OSPF Areas Why OSPF is Complicated Part 2 2005/03/11 (C) Herbert - PowerPoint PPT Presentation

OSPF – Areas Why OSPF is Complicated Part 2 2005/03/11 (C) Herbert Haas

“An algorithm must be seen to be believed” Donald .E. Knuth

OSPF Areas  To improve performance divide the whole OSPF domain in multiple Areas  Restrict Router LSA and Network LSA within these Areas  All areas must be connected to the so-called "Backbone Area"  "Area 0" 2005/03/11 (C) Herbert Haas 3

ABR Area Border Router (ABR): Note: Terminates Router LSAs Network Summary LSAs and Network LSAs are Distance Vector Forwards Network Summary LSAs Area 0 updates !!! LSA 3 3 A LSA 3 S L ABR LSA 3 ABR ABR LSA 3 2 LSA 3 A LSA 1 LSA 3 S L LSA 3 LSA 2 L Area 1 S A 1 LSA 1 LSA 2 Area 2 Area 5 Router LSA LSA 1 Network LSA LSA 2 Network Summary LSA LSA 3 2005/03/11 (C) Herbert Haas 4

ASBR When an ABR receives an Autonomous System AS External LSA it emits ASBR Summary LSAs Border Router (ASBR) to all routers Imports foreign routes via AS External LSA Area 0 LSA 5 LSA 5 LSA 4 LSA 5 LSA 4 4 ABR A S L ABR ABR LSA 5 LSA 5 4 A LSA 4 S L 4 ASBR LSA 5 A LSA 5 LSA 5 S L LSA 5 Area 1 LSA 5 5 A S L Area 2 Area 5 Router LSA LSA 1 Network LSA ASBR Summary LSA LSA 2 LSA 4 Network Summary LSA AS External LSA LSA 3 LSA 5 2005/03/11 (C) Herbert Haas 5

Stub Area Area 0 LSA 5 LSA 3 LSA 4 4 ABR A S L ABR LSA 2 LSA 5 ABR LSA 5 LSA 3 3 A LSA 3 ASBR LSA 1 S LSA 5 L LSA 5 Area 1 AS External LSA and ASBR Summary LSA are not sent into a Stub Area Stub Area 5 Area 2 Router LSA LSA 1 Network LSA ASBR Summary LSA LSA 2 LSA 4 Network Summary LSA AS External LSA LSA 3 LSA 5 2005/03/11 (C) Herbert Haas 6

Totally Stubby Area Cisco Specific Area 0 LSA 5 LSA 3 LSA 4 4 ABR A S L ABR LSA 2 LSA 5 ABR LSA 5 LSA 3 ASBR LSA 1 LSA 5 LSA 5 Area 1 No external or summary LSA are sent into a Totally Totally Stubby Area Area 5 Stubby Area 2 Router LSA LSA 1 Network LSA ASBR Summary LSA LSA 2 LSA 4 Network Summary LSA AS External LSA LSA 3 LSA 5 2005/03/11 (C) Herbert Haas 7

Not So Stubby Area (NSSA) ABR will translate the Type 7 LSA into a Type 5 LSA only if the Type 7 LSA has the P-bit set to 1 Area 0 LSA 5 LSA 5 LSA 3 LSA 4 4 ABR A S L ABR LSA 2 LSA 5 ABR LSA 5 LSA 3 3 LSA 3 A S L ASBR LSA 1 LSA 5 LSA 7 LSA 5 Area 1 LSA 7 ASBR ASBR advertizes routes NSSA of another routing Area 5 Area 2 domain via NSSA External LSA Router LSA LSA 1 Network LSA ASBR Summary LSA LSA 2 LSA 4 Network Summary LSA AS External LSA LSA 3 LSA 5 NSSA External LSA LSA 7 2005/03/11 (C) Herbert Haas 8

Summarization  Efficient OSPF address design requires hierarchical addressing  Address plan should support summarization at ABRs Area 0 2 2 20/8 / 8 21/8 22.1.0.0/16 20.1.0.0/16 ... ... 22.254.0.0/16 20.254.0.0/16 21.1.0.0/16 ... Area 30 21.254.0.0/16 Area 10 Area 20 2005/03/11 (C) Herbert Haas 9

