Post on 10-Apr-2018
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Configuring OSPF Part 1 of 2
CIS 185 CCNP ROUTE
Rick GrazianiCabrillo College
graziani@cabrillo.edu
Last Updated: Fall 2010
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Topics
Review of OSPF
Areas
LSAs
show ip ospf database (summary of link state database)
show ip route
Stub Areas
Totally Stubby Areas
E1 and E2 routes
Default Routes
Route Summarization
NSSA (Not So Stubby Areas)
Multiple ABR Scenario
Multiple ASBR Scenario
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Single Area OSPF - Review
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Introduction to OSPF
OSPF is:
Classless
Link-state routing protocol
Uses the concept of areas for scalability
RFC 2328 defines the OSPF metric as an arbitrary value called cost.
Cisco IOS software uses bandwidth to calculate the OSPF cost metric.
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The network Command
The area area-idrefers to the OSPF area.
A group of OSPF routers that share link-state information.
All OSPF routers in the same area must have the same link-state
information in their link-state databases.This is accomplished by routers flooding their individual link
states to all other routers in the area.
Router(config-router)# networknetwork-address wildcard-mask a
rea area-id
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1 Flooding of link-state
information
2 Building a
Topological
Database
3 SPF Algorithm
4 SPF Tree
5 Routing Table
Link State Concepts
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Before two routers can form an OSPF neighbor adjacency, they
must agree on three values:
Hello intervalDead interval
Both the interfaces must be part of the same network, including
having the same subnet mask.
IP MTU must match
Neighbors and
Adjacencies
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Hello Intervals
By default, OSPF Hello packets are sent:
10 seconds on multiaccess and point-to-point segments
30 seconds on nonbroadcast multiaccess (NBMA) segments (Frame
Relay, X.25, ATM).
In most cases, use multicast addressALLSPFRouters at 224.0.0.5.
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Dead Intervals
Cisco uses a default of four times the Hello interval.
40 seconds - Multiaccess and point-to-point segments.
120 seconds - NBMA networks.
Dead interval expires
OSPF removes that neighbor from its link-state database.
Floods the link-state information about the down neighbor out all
OSPF-enabled interfaces.
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Modifying OSPF Intervals
Dead time is counting down from 40 seconds. Refreshed every 10 seconds when R1 receives a Hello from the neighbor.
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.3.3.3 0 FULL/ - 00:00:35 192.168.10.6 Serial0/0/1
10.2.2.2 0 FULL/ - 00:00:36 192.168.10.2 Serial0/0/0
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Modifying OSPF Intervals
Router(config-if)# ip ospf hello-interval seconds
Router(config-if)# ip ospf dead-interval seconds
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Basic OSPF Configuration Lab Topology
The router ospf command
The network command
OSPF Router ID
Verifying OSPF
Examining the Routing Table
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OSPF Router ID is an IP address used to uniquely identify an OSPF router.
Also used in the DR and BDR process.
1.Use the IP address configured with the OSPF router-idcommand.
2.Highest IP address of any of its loopback interfaces.
3.Highest active IP address of any of its physical interfaces.
OSPF Router ID
Router ID?
Router ID?
Router ID?
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Verifying New Router IDs (Loopbacks)R1# show ip protocols
Routing Protocol is ospf 1Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 10.1.1.1
R2# show ip protocols
Routing Protocol is ospf 1
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 10.2.2.2
R3# show ip protocols
Routing Protocol is ospf 1
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 10.3.3.3
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Verifying OSPF
Neighbor ID: The router ID of the neighboring router.
Pri: The OSPF priority of the interface.
State: The OSPF state of the interface.
Dead Time:
Address: The IP address of the neighbors interface
Interface: Local interface
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.3.3.3 1 FULL/ - 00:00:30 192.168.10.6 Serial0/0/1
10.2.2.2 1 FULL/ - 00:00:33 192.168.10.2 Serial0/0/0
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R1# show ip ospf interface serial 0/0/0
Serial0/0/0 is up, line protocol is up
Internet Address 192.168.10.1/30, Area 0
Process ID 1, Router ID 10.1.1.1,Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Verifying OSPF
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Verifying OSPF
R1# show ip protocolsRouting Protocol is ospf 1
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 10.1.1.1
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4Routing for Networks:
172.16.1.16 0.0.0.15 area 0
192.168.10.0 0.0.0.3 area 0
192.168.10.4 0.0.0.3 area 0
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway Distance Last Update
10.2.2.2 110 11:29:29
10.3.3.3 110 11:29:29
Distance: (default is 110)
OSPF Process ID
OSPF Router ID
Networks OSPF is
advertising that are
originatingfrom this router
OSPF Neighbors
Administrative Distance
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Verifying OSPFR1# show ip ospf
Routing Process ospf 1 with ID 10.1.1.1
Start time: 00:00:19.540, Time elapsed: 11:31:15.776
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
Minimumhold 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
Area BACKBONE(0)
Number of interfaces in thisarea is 3
Areahas no authentication
SPFalgorit
hm l
ast executed 11:30:31.628
ago
SPF algorithm executed 5 times
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Verifying OSPF
Any time a router receives new information about the topology (addition,deletion, or modification of a link), the router must:
Rerun the SPF algorithm
Create a new SPF tree
Update the routing table
The SPF algorithm is CPU intensive, and the time it takes for calculationdepends on the size of the area.
R1# show ip ospf
Initial SPF schedule delay 5000 msecs
Minimumhold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
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Verifying OSPF
A flapping link can cause OSPF routers in an area to constantly recalculatethe SPF algorithm, preventing proper convergence.
If there is a route in the routing table the router will continue to forwardthe packet.
SPF schedule delay.
To minimize this problem, the router waits 5 seconds (5000 msec) afterreceiving an LSU before running the SPF algorithm.
Minimum hold time:
To prevent a router from constantly running the SPF algorithm, there isan additional hold time of 10 seconds (10,000 ms).
The router waits 10 seconds after running the SPF algorithm beforererunning the algorithm.
R1# show ip ospf
Initial SPF schedule delay 5000 msecs
Minimumhold time between two consecutive SPFs 10000 msecs
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Verifying OSPF
R1# show ip ospf interface serial 0/0/0
Serial0/0/0 is up, line protocol is up
Internet Address 192.168.10.1/30, Area 0
Process ID 1, Router ID 10.1.1.1,Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
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Examining the Routing Table
Unlike RIPv2 and EIGRP, OSPF does not automatically summarize at major
network boundaries.
