CCIE notes ---OSPF

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  •   Posted on: 2019-04-19
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1) Basic characteristics

1 Link status: The routing table is not sent, it is the link status.

2 update method: trigger update incremental update.

3 There is no automatic summary, manual summary, divided into regional summary and external route summary.

4 hierarchical network design

5 support VLSM CIDR (classless routing protocol)


2) 3 tables


1 neighbor table

Neighbors after the adjacency relationship (must be on the same network segment, must be directly connected, the mask must be the same)

2LSDB link state database






3RIB routing table

Optimal path O OIA OE1 OE2 ON1ON2 OIA* OE*


3) Message


Hello: Discovers and maintains adjacencies (router-id, time, neighbor, area, dr / bdr, stub, auth, priority). Multicast also has unicast. The HELLO package always has a mask, and all direct connection masks are different and will not establish a neighbor. (important)

DBD: Retrieving information from the local network. Elect the master-slave relationship and control the synchronization of data. I M MS (unicast)

LSR: Request

LSU: Update Multicast

LSACK: reliable send multicast

TWO-WAY: I saw my router-id in the received HELLO package. (two-way)

Exstart: Exchange DBD (There is no LSA for the election of the master-slave relationship, and there is exchange for the exchange.)

I indicates whether it is the first packet.

M indicates whether it is the last packet.

MS represents the master-slave relationship.

Exchange (loading): Forms a link state request list and sends it to the other party. Know that this request list is empty. Will enter the FULL state. All requests are sent.

Full status.

OSPF wait time, no one told me during this time, I am DRBDR. This waiting time is forty seconds. OSPF does not preempt. (unless the priority of the DR is changed to 0) (important)


4) Neighbor TS


1OSPF is very strict, the neighbor mask is different, and the neighbor cannot be established.

2 normal network 10 dead 40 / NBMA 40 dead 120

The inconsistency of Hello must not establish a neighbor relationship.

Dead inconsistencies can't establish neighbor relationships.

Change the Hello time, the Dead time will automatically become four times the Hello time.

Change Dead time, Hello time will not change -=! ! !

3 OSPF router-id can not establish adjacency

4 different areas (areas occur on the interface). Nor can you establish a neighbor.

The 5stub flag is different and cannot establish a neighbor.

6 Inconsistent network types can affect neighbor relationships, but neighbors can be established.


8 bottom layer 2 layer frame relay


10passive-interface OSPF never has a one-way neighbor (important) does not make sense.

11 slave address can not establish a neighbor, only the primary address.


5) LSA type (11 types)----> routing routing


1Router Link LSA (generated by each router)

LSA1 is sent in a different way and is contained in a specific source address, which can be seen in the link count in show ip ospf database. (important)

The update source is the peer straight port address.

2Network LSA (DR generation)

The above two will not cross the area

3Network Summary LSA (ABR Send) Class 1 and Class 2 Expressions in Other Areas OIA

4ASBR Summary LSA asbr router-id Identifies who the current ASBR is. There are four categories in four categories.

5AS External LSA indicates what the specific external route is.

6 OSPF for multicast

7NSSA's External LSA

8External attributes LSA (BGP fully advertised into OSPF)

9opaque LSA (local link)

10opaque LSA (local area)

No. 9 and No. 10 are the second class of IPV6.

11 when ospf hit TAG is eleven




The distribute-list can only be used in the IN direction for OSPF. OSPF does not pass the routing table and has no effect on the next one. EIGRP and RIP will have an impact. (important)


LSA type


ADV (who advertised)

Link-id (indicates who)

The ADV of the three types of LSAs is determined by the last ABR. The routing code is OIA

The two types of LSAs are generated by the ABR of the area where the ASBR is located. It will also change as the region changes. The four types of LSAs have no routing code, just an identifier. Identifies where the ASBR is.

The three types of LSAs do not change with the change of the area.

4 NSSA area ABR is regarded as ASBR. In this ABR which is regarded as ASBR, seven categories are designed for five categories. The four categories will only appear because of the emergence of the five categories, so when the five areas are flooded to the next area, the ABR of the next area will replace the five types of LSAs with a four-class LSA. The seven categories do not spread across regions, so there is no need for four categories, but the five categories are to be exaggerated for regional communication, so four categories are needed. (important)


OSPF route routing



O's route takes precedence over OIA

OIA due to OE1/ON1

OE1 is greater than OE2

ON1 is greater than ON2

Both OSPF and EIGRP accumulate the COST value when the interface receives it. Only RIP accumulates the COST value when it is sent. (important)

OE1 is better than ON1

OE1 is better than ON2


Both OE2 compare the cost of reaching the ASBR first. The smaller the better. The cost of reaching the ASBR is the same, and the load is balanced.


