Configuring OSPF – Part 1 of 2
CIS 185 CCNP ROUTE
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
Last Updated: Fall 2010
Topics
 Review of OSPF
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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
2
Single Area OSPF - Review
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.
4
The network Command
Router(config-router)# network network-address wildcard-mask area area-id
 The area area-id refers 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.
5
Link State Concepts
1 – Flooding of link-state
information
5 – Routing Table
3 – SPF Algorithm
2 – Building a
Topological
Database
4 – SPF Tree
6
Neighbors and
Adjacencies
 Before two routers can form an OSPF neighbor adjacency, they
must agree on three values:
 Hello interval
 Dead interval
 Both the interfaces must be part of the same network, including
having the same subnet mask.
 IP MTU must match
7
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 address ALLSPFRouters at 224.0.0.5.
8
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.
9
Modifying OSPF Intervals
R1# show ip ospf neighbor
Neighbor ID
10.3.3.3
10.2.2.2
Pri
0
0
State
FULL/ FULL/ -
Dead Time
00:00:35
00:00:36
Address
192.168.10.6
192.168.10.2
Interface
Serial0/0/1
Serial0/0/0
 Dead time is counting down from 40 seconds.
 Refreshed every 10 seconds when R1 receives a Hello from the neighbor.
10
Modifying OSPF Intervals
Router(config-if)# ip ospf hello-interval seconds
Router(config-if)# ip ospf dead-interval seconds
11
Basic OSPF Configuration
 Lab Topology
 The router ospf command
 The network command
 OSPF Router ID
 Verifying OSPF
 Examining the Routing Table
OSPF Router ID
Router ID?
Router ID?
Router ID?
 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-id command.
2. Highest IP address of any of its loopback interfaces.
3. Highest active IP address of any of its physical interfaces.
13
Verifying New Router IDs (Loopbacks)
R1# 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 10.1.1.1
<output omitted>
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
<output omitted>
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
<output omitted>
14
Verifying OSPF
R1# show ip ospf neighbor
Neighbor ID
10.3.3.3
10.2.2.2






Pri
1
1
State
FULL/ FULL/ -
Dead Time
00:00:30
00:00:33
Address
192.168.10.6
192.168.10.2
Interface
Serial0/0/1
Serial0/0/0
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 neighbor’s interface
Interface: Local interface
15
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
<output omitted>
16
Verifying OSPF
R1# show ip protocols
Routing Protocol is “ospf 1”
OSPF Process ID
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
OSPF Router ID
Router ID 10.1.1.1
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
172.16.1.16 0.0.0.15 area 0
Networks OSPF is
192.168.10.0 0.0.0.3 area 0
advertising that are
192.168.10.4 0.0.0.3 area 0
originating from this router
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway
Distance
Last Update
10.2.2.2
110
11:29:29
OSPF Neighbors
10.3.3.3
110
11:29:29
Distance: (default is 110)
Administrative Distance
17
Verifying OSPF
R1# show ip ospf
<some output omitted>
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
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
Area BACKBONE(0)
Number of interfaces in this area is 3
Area has no authentication
SPF algorithm last executed 11:30:31.628 ago
SPF algorithm executed 5 times
18
Verifying OSPF
R1# show ip ospf
<some output omitted>
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
 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 calculation
depends on the size of the area.
19
Verifying OSPF
R1# show ip ospf
<some output omitted>
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
 A flapping link can cause OSPF routers in an area to constantly recalculate
the SPF algorithm, preventing proper convergence.
 If there is a route in the routing table the router will continue to forward
the packet.
 SPF schedule delay.
 To minimize this problem, the router waits 5 seconds (5000 msec) after
receiving an LSU before running the SPF algorithm.
 Minimum hold time:
 To prevent a router from constantly running the SPF algorithm, there is
an additional hold time of 10 seconds (10,000 ms).
 The router waits 10 seconds after running the SPF algorithm before
rerunning the algorithm.
20
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
<output omitted>
21
Examining the Routing Table
R1# show ip route
Codes: <some code output omitted>
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
C
C
O
O
C
O
C
192.168.10.0/30 is subnetted, 3 subnets
192.168.10.0 is directly connected, Serial0/0/0
192.168.10.4 is directly connected, Serial0/0/1
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
172.16.1.32/29 [110/65] via 192.168.10.6, 14:27:57, Serial0/0/1
172.16.1.16/28 is directly connected, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
10.10.10.0/24 [110/65] via 192.168.10.2, 14:27:57, Serial0/0/0
10.1.1.1/32 is directly connected, Loopback0
 Unlike RIPv2 and EIGRP, OSPF does not automatically summarize at major
network boundaries.
