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Introduction to IP Routing Graduate Program in Computer Science Aristotle University of Thessaloniki Ver.091014 IP as Routing Protocol IP is a connectionless, unreliable, best-effort delivery protocol. IP accepts whatever data is passed down to it from the upper layers and forwards the data in the form of IP Packets. All the nodes are identified using an IP address. Packets are delivered from the source to the destination using IP address IP Routing Source Destination Application Application Transport Router Transport Network Network Network Link Link Link Routing Table Destination IP address IP address of a next-hop router Flags Network interface specification IP Routing How does a device know where to send a packet? All devices need to know what IP addresses are on directly attached networks If the destination is on a local network, send it directly there IP Routing (cont) If the destination address isn’t local Most non-router devices just send everything to a single local router Routers need to know which network corresponds to each possible IP address Router A router is a device that determines the next network point to which a packet should be forwarded toward its destination Allow different networks to communicate with each other A router creates and maintains a table of the available routes and their conditions, and uses this information to determine the best route for a given packet. A packet will travel through a number of network points with routers before arriving at its destination. There can be multiple routes defined. The route with a lower weight/metric will be tried first. IP Routing Packet Propagation IP Routing Protocols Static Routing Dynamic Routing IGP (Interior Gateway Protocol): Route data within an Autonomous System • RIP (Routing Information Protocol) • RIP-2 (RIP Version 2) • OSPF (Open Shortest Path First) • IGRP (Interior Gateway Routing Protocol) • EIGRP (Enhanced Interior Gateway Routing Protocol) • IS-IS (Intermediate System to Intermediate System) EGP (Exterior Gateway Protocol): Route data between Autonomous Systems • BGP (Border Gateway Protocol) Terminology Autonomous System (AS) Each AS is a group of networks & routers administered by a single authority using a common routing protocol. Interior Gateway Protocol (IGP) Routers within single AS communicate using one of several dynamic routing protocols, known generically as an IGP. Exterior Gateway Protocols (EGP) Communication between routers belonging to different AS requires additional protocol, so-called EGP. Terminology Split Horizon • Router B sends info to Router A about router’s C networks • Router A now knows about router’s C networks • Router A will NOT tell B about router’s C networks • Thus, loops are prevented Terminology • Router B sends info to Router A about router’s C networks Split • Router A now Horizon knows about router’s C with networks Poison Reverse • Router A will tell B that router’s C networks are unreachable through A Classful Routing Protocols Classful routing protocols do not send subnet mask information in routing updates. The first routing protocols, such as RIP When network addresses were allocated based on classes. • Class A, B, or C. Routing protocol did not need to include the subnet mask in the routing update. • Network mask determined based on value of first octet of the network address. Classful & Classless Classful (does not support CIDR and VLSM) Classless (supports CIDR and VLSM) Interior Routing Protocols or Interior Gateway Protocols (IGP) Distance Vector RIPv1 – Simple, Classful, limited metrics (hop count) RIPv2 – Simple, Classless, limited metrics (hop count) Cisco Proprietary IGRP – Simple, Classful, better metric (BW, delay, reliab., load) EIGRP – Simple, Classless, same metric, DUAL (backup routes) Link State OSPF – Perceived complex, classless, Cisco metric BW, IETF IS-IS - Perceived complex, classless, metric “default”, ISO Introduction to Distance Vector Routing Protocols Configuring and