Presentation Ospf Ranjeetv0.2

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OSPF Routing Protocol

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Presentation Ospf Ranjeetv0.2

  1. 1. 1<br /> Introduction to<br />OSPF Protocol Design<br />By:<br />Ranjeet Saini<br />Engineering Test Lead<br />Agnity Technologies, Inc.<br />March, 2008<br />
  2. 2. 2<br />Agenda<br />References & Standard<br />II. Terminology<br />OSPF Format<br />IV. OSPF Algorithm<br />
  3. 3. 3<br />References & Standard<br />RFC 2328 OSPF Version 2 April, 1998<br /> by John Moy<br />2. RFC 2370 The OSPF Opaque LSA Option April, 1998<br /> by R. Coltun<br />Understanding TCP/IP December, 1995<br /> SynOptics Communications<br />4. RFC 1349 Type of Service in the Internet Protocol July, 1992<br />
  4. 4. 4<br />References & Standard<br />II. Terminology<br />OSPF Format<br />IV. OSPF Algorithm<br />
  5. 5. 5<br />Internet Routing<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Core System<br />Area Border Router<br />Area Border Router<br />R7<br />R8<br />R1<br />R2<br />Area Border Router<br />R9<br />R3<br />R4<br />R5<br />Autonomous System #1<br />Autonomous System #3<br />R6<br />Autonomous System #2<br />
  6. 6. 6<br />Exterior Gateway Protocol<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />IGP1<br />IGP2<br />IGP1<br />IGP1<br />IGP2<br />IGP2<br />EGP<br />IGP1<br />IGP2<br />Autonomous System1<br />Autonomous System #2<br />An External Links Advertisement originates for each destination outside<br />The AS, and these advertisements are in turn flooded throughout the AS.<br />An External Links Advertisement is used for externally derived routing<br />Information obtained by another routing protocol such as EGP or BGP.<br />
  7. 7. 7<br />Terminology<br />Autonomous Systems(AS)<br /> Each AS is a group of networks & routers administered by single<br /> authority using a common routing protocol.<br />Interior Gateway Protocol(IGP)<br /> Routers within single AS communicate using one of several dynamic<br /> routing protocols, known generically as an IGP.<br />Exterior Gateway Protocols(EGP)<br /> Communication between routers belonging to different AS requires<br /> additional protocol, so-called EGP.<br />Open Shortest Path First(OSPF)<br /> is an Interior Gateway Protocol(IGP) IP routing protocol.<br />
  8. 8. 8<br />Configurable Metrics<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Status<br />Status<br />Status<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Hop = 1<br />Cost= 10<br />Hop = 1<br />Cost= 10<br />T1<br />T1<br />56Kb<br />Hop = 1<br />Cost= 100<br />B<br />A<br />Using RIP, traffic would be routed over slow 56K link since the hop count<br />Metric is 1. Using OSPF as the IGP, traffic can be routed over faster T-1<br />Link since total cost would be 20.<br />For single destination, there may be separate routing table entries for each<br />Type Of Service. A metric for TOS 0 must always be specified.<br />
  9. 9. 9<br />Network Types<br />OSPF operates over below physical networks :<br />Point-to-point Network A network joining single pair of routers.<br />Broadcast Network A network with more than 2 attached routers, and the ability<br /> to address single physical messages to all of attached routers.<br />Non-broadcast Network A network with more than 2 attached router, but having no<br /> broadcast capability such as X.25 public data network.<br />DR<br />BDR<br />
  10. 10. 10<br />Adjacencies<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Filter%<br />Filter%<br />Filter%<br />Status<br />Forward%<br />Status<br />Forward%<br />Status<br />Forward%<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Full/Half<br />Full/Half<br />Full/Half<br />An “adjacency” is a two-way communication between <br />selected neighboring routers for the purpose of exchanging<br />routing information through link-state advertisements.<br />Router<br />Router<br />Adjacency<br />Router<br />
