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Alcatel-Lucent Routing Protocols. Module 1 — Introduction Module 2 — Static Routing and Default Routes Module 3 — Routing Information Protocol Module 4 – Link-State Protocols Module 5 — Open Shortest Path First Module 6 — Intermediate System–to–Intermediate System

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Alcatel-Lucent Routing Protocols


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    1. Alcatel-Lucent Routing Protocols Module 1— Introduction Module 2 — Static Routing and Default Routes Module 3 — Routing Information Protocol Module 4 – Link-State Protocols Module 5 — Open Shortest Path First Module 6 — Intermediate System–to–Intermediate System Module 7 — Border Gateway Protocol

    2. Alcatel-Lucent Routing Protocols Module 1— Introduction

    3. IP Addressing — Basic Subnetting • Subnetting allows a network to be subdivided into smaller networks with routing between them. • With basic subnetting, each segment uses the same subnet mask. • Potential for wasting IP addresses on links that do not require high client density • Easiest to implement • Required for classful routing protocols • VLSM allows the use of different subnet masks for different parts of the network.

    4. IP Addressing — VLSM • Different subnet masks per network • Routing protocols must advertise the subnet mask with updates • More efficient use of IP addressing than basic subnetting • Requires a good understanding of subnetting • RFC 1878 defines VLSM • Routing protocols that support VLSM are: • RIPv2 • OSPF • IS-IS • BGP

    5. Network Network Network Multicast Host Network Multicast Network Network Host Multicast Host Host Multicast Host Host IP Addressing Review • IP addresses are broken into classes: A, B, C, and D Class A: 255.0.0.0 or /8 Class B: 255.255.0.0 or /16 Class C: 255.255.255.0 or /24 Class D: 255.255.255.255 or /32

    6. Section Objectives • Introduction to IP routing • Review of IP forwarding • Control plane vs. data plane functions • Common layer 3 routing protocols • Distance vector • Link state • Classful and classless addressing • Variable length subnet masking • Classless interdomain routing • Private IP addresses • Network address translation (NAT/PAT)

    7. Source Dest. S D F C S Data 1.1.1.2 2.2.2.2 A B Source Dest. WAN F C S Data 1.1.1.2 2.2.2.2 PPP Source Dest. S D F C S Data 1.1.1.2 2.2.2.2 C D Movement of Data 2.2.2.2 1.1.1.2 (MAC address = A) (MAC address = D) 2.2.2.1 1.1.1.1 (MAC address = C) (MAC address = B) 3.3.3.2 3.3.3.1

    8. Packet Forwarding • When a router receives a packet, it: • Compares the destination IP address of the packet to the FIB • Looks for the longest (most specific) match • If no match is found, the packet is dropped. • If the packet is to be forwarded, the next hop and egress interface must be known. • If a match is found, the packet is sent to the next-hop address via the interface specified in the FIB. • The next-hop is the next router in the path toward the destination. • The egress interface is required for encapsulation.

    9. Common IP Routing Protocols • Legacy routing protocols: • RIP version 1 • RIP version 2 • Modern routing protocols: • OSPF • IS-IS • BGP

    10. Distance Vector Protocols • Distance = How far away • Vector = What direction (interface) • RIPv1, RIPv2, and BGP are distance vector protocols Int 1/1/2 IP – 1.1.1.1 Int 1/1/2 IP – 2.2.2.1 Int 1/1/1 Int 1/1/1 IP – 3.3.3.2 IP – 3.3.3.1 Routing Table: 1.1.1.0 – Direct 1/1/2 3.3.3.0 – Direct 1/1/1 2.2.2.0 – 1 hop via 1/1/1 Routing Table: 2.2.2.0 – Direct 1/1/2 3.3.3.0 – Direct 1/1/1 1.1.1.0 – 1 hop via 1/1/1

    11. Link-State Protocols • Link = An interface • State = Active or inactive interface • OSPF and IS-IS are link-state protocols • More complex than distance vector • Faster convergence • Triggered updates • Three databases: • Adjacency — Neighbor database • Topology — Link-state database • Routing — Forwarding database

