CCIE Study Notes-OSPF

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CCIE Study Notes-OSPF

Area area-ID default-cost

Set the default route overhead to broadcast to stub, total stub, and NSSA on the ABR or ASBR. The default value is 1.

Router OSPF 1

Area 1 default-cost 10

Area area-id nssa no-redistribution

Connect the NSSA region to the ABR of area 0. Do not allow this ABR to publish the route re-published to this ABR to NSSA, but only to area 0.

Router OSPF 1

Area 1 NSSA no-redistribution

Area area-id nssa default-information-Originate

Make an area NSSA and declare an O * N2 default route (not available by default) to this area. Configure the default route on NSSA abr, configure a default route on the nssaasbr.

R2 (config-router) # area 1 nssadefault-information-Originate

Area area-ID range IP-Address Mask advertise/Not-advertise

A Summary Area route is used to suppress the detailed route. Not-advertise does not allow the ABR to advertise the summary route (of course, the detailed route is not declared). The advertise does not have the same information.

R3 (config-router) # area 1 range 3.0.0.0255.0.0.0 not-advertise

Area Transit-area-ID virtual-link route-idretransmit-interval seconds

Resend time when LSA does not receive the response on the virtual link

R2 (config-router) # area 1 virtual-link 1.1.1.1retransmit-interval 10

Area Transit-area-ID virtual-link route-idretransmit-delay seconds

When an LSA is created, the age value of the LSA is set to 0, and the transmission delay is added to the age. This command sets the transmission delay of the virtual link. The default value is 1.

Auto-cost reference-bandwidth

Sets the reference bandwidth used to calculate the cost value. The default value is 100 Mbit.

R2 (config-router) # auto-costreference-bandwidth 1000

Default-Information original route-Map

The default route is declared only when the route in route-map is available. If always are used, the condition of route-map is ignored.

R1 (config-router) # default-informationoriginate route-map CLC

Distribute-list access-list-number in interface-typeinterface-Number

Prevents route entry from being learned from the specified interface into the route table

R2 (config-router) # distribute-List 1 in fastethernet 1/0

Distribute-list access-list-number out routing-Process

Blocks routes from republishing from other routing processes to OSPF from being placed in the OSPF link status database.

R2 (config-router) # distribute-List 1 outeigrp 1

Neighbor IP-address cost

The cost specified to reach the neighbor. It is only used for the point-to-multi-point interface (ip ospf network point-to-multipoint)

R2 (config-router) # Neighbor 10.1.1.1cost 10

Neighbor IP-address database-filter all out

If there are two links to the neighbor, this command can prevent one link from sending the LSA to the neighbor and reduce the LSA flooding. It can only be used on the nbma and multi-point interfaces. Note that IP-address is not the neighbor's rid, but the peer IP address of the adjacent side.

R2 (config-router) # Neighbor 10.1.1.1database-filter all out

Neighbor IP-address poll-interval Interval

After manually specifying a neighbor, if the neighbor Hello packet is not received within the holddown-time period, the neighbor is determined to be down. This is the result of poll-interval sending hello to the neighbor to check whether the neighbor is up, the polling interval is less than the normal hello-interval, and cannot be used on the point-to-point interface.

R2 (config-router) # Neighbor 10.1.1.1poll-interval 60

Neighbor IP-address priority

OSPF priority of the neighbor of the given IP Address

Redistribution routing-process-ID tag-Value

Tag The re-release route while re-publishing

R2 (config-router) # redistribute VPN 1 tag100 subnets

Summary-address IP-Address Mask tag Value

Add labels when summarizing external routes

R2 (config-router) # Summary-address 3.0.0.0255.0.0.0 tag 100

Ip ospf database-fiter all out

Block LSA proliferation on the Link

R2 (config-If) # ip ospf database-filter allout

Ip ospf demand-Circuit

OSPF on-demand link. No periodic hello and update occurs. It is used after the topology is stable. In the node-to-multi-point topology, only the multi-point end can be configured with this command.

R2 (config-If) # ip ospf demand-Circuit

Ip ospf flood-direction ction

Do not age is carried when LSA is generated, so that the default 30-minute LSA flooding failure

R2 (config-If) # ip ospf flood-direction ction

Ip ospf Mtu-ignore

MTU is ignored when OSPF is set up. By default, if MTU does not match, the DBD package of the other party is ignored, and the neighbor relationship is stuck in the exstart status.

