NP, OSPF route aggregation

And RIP Different ,OSPF Automatic route aggregation is not supported , Only manual route aggregation is supported .OSPF There are two mechanisms for route aggregation ： Inter region route aggregation and external route aggregation . Inter area routing aggregation must be configured in ABR Routers , refer to ABR In the area directly connected to yourself （Area） Medium Type-1 and Type-2 LSA convert to Type-3 LSA when , Pair generated Type-3 LSA Aggregate . External route aggregation must be configured in ASBR Routers , refer to ASBR Yes Type-5 LSA Aggregate .

Inter region routing aggregation is ABR Aggregate the routes in the directly connected area , So as to reduce the spread to other areas directly connected to themselves Type-3 LSA The number of . We need to pay attention to ： Inter area routing can only be aggregated by Type-1 LSA or Type-2 LSA Generated route ; If the router is transmitted from the outside or other areas to the area （ Or routing is by Type-5 LSA or Type-3 LSA Generated ）, Then for such a route ABR It is not possible to aggregate .

External route aggregation refers to ASBR On the router, for the introduction of OSPF Aggregation of external routes of the network , The aim is to reduce OSPF Network Type-5 LSA The number of . External route aggregation must be entered in the external route OSPF Online ASBR on ; External route into OSPF After network , stay ABR There is no corresponding Type-5 LSA To aggregate .

about NSSA Area , When the area ABR take Type-7 LSA Convert to Type-5 LSA when , The ABR Can also act as ASBR Role , Also on Type-5 LSA Aggregate . We need to pay attention to ： When NSSA There are multiple stations in the area ABR when , Must be Router-ID maximal ABR Conduct Type-7 LSA To Type-5 LSA The conversion operation of .NSSA There are two ways to aggregate external routes in a region , One is in NSSA Regional ASBR Directly aggregate external routes , The other is in NSSA In the region Router-ID maximal 、 Responsible for Type-7 LSA convert to Type-5 LSA Of ABR To aggregate on .

R1、R2、R3 Network router for the company headquarters ,R4 Router for branch office ,R5 For external non OSPF The router of the network ,SW1 For the internal exchange of the headquarters ,R1、R2、R3、R4、SW1 function OSPF agreement .PC1、PC2、PC3、 Respectively belong to vlan2 vlan 3 vlan 4.SW1 And R1 The link between belongs to vlan5, And belongs to the area 1.R1 And R2 R1 And R3 The link between them belongs to the area 0.R4 And R2 R4 And R3 Belongs to the area 2. Area 2 It's a NSSA Area ,R4 Use static routing to R5 Of Loopback The external network simulated by the interface . The network administrator needs to realize the intercommunication of the whole network , Keep it as simple as possible LSDB And optimize routing tables .

Interface IP The configuration will not be repeated , Next deploy OSPF.
SW1 To configure


R1 To configure

R2 To configure

R3 To configure

R4 To configure OSPF And configure the static route to the external network , And introduce .

// see R1 The state of our neighbors （ All States are Full）

// see R1 The routing table for

// You can see R1 All non direct routes have been received on , The whole network has realized interworking .

// see R2 Of LSDB

// You can see right now R2 For each PC The networks to which they belong are maintained separately Type-3 LSA (Sum-Net LSA)

// see R2 The routing table for

// You can see right now R2 Have each in the routing table PC The route of the network . In order to reduce the LSDB in Type-3 LSA And the number of routing entries in the routing table , Next, we will conduct inter region routing aggregation .