R1# show ip route
Codes: D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
192.168.10.0/30 is subnetted, 3 subnets
C 192.168.10.0 is directly connected, Serial0/0/0
C 192.168.10.4 is directly connected, Serial0/0/1
O 192.168.10.8 [110/128] via 192.168.10.2, 14:27:57, Serial0/0/0
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
O 172.16.1.32/29 [110/65] via 192.168.10.6, 14:27:57, Serial0/0/1
C 172.16.1.16/28 is directly connected, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O 10.10.10.0/24 [110/65] via 192.168.10.2, 14:27:57, Serial0/0/0
C 10.1.1.1/32 is directly connected, Loopback0
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The OSPF Metric OSPF Metric
Modifying the Cost of the Link
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OSPF Metric
The OSPF metric is called cost. The following passage is from RFC 2328:
A cost is associated with the output side of each router interface. This
cost is configurable bythe system administrator. The lower the cost, the
more likelythe interface is tobe used to forward data traffic.
RFC 2328 does not specify which values should be used to determine the
cost.
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OSPF Metric
Cisco IOS software uses the cumulative bandwidths of the outgoing
interfaces from the router to the destination network as the cost value.
108 is known as the reference bandwidth
Cisco IOS Cost for OSPF = 108
/bandwidth in bps
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Reference Bandwidth
When this command is necessary, it is recommended that it is usedon all
routers so the OSPF routingmetric remains consistent.
R1(config-router)#auto-co
st reference-
bandwidt
h?
1-4294967 The reference bandwidth in terms of Mbits per second.
R1(config-router)# auto-cost reference-bandwidth 10000
To increase it to 10GigE(10 Gbps Ethernet) speeds, you need to change the reference
bandwidth to 10,000.
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T1 cost 64 + Fast Ethernet cost 1 = 65
The Cost = 64 refers to the default cost of the serial interface,
108/1,544,000 bps = 64, and not to the actual 64-Kbps speed of the link.
R1# show ip route
O 10.10.10.0/24 [110/65] via 192.168.10.2, 14:27:57, Serial0/0/0
OSPF
Accumulates Cost
Serial interfaces bandwidth value
defaults to T1 or 1544 Kbps.
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Default Bandwidth on Serial Interfaces
On Cisco routers, the bandwidth value on many serial interfaces
defaults to T1 (1.544 Mbps).
R1#show interf
ace
seri
al 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is GT96K Serial
Description: Link to R2
Internet address is 192.168.10.1/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
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Modifying the Cost of the Link
The bandwidth command is used to modify the bandwidth value
used by the Cisco IOS software in calculating the OSPF cost metric.
Same as with EIGRP
Router(config-if)#ba
ndwidth
bandwidth-k
bps
R1(config)# inter serial 0/0/0
R1(config-if)# bandwidth 64
R1(config-if)# inter serial 0/0/1
R1(config-if)# bandwidth 256
R1(config-if)# end
R1# show ip ospf interface serial 0/0/0
Serial0/0 is up, line protocol is up
Internet Address 192.168.10.1/30, Area 0
Process ID 1, Router ID 10.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
100,000,000/64,000 = 1562
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The ip ospf cost Command
An alternative method to using the bandwidth command is to usethe ip ospf cost command, which allows you to directly specifythe cost of an interface.
This will not change the output of the show ip ospf interfacecommand,
R1(config)# interface serial 0/0/0
R1(config-if)# ip ospf cost 1562
R1(config)# inter serial 0/0/0
R1(config-if)# bandwidth 64R1(config-if)# end
R1# show ip ospf interface serial 0/0/0
Serial0/0 is up, line protocol is up
Internet Address 192.168.10.1/30, Area 0
Process ID 1, Router ID 10.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
100,000,000/64,000 = 1562
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OSPF and Multiaccess
Networks Challenges in Multiaccess Networks
DR/BDR Election Process
OSPF Interface Priority
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Solution: Designated Router
OSPF elects a Designated Router (DR) to be the collection and distribution
point for LSAs sent and received. A Backup Designated Router (BDR) is also elected in case the DR fails.
All other routers become DROthers.
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DR/BDR Election
The following criteria are applied:
1. DR: Router with the highest OSPF interface priority.
2.BDR: Router with the second highest OSPF interface priority.
3.If OSPF interface priorities are equal, the highest router ID is used to
break the tie.
Default OSPF interface priority is 1.
Current configuration, the OSPF router ID is used to elect the DR and BDR.
DR
BDR
DROther
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RouterA# show ip ospf interface fastethernet 0/0
FastEthernet0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 0
Process ID 1, Router ID 192.168.31.11, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DROTHER, Priority 1
DesignatedRouter (ID) 192.168.31.33, Interface address 192.168.1.3
Backup Designated router (ID) 192.168.31.22, Interface address192.168.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Verifying Router States
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Timing of DR/BDR Election
If I booted first and started
the election before the
others were ready, I would
be the DR!
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Timing of DR/BDR Election
When the DR is elected, it remains the DR until one of the following
conditions occurs:
The DR fails.The OSPF process on the DR fails.
The multiaccess interface on the DR fails.
If the DR fails, the BDR assumes the role of DR, and an election is held to
choose a new BDR.
DR failed! I am now the
DR! Elections will now
happened for BDR
I am now
the BDR!
DR
BDR
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If a new router enters the network after the DR and BDR have been
elected, it willnotbecome the DRor the BDR even if it has a higher
OSPF interface priorityor router ID than the current DRor BDR.
DR
BDR
Timing of
DR/BDR
Election
DROther
I am a new router with the highest
Router ID. I cannot force a new
DR or BDR election, so I am aDROther.
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A previous DR does not regain DR status if it returns to the network.
DR
BDR
Timing of
DR/BDR
Election
DROther
Im back but I dont
get to become DR
again. I am now just a
DROther.
DROther
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If the BDR fails, an election is held among the DROthers to see which router
will be the new BDR.
DR
BDR
Timing of
DR/BDR
Election
BDR
Amongst the
DROthers I have the
highest Router ID, soI am the new BDR!
DROther
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RouterB fails.
Because RouterD is the current BDR, it is promoted to DR.
RouterC becomes the BDR.
DR
BDR
Timing of
DR/BDR
Election
BDR
I am now the new DR!
DROther
I am now the new
BDR!
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Timing of DR/BDR Election
We can change the OSPF interface priority to better control our DR/BDRelections.
