Effect of autosummary

Router6 will not add 10.0.0.0/8 network, because it already has 10.10.10.1/30 on its fast ethernet. Same for all routers.

Check the debug command
*Mar  1 00:14:17.495: IP-EIGRP(Default-IP-Routing-Table:1): route installed for 20.0.0.0  (Summary)
*Mar  1 00:14:17.559: IP-EIGRP(Default-IP-Routing-Table:1): 10.10.10.1/32 – don’t advertise out Serial0/1
*Mar  1 00:14:17.559: IP-EIGRP(Default-IP-Routing-Table:1): 10.10.10.2/32 – don’t advertise out Serial0/1
*Mar  1 00:14:17.559: IP-EIGRP(Default-IP-Routing-Table:1): 10.10.10.3/32 – don’t advertise out Serial0/1
*Mar  1 00:14:17.559: IP-EIGRP(Default-IP-Routing-Table:1): 20.0.0.0/8 - poison advertise out Serial0/1
*Mar  1 00:14:17.559: IP-EIGRP(Default-IP-Routing-Table:1): Int 20.0.0.0/8 metric 2169856 – 1657856 512000
*Mar  1 00:14:17.599: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.0.0.0/8 metric 2172416 – 1657856 514560
*Mar  1 00:14:17.671: IP-EIGRP(Default-IP-Routing-Table:1): Processing incoming REPLY packet
*Mar  1 00:14:17.671: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.0.0.0/8 M 2172416 – 1657856 514560 SM 28160 – 25600 2560
*Mar  1 00:14:17.671: IP-EIGRP(Defa
R4(config-routult-IP-Routing-Table:1): route installed for 10.0.0.0  ()
*Mar  1 00:14:17.671: IP-EIGRP(Default-IP-Routing-Table:1): route installed for 10.0.0.0  (Summary)
*Mar  1 00:14:17.687: IP-EIGRP(Default-IP-Routing-Table:1): 10.0.0.0/8 – do advertise out Serial0/1
*Mar  1 00:14:17.687: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.0.0.0/8 metric 128256 – 256 128000er)#
R4(config-router)#
*Mar  1 00:49:56.087: IP-EIGRP(Default-IP-Routing-Table:1): Processing incoming QUERY packet
*Mar  1 00:49:56.091: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.20.20.2/32 M 4294967295 – 25600 4294967295 SM 4294967295 – 25600 4294967295
*Mar  1 00:49:56.091: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.20.20.3/32 M 4294967295 – 25600 4294967295 SM 4294967295 – 25600 4294967295
*Mar  1 00:49:56.111: IP-EIGRP(Default-IP-Routing-Table:1): 10.20.20.2/32 – not in IP routing table
*Mar  1 00:49:56.111: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.20.20.2/32 metric 4294967295 – 0 4294967295
*Mar  1 00:49:56.111: IP-EIGRP(Default-IP-Routing-Table:1): 10.20.20.3/32
R4(config-router)#- not in IP routing table
*Mar  1 00:49:56.115: IP-EIGRP(Default-IP-Routing-Table:1): Int 10.20.20.3/32 metric 4294967295 – 0 4294967295

Filter Routes (OspF)

OSPF supports several methods to filter routes. However, the OSPF’s internal logic restricts most filtering, requiring that the filtering be done either on an ABR or ASBR.

This logic relies on all routers inside the area having an identical copy of the LSDB for that area.

For interarea routes, OSPF uses distance vector logic. The intra-area SPF calculation includes the calculation of the metric of the best route to reach each ABR in the area. To choose the best interarea route, a router uses distance vector logic of taking its known metric to reach the ABR and adds the metric for that subnet as advertised by the ABR.

