Link State - cosy.univ-reims.frcosy.univ-reims.fr/~lsteffenel/cours/FC/BSCI3.pdfNetwork Types show...

Link State

1 – Flooding of link-state information

2 – Building a 3 – SPF Algorithm

5 – Routing Table

Topological Database

4 – SPF Tree

OSPF Hello Protocol

• OSPF routers send Hellos on OSPF enabled interfaces:–Default every 10 seconds on multi-access and point-to-point segments

Default every 30 seconds on NBMA segments–Default every 30 seconds on NBMA segments–Most cases OSPF Hello packets are sent as multicast to ALLSPFRouters(224.0.0.5)

• HelloInterval - Cisco default = 10 seconds or 30 seconds and can be changed with the command ip ospf hello-interval.

R t D dI t l Th i d i d th t th t ill it t h• RouterDeadInterval - The period in seconds that the router will wait to hear a Hello from a neighbor before declaring the neighbor down.

–Cisco uses a default of four-times the HelloInterval and can be changed with the command ip ospf dead-interval.

• Note: For routers to become adjacent, the Hello, DeadInterval and networktypes must be identical between routers OR Hello packets get dropped!

Network Types

show ip ospf interface

Unless you are configuring an NBMA network like Frame Relay, this won’t be an issue.

• Many administrators prefer to use point-to-point or point-to-multipoint for NMBA to avoid the DR/BDR and full-mesh issues.

Configuring Basic OSPF

t f id [ f ]Router(config)#

router ospf process-id [vrf vpn-name]

Enable one or more OSPF routing processes.

network ip-address wildcard-mask area area-id

Router(config-router)#

Define the interfaces that OSPF will run on.

Router(config-if)#Router(config if)#

ip ospf process-id area area-id [secondaries none]

Optional method to enable OSPF explicitly on an interface.

Configuring OSPF

OSPF’s Metric is Cost (Bandwidth)

Cisco default interface costs:• 56-kbps serial link = 1785• 64-kbps serial link = 1562 128-kbps serial link = 781• T1 (1.544-Mbps serial link) = 64• E1 (2.048-Mbps serial link) = 48

Cost = 100 000 000/B d idthE1 (2.048 Mbps serial link) 48

• 4-Mbps Token Ring = 25• Ethernet = 10

16 Mb T k Ri 6

100,000,000/Bandwidth

• 16-Mbps Token Ring = 6• Fast Ethernet = 1• Problem: Gigabit Ethernet and faster = 1Notes: • Cisco routers default to T1 (1.544 Mbps) on all serial interfaces and require

manual modification with the bandwidth command.• ospf auto-cost reference-bandwidth reference-bandwidth can be

used to modify the reference-bandwidth for higher speed interfaces

Changing the Cost Metric

• The cost, or metric, is an indication of the overhead to send packets over an interface Default = (100 Mbps)/(bandwidthpackets over an interface. Default (100 Mbps)/(bandwidth in Mbps).

RouterA(config-router)#

auto-cost reference-bandwidth ref-bw

( g )#

Sets the reference bandwidth to values other than 100 Mbps

R t A( fi if)#

Sets the reference bandwidth to values other than 100 Mbps (legal values range from 1 to 4,294,967 in Mbps).

ip ospf cost interface-cost

RouterA(config-if)#

Overrides the default cost calculation Values from 1 toOverrides the default cost calculation. Values from 1 to 65535 can be defined.

OSPF Router ID• The router is known to OSPF by the OSPF router ID number.• LSDBs use the OSPF router ID to differentiate one router from the

nextnext.• By default, the router ID is the highest IP address on an active

interface at the moment of OSPF process startup.If no interface is up when the OSPF process starts you will get the following error message:If no interface is up when the OSPF process starts, you will get the following error message:

R1(config)#router ospf 1

2w1d: %OSPF-4-NORTRID: OSPF process 1 cannot start.

• If a loopback interface exists, the router ID is the highest IP address on any active loopback interface.

• The OSPF router-id command can be used to override the OSPF router ID.

• Using a loopback interface or a router-id command is recommended for stability.y

OSPF router-id Command

router-id ip-address


This command is configured under the router ospf [process-id]command.A i bit 32 bit l i IP dd f t (d tt d d i l)Any unique arbitrary 32-bit value in an IP address format (dotted decimal) can be used.If this command is used on an OSPF process that is already active, then the

t ID t k ff t ft th t l d ft l t ti fnew router ID takes effect after the next reload or after a manual restarting of the OSPF process using:

Router#clear ip ospf process

Router(config)#router ospf 1Router(config-router)#router-id 172.16.1.1

Router#clear ip ospf process

OSPF over NBMA Topology Modes of OperationOperation

• RFC 2328 -compliant modes are as follows:N b d t (NBMA)Nonbroadcast (NBMA)Point-to-multipoint

• Additional modes from Cisco are as follows:Additional modes from Cisco are as follows:Point-to-multipoint nonbroadcastBroadcastPoint-to-point

Router(config if)#

ip ospf network [{broadcast | non-broadcast | point-to-multipoint [non-broadcast] | point-to-point}]

Router(config-if)#

This interface command defines OSPF network type.

RFC-compliant Non-broadcast Modep

• One IP subnet.• Neighbors must be manuallyNeighbors must be manually

configured.• DR and BDR elected.• DR and BDR need to have full• DR and BDR need to have full

connectivity with all other routers.

• Typically used in a full mesh• Typically used in a full mesh topology.

RTB(config-if)#ip ospf network non-broadcast--------RTB(config-router)#network 3.1.1.0 0.0.0.255 area 0RTB(config-router)#neighbor 3.1.1.1RTB(config-router)#neighbor 3.1.1.3

RFC-compliant Point-to-Multipoint Modep p

• One IP subnet.• Uses multicast OSPF hello• Uses multicast OSPF hello

packet to automatically discover neighbors.

• DR and BDR not required• DR and BDR not required• Typically used in a partial-

mesh or hub-and-spoke topologytopology.