22
The OSPF Metric
 OSPF Metric
 Modifying the Cost of the Link
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 by the system administrator. The lower the cost, the
more likely the interface is to be used to forward data traffic.
 RFC 2328 does not specify which values should be used to determine the
cost.
24
OSPF Metric
Cisco IOS Cost for OSPF = 108/bandwidth in bps
 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
25
Reference Bandwidth
R1(config-router)# auto-cost reference-bandwidth ?
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.
 When this command is necessary, it is recommended that it is used on all
routers so the OSPF routing metric remains consistent.
26
OSPF
Accumulates Cost
Serial interfaces bandwidth value
defaults to T1 or 1544 Kbps.
R1# show ip route
O
10.10.10.0/24 [110/65] via 192.168.10.2, 14:27:57, Serial0/0/0
 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.
27
Default Bandwidth on Serial Interfaces
R1# show interface serial 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
 On Cisco routers, the bandwidth value on many serial interfaces
defaults to T1 (1.544 Mbps).
28
Modifying the Cost of the Link
Router(config-if)# bandwidth bandwidth-kbps
R1(config)# inter serial 0/0/0
R1(config-if)# bandwidth 64
R1(config-if)# inter serial 0/0/1
100,000,000/64,000 = 1562
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,
<output omitted>
 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
29
The ip ospf cost Command
R1(config)# inter serial 0/0/0
R1(config-if)# bandwidth 64
R1(config-if)# end
R1# show ip ospf interface serial
Serial0/0 is up, line protocol is
Internet Address 192.168.10.1/30,
Process ID 1, Router ID 10.1.1.1,
<output omitted>
0/0/0 100,000,000/64,000 = 1562
up
Area 0
Network Type POINT_TO_POINT, Cost: 1562
R1(config)# interface serial 0/0/0
R1(config-if)# ip ospf cost 1562
 An alternative method to using the bandwidth command is to use
the ip ospf cost command, which allows you to directly specify
the cost of an interface.
 This will not change the output of the show ip ospf interface
command,
30
OSPF and Multiaccess
Networks
 Challenges in Multiaccess Networks
 DR/BDR Election Process
 OSPF Interface Priority
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.
32
224.0.0.5
224.0.0.6
DROther
DROther
DROther
DROther
DROther
DROther
 DROthers only form full adjacencies with the DR and BDR in the network.
 send their LSAs to the DR and BDR
 using the multicast address 224.0.0.6 (ALLDRouters, all DR routers).
 R1 sends LSAs to the DR.
 The BDR listens, too.
 The DR is responsible for forwarding the LSAs from R1 to all other routers.
 DR uses the multicast address 224.0.0.5 (AllSPFRouters, all OSPF routers).
 Only one router doing all the flooding.
33
DR/BDR Election
BDR
DROther
DR
 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.
34
Verifying Router States
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
Designated Router (ID) 192.168.31.33, Interface address 192.168.1.3
Backup Designated router (ID) 192.168.31.22, Interface address
192.168.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
<output omitted>
35
Timing of DR/BDR Election
If I booted first and started
the election before the
others were ready, I would
be the DR!
36
Timing of DR/BDR Election
DR failed! I am now the
DR! Elections will now
happened for BDR
DR
I am now
the BDR!
BDR
 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.
37
DR
Timing of
DR/BDR
Election
BDR
I am a new router with the highest
Router ID. I cannot force a new
DR or BDR election, so I am a
DROther.
DROther
 If a new router enters the network after the DR and BDR have been
elected, it will not become the DR or the BDR even if it has a higher
OSPF interface priority or router ID than the current DR or BDR.
38
DR
Timing of
DR/BDR
Election
I’m back but I don’t
get to become DR
again. I am now just a
DROther.
BDR
DROther
DROther
 A previous DR does not regain DR status if it returns to the network.
39
DR
Timing of
DR/BDR
Election
BDR
DROther
Amongst the
DROthers I have the
highest Router ID, so
I am the new BDR!
BDR
 If the BDR fails, an election is held among the DROthers to see which router
will be the new BDR.
40
DR
Timing of
DR/BDR
Election
I am now the new
BDR!
BDR
DROther
I am now the new DR!
BDR
 RouterB fails.
 Because RouterD is the current BDR, it is promoted to DR.
 RouterC becomes the BDR.