Filter the LSA Type 3

area (area-number) filter-list prefix (prefix-list name)  in | out

The need for the in and out parameters makes more sense when you consider an ABR connected to at least three areas. Because packets can be forwarded through another link

 

Distribute-list

For instance, if an area has 20 routers, and the engineer wants to filter the route so that five of the routers do not learn the route, Type 3 LSA filtering cannot be used. Type 3 LSA filtering can only filter the LSA from being flooded throughout the entire area.
The next feature discussed in this section, referenced as filtering with distribute lists (based the configuration command it uses), allows individual routers to filter OSPF routes from getting into their respective IP routing tables. This type of filtering injects logic between the SPF algorithm on a router and that same router’s IP routing table. This feature does not change the LSDB flooding process, does not change the LSAs added by ABRs or ASBRs, and does not change the SPF algorithm’s choice of best route. However, when SPF chooses routes to add to the IP routing table, if a router has been configured with a distribute-list in OSPF router subcommand, enabling this feature, that router then filters the routes before adding them to that router’s IP routing table.

The mechanics of the distribute-list router subcommand has a few surprises, which are summarized in this list:

·         The command requires either an in or out direction. Only the in direction works for

filtering routes as described in this section.

·          The command must refer to either a numbered ACL, named ACL, prefix list, or route map. Regardless, routes matched with a permit action are allowed into the routing table, and routes matched with a deny action are filtered.

·         Optionally, the command can include the interface interface-name-and-number parameters. The router compares these parameters to the route’s outgoing interface.

Configuration of Distribute list

Router(config)# router ospf 1

                         distribute-list prefix-list (distribute-list) in interface ( name and number)

Manual Summarization at ABRs

The more difficult task with OSPF route summarization occurs when planning the design of IP address blocks and OSPF areas. When the IP addressing plan and OSPF design have been completed, if the subnet numbers inside an area happen to be from the same general range, and none of the subnet in that range exist in other OSPF areas, then a reasonable summary route can be created at the ABRs connected to that area. Without first having such a reasonable block of addresses, route summarization may not be a useful option.

After a range of subnets has been chosen for summarization, the parameters in the area range command must be planned. This command defines the parameters for the summary route, most notably the origin area from which the subnets exist, and the subnet number/mask that defines the summary route that should be advertised. The generic version of the command is listed next, followed by some notes about the various parameters:

area (area-id) range (ip-address) (mask) [cost (cost)]

1.     The configured area number refers to the area where the subnets exist; the summary will be advertised into all other areas connected to the ABR.

2.    The ABR compares the summary route’s range of addresses with all intra-area OSPF routes, in the origin area, for which the ABR is creating Type 3 LSAs. If at least one subordinate subnet exists (subnets that sit inside the range), then the ABR advertises the summary route as a Type 3 LSA.

3.     The ABR does not advertise the subordinate subnet’s Type 3 LSAs.

4.    The ABR assigns a metric for the summary route’s Type 3 LSA, by default, to match the best metric among all subordinate subnets.

5.    The area range command can also explicitly set the cost of the summary.

6.    If no subordinate subnets exist, the ABR does not advertise the summary.

If you add the summary-address prefix mask OSPF subcommand, OSPF will then attempt to summarize the external routes by creating a Type 5 LSA for the summary route, and by no longer advertising the Type 5 LSAs for the subordinate subnets.

ASBR

Summary-address prefix mask [not advertised]

ABRs

Area (area-id) range ip address mask

Stub Area

For totally stubby areas, only the ABR must have the no-summary keyword on the
area (area-id) stub no-summary command. However, including this keyword on internal routers does not cause a problem.

show ip ospf
–Confirms with one (highlighted) line that the router believes that the area is a stub area.

show ip ospf database summary 0.0.0.0
–By definition, this command lists all summary (Type 3) LSAs with prefix 0.0.0.0. It lists two such LSAs, created by R1 and R2 (RIDs 1.1.1.1 and 2.2.2.2, respectively), both with metric 1 (the default setting).

show ip ospf database database-summary
–This command lists statistics about the numbers of and types of LSAs in the database. The counters show 0 Type 5 LSAs, and a few dozen Type 3s–confirming that the area, while stubby, is not totally stubby.

