Module 3 - Multiarea OSPF Operation pptx

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BSCI Module 3 Lesson 6 - Multiarea OSPF
Operation
OSPF
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Objective
 Large OSPF Network Issues
 OSPF LSA Types
 OSPF LSA Types (cont.)
 Interpreting the OSPF LSDB and Routing Table
 Interpreting the Routing Table
 Calculating Costs for E1 and E2 Routes
 Configuring OSPF LSDB Overload Protection
 Changing the Cost Metric
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Large OSPF Network Issues
 Hierarchical area routing separates a large internetwork
into multiple areas. When you use this technique,
interarea routing still occurs, but many of the internal
routing operations, such as SPF calculations, remain
within individual areas.
–Reduced frequency of SPF calculations
–Smaller routing table
–Reduced LSU overhead

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LSA Types
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LSA Type 1 Link Types
Link
Type
Description Link-state ID
1
Point-to-point connection to another
router
Neighboring router ID
2 Connection to a transit network IP address of DR
3 Connection to a stub network
IP network/subnet
number
4 Virtual link Neighboring router ID
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The Link ID in the OSPF Database
RouterA#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 count
10.0.0.11 10.0.0.11 548 0x80000002 0x00401A 1
10.0.0.12 10.0.0.12 549 0x80000004 0x003A1B 1
100.100.100.100 100.100.100.100 548 0x800002D7 0x00EEA9 2
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
172.31.1.3 100.100.100.100 549 0x80000001 0x004EC9
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.1.0.0 10.0.0.11 654 0x80000001 0x00FB11
10.1.0.0 10.0.0.12 601 0x80000001 0x00F516
<output omitted>
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LSA Type 1: Router LSA
 One router LSA (type 1) for every router in an area:
–Includes list of directly attached links
 Identified by the router ID of the originating router
 Floods within its area only; does not cross ABR
 Link-state ID depends on link type
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LSA Type 1: Router LSA
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Type 1: Router LSAs
 The command show ip ospf database router will list all of the Router
LSAs in a database.
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LSA Type 2: Network LSA
 Advertised by the DR of the broadcast network
 Floods within its area only; does not cross ABR
 Link-state ID is the DR
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LSA Type 2: Network LSA
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Type 2: Network LSAs
 The command show ip ospf database network is used to observe a
Network LSA.
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LSA Type 3: Summary LSA
 Advertised by the ABR of originating area.

 Regenerated by subsequent ABRs to flood throughout
the autonomous system.
 By default, routes are not summarized, and type 3 LSA
is advertised for every subnet.
 Link-state ID is the network or subnet advertised in the
summary LSA
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LSA Type 3: Summary LSA
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Type 3: ABR Summary LSAs
 The command show ip ospf database summary is used to display the
network summary LSAs in the database.
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LSA Type 4: Summary LSA
 Summary (type 4) LSAs are used to advertise an ASBR to
all other areas in the autonomous system.
 They are generated by the ABR of the originating area.
 They are regenerated by all subsequent ABRs to flood
throughout the autonomous system.
 Link-state ID is the router ID of the ASBR.
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Type 4: ASBR Summary LSAs
 The command show ip ospf database asbr-summary is used to display
ASBR Summary LSAs
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LSA Type 5: External LSA
 External (type 5) LSAs are used to advertise networks from
other autonomous systems.
 Type 5 LSAs are advertised and owned by the originating
ASBR. external LSAs are flooded throughout the autonomous
system
 The Link-state ID is the external network number.
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Type 5: Autonomous System External LSAs
 The command show ip ospf data base externaldisplays AS External
LSAs
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LSA Types: 6, 7, 8
 Group Membership LSAs are used in an enhancement of OSPF
known as Multicast OSPF (MOSPF). MOSPF routes packets from

a single source to multiple destinations, or group members, which
share a class D multicast address. Although Cisco supports other
multicast routing protocols, MOSPF is not supported as of this
writing.
 NSSA External LSAs are originated by ASBRs within not-so-
stubby areas (NSSAs
 External Attributes LSAs were proposed as an alternative to
running Internal BGP (iBGP), to transport BGP information across
an OSPF domain. This LSA is not supported in IOS.
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Type 7: Not-So-Stubby Area LSAs
 The command show ip ospf database nssa-externaldisplays NSSA
external LSAs
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LSA Operation Example
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LSA Types: 9, 10, 11
 Opaque LSAs are a class of LSAs that consist of a standard LSA
header followed by application-specific information.
 The Information field can be used directly by OSPF or indirectly by
other applications to distribute information throughout the OSPF

domain.
 Opaque LSAs have been used to add various extensions to OSPF,
such as traffic engineering parameters for Multiprotocol Label
Switching (MPLS) networks
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Interpreting the OSPF Database
RouterA#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 count
10.0.0.11 10.0.0.11 548 0x80000002 0x00401A 1
10.0.0.12 10.0.0.12 549 0x80000004 0x003A1B 1
100.100.100.100 100.100.100.100 548 0x800002D7 0x00EEA9 2
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
172.31.1.3 100.100.100.100 549 0x80000001 0x004EC9
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.1.0.0 10.0.0.11 654 0x80000001 0x00FB11
10.1.0.0 10.0.0.12 601 0x80000001 0x00F516
<output omitted>
ADV Router: Advertising router; the source router of the LSA
Link count: Total number of directly attached links, used only on
router LSAs
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Interpreting the Routing Table
 When an ABR receives summary LSAs, it adds them to
its LSDB and regenerates them into the local area.
When an ABR receives external LSAs, it adds them to
its LSDB and floods them into the area.