maintaining static routes for a large network would be overwhelming. What happens when that link goes down at 3:00 a.m.? Introduction to Distance Vector Routing Protocols RIP: Routing Information Protocol originally specified in RFC 1058. Metric: Hop count Hop count greater than 15 means network is unreachable. Routing updates: Broadcast/multicast every 30 seconds IGRP: Interior Gateway Routing Protocol - Cisco proprietary Composite metric: Bandwidth, delay, reliability and load Routing updates: Broadcast every 90 seconds IGRP is the predecessor of EIGRP and is now obsolete EIGRP: Enhanced IGRP – Cisco proprietary It can perform unequal-cost load balancing. It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path. No periodic updates, only when a change in topology. IGRP and EIGRP: Cisco never submitted RFCs to IETF for these protocols. Meaning of Distance Vector Distance vector Routes are advertised as vectors of distance and direction. Distance is defined in terms of a metric Such as hop count, Direction is simply the: Next hop router or exit interface. Routing protocol Does not know the topology of an internetwork. Only knows the routing information received from its neighbors. Distance Vector routing protocol does not have the knowledge of the entire path to a destination network. Meaning of Distance Vector R1 knows that: Distance: to 172.16.3.0/24 is 1 hop Direction: out interface S0/0/0 toward R2 Remember: R1 does not have a topology map, it only knows distance and direction! Operation of Distance Vector Routing Protocols Periodic updates Some distance vector routing protocols periodically broadcast the entire routing table to each of its neighbors. (RIP and IGRP) 30 seconds for RIP 90 seconds for IGRP Inefficient: updates consume bandwidth and router CPU resources Periodic updates always sent, even no changes for weeks, months,… Operation of Distance Vector Routing Protocols Neighbor of R1 Neighbor of R1 Neighbors are: routers that share a link use the same routing protocol. Router is only aware of: Network addresses of its own interfaces Network addresses that its neighbors know. It has no broader knowledge of the network topology. R3 is unaware of R1 and learns R1’s networks by R2, R4 Link-State Protocol Operation Link-state routing protocol can create a “complete view,” or topology, of the network. Like having a complete map of the network topology Link-state protocols are associated with Shortest Path First (SPF) calculations. A link-state router uses the link-state information to: Create a topology map Select the best path to all destination networks in the topology. Link-State Protocol Operation Link-state protocols work best in situations where The network design is hierarchical, usually occurring in large networks. The administrators have a good knowledge of the implemented link-state routing protocol. Fast convergence of the network is crucial. Link-state protocols are triggered on events and do not rely on periodic updates – 30/90 seconds network downtime is UNACCEPTABLE! Link-State Protocol Characteristics With link-state routing protocols, each router has the full picture of the network topology, and can independently make a decision based on an accurate picture of the network topology. To do so, each link-state router keeps a record of: Its immediate neighbor routers. All the other routers in the network, or in its area of the network, and their attached networks. The best paths to each destination. Link-State Protocol Advantages Respond quickly to network changes. Send triggered updates when a network change occurs. Send periodic updates (link-state refresh), at long intervals, such as every 30 minutes. Uses LSAs to confirm topology information before the information ages out of the link-state database. OSPF Router Tables / Databases OSPF maintains three databases which are used to create three tables. Database Adjacency Database Link-state Database Forwarding Database Table Description Neighbor Table • List of all neighbor routers to which a router