RTB(config-if)#ip ospf network point-to-multipoint--------RTB(config-router)#network 3.1.1.0 0.0.0.255 area 0RTB(config router)#network 3.1.1.0 0.0.0.255 area 0

Cisco’s Point-to-Multipoint Non-broadcast mode• Cisco extension to RFC-

compliant point-to-multipoint modemode

• Must statically define neighbors, like nonbroadcast mode

• Like point to multipoint mode• Like point-to-multipoint mode, DR/BDR not elected

• Used in special cases where neighbors cannot be utomaticallyneighbors cannot be utomatically discovered

RTB(config-if)#ip ospf network point-to-multipoint non-broadcast--------RTB(config-router)#network 3.1.1.0 0.0.0.255 area 0RTB(config-router)#neighbor 3 1 1 1 cost 10RTB(config router)#neighbor 3.1.1.1 cost 10RTB(config-router)#neighbor 3.1.1.3 cost 20

Cisco’s Broadcast ModeCisco s Broadcast Mode

• Makes a WAN interface appear to be a LANappear to be a LAN

• One IP subnet• Uses multicast hellos to

di i hbdiscover neighbors• DR and BDR elected• Requires a full mesh.

RTB(config-if)#ip ospf network broadcast--------RTB(config-router)#network 3.1.1.0 0.0.0.255 area 0

Cisco’s Point-to-Point mode

One IP subnet per subinterface pair

No DR or BDR election

Used when only two routers need to form an adjacency on a pair of interfaces

Same properties as any physical point-to-point physical interface

RTB(config)#interface serial 0/0.1RTB(config-subif)#ip address 3.1.1.2 255.255.255.0RTB(config-subif)#interface serial 0/0.2 RTB(config-subif)#ip address 4.1.1.2 255.255.255.0--------RTB(config-router)#network 3.1.1.0 0.0.0.255 area 0RTB(config-router)#network 4.1.1.0 0.0.0.255 area 0

The neighbor command options

neighbor ip-address [priority number] [poll-intervalnumber] [cost number] [database-filter all]


Used to statically define neighbor relationships in an NBMA network

Option Description

priority number Specifies the priority of neighbor. Default is zero, which means neighbor can never be DR.which means neighbor can never be DR.

poll-interval number

Amount of time a NBMA interface waits before sending hellos to the neighbor even if the neighbor is inactive.

cost number

Assigns a cost to the neighbor from 1 to 65535. Neighbors with no specific cost configured will assume the cost of the interface, based on the ip ospf cost command (Not used with NBMA)ospf cost command. (Not used with NBMA)

database-filter all Filters outgoing LSAs to an OSPF neighbor

OSPF over NBMA Topology Summary

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– 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 l l ti d l f h ithi th t– SPF re-calculations are done only for changes within that area.• Large routing table

– Typically, the larger the area the larger the routing table.yp y, g g g– A larger routing table requires more memory and takes more time to

perform the route look-ups.

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-areaWith this technique, routing still occurs between the areas (called inter-arearouting), but many of the smaller internal routing operations, such as recalculating the database – re-running the SPF algorithm, are restricted within an area.

OSPF Router Types

LSA Types

Link TypesLink Types

LinkLink Type Description Link-state ID

1 Point-to-point connection to another router Neighboring router IDou e

2 Connection to a transit network IP address of DR

3 Connection to a stub network IP network/subnet b3 Connection to a stub network number

4 Virtual link Neighboring router ID

RouterA#show ip ospf database

Interpreting the OSPF DatabaseRouterA#show ip ospf database

OSPF Router with ID (10.0.0.11) (Process ID 1)Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count10.0.0.11 10.0.0.11 548 0x80000002 0x00401A 110 0 0 12 10 0 0 12 549 0 80000004 0 003A1B 110.0.0.12 10.0.0.12 549 0x80000004 0x003A1B 1100.100.100.100 100.100.100.100 548 0x800002D7 0x00EEA9 2

Net Link States (Area 0)Link ID ADV Router Age Seq# Checksum172.31.1.3 100.100.100.100 549 0x80000001 0x004EC9

Summary Net Link States (Area 0)Link ID ADV Router Age Seq# Checksum10.1.0.0 10.0.0.11 654 0x80000001 0x00FB1110.1.0.0 10.0.0.12 601 0x80000001 0x00F516<output omitted><output omitted>

Link ID: Identifies each LSA.

ADV router: Advertising router; the source router of the LSA.

Age: The maximum age counter in seconds; the maximum age is 1 hour or 3,600 seconds.

Seq#: Sequence number of the LSA; this number begins at 0x80000001 and increases with each update of the LSA.

Checksum: Checksum of the individual LSA to ensure reliable receipt of that LSAChecksum: Checksum of the individual LSA to ensure reliable receipt of that LSA.

Link count: Total number of directly attached links, used only on router LSAs. The link count includes all point-to-point, transit, and stub links. Each point-to-point serial link counts as two; all other links count as one, including Ethernet links.

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 h OSPF b l tti t th i li k t t• 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• Originated by an ASBR connected to an NSSA. • Type 7 messages can be flooded throughout NSSAs and translated• Type 7 messages can be flooded throughout NSSAs and translated

into LSA Type 5 messages by ABRs. • Routes learned via Type-7 LSAs are denoted by either a “N1” or and

“N2” in the routing table. (Compare to E1 and E2).g ( p )• We will discuss this more later when we look at NSSA areas.

Area Types

• Standard or Normal Areas– Backbone– Non-Backbone

• Stub– Stub Area

T t ll St bb A (TSA)– Totally Stubby Area (TSA)– Not-so-stubby-area (NSSA)

Area Types

Overview of Normal Areas

Routes Received on all OSPF Routers

Receives all routes from within A.S.:• Within the local area (Intra-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:• From external AS’s – LSA 5• As long as routes are being redistributed by the ASBR.