    12. Link-State Protocols (continued) • Adjacency database • Link-state database • Forwarding database RTR - C Network 2.2.2.0/24 1/1/2 RTR - A RTR - B 1/1/1 Adjacency Database RTR-B – on 1/1/1 RTR-C – on 1/1/2 2.2.2.0/24 – via 1/1/1 cost 20 – via 1/1/2 cost 40 LSDB Routing Table: 2.2.2.0/24 – via 1/1/1

    13. OSPF RIB RIP RIB RTM Routing Table Management • Each routing protocol populates its routes into its RIB. • Each protocol independently selects its best routes based on the lowest metric. • The best routes from each protocol are sent to the RTM.

    14. FIB RIP RIB OSPF RIB BGP RIB Preference • The RTM may have a best route from multiple protocols. • Selection is based on lowest preference value. • The RTM sends its best route to the FIB. • This route is the active route and is used for forwarding. OSPF RTM OSPF BGP

    15. Default Preference Table

    16. IP Addressing — Classful and Classless Classful 12.1.0.0/16 10.1.1.0/24 10.0.0.0 10.1.1.0 Routing Table: 12.1.0.0 – direct 1/1/2 192.1.1.0 – direct 1/1/1 10.0.0.0 – 1 hop via 1/1/1 10.1.2.0/24 192.1.1.0/24 Classless 10.1.1.0/24 10.1.2.0/24 12.1.0.0/16 10.1.1.0/24 10.1.1.0/24 Routing Table: 12.1.0.0/16 – direct 1/1/2 192.1.1.0 /24 – direct 1/1/1 10.1.1.0/24 – 2 hops via 1/1/1 10.1.2.0/24 – 1 hop via 1/1/1 10.1.2.0/24 192.1.1.0/24

    17. IP Addressing — VLSM • Different subnet masks per network • Routing protocols must advertise the subnet mask with updates. • High-order bits are not reusable. • Routing decisions are made based on the longest match. • A more efficient use of IP addressing than basic subnetting • Requires a good understanding of subnetting • RFC 1878 defines VLSM. • Routing protocols that support VLSM are: • RIPv2 • OSPF • IS-IS • BGP

    18. IP Addressing — VLSM Example 172.16.0.0 – 10101100.00010000.00000000.00000000 – Reserved for WAN segments 172.16.1.0 – 10101100.00010000.00000001.hhhhhhhh – First Ethernet segment …. 172.16.254.0 – 10101100.00010000.11111110.hhhhhhhh – Last Ethernet segment 255.255.255.0 – 11111111.11111111.11111111.00000000 – Ethernet mask 172.16.0.4 – 10101100.00010000.00000000.000001 hh – First WAN segment 172.16.0.252 – 10101100.00010000.00000000.111111 hh – Last WAN segment 255.255.255.252 – 11111111.11111111.11111111.111111 00 – WAN mask

    19. Alcatel-Lucent Routing Protocols Module 2 — Static Routing and Default Routes

    20. Routers need to know where networks are located and how best to access them. This can be accomplished statically with administrative commands. What a Router Needs to Know 1.1.1.0/24 2.2.2.0/24 1.1.1.1 2.2.2.1 R1 R2 3.3.3.0/30 3.3.3.2 3.3.3.1 Routing Table: 1.1.1.0/24 – Direct 3.3.3.0/30 – Direct 2.2.2.0/24 – static via 3.3.3.2 Routing Table: 2.2.2.0/24 – Direct 3.3.3.0/30 – Direct 1.1.1.0/24 – static via 3.3.3.1

    21. Static Routes — Basic Static Routes static-route 0.0.0.0/0 next-hop 3.3.3.1 2.2.2.0/24 R1 R2 Corporate Headquarters 3.3.3.2 3.3.3.1 static-route 2.2.2.0/24 next-hop 3.3.3.2 • Configuration of static routes between stub networks and corporate locations