  11. 11. 11<br />Routing Area<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />30+<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />50<br />10<br />Collision<br />50<br />Collision<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />20<br />20<br />1<br />1<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />5<br />Tx/Rx<br />5<br />5<br />Tx/Rx<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Demo<br />Demo<br />SNMP<br />Demo<br />SNMP<br />Demo<br />Demo<br />Status<br />Filter%<br />SNMP<br />Forward%<br />Filter%<br />Forward%<br />Filter%<br />Filter%<br />SNMP<br />Status<br />Filter%<br />SNMP<br />Forward%<br />Forward%<br />Config<br />Link<br />Config<br />Link<br />Config<br />Link<br />Config<br />Link<br />Forward%<br />Config<br />Link<br />Status<br />Status<br />Status<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Full/Half<br />Full/Half<br />Full/Half<br />Full/Half<br />Full/Half<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Area 2<br />Area 1<br />N9<br />N10<br />Router<br />N1<br />N3<br />AS 200<br />Router<br />Router<br />AS 100<br />Area Border Router<br /> (ABR)<br />N6<br />N7<br />N8<br />N4<br />N2<br />Router<br />Router<br />N5<br />AS 300<br />Note : Each area has its own topological link-state database. All routers within an area contain<br /> Router LSAs & Network LSAs.<br />Router is Autonomous System Boundary Router(ASBR).<br />
  12. 12. 12<br />Routing Area(Con’t)<br />OSPF allows collections of contiguous networks and hosts to be grouped<br />together. This group, along with the routers having interfaces connected<br />to the networks in this group, is called an “area”.<br />A single area limits the boundary for Link-Stat Advertisement(LSA) flooding.<br />the Shortest Path First(SPF) tree is computed on a per-area basis, and any<br />intra-area destinations are derived from the SPF tree.<br />All areas must have at least one route/interface connected to area 0.0.0.0(<br />the backbone area).<br />An Area Border Router(ABR) is an OSPF router having interface connected<br />to multiple areas. ABRs must keep a distinct link-state database for each<br />area, and run the SPF algorithm on distinct database.<br />
  13. 13. 13<br />Routing Area- Backbone Area<br />If an AS is divided into areas, the areas must be connected to each other<br />Via special area called the “Backbone Area”. Backbone consists of those<br />Networks not contained in any area.<br />All ABRs in an AS must belong to the Backbone Area. Backbone area is<br />assigned an area_ID to 0.0.0.0<br />Backbone<br /> Area<br />AS 300<br />Area-1<br />ABR<br />Area-2<br />ABR<br />Area-3<br />ABR<br />
  14. 14. 14<br />Backbone Area(Con’t)<br />An ABR connected to the Backbone executes two copies of OSPF protocol:<br />Operates on the interface connected to local area and accept flooded<br /> advertisements from other routers that are members of the area<br />Executes over the interface that connects to the backbone. This second<br /> copy won’t propagate flooded advertisements from the area across<br /> the backbone. Instead, it sends Summary Link Advertisements over<br /> the backbone so that attached area can learn about backbone reachability.<br />
  15. 15. 15<br />Stub Area<br />OSPF Domain<br />AS 101<br />RIP or <br />IGP<br />Area<br />0.0.0.0<br />Stub<br />Area 51<br />0.0.0.0 Default<br />ASBR<br />When an OSPF area within an AS has a single entry/exit router that<br />is used by all externally addressed traffic, it is possible to block the<br />import of the AS External Link Advertisements into the area :<br /> ~ No LSA type 4 & 5’s<br /> ~ ASBRs are not supported with stub area<br /> ~ Virtual links are not supported in stub area<br /> ~ The ABR must be configured as default router for stub area<br /> ~ The ASBR can be configured to be disabled for an area<br />