Default Routes• Received only if default information originate command was used (later)• 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

Multi Area OSPF

Normal Areas

11.0.0.0/812.0.0.0/813.0.0.0/8

Normal Areas

ASBR

10.1.0.0/24

Lo - RouterID

Lo - RouterID192.168.1.1/32

ABR-1 ABR-2.1

.1

.2 .3

192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

Area 0

172.16.1.0/24

172.16.51.0/24172.16.10.4/30

.5

6

InternalArea 51 172.16.0.0/16

172.16.20.0/24

.6

.1Lo - RouterID192.168.4.1/32

Area 1

1. OSPF Multi-Areas - All Normal Areas

ASBRrouter ospf 1redistribute static

ABR-2interface FastEthernet0ip address 172.16.1.3 255.255.255.0

network 172.16.1.0 0.0.0.255 area 0!

ip ospf priority 100!router ospf 1network 172.16.1.0 0.0.0.255 area 0

ABR-1interface FastEthernet0/0ip address 172 16 1 2 255 255 255 0

network 172.16.1.0 0.0.0.255 area 0network 172.16.10.4 0.0.0.3 area 1

Internalip address 172.16.1.2 255.255.255.0ip ospf priority 200

router ospf 1network 172 16 1 0 0 0 0 255 area 0

router ospf 1network 172.16.0.0 0.0.255.255 area 1

network 172.16.1.0 0.0.0.255 area 0network 172.16.51.0 0.0.0.255 area 51 ABR contains network

statements for each area it belongs to, using the proper area al eproper area value.

LSA 1 - Router Link States

11.0.0.0/812.0.0.0/813.0.0.0/8

Multi Area OSPF

Normal AreasLSA 1’s being sent within Area 0

ASBR

10.1.0.0/24

Lo RouterID

Lo - RouterID192.168.1.1/32

o a eas

ABR-1 ABR-2.1

.1

.2 .3

Lo - RouterID192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

LSA 1LSA 1 LSA 1

ABR-1 ABR-2

Area 0

172.16.1.0/24

172 16 51 0/24172.16.10.4/30

.5

6

Pri 100Pri 200


172.16.51.0/24

172.16.20.0/24

.6

.1Lo - RouterID192.168.4.1/32

Area 1

172.16.20.0/24


11.0.0.0/812.0.0.0/813.0.0.0/8

Multi Area OSPF

Normal AreasLSA 1’s being sent within other areas

ASBR

10.1.0.0/24

Lo RouterID

Lo - RouterID192.168.1.1/32

Normal Areas

ABR-1 ABR-2.1

.1

.2 .3

Lo - RouterID192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

LSA 1LSA 1LSA 1 LSA 1

ABR-1 ABR-2

Area 0

172.16.1.0/24

172 16 51 0/24172.16.10.4/30

.5

6

Pri 100Pri 200

LSA 1

LSA 1


172.16.51.0/24

172.16.20.0/24

.6

.1Lo - RouterID192.168.4.1/32

LSA 1 LSA 1

Area 1

172.16.20.0/24

LSA 1 - Router Link StatesFor Router Links: • The Link State ID is always the same as the Advertising Router• Advertising Router is the Router ID of the router that created this LSA 1

Internal#show ip ospf dataOSPF Router with ID (192.168.4.1) (Process ID 1)OSPF Router with ID (192.168.4.1) (Process ID 1)

Router Link States (Area 1)

(LSA 1 - Links in the area to which this router belongs.)(LSA 1 Links in the area to which this router belongs.)Link ID ADV Router Age Seq# Checksum Link count192.168.3.1 192.168.3.1 898 0x80000003 0xCE56 2192 168 4 1 192 168 4 1 937 0x80000003 0xFD44 3192.168.4.1 192.168.4.1 937 0x80000003 0xFD44 3

• Conclusion: Router Link States (LSA1’s) should display all the Router IDs of routers in that area including its ownIDs of routers in that area, including its own.

• reminder: LSA 1 -> “my one area”


ABR-2 - show ip route

172 16 0 0/16 is variably subnetted 4 subnets 3 masks172.16.0.0/16 is variably subnetted, 4 subnets, 3 masksO IA 172.16.51.1/32 [110/2] via 172.16.1.2, 00:11:44, FastEthernet0O 172.16.20.0/24 [110/782] via 172.16.10.6, 00:12:29, Serial0C 172.16.10.4/30 is directly connected, Serial0C 172.16.1.0/24 is directly connected, FastEthernet0O E2 11.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0O E2 12.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0O E2 13.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0

192.168.3.0/32 is subnetted, 1 subnetsC 192.168.3.1 is directly connected, Loopback1

• Denoted by just an “O” in the routing table, or a “C”• Why is there only just an ”O” for this network and not the other

networks?networks?– Directly connected or via another area.

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 isDenoted 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 an area.• ABR may include a set of LSA 2s for each area it belongs to.


11.0.0.0/812.0.0.0/813.0.0.0/8

Multi Area OSPF

Normal Areas

No LSA 2’s for ABR-1 in Area 51, or for Internal because no

ASBR

10.1.0.0/24

Lo - RouterID

Lo - RouterID192.168.1.1/32

o a easInternal because no other routers on multi-access segment.

LSA 2

ABR-1 ABR-2.1

.1

.2 .3

192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

DR LSA 2

LSA 2

Area 0

172.16.1.0/24

172.16.51.0/24172.16.10.4/30

.5

6

LSA 2

LSA 2

LSA 2flooded


172.16.20.0/24

.6

.1Lo - RouterID192.168.4.1/32

flooded

DR

LSA 2

Area 1


ASBR#show ip ospf data

OSPF Router with ID (192.168.1.1) (Process ID 1)( ) ( )

Net Link States (Area 0)

(LSA 2 - Generated by the DR)

Link ID ADV Router Age Seq# Checksum172.16.1.2 192.168.2.1 201 0x8000000D 0xCFE8

• Link ID 172.16.1.2 = IP address of DR on MultiAccess Network• ADV Router 192.168.2.1 = Router ID of DR• Conclusion: Net Link States (LSA2’s) should display the RouterIDs of

the DRs on all multi-access networks in the area and their IP addresses.