41
Timing of DR/BDR Election
How can we make sure
RouterB is the DR and
RouterA is the BDR,
regarless of RouterID
values?
To simplify our discussion, we
removed RouterD from the topology.
Want to be DR
Highest Router ID
Want to be
BDR
 We can change the OSPF interface priority to better control our DR/BDR
elections.
42
OSPF Interface Priority
Router(config-if)# ip ospf priority {0 - 255}
 Control the election of these routers with the ip ospf priority interface
command.
 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 in
another.
43
OSPF Interface Priority
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
Designated Router (ID) 192.168.31.33, Interface address 192.168.1.3
Backup Designated router (ID) 192.168.31.22, Interface address
192.168.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
<output omitted>
 The OSPF interface priority can be viewed using the show ip ospf
interface command.
44
Highest priority wins
Pri = 100
Pri = 200
RouterA(config)# interface fastethernet 0/0
RouterA(config-if)# ip ospf priority 200
RouterB(config)# interface fastethernet 0/0
RouterB(config-if)# ip ospf priority 100
 After doing a shutdown and a no shutdown on the Fast Ethernet
0/0 interfaces of all three routers, we see the result of the change of
OSPF interface priorities.
45
Clarifications regarding DR/BDR
 Hello packets are still exchanged between all routers on a multiaccess 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 of IP packets still takes the lowest cost route, which
might be between two DROthers.
46
More OSPF Configuration
 Redistributing an OSPF Default Route
 Fine-tuning OSPF
Redistributing
an OSPF
Default Route
The static default route is using the
loopback as an exit interface
because the ISP router in this
topology does not physically exist.
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
 If the default-information originate command is not used, the
default “quad zero” route will not be propagated to other routers in the
OSPF area.
48
R3’s 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, Serial0/0/0
C
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, Loopback0
O
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
49
External Type 2 Route
R3# show ip route
O*E2 0.0.0.0/0 [110/1] via 192.168.10.5, 00:00:27, Serial0/0/0
 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 that
route.
 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
50
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 router’s Router ID
“Hi, my name is Carlos.”
“Hi, my name is Maria.”
Two-way State – Hello received, and with this router’s 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
4. Calculating the Routing Table
ExStart State
Exchange State
5. Maintaining the LSDB and Routing Table
Loading State
Full State (Routers are “fully adjacent”)
1. Establishing Adjacencies
Hello 10.6.0.1 10.5.0.1
Hello 10.6.0.1
Down
Init
2-way
Down
Init
2-way
Hello 10.5.0.1
Hello 10.5.0.1 10.6.0.1
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 router’s interface
will transition to the two-way state.
 Now, the router is ready to take the relationship to the next level.
52
Steps to OSPF Operation with States (cont)
Explanations in Notes Section
53
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 change
in topology (this includes when a routers are first booted).
OSPF uses hop-by-hop flooding of LSAs; an LSA received on one
interface are flooded out other OSPF enabled interfaces.
If a link state entry in the LSDB (Link State DataBase) reaches an age of 60
minutes (MaxAge) without being updated, it is removed and SPF is
recalculated.
Every 30 minutes (LSRefreshTime), OSPF routers flood only their link
states 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 a
value of 60 minutes (MAXAGE).
Single Area OSPF
End of Review
CIS 185 Advanced Routing
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
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 rebuild
the 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 to
perform the route look-ups.
Solution: Divide the network into multiple areas
56
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-area
routing).
 Some operations are restricted within an area:
 Flooding of LSAs
 Recalculating the database
 Re-running the SPF algorithm
57
OSPF Router Types
58
OSPF
Router
Types
Internal: Routers with all their interfaces within the same area
Backbone: Routers with at least one interface connected to area 0
ASBR: (Autonomous System Boundary Router): Routers that have at
least one interface connected to an external internetwork (another
autonomous system)
ABR: (Area Border Router): Routers with interfaces attached to
multiple areas.
59
An advantage of Multiple Areas
 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 a
topology 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.
60
OSPF Packet Types
 In CCNA we discussed various OSPF packets
OSPF packet types
61
OSPF Type 4 - Link State Advertisements
 In CCNP we will look at OSPF Type 4 packets more closely
OSPF packet types
62
OSPF packet types
OSPF Type-4 packets have 7 LSA packets (later)
63
LSA Types
LSAs used for discovering routes and reaching Full State, along with
Maintain Routes
64
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 to
build 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
65
Area Types
 Standard or Normal Areas
 Backbone
 Non-Backbone
 Stub Areas
 Stub Area
 Totally Stubby Area
 Not-so-stubby-area (NSSA)
66
Area Types
67
Part I - LSAs using all normal areas
Multi Area OSPF
What are the router
types?