Virtual Links  Another way to Area 0 connect to area 0 using a point-to-point ABR unicast tunnel Virtual Link  Transit area must Area 1 have full routing information ABR  Must not be stub area  Bad Design! Area 2 2005/03/11 (C) Herbert Haas 10

Virtual Link Example  Now router 3.3.3.3 has Area 0 an interface in area 0 4.0.0.1  Thus router 3.3.3.3 Router 1.1.1.1 5.0.0.1 becomes an ABR  Generates summary 5.0.0.2 LSA for network Router Area 1 2.2.2.2 7.0.0.0/8 into area 1 and 6.0.0.2 area 0  Also summary LSAs in 6.0.0.3 Router area 2 for all the 3.3.3.3 information it learned 7.0.0.3 from areas 0 and 1 Area 2 2005/03/11 (C) Herbert Haas 11

Virtual Link Configuration Example router ospf 5 Area 0 network 4.0.0.0 0.255.255.255 area 0 network 5.0.0.0 0.255.255.255 area 1 4.0.0.1 area 1 virtual-link 3.3.3.3 Router 1.1.1.1 5.0.0.1 5.0.0.2 Router Area 1 2.2.2.2 6.0.0.2 router ospf 5 6.0.0.3 network 7.0.0.0 0.255.255.255 area 2 Router network 6.0.0.0 0.255.255.255 area 1 3.3.3.3 area 1 virtual-link 1.1.1.1 7.0.0.3 Area 2 2005/03/11 (C) Herbert Haas 12

GRE instead of Virtual Link  Alternative solution  Good: Transit area can be a also a stub area  Bad: All traffic is encapsulated  Not only routing traffic  Increased overhead 2005/03/11 (C) Herbert Haas 13

Summary  Area concept supports large networks  Keeps topology table small  Reduces routing traffic  But additional LSA types necessary  Inter-Area Routing is Distance Vector  Originally OSPF designed for ToS routing – too resource greedy! 2005/03/11 (C) Herbert Haas 14

Quiz  When should we split the OSPF domain into areas?  What about Areas and addressing plans?  Why must all areas be connected to the backbone area? 2005/03/11 (C) Herbert Haas 15

OSPF Areas Why OSPF is Complicated Part 2 2005/03/11 (C) Herbert - PowerPoint PPT Presentation

OSPF Areas Why OSPF is Complicated Part 2 2005/03/11 (C) Herbert Haas An algorithm must be seen to be believed Donald .E. Knuth OSPF Areas To improve performance divide the whole OSPF domain in multiple Areas Restrict

OSPF Fast Hellos OSPF HelloInterval and RouterDeadInterval OSPF timers are included in the OSPF

OSPF Router Types OSPF Router Types There are four types of OSPF routers. Router types are

r2#debug ip ospf events OSPF events debugging is on *Sep 24 18:56:35.764 KRSK: OSPF: Send hello

OSPF Traffic Engineering (TE) Express Path draft-giacalone-ospf-te-express-path-00.txt

Use of OSPF-MDR in Single-Hop Broadcast Networks draft-ogier-ospf-manet-single-hop-00 Richard

OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r < curtis@ans.net > URLs

Communication Systems OSPF, BGP University of Freiburg Computer Science Computer Networks and

Advertising Per-node Administrative Tags in OSPF draft-hegde-ospf-node-admin-tag-01 Shraddha

OSPF Extended Link Attributes P. Psenak, A.Lindem Cisco Systems IETF 88, November 3-8, 2013

Lab Course RouterLab OSPF - Open Shortest Path First (RFC 2328) Some of the slides come

Lab Course RouterLab Open Shortest Path First (OSPF) Miscellaneous Don't set enable

OSPF Multiaccess Networks The IETF Routing Master Part 3 2005/03/11 (C) Herbert Haas