• reminder: LSA 2 -> “Generated by the D R”1 2

LSA 3 – Summary Net Link States

11.0.0.0/812.0.0.0/813.0.0.0/8

Multi Area OSPF

Normal AreasLSA 1’s are sent as LSA 3’s into other areas by the ABRs

ASBR

10.1.0.0/24

Lo - RouterID

Lo - RouterID192.168.1.1/32

o a easareas by the ABRs.

LSA 1

ABR-1 ABR-2.1

.1

.2 .3

192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

LSA 1LSA 1LSA 1

Area 0

172.16.1.0/24

172.16.51.0/24172.16.10.4/30

.5

6

LSA 3 LSA 3


172.16.20.0/24

.6

.1Lo - RouterID192.168.4.1/32

Area 1


11.0.0.0/812.0.0.0/813.0.0.0/8

Don’t forget about the LSA 1’s from Area 0.

Multi Area OSPF

Normal Areas

ASBR

10.1.0.0/24

Lo RouterID

Lo - RouterID192.168.1.1/32

o a eas

ABR-1 ABR-2.1

.1

.2 .3

Lo - RouterID192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

LSA 1LSA 1LSA 3

LSA 1

ABR-1 ABR-2

Area 0

172.16.1.0/24

172 16 51 0/24172.16.10.4/30

.5

6

Pri 100Pri 200

LSA 3


172.16.51.0/24

172.16.20.0/24

.6

.1Lo - RouterID192.168.4.1/32

Area 1

172.16.20.0/24


ASBRASBR# show ip ospf database

S i k S ( 0)Summary Net Link States (Area 0)Link ID ADV Router Age Seq# Checksum

(Area 1 networks - Advertising Router ABR-2)(Area 1 networks Advertising Router ABR 2)172.16.10.4 192.168.3.1 278 0x80000001 0xD126 172.16.20.0 192.168.3.1 278 0x80000001 0xA746

(Area 51 networks - Advertising Router ABR-1)172.16.51.1 192.168.2.1 206 0x80000005 0xA832

• Conclusion: We should see networks in other areas and the ABR advertising• Conclusion: We should see networks in other areas and the ABR advertising that route.

• reminder: LSA 3 -> “networks sent by the A B R”1 2 3


ASBRASBR# show ip route

/172.16.0.0/16 is variably subnetted, 4 subnets, 3 masksO IA 172.16.51.1/32 [110/2] via 172.16.1.2, 00:02:54, FastEthernet0/0O IA 172.16.20.0/24 [110/783] via 172.16.1.3, 00:02:54, FastEthernet0/0O IA 172.16.10.4/30 [110/782] via 172.16.1.3, 00:02:54, FastEthernet0/0C 172.16.1.0/24 is directly connected, FastEthernet0/0

10.0.0.0/24 is subnetted, 1 subnetsC 10.1.0.0 is directly connected, FastEthernet0/1S 11.0.0.0/8 is directly connected, Null0S 12.0.0.0/8 is directly connected, Null0

192.168.1.0/32 is subnetted, 1 subnetsC 192.168.1.1 is directly connected, Loopback0S 13.0.0.0/8 is directly connected, Null0/ y ,

LSA 4 – ASBR Summary Link States

• LSA 4 – ASBR Summary LSA• Originated by the ABR.• Flooded throughout the backbone area to the other

ABRs.• Describes the reachability to the ASBRsDescribes the reachability to the ASBRs• Advertises an ASBR (Router ID) not a network• Included in routing table as an “IA” route.• Same format as a LSA 3 - Summary LSA, except LSA 4

ASBR Summary LSA.

Exceptions• Not flooded to Stub and Totally Stubby networks.

11.0.0.0/812.0.0.0/813.0.0.0/8 Normal Areas

ASBR

10.1.0.0/24

L R t ID

Lo - RouterID192.168.1.1/32ASBR

ABR 1 ABR 21

.1

.2 .3

Lo - RouterID192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

LSA 4LSA 5’s flooded

ABR-1 ABR-2

Area 0

172.16.1.0/24

172 16 51 0/24172.16.10.4/30

.1

.5Pri 100Pri 200

LSA 4


172.16.51.0/24

172 16 20 0/24

.6

.1Lo - RouterID192.168.4.1/32

LSA 4LSA 4

Area 1

Area 1

172.16.20.0/24 Area 1

• Flooded thro gho t the backbone area to the other ABRs• Flooded throughout the backbone area to the other ABRs.• Describes the reachability to the ASBRs

LSA 4 – ASBR Summary Link States

ABR-2ABR-2# show ip ospf databasep p

Summary ASB Link States (Area 1)LSA 4 - Reachability to ASBR.

Not flooded to Stub and Totally Stubby networks.

Link ID ADV Router Age Seq# Checksum192.168.1.1 192.168.3.1 801 0x80000003 0x93CC

• Conclusion: Routers in non-area 0, should see Router ID of ASBR d it ABR t t thand its ABR to get there .

• reminder: LSA 4 -> “Reachability to the A S B R”1 2 3 4

LSA 5 - AS External Link States

• LSA 5 – AS External LSA • Originated by the ASBR. • Describes destination networks external to the Autonomous

System • Flooded throughout the OSPF AS, except to stub and totally stubby

areas• Denoted in routing table as E1 or E2 (default) route (see later)

• ASBR – Router which “redistributes” routes into the OSPF domain.