Backbone
Area
Normal Areas
ASBR
Internal
ABR
ABR
Internal
Internal
Internal
68
Part I - LSAs using all normal areas
Routes Received on all OSPF Routers
Overview of Normal 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, LSA 4, LSA 5
Receives all routes from External A.S.’s (External AS means routes not
from this OSPF routing domain):

From external AS’s – LSA 5

As long as routes are being redistributed by the ASBR (more later)
Default Route

Received only if default-information-originate command was used
(later)

If default-information-originate command is not used, then the
default route is not received
69
1. OSPF Multi-Areas - All Normal Areas
R33
R3
router ospf 1
network 172.16.1.0 0.0.0.255 area 1
network 172.30.1.0 0.0.0.255 area 1
router 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
R22
router ospf 1
network 172.16.1.0 0.0.0.255 area 1
network 172.30.2.0 0.0.0.255 area 1
R1
router 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
R2
router 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
R100
router 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
R200
router ospf 1
network 99.0.0.4 0.0.0.3 area 51
network 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.
70
Part I - LSAs using all normal areas
Multi Area OSPF
What are the router
types?
Backbone
Area
Normal Areas
ASBR
Internal
ABR
ABR
Internal
Internal
Internal
71
Part I - LSAs using all normal areas
Multi Area OSPF
What are the router
types?
Backbone
Area
Normal Areas
ASBR
Internal
ABR
ABR
Internal
Internal
Internal
72
Part I - LSAs using all normal areas
Multi Area OSPF
What are the router
types?
Backbone
Area
Normal Areas
ASBR
Internal
ABR
ABR
Internal
Internal
Internal
73
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 with
the different types of LSAs.
 To view the link state database use: show ip ospf database
[router|network|…]
LSA Header
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
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
74
LSA 1 - Router Link States
 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.
B
15
“Leaf” network
A
2
C
5
Router A’s LSA 1s
which are flooded to all
other routers in this
area.
D
 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 directly
connected.
 ABR will include a set of LSA 1’s 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.
75
LSA 1 - Router Link States
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
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
...
|
76
LSA 1 – Router Link States
LSA 1’s
LSA 1’s
LSA 1’s
 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.
77
R100# show ip ospf database
OSPF Router with ID (100.100.100.100) (Process ID 1)
Router Link States (Area 51) <- Note the Area
(LSA 1 - Links in this area.)
Link ID
3.3.3.3
100.100.100.100
200.200.200.200
ADV Router
3.3.3.3
100.100.100.100
200.200.200.200
Age
42
10
10
Seq#
0x80000004
0x80000005
0x80000002
Checksum
0x00168d
0x00472f
0x00db5f
LinkCnt
4
4
1
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 (LSA1’s) should display all the RouterIDs of
routers in that area, including its own.
 Rick’s reminder: LSA 1 -> “my one area”
78
LSA 1 - Router Link States
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
• Denoted by just an “O” in the routing table, or a “C”
• Note: Only partial routing tables will be shown
79
LSA 1 - Router Link States
LSA 1’s
LSA 1’s
LSA 1’s
80
LSA 2 - Network Link States
LSA 2 – Network LSA
 Generated by the DR on every multi-access network
 Denoted by just an “O” in the routing table or “C” if the network is
directly connected.
 Flooded only within the originating area.
 LSA 2’s are in link state database for all routers within area, even
those routers on not on multi-access networks or DRs on other multiaccess networks in the same area.
 ABR may include a set of LSA 2s for each area it belongs to.
81
LSA 2 - Network Link States
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 |
2
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Link State ID
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Advertising Router
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
LS sequence number
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
LS checksum
|
length
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Network Mask
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Attached Router
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
...
|
82
LSA 2s
LSA 2’s
LSA 2’s
 LSA 2s flooded within area by DR.
83
LSA 2 - Network Link States
R3# show ip ospf database
Link ID
99.0.0.6
Net Link States (Area 51)
ADV Router
Age
200.200.200.200 241
Seq#
Checksum
0x80000002 0x006159
• Link ID IP address of DR on MultiAccess Network
• ADV Router Router ID of DR
• Bottom line: Net Link States (LSA2’s) should display the RouterIDs of
•
the DRs on all multi-access networks in the area and their IP
addresses.
Rick’s reminder: LSA 2 -> “Ethernet = Layer 2 or D R”
1 2
84
LSA 2 - Network Link States
LSA 2’s
LSA 2’s
85
LSA 3 – Summary Net Link States
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 3’s 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.