  16. 16. 16<br />Virtual Link<br />A virtual link can be configured to allow the connection of an ABR to backbone<br />When the ABR and its are aren’t contiguous to the backbone.<br />In below figure, Area 1 cannot directly learn all inter-area from the other areas<br />Since it lacks a direct connection to the backbone. Area 1 is connected to the<br />Backbone by a virtual link between the ABRs in Area 2. All inter-area routes <br />From the backbone are flooded over virtual link to the ABR in Area 1. The ABR<br />In Area 1 will summarize all intra-area routes for Area 1 over virtual link for<br />Transmission on the backbone.<br />AS 200<br />Area 1<br />Area2<br />ABR<br />Area 4<br />ABR<br />Router<br />Router<br />Router<br />ABR<br />Area 3<br />ABR<br />Router<br />Backbone<br />
  17. 17. 17<br />Virtual Link(Con’t)<br />Virtual Link<br />Area <br />0.0.0.0<br />Area<br />0.0.0.51<br />Area<br />0.0.0.7<br />ABR<br />ABR<br />Any physical arrangement of areas can be logically attached to the <br />Backbone through a virtual link.<br />Virtual links allow summary-LSAs to be tunneled across a non-<br />Backbone area to exchange the routing information.<br />
  18. 18. 18<br />Virtual Link(Con’t)<br />C<br />A<br />D<br />Virtual link<br />Area 51<br />Data<br />Area <br />0.0.0.0<br />B<br />Area<br />0.0.0.7<br />Data<br />Area 52<br />Data<br />Virtual link<br />The exchange of routing information continues to follow via<br />virtual link but the forwarding of data packets does not.<br />A data packets from router C destine for router D would go<br />through routers A & B, but not through Area 0.<br />
  19. 19. 19<br />Area Routing Advantages<br />Routing Area greatly reduce the amount of routing information<br />traffic that must be propagated throughout entire AS<br />Areas allow the development of a hierarchy of routing information,<br />thus protecting each area from external routing information.<br />The area’s information is hidden from routers outside of the area.<br />This “information hiding” technique is important from a security <br />standpoint, since it prohibits other areas from identifying the <br />physical topology of an area.<br />
  20. 20. 20<br />References & Standard<br />II. Terminology<br />OSPF Format<br />IV. OSPF Algorithm<br />
  21. 21. 21<br />IPv4 Format<br />0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 <br />Total Length<br />0<br />Type Of Service<br />LEN<br />VERS<br />Identification<br />Fragment Offset<br />4<br />Flags<br />Protocol= 89<br />Time To live <br /> = 1<br />8<br />Header Checksum<br />Source IP Address<br />C<br />E<br />Destination IP Address<br />10<br />Padding<br />Option<br />14<br />D A T A<br />Total: 20 bytes<br />
  22. 22. 22<br />OSPF Assigned Class D Address<br />Multicast Class D addresses assigned for OSPF :<br />224.0.0.5 All OSPF routers must be capable of transmitting &<br /> receiving packets with this destination IP address<br />224.0.0.6 All OSPF Designated Routers must be capable of<br /> receiving packets with this destination address. This<br /> includes the Backup Designated Router.<br />IP Address MAC <br />224.0.0.5 01005E-000005<br />224.0.0.6 01005E-000006<br />Note : OSPF multicast addresses are used on both point-to-point links & multi-access<br /> networks, but does not use over non-broadcast networks or virtual links.<br /> To ensure that multicast OSPF messages won’t travel multiple hops, their IP TTL<br /> must be set to 1.<br />
  23. 23. 23<br />OSPF Packet Header<br />0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 <br />Packet Length<br />Type<br />0<br />4<br />8<br />C<br />10<br />14<br />Version No.<br />Router ID<br />Area ID<br />AuType<br />Header Checksum<br />Authentication<br />Type Description<br /> 1 Hello<br /> 2 Database Description<br /> 3 Link State Request<br /> 4 Link State Update<br /> 5 Link State Acknowledgment<br />OSPF Packet Header = 24 bytes<br />