ExceptionsExceptions• Not flooded to Stub and Totally Stubby networks.• More on this later

11.0.0.0/812.0.0.0/813.0.0.0/8 Normal Areas

ASBRrouter ospf 1

redistribute staticnetwork 172.16.1.0 0.0.0.255 area 0

i t 11 0 0 0 255 0 0 0 N ll0

ASBR

10.1.0.0/24

1Lo - RouterID192 168 2 1/32

Lo - RouterID192.168.1.1/32

LSA 5’s flooded

ip route 11.0.0.0 255.0.0.0 Null0ip route 12.0.0.0 255.0.0.0 Null0ip route 13.0.0.0 255.0.0.0 Null0

ABR-1 ABR-2.1

.1

.2 .3

192.168.2.1/32

Lo - RouterID192.168.3.1/32

Pri 100Pri 200

LSA 5

LSA 5 s floodedLSA 5

Area 0

172.16.1.0/24

172.16.51.0/24172.16.10.4/30

.5

.6

LSA 5

LSA 5


172.16.20.0/24

.1Lo - RouterID192.168.4.1/32LSA 5

LSA 5

Area 1• “Redistribute” command creates an ASBR router.• This flood is originated by the ASBR. • It describes destination networks external to the OSPF Routing

Domain• It’s flooded throughout the OSPF AS, except to stub and totally stubby

areas

LSA 5 - AS External Link StatesABR-2ABR-2# show ip ospf database

AS External Link States

LSA 5 - External Networks originated by the ASBRLSA 5 - External Networks originated by the ASBR, Flooded throughout A.S. except to Stub and Totally Stubby

Link ID ADV Router Age Seq# Checksum Tag11 0 0 0 192 168 1 1 1191 0 80000001 0 3FEA 011.0.0.0 192.168.1.1 1191 0x80000001 0x3FEA 012.0.0.0 192.168.1.1 1191 0x80000001 0x32F6 013.0.0.0 192.168.1.1 1191 0x80000001 0x2503 0

• Conclusion: All Routers should see External networks and the Router ID of ASBR to get there .

• reminder: LSA 5 -> O T H E R networks1 2 3 4 51 2 3 4 5


ABR-2ABR-2# show ip route

172.16.0.0/16 is variably subnetted, 4 subnets, 3 masksO IA 172.16.51.1/32 [110/2] via 172.16.1.2, 00:11:44, FastEthernet0O 172.16.20.0/24 [110/782] via 172.16.10.6, 00:12:29, Serial0C 172.16.10.4/30 is directly connected, Serial0C 172.16.1.0/24 is directly connected, FastEthernet0O E2 11.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0O E2 12.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0O E2 13.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0

192.168.3.0/32 is subnetted, 1 subnetsC 192.168.3.1 is directly connected, Loopback1

• Designated by “E2”g y• Notice that the cost is 20 for all three routes, we will see why later. • It has to do with E2 routes and where the default cost is 20.

– Redistribute command: If a value is not specified for the metric option, and f f fno value is specified using the default-metric command, the default

metric value is 0, except for OSPF where the default cost is 20.


E1 vs. E2 External Routes• External routes fall under two categories:

– external type 1 – external type 2

• The difference between the two is in the way the cost (metric) of the• 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 routethe interior cost to reach that route.

• A type 1 cost is the addition of the external cost and the internal costused to reach that route.

• A t 1 t i l f d t 2 t f th• A type 1 route is always preferred over a type 2 route for the same destination.

• More later…

Stub Areas

Considerations for both Stub and Totally Stubby Areas

• An area could be qualified a stub when:q

– There is a single exit point (a single ABR) from that area.

– If routing to outside of the area does not have to take an optimal thpath.

– The area is not needed as a transit area for virtual links (later).

– The ASBR is not within the area– The ASBR is not within the 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.

Stub Areas

ABR-2

router ospf 1router ospf 1network 172.16.1.0 0.0.0.255 area 0network 172.16.10.4 0.0.0.3 area 1area 1 stub << Command: area area stubarea 1 stub Command: area area stub

Internal

router ospf 1network 172.16.0.0 0.0.255.255 area 1area 1 stub << Command: area area stub

• All routers in the area must be configured as “stub” including the ABRincluding the ABR

11.0.0.0/812.0.0.0/813.0.0.0/8

ASBR

10.1.0.0/24


1

.1

.2 .3

Lo - RouterID192.168.2.1/32

192.168.1.1/32

Lo - RouterID192 168 3 1/32

LSA 4LSA 3ABR-1 ABR-2

Area 0

172.16.1.0/24

172.16.10.4/30

.1

.5

192.168.3.1/32Pri 100Pri 200 LSA 4

X BlockedLSA 5

Blocked XLSA 5LSA 3

InternalArea 51

Area 0

172.16.0.0/16

172.16.51.0/24 .6

.1Lo - RouterID192.168.4.1/32

St b Area

Default route to ABR

Area 1

172.16.20.0/24Stub Area injected Area 1

Totally Stubby Areas

“Cisco proprietary”, however the RFC does make some provisions for this as an optional feature.

Same considerations as with Stub areas, except:

• ABR blocks all LSA 3s, except propagating a default route.• Default route is injected into totally stubby area by ABR


ABR-2

router ospf 1network 172.16.1.0 0.0.0.255 area 0network 172.16.10.4 0.0.0.3 area 1area 1 stub no summaryarea 1 stub no-summary

^^ Command: area area stub no-summaryCreates a totally stubby area. No Type 3 e 4 LSAs

Internal

router ospf 1network 172.16.0.0 0.0.255.255 area 1area 1 stub

^^ Command: area area stub

11.0.0.0/812.0.0.0/813.0.0.0/8

ASBR

10.1.0.0/24


1

.1

.2 .3

Lo - RouterID192.168.2.1/32

192.168.1.1/32

Lo - RouterID192 168 3 1/32

LSA 4LSA 3ABR-1 ABR-2

Area 0

172.16.1.0/24

172.16.10.4/30

.1

.5

192.168.3.1/32Pri 100Pri 200 LSA 4

X BlockedLSA 5

Blocked XLSA 5LSA 3

X

InternalArea 51

Area 0

172.16.0.0/16

172.16.51.0/24 .6

.1Lo - RouterID192.168.4.1/32

Totall St bb Area

Default route to ABR

1

Area 1

172.16.20.0/24Totally Stubby Area injected Area 1


InternalInternal# show ip routeInternal# show ip routeGateway of last resort is 172.16.10.5 to network 0.0.0.0

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masksC 172 16 20 0/24 is directly connected FastEthernet0C 172.16.20.0/24 is directly connected, FastEthernet0C 172.16.10.4/30 is directly connected, Serial0

192.168.4.0/32 is subnetted, 1 subnetsC 192.168.4.1 is directly connected, Loopback0O*IA 0 0 0 0/0 [110/782] i 172 16 10 5 00 03 09 S i l0O*IA 0.0.0.0/0 [110/782] via 172.16.10.5, 00:03:09, Serial0

• 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)

NSSA (Not So Stubby Area)

• Relatively new, these standards are based on OSPF enhancement, RFC 1587.