 

Ip ospf demand-Circuit

You only need to declare the on-demand circuit at one end of the point-to-point circuit or the multi-point end of the point-to-point circuit. On-demand links should not be implemented on broadcast media, because such a network cannot suppress the sending of hello packets, so that the link remains active. Only when DC-bit is set for all LSAs in the link status database of a region, lsa with the donotage (IP ospfflood-Re) bit is allowed to enter the region. If OSPF on an on-demand circuit is configured with a virtual link to traverse this on-demand circuit, this virtual link will also be seen as an on-demand circuit.

Show ip ospf border-routersospf route table search

1. The most precisely matched route

2. intra-region path

3. Inter-region path

4. E1

5. E2

Ip ospf name-Lookup

Use IP name-server x. x to query domain name services. In this way, OSPF neighbors are viewed. NID and adv router are replaced with their names in the OSPF database.

Area 1 NSSA translate type7 suppress-fa

When type 7 is converted to type 5, the forward address is also converted to type 5. If this address is not reachable (for example, restricted by area range not-advertise), the target address will not be placed in the route table. This command changes FA to 0.0.0.0, that is, the traffic to reach the external address is directed to the ABR of the Conversion Type 7 to the type 5.

 

FA is the field in the type 5 LSA advertised by ASBR. Its role is to tell the router in the OSPF domain how to quickly reach the next hop address of the route advertised by lsa5. To avoid ASBR as the next hop on the broadcast network of the OSPF internal router, and then the ASBR forwards the next hop to the correct one, resulting in additional routes. To put it simply, the FA field is similar to the "third-party next hop" concept in the BGP protocol and mainly plays a role in the broadcast sharing network. If fa is not 0, route optimization is performed based on the metric calculated to the FA address, rather than the metric calculated to the ASBR.

When OSPF is not enabled for the interface associated with the next hop (interconnect) that introduces the route, FA is set to 0.

2. If all of the following conditions are met, the FA field in type5 LSA is set to non-0:

1. On the ASBR, OSPF is enabled for the interface associated with the next hop of the introduced external route.

Within the command range.

2. On the ASBR, the passive interface cannot be configured for the interface associated with the next hop of the introduced external route;

// The first two rules ensure that the LSA can be advertised.

3. On the ASBR, the OSPF network type configured with the interface that introduces the next hop of an external route cannot be P2P or p2mp.

// Ensure that the network type is broadcast or nbma shared network.

Network

The network command is executed continuously, and the network command after it can only affect the interfaces that do not match the previous network command.

Authentication

If MD5 is configured with two keys, for example, ip ospf message-digest-key 15 MD5 cisco15 and ip ospf message-digest-key 15 MD5 cisco15, then, the interface will send two duplicate copies for each OSPF Packet, and the packet sent for key 15 will not be stopped until few neighbors use the key 20 packet.

Virtual Link

The region where the virtual link is located cannot be the remote area or the Remote Area. The virtual link is regarded as in Area 0.

Area area-ID filter-list prefic prefix_list_name [Out | in]

Filter the lsa3 that enters an area or the lsa3 that goes out of an area.

Default-Metric

Specify the OSPF measurement for all routes that are republished to OSPF. The Metric allocation measurement in redistribute is better than the defualt-metric allocation measurement. The default value is 20.

Modify Management Distance

Router OSP 1

Distance 130.

Distance 110 0.0.0000000000000255 1

! Set the Management Distance of routes generated by all OSPF neighbors and acl1 to 110, and the remaining value to 130, which can be used to prevent sub-optimal routing problems during dual-point bidirectional re-release.

Ospfv3 changes

1. A single link can belong to multiple subnets and allow two neighbors on the same link but belong to different IPv6 subnets to exchange data packets.

2. the routing LSA and network LSA do not carry IP addresses.

3. Neighbors are always identified by the RID. Originally, interfaces were used to identify neighbors in broadcast or nbma, while other peers were identified by the RID.

4. Use the local link address as the source address and next hop

5. Different instances are allowed on each link.

6. Add the advertised prefix to the new region prefix LSA. In this way, the router LSA and network LSA only represent the router node information, if the prefix changes or the status of the peripheral link changes, the LSA will spread in the region, the prefix LSA does not trigger SPF running (changes in the prefix will not affect the branches of the SPF tree in any way ).

7. Put only information related to the direct connection neighbor (such as the local link address and IPv6 prefix related to the link) into the link LSA, only Local Link spread (originally in the router LSA or network LSA ).

Configuration

Int F1/0

IPv6 OSPF 1 A 0

 

Multiple instances on one link (all instances are in instance 0 by default): ipv6 OSPF 1 A 0 instance 1. The OSPF instance that receives the hello interface must be the same as the instance in Hello, otherwise it will be discarded.

 

Summary of external regions:

IPv6 router OSPF 1

Summary-Prefix 2001: db8: 0: 20:/61 tag 4

 

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