  24. 24. 24<br />OSPF Hello Packet<br />Type<br />= 1<br />Hello<br />Packet Length<br />Version No.<br /> Network Mask<br />HelloInterval Option Rtr Pri<br /> RouterDeadInterval<br /> Designated Router<br /> Backup Designated Router <br /> Neighbor<br /> : <br /> : <br />Router ID<br />Area ID<br />Entry 1<br />(24 bytes)<br />Checksum<br />AuType<br />Authentication<br /> Network Mask<br />HolloInterval Option Rtr Pri<br /> RouterDeadInterval<br /> Designated Router<br /> Backup Designated Router<br /> Neighbor<br />D A T A<br />Entry n<br />Note: DR/BDR = 0 means no designated router<br />
  25. 25. 25<br />Hello Message Contents<br />The router’s “Router Priority” used to determine the Designated<br />Router & Backup Designated Router.<br />The hello interval in which the transmitting router sends Hello<br />packets on given network.<br />The interval(in seconds) in which the transmitting router expects<br />to receive Hello packets from a neighbor before determining <br />that the neighbor is down.<br />A list of routers from which Hello packets have been recently<br />received.<br />The router’s current choice fro the Designated Router & Backup<br />Designated Router. A value of zero in these fields indicates that<br />one has not yet been selected.<br />
  26. 26. 26<br />The OSPF Optional Capability<br /> 6 5 4 3 2 1 0<br />- - DC EA N/P MC E -<br />AS-external-LSAs are flooded<br />Whether IP multicast datagrams are forwarded<br /> The handling of Type-7 LSAs<br />The router’s willingness to receive & forward<br />External-attributes-LSAs<br />The router’s handling of demand circuits<br />
  27. 27. 27<br />Designated Router & Backup Designated Router<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />20<br />20<br />20<br />20<br />1<br />1<br />1<br />1<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Demo<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Forward%<br />Filter%<br />Config<br />Link<br />SNMP<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Status<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />Full/Half<br />10 <br />M/ 100 M<br />DR<br />Router<br />Router<br />Router<br />Multi-access Network<br />Router<br />BDR<br />Router<br />X 2X 3X<br />Each router on the network exchanges link-state information(forms an adjacency)<br />Only with the Designated Router(DR) and the Backup Designated Router(BDR).<br />Each neighbor exchanged information with a DR & BDR specified, the number of<br />Exchanges is reduced to O(2n). <br />The router with the highest configured Router Priority is elected DR.<br />The BDR is elected at the same time as the DR. The router with second highest<br />Router Priority is elected the BDR.<br />
  28. 28. 28<br />OSPF Database Description Packet<br />Type<br />= 2<br />Packet Length<br />Version No.<br />Router ID<br />Area ID<br />0<br />4<br />8<br />C<br />10<br />14<br />18<br />Interface MTU Option 0 0 0 0 0 I M MS<br />Checksum<br />AuType<br />DD Sequence number<br />Authentication<br />Authentication<br />An LSA Header<br />D A T A<br />:<br />:<br />:<br />
  29. 29. 29<br />Link State Request Packet<br />Type<br />= 3<br />Packet Length<br />Version No.<br />Router ID<br />Area ID<br />LS Type<br />0<br />4<br />8<br />Checksum<br />AuType<br />Link State ID<br />Advertising Router<br />Authentication<br />:<br />:<br />:<br />D A T A<br />
  30. 30. 30<br />Link State Update Packet<br />Type<br />= 24<br />Packet Length<br />Version No.<br />Router ID<br />Area ID<br /># LSA<br />0<br />4<br />8<br />C<br />10<br />14<br />18<br />Checksum<br />AuType<br />Authentication<br /> LSAs<br />D A T A<br />:<br />:<br />:<br />
