

* * factors affecting the establishment of neighbors * *

1. RID cannot be the same.

Router ospf 1

Router-id x.x.x.x

Clear ip ospf process

2. The region ID must be the same

3. Authentication must be successful (authentication type must be the same and password must be the same)

4. The subnet mask must be the same (in special cases)

5. Hello time must be the same.

Interface fas0/0

Ip ospf hello-interval {value}

6. Dead time must be the same.

Interface fas0/0

Ip ospf dead-interval {value}

7. The special tag bits must be the same

8. Priority must not all be 0 (in special cases)

Layer 9 and layer 3 MTU must be the same, otherwise they will be stuck in Exatart state.

Interface fas0/0

Ip mtu + num (e.g. 1499)

* * OSPF status * *

1.Down: no information has been exchanged with other routers in this state. The hello packet is first sent out its ospf interface, and the DR (in the case of a broadcast network) or any other router is not known. The hello packet is sent using the multicast address 224.0.0.5.

2.Attempt: only suitable for NBMA networks, where neighbors are manually specified in NBMA networks, the router will use HelloInterval instead of PollInterval to send Hello packets.

3.Init: the initialization received the Hello packet, but the 2-Way communication is still not established.

4.two-way: two-way session establishment, while RID appears in each other's neighbor list. (if it is a broadcast network: for example: Ethernet. DR,BDR should be elected at this time.

5.ExStart: the initial state of information exchange, in which the local router and its neighbors will establish a Master/Slave relationship, and the router with a large ID becomes Master.

6.Exchange: information exchange status: the local router exchanges one or more DBD packets (also known as DDP) with its neighbors. DBD contains summary information about LSA entries in LSDB).

7.Loading: information loading status: after receiving the DBD, use LSACK to group to confirm that the DBD has been received. Compare the information received with the information in LSDB. If there is an updated link-state entry in the DBD, send a LSR to the other party to request a new LSA.

8.Full: full adjacency status, which indicates that the databases of both parties are fully synchronized

* * principles for selecting DR and BDR * *

1. Those with priority 0 will not participate in the election.

two。 The router with high priority is DR

3. When the priority is the same, router ID greatly DR. Router ID is subject to the maximum ip in the loopback interface. If there is no loopback interface, the maximum ip of the real interface shall prevail.

4. By default, the priority is 1

* * five network types defined by OSPF * *

Types

Layer 2

Hello and dead

DR/BDR

Whether to send the package on its own initiative

Broadcast: broadcast

(MA, multi-access)

When the layer 2 protocol is ethernet

Corresponding to the type of broadcast network

Hello is 10s.

Dead is 40s.

Need to elect DR/BDR

Port initiatively sends packets in multicast mode (224.0.0.5AG6)

Non-broadcast:

Non-broadcast. (NBMA)

When the layer 2 protocol is Frame-relay

The corresponding non-broadcast network type

Hello is 30s.

Dead is 120s.

Need to elect DR/BDR

The port does not send packets actively, and the method of sending packets is unicast

[OSPF implements unicast: neighbor x.x.x.x]

Point-to-point

Point-to-point (P2P)

When the layer 2 protocol is HDLC\ PPP

Corresponding to the type of point-to-point network

Hello is 10s.

Dead is 40s.

No need to elect DR/BDR

Port initiatively sends packets by multicast (224.0.0.5)

Point-to-Multipoint:

Point to multipoint (p2mp)

Hello is 30s.

Dead is 120s.

No need to elect DR/BDR

Port initiatively sends packets by multicast (224.0.0.5)

Point-to-Multipoint non-broadcast:

Point to multipoint (p2mp-NB)

Hello is 30s.

Dead is 120s.

No need to elect DR/BDR

The port does not send packets actively, and the method of sending packets is unicast

* * LSA type * *

Type 1 LSA:router LSA

Any router will generate a Class 1 LSA in any area.

Type 1 LSA can be understood as "self-introduction", which is used to indicate which links enter the area, which devices are connected and how they are connected, and what is the distance from each other.

Type 1 LSA can only be transmitted within one area.

Link-id: RID of the router

Adv: RID of the router

Transmission range: can only be within one area

Whether the ADV has changed: no change

Type 2 LSA:net Link state

This type of LSA can only be found in the network environment where DR is elected.

Only DR is qualified to produce type 2 LSA.

Link-id: indicates the interface IP address of DR

RID of ADV:DR

Transmission range: within an area

Whether the ADV has changed: no change

/ / based on class 1 LSA or type 1 and 2 LSA in LSDB, you can calculate the route within an area, called O route.

Type 3 LSA:summary net link state

Transfer routing information between different areas

Only ABR can produce this type of LSA.

After the three types of LSA are generated by ABR, they first enter into OSPF area 0, and then forward them to other regions.

ABR:

1. "intra-domain-O" routes in non-zero areas can be transformed into three types of LSA and sent to area 0.

2. The "intra-domain-O" route in area 0 can be transformed into three types of LSA and sent to non-0 area, or the "inter-domain-OIA" route in area 0 can be transformed into a new type 3 LSA and sent to other non-0 area.

3. You must not forward three types of LSA in a non-0 area to an area 0.

Link-id: indicates the prefix of the route

RID of adv:ABR

Transmission range: within an area

Whether the ADV has changed: yes

Type 4 LSA:summary ASB link state

It is specially designed to assist type 5 LSA to calculate routing.

The message is the RID of ASBR

Is generated by ABR in the same area as ASBR

It changes with each ABR,ADV passed during the delivery process.

Link-id: represents the RID of ASBR

Adv:ABR

Transmission range: within the same area

Whether ADV has changed: yes

Type 5 LSA:external LSA

Represents the external route of OSPF, without any concept of area

It can be unimpeded in the OSPF network.

Where there is OSPF, there are five types of LSA.

Link-id: indicates the external routing prefix

RID of adv:ASBR

Transmission range: no limit

Whether ADV has changed: no

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