• NSSA allows an area to remain a stub area, but carry external routing information (Type 7 LSAs) from its stubby end, back towards the OSPF backbone. XTERNAL

• 1 2 3 4 5 6 7• ASBR in NSSA injects external routing information into the backbone

and the NSSA area, but rejects external routing information coming from the ABR.

• The ABR does not inject a default route into the NSSA. – This is true for a NSSA Stub, but a default route is injected for a , j

NSSA Totally Stubby area.

NSSAArea 2

Backbone AreaArea 0Default route via RTG

NSSA Generic

Area 2 Area 0

RIPRTH

Default route via RTG

LSA 7

RTD

RTE

RTGLSA 7

LSA 7

LSA 7LSA 5

ASBR

ABR (PossibleASBR)

RTARTB

RTCRTF

LSA 7LSA 7

LSA 7 LSA 7LSA 7s BlockedLSA 7 LSA 7 Blocked

Configuring NSSA Stub AreaConfigured for all routers in Area 2:router ospf 1network 172.16.2.0 0.0.0.255 area 2area 2 nssa

NSSA (Not So Stubby Area)

NSSA Stub and NSSA Totally Stubby• There are two types of NSSA:yp

– Stub– Totally Stubby

NSSA –Stub and Totally Stubby

NSSA stub areas:

• NSSAs that block type 4 and 5, but allow type 3.

• To make a stub area into an NSSA, use the following command under the OSPF configuration.

• This command must be configured on all routers in area 2. g

router ospf 1area 2 nssa

NSSA Totally Stubby areas:

• NSSAs that block type 4, 5 and 3, but allow a default.yp , ,

• This command must be configured on ABR router in area 2.

router ospf 1router ospf 1area 2 nssa no-summary

NSSAArea 2


NSSA Stub Areas

Area 2 Area 0

RIPRTH


LSA 7

LSA 3sRTH routes:N1/N2

LSA 4s & LSA 5sXRTD

RTE

RTGLSA 7

LSA 7

LSA 7LSA 5

0.0.0.0/0XRTH routes:E1/E2

X

ASBR

ABR (PossibleASBR)

RTARTB

RTCRTF

LSA 7LSA 7


Area 2 routers:router ospf 1

network 172.16.2.0 0.0.0.255 area 2area 2 nssa

NSSAArea 2


NSSA Totally Stubby Areas

Area 2 Area 0

RIPRTH


LSA 7

LSA 3sXRTH routes: N1/N2LSA 4s & LSA 5sX

RTD

RTE

RTGLSA 7

LSA 7

LSA 7LSA 5

0.0.0.0/0 RTH routes:E1/E2

X

ASBR

ABR (PossibleASBR)

RTARTB

RTCRTF

LSA 7LSA 7


RTB (ABR): router ospf 1

network 172 16 1 0 0 0 0 255 area 0network 172.16.1.0 0.0.0.255 area 0network 172.16.2.0 0.0.0.255 area 2 area 2 nssa no-summary

Area 2 routers: router ospf 1

network 172.16.2.0 0.0.0.255 area 2area 2 nssa

Virtual Links

• A virtual link has the following two requirements:– It must be established between two routers that share a commonIt must be established between two routers that share a common

area and are both ABRs.

One of these two routers must be connected to the backbone– One of these two routers must be connected to the backbone.

•• “should be used only as a “should be used only as a temporary fixtemporary fix to an unavoidable topology to an unavoidable topology problem ”problem ”problem.”problem.”

Virtual Links

The command to configure a virtual link is as follows:g

area <area-id> virtual-link <remote-router-id>

RTA(config)#router ospf 1

RTA(config-router)#network 192.168.0.0 0.0.0.255 area 51

RTA(config-router)#network 192.168.1.0 0.0.0.255 area 3

RTA(config-router)#area 3 virtual-link 10 0 0 1RTA(config router)#area 3 virtual-link 10.0.0.1

RTB(config)#router ospf 1

RTB(config-router)#network 192.168.1.0 0.0.0.255 area 3

RTB(config-router)#network 192.168.2.0 0.0.0.255 area 0

RTB(config-router)#area 3 virtual-link 10.0.0.2

Route Summarization

InterInter--Area Route Summarization Area Route Summarization -- Area RangeArea Range• By default ABRs do not summarize routes between areas.

• Route summarization is the consolidation of advertised addresses• Route summarization is the consolidation of advertised addresses.

• This feature causes a single summary route to be advertised to other areas by an ABR.

• In OSPF, an ABR will advertise networks in one area into another area.

Router(config-router)# area area-id range network-address subnet-mask

• area-id - Identifier of the area about which routes are to bearea id Identifier of the area about which routes are to be summarized. (From area)

ABR

router ospf 100

area 1 range 195.16.0.0 255.255.0.0

Route Summarization

External Route Summarization External Route Summarization -- summarysummary--addressaddress• When redistributing routes from other protocols into OSPF (later), each route is

advertised individually in an external link state advertisement (LSA).

• However, you can configure the Cisco IOS softwareCisco IOS software to advertise a single route for all the redistributed routes that are covered by a specified network address and mask.

• Doing so helps decrease the sizedecrease the size of the OSPF link state database.

