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Transcript
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 Alcatel-Lucent Routing Protocols Module 1 — Introduction 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. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 3 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 4 All rights reserved © 2006-2007 Alcatel-Lucent IP Addressing Review IP addresses are broken into classes: A, B, C, and D Class A: 255.0.0.0 or /8 Network Host Host Host Class B: 255.255.0.0 or /16 Network Network Host Host Class C: 255.255.255.0 or /24 Network Network Network Host Class D: 255.255.255.255 or /32 Multicast Multicast Multicast Multicast Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 5 All rights reserved © 2006-2007 Alcatel-Lucent 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) Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 6 All rights reserved © 2006-2007 Alcatel-Lucent Movement of Data 1.1.1.2 (MAC address = A) 2.2.2.2 (MAC address = D) 1.1.1.1 (MAC address = B) 2.2.2.1 (MAC address = C) 3.3.3.2 3.3.3.1 Source Dest. S D 1.1.1.2 2.2.2.2 A B F C Data S Source Dest. WAN 1.1.1.2 2.2.2.2 PPP F C Data S Source Dest. S D 1.1.1.2 2.2.2.2 C D F C Data S Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 7 All rights reserved © 2006-2007 Alcatel-Lucent 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. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 8 All rights reserved © 2006-2007 Alcatel-Lucent Common IP Routing Protocols Legacy routing protocols: RIP version 1 RIP version 2 Modern routing protocols: OSPF IS-IS BGP Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 9 All rights reserved © 2006-2007 Alcatel-Lucent Distance Vector Protocols Distance = How far away Vector = What direction (interface) RIPv1, RIPv2, and BGP are distance vector protocols Int 1/1/2 Int 1/1/2 IP – 1.1.1.1 IP – 2.2.2.1 Int 1/1/1 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 Alcatel-Lucent Interior Routing Protocols and High Availability Int 1/1/1 IP – 3.3.3.2 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 Module 0 | 10 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 11 All rights reserved © 2006-2007 Alcatel-Lucent Link-State Protocols (continued) Adjacency database Link-state database Forwarding database RTR - C Network 1/1/2 2.2.2.0/24 RTR - A RTR - B 1/1/1 Adjacency Database RTR-B – on 1/1/1 RTR-C – on 1/1/2 LSDB 2.2.2.0/24 – via 1/1/1 cost 20 – via 1/1/2 cost 40 Alcatel-Lucent Interior Routing Protocols and High Availability Routing Table: 2.2.2.0/24 – via 1/1/1 Module 0 | 12 All rights reserved © 2006-2007 Alcatel-Lucent 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. OSPF RIP RIB Alcatel-Lucent Interior Routing Protocols and High Availability RIB RTM Module 0 | 13 All rights reserved © 2006-2007 Alcatel-Lucent 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. RIP RIB OSPF OSPF RIB RTM FIB BGP OSPF BGP RIB Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 14 All rights reserved © 2006-2007 Alcatel-Lucent Default Preference Table Route type Direct attached Static OSPF internal IS-IS Level 1 internal IS-IS Level 2 internal RIP OSPF external IS-IS Level 1 external IS-IS Level 2 external BGP Alcatel-Lucent Interior Routing Protocols and High Availability Preference 0 5 10 15 18 100 150 160 165 170 Configurable No Yes Yes Yes Yes Yes Yes Yes Yes Yes Module 0 | 15 All rights reserved © 2006-2007 Alcatel-Lucent IP Addressing — Classful and Classless Classful 10.1.1.0/24 10.0.0.0 10.1.1.0 10.1.2.0/24 12.1.0.0/16 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 1/1/1 192.1.1.0/24 Classless 10.1.1.0/24 10.1.1.0/24 10.1.1.0/24 10.1.2.0/24 Alcatel-Lucent Interior Routing Protocols and High Availability 10.1.2.0/24 192.1.1.0/24 12.1.0.0/16 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 Module 0 | 16 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 17 All rights reserved © 2006-2007 Alcatel-Lucent IP Addressing — VLSM Example 172.16.0.0 – 172.16.1.0 – …. 172.16.254.0 – 255.255.255.0 – 10101100.00010000.00000000.00000000 – Reserved for WAN segments 10101100.00010000.00000001.hhhhhhhh – First Ethernet segment 172.16.0.4 – 172.16.0.252 – 255.255.255.252 – 10101100.00010000.00000000.000001 hh – First WAN segment 10101100.00010000.00000000.111111 hh – Last WAN segment 11111111.11111111.11111111.111111 00 – WAN mask 10101100.00010000.11111110.hhhhhhhh – Last Ethernet segment 11111111.11111111.11111111.00000000 – Ethernet mask Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 18 All rights reserved © 2006-2007 Alcatel-Lucent Alcatel-Lucent Routing Protocols Module 2 — Static Routing and Default Routes What a Router Needs to Know 1.1.1.0/24 1.1.1.1 2.2.2.0/24 R1 3.3.3.0/30 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 2.2.2.1 R2 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 • Routers need to know where networks are located and how best to access them. • This can be accomplished statically with administrative commands. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 20 All rights reserved © 2006-2007 Alcatel-Lucent Static Routes — Basic Static Routes static-route 0.0.0.0/0 next-hop 3.3.3.1 R1 Corporate Headquarters 3.3.3.1 2.2.2.0/24 R2 3.3.3.2 static-route 2.2.2.0/24 next-hop 3.3.3.2 • Configuration of static routes between stub networks and corporate locations Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 21 All rights reserved © 2006-2007 Alcatel-Lucent Static Routes — Configuration Example 2.2.2.0/24 Corporate Headquarters R1 3.3.3.1 R2 3.3.3.2 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 22 All rights reserved © 2006-2007 Alcatel-Lucent 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 3.3.3.1 Remote Static 01d02h 1 5 ---------------------------------------------------------------------------- Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 23 0 All rights reserved © 2006-2007 Alcatel-Lucent Static Routes — Floating Static Routes Backup 2.2.2.0/24 1.1.1.2 1.1.1.1 R1 Corporate R2 Primary path Headquarters 3.3.3.1 3.3.3.2 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 24 All rights reserved © 2006-2007 Alcatel-Lucent 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 ============================================================================== Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 25 All rights reserved © 2006-2007 Alcatel-Lucent Static Route Verification — Show Command (continued) 2.2.2.0/24 Corporate Headquarters R1 3.3.3.1 R2 3.3.3.2 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 ============================================================================== Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 26 All rights reserved © 2006-2007 Alcatel-Lucent Static Routes — Ping Command 2.2.2.2 2.2.2.0/24 Corporate 3.3.3.1 3.3.3.2 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# Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 27 All rights reserved © 2006-2007 Alcatel-Lucent Static Routes — Traceroute Command 2.2.2.2 2.2.2.0/24 Corporate Headquarters R1 R2 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 28 All rights reserved © 2006-2007 Alcatel-Lucent Learning Assessment 1. Do static routes have a higher or lower preference value than dynamic routes? 2. What is the command syntax to create a static route in the 7750 SR? 3. 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? Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 29 All rights reserved © 2006-2007 Alcatel-Lucent Alcatel-Lucent Routing Protocols Module 3 — Routing Information Protocol Section Objectives Distance vector overview Split horizon Route poisoning Poison reverse Hold-down timers Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 31 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability RTR-D Module 0 | 32 All rights reserved © 2006-2007 Alcatel-Lucent 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 Update from neighbor Alcatel-Lucent Interior Routing Protocols and High Availability Sent to neighbor routers Module 0 | 33 All rights reserved © 2006-2007 Alcatel-Lucent Split Horizon An adjacent router does not advertise networks back to the source of the network information. 10.0.0.0 – 2 hops RTR-A Routing Table: 10.0.0.0 – 2 hops via 1/1/1 Alcatel-Lucent Interior Routing Protocols and High Availability 10.0.0.0 – 1 hop RTR-B X 10.0.0.0 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 Module 0 | 34 All rights reserved © 2006-2007 Alcatel-Lucent 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 – 16 hops 10.0.0.0 – 16 hops 10.0.0.0 X RTR-A Routing Table: 10.0.0.0 – 16 hops via 1/1/1 Routing Table: 10.0.0.0 – 2 hops via 1/1/1 Alcatel-Lucent Interior Routing Protocols and High Availability RTR-B RTR-C Routing Table: 10.0.0.0 – 16 hops via 1/1/1 Routing Table: 10.0.0.0 – 1 hop via 1/1/1 Routing Table: 10.0.0.0 – 16 hops via 1/1/1 Routing Table: 10.0.0.0 – 0 hops via 1/1/1 Module 0 | 35 All rights reserved © 2006-2007 Alcatel-Lucent 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 10.0.0.0 — 16 hops Poison reverse Poison reverse 