    22. Static Routes — Configuration Example 2.2.2.0/24 R1 R2 Corporate Headquarters 3.3.3.2 3.3.3.1 config>router> static-route 2.2.2.0/24 next-hop 3.3.3.2 config>router> static-route 0.0.0.0/0 next-hop 3.3.3.1

    23. Default Routes — Basic Default Route 2.2.2.0/24 R1 R2 Corporate Headquarters 3.3.3.1 3.3.3.2 R2# show router route-table ============================================================================ Route Table ============================================================================ Dest Address Next Hop Type Protocol Age Metric Pref ---------------------------------------------------------------------------- 3.3.3.0/24 System Local Local 01d02h 0 0 2.2.2.0/24 System Local Local 08d03h 0 0 0.0.0.0/0 3.3.3.1 Remote Static 01d02h 1 5 ----------------------------------------------------------------------------

    24. Static Routes — Floating Static Routes Backup 2.2.2.0/24 1.1.1.2 1.1.1.1 R1 R2 Corporate Headquarters Primary path 3.3.3.2 3.3.3.1 config>router> static-route 2.2.2.0/24 next-hop 3.3.3.2 config>router> static-route 2.2.2.0/24 next-hop 1.1.1.2 preference 200 • Configuration of a floating static route between stub networks and corporate locations

    25. Static Route Verification — Show Command • The command below shows static routes configured in the routing table. Context: show>router> Syntax: static-route [[ip-prefix [/mask]] | [preference preference] | [next-hop ip-addr] | tag tag Example: R1# show router route-table protocol static ============================================================================== Route Table (Router: Base) ============================================================================== Dest Address Next Hop Type Proto Age Metric Pref ------------------------------------------------------------------------------- 2.2.2.0/24 3.3.3.2 Remote Static 00h01m34s 1 5 2.2.2.0/24 1.1.1.2 Remote Static 00h01m15s 1 200 ------------------------------------------------------------------------------- No. of Routes: 1 ==============================================================================

    26. Static Route Verification — Show Command (continued) 2.2.2.0/24 R1 R2 Corporate Headquarters 3.3.3.2 3.3.3.1 R1# show router route-table 2.2.2.0/24 ============================================================================== Route Table (Router: Base) =============================================================================== Dest Address Next Hop Type Proto Age Metric Pref ------------------------------------------------------------------------------- 2.2.2.0/24 3.3.3.2 Remote Static 00h02m54s 1 5 ------------------------------------------------------------------------------- No. of Routes: 1 ==============================================================================

    27. Static Routes — Ping Command 2.2.2.2 2.2.2.0/24 3.3.3.2 3.3.3.1 Corporate Headquarters R1# ping 2.2.2.2 detail PING 2.2.2.2: 56 data bytes 64 bytes from 2.2.2.2 via fei0: icmp_seq=0 ttl=64 time=0.000 ms. 64 bytes from 2.2.2.2 via fei0: icmp_seq=1 ttl=64 time=0.000 ms. 64 bytes from 2.2.2.2 via fei0: icmp_seq=2 ttl=64 time=0.000 ms. 64 bytes from 2.2.2.2 via fei0: icmp_seq=3 ttl=64 time=0.000 ms. 64 bytes from 2.2.2.2 via fei0: icmp_seq=4 ttl=64 time=0.000 ms. ---- 2.2.2.2 PING Statistics ---- 5 packets transmitted, 5 packets received, 0.00% packet loss round-trip min/avg/max/stddev = 0.000/0.000/0.000/0.000 ms R1#

    28. Static Routes — Traceroute Command 2.2.2.2 2.2.2.0/24 R1 R2 Corporate Headquarters 3.3.3.2 3.3.3.1 R1# traceroute 2.2.2.2 traceroute to 2.2.2.2, 30 hops max, 40 byte packets 1 3.3.3.2 <10 ms <10 ms <10 ms 2 2.2.2.2 <10 ms <10 ms <10 ms

    29. Learning Assessment • Do static routes have a higher or lower preference value than dynamic routes? • What is the command syntax to create a static route in the 7750 SR? • A router has a default route, a static route to 10.10.8.0/24, and a route to 10.8.0.0/14 learned from RIP. Which route is used for a packet with destination address 10.10.10.10?