  31. 31. 31<br />Link State Acknowledgment Packet<br />Type<br />= 5<br />Packet Length<br />Version No.<br />Router ID<br />Area ID<br />0<br />4<br />8<br />C<br />10<br />14<br />18<br />Checksum<br />AuType<br />An LSA Header<br />Authentication<br />:<br />:<br />:<br />D A T A<br />
  32. 32. 32<br />Forming Adjacency<br />IP-172.16.32.1RID-100.100.100.4<br />IP-172.16.32.2RID-100.100.100.6<br />DownInit<br />Down<br />Hello (Packet 15 & 17)<br />2-WayExStart<br />Hello (Packet 16 & 18)<br />ExStart<br />DB Description (Packet 19 & 21)<br />Exchange<br />Exchange<br />Exchange<br />DB Description (Packet 20)<br />Link State Request (Packet 22)<br />Loading<br />Loading<br />Link State Update (Packet 25)<br />(Adjacency Up)<br />Full<br />Full<br />Full<br />Hello<br />Hello<br />
  33. 33. 33<br />OSPF LSA Header<br />0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 <br />0<br />4<br />8<br />C<br />10<br />LS type<br />Option<br />LS age<br />Link State ID<br />Advertising Router<br />LS sequence number<br />LS Checksum<br />Length<br />Type Description<br /> 1 Router-LSAs<br /> 2 Network-LSAs<br /> 3 Summary-LSAs (IP network)<br /> 4 Summary-LSAs (ASBR)<br /> 5 AS-external-LSAs<br />OSPF LSA Header = 20 bytes<br />
  34. 34. 34<br />Router-LSAs Format<br />LS age<br />Options<br />LS Type= 1<br />Link State ID<br />Advertising Router<br />LS sequence number<br /> 0 V E B 0 No. of Links<br />0<br />4<br />8<br />C<br />10<br />14<br />18<br />Length<br />Checksum<br />Link State ID<br />Link Data<br />D A T A<br />Type # TOS Metric<br />:<br />:<br />Note: V for virtual link;<br /> E for AS boundary router<br /> B for Area Border router.<br /> Each router in an area originates a router-LSA.<br />
  35. 35. 35<br />Router-LSAs Format(Con’t)<br /> Type Description<br /> 1 Point-to-point connection to another router<br /> 2 Connection to a transit network<br /> 3 Connection to a stub network<br /> 4 Virtual link<br />Type Link ID Link Data<br /> 1 Neighboring router’s Router ID Interface’s MIB ifIndex value<br /> 2 IP address of Designated Router DR IP address<br /> 3 IP network / subnet number Network IP address<br /> 4 Neighboring router’s Router ID Network IP address<br />
  36. 36. 36<br />Network-LSAs Format<br />LS age<br />Options<br />LS Type=2<br />0<br />4<br />8<br />C<br />10<br />14<br />18<br />Link State ID<br />Advertising Router<br />LS sequence number<br />Length<br />Checksum<br />Network Mask<br />Attached Router<br />Note: the distance from network to all attached routers is 0. <br /> Network-LSA is originated by the network’s DR.<br />
  37. 37. 37<br />Summary-LSAs(IP network) Format<br />LS age<br />Options<br />LS Type=3<br />Link State ID<br />Advertising Router<br />Network Mask<br />0<br />4<br />8<br />LS sequence number<br />0 metric<br />Length<br />Checksum<br />TOS TOS metric<br />:<br />:<br />:<br />D A T A<br />Note: Link State ID= 0.0.0.0 & Network mask= 0.0.0.0<br /> if default summary route.<br /> Metric is the cost of this route.<br />
  38. 38. 38<br />Summary-LSAs(ASBR) Format<br />LS age<br />Options<br />LS Type=4<br />Link State ID<br />Advertising Router<br />Network Mask<br />0<br />4<br />8<br />LS sequence number<br />0 metric<br />Length<br />Checksum<br />TOS TOS metric<br />:<br />:<br />:<br />D A T A<br />
  39. 39. 39<br />As-external-LSAs Format<br />LS age<br />Options<br />LS Type= 5<br />Link State ID<br />Advertising Router<br />Network Mask<br />0<br />4<br />8<br />C<br />10<br />14<br />LS sequence number<br />E 0 metric<br />Length<br />Checksum<br />Forwarding address<br />External Route Tag<br />D A T A<br />E TOS TOS metric<br />Forwarding address<br />:<br />:<br />:<br />
  40. 40. 40<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Filter%<br />Filter%<br />Filter%<br />Status<br />Forward%<br />Status<br />Forward%<br />Status<br />Forward%<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Full/Half<br />Full/Half<br />Full/Half<br />Shortest Path Tree<br />Network1<br />Router1<br />Network2<br />Cost = 20<br />Router2<br />Network3<br />Cost = 30<br />Router3<br />Network4<br />