86
LSA 3 – Summary LSAs
LSA 1’s
ABR
ABR
LSA 3’s
LSA 3’s
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 3’s 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.
87
LSA 3 – Summary LSAs
LSA 3’s
ABR
ABR
LSA 1’s
LSA 3’s
88
LSA 3 – Summary LSAs
LSA 3’s
LSA 3’s
LSA 1’s
89
LSA 3 – Summary Net Link States
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
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
...
|
90
LSA 3 – Summary Net Link States
LSA 1’s
X
New or
change, do
not run SPF
algorithm.
LSA 3’s
LSA 3’s
Process
using DV
technique
not LSA 1
Link States.
•
•
•
•
Routers only see the topology of the area they belong to.
When a link in one area changes, the adjacent routers originate in LSA 1’s and
flood them within the area, causing intra-area (internal) routers to re-run the
SPF 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.
91
LSA 3 – Summary Net Link States
LSA 1’s
LSA 3’s
LSA 3’s
•
•
•
•
ABRs calculate intra-area routes and announce them to all other areas as
inter-area routes, using LSA 3’s.
OSPF ABRs will only announce inter-area routes that were learned from the
backbone area, area 0.
The backbone area serves as a repository for inter-area routes.
This keeps OSPF safe from routing loops.
92
Area 0
Backbone Area
LSA 1’s
RTA
RTB
LSA 3
LSA 3
Area 1
Area 51
RTC
•
•
•
•
Not ABR
In normal operation, OSPF ABRs will only announce inter-area
routes that were learned from the backbone area, area 0.
RTC does not forward LSA 3’s from Area 1 to Area 51, and does not
forward LSA 3’s from Area 51 to Area 1.
The backbone area serves as a repository for inter-area routes.
This keeps OSPF safe from routing loops.
93
Normal Areas
Area 0
Backbone Area
LSA 3
RTA
RTB
LSA 3
LSA 1’s
Area 1
Area 51
RTC
Not ABR
• RTC does not forward the LSA 3’s back into Area 1, or routing loops
•
•
may develop.
Note: RTC will create LSA 1’s and flood them within the appropriate
area.
OSPF specification states that ABRs are restricted to considering LSA 3’s only
from the backbone area to avoid routing information loops.
94
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.
Area 1 routers re-run
SPF, creates new SPF
tree and updates
routing table.
Normal Areas
Area 0
Backbone Area
LSA 3
RTA
RTB
LSA 3
LSA 1’s
Area 1
X
Area 51
RTC
Topology Change: Down Link
• When a router detects a topology change it immediately sends out LSA
1’s (Router LSAs) with the change.
• Age of the LSA is set to MaxAge (3,600 seconds) – Routers remove
this entry from their LSDB (Link State Data Base).
• Routers that receive the LSA 1’s, within the area of the change:
• Re-run their SPF algorithm
• Build a new SPF tree
95
• Update IP routing tables. (Continued next slide)
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.
Area 1 routers re-run
SPF, creates new SPF
tree and updates
routing table.
Normal Areas
Area 0
Backbone Area
LSA 3
RTA
RTB
LSA 3
LSA 1’s
Area 1
X
Area 51
RTC
Topology Change: 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.
96
LSA 3 – Summary Net Link States (INTERNAL)
ABR
R33# show ip ospf database
Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
10.0.0.0
1.1.1.1
130
0x8000000c
9.0.0.0
1.1.1.1
130
0x8000000d
192.168.2.0
1.1.1.1
130
0x8000000e
11.0.0.0
1.1.1.1
130
0x8000000f
172.16.10.0
1.1.1.1
130
0x80000010
172.16.11.0
1.1.1.1
130
0x80000011
99.0.0.0
1.1.1.1
130
0x80000012
99.0.0.4
1.1.1.1
130
0x80000013
99.1.0.0
1.1.1.1
130
0x80000014
Checksum
0x00ec09
0x00ec09
0x00ec09
0x00ec09
0x00ec09
0x00ec09
0x00ec09
0x00ec09
0x00ec09
•
•
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 that
route.
