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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 Areas LSAs show ip ospf database (summary of link state database) show ip route Stub Areas Totally Stubby Areas E1 and E2 routes - PowerPoint PPT Presentation
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Configuring OSPF – Part 1 of 2
CIS 185 CCNP ROUTE
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
Last Updated: Fall 2010
2
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
Single Area OSPF - Review
4
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.
5
The network Command
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.
Router(config-router)# network network-address wildcard-mask area area-id
6
1 – Flooding of link-state information
2 – Building a Topological Database
3 – SPF Algorithm
4 – SPF Tree
5 – Routing Table
Link State Concepts
7
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
Neighbors and Adjacencies
8
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.
9
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.
10
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
11
Modifying OSPF IntervalsRouter(config-if)# ip ospf hello-interval seconds
Router(config-if)# ip ospf dead-interval seconds
Basic OSPF Configuration
Lab Topology The router ospf command The network command OSPF Router ID Verifying OSPF Examining the Routing Table
13
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.
OSPF Router ID
Router ID?
Router ID?
Router ID?
14
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>
15
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 neighbor’s 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
16
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>
Verifying OSPF
17
Verifying OSPF
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
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
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 originating from this router
OSPF Neighbors
Administrative Distance
18
Verifying OSPFR1# 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
19
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 calculation depends on the size of the area.
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
20
Verifying OSPF
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.
R1# show ip ospf
<some output omitted>
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
21
Verifying OSPFR1# 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>
22
Examining the Routing Table
Unlike RIPv2 and EIGRP, OSPF does not automatically summarize at major network boundaries.
R1# show ip route
Codes: <some code output omitted>
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
The OSPF Metric
OSPF Metric Modifying the Cost of the Link
24
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.
25
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
26
Reference Bandwidth
When this command is necessary, it is recommended that it is used on all routers so the OSPF routing metric remains consistent.
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.
27
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.
28
Default Bandwidth on Serial Interfaces
On Cisco routers, the bandwidth value on many serial interfaces defaults to T1 (1.544 Mbps).
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
29
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)# bandwidth bandwidth-kbps
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,
<output omitted>
100,000,000/64,000 = 1562
30
The ip ospf cost Command
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,
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 64
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
<output omitted>
100,000,000/64,000 = 1562
OSPF and Multiaccess Networks
Challenges in Multiaccess Networks DR/BDR Election Process OSPF Interface Priority
32
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.
33
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.
DROther
DROther DROther DROther
DROther
DROther
224.0.0.6
224.0.0.5
34
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
35
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>
Verifying Router States
36
Timing of DR/BDR Election
If I booted first and started the election before the others were ready, I would be the DR!
37
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
38
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.
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 a DROther.
39
A previous DR does not regain DR status if it returns to the network.
DR
BDR
Timing of DR/BDR Election
DROther
I’m back but I don’t get to become DR again. I am now just a DROther.
DROther
40
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, so I am the new BDR!
DROther
41
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!
42
Timing of DR/BDR Election
We can change the OSPF interface priority to better control our DR/BDR elections.
How can we make sure RouterB is the DR and RouterA is the BDR, regarless of RouterID values?
Want to be DR
Want to be BDR
Highest Router ID
To simplify our discussion, we removed RouterD from the topology.
43
OSPF Interface Priority
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.
Router(config-if)# ip ospf priority {0 - 255}
44
OSPF Interface Priority
The OSPF interface priority can be viewed using the show ip ospf interface command.
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>
45
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.
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
Pri = 200
Pri = 100
Highest priority wins
46
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 of IP packets still takes the lowest cost route, which might be between two DROthers.
More OSPF Configuration
Redistributing an OSPF Default Route Fine-tuning OSPF
48
Redistributing an OSPF Default Route
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.
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 using the loopback as an exit interface because the ISP router in this topology does not physically exist.
49
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
50
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 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
R3# show ip route
O*E2 0.0.0.0/0 [110/1] via 192.168.10.5, 00:00:27, Serial0/0/0
Steps to OSPF Operation with States
1. Establishing router adjacencies (Routers are adjacent)Down State – No Hello receivedInit 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 onlyExStart State with DR and BDRTwo-way State with all other routers
3. Discovering RoutesExStart StateExchange StateLoading StateFull State (Routers are “fully adjacent”)
4. Calculating the Routing Table
5. Maintaining the LSDB and Routing Table
52
Hello 10.6.0.1
Hello 10.5.0.1
Hello 10.6.0.1 10.5.0.1
Hello 10.5.0.1 10.6.0.1
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 router’s interface will transition to the two-way state.
Now, the router is ready to take the relationship to the next level.
1. Establishing Adjacencies
53
Steps to OSPF Operation with States (cont)
Explanations in Notes Section
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
56
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
57
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
58
OSPF Router Types
59
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.
60
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.