10.0.0.0 — 16 hops 10.0.0.0 — 16 hops 10.0.0.0 X RTR-A Routing Table: 10.0.0.0 — 16 hops via 1/1/1 Routing Table: 10.0.0.0 — 2 hops via 1/1/1 Alcatel-Lucent Interior Routing Protocols and High Availability RTR-B RTR-C Routing Table: 10.0.0.0 — 16 hops via 1/1/1 Routing Table: 10.0.0.0 — 1 hop via 1/1/1 Routing Table: 10.0.0.0 — 16 hops via 1/1/1 Routing Table: 10.0.0.0 — 0 hops via 1/1/1 Module 0 | 36 All rights reserved © 2006-2007 Alcatel-Lucent 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 — 16 hops 10.0.0.0 — 16 hops 10.0.0.0 X RTR-A RTR-B RTR-C Routing Table: 10.0.0.0 162 hop 10.0.0.0–— hops– Via via 1/1/1 Routing Table: 10.0.0.0– — hop– 10.0.0.0 161hop via 1/1/1 Via 1/1/0 Hold-down timer 180 seconds Hold-down timer 180 seconds Alcatel-Lucent Interior Routing Protocols and High Availability Routing Table: 10.0.0.0–— hops– 10.0.0.0 160 hop via 1/1/1 Via 1/1/1 Module 0 | Hold-down timer 180 seconds 37 All rights reserved © 2006-2007 Alcatel-Lucent Combined Loop Avoidance Techniques Combined, all attributes function as follows: 10.0.0.0 — 16 hops 10.0.0.0 — 16 hops Poison reverse 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: 10.0.0.0 162 hop 10.0.0.0–— hops– Via 1/1/0 via 1/1/1 Routing Table: 10.0.0.0– — hop– 10.0.0.0 161hop via 1/1/1 Via 1/1/1 Routing Table: 10.0.0.0–—160 hop hops– 10.0.0.0 via 1/1/1 Via 1/1/0 Hold-down timer 180 seconds Hold-down timer 180 seconds Hold-down timer 180 seconds Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 38 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 39 All rights reserved © 2006-2007 Alcatel-Lucent RIP Overview (continued) 100 Mb/s RTR-A RTR-B 1 Gb/s 1 Gb/s RTR-C Alcatel-Lucent Interior Routing Protocols and High Availability 1 Gb/s RTR-D Module 0 | 40 All rights reserved © 2006-2007 Alcatel-Lucent RIPv1 vs. RIPv2 RIPv1 RIPv2 Defined in RFC 1058 Defined in RFCs 1721, 1722, and 2453 Classful routing protocol Classless routing protocol No subnet mask in updates Sends subnet mask in updates Does not support VLSM Supports VLSM and CIDR No manual route summarization Manual route summarization Does not support authentication Supports authentication Broadcast updates Multicast or broadcast updates Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 41 All rights reserved © 2006-2007 Alcatel-Lucent RIP – Major Component Configuration Router Interface (assumed to be already complete) Route policies RIP Group Neighbor Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 42 All rights reserved © 2006-2007 Alcatel-Lucent Alcatel-Lucent Routing Protocols Module 4 – Link-State Protocols Distance Vector vs. Link State Distance vector •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 Alcatel-Lucent Interior Routing Protocols and High Availability Link state •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 Module 0 | 44 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 45 All rights reserved © 2006-2007 Alcatel-Lucent 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 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 46 All rights reserved © 2006-2007 Alcatel-Lucent Link State Overview (continued) Adjacency database Link-state database Forwarding database RTR - C Network 1/1/1 RTR - A 2.2.2.0/24 1/1/2 Adjacency database RTR-B – on 1/1/2 RTR-C – on 1/1/1 Alcatel-Lucent Interior Routing Protocols and High Availability RTR - B LSDB 2.2.2.0/24 via 1/1/2 cost 20 via 1/1/1 cost 40 Routing table 2.2.2.0/24 via 1/1/2 Module 0 | 47 All rights reserved © 2006-2007 Alcatel-Lucent Link State Overview (continued) 2.2.2.0/30 .1 10.0.0.0/8 .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 10.0.0.0/8 Via 2.2.2.1 Cost 10 Via 3.3.3.1 Cost 20 … Alcatel-Lucent Interior Routing Protocols and High Availability Step 3 – SPF algorithm determines the best path to destination networks 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 … Module 0 | 48 All rights reserved © 2006-2007 Alcatel-Lucent Exchanging Link-State Information R1 A R2 B R1 Link-state packet R3 C R2 Link-state packet D R3 Link-state packet A 10 B 10 C 10 B 10 C 10 D 10 Routers exchange LSPs with each other. Each begins with directly connected networks for which it has direct link-state information. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 49 All rights reserved © 2006-2007 Alcatel-Lucent Building a Topological Database R1 A R2 B R1 Link-state packet R3 C R1 Link-state packet D R1 Link-state packet A 10 A 10 A 10 B 10 B 10 B 10 R2 Link-state packet R2 Link-state packet R2 Link-state packet B 10 B 10 B 10 C 10 C 10 C 10 R3 Link-state packet R3 Link-state packet R3 Link-state packet C 10 C 10 C 10 D 10 D 10 D 10 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 50 All rights reserved © 2006-2007 Alcatel-Lucent Calculating the SPF Tree and Populating the Routing Table R1 A R2 B R3 C D R1 Link-state packet A 10 B 10 SPF 1 R2 Link-state packet B 10 C 10 R3 Link-state packet C 10 D 10 Alcatel-Lucent Interior Routing Protocols and High Availability 2 SPF tree 3 R1 Routing table Module 0 | 51 All rights reserved © 2006-2007 Alcatel-Lucent SPF Algorithm R1 LSDB R3 10 10.0.0.0/8 (net1) 100 R1 5 R1, R1, R2, R2, R3, R3, R3, R2, 5 R3, 10 R1, 5 R3, 100 R1, 10 R2, 100 net1, 0 R2 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 52 All rights reserved © 2006-2007 Alcatel-Lucent SPF Algorithm (continued) Step R3 10 10.0.0.0/8 (net1) 100 Candidate Cost to root 1 — — R1, R1, 0 2 R1, R2, 5 R1, R3, 10 5 10 R1, R1, 0 3 R1, R3, 10 10 R1, R1, 0 R1, R2, 5 4 R1, R3, 10 R2, R3, 100 10 105 R1, R1, 0 R1, R2, 5 5 R3, net1, 0 10 6 — — R1, R1, R1, R1, R1, R1, R3, R1 5 R2 Alcatel-Lucent Interior Routing Protocols and High Availability SPF tree Module 0 | 53 R1, 0 R2, 5 R3, 10 R1, 0 R2, 5 R3, 10 net1, 0 All rights reserved © 2006-2007 Alcatel-Lucent Link State – Topology Change Link-state updates are driven by topology changes. Run SPF Update routing table Topology change Link-state information Alcatel-Lucent Interior Routing Protocols and High Availability Run SPF Update routing table Run SPF Update routing table Module 0 | 54 All rights reserved © 2006-2007 Alcatel-Lucent Sequence Numbers Sequence numbers must be included in the link-state information. Without sequence numbers, the link-state information could be flooded indefinitely. The sequence number remains the same, router-to-router, during the flooding process. In a link-state environment, routers use the sequence numbers for the following decisions when they receive linkstate updates: If the sequence number is lower than the one in the database, the link-state information is discarded. If the sequence number is the same as the one in the database, an ACK is sent. The link-state information is then discarded. If the sequence number is higher, the link-state information is populated in the topological database, an ACK is sent, and the link-state information is forwarded to its neighbors. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 55 All rights reserved © 2006-2007 Alcatel-Lucent Sequence Numbers (continued) A R1 B R2 R3 C D R1 Link-state packet R1 Link-state packet R1 Link-state packet Seq=2 Seq=1 Seq=1 A R1 B R2 R3 C D R1 Link-state packet R1 Link-state packet R1 Link-state packet Seq=2 Seq=2 Seq=1 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 56 All rights reserved © 2006-2007 Alcatel-Lucent Sequence Numbers (continued) R1 receives 2 copies of the link-state information for network Z. — R1 must decide what to do with the second copy of the linkstate information it receives. R1 B R2 Cost 10 R3 C Cost 10 Cost 10 A Cost 10 F R6 Cost 20 Alcatel-Lucent Interior Routing Protocols and High Availability D E Z Cost 20 R5 R4 Module 0 | 57 All rights reserved © 2006-2007 Alcatel-Lucent Link-State Information Aging Link-state information includes an age field. The age of newly created link-state information is set to 0 for OSPF and 1200 for IS-IS. It is incremented by every hop during the flooding procedure for OSPF and is decremented for IS-IS. The link-state age is also incremented for OSPF and decremented for IS-IS as it is held in the topological database. Maximum age When the link-state information reaches its maximum age, it is no longer used for routing. The link-state information is flooded to the neighbors with the maximum age, and the linkstate information is removed from the topological database. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 58 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS – Packet Processing A router deals with topology changes as follows: LSU/LSA Is entry in Yes LSDB? Ignore same? No No Add to LSDB Send ACK Yes Sequence No. Yes Is sequence number higher than one in LSDB? No Flood LSA Send LSU back with newer information Run SPF End Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 59 All rights reserved © 2006-2007 Alcatel-Lucent Hierarchy in Link-State Networks Scalability issues exist for link-state networks: The size of the link-state database increases exponentially with the size of the network. The complexity of the SPF calculation also increases exponentially. A topology change requires complete recalculation of the forwarding table on every router. Hierarchy allows a large routing domain to be split into several smaller routing domains. IS-IS and OSPF both implement hierarchy but use different techniques. Hierarchy results in suboptimal routing. Hierarchy is less common than in the past due to the increased capacity of routers. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 60 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS – Hierarchical View Integrated IS-IS Network L1 L2 Area 2 L1/L2 L1 L1/L2 Area 3 L1/L2 L1 Area 1 Alcatel-Lucent Interior Routing Protocols and High Availability L1 L2 L1/L2 Backbone (Level 2) links Level 1 links Level 1 Level 2 Level 1/Level 2 Module 0 | 61 All rights reserved © 2006-2007 Alcatel-Lucent OSPF – Hierarchical View (continued) OSPF Hierarchical Routing Area 0.0.0.0 Area 0.0.0.1 Alcatel-Lucent Interior Routing Protocols and High Availability Area 0.0.0.2 Module 0 | 62 All rights reserved © 2006-2007 Alcatel-Lucent Alcatel-Lucent Routing Protocols Module 5 — Open Shortest Path First OSPF — RFC History 1987 OSPF workgroup formed OSPF v1 RFC 1131 defined OSPF v2 RFC 1247 defined OSPF v2 Updated RFC 1583 OSPF v2 Updated RFC 2178 OSPF v2 Updated RFC 2328 OSPF work in progress OSPF for IPv6 RFC 2740 1989 1991 1994 1997 1998 1999 Present Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 64 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Protocol Overview Link state-driven updates, periodic hellos Classless routing protocol Subnet mask sent in update Support for VLSM, CIDR, and manual route summarization Support for authentication Maintenance of multiple databases Multicast addressing – 224.0.0.5 and 224.0.0.6 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 65 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Key Features Key OSPF features are: Backbone areas Stub areas NSSAs Virtual links Authentication Support for VLSM and CIDR Route redistribution Routing interface parameters OSPF-TE extensions Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 66 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Protocol Comparison Feature RIPv2 IS-IS OSPF Updates Periodic Incremental Incremental Update type Broadcast/Multicast L2 Multicast L3 Multicast Transport UDP Layer 2 IP Authentication Simple and MD5 Metric Hops Cost Cost Metric type Distance vector Link-state Link-state VLSM / CIDR support Yes Yes Yes Topology size Small/Medium Large Large Convergence Slow Fast Fast Alcatel-Lucent Interior Routing Protocols and High Availability Simple and MD5 Simple and MD5 Module 0 | 67 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Link-State Protocol Comparison Feature IS-IS OSPF Updates Incremental Incremental Multicast layer Layer 2 Layer 3 Authentication Simple and MD5 Simple and MD5 Metric Default: all ports cost 10 Auto-calculation on interface Metric type Link-state Link-state LSA types L1 and L2 Multiple types Area hierarchy Not required Backbone area Area boundaries On segment At interface Convergence Fast Fast Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 68 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Path Determination OSPF uses SPF for path determination. SPF uses cost values to determine the best path to a destination. RTR-C 10.0.0.0 Cost 125 Cost 125 Cost 0 Cost 10 RTR-A RTR-B Cost 125 RTR-A 10.0.0.0 – Cost 260 via RTR C *10.0.0.0 – Cost 135 via RTR B * = Best path Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 69 All rights reserved © 2006-2007 Alcatel-Lucent Calculating Link Cost Cost = reference-bandwidth ÷ bandwidth The default reference-bandwidth is 100 000 000 kb/s or 100 Gb/s. The default auto-cost metrics for various link speeds are as follows: — 10-Mb/s link default cost of 10 000 — 100-Mb/s link default cost of 1000 — 1-Gb/s link default cost of 100 — 10-Gb/s link default cost of 10 The cost is configurable. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 70 All rights reserved © 2006-2007 Alcatel-Lucent Configuration Basics Interfaces must be configured in an OSPF area. By default, interfaces in an area are advertised by OSPF. Routes received through OSPF are advertised by OSPF. No other routes are advertised by default. Verify that adjacencies are formed with neighbors. Verify that routes are in the routing table. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 71 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Multicast Addressing OSPF uses class D multicast addresses in the range 224.0.0.0 to 239.255.255.255. Specially reserved addresses for OSPF: 224.0.0.5: All routers that speak OSPF on the segment 224.0.0.6: All DR/BDRs on the segment IP multicast addresses use the lower 23 bits of the IP address as the low-order bits of the MAC multicast address 01-005E-XX-XX-XX. 224.0.0.5 = MAC 01-00-5E-00-00-05 224.0.0.6 = MAC 01-00-5E-00-00-06 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 72 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Generic Packet OSPF packets use protocol number 89 in the IP header. OSPF is its own transport layer. Link header IP header OSPF packet types Link trailer IP header protocol ID 89 = OSPF Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 73 All rights reserved © 2006-2007 Alcatel-Lucent OPSF — Packet Types OSPF OSPF OSPF OSPF OSPF hello database descriptor link-state request link-state update link-state ACK Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 74 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Link Topology Types Multi-access Point-to-point Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 75 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Router ID Each router must have a router ID, the ID by which the router is known to OSPF. The default RID is the last 32 bits of the chassis MAC address. Configuring a system interface overrides the default. — Using a system interface is easier to document. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 76 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Point-to-Point Segments On point-to-point links, there is no need for a DR or BDR. All packets are sent via IP multicast address 224.0.0.5. Usually a leased-line (i.e., HDLC, PPP) segment Can be configured on point-to-point Ethernets RTR - C Network 2.2.2.0/24 RTR - A Alcatel-Lucent Interior Routing Protocols and High Availability RTR - B Module 0 | 77 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — LAN Communication Election of the DR and BDR in multi-access networks: A B 1.1.1.5 1.1.1.4 RTR-A RTR-B Has the highest Has the second highest RID, so it will be RID, so it will be the BDR the DR C D E 1.1.1.1 1.1.1.2 1.1.1.3 Each router sends hellos. The router with the highest priority is the DR. If all priorities are the same, the DR is the router with the highest RID. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 78 All rights reserved © 2006-2007 Alcatel-Lucent OSPF — Exchanging Updates in a LAN Election of the DR and BDR in multi-access networks: RTR-A (DR) RTR-B (BDR) 1.1.1.5 1.1.1.4 RTR-C sends update to RTR-A sends update to All DRs using IP address All OSPF routers using 224.0.0.6 IP address 224.0.0.5 RTR-C D E 1.1.1.1 1.1.1.2 1.1.1.3 Routers use the 224.0.0.6 IP address to send updates to the DRs. The BDR monitors the DR to ensure that it sends updates. The DR uses 224.0.0.5 to send updates to all OSPF routers. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 79 All rights reserved © 2006-2007 Alcatel-Lucent Alcatel-Lucent Routing Protocols Module 6 — Intermediate System–to–Intermediate System IS-IS — Protocol Overview Development began prior to that of OSPF. The U.S. government required ISPs to use IS-IS for early stages of the Internet. IS-IS supports IPv6. Many large enterprise networks and ISPs use IS-IS due to the scalability and stability of the protocol. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 81 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — RFC History 1990 RFC 1142 Original RFC RFC 1195 TCP/IP support 1990 1992 ISO 10589 released 1994 ….. 2002 RFC 1629 NSAP and Internet Other IS-IS RFCs released Present RFC 33509 TLV code points IS-IS work in progress Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 82 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Protocol Overview (continued) Link-state driven updates, periodic hellos Classless routing protocol Subnet mask sent in update Support for VLSM, CIDR, and manual route summarization Support for authentication Maintenance of multiple databases Layer 2 multicast addressing Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 83 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Key Features Key IS-IS features are: Area hierarchy Authentication Support for VLSM and CIDR Route redistribution Routing interface parameters IS-IS TE extensions Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 84 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Protocol Comparison Feature RIPv2 OSPF IS-IS Updates Periodic Incremental Incremental Update type Broadcast/Multicast L3 Multicast L2 Multicast Authentication