Rick’s reminder: LSA 3 -> “networks sent by the A B R”
1 2 3
•
97
LSA 3 – Summary Net Link States (ABR)
R1# show ip ospf database
Summary Net Link States (Area 1) <- Per Area
Link ID
ADV Router
Age
Seq#
Checksum
10.0.0.0
1.1.1.1
255
0x8000000c 0x00ec09
9.0.0.0
1.1.1.1
255
0x8000000d 0x00ec09
192.168.2.0
1.1.1.1
255
0x8000000e 0x00ec09
11.0.0.0
1.1.1.1
255
0x8000000f 0x00ec09
172.16.10.0
1.1.1.1
255
0x80000010 0x00ec09
172.16.11.0
1.1.1.1
255
0x80000011 0x00ec09
99.0.0.0
1.1.1.1
255
0x80000012 0x00ec09
99.0.0.4
1.1.1.1
255
0x80000013 0x00ec09
99.1.0.0
1.1.1.1
255
0x80000014 0x00ec09
•
•
•
ABR will show all routes it is injecting into the other area including:
• LSA 3s from other areas
• LSA 1s from it’s adjacent area it is injecting into this area
Bottom line: Should see networks in other areas and the ABR advertising that
route.
Rick’s reminder: LSA 3 -> “networks sent by the A B R”
1 2 3
98
LSA 3 – Summary Net Link States
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, Serial0/0
O 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
• Routes learned via LSA type 3s are denoted by an “IA” (Inter-Area
Routes) in the routing table.
99
LSA 1’s
LSA 3’s
LSA 3’s
100
LSA 4 – ASBR
Summary Link
States
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.
 More on this later
101
LSA 4 – ASBR Summary Link States
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
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
...
|
102
LSA 4 – ASBR Summary Link States
LSA 4
LSA 1’s
(e bit)
LSA 4
 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.
103
LSA 4 – ASBR Summary Link States (ABR)
ABR
R1# show ip ospf database
Summary ASB Link States (Area 1)
Link ID
2.2.2.2
ASBR
ADV Router
1.1.1.1
Age
1482
Seq#
Checksum
0x8000000b 0x00ec09
(This) 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 ASBR
•
and its ABR to get there .
Rick’s reminder: LSA 4 -> “Reachability to the A S B R”
104
LSA 4 – ASBR Summary Link States (INTERNAL)
ABR
R33# show ip ospf database
Summary ASB Link States (Area 1)
Link ID
2.2.2.2
ASBR
ADV Router
1.1.1.1
Age
130
Seq#
Checksum
0x8000000b 0x00ec09
(Advertising) 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 ASBR
•
and its ABR to get there .
Rick’s reminder: LSA 4 -> “Reachability to the A S B R”
1 2 3 4
105
LSA 4 – ASBR Summary Link States
LSA 4
LSA 1’s
e bit
LSA 4
106
LSA 5 - AS External
Link States
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.
 More on this later
107
LSA 5 - AS External Link States
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
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
...
|
108
Added ->
ASBR
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
109
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5
LSA 5’s
LSA 5
 “Redistribute” command creates an ASBR router.
 LSA 5s
 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
110
ASBR
R1# show ip ospf database
Type-5 AS External Link States
Link ID
0.0.0.0
57.0.0.0
ADV Router
2.2.2.2
2.2.2.2
Age
2088
2089
<- Note, NO Area!
R2 (ASBR)
router
ospf 1
Seq#
Checksum Tag
redistribute
0x80000003static
0x00ddeb 1
default-information
originate
0x80000003 0x00ddeb
0
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
Note: Packet Tracer does not support LSA 5’s
for redistributed routes
•
•
•
•
•
Link ID = External Networks
ADV Router = Router ID of ASBR
Note: For ABRs: There is only one set of “AS External Link States” in
database summary. In other words, an ABR router will only show one set of
“AS External Link States,” not one per area.
Bottom line: All Routers should see External networks and the Router ID of
ASBR to get there .
Rick’s reminder: LSA 5 -> O T H E R networks
1 2 345
111
LSA 5 - AS External Link States
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 not
specified for the metric option, and no value is specified using the defaultmetric command, the default metric value is 0, except for OSPF where the
default cost is 20.
Cost of 1 for the redistributed route.
112
LSA 5 - AS External Link States
R33# show ip ospf database
Type-5 AS External Link States
Link ID
0.0.0.0
57.0.0.0
ADV Router
2.2.2.2
2.2.2.2
<- Note, NO Area!
Age
278
1187
Seq#
Checksum Tag
0x80000003 0x00ddeb 1
0x80000003 0x00ddeb 0
R33# 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
113
LSA 5 - AS External Link States
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 the
interior cost to reach that route.
 A type 1 cost is the addition of the external cost and the internal cost
used to reach that route.
 A type 1 route is always preferred over a type 2 route for the same
destination.