How can we make sureRouterB is the DR and
RouterA is the BDR,
regarless of RouterID
values?
Want tobe DR
Want tobe
BDR
Highest Router ID
To simplifyour discussion, we
removed RouterD from the topology.
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OSPF Interface Priority
Control the election of these routers with the ip ospf priority interfacecommand.
Priority (Highest priority wins):
0 = Cannot become DR or BDR
1 = Default
Therefore, the router ID determines the DR and BDR.
Priorities are an interface-specific value, they provide better control of the
OSPF multiaccess networks.
They also allow a router to be the DR in one network and a DROther inanother.
Router(config-if)# ip os
pf priority {0 - 255}
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After doing a shutdown and a no shutdown on the Fast Ethernet0/0 interfaces of all three routers, we see the result of the change of
OSPF interface priorities.
RouterA(config)# interface fastethernet 0/0
RouterA(config-if)# ip ospf priority 200
RouterB(config)# interface fastethernet 0/0
RouterB(config-if)# ip os
pf priority 100
Pri = 200
Pri = 100
Highest prioritywins
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Clarifications regarding DR/BDR
Hello packets are still exchanged between all routers on a multi-
access segment (DR, BDR, DROthers,.) to maintain neighbor
adjacencies.
OSPF LSA packets (coming) are packets which are sent from the
BDR/DROthers to the DR, and then from the DR to the
BDR/DROthers. (The reason for a DR/BDR.)
Normal routing ofIP packets still takes the lowest cost route, which
might be between two DROthers.
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More OSPF Configuration Redistributing an OSPF Default Route
Fine-tuning OSPF
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Redistributing
an OSPF
Default Route
If the default-information originate command is not used, thedefault quad zero route will not be propagated to other routers in the
OSPF area.
R1(config)# interface loopback 1
R1(config-if)# ip add 172.30.1.1 255.255.255.252
R1(config-if)# exit
R1(config)# ip route 0.0.0.0 0.0.0.0 loopback 1
R1(config)# router ospf 1
R1(config-router)# default-information originate
The static default route is usingthe
loopback as an exit interface
because the ISP router in this
topologydoes not physicallyexist.
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R3s Routing Table
R3# show ip route
Gateway of last resort is 192.168.10.5 to network 0.0.0.0
192.168.10.0/30 is subnetted, 3 subnets
O 192.168.10.0 [110/1952] via 192.168.10.5, 00:00:38, S0/0/0
C 192.168.10.4 is directly connected, Serial0/0/0C 192.168.10.8 is directly connected, Serial0/0/1
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.1.32/29 is directly connected, FastEthernet0/0
O 172.16.1.16/28 [110/391] via 192.168.10.5, 00:00:38, S0/0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.3.3.3/32 is directly connected, Loopback0O 10.10.10.0/24 [110/782] via 192.168.10.9, 00:00:38, S0/0/1
O*E2 0.0.0.0/0 [110/1] via 192.168.10.5, 00:00:27, Serial0/0/0
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External Type 2 Route
E2 denotes that this route is an OSPF External Type 2 route.
OSPF external routes fall in one of two categories:
External Type 1 (E1)
External Type 2 (E2)
OSPF accumulates cost for an E1 route as the route is being propagated
throughout the OSPF area.
This process is identical to cost calculations for normal OSPF internal routes.
E2 route is always the external cost, irrespective of the interior cost to reach thatroute.
In this topology, because the default route has an external cost of 1 on the
R1 router, R2 and R3 also show a cost of 1 for the default E2 route.
E2 routes at a cost of 1 are the default OSPF configuration.
More later
R3# show ip route
O*E2 0.0.0.0/0 [110/1] via 192.168.10.5, 00:00:27, Serial0/0/0
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Steps to OSPF Operation with States
1. Establishing router adjacencies (Routers are adjacent)
Down State No Hello received
Init State Hello received, but not with this routers Router ID
Hi, my name is Carlos. Hi, my name is Maria.
Two-way State Hello received, and with this routers Router ID
Hi, Maria, my name is Carlos. Hi, Carlos, my name is Maria.
2. Electing DR and BDR Multi-access (broadcast) segments only
ExStart State with DR and BDR
Two-way State with all other routers
3. Discovering Routes
ExStart State
Exchange State
Loading State
Full State (Routers are fully adjacent)
4. Calculating the Routing Table
5. Maintaining the LSDB and Routing Table
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Hello 10.6.0.1
Hello 10.5.0.1
Hello 10.6.0.110.5.0.1
Hello 10.5.0.110.6.0.1
DownInit DownInit2-way 2-way
Down State - Init State Two Way State
Down State - OSPF routers send Hello packets at regular intervals (10 sec.) to establish
neighbors.
When a router (sends or) receives its first Hello packet, it enters the init state.Hello packet contains a list of known neighbors.
When the router sends a Hello packet (unicast reply) to the neighbor with its RouterID and
the neighbor sends a Hello packet packet back with that Router ID, the routers interface
will transition to the two-way state.
Now, the router is ready to take the relationship to the next level.
1. Establishing Adjacencies
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Steps to OSPF Operation with States (cont)
Explanations in Notes Section
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Couple of notes on link state flooding
OSPF is a link state routing protocol and does not send periodic updates
like RIP.
OSPF only floods link state state advertisements when there is a changein topology (this includes when a routers are first booted).
OSPF uses hop-by-hop flooding of LSAs; an LSA received on oneinterface are flooded out other OSPF enabled interfaces.
If a link state entry in the LSDB (Link State DataBase) reaches an age of60minutes (MaxAge) without being updated, it is removed and SPF isrecalculated.
Every 30 minutes (LSRefreshTime), OSPF routers flood only their linkstates to all other routers (in the area).
This is known as a paranoid update
These do not trigger SPF recalculations. Special note: When a link goes down and a router wants to send a LSA to
tell other routers to remove this link state, it sends this link state with avalue of60 minutes (MAXAGE).
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Single Area OSPF
End of Review
CIS 185 Advanced Routing
Rick GrazianiCabrillo College
graziani@cabrillo.edu
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Issues with large OSPF nets Large link-state table
Each router maintains a LSDB for all links in the area
The LSDB requires the use of memory
Frequent SPF calculations
A topology change in an area causes each router to re-run SPF to rebuildthe SPF tree and the routing table.
A flapping link will affect an entire area.
SPF re-calculations are done only for changes within that area.
Large routing table
Typically, the larger the area the larger the routing table.
A larger routing table requires more memory and takes more time toperform the route look-ups.