Trouble The Stub Area

Area 234 is configured as STUB area.

check that Area 234 is configured as Stub.

On Router 1
R1#sh ip ospf
 Routing Process "ospf 1" with ID 1.1.1.1
 Start time: 00:05:48.280, Time elapsed: 00:07:36.756
 Supports only single TOS(TOS0) routes
 Supports opaque LSA
 Supports Link-local Signaling (LLS)
 Supports area transit capability
 Router is not originating router-LSAs with maximum metric
 Initial SPF schedule delay 5000 msecs
 Minimum hold time between two consecutive SPFs 10000 msecs
 Maximum wait time between two consecutive SPFs 10000 msecs
 Incremental-SPF disabled
 Minimum LSA interval 5 secs
 Minimum LSA arrival 1000 msecs
 LSA group pacing timer 240 secs
 Interface flood pacing timer 33 msecs
 Retransmission pacing timer 66 msecs
 Number of external LSA 0. Checksum Sum 0x000000
 Number of opaque AS LSA 0. Checksum Sum 0x000000
 Number of DCbitless external and opaque AS LSA 0
 Number of DoNotAge external and opaque AS LSA 0
 Number of areas in this router is 1. 0 normal 1 stub 0 nssa
 Number of areas transit capable is 0
 External flood list length 0
    Area 234
        Number of interfaces in this area is 3
        It is a stub area
        Area has no authentication
        SPF algorithm last executed 00:04:48.012 ago
        SPF algorithm executed 4 times
        Area ranges are
        Number of LSA 23. Checksum Sum 0x154B32
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0

R1#sh ip ospf database database-summary

            OSPF Router with ID (1.1.1.1) (Process ID 1)

Area 234 database summary
      LSA Type      Count    Delete   Maxage

you can there is no LSA 5 in database summary. 

R1#sh ip ospf database summary 0.0.0.0

This command lists all summary (LSA 3) with prefix 0.0.0.0. It list two such LSAs from 3.3.3.3 and 4.4.4.4

    OSPF Router with ID (1.1.1.1) (Process ID 1)

                Summary Net Link States (Area 234)

  Routing Bit Set on this LSA
  LS age: 1156
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0x57DA
  Length: 28
  Network Mask: /0
        TOS: 0  Metric: 1

  Routing Bit Set on this LSA
  LS age: 1155
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000001
  Checksum: 0x39F4
  Length: 28
  Network Mask: /0
        TOS: 0  Metric: 1

Check the cost of default route generated by ABRs in Area 234

Router1

O*IA 0.0.0.0/0 [110/2] via 14.14.14.2, 00:15:23, FastEthernet0/0
                         [110/2] via 13.13.13.2, 00:15:23, FastEthernet2/0


both the ABRs are generated Default route with metric 1 in area 234

what if i want the packets to take route through router3 for networks in BackBone Area.

change the area default cost at ABRs.


R3(config)#router ospf 1
                  area 234 defalut-cost 10
R4(config)#router ospf 1
                  area 234 defalut-cost 20


Any internal router will select low cost path for exit.


R1#sh ip route | in 0.0.0.0
Gateway of last resort is 13.13.13.2 to network 0.0.0.0
O*IA 0.0.0.0/0 [110/11] via 13.13.13.2, 00:00:15, FastEthernet2/0




Default route on Router4 is available when router3 will fail.


Change the state of R1 interface F2/0 and F1/0


int f2/0
sh
int f1/0
sh


Now the Router1 have no route to R3, and it will chose R4


R1#sh ip route | in 0.0.0.0
Gateway of last resort is 14.14.14.2 to network 0.0.0.0
O*IA 0.0.0.0/0 [110/21] via 14.14.14.2, 00:00:08, FastEthernet0/0