 More later…
114
Stub Areas
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.
116
Stub Area
117
Stub Areas
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 ABR
 External Routes: Once the ABR gets a packet headed to a default route, it must have
a default route, either static or propagated by the ASBR via default information
originate (coming!)
Configuration:
 All routers in the area must be configured as “stub”
118
Stub Areas –
Additional Commands
R3 (ABR)
router ospf 1
area 51 stub
<< Command: area area stub
R100 (INTERNAL)
router ospf 1
area 51 stub
<< Command: area area stub
R200 (INTERNAL)
router ospf 1
area 51 stub
•
<< Command: area area stub
All routers in the area must be configured as “stub”
including the ABR
119
LSA 1s still
sent within
each area.
Stub Area
LSA 3
LSA 4
LSA 5
LSA 3
LSA 4 Blocked
LSA 5 Blocked
Default
route to
ABR
injected
•
•
•
•
We only see routes in
our area, other areas,
and a default route.
No external routes.
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.
120
Stub Areas
R100# show ip ospf database
Summary Net Link States (Area 51)
Link ID
9.0.0.0
0.0.0.0
11.0.0.0
192.168.2.0
10.0.0.0
172.16.2.0
172.16.1.0
172.30.2.0
172.30.1.0
ADV Router
3.3.3.3
3.3.3.3
3.3.3.3
3.3.3.3
3.3.3.3
3.3.3.3
3.3.3.3
3.3.3.3
3.3.3.3
Age
1752
1612
625
614
614
614
614
614
614
Seq#
0x80000037
0x80000038
0x80000039
0x8000003a
0x8000003b
0x8000003c
0x8000003d
0x8000003e
0x8000003f
Checksum
0x00ba22
0x00ca50
0x00db11
0x00dd10
0x00dd10
0x00dd10
0x00dd10
0x00dc11
0x00dc11
• No LSA 4s or LSA 5s for stub area routers.
• Default Route injected by ABR (LSA 3)
121
Stub Areas
R200# show ip route
O IA
O IA
O IA
O
C
O
C
O IA
O IA
O
O
O IA
O IA
O IA
C
O*IA
9.0.0.0/30 is subnetted, 1 subnets
9.0.0.0 [110/129] via 99.0.0.5, 00:25:52, FastEthernet0/0
LSA 1’s1 subnets
(Within area)
10.0.0.0/30 is subnetted,
10.0.0.0 [110/1691] via 99.0.0.5, 00:25:52, FastEthernet0/0
LSA 3’s (Other areas)
11.0.0.0/30 is subnetted, 1 subnets
No LSA
4’s (ASBR)
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
No LSA 5’s (External routes)
99.0.0.0/30 [110/65] via 99.0.0.5, 00:25:52, FastEthernet0/0
Default connected,
Route (Injected
by ABR)
99.0.0.4/30 is directly
FastEthernet0/0
99.1.0.0/16 [110/2] via 99.0.0.5, 00:25:52, FastEthernet0/0
NOTE on default route:
99.2.0.0/16 is directly connected, FastEthernet0/1
ABR will
advertise a default route with a cost of 1
172.16.0.0/24 is subnetted,
4 subnets
172.16.1.0 [110/1692] via 99.0.0.5, 00:25:52, FastEthernet0/0
cost of 65 = 1 (Default) +1 (Fa) + 64 (serial link)
172.16.2.0 [110/1692] via 99.0.0.5, 00:25:52, FastEthernet0/0
The
cost
can be FastEthernet0/0
modified with the ospf command:
172.16.10.0 [110/66]
viadefault
99.0.0.5,
00:25:52,
172.16.11.0 [110/66] ABR(config-router)#
via 99.0.0.5, 00:25:52, FastEthernet0/0
area area-id default172.30.0.0/24 is subnetted, 2 subnets
cost cost
172.30.1.0 [110/1693] via 99.0.0.5, 00:25:52, FastEthernet0/0
172.30.2.0 [110/1693] via 99.0.0.5, 00:25:52, FastEthernet0/0
192.168.2.0/24 [110/1628] via 99.0.0.5, 00:25:52, FastEthernet0/0
200.200.200.0/32 is subnetted, 1 subnets
200.200.200.200 is directly connected, Loopback0
0.0.0.0/0 [110/66] via 99.0.0.5, 00:25:52, FastEthernet0/0
•
•
•
122
Stub Areas
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, FastEthernet0/1
172.30.0.0/24 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
• 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.