Solution: Divide the network into multiple areas
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OSPF uses Areas
Hierarchical routing enables you to separate large internetworks(autonomous systems) into smaller internetworks that are called areas.
With this technique, routing still occurs between the areas (called inter-arearouting).
Some operations are restricted within an area:
Flooding of LSAs
Recalculating the database
Re-running the SPF algorithm
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OSPF Router Types
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OSPF
Router
Types
InternalInternal: Routers with all their interfaces within the same area
BackboneBackbone: Routers with at least one interface connected to area 0
ASBRASBR: (Autonomous System Boundary Router): Routers that have at
least one interface connected to an external internetwork (another
autonomous system)
ABRABR: (Area Border Router): Routers with interfaces attached to
multiple areas.
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Question: I understand the routing table is recalculated every time the router receives
an new version of an LSA. Does OSPF recalculate its routing table when their is atopology change in another area? show ip ospf displays no change in SPF execution, but
show ip ospf database shows a change in the topology?
Answer: Good question! OSPF areas are designed to keep issues like flapping links
within an area.
SPF is not recalculated if the topology change is in another area.The interesting thing is that OSPF distributes inter-area (between areas) topology
information using a distance-vector method.
OSPF uses link-state principles only within an area.
ABRs do not announce topological information between areas, instead, only routing
information is injected into other areas.
ABRs relay routing information between areas via distance vector technique similar
to RIP or EIGRP.
This is why show ip ospf does not show a change in the number of times SPF has
been executed when the topology change is in another area.
Note: It is still a good idea to perform route summarization between areas, announcing
multiple routes as a single inter-area route. This will hide any changes in one area from
affecting routing tables in other areas.
An advantage of Multiple Areas
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OSPF Packet Types
In CCNA we discussed various OSPF packets
OSPF packet types
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OSPF packet types
OSPF Type-4 packets have 7 LSA packets (later)
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LSAs used for discovering routes and reaching Full State, along with
Maintain Routes
LSA Types
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LSA Types
LSA Types 1 through 5
We will look at these in detail as we discuss areas in this chapter.
LSA Type 6 MOSPF (Multicast OSPF)
Not supported by Cisco.
MOSPF enhances OSPF by letting routers use their link-state databases tobuild multicast distribution trees for the forwarding of multicast traffic.
LSA Type 7 NSSA External Link Entry
Next presentation!
LSA Type 8 External attributes LSA for BGP
Not supported by Cisco N/A
LSA Type 9, 10, or 11 Opaque LSAs
Future upgrades
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Area Types
Standard or Normal Areas
Backbone
Non-Backbone
Stub Areas
Stub Area
Totally Stubby Area
Not-so-stubby-area (NSSA)
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Area Types
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Part I - LSAs using all normal areas
Multi Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone
Area
What are the router
types?
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Routes Received on all OSPF Routers
Overview ofNormal Areas This will all be explained!
Receives all routes from within A.S.:
Within the local area LSA 1 and LSA 2
From other areas (Inter-Area) LSA 3, LSA4, LSA 5
Receives all routes from External A.S.s (External AS means routes notfrom this OSPF routing domain):
From external ASs LSA 5
As long as routes are being redistributed by the ASBR (more later)
Default Route
Received only ifdefault-information-originate command was used(later)
Ifdefault-information-originate command is not used, then the
default route is not received
Part I - LSAs using all normal areas
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1. OSPF Multi-Areas - All Normal Areas
R33
router ospf 1network 172.16.1.0 0.0.0.255 area 1
network 172.30.1.0 0.0.0.255 area 1
R22router ospf 1
network 172.16.1.0 0.0.0.255 area 1
network 172.30.2.0 0.0.0.255 area 1
R1router ospf 1
network 10.0.0.0 0.0.0.3 area 0
network 9.0.0.0 0.0.0.3 area 0
network 172.16.1.0 0.0.0.255 area 1
network 172.16.2.0 0.0.0.255 area 1
R2router ospf 1
network 192.168.2.0 0.0.0.255 area 0
network 10.0.0.0 0.0.0.3 area 0
network 11.0.0.0 0.0.0.3 area 0
default-information originate
ip route 0.0.0.0 0.0.0.0 serial 0/2
R3router ospf 1
network 11.0.0.0 0.0.0.3 area 0
network 9.0.0.0 0.0.0.3 area 0
network 172.16.10.0 0.0.0.255 area 51
network 172.16.11.0 0.0.0.255 area 51
network 99.0.0.0 0.0.0.3 area 51
R100router ospf 1
network 99.0.0.0 0.0.0.3 area 51
network 99.1.0.0 0.0.255.255 area 51
network 99.0.0.4 0.0.0.3 area 51
R200router ospf 1
network 99.0.0.4 0.0.0.3 area 51network 99.0.0.0 0.0.255.255 area 51
ABR contains network statements for
each area it belongs to, using the
proper area value.
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Part I - LSAs using all normal areas
Multi Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone
Area
What are the routertypes?
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Part I - LSAs using all normal areas
Multi Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone
Area
What are the routertypes?
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Part I - LSAs using all normal areas
Multi Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone
Area
What are the routertypes?
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Understanding LSAs (FYI ONLY) show ip ospf database
This is not the link state database, only a summary.It is a tool to help determine what routes are included in the routing table.
We will look at this output to learn the tool as well as become familiar withthe different types of LSAs.
To view the link state database use: show ip ospf database[router|network|]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LSA Header
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LSA 1 Router LSA
Generated by each router for each area it belongs to.
Describes the states of the links in the area to which this router belongs.
Flooded only within the area. On multi-access networks, sent to the DR.
Denoted by just an O in the routing table or C if the network is directlyconnected.
ABR will include a set of LSA 1s for each area it belongs to.
When a new LSA 1 is received and installed in the LSDB, the router forwards
that LSA, using hop-by-hop or asynchronous flooding.
A C
D
2
5
B
15 RouterAs LSA1s
which are flooded to all
other routers in thisarea.
Leaf network
LSA 1 - Router Link States
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| LS age | Options | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| 0 |V|E|B| 0 | # links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
LSA 1 - Router Link States
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LSA 1 Router Link States
LSA 1sLSA 1s
LSA 1s
Each router floods their LSA 1s ONLY within their own area.
LSA 1s only announce the links (networks) within the area.
Router receives LSA 1s from neighbor, floods those LSA 1s to other
neighbors within the same area.