IETF 91 Honolulu Yang Data Model for OSPF Protocol

OSPF TE Topology-Transparent Zone

FOCUS AREAS FOCUS AREAS FOCUS AREAS FOCUS AREAS Our Our Vision Vision Our Our Vision

Designation of Areas under Evacuation Orders under Evacuation Orders Legend Legend Areas where

Using an Abstract Representation Aditya Akella Aaron Gember-Jacobson, Raajay Viswanathan and

Theophilus Benson (tbenson@cs.wisc.edu) Aditya Akella (akella@cs.wisc.edu) David A Maltz

Research challenges in the large-scale computational modeling of networks Wenji Wu, Phil DeMar

A 2011 Till Bargheer c Mostly based on [1003.6120] with Florian Loebbert and Carlo Meneghelli

Routing Security* CSE598K/CSE545 - Advanced Network Security Prof. McDaniel - Spring 2008 *

CMPSC443 - Introduction to Computer and Network Security Module: Routing Security Professor

Multi Layer Performance Based PCE Enhancements to ONOS Controller for SD WAN Packet Optical

One step is enough David Ripley Monash University http://davewripley.rocks/docs/osie-slides.pdf

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OSPF Areas Why OSPF is Complicated Part 2 2005/03/11 (C) Herbert - PowerPoint PPT Presentation

OSPF Areas Why OSPF is Complicated Part 2 2005/03/11 (C) Herbert Haas An algorithm must be seen to be believed Donald .E. Knuth OSPF Areas To improve performance divide the whole OSPF domain in multiple Areas Restrict

OSPF Fast Hellos OSPF HelloInterval and RouterDeadInterval OSPF timers are included in the OSPF

OSPF Router Types OSPF Router Types There are four types of OSPF routers. Router types are

r2#debug ip ospf events OSPF events debugging is on *Sep 24 18:56:35.764 KRSK: OSPF: Send hello

OSPF Traffic Engineering (TE) Express Path draft-giacalone-ospf-te-express-path-00.txt

Use of OSPF-MDR in Single-Hop Broadcast Networks draft-ogier-ospf-manet-single-hop-00 Richard

OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r &lt; curtis@ans.net &gt; URLs

Communication Systems OSPF, BGP University of Freiburg Computer Science Computer Networks and

Advertising Per-node Administrative Tags in OSPF draft-hegde-ospf-node-admin-tag-01 Shraddha

OSPF Extended Link Attributes P. Psenak, A.Lindem Cisco Systems IETF 88, November 3-8, 2013

Lab Course RouterLab OSPF - Open Shortest Path First (RFC 2328) Some of the slides come

Lab Course RouterLab Open Shortest Path First (OSPF) Miscellaneous Don't set enable

OSPF Multiaccess Networks The IETF Routing Master Part 3 2005/03/11 (C) Herbert Haas

IETF 91 Honolulu Yang Data Model for OSPF Protocol

OSPF TE Topology-Transparent Zone

FOCUS AREAS FOCUS AREAS FOCUS AREAS FOCUS AREAS Our Our Vision Vision Our Our Vision

Designation of Areas under Evacuation Orders under Evacuation Orders Legend Legend Areas where

Using an Abstract Representation Aditya Akella Aaron Gember-Jacobson, Raajay Viswanathan and

Theophilus Benson (tbenson@cs.wisc.edu) Aditya Akella (akella@cs.wisc.edu) David A Maltz

Research challenges in the large-scale computational modeling of networks Wenji Wu, Phil DeMar

A 2011 Till Bargheer c Mostly based on [1003.6120] with Florian Loebbert and Carlo Meneghelli

Routing Security* CSE598K/CSE545 - Advanced Network Security Prof. McDaniel - Spring 2008 *

CMPSC443 - Introduction to Computer and Network Security Module: Routing Security Professor

Multi Layer Performance Based PCE Enhancements to ONOS Controller for SD WAN Packet Optical

One step is enough David Ripley Monash University http://davewripley.rocks/docs/osie-slides.pdf

Sambuz

Useful Links

Newsletter

Mail Us

OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r < curtis@ans.net > URLs