123
Totally Stubby Areas
Totally Stubby
Area
125
Totally Stubby
Areas
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”
126
Totally Stubby
Areas
R1: (ABR)
router ospf 1
area 1 stub no-summary
^^ Command: area area stub no-summary
R22 and R33: (INTERNAL ROUTERS)
router ospf 1
area 1 stub
^^ Command: area area stub
127
LSA 1s still
sent within
each area.
Totally
Stubby Area
Blocked LSA 3
Blocked LSA 4
Blocked LSA 5
Default
route to
ABR
injected
•
•
•
We only see routes in our area
and a default route.
No inter-area or external routes.
Stub Area
LSA 3
LSA 4 Blocked
LSA 5 Blocked
Default
route to
ABR
injected
We only see routes in
our area, other areas,
and a default route.
No external routes.
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.
128
Changes in other areas and external routes no longer affect Stub Area routing tables.
Totally Stubby
Areas
R33# show ip route
Note: Packet Tracer does not support
Totally Stubby Networks (yet)
33.0.0.0/32 is subnetted, 1 subnets
C
33.33.33.33 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 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 is subnetted, 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
•
•
•
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)
129
Totally Stubby Areas
R1# show ip route
C
C
C
O
O IA
O IA
O IA
C
C
O IA
O IA
O
O
O
O*E2
1.0.0.0/32 is subnetted, 1 subnets
1.1.1.1 is directly connected, Loopback0
9.0.0.0/24 is subnetted, 1 subnets
9.0.0.0 is directly connected, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
10.0.0.0 is directly connected, Serial0/0
11.0.0.0/30 is subnetted, 1 subnets
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
99.0.0.0/30 [110/1690] via 10.0.0.2, 00:05:26, Serial0/0
99.0.0.4/30 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0
99.1.0.0/16 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0
172.16.0.0/24 is subnetted, 4 subnets
172.16.1.0 is directly connected, FastEthernet0/0
172.16.2.0 is directly connected, FastEthernet0/1
172.16.10.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0
172.16.11.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0
172.30.0.0/24 is subnetted, 2 subnets
172.30.1.0 [110/2] via 172.16.1.2, 00:04:51, FastEthernet0/0
172.30.2.0 [110/2] via 172.16.1.3, 00:04:41, FastEthernet0/0
192.168.2.0/24 [110/65] via 10.0.0.2, 00:05:26, Serial0/0
0.0.0.0/0 [110/1] via 10.0.0.2, 00:05:26, Serial0/0
• 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.
130
Quick Review
131
LSA 1s – Router LSAs
LSA 1’s
LSA 1’s
LSA 1’s
 show ip ospf database – Router Link States (LSA 1’s)
 Should display all the RouterIDs of routers in that area,
including its own.
 show ip route – “O” routes
 Routes within that area
132
LSA 2s – Network LSAs
LSA 2’s
LSA 2’s
 show ip ospf database – Net Link States (LSA 2’s)
 Net Link States (LSA2’s) should display the RouterIDs of the
DRs on all multi-access networks in the area and their IP
addresses.
 show ip route – “O” routes
 Routes within that area
133
LSA 3 – Summary LSAs
LSA 3’s
LSA 3’s
LSA 1’s
 show ip ospf database – Summary Net Link States (LSA 3’s)
 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
134
LSA 4 – ASBR Summary Link States
LSA 4
LSA 1’s
ebit
LSA 4
 show ip ospf database – Summary Net Link States (LSA 3’s)
 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
135
LSA 5 – External Link States
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5
LSA 5’s
LSA 5




“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
136
Stub Area
LSA 1s still
sent within
each area.
Stub Area
LSA 3
LSA 4
LSA 5
LSA 3
LSA 4 Blocked
LSA 5 Blocked
Default
route to
ABR
injected
•
•
•
•
We only see routes in
our area, other areas,
and a default route.
No external routes.
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.
137
Totally Stubby Area
Totally
Stubby Area
Blocked LSA 3
Blocked LSA 4
Blocked LSA 5
Default
route to
ABR
injected
•
•
•
We only see routes in our area
and a default route.
No inter-area or external routes.
LSA 1s still
sent within
each area.
Stub Area
LSA 3
LSA 4 Blocked
LSA 5 Blocked
Default
route to
ABR
injected
We only see routes in
our area, other areas,
and a default route.
No external routes.
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.
138
Changes in other areas and external routes no longer affect Stub Area routing tables.
Multi Area OSPF – Part 1 of 2
CIS 185 Advanced Routing
Rick Graziani
Cabrillo College
graziani@cabrillo.edu