Area type


Backbone area


Non-backbone area


Special area


STUB area: Filters four types of five types of LSAs and automatically generates an OIA default route with an asterisk.

How to fully route in this area will report an error and will not generate five types of routes. (important)

Accept three categories and also send three categories to the outside.

TotallStub area: area 1 stub no summary on the ABR. That's it. For other routes, just add area 1stub.

There are only three categories. Filter three or four types of LSAs. Three categories can be generated outward, although they do not accept it.


The biggest feature allows the existence of ASBR, filtering four categories and five categories as STUB, but can advertise external routes. NSSA does not generate a default route. The default route is not O*IA, it is O*N2.

On the ABR, AREA 1NSSAdefault-information-origina generates a default route (need to have a static route locally, otherwise add ALWAYS, the route type is O*E2). Fully routed on the ABR to enter the NSSA area.

On the abr, area1 nss followed by no redistr will not enter the NSSA area. (important)

Totall area:

Will generate a default route O*IA

Will produce three types of LSAs




Inter-area route summary:

Area 1 range summary address parameter

Doing a summary will also produce NULL 0

Delete the NULL 0 route command, under the process: no discard-route

The summary must be configured on the ABR in the area generated by the detail area (important)

Summary routing overhead

If the parameters are on the ad ad, the details will not be announced, and the filtering will be used.

External route summary:

Do it on the ASBR, under the process, summaryaddress summary address.


OSPF authentication:


1 is plain text authentication

0 is no certification

2 MD5 certification

No password is null authentication. (important)

Regional certification:

Clear text authentication:

Be sure to declare it, but you can leave it without a password. Clear text authentication.

Ciphertext authentication:

The youngest authentication mechanism, the last configured password takes effect. (important)

Left: key 1 cisco right: key 1 cisco

Key 2 ccie

OSPF's retreat mechanism, if the youngest password does not pass, it is compared with the old one. Once the authentication is passed, KEY1 KEY2 is sent out together. Because there is no wheeled authentication mechanism, there is this youngest and retrogressive mechanism.


Virtual link:


The hello package is suppressed, but the first time HELLO unicast is sent to establish a neighbor. Network type point-to-point.

Area 0 has authentication, and the virtual link also needs to be configured with authentication.

In the area 0, the virtual link is connected to two areas that cannot be restored.

Skip area 0 You can type tunnel on area 0. Tunnel mode .tunnel port COST six 1 to avoid sub-optimal paths.

tunnelIP is to be announced into the IP to be announced

An area of ​​OSPF recommends 25 routers to maintain 5000 routing entries.

SHOWIP OSPF DATABASE sees the time in seconds and floods every 30 minutes.


OSPF network type


Interface type and network type are separated

(Example: The network type of ospf is just OSPF's own.)

PTP: The reason why DRBDR is not selected is because the local priority is 0.




2PTP HELLO 10 seconds

3B HELLO 10 seconds

4PTM HELLO 30 seconds will generate a 32-bit route, this is not a 32-bit exchange


The Frame Relay multipoint subinterface runs the OSPF default interface network type: NBMA is the same as the primary interface.

Frame Relay Point to Drop Subinterface: Point to Point

The hubAND spoke can cause confusion in the DR BDR. Leading to routing school confusion. The phenomenon of OSPF comprehensive experiment II. (important) solution, manually select DR.

Point-to-point above the HUB-SPOKE will cause the neighbor to float. Because only one neighbor can establish a neighbor relationship at the same time. (important)

The type of network on both sides is different, which will result in different HELLO time. If the HELLO time is different, the neighbor will not be established.

Thinking questions, BDR does not learn the update content of the address with the destination address of .6?

Answer: You can learn from DR


Process under area [num] filter-list prefix [name] in/out

Can filter any LSA

OSPF Fast HELLO Packet Features

Ipospf dead-interval minimal hello-multiplier 3

Knock on both sides

The death time is defined as one second, and three packets are sent in one second.

External route forwarding address (important)

The default is the maximum loopback address (the address in the network)

View command: (important)

Ship ospf database nssa-external

Area 1 nssa traslate type7 suppresss-fa()

View the effect command:

Sh ip ospf database external

Turn the next address of the external route into yourself

Forwarding address of the external route


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