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LSA 1 - Router Link States
For Router Links:
Link State ID: Advertising Router ID Advertising Router: Router ID of the router that created this LSA 1
Bottom line: Router Link States (LSA1s) should display all the RouterIDs of
routers in that area, including its own.
Ricks reminder: LSA 1 -> my one area
R100# show ip ospf database
OSPF Router with ID (100.100.100.100) (Process ID 1)
Router Link States (Area 51)
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R100# show ip route
172.16.0.0/24 is subnetted, 4 subnets
O 172.16.10.0 [110/65] via 99.0.0.1, 00:08:30, Serial0/0
O 172.16.11.0 [110/65] via 99.0.0.1, 00:08:30, Serial0/0
LSA 1 - Router Link States
Denoted by just an O in the routing table, or a C
Note: Only partial routing tables will be shown
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LSA 1sLSA 1s
LSA 1s
LSA 1 - Router Link States
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LSA 2 Network LSA
Generated by the DR on every multi-access network Denoted by just an O in the routing table orC if the network is
directly connected.
Flooded only within the originating area.
LSA 2s are in link state database forall routers within area, even
those routers on not on multi-access networks or DRs on other multi-access networks in the same area.
ABR may include a set of LSA 2s for each area it belongs to.
LSA 2 - Network Link States
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0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AttachedRouter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
LSA 2 - Network Link States
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LSA 2s
LSA 2s flooded within area by DR.
LSA 2s
LSA 2s
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LSA 2s
LSA 2s
LSA 2 - Network Link States
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LSA 3 Summary LSA
Originated by the ABR.
Describes links between ABR and Internal Routers of the Local Area
ABR will include a set of LSA 3s for each area it belongs to.
LSA 3s are flooded throughout the backbone (Area 0) and to other ABRs.
Routes learned via LSA type 3s are denoted by an IA (Inter-area) in the
routing table.
LSA 3 Summary Net Link States
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LSA 3 Summary LSAs
LSA 3 Summary LSA Originated by the ABR.
Describes links between ABR and Internal Routers of the Local Area
ABR will include a set of LSA 3s for each area it belongs to.
LSA 3s are flooded throughout the backbone (Area 0) and to other ABRs.
Routes learned via LSA type 3s are denoted by an IA (Inter-area) in the
routing table.
LSA 3sLSA 1s
LSA 3s
ABRABR
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LSA 3 Summary LSAs
LSA 1sLSA 3s
LSA 3s
ABR ABR
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LSA 3 Summary LSAs
LSA 3sLSA 3s
LSA 1s
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 3 or 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| TOS | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
LSA 3 Summary Net Link States
LSA 3 S N t Li k St t
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Routers only see the topology of the area they belong to. When a link in one area changes, the adjacent routers originate in LSA 1s and
flood them within the area, causing intra-area (internal) routers to re-run theSPF and recalculating the routing table.
ABRs do not announce topological information between areas. ABRs only inject routing information into other areas, which is basically a
distance-vector technique.
LSA 3sLSA 1s
LSA 3s
Process
using DV
technique
not LSA 1
Link States.
New or
change, do
not run SPF
algorithm.
LSA 3 Summary Net Link States
X
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Area 0
Backbone Area
Area 51Area 1
RTA RTB
RTC
LSA 3 LSA 3
LSA 1s
Not ABR
In normal operation, OSPF ABRs will only announce inter-arearoutes that were learned from the backbone area, area 0.
RTC does not forward LSA 3s from Area 1 to Area 51, and does notforward LSA 3s from Area 51 to Area 1. The backbone area serves as a repository for inter-area routes. This keeps OSPF safe from routing loops.
Normal Areas
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Area 0
Backbone Area
Area 51Area 1
RTA RTB
RTC
LSA 3
LSA 3
Normal Areas
LSA 1s
Not ABR
RTC does not forward the LSA 3s back into Area 1, or routing loopsmay develop.
Note: RTC will create LSA 1s and flood them within the appropriatearea. OSPF specification states that ABRs are restricted to considering LSA 3s only
from the backbone area to avoid routing information loops.
Normal AreasUpdate is sent to Area 0 and Area
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Area 0
Backbone Area
Area 51Area 1
RTA RTB
RTC
LSA 1s
LSA 3
LSA 3
X
Area 1 routers re-run
SPF, creates new SPF
tree and updatesrouting table.
Update is sent to Area 0 and Area
51 routers using a distance
vector update technique. SPF not
re-run, but routers update routing
table.
TopologyChange: Down Link
When a router detects a topology change it immediately sends out LSA1s (Router LSAs) with the change.
Age of the LSA is set to MaxAge (3,600 seconds) Routers removethis entry from their LSDB (Link State Data Base).
Routers that receive the LSA 1s, within the area of the change: Re-run their SPF algorithm Build a new SPF tree
Update IP routing tables. (Continued next slide)
Normal AreasUpdate is sent to Area 0 and Area
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Area 0
Backbone Area
Area 51Area 1
RTA RTB
RTC
LSA 1s
LSA 3
LSA 3
X
Area 1 routers re-run
SPF, creates new SPF
tree and updates
routing table.
Update s se t to ea 0 a d ea
51 routers using a distance
vector update technique. SPF not
re-run, but routers update routing
table.
TopologyChange: Down Link
ABR RTA receives the LSA 1 and recalculate their SPF for that area,Area 1.
RTA floods the change as a LSA 3 within its other area, Area 0. RTB receives the LSA 3 and floods it within Area 51. Area 0 and Area 51 routers do not recalculate their SPFs, but inject the
change into their routing tables.
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R33# show ip ospf database
Summary Net Link States (Area 1)Link ID ADV Router Age Seq# Checksum
10.0.0.0 1.1.1.1 130 0x8000000c 0x00ec09
9.0.0.0 1.1.1.1 130 0x8000000d 0x00ec09
192.168.2.0 1.1.1.1 130 0x8000000e 0x00ec09
11.0.0.0 1.1.1.1 130 0x8000000f 0x00ec09
172.16.10.0 1.1.1.1 130 0x80000010 0x00ec09
172.16.11.0 1.1.1.1 130 0x80000011 0x00ec09
99.0.0.0 1.1.1.1 130 0x80000012 0x00ec09
99.0.0.4 1.1.1.1 130 0x80000013 0x00ec09
99.1.0.0 1.1.1.1 130 0x80000014 0x00ec09
LSA 3 Summary Net Link States (INTERNAL)
Link ID = IP network addresses of networks in other areas ADV Router = ABR Router ID sending the LSA-3
Bottom line: Should see networks in other areas and the ABR advertising thatroute.