    30. Alcatel-Lucent Routing Protocols Module 3 — Routing Information Protocol

    31. Section Objectives • Distance vector overview • Split horizon • Route poisoning • Poison reverse • Hold-down timers

    32. Distance Vector Overview • Routers send periodic updates to physically adjacent neighbors • Updates contain the distance (how far) and vectors (direction) for networks RTR-B RTR-A 100 Mb/s 1 Gb/s 1 Gb/s 1 Gb/s RTR-C RTR-D

    33. Distance Vector Overview (continued) • The router processes and compares the information contained in the routing update received with what is in its routing table. Process and compare with routing table Periodic update Sent to neighbor routers Update from neighbor

    34. Split Horizon • An adjacent router does not advertise networks back to the source of the network information. 10.0.0.0 10.0.0.0 – 2 hops 10.0.0.0 – 1 hop X RTR-A RTR-B RTR-C Routing Table: 10.0.0.0 – 2 hops via 1/1/1 Routing Table: 10.0.0.0 – 1 hop via 1/1/1 Routing Table: 10.0.0.0 – 0 hops via 1/1/1

    35. Route Poisoning • When a network goes away, the sourcing router sets the hop value to infinity and sends a triggered update to its neighbors. 10.0.0.0 10.0.0.0 – 16 hops 10.0.0.0 – 16 hops X RTR-A RTR-B RTR-C Routing Table: 10.0.0.0 – 16 hops via 1/1/1 Routing Table: 10.0.0.0 – 16 hops via 1/1/1 Routing Table: 10.0.0.0 – 16 hops via 1/1/1 Routing Table: 10.0.0.0 – 2 hops via 1/1/1 Routing Table: 10.0.0.0 – 1 hop via 1/1/1 Routing Table: 10.0.0.0 – 0 hops via 1/1/1

    36. Poison Reverse • Poison reverse is the only time that split horizon is violated. This helps to avoid loop creation when a network fails. 10.0.0.0 — 16 hops Poison reverse 10.0.0.0 — 16 hops Poison reverse 10.0.0.0 — 16 hops 10.0.0.0 — 16 hops 10.0.0.0 X RTR-A RTR-B RTR-C Routing Table: 10.0.0.0 — 16 hops via 1/1/1 Routing Table: 10.0.0.0 — 16 hops via 1/1/1 Routing Table: 10.0.0.0 — 16 hops via 1/1/1 Routing Table: 10.0.0.0 — 2 hops via 1/1/1 Routing Table: 10.0.0.0 — 1 hop via 1/1/1 Routing Table: 10.0.0.0 — 0 hops via 1/1/1

    37. Hold-Down Timers • Hold-down timers provide time for other routers to converge and reduce loops from being created when a network fails. 10.0.0.0 10.0.0.0 — 16 hops 10.0.0.0 — 16 hops X RTR-A RTR-B RTR-C Routing Table: 10.0.0.0 — 1 hop via 1/1/1 Routing Table: 10.0.0.0 — 0 hops via 1/1/1 Routing Table: 10.0.0.0 – 16 hop – Via 1/1/1 Routing Table: 10.0.0.0 – 16 hop – Via 1/1/0 Routing Table: 10.0.0.0 – 16 hop – Via 1/1/1 Routing Table: 10.0.0.0 — 2 hops via 1/1/1 Hold-down timer 180 seconds Hold-down timer 180 seconds Hold-down timer 180 seconds