#Router(config-router)# summarysummary--address address networknetwork--address subnetaddress subnet--maskmask

ASBRrouter ospf 100summary-address 195.16.0.0 255.255.0.0

Injecting Default Routes into OSPF

There are two ways to generate a default. 1) default-information originate

• If the ASBR already has the default route (ip route 0.0.0.0 0.0.0.0), you can advertise 0.0.0.0 into the area.

2) default-information originate alwaysalways

• If the ASBR doesn't have the route (ip route 0.0.0.0 0.0.0.0), you can ( p ), yadd the keyword alwaysalways to the defaultdefault--information originateinformation originatecommand, and then advertise 0.0.0.0.

Redistributing External Routesrouter ospf 1redistribute routing-protocol metric-type [1|2]

• metric-type 1 - A type 1 cost is the addition of the external cost and the internal costused to reach that route.

redistribute rip [metric value] metricmetric--type type 11

ASBRrouter ospf 1redistribute rip metric 500 metric-type 1

• metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that routethe interior cost to reach that route.

redistribute rip [metric value] metricmetric--type type 22

ASBRrouter ospf 1router ospf 1redistribute rip metric 500 metric-type 2

Configuring Simple Authentication

A router, by default, trusts that routing information received, has come from a router that should be sending it. ☺g

Rtr(config-if)# ip ospf authentication-key passwd

• Configured on an interfaceConfigured on an interface• password = Clear text unless message-digest is used (next)

–Easily captured using a packet snifferPasswords do not have to be the same throughout an area but they must–Passwords do not have to be the same throughout an area, but they must

be same between neighbors.

After a password is configured you enable authentication for the area on allAfter a password is configured, you enable authentication for the area on all participating area routers with:

Rtr(config-router)# area area authentication

• Configured for an OSPF area in ospf router mode• Configured for an OSPF area, in ospf router mode.

Configuring Simple Authentication

s1 s270.0.0.0/8 172.16.0.0/16

RouterA RouterB

192.16.64.1/24 192.16.64.2/24

RouterA RouterB

RouterA

interface Serial1

ip address 192.16.64.1 255.255.255.0

ip ospf authentication-key secret

RouterB

interface Serial2

ip address 192.16.64.2 255.255.255.0

ip ospf authentication-key secretip ospf authentication key secret

!

router ospf 10

network 192.16.64.0 0.0.0.255 area 0

ip ospf authentication key secret

!

router ospf 10

network 172.16.0.0 0.0.255.255 area 0

network 70.0.0.0 0.255.255.255 area 0

area 0 authentication

network 192.16.64.0 0.0.0.255 area 0

area 0 authentication

Configuring MD5 Encrypted Authentication

Rtr(config-if)# ip ospf message-digest-key key-id md5 passwordp

• Key-id = 1 to 255, must match on each router to authenticate. • md5 = Encryption-type • password = encryptedpassword encrypted

–Passwords do not have to be the same throughout an area, but they must be same between neighbors.

After a password is configured, you enable authentication for the area on all participating area routers with:

Rtr(config-router)# area area authentication [message-Rtr(config router)# area area authentication [messagedigest]

• message-digest option must be used if using message-digest-key• If optional message-digest is used a message digest or hash of theIf optional message digest is used, a message digest, or hash, of the

password is sent.

Configuring MD5 Encrypted Authentication

s1 s270.0.0.0/8 172.16.0.0/16

RouterA RouterB

192.16.64.1/24 192.16.64.2/24

RouterA RouterB

RouterA

interface Serial1

ip address 192.16.64.1 255.255.255.0

ip ospf message-digest-key 1 md5 secret

RouterB

interface Serial2

ip address 192.16.64.2 255.255.255.0

ip ospf message-digest-key 1 md5 secretip ospf message digest key 1 md5 secret

!

router ospf 10

network 192.16.64.0 0.0.0.255 area 0

ip ospf message digest key 1 md5 secret

!

router ospf 10

network 172.16.0.0 0.0.255.255 area 0

network 70.0.0.0 0.255.255.255 area 0

area 0 authentication message-digest

network 192.16.64.0 0.0.0.255 area 0

area 0 authentication message-digest

Know your outputs

• show ip route• show ip ospfp p• show ip ospf neighbor• show ip ospf border-router• show ip database• show ip interface

show ip route

Router# show ip route172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks

O IA 172.16.51.1/32 [110/783] via 172.16.1.2, 00:11:44, FastEthernet0

O 172.16.20.0/24 [110/782] via 172.16.10.6, 00:12:29, Serial0C 172.16.10.4/30 is directly connected, Serial0C 172.16.1.0/24 is directly connected, FastEthernet0O E2 11.0.0.0/8 [110/20] via 172.16.1.1, 00:11:44, FastEthernet0O E1 12.0.0.0/8 [110/782] via 172.16.1.1, 00:11:44, FastEthernet0

• O = OSPF routes within the same area (intra-area routes)• 110/number = Administrative Distance/metric (cumulative 108/bandwidth)• E2 = Routes outside of the OSPF routing domain redistributed into OSPF• E2 = Routes outside of the OSPF routing domain, redistributed into OSPF.