Ricks reminder: LSA 3 -> networks sent by the A B R1 2 3
ABR
S 3 S S ( )
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R1# show ip ospf database
Summary Net Link States (Area 1) networks sent by the A B R
1 2 3
LSA 3 Summary Net Link States
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R2# show ip route
99.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O IA 99.0.0.0/30 [110/1626] via 11.0.0.2, 00:43:01, Serial0/1
O IA 99.0.0.4/30 [110/1627] via 11.0.0.2, 00:43:01, Serial0/1
O IA 99.1.0.0/16 [110/1627] via 11.0.0.2, 00:43:01, Serial0/1
172.16.0.0/24 is subnetted, 4 subnets
O IA 172.16.1.0 [110/65] via 10.0.0.1, 00:42:21, Serial0/0
O IA 172.16.2.0 [110/65] via 10.0.0.1, 00:42:51, Serial0/0O IA 172.16.10.0 [110/1563] via 11.0.0.2, 00:43:01, Serial0/1
O IA 172.16.11.0 [110/1563] via 11.0.0.2, 00:43:01, Serial0/1
172.30.0.0/24 is subnetted, 2 subnets
O IA 172.30.1.0 [110/66] via 10.0.0.1, 00:42:21, Serial0/0
O IA 172.30.2.0 [110/66] via 10.0.0.1, 00:42:21, Serial0/0
LSA 3 Summary Net Link States
Routes learned via LSA type 3s are denoted by an IA (Inter-AreaRoutes) in the routing table.
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LSA 4 ASBR Summary LSA
Originated by the ABR. Flooded throughout the area.
Describes the reachability to the ASBRs
Advertises an ASBR (Router ID) not a network
Included in routing table as an IA route.
Exceptions
Not flooded to Stub and Totally Stubby networks.
LSA 4 ASBR
Summary Link
States
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 3 or 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
LSA 4 ASBR Summary Link States
LSA 4 ASBR S Li k St t
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LSA 4 ASBR Summary Link States
How does the ABRs know about the ASBR?
ASBR sends a type 1 Router LSA with a bit (external bit e bit) that
is set to identify itself as the ASBR.
LSA 1s
(e bit)
LSA 4
LSA 4
LSA 4 ASBR S Li k St t (ABR)
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R1# show ip ospf database
Summary ASB Link States (Area 1)
Link IDADV
Router
Age Seq#
Check
sum
2.2.2.2 1.1.1.1 1482 0x8000000b 0x00ec09
LSA 4 ASBR Summary Link States (ABR)
Link ID - Router ID of ASBR ADV Router - Router ID ABR advertising route
Bottom line: Routers in non-area 0, should see Router ID of ASBRand its ABR to get there .
Ricks reminder: LSA 4 -> Reachability to the A S B R
ASBR (This) ABR
ABR
LSA 4 ASBR Summary Link States (INTERNAL)
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R33# show ip ospf database
Summary ASB Link States (Area 1)
Link ID ADVRouter Age Seq# Checksum
2.2.2.2 1.1.1.1 130 0x8000000b 0x00ec09
LSA 4 ASBR Summary Link States (INTERNAL)
Link ID - Router ID of ASBR ADV Router - Router ID ABR advertising route
Bottom line: Routers in non-area 0, should see Router ID of ASBRand its ABR to get there .
Ricks reminder: LSA 4 -> Reachability to the A S B R1 2 3 4
ASBR (Advertising) ABR
ABR
LSA 4 ASBR Summary Link States
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LSA 1s
e bitLSA 4
LSA 4
LSA 4 ASBR Summary Link States
LSA 5 - AS External
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LSA 5 AS External LSA
Originated by the ASBR. Describes destination networks external to the Autonomous System (This
OSPF Routing Domain)
Flooded throughout the OSPF AS except to stub and totally stubby areas
Denoted in routing table as E1 or E2 (default) route (soon)
ASBR Router which redistributes routes into the OSPF domain.
Exceptions
Not flooded to Stub and Totally Stubby networks.
LSA 5 AS External
Link States
LSA 5 AS External Link States
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| 0 | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| TOS | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
LSA 5 - AS External Link States
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R2 (ASBR)
router ospf 1
redistribute static
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Redistribute command creates an ASBR router.
LSA 5sOriginated by the ASBR.
Describes destination networks external to the OSPF Routing Domain
Flooded throughout the OSPF AS except to stub and totally stubbyareas
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5sLSA 5
LSA 5
ASBR
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R1# show ip ospf database
Type-5 AS External Link States O T HE R networks1 2 3 4 5
Note: Packet Tracer does not support LSA 5s
for redistributed routes
R2 (ASBR)router ospf 1
redistribute static
default-information originate
ip route 0.0.0.0 0.0.0.0 ser 0/2
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5 - AS External Link States
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R1# show ip route
O E2 57.0.0.0/8 [110/20] via 10.0.0.2, 00:16:02, Serial0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:16:02, Serial0/0
Designated by E2 Notice that the cost is 20 for all redistributed routes, we will see why later. It has to do with E2 routes and where the default cost is 20.
Redistribute command (Route Optimization chapter): If a value is notspecified for the metric option, and no value is specified using the default-metric command, the default metric value is 0, except forOSPF where thedefault cost is 20.
Cost of 1 for the redistributed route.
LSA 5 AS External Link States
LSA 5 - AS External Link States
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R33# show ip ospf database
Type-5 AS External Link States
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E1 vs.E2 External Routes External routes fall under two categories:
external type 1
external type 2 (default)
The difference between the two is in the way the cost (metric) of the route
is being calculated.
The cost of a type 2 route is always the external cost, irrespective of theinterior cost to reach that route.
A type 1 cost is the addition of the external cost and the internal costused to reach that route.
A type 1 route is always preferred over a type 2 route for the samedestination.
More later
LSA 5 - AS External Link States
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Stub Areas
Stub Areas
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Stub Areas
Considerations for both Stub and Totally Stubby Areas
An area could be qualified a stub when:
There is a single exit point (a single ABR) from that area. More than
one ABR can be used, but be ready to accept non-optimal routing
paths.
If routing to outside of the area does not have to take an optimal path.
The area is not needed as a transit area for virtual links (later).
The ASBR is not within the stub area
The area is not the backbone area (area 0)
Stub areas will result in memory and processing savings depending upon
the size of the network.