Simple and MD5 Metric Hops Cost Cost Metric type Distance vector Link-state Link-state VLSM / CIDR support Yes Yes Yes Topology size Small Very large Very large Summarization Manual Manual Manual Convergence Slow Fast Fast Alcatel-Lucent Interior Routing Protocols and High Availability Simple and MD5 Simple and MD5 Module 0 | 85 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Link-State Protocol Comparison Feature IS-IS OSPF Updates Incremental Incremental Multicast layer Layer 2 Layer 3 Authentication Simple and MD5 Simple and MD5 Metric Default: all ports cost 10 Auto-calculation on interface Metric type Link-state Link-state Update types L1 and L2 Multiple types Area hierarchy Not required Backbone area Area boundaries On segment At interface Convergence Fast Fast Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 86 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Frequently Used Terms Area — Corresponds to the level 1 subdomain End system — Typically a computer, printer, or other attached device Intermediate system — Router in an IS-IS network Neighbor — A physically adjacent router Adjacency — A separate adjacency is created for each neighbor on a circuit and for each level of routing (level 1 and level 2) on a broadcast circuit. Circuit — A single locally attached network Link — The communication path between 2 neighbors CSNP — Complete sequence number PDU PSNP — Partial sequence number PDU PDU — Protocol data unit Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 87 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Frequently Used Terms (continued) Designated IS — The intermediate system in a LAN that is designated to generate updates on behalf of the nodes in the LAN Pseudo node — When a broadcast subnetwork has n connected intermediate systems, the broadcast subnetwork itself is considered to be a pseudo node. Broadcast subnetwork — A multi-access subnetwork (such as Ethernet) that supports the capability of addressing a group of attached systems with a single PDU General topology subnetwork — A topology that is modeled as a set of point-to-point links, each of which connects 2 systems Routing subdomain — A set of intermediate systems and end systems that are located within the same routing domain Level 2 subdomain — The set of all level 2 intermediate systems in a routing domain Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 88 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Protocol Overview IS-IS uses SPF for path determination. SPF uses cost values to determine the best path to a destination. RTR-C 10.0.0.0 Cost: 10 Cost: 10 Cost: 10 Cost: 10 RTR-A RTR-B Cost: 10 RTR-A 10.0.0.0: cost 30 via RTR-C Packet flow *10.0.0.0: cost 20 via RTR-B * = Best path Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 89 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — ISO Network Addressing IS-IS uses unique addressing (OSI NSAP addresses) compared to that of other IP routing protocols. Each address identifies the area, system, and sector. Routers with common area addresses form L1 adjacencies. Routers with different area addresses form L2 adjacencies, if capable. 2-layer hierarchy: Level 1: Builds the local area topology and forwards traffic to other areas through the nearest L1/L2 router Level 2: Exchanges prefix information and forwards traffic between areas Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 90 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — ISO Network Addressing (continued) Layer 2 multicast addressing is implemented to support ISIS. On Ethernet, the following multicast addresses are reserved: L1 updates use 01-80-C2-00-00-14. L2 updates use 01-80-C2-00-00-15. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 91 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Link-State Overview L1 L2 Area 49.0002 L1/L2 L1/L2 L1 Area 49.0003 L1/L2 L1 Area 49.0001 Alcatel-Lucent Interior Routing Protocols and High Availability L1 L2 L1/L2 Backbone (level 2) link Level 1 link Level 1 Level 2 Level 1/level 2 Module 0 | 92 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — NSAP Addressing IDP AFI IDI DSP High Order-DSP System ID SEL 6 1 variable Area ID System Address NSEL NSAP — Network service access point IDP — Initial domain part DSP — Domain specific part AFI — Authority and format indicator IDI — Initial domain identifier (e.g., 49 is local assigned, binary) High Order-DSP — High Order Domain Specific Part SEL — N-selector (NSEL) Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 93 