An advantage of Multiple Areas
61
OSPF Packet Types In CCNA we discussed various OSPF packets
OSPF packet types
62
OSPF Type 4 - Link State Advertisements
In CCNP we will look at OSPF Type 4 packets more closely
OSPF packet types
63
OSPF packet types
OSPF Type-4 packets have 7 LSA packets (later)
64
LSAs used for discovering routes and reaching Full State, along with Maintain Routes
LSA Types
65
LSA TypesLSA 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
66
Area Types
Standard or Normal Areas Backbone Non-Backbone
Stub Areas Stub Area Totally Stubby Area Not-so-stubby-area (NSSA)
67
Area Types
68
Part I - LSAs using all normal areasMulti Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone Area
What are the router types?
69
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
Part I - LSAs using all normal areas
70
1. OSPF Multi-Areas - All Normal AreasR33router ospf 1 network 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 originateip 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 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.
71
Part I - LSAs using all normal areasMulti Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone Area
What are the router types?
72
Part I - LSAs using all normal areasMulti Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone Area
What are the router types?
73
Part I - LSAs using all normal areasMulti Area OSPF
Normal Areas
ASBR
ABR ABRInternal
Internal
Internal
Internal
Backbone Area
What are the router types?
74
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|…]
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
75
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 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.
A C
D
2
5
B
15 Router A’s LSA 1s which are flooded to all other routers in this area.
“Leaf” network
LSA 1 - Router Link States
76
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
77
LSA 1 – Router Link States
LSA 1’sLSA 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.
78
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”
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 ADV Router Age Seq# Checksum LinkCnt3.3.3.3 3.3.3.3 42 0x80000004 0x00168d 4100.100.100.100 100.100.100.100 10 0x80000005 0x00472f 4200.200.200.200 200.200.200.200 10 0x80000002 0x00db5f 1
79
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
80
LSA 1’sLSA 1’s
LSA 1’s
LSA 1 - Router Link States
81
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 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
82
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
LSA 2 - Network Link States
83
LSA 2s
LSA 2s flooded within area by DR.
LSA 2’s
LSA 2’s
84
R3# show ip ospf database
Net Link States (Area 51)
Link ID ADV Router Age Seq# Checksum
99.0.0.6 200.200.200.200 241 0x80000002 0x006159
LSA 2 - Network Link States
• 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
85
LSA 2’s
LSA 2’s
LSA 2 - Network Link States
86
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.
LSA 3 – Summary Net Link States
87
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 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.
LSA 3’sLSA 1’s
LSA 3’s
ABRABR
88
LSA 3 – Summary LSAs
LSA 1’sLSA 3’s
LSA 3’s
ABR ABR
89
LSA 3 – Summary LSAs
LSA 3’sLSA 3’s
LSA 1’s
90
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
91
• 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.
LSA 3’sLSA 1’s
LSA 3’s
Process using DV technique not LSA 1 Link States.
New or change, do not run SPF algorithm.
LSA 3 – Summary Net Link States
X
92
• 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.
LSA 3’sLSA 1’s
LSA 3’s
LSA 3 – Summary Net Link States
93
Area 0Backbone Area
Area 51Area 1
RTA RTB
RTC
LSA 3 LSA 3
LSA 1’s
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.
94
Area 0Backbone Area
Area 51Area 1
RTA RTB
RTC
LSA 3
LSA 3
Normal Areas
LSA 1’s
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.
95
Area 0Backbone Area
Area 51Area 1
RTA RTB
RTC
Normal Areas
LSA 1’s
LSA 3
LSA 3
X
Area 1 routers re-run SPF, creates new SPF tree and updates routing 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.
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 • Update IP routing tables. (Continued next slide)
96
Area 0Backbone Area
Area 51Area 1
RTA RTB
RTC
Normal Areas
LSA 1’s
LSA 3
LSA 3
X
Area 1 routers re-run SPF, creates new SPF tree and updates routing 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.
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.
97
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 that route.
• Rick’s reminder: LSA 3 -> “networks sent by the A B R” 1 2 3
ABR
98
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
LSA 3 – Summary Net Link States (ABR)
• 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
99
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
LSA 3 – Summary Net Link States
• Routes learned via LSA type 3s are denoted by an “IA” (Inter-Area Routes) in the routing table.
100
LSA 3’sLSA 1’s
LSA 3’s
101
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
LSA 4 – ASBR Summary Link States
102
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
103
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 1’s (e bit)
LSA 4
LSA 4
104
R1# show ip ospf database
Summary ASB Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
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 ASBR and its ABR to get there .
• Rick’s reminder: LSA 4 -> “Reachability to the A S B R” 1 2 3 4
ASBR (This) ABR
ABR
105
R33# show ip ospf database
Summary ASB Link States (Area 1)
Link ID ADV Router 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 ASBR and its ABR to get there .
• Rick’s reminder: LSA 4 -> “Reachability to the A S B R” 1 2 3 4
ASBR (Advertising) ABR
ABR
106
LSA 1’s e bit
LSA 4
LSA 4
LSA 4 – ASBR Summary Link States
107
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
LSA 5 - AS External Link States
108
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
109
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
Added ->
ASBR
110
“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
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5’sLSA 5
LSA 5
111
R1# show ip ospf database Type-5 AS External Link States <- Note, NO Area!