– Default is E2 with a cost of 20 and does not get modified within the OSPF• O IA = OSPF routes from another area (inter-area routes)• E1 = Routes outside of the OSPF routing domain and get additional cumulative

costs added on by each router, just like other OSPF routes.

show ip ospfRouter#show ip ospfRouting Process "ospf 1" with ID 192.168.3.1Supports only single TOS(TOS0) routesSupports only single TOS(TOS0) routesIt is an area border routerSPF schedule delay 5 secs, Hold time between two SPFs 10 secsMinimum LSA interval 5 secs. Minimum LSA arrival 1 secsNumber of external LSA 3. Checksum Sum 0x97E3 Number of DCbitless external LSA 0Number of DoNotAge external LSA 0Number of areas in this router is 2. 2 normal 0 stub 0 nssaExternal flood list length 0

Area BACKBONE(0)Number of interfaces in this area is 1Number of interfaces in this area is 1Area has no authenticationSPF algorithm executed 8 times<text omitted>

Area 1<text omitted>

show ip ospf interfaceRouter# show ip ospf interfaceEthernet0 is up, line protocol is upInternet Address 206.202.2.1/24, Area 1Process ID 1, Router ID 1.2.202.206, Network Type BROADCAST, Cost: 10Transmit Delay is 1 sec, State BDR, Priority 1Designated Router (ID) 2.2.202.206, Interface address 206.202.2.2Backup Designated router (ID) 1.2.202.206, Interface address 206.202.2.1Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5Hello due in 00:00:00

Neighbor Count is 1, Adjacent neighbor count is 1Adjacent with neighbor 2.2.202.206 (Designated Router)j g ( g )

Suppress hello for 0 neighbor(s)Serial0 is up, line protocol is upInternet Address 206.202.1.2/24, Area 1Process ID 1 Router ID 1 2 202 206 Network Type POINT TO POINT Cost:Process ID 1, Router ID 1.2.202.206, Network Type POINT_TO_POINT, Cost: 64Transmit Delay is 1 sec, State POINT_TO_POINT,Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5Hello due in 00:00:04Hello due in 00:00:04

Neighbor Count is 1, Adjacent neighbor count is 1Adjacent with neighbor 2.0.202.206

Suppress hello for 0 neighbor(s)

show ip ospf neighbor

RouterB#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface1.5.202.206 1 FULL/DROTHER 00:00:33 206.202.0.3 Ethernet01.10.202.206 1 FULL/BDR 00:00:32 206.202.0.4 Ethernet01.0.202.206 1 2WAY/DROTHER 00:00:30 206.202.0.1 Ethernet0/1.2.202.206 1 FULL/ - 00:00:32 206.202.1.2 Serial0

• In this example, we are the DR

• DROTHER may be in FULL or 2 WAY state, both cases are normal.

• Usually if there are multiple DROTHERs, they will be in either FULL or 2WAY state but not both.

debug ip ospf adj (adjacency)Router# debug ip ospf adj04:19:46: OSPF: Rcv hello from 201.0.0.1 area 0 from FastEthernet0 192.168.20.104:19:46: OSPF: 2 Way Communication to 201.0.0.1 on FastEthernet0, state 2WAY04:19:46: OSPF: End of hello processing<text omitted>04:20:22: OSPF: end of Wait on interface FastEthernet004:20:22: OSPF: DR/BDR election on FastEthernet004 20 22 OSPF El t BDR 200 0 0 104:20:22: OSPF: Elect BDR 200.0.0.104:20:22: OSPF: Elect DR 200.0.0.104:20:22: OSPF: Elect BDR 201.0.0.104:20:22: OSPF: Elect DR 200.0.0.104:20:22: DR: 201.0.0.1 (Id) BDR: 200.0.0.1 (Id)04:20:23: OSPF: Rcv DBD from 201.0.0.1 on FastEthernet0 seq 0x2657 opt 0x2 flag0x7 len 32 mtu 1500 state EXSTART04:20:23: OSPF: NBR Negotiation Done. We are the SLAVE04:20:23: OSPF: Send DBD to 201.0.0.1 on FastEthernet0 seq 0x2657 opt 0x2 flag 0 x2 len 9204 20 23 OS f 201 0 0 1 t th t0 0 2658 t 0 2 fl04:20:23: OSPF: Rcv DBD from 201.0.0.1 on FastEthernet0 seq 0x2658 opt 0x2 flag0x3 len 72 mtu 1500 state EXCHANGE<text omitted>04:20:23: OSPF: Synchronized with 201.0.0.1 on FastEthernet0, state FULL

• Displays adjacency information including Hello processing, DR/BDR election, authentication, and the “Steps to OSPF Operation.”

debug ip ospf eventsRouter# debug ip ospf events08:00:56: OSPF: Rcv hello from 201.0.0.1 area 0 from FastEthernet0 192.168.20.108:00:56: OSPF: Mismatched hello parameters from 192 168 20 108:00:56: OSPF: Mismatched hello parameters from 192.168.20.108:00:56: Dead R 40 C 20, Hello R 10 C 5 Mask R 255.255.255.252 C

255.255.255.252

Sh h f th i f ti d b i f dj i th i• Shows much of the same information as debug ip ospf adj in the previous slide including, adjacencies, flooding information, designated router selection, and shortest path first (SPF) calculation.

• This information is also displayed with debug ip ospf events.

• R = Received

• C = Current• C = Current

OSPF Configuration Commands - ReviewRequired Commands:Required Commands:Rtr(config)# router ospf process-idRtr(config-router)#network address wildcard-mask area area-id

Optional Commands:Optional Commands:Rtr(config-router)# default-information originate (Send default)Rtr(config-router)# area area authentication (Plain authen.)Rtr(config-router)# area area authentication message-digest g g g

(md5 authen.)Rtr(config)# interface loopback number (Configure lo as RtrID)Rtr(config)# interface type slot/portRtr(config-if)# ip ospf priority <0-255> (DR/BDR election)Rtr(config-if)# bandwidth kbps (Modify default bandwdth)RTB(config-if)# ip ospf cost cost (Modify inter. cost)Rtr(config-if)# ip ospf hello-interval seconds (Modify Hello)Rtr(config-if)# ip ospf hello-interval seconds (Modify Hello)Rtr(config-if)# ip ospf dead-interval seconds (Modify Dead)Rtr(config-if)# ip ospf authentication-key passwd (Plain/md5authen)Rtr(config-if)# ip ospf message-digest-key key-id md5 passwordp p g g y y p

OSPF Show Commands - Review

Router# show ip routeRouter# show ip ospfRouter# show ip ospfRouter# show ip ospf interfaceRouter# show ip ospf neighborRouter# show ip ospf databaseRouter# debug ip ospf adjRouter# debug ip ospf events

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