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Protocol Characteristics Item Value Maximum metric value assignable to a link Maximum metric value for a path All L1 IS multicast address All L2 IS multicast address SAP for IS-IS on 802.3 LANs Protocol discriminator for IS-IS NSAP selector for IS-IS Sequence modulus Size of LSP, which all IS routers must be able to handle Maximum age Zero life age Maximum number of area addresses in a single area Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 16 777 215 4 261 412 864 01-80-C2-00-00-14 01-80-C2-00-00-15 FE 83 00 232 1492 1200 60 3 94 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Packet Format IS-IS packets use layer 2 encapsulation of the media. The Ethernet type field is set to 0xFEFE to denote an IS-IS packet instead of an IP packet. The TLV identifies the type of information in the IS-IS packet. IS-IS packets are called PDUs. Ethernet header Type = 0xFEFE IS-IS header Alcatel-Lucent Interior Routing Protocols and High Availability IS-IS TLV Link trailer Module 0 | 95 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Packet Format Details Ethernet destination address: 01-80-C2-00-00-14 – L1 updates 01-80-C2-00-00-15 – L2 updates Ethernet source address: source router interface MAC address 802.3 LLC DSAP and SSAP = FE:FE Layer 3 protocol discriminator: 83 Ethernet header Type = 0xFEFE IS-IS header Alcatel-Lucent Interior Routing Protocols and High Availability IS-IS TLV Link trailer Module 0 | 96 All rights reserved © 2006-2007 Alcatel-Lucent IS-IS — Packet Format Details (continued) IS-IS sends PDUs. PDUs are encapsulated directly into the layer 2 frame. There are 4 types of PDUs: Hello (ESH, ISH, and IIH) — Maintain adjacencies LSP (link-state packet) — Information about neighbors and links, generated by all L1 and L2 routers PSNP (Partial Sequence Number PDU) — Specific requests and responses about links, generated by all L1 and L2 routers CSNP — Complete list of LSPs exchanged to maintain database consistency Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 97 All rights reserved © 2006-2007 Alcatel-Lucent Alcatel-Lucent Routing Protocols Module 7 — Border Gateway Protocol BGP Scope Enables the exchange of routing information between autonomous systems (AS) An AS is a collection of routers that are under a single administration, which presents a consistent routing policy. Enables the implementation of administrative policies BGP has already scaled to: Large number of ASs Large number of neighbors Large volume of table entries High rate of change Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 99 All rights reserved © 2006-2007 Alcatel-Lucent Autonomous Systems in BGP AS-65002 AS-65003 • An AS is a group of networks and network equipment under a common administration. AS-65001 Alcatel-Lucent Interior Routing Protocols and High Availability • IGP protocols such as OSPF, IS-IS, and RIP run in an AS. • BGP is used to connect ASs. Module 0 | 100 All rights reserved © 2006-2007 Alcatel-Lucent Autonomous Systems in BGP (continued) Public autonomous systems: Assigned by ARIN or another authority Must be used when connecting to other ASs on the Internet. Range from 0 to 64 511 Private autonomous systems: Assigned by ISPs (for some clients) and local administrators Not allowed to be advertised to other ISPs or on the Internet Range from 64 512 to 65 535 Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 101 All rights reserved © 2006-2007 Alcatel-Lucent BGP Features Path vector protocol: Neighbor is any reachable device Unicast exchange of information Reliability using TCP Uses well-known TCP port 179 Periodic keepalive for session management Event-driven Robust metrics Authentication Similar behavior as other TCP/IP applications Because BGP peers are not always directly connected, BGP relies on IGP to route between peers. Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 102 All rights reserved © 2006-2007 Alcatel-Lucent eBGP vs. iBGP Overview 2 types of BGP sessions are possible. The routers may be in different ASs: Called external BGP or eBGP Typically directly connected, but not mandatory Different administrations The routers may be in the same AS: Called internal BGP or iBGP Typically remote, but could be directly connected Same administration Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 103 All rights reserved © 2006-2007 Alcatel-Lucent www.alcatel-lucent.com Alcatel-Lucent Interior Routing Protocols and High Availability Module 0 | 104 All rights reserved © 2006-2007 Alcatel-Lucent