OSPF advanced configuration redistribution virtual link theory
One, route redistribution
(1) Understanding of route redistribution
1. A single IP routing protocol is the preferred solution for IP routing in the management network.
2. Cisco IOS can execute multiple routing protocols. Each routing protocol and the network served by the routing protocol belong to the same autonomous system.
3. Cisco IOS uses routing Redistribution feature to exchange routing information created by different protocols
(2) Consideration of route redistribution
1. Measurement value
2. Management distance
Two, OSPF redistribution routing
(1) The path type of redistribution to the route in the OSPF domain
1. Type 1 external path (Type 1 external path, E1)
2. Type 2 external path (Type 2 external path, E2) is
mainly used for routing when there are 2 or more ASBRs leading to the same external network
(2) The router has two paths E1 and E2 to the external destination network
Type E1 (focus on internal and external costs) Type E2 (focus on external costs only)
3. NSSA area
(1) NSSA area is an addendum to OSPF RFC
1. A special LSA type is defined 7
2. It provides advantages similar to stub area and totally stubby area
3. It can include ASBR
(2) OSPF link status notification
1, LSA7 (NSSA External LSA, NSSA External LSA)
Four, advanced configuration commands
OSPF route redistribution configuration commands
[R1]rip 1 ###Configuration rip
[R1-rip-1]version 2
[R1-rip-1] undo summary
[R1-rip-1] network 11.0.0.0
[R1-rip-1] import-route ospf 1 cost 3
>>>>>Inject the ospf protocol into rip for route redistribution. The path type defaults to path type 2 (external cost), and the cost cost is 3 (the metric value for rip is the number of hops), and the rip medium weight To distribute ospf, you need to specify the cost value [R1-rip-1]ospf 1
[R1-ospf-1]import-route rip 1 type 1 cost 1
>>>>>>Inject the external rip protocol into OSPF for route redistribution, Use path type 1 (internal cost + external cost), cost cost is 1 (cosT=100M/BW)
[r1-ospf-1] default-route-advertise always ###ospf redistribution default route
[r2-ospf-1]import-route direct ###ospf redistribution direct route
[r2-ospf-1]import- route static ###ospf redistributes static routes
Note: When injecting default and static routes into ospf, direct routes must be configured
Non-pure peripheral area configuration commands
---------ABR and intra-area routing configuration-----------
[R4]ospf 1
[R4-ospf-1] area 1
[R4-ospf-1]network xxxxx. xxx ## Declare the directly connected network segment first, then configure
[R4-ospf-1-area-0.0.0.1]nssa
Five, OSPF summary
(1) Six common types of LSA
1 LSA1 LSA2 LSA3 LSA4 LSA5 LSA7
(2) LSA that allows flooding in each area
(3) OSPF path type
1. In-area routes, out-of-area routes, type 1 external paths and type 2 external paths
(4) The priority of OSPF path type
1. Intra-area path: Priority 1
2. Inter-area path: Priority 2
3. E1 external path: Priority 3
4. E2 external path: Priority 4
>1 means the highest priority, 4 means the lowest priority
> When adding routing entries to the routing table, if the destination network segment is the same, the routing strip with higher priority will be selected and added to the routing table.
Six, OSPF address summary
(1) The role of OSPF address summary
1. Address summarization also saves resources by reducing the number of flooded LSAs
2. It can save resources by shielding some unstable details of the network
3. Reduce routing entries in the routing table
(2) Inter-area route summary configuration
Router(config-router)#area area-id range ip-address mask
(Three), external route summary configuration
Router(config-router)#summary-address ip-address mask
(4) OSPF address summary
192.168.1.0/24 192.168.00000 001.0/24
192.168.2.0/24 192.168.00000 010.0/24
192.168.3.0/24 192.168.00000 011.0/24
192.168.4.0/24 192.168.00000 100.0/24
192.168.5.0/24 192.168.00000 101.0/24
192.168.6.0/24 192.168.00000 110.0/24
16+5-21
192.168.00000000.0/21=192.168.0.0/21
Seven, OSPF virtual link
(1) Virtual link
1. Refers to a link connected to the backbone area through a non-backbone area
(2) The purpose of the virtual link
1. Connect an area to the backbone area
through a non-backbone area 2. Connect part of the area on both sides of a segmented backbone area through a non-backbone area
(3) 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. The virtual link helps to provide Logical redundancy
(4) Virtual link configuration commands
Router(config-router)# area area-id vritual-link router-id
(5) Virtual link configuration commands
The non-backbone area must be directly connected to the backbone area. If it is not directly connected to the backbone area, a virtual link needs to be configured between two ABRs that traverse a non-backbone area.
The establishment of a virtual link needs to rely on the area where the underlying real link is located to transmit OSPF messages (hello, etc.). Therefore, if the traversal transmission area of the bottom layer is unstable, the virtual link of the upper layer is unstable, which affects the stability of the backbone area of the entire network. Therefore, this method is generally not recommended. If you have to use it, it is only a temporary solution.
----------- Configure virtual links on both ends of the non-backbone area being traversed--------
[R2]ospf 1
[R2-ospf-1] area 1
[R2 -ospf-1-area-0.0.0.1]vlink-peer 1.1.1.1 ##Specify the route ID of the ABR at both ends of the traversed area
[R1]ospf 1
[R1-ospf-1] area 1
[R1-ospf-1 -area-0.0.0.1]vlink-peer 2.2.2.2
[R1]display ospf vlink ###View the local OSPF neighbor relationship established through the virtual link