has established bidirectional communication. • This table is unique for each router. • Can be viewed using the show ip ospf neighbor command. Topology Table • • • • Routing Table List of information about all other routers in the network. The database shows the network topology. All routers within an area have identical link-state databases. Can be viewed using the show ip ospf database command. • List of routes generated when an algorithm is run on the linkstate database. • Each router’s routing table is unique and contains information on how and where to send packets to other routers. • Can be viewed using the show ip route command. Link-State Advertisements (LSAs) When a change occurs in the network topology, the router experiencing the change creates a link-state advertisement (LSA) concerning that link. LSAs are also called link-state protocol data units (PDUs). The LSA is multicasted to all neighboring devices using either 224.0.0.5 or 224.0.0.6. and confirmed! Routers receiving the LSA immediately forward it to all neighboring routers. Link-State Database (LSDB) Routers receiving add the LSA to their link-state database (LSDB). The LSDB is used to calculate the best paths through the network. OSPF best route calculation is based on Edsger Dijkstra's shortest path first (SPF) algorithm. SPF Routing Algorithm The SPF algorithm accumulates costs along each path, from source to destination. The accumulated costs is then used by the router to build a topology table. SPF Tree and Routing Table The topology table is essentially an SPF tree which contains a listing of all OSPF networks and the costs to reach them. The resulting best routes are then considered to be added to the routing table. OSPF Areas To minimize processing and memory requirements, OSPF can divide the routing topology into a two-layer hierarchy called areas. Characteristics of OSPF areas include: Minimizes routing table entries. Localizes impact of a topology change within an area. Detailed LSA flooding stops at the area boundary. Requires a hierarchical network design. OSPF Two-Layer Hierarchy Backbone Area Referred to as Area 0 Also known as the Transit Area Regular (Standard) Areas Also known as non-backbone areas All regular areas must connect to the backbone area Standard areas can be further defined as stub areas, totally stubby areas, and Not-sostubby areas (NSSAs) Cisco recommends: • An area should have no more than 50 routers. • A router should not be in more than 3 areas. If link between A – B goes down, it is of no general interest Purpose of a Metric Routing protocol metrics: RIP: Hop count IGRP and EIGRP: Bandwidth, delay, reliability and load OSPF (Cisco’s version): Bandwidth IS-IS: Four values (Cisco uses “default”) – Covered in CCNP BGP: Attributes – Covered in CCNP Metric Parameters 56 Kbps R1 to reach the 172.16.1.0/24 network. RIP: Fewest number of hops via R2. OSPF: Path with the lowest cost through R3. This results in faster packet delivery. Configuring RIP Example 10.64.0.0 /24 .1 R1 Fa0/0 R1(config)# router R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)# rip version 2 network 10.0.0.0 no auto-summary exit R2(config)# router R2(config-router)# R2(config-router)# R2(config-router)# R2(config-router)# rip version 2 network 10.0.0.0 no auto-summary exit 10.2.1.0 /24 .2 .2 Fa0/0 R2 S0/0/1 64 kbps .1 S0/0/1 R3 Verifying RIP Command Description show ip protocols Displays networks router is advertising, route sources & administrative distance show ip route Displays the routing table OSPF Metric Calculation Lower Cost The OSPF metric calculation is based on cost. Bandwidth Cost is an indication of the overhead required to send packets across a certain interface. High The cost of an interface is inversely proportional to the bandwidth of that interface. A higher bandwidth is attributed a lower cost. A lower bandwidth is attributed a higher cost. Low Higher Cost OSPF Cost Formula Cost = 100,000,000 / Bandwidth (bps) For example: • 10BaseT • T1 = 100,000,000 / 10,000,000 = 100,000,000 / 1,544,000 = 10 = 64 Configuring Single-Area OSPF Example OSPF Area 0 10.64.0.0 /24 .1 R1 Fa0/0 10.2.1.0 /24 .2 .2 Fa0/0 R2 R1(config)# interface Fa0/0 R1(config-if)# ip address 10.64.0.1 255.255.255.0 R1(config-if)# no shut R1(config-if)# exit R1(config)# R2(config)# interface Fa0/0 R2(config-if)# ip address 10.64.0.2 255.255.255.0 R2(config-if)# no shut R2(config-if)# interface S0/0/1 R2(config-if)# ip address 10.2.1.2 255.255.255.0 R2(config-if)# bandwidth 64 R2(config-if)# no shut R2(config-if)# exit R2(config)# R3(config)# interface S0/0/1 R3(config-if)# ip address 10.2.1.1 255.255.255.0 R3(config-if)# bandwidth 64 R3(config-if)# no shut R3(config-if)# exit R3(config)# S0/0/1 64 kbps .1 S0/0/1 R3 Configuring Single-Area OSPF Example OSPF Area 0 10.64.0.0 /24 .1 R1 Fa0/0 10.2.1.0 /24 .2 .2 Fa0/0 R2 S0/0/1 R1(config)# router ospf 1 R1(config-router)# network 10.0.0.0 0.255.255.255 area 0 R1(config-router)# R2(config)# router ospf 50 R2(config-router)# network 10.2.1.2 0.0.0.0 area 0 R2(config-router)# network 10.64.0.2 0.0.0.0 area 0 R2(config-router)# R3(config)# router ospf 100 R3(config-router)# network 10.2.1.1 0.0.0.0 area 0 R3(config-router)# 64 kbps .1 S0/0/1 R3 Configuring Multi-Area OSPF Example OSPF Area 1 OSPF Area 0 10.64.0.0 /24 .1 R1 Fa0/0 10.2.1.0 /24 .2 .2 Fa0/0 R2 S0/0/1 R1(config)# router ospf 1 R1(config-router)# network 10.0.0.0 0.255.255.255 area 0 R1(config-router)# R2(config)# router ospf 50 R2(config-router)# network 10.2.1.2 0.0.0.0 area 1 R2(config-router)# network 10.64.0.2 0.0.0.0 area 0 R2(config-router)# R3(config)# router ospf 100 R3(config-router)# network 10.2.1.1 0.0.0.0 area 1 R3(config-router)# 64 kbps .1 S0/0/1 R3 Alternate Multi-Area OSPF Configuration OSPF Area 1 OSPF Area 0 10.64.0.0 /24 .1 R1 Fa0/0 10.2.1.0 /24 .2 .2 Fa0/0 R2 S0/0/1 R1(config)# router ospf 1 R1(config-router)# network 10.0.0.0 0.255.255.255 area 0 R1(config-router)# R2(config)# interface S0/0/1 R2(config-if)# ip ospf 50 area 1 R2(config-if)# exit R2(config)# R2(config)# router ospf 50 R2(config-router)# network 10.64.0.2 0.0.0.0 area 0 R2(config-router)# R3(config)# router ospf 100 R3(config-router)# network 10.2.1.1 0.0.0.0 area 1 R3(config-router)# 64 kbps .1 S0/0/1 R3 Verifying OSPF Command Description show ip protocols Displays OSPF process ID, router ID, networks router is advertising & administrative distance show ip ospf neighbors Displays OSPF neighbor relationships. show ip route Displays the routing table. show ip ospf interface Displays hello interval and dead interval show ip ospf Displays OSPF process ID, router ID, OSPF area information & the last time SPF algorithm calculated LSNDI RMRA 4 Feb 2008 OSPF vs… OSPF requires more resources from router Fast convergence Less overhead – good for large networks Supports VLSM Complex to configure for advanced needs! 43 LSNDI RMRA 4 Feb 2008 …vs EIGRP EIGRP – Cisco proprietary routing protocol Uses partial updates and neighbour discovery Like OSPF but easier to configure Good for large multiprotocol networks that use Cisco routers 44 LSNDI RMRA 4 Feb 2008 Setting up EIGRP Needs Autonomous System Number Router(config)#router eigrp 123 Router(config-router)#net 192.168.1.1 0.0.0.3 Router(config-router)#net 22.22.22.0 0.0.0.255 Router(config-router)#exit Uses Wildcard Mask 45 LSNDI RMRA 4 Feb 2008 Verifying EIGRP Router# show ip protocols This shows the routing protocol in use and other useful information too Router# sh ip eigrp ? interfaces IP-EIGRP interfaces neighbors IP-EIGRP neighbors topology IP-EIGRP Topology Table traffic IP-EIGRP Traffic Statistics 46 LSNDI RMRA 4 Feb 2008 Εργασία Στο zip αρχείο διάλεξη 10 - εργασία.zip υπάρχει ένα pkt αρχείο με μια δικτυακή τοπολογία που της λείπει το routing, με αποτέλεσμα οι υπολογιστές των διαφόρων υποδικτύων να μην μπορούν να επικοινωνήσουν μεταξύ τους. Αποκαταστήστε την δρομολόγηση μεταξύ των υποδικτύων σύμφωνα με τις οδηγίες των διαφανειών που επίσης βρίσκονται εντός του zip αρχείου. Παραδοτέο: ένα pdf με όλα τα βήματά σας καθώς και τα αποτελέσματα των βημάτων. 47