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Stub Area
Stub Areas
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Receives all routes from within A.S.:
Within the local area - LSA 1s and LSA 2s (if appropriate)
From other areas (Inter-Area) - LSA 3s
Does not receive routes from External A.S. (External Routes).
ABR:
ABR blocks all LSA 4s and LSA 5s.
If LSA 5s are not known inside an area, LSA 4s are not necessary.
LSA 3s are propagated by the ABR.
Note: Default route is automatically injected into stub area by ABRExternal Routes: Once the ABR gets a packet headed to a default route, it must havea default route, either static or propagated by the ASBR via default informationoriginate (coming!)
Configuration:
All routers in the area must be configured as stub
Stub Areas
Stub Areas
Additi l C d
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R3 (ABR)
router ospf 1
area 51 stub
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Stub Area
LSA 4 LSA 4 Blocked
LSA 5 BlockedLSA 5
LSA 3LSA 3
Defaultroute to
ABR
injected
Sent by ABR: LSA 3s (Inter-Area routes)
Blocked: LSA 4s (reachability to ASBR) LSA 5s (External routes)
The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own.
Changes in External routes no longer affect Stub Area routing tables.
We only see routes in
our area, other areas,
and a default route.
No external routes.
each area.
Stub Areas
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R100# show ip ospf database
Summary Net Link States (Area 51)
Link ID ADV Router Age Seq# Checksum
9.0.0.0 3.3.3.3 1752 0x80000037 0x00ba22
0.0.0.0 3.3.3.3 1612 0x80000038 0x00ca5011.0.0.0 3.3.3.3 625 0x80000039 0x00db11
192.168.2.0 3.3.3.3 614 0x8000003a 0x00dd10
10.0.0.0 3.3.3.3 614 0x8000003b 0x00dd10
172.16.2.0 3.3.3.3 614 0x8000003c 0x00dd10
172.16.1.0 3.3.3.3 614 0x8000003d 0x00dd10
172.30.2.0 3.3.3.3 614 0x8000003e 0x00dc11
172.30.1.0 3.3.3.3 614 0x8000003f 0x00dc11
No LSA 4s orLSA 5s for stub area routers. Default Route injected by ABR (LSA 3)
Stub Areas
Stub Areas
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R200# show ip route
9.0.0.0/30 issubnetted, 1 subnets
O IA 9.0.0.0 [110/129] via 99.0.0.5, 00:25:52, FastEthernet0/0
10.0.0.0/30 issubnetted, 1 subnets
O IA 10.0.0.0 [110/1691] via 99.0.0.5, 00:25:52, FastEthernet0/0
11.0.0.0/30 issubnetted, 1 subnets
O IA 11.0.0.0 [110/1627] via 99.0.0.5, 00:25:52, FastEthernet0/0
99.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O 99.0.0.0/30 [110/65] via 99.0.0.5, 00:25:52, FastEthernet0/0
C 99.0.0.4/30 is directly connected, FastEthernet0/0
O 99.1.0.0/16 [110/2] via 99.0.0.5, 00:25:52, FastEthernet0/0
C 99.2.0.0/16 is directly connected, FastEthernet0/1
172.16.0.0/24 issubnetted, 4 subnets
O IA 172.16.1.0 [110/1692] via 99.0.0.5, 00:25:52, FastEthernet0/0
O IA 172.16.2.0 [110/1692] via 99.0.0.5, 00:25:52, FastEthernet0/0
O 172.16.10.0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0
O 172.16.11.0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0
172.30.0.0/24 issubnetted, 2 subnetsO IA 172.30.1.0 [110/1693] via 99.0.0.5, 00:25:52, FastEthernet0/0
O IA 172.30.2.0 [110/1693] via 99.0.0.5, 00:25:52, FastEthernet0/0
O IA 192.168.2.0/24 [110/1628] via 99.0.0.5, 00:25:52, FastEthernet0/0
200.200.200.0/32 issubnetted, 1 subnets
C 200.200.200.200 is directly connected, Loopback0
O*IA 0.0.0.0/0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0
LSA 1s (Within area)
LSA 3s (Other areas)
No LSA 4s (ASBR)
No LSA 5s (External routes)
Default Route (Injected by ABR)
NOTE on default route:
ABR will advertise a default route with a cost of 1 cost of65 = 1 (Default) +1 (Fa) +64 (serial link) The default cost can be modified with the ospf command:
ABR(config-router)# area area-iddefault-
cost cost
Stub Areas
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R3# show ip route
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
9.0.0.0/30 is subnetted, 1 subnets
C 9.0.0.0 is directly connected, Serial0/2
10.0.0.0/30 is subnetted, 1 subnets
O 10.0.0.0 [110/1626] via 11.0.0.1, 00:00:41, Serial0/3
11.0.0.0/30 is subnetted, 1 subnets
C 11.0.0.0 is directly connected, Serial0/3
99.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C 99.0.0.0/30 is directly connected, Serial0/0
O 99.0.0.4/30 [110/65] via 99.0.0.2, 00:00:46, Serial0/0
O 99.1.0.0/16 [110/65] via 99.0.0.2, 00:00:46, Serial0/0
172.16.0.0/24 is subnetted, 4 subnets
O IA 172.16.1.0 [110/1627] via 11.0.0.1, 00:00:31, Serial0/3
O IA 172.16.2.0 [110/1627] via 11.0.0.1, 00:00:31, Serial0/3
C 172.16.10.0 is directly connected, FastEthernet0/0
C 172.16.11.0 is directly connected, FastEthernet0/1172.30.0.0/24 is subnetted, 1 subnets
O IA 172.30.1.0 [110/1628] via 11.0.0.1, 00:00:01, Serial0/3
O 192.168.2.0/24 [110/1563] via 11.0.0.1, 00:00:41, Serial0/3
O*E2 0.0.0.0/0 [110/1] via 11.0.0.1, 00:00:41, Serial0/3
Stub Areas
Notice, there is no automatic default route on ABR, as there are with the
internal stub routers. This default route came from the ASBR. In other words the ABR will inject the default route into the stub
area whether or not it has a default route in its routing table.
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Totally Stubby Areas
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Totally Stubby
Area
Totally Stubby
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Receives routes from within A.S.:
Only from within the local area - LSA 1s and LSA 2s (if appropriate)
Does not receive routes from other areas (Inter-Area) - LSA 3s
Does not receive routes from External A.S. (External Routes)
ABR:
ABR blocks all LSA 4s and LSA 5s.