  41. 41. 41<br />Link State Database<br />R1 R2 R3<br />(N1-0) (N2-0) (N3-0)<br />(N2-0) (N3-0) (N4-0)<br />(R2-20) (R1-20) (R2-30)<br /> (R3-30)<br />From the Link-State Database, each router builds a shortest path tree<br />using itself as the root.<br />Each node of the tree shows the shortest, or best cost path to<br />the vertex from the root.<br />Each router then build its routing table from the shortest path tree.<br />
  42. 42. 42<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Filter%<br />Filter%<br />Filter%<br />Status<br />Forward%<br />Status<br />Forward%<br />Status<br />Forward%<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Full/Half<br />Full/Half<br />Full/Half<br />Shortest Path Tree & Routing Table<br />Network1<br />R1<br />20<br />Router1<br />R2<br />N2<br />N1<br />30<br />Network2<br />N3<br />Cost = 20<br />Router2<br />R3<br />Network3<br />N4<br />Cost = 30<br />Router3<br />Routing Table for R1<br />Destination Next Hop Metric<br /> N1 Direct 0<br /> N2 Direct 0<br /> N3 R2 20<br /> N4 R2 50<br />Network4<br />
  43. 43. 43<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Filter%<br />Filter%<br />Filter%<br />Status<br />Forward%<br />Status<br />Forward%<br />Status<br />Forward%<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Full/Half<br />Full/Half<br />Full/Half<br />Shortest Path Tree & Routing Table(Con’t)<br />R2<br />Network1<br />Router1<br />20<br />30<br />R1<br />N3<br />N2<br />R3<br />Network2<br />Cost = 20<br />Router2<br />N4<br />N1<br />Network3<br />Cost = 30<br />Routing Table for R2<br />Router3<br />Destination Next Hop Metric<br /> N1 R1 20<br /> N2 Direct 0<br /> N3 Direct 0<br /> N4 R3 30<br />Network4<br />
  44. 44. 44<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-8MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Util%<br />Util%<br />Util%<br />Demo<br />Demo<br />Demo<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Config<br />Link<br />SNMP<br />Filter%<br />Filter%<br />Filter%<br />Status<br />Forward%<br />Status<br />Forward%<br />Status<br />Forward%<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Full/Half<br />Full/Half<br />Full/Half<br />Shortest Path Tree & Routing Table(Con’t)<br />R3<br />Network1<br />Router1<br />30<br />R2<br />20<br />N3<br />N4<br />Network2<br />Cost = 20<br />Router2<br />R1<br />N2<br />N1<br />Network3<br />Cost = 30<br />Routing Table for R3<br />Router3<br />Destination Next Hop Metric<br /> N1 R2 50<br /> N2 R2 30<br /> N3 Direct 0<br /> N4 Direct 0<br />Network4<br />
  45. 45. 45<br />When Router re-calculate SPF tree?<br /><ul><li>When an intra-area route has been added, deleted or modified
  46. 46. When an inter-area route has been added, deleted or modified
  47. 47. When a router has an interface that becomes active in an area
  48. 48. When a router’s virtual link changes
  49. 49. When an external route changes
  50. 50. When a router that was an ASBR is no longer an ASBR</li></li></ul><li>46<br />References & Standard<br />II. Terminology<br />OSPF Format<br />IV. OSPF Algorithm<br />
  51. 51. 47<br />Features of Link-State Algorithm<br />OSPF uses a Link-State Routing Algorithm.<br />All routers maintain identical routing tables.<br />The database of each router describes complete topology of<br />the router’s domain. The router’s domain may be the<br />entire AS, or an area within the AS.<br />Each router uses the database to calculate a set of shortest<br />paths to all destinations. The routing table is built from<br />these calculation.<br />