    38. Combined Loop Avoidance Techniques • Combined, all attributes function as follows: 10.0.0.0 — 16 hops Poison reverse 10.0.0.0 — 16 hops Poison reverse 10.0.0.0 — 16 hops 10.0.0.0 — 16 hops 10.0.0.0 X RTR-A RTR-B RTR-C Routing Table: 10.0.0.0 — 1 hop via 1/1/1 Routing Table: 10.0.0.0 — 0 hops via 1/1/1 Routing Table: 10.0.0.0 – 16 hop – Via 1/1/0 Routing Table: 10.0.0.0 – 16 hop – Via 1/1/1 Routing Table: 10.0.0.0 – 16 hop – Via 1/1/0 Routing Table: 10.0.0.0 — 2 hops via 1/1/1 Hold-down timer 180 seconds Hold-down timer 180 seconds Hold-down timer 180 seconds

    39. RIP Overview • Uses a hop-count metric • Sends updates of the routing table to neighbors • Maximum of 15 hops; 16 hops equals infinity • 30-second advertisement interval by default • Authentication is available in RIPv2 • VLSM is supported by RIPv2

    40. RIP Overview (continued) 100 Mb/s RTR-B RTR-A 1 Gb/s 1 Gb/s 1 Gb/s RTR-C RTR-D

    41. RIPv1 vs. RIPv2

    42. RIP – Major Component Configuration • Router • Interface (assumed to be already complete) • Route policies • RIP • Group • Neighbor

    43. Alcatel-Lucent Routing Protocols Module 4 – Link-State Protocols

    44. Distance Vector vs. Link State Distance vector Link state • Views the network topology from the neighbor’s perspective • Adds distance vectors from router to router • Frequent, periodic updates: slow convergence • Passes copies of the routing table to neighbor routers • Has a common view of the entire network topology • Calculates the shortest path to other routers • Event-triggered updates: faster convergence • Passes link-state routing updates to other routers

    45. Link State Overview Link state-driven updates, periodic hellos Classless routing protocol Sends subnet mask in update Supports VLSM, CIDR, and manual route summarization Supports authentication Maintains multiple databases Sends updates using multicast addressing

    46. Link State Overview (continued) • Link = An interface • State = Active or inactive interface, cost • IS-IS and OSPF are link-state protocols • More complex than distance vector • Faster convergence • Triggered updates • Three databases: • Adjacency – neighbor database • Topology – link-state database • Routing – forwarding database

    47. Link State Overview (continued) • Adjacency database • Link-state database • Forwarding database RTR - C Network 2.2.2.0/24 1/1/1 1/1/2 RTR - A RTR - B Adjacency database RTR-B – on 1/1/2 RTR-C – on 1/1/1 2.2.2.0/24 via 1/1/2 cost 20 via 1/1/1 cost 40 LSDB Routing table 2.2.2.0/24 via 1/1/2

    48. Link State Overview (continued) 2.2.2.0/30 10.0.0.0/8 .1 .2 .2 Step 1 – Updates received from peers .1 3.3.3.0/30 Routing table 10.0.0.0/8 via 2.2.2.1 … Step 2 – Topology database created Step 3 – SPF algorithm determines the best path to destination networks 10.0.0.0/8 Via 2.2.2.1 Cost 10 Via 3.3.3.1 Cost 20 … Step 4 – Routing table created 10.0.0.0/8 Via 2.2.2.1 Cost 10 – BEST Via 3.3.3.1 Cost 20 …

    49. R3 Link-state packet R1 Link-state packet R2 Link-state packet B C A 10 10 10 C D B 10 10 10 Exchanging Link-State Information R1 R2 R3 B C D A Routers exchange LSPs with each other. Each begins with directly connected networks for which it has direct link-state information.

    50. R3 Link-state packet R3 Link-state packet R2 Link-state packet R1 Link-state packet R2 Link-state packet R2 Link-state packet R1 Link-state packet R1 Link-state packet R3 Link-state packet C B C A A B C A B 10 10 10 10 10 10 10 10 10 B D B C C D D B C 10 10 10 10 10 10 10 10 10 Building a Topological Database R1 R2 R3 B C D A