ABR blocks all LSA 3s, except propagating a default route.
Default route is injected into totally stubby area by ABR.
Configuring:
All routers must be configured as stub
ABR must be configured as stub no-summary
Areas
Totally Stubby
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R1: (ABR)
router ospf 1
area 1 stub no-summary
^^ Command: area area stubno-summary
R22 andR33: (INTERNAL ROUTERS)
router ospf 1
area 1 stub
^^ Command: area area stub
Areas
Totally
LSA 1s still
sent within
each area.
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Stub Area
LSA 4 LSA 4 Blocked
LSA 5 BlockedLSA 5
LSA 3LSA 3
Defaultroute to
ABR
injected
Blocked:
LSA 3s (Inter-Area routes) LSA 4s (reachability to ASBR) LSA 5s (External routes)
The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own.
Changes in other areas and external routes no longer affect Stub Area routing tables.
We only see routes in
our area, other areas,
and a default route.
No external routes.
Stubby Area
Blocked
BlockedBlocked
Default
route to
ABR
injectedWe only see routes in our area
and a default route.
No inter-area or external routes.
Totally Stubby
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R33# show ip route
33.0.0.0/32 issubnetted, 1 subnets
C 33.33.33.33 is directly connected, Loopback0172.16.0.0/24 issubnetted, 2 subnets
C 172.16.1.0 is directly connected, FastEthernet0/0
O 172.16.2.0 [110/2] via 172.16.1.1, 00:02:13, FastEthernet0/0
172.30.0.0/24 issubnetted, 2 subnets
C 172.30.1.0 is directly connected, FastEthernet0/1
O 172.30.2.0 [110/2] via 172.16.1.3, 00:02:23, FastEthernet0/0
O*IA 0.0.0.0/0 [110/2] via 172.16.1.1, 00:02:13, FastEthernet0/0
Areas
Default route is injected into totally stubby area by ABR for all other networks(inter-area and external routes)
Does not receive routes from other areas (Inter-Area)
Does not receive routes from External A.S. (External Routes)
Note: Packet Tracer does not support
Totally Stubby Networks (yet)
Totally Stubby Areas
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R1# show ip route
1.0.0.0/32 issubnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
9.0.0.0/24 issubnetted, 1 subnets
C 9.0.0.0 is directly connected, Serial0/1
10.0.0.0/30 issubnetted, 1 subnets
C 10.0.0.0 is directly connected, Serial0/0
11.0.0.0/30 issubnetted, 1 subnets
O 11.0.0.0 [110/1626] via 10.0.0.2, 00:05:26, Serial0/0
99.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O IA 99.0.0.0/30 [110/1690] via 10.0.0.2, 00:05:26, Serial0/0
O IA 99.0.0.4/30 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0
O IA 99.1.0.0/16 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0
172.16.0.0/24 issubnetted, 4 subnets
C 172.16.1.0 is directly connected, FastEthernet0/0
C 172.16.2.0 is directly connected, FastEthernet0/1O IA 172.16.10.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0
O IA 172.16.11.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0
172.30.0.0/24 issubnetted, 2 subnets
O 172.30.1.0 [110/2] via 172.16.1.2, 00:04:51, FastEthernet0/0
O 172.30.2.0 [110/2] via 172.16.1.3, 00:04:41, FastEthernet0/0
O 192.168.2.0/24 [110/65] via 10.0.0.2, 00:05:26, Serial0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:05:26, Serial0/0
y y
Notice, there is no automatic default route on ABR, as thereare with the internal stub routers.
This default route came from the ASBR. In other words the ABR will inject the default route into
the stub area whether or not it has a default route in its
routing table.
Quick Review
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LSA 1s Router LSAs
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show ip ospf database Router Link States (LSA 1s)Should display all the RouterIDs of routers in that area,
including its own.
show ip route O routes
Routes within that area
LSA 1sLSA 1s
LSA 1s
LSA 2s Network LSAs
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show ip ospf database Net Link States (LSA 2s)Net Link States (LSA2s) should display the RouterIDs of theDRs on all multi-access networks in the area and their IPaddresses.
show ip route O routes
Routes within that area
LSA 2s
LSA 2s
LSA 3 Summary LSAs
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LSA 3sLSA 3s
LSA 1s
show ip ospf database Summary Net Link States (LSA 3s)Link ID = IP network addresses of networks in other areas
ADV Router = ABR Router ID sending the LSA-3
show ip route IA (Inter-Area Routes)
Routes in other areas
LSA 4 ASBR Summary Link States
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show ip ospf database Summary Net Link States (LSA 3s)Link ID = IP network addresses of networks in other areas
ADV Router = ABR Router ID sending the LSA-3
show ip route IA (Inter-Area Routes)
Routes in other areas
LSA 1s
ebitLSA 4
LSA 4
R2 (ASBR)
LSA 5 External Link States
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Redistribute command creates an ASBR router.
Originated by the ASBR.
Describes destination networks external to the OSPF Routing Domain
Flooded throughout the OSPF AS except to stub and totally stubby areas
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5sLSA 5
LSA 5
Stub Area LSA 1s stillsent within
each area.
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Stub Area
LSA 4 LSA 4 Blocked
LSA 5 BlockedLSA 5
LSA 3LSA 3
Defaultroute to
ABR
injected
Sent by ABR: LSA 3s (Inter-Area routes)
Blocked: LSA 4s (reachability to ASBR) LSA 5s (External routes)
The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own.
Changes in External routes no longer affect Stub Area routing tables.
We only see routes in
our area, other areas,
and a default route.
No external routes.
Totally
St bb A
Totally Stubby Area LSA 1s stillsent within
each area.
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Stub Area
LSA 4 LSA 4 Blocked
LSA 5 BlockedLSA 5
LSA 3LSA 3
Defaultroute to
ABR
injected
Blocked:
LSA 3s (Inter-Area routes) LSA 4s (reachability to ASBR) LSA 5s (External routes)
The ABR injects a default route into the stub area, pointing to the ABR. This does not mean the ABR has a default route of its own.
Changes in other areas and external routes no longer affect Stub Area routing tables.
We only see routes in
our area, other areas,
and a default route.
No external routes.
Stubby Area
Blocked
BlockedBlocked
Default
route to
ABR
injectedWe only see routes in our area
and a default route.
No inter-area or external routes.
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Multi Area OSPF Part 1 of 2
CIS 185 Advanced Routing
Rick Graziani
Cabrillo College
graziani@cabrillo.edu