  52. 52. 48<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />Rate %<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />1 2 3 4 5 6 7 8<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />30+<br />30+<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />90+<br /> 1<br />X 2X 3X 4X 5X 6X 7X 8MDI-X-or-MDI<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />Fast SwitcHub-8mi<br />20<br />70<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />Collision<br />50<br />10<br />50<br />10<br />Collision<br />50<br />Collision<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />5<br />35<br />20<br />20<br />20<br />20<br />20<br />1<br />1<br />1<br />1<br />1<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />100<br />M<br />10<br />5<br />Tx/Rx<br />5<br />5<br />Tx/Rx<br />Tx/Rx<br />5<br />Tx/Rx<br />5<br />Tx/Rx<br />Util%<br />Util%<br />Util%<br />Util%<br />Util%<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Full Duplex<br />PWR<br />1<br />Demo<br />Demo<br />SNMP<br />Demo<br />SNMP<br />Demo<br />Demo<br />Status<br />Filter%<br />SNMP<br />Forward%<br />Filter%<br />Forward%<br />Filter%<br />Filter%<br />SNMP<br />Status<br />Filter%<br />SNMP<br />Forward%<br />Forward%<br />Config<br />Link<br />Config<br />Link<br />Config<br />Link<br />Config<br />Link<br />Forward%<br />Config<br />Link<br />Status<br />Status<br />Status<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Select/Link<br />Diag<br />Diag<br />Diag<br />Diag<br />Diag<br />Full/Half<br />Full/Half<br />Full/Half<br />Full/Half<br />Full/Half<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />10 <br />M/ 100 M<br />Example of Link-State Algorithm<br />Area 2<br />Area 1<br />N9<br />N10<br />ASBR<br />N1<br />N3<br />AS 200<br />Router<br />Router<br />AS 100<br />Area Border Router<br /> (ABR)<br />N6<br />N7<br />N8<br />N4<br />N2<br />Router<br />ASBR<br />N5<br />AS 300<br />
  53. 53. 49<br />Basic Operation of Link-State Algorithm<br />Exchange of Routing Information<br /> - Each router periodically sends out a description of its connections to<br /> its neighbors.<br /> - Routers are neighbors if they are directly connected via a common network.<br /> - A router sends the LSA to each of its neighbors. The LSA includes a listing<br /> of all interfaces & configured “cost” of each link and each configured cost-<br /> TOS pairing.<br />2) Routing Area<br /> - The LSA is flooded throughout the router’s domain. The router’s domain<br /> may be entire AS, or limited area within the AS.<br /> - Areas are configured by assigning an area_ID for each router interface.<br /> If the area_ID is identical for all ports on a router, then the router is <br /> contained in a single area.<br />3) Link-State Database<br /> - Each router in the domain maintains an identical, synchronized copy of a<br /> database composed of this link-state information.<br /> - Router belonging to multiple areas maintain a separate Link_State database<br /> for each area.<br />
  54. 54. 50<br />Basic Operation of Link-State Algorithm(Con’t)<br />4) Shortest Path Tree<br /> - Each router runs an algorithm on the database used to create a shortest-path<br /> tree. A different shortest-path tree is constructed for each TOS support.<br /> - The shortest-path tree contains the shortest path to every router and<br /> every network that other routers can reach. The router performing the<br /> calculation places itself at the root of each tree.<br />5) Routing Table<br /> - The resulting shortest-path trees determine total cost to the destination<br /> network and next hop router. The shortest-path trees are used as the<br /> basis of creating the routing table. A different routing table is created<br /> for each TOS.<br />6) Optional TOS Support<br /> - OSPF allows the network administrator to configure OSPF routers to<br /> calculate/use only single routing table(TOS 0 table).<br /> - A router desiring to calculate/use single table informs its peers by resetting <br /> the TOS-capable bit in the option field of the router’s links advertisement.<br /> If a route cannot be found that uses a non-zero TOS value, the traffic is<br /> forwarded along the TOS 0 route.<br />