Link ID ADV Router Age Seq# Checksum Tag0.0.0.0 2.2.2.2 2088 0x80000003 0x00ddeb 157.0.0.0 2.2.2.2 2089 0x80000003 0x00ddeb 0
• 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 3 4 5
Note: Packet Tracer does not support LSA 5’s for redistributed routes
ASBR
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
112
R1# show ip route
O E2 57.0.0.0/8 [110/20] via 10.0.0.2, 00:16:02, Serial0/0O*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 default-metric command, the default metric value is 0, except for OSPF where the default cost is 20.
• Cost of 1 for the redistributed route.
LSA 5 - AS External Link States
113
R33# show ip ospf database
Type-5 AS External Link States <- Note, NO Area!
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 2.2.2.2 278 0x80000003 0x00ddeb 1
57.0.0.0 2.2.2.2 1187 0x80000003 0x00ddeb 0
LSA 5 - AS External Link States
R33# show ip route
O E2 57.0.0.0/8 [110/20] via 10.0.0.2, 00:16:02, Serial0/0O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:16:02, Serial0/0
114
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…
LSA 5 - AS External Link States
Stub Areas
116
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.
117
Stub Area
118
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”
Stub Areas
119
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
Stub Areas – Additional Commands
• All routers in the area must be configured as “stub” including the ABR
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Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route 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.
LSA 1s still sent within each area.
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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 0x00ca50
11.0.0.0 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 or LSA 5s for stub area routers.
• Default Route injected by ABR (LSA 3)
Stub Areas
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R200# show ip route
9.0.0.0/30 is subnetted, 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 is subnetted, 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 is subnetted, 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 is subnetted, 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 is subnetted, 2 subnets
O 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 is subnetted, 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
Stub Areas
LSA 1’s (Within area)
LSA 3’s (Other areas)
No LSA 4’s (ASBR)
No LSA 5’s (External routes)
Default Route (Injected by ABR)
NOTE on default route:
• ABR will advertise a default route with a cost of 1
• cost of 65 = 1 (Default) +1 (Fa) + 64 (serial link)
• The default cost can be modified with the ospf command:
ABR(config-router)# area area-id default-cost cost
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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, FastEthernet0/1
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
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.
Totally Stubby Areas
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Totally Stubby Area
126
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”
Totally Stubby Areas
127
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
Totally Stubby Areas
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Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route 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.
Totally Stubby Area
BlockedBlockedBlocked
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.
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R33# show ip route
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
Totally Stubby 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)
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R1# show ip route
1.0.0.0/32 is subnetted, 1 subnetsC 1.1.1.1 is directly connected, Loopback0 9.0.0.0/24 is subnetted, 1 subnetsC 9.0.0.0 is directly connected, Serial0/1 10.0.0.0/30 is subnetted, 1 subnetsC 10.0.0.0 is directly connected, Serial0/0 11.0.0.0/30 is subnetted, 1 subnetsO 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 masksO IA 99.0.0.0/30 [110/1690] via 10.0.0.2, 00:05:26, Serial0/0O IA 99.0.0.4/30 [110/1691] via 10.0.0.2, 00:05:26, Serial0/0O IA 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 subnetsC 172.16.1.0 is directly connected, FastEthernet0/0C 172.16.2.0 is directly connected, FastEthernet0/1O IA 172.16.10.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0O IA 172.16.11.0 [110/1627] via 10.0.0.2, 00:05:26, Serial0/0 172.30.0.0/24 is subnetted, 2 subnetsO 172.30.1.0 [110/2] via 172.16.1.2, 00:04:51, FastEthernet0/0O 172.30.2.0 [110/2] via 172.16.1.3, 00:04:41, FastEthernet0/0O 192.168.2.0/24 [110/65] via 10.0.0.2, 00:05:26, Serial0/0O*E2 0.0.0.0/0 [110/1] via 10.0.0.2, 00:05:26, Serial0/0
Totally Stubby 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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Quick Review
132
LSA 1s – Router LSAs
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
LSA 1’sLSA 1’s
LSA 1’s
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LSA 2s – Network LSAs
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
LSA 2’s
LSA 2’s
134
LSA 3 – Summary LSAs
LSA 3’sLSA 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
135
LSA 4 – ASBR Summary Link States
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
LSA 1’s ebit
LSA 4
LSA 4
136
“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 5’sLSA 5
LSA 5
LSA 5 – External Link States
137
Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route 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.
Stub Area LSA 1s still sent within each area.
138
Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route 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.
Totally Stubby Area
BlockedBlockedBlocked
Default route to ABR injected
We only see routes in our area and a default route.
No inter-area or external routes.
Totally Stubby Area LSA 1s still sent within each area.
Multi Area OSPF – Part 1 of 2
CIS 185 Advanced Routing
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
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