// stay SW1 Use command on abr-summary Configure inter region routing aggregation

// see R1 Of LSDB And routing table


// You can see ,R1 Of LSDB For each PC The networks to which they belong are maintained separately Type-3 LSA, In the routing table for each PC The networks to which they belong maintain separate routes , It shows that configuring inter region routing aggregation does not work , The reason is that only in the ABR Routing aggregation between regions can only be carried out on . Delete SW1 Routing aggregation configuration on
[SW1-ospf-10-area-0.0.0.1]undo abr-summary 20.0.0.0 255.255.252.0

// stay ABR Router R2 Region 0 Configure inter domain routing aggregation in

// see R4 Of LSDB And routing table


// You can see R4 stay LSDB For each PC The network is maintained separately Type-3 LSA , In the routing table for each PC The networks to which they belong maintain separate routes ,ABR Router R2 The regional route aggregation configured on does not work , as a result of ABR Inter region route aggregation can only be performed on the regions directly connected to them . Delete R2 Routing aggregation configuration on
[R2-ospf-10-area-0.0.0.0]undo abr-summary 20.0.0.0 255.255.252.0

// stay ABR Router R1 Area 1 Configure routing aggregation in

// see R2 Of LSDB And routing table


You can see ,R2 Of LSDB There is no separate maintenance for each network in the Type-3 LSA, Maintain the aggregated Type-3 LSA;R2 To each station in the routing table PC The network detail route is also replaced by the aggregated route .

// Configure external route aggregation
With Type-7 LSA In the form of OSPF The external routes of the network are still not aggregated ,LSDB A separate route will still be maintained for each external route LSA, The routing table will also be used for each such LSA Generate detailed routing .
R4 Upper use asbr-summary Configure external route aggregation

// see R4 Of LSDB And routing table

// You can see R1 Of LSDB There are no details in Type-5 LSA, Only the aggregated Type-5 LSA,R1 There are no detailed routes of external networks in the routing table , Only aggregated routes .

// see R2 Of LSDB And routing table


// You can see ,R2 Of LSDB There are no details in Type-5 LSA and Type-7 LSA, Only after polymerization Type-5 LSA and Type-7 LSA,R2 There are no detailed routes of the external network in the routing table , Only aggregated routes .

// stay NSSA Regional ABR Configure external route aggregation on
Due to the region 2 yes NSSA Area , In this area ABR The router will Type-7 LSA Convert to Type-5 LSA, And flood the area 0.
Delete first R4 Routing aggregation configuration on , And then in the area 2 Of ABR Router R2 Configure external route aggregation on
[R4-ospf-10]undo asbr-summary 20.0.5.0 255.255.255.252

[R2-ospf-10]asbr-summary 20.0.5.0 255.255.255.252

// see R1 Of LSDB

// Can be observed ,R1 Of LSDB There is a corresponding route for each external detailed route in Type-5 LSA , Description in ABR Router R2 The external route aggregation configuration on does not take effect . original , take Type-7 LSA Convert to Type-5 LSA Yes. Router-ID The larger ABR Router R3, therefore , stay R2 The external route aggregation configuration on cannot take effect .

// see R1 Routing table on

// You can see R1 The routes on are all detailed routes

Keep it now R2 External route aggregation configuration on , And in R3 Configure external route aggregation on .
[R3-ospf-10]asbr-summary 20.0.5.0 255.255.255.252

When the configuration is complete , see R1 Of LSDB And routing table


//

You can see R1 Of LSDB There are no details in the Type-5 LSA, Only Advrouter by R3（10.0.3.3） After polymerization Type-5 LSA, There are no detailed routes of external networks in the routing table , The next hop of the aggregation route of only the external network is R3（10.0.13.3）, This explanation R3 The external route aggregation configuration on has taken effect .

close R3 Of G0/0/1 Interface , Analog fault .
[R3]int g 0/0/1
[R3-GigabitEthernet0/0/1]shutdown

// see R1 Of LSDB

// You can see R1 After polymerization on Type-5 LSA Of Abvrouter Turned into R2（10.0.2.2）.

see R1 The routing table for

// You can see R1 The next hop of aggregate routing to the external network becomes R2（10.0.12.2）. explain ,ABR Router R2 The external route aggregation configuration on is , Yes ABR Router R3 A redundant backup of the external route aggregation configuration on .