  55. 55. 51<br />How to Forward datagrams<br />The forwarding process uses routing tables to route datagrams.<br />The destination network number is extracted from an incoming<br /> datagram.<br />The TOS field is examined for information pointing to <br />The datagram is forwarded towards its final destination.<br /> Datagram having same final destination may be routed along<br /> different paths based on the TOS requested by the source station.<br />
  56. 56. 52<br />Initial Link-State Database Synchronization<br />A pair of routers attempting to become adjacent send a summary of their Link-<br />State databases to one another. This summary is called a <br />“Database Description Packet”.<br />The Database Description Packet consists of a list of abbreviated link-state<br />Advertisements(LSA).<br />Based on the Database Description Packet received from its neighbor, each<br />router builds a list of requests for LSAs, required to update its own database.<br />A router builds this list by checking its link-state database for a copy of each<br />LSA received in the summary. If the router doesn’t have a particular LSA <br />in its link-state database, or determines that its neighbor has a more recent <br />version of A LSA, that LSA is added to the request list.<br />Each router sends this list in a Link-State Request packet to its neighbor.<br />Each router responds to a received Link-State Request packet with a Link-<br />State Update packet containing the requested LSAs. The neighbors become<br />Fully adjacent when they have received all requested LSAs.<br />Once the routers become fully adjacent, they run the SPF algorithm on the data-<br />Base, add OSPF routes to their routing tables, and periodically exchange LSAs.<br />
  57. 57. 53<br />Maintain Link-State Database Synchronization<br />Flooding Procedure<br />When an LSA is flooded, it is passed from a router to an adjacent router until<br />It has been distributed throughout the routing domain.<br />Each router determines, individually, whether the LSA should be passed to<br />An adjacent neighbor. More details are described in Section 13, 13.3 & 13.4 of<br />RFC 2328.<br />Reliable Updates<br />Reliability is accomplished by requiring that both the receipt and transfer of<br />an LSA be acknowledged by adjacent router. In the absence of such an<br />acknowledgment, the source router retransmits the LSA until it is acknowledged.<br /> - Each router originates a router-LSA.<br /> - Area Border routers originate a single summary-LSA for each known inter-<br /> area destination.<br /> - AS Boundary routers originate a single As-external-LSA for each known<br /> AS external destination.<br />(Ten events can cause new instance of an LSA to be originated)<br />
  58. 58. 54<br />Maintain LS Database Synchronization(Con’t)<br />Link-State Age<br />An LSA’s age field is periodically incremented while residing in a router’s link-<br />state database. It is possible for an LSA to reach an age where it is no longer used<br />in the flooding procedure, and must be flushed from the link-state database. If<br />There’s a change in the link-state database, a new shortest-path tree is constructed<br />and the routing table is updated.<br />Link-State Sequence Numbers<br />A common event is for an LSA to be replaced by the receipt of more recent LSA <br />from its adjacent neighbor. Each LSA contains 32-bit sequence number used<br />by OSPF routers to detect old, or duplicate LSAs. A linearly ordered<br />sequence number is used for LSA identification. All routers keep their link-state <br />databases synchronized by ageing LSAs in their database, and updating with<br />new incoming LSAs.<br />

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