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Petrozavodsk State University, Alex Moschevikin, 2003

IP routing protocols. Interior Routing Protocols RIP, RIP2 (Routing Information Protocol) HELLO (not used at the moment) IS-IS ( Intermediate System to Intermediate System ) IGRP ( Interior Gateway Routing Protocol ) OSPF ( Open Shortest Path First ) Exterior Routing Protocols

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Petrozavodsk State University, Alex Moschevikin, 2003

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  1. IP routing protocols • Interior Routing Protocols • RIP, RIP2 (Routing Information Protocol) • HELLO (not used at the moment) • IS-IS (Intermediate System to Intermediate System) • IGRP (Interior Gateway Routing Protocol) • OSPF (Open Shortest Path First) • Exterior Routing Protocols • EGP (Exterior Gateway Protocol) • BGP (Border Gateway Protocol) Rev. 1.01 / 15.01.2007 Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  2. IP routing and OSI RM IP routing information Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 APPLICATION TCP IP Physical PRESENTATION SESSION IP routing TRANSPORT NETWORK DATA LINK PHYSICAL TCP/IP OSI/RM Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  3. First IP router at ARPANET Interface Message Processor Bolt, Beranek and Newman, Inc., United States The Interface Message Processor (IMP) was the first packet router for the ARPANET, the predecessor of today’s Internet. Inside was a Honeywell 516 minicomputer with only 6,000 words of software to monitor network status and gather statistics. The first ARPANET transmission occurred between the University of California in Los Angeles and Stanford Research Institute in Menlo Park, California, at 22:30 PST on October 29, 1969. Speed:520,833 Add/s Memory Size:12K Cost:$82,200 IMP development teamc. 1965 Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  4. IP routing Ethernet-based scheme Source IP datagram 194.0.1.100 ==> 194.0.32.4 Destination default gateway 194.0.1.1 194.0.1.100 194.0.32.4 Source and destination IP addresses remain the same from hop to hop, but MAC addresses are substituted by routers and correspond to the certain source and destination interfaces in each LAN 194.0.1.1 194.0.32.1 Eth0 Eth1 IP router 1 IP router 2 routing table net gateway if 194.0.1.0 Eth0 194.0.4.0 Eth1 194.0.8.0 194.0.8.128 ppp0 Default ppp0 routing table 194.0.8.0 ppp0 194.0.32.0 Eth1 194.0.8.1 194.0.8.128 ppp0 ppp0 Eth1 194.0.4.1 Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  5. Routing tables • Routing Tables & static routing • Dynamic routing (inter-domain and intra-domain) $ /sbin/route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.64.64.1 * 255.255.255.255 UH 0 0 0 ppp0 172.16.227.0 * 255.255.255.0 U 0 0 0 vmnet8 172.16.216.0 * 255.255.255.0 U 0 0 0 vmnet1 127.0.0.0 * 255.0.0.0 U 0 0 0 lo default 10.64.64.1 0.0.0.0 UG 0 0 0 ppp0 vmnet* - виртуальные интерфейсы VmWare • Routing tablesare used in IP forwarding ("netstat -rn") • Routingtable may be altered by: • a) ‘route’ command • b) routing daemon (eg: ‘routed’) • c) ICMP redirect message. Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  6. Routing tables Fields: destination, gateway, flags, metric Destination: can be a host address or a network address. Subnet mask also present, but implicit for this discussion. If the ‘H’ flag is set, it is the host address. Gateway: router/next hop IP address. The ‘G’ flag says whether the destination is directly connected (link address & IP address refer to destination), or indirectly connected (link address refers to router’s, IP address refers to destination) U flag: Is route up ? G: router (indirect vs direct) H flag: host (dest field: host or n/w address?) D & M flags: created/modified by ICMP redirect Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  7. Routing tables c:\>netstat -rn (dial-up access to Electrosvyaz') Active routes: Net addressMask GatewayInterface Metric 0.0.0.0 0.0.0.0 217.107.59.114 217.107.59.114 1 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 217.107.59.0 255.255.255.0 217.107.59.114 217.107.59.114 1 217.107.59.114 255.255.255.255 127.0.0.1 127.0.0.1 1 217.107.59.255 255.255.255.255 217.107.59.114 217.107.59.114 1 224.0.0.0 224.0.0.0 217.107.59.114 217.107.59.114 1 255.255.255.255 255.255.255.255 217.107.59.114 217.107.59.114 1 guess local IP address Active connections: (after establishing few POP3 sessions) NameLocal address External address Condition TCP 217.107.59.114:1037 194.85.172.211:110 ESTABLISHED TCP 217.107.59.114:1038 195.161.9.73:110 TIME_WAIT TCP 217.107.59.114:1040 195.161.136.3:110 ESTABLISHED TCP 217.107.59.114:1041 217.107.58.235:110 ESTABLISHED TCP 217.107.59.114:1042 194.85.172.129:110 ESTABLISHED Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  8. Routing daemons • irdd daemonimplements the Internet Router Discovery (IRD) protocol. • routed daemon implements version I of the Routing Information Protocol (RIP I) to exchange routing information. • gated daemon now implements the SNMP Multiplexing (SMUX) protocol, which provides support for the following Simple Network Management Protocol (SNMP) Management Information Bases (MIBs) and EGP, BGP, RIP2, OSPF as well. Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  9. Distance vector vs Link State routing • DISTANCE VECTOR: • Distance vector protocols count the number of devices data must flow through to reach a destination. Each device is referred to as a 'hop'. Routes with lower hop counts are preferred. • Very little overhead in terms of processor power and memory. • Algorithm chooses the best route according to the hop count metric. • LINK STATE: • Link State protocols track the status and connection type (and therefore speed) of each link, and produce a calculated metric based on these and other factors, including some set by the network administrator. • more processor power and memory, take longer to converge, and therefore longer to recover from network outages. Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  10. Distance vector vs Link State routing 128kb ISDN 128kb ISDN A D A D 100Mb Eth 100Mb Eth 100Mb Eth 100Mb Eth B C B C 10Mb Eth 10Mb Eth DISTANCE VECTOR A ==> D LINK STATE A==>B==>C==>D A, B, C, D - routers Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  11. RIP • RIP: Routing Information Protocol • Active (routers advertise their route tables) and passive (hosts) devices • Key fields of RIP packet: command, AFI, IP address, metric • Command: request and response. • Address Family Identifier (AFI): 2 for IP. • IP address: subnet masks are not passed => variable length subnet masks (VSLMs) cannot be supported. The routers have to know apriori what subnet masks are being used. Convention: 255.255.255.0 • Metric: hop count. Max = 16 (“infinity”) Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  12. RIP cont'd • RIP supports both point-to-point & broadcast links, uses port 520 in UDP. Normal mode = broadcast packets => overhead of each station processing it. • Each RIP packet can contain upto 25 addresses. Usually a table can fit inside one packet. • Router advertises its tables to neighbors every 30 s. Route is reinitialized (as 16 or infinity) if no refresh for 180 s, and may be removed later. • Triggered updates: inform neighbors when table changes. • Delay updates to avoid “update storms”. Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  13. RIP problems • Counting-to-infinity problem • Simple configuration A->B->C. If C fails, B needs to update and thinks there is a route through A. A needs to update and thinks there is a route through B. • No clear solution, except to set infinity to be small (eg 16 in RIP) • Slow convergence after topology change • Due to count to infinity problem • Also information cannot propogate through node until it recalculates routing info B C A Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  14. RIP problems • Black-holes • If one node goes broke and advertises route of zero to several key networks, all nodes immediately point to it. • General problem in distance-vector methods • How to install a fix in a distributed manner? • Require protocol to be “self-stabilizing” I.e even if some nodes are faulty, once they are isolated, the system should quickly return to normal operation • Broadcasts => resources from all nodes • Does not support VLSMs • No authentication Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  15. RIPv2 (RIP II) • Provides: • VLSM support (subnet mask in reserved field of RIP packet) • authentication • multicasting (224.0.0.0) • “wire-sharing” by multiple routing domains (reduce the volume of tranferred data of the Internet routing tables due to CIDR) Internet B A 10.0.1.128/25 (10.0.1.128- 10.0.1.255) info on routing to net with 24-bit mask 10.0.1.0/24 (10.0.1.0- 10.0.1.255) 10.0.1.0/26 (10.0.1.0- 10.0.1.63) 10.0.1.64/26 (10.0.1.64- 10.0.1.127) different IP nets, maybe different physical nets Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  16. Interior Gateway Routing Protocol • As RIP: • distance vector protocol • routing update messages • Not as RIP: • implemented only in Cisco routers • composite metric, factoring weighted, that is calculated bymathematical values for internetwork delay, bandwidth, reliability, and load. These constants are expressed as certain metric and administrator can vary it. • IGRP permits multipath routing (round-robin algorithm of choosing the way of available routes even if they are of not equal metric) Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  17. Stability features of IGRP Holddown: after the break of router other routers begin to exchange information on the changed scheme (triggered). But if at this moment regular routing update will take place (somebody don't know about breakdown) tables will be not correct. Holddowns tell routers to hold down any changes that might affect routes for some period of time. The holddown period usually is calculated to be just greater than the period of time necessary to update the entire network with a routing change. Split-horizon (solving counting to infinity): If A’s route to C is through B, then A advertises C’s route (only to B) as infinity. C D triggered B A regular E B C A Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  18. Stability features of IGRP (cont'd) Split horizons should prevent routing loops between adjacent routers, but poison-reverse updates are necessary to defeat larger routing loops. Increases in routing metrics generally indicate routing loops. Poison-reverse updates then are sent to remove the route and place it in holddown. In Cisco's implementation of IGRP, poison-reverse updates are sent if a route metric has increased by a factor of 1.1 or greater. IGRP timers: update timerfrequency of routing update messages (90 seconds) invalid timerroute is invalid after … (3 times of update period) hold-time variable specifies the holddown period (invalid+10s) flush timer flushed the route from the routing table (7 times of update) Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  19. Open Shortest Path First • Open + SPF (Dijkstra’s algorithm) • OSPF runs directly on top of IP (not over UDP) • Unlike RIP, OSPF can operate with hierarchy. (Autonomous System - common administration and common routing strategy, OSPF - IGP, but is capable of receiving routes from and sending routes to other ASs). • Link State protocol: • calls for the sending of link-state advertisements (LSAs) to all other routers within the same hierarchical area • LSA: attached interfaces, metrics, and other variables • routers accumulate link-state information and use the SPF algorithm to calculate the shortest path to each node Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  20. Open Shortest Path First virtual backbone link area 2 AS C area 1 F area 3 A H1 E D G B H2 H • AS can be divided into a number of areas (the same topological database for routers in the same area) • E, F, G - Area Border Routers • E, F, G, H - backbone • Router A knows only about routers B and E • Two different types of OSPF routing: intra-area and interarea routing • The backbone topology is invisible to all intra-area routers, as are individual area topologies to the backbone Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  21. OSPF algorithm • Each participating router distributes its local state (i.e., the router's usable interfaces and reachable neighbors) to others inside area or backbone • From the topology database, each router constructs a tree of the shortest paths with itself as the root (the route to each destination in the AS) • OSPF chooses the least cost path as the best path • Table of shortest paths = routing table • Key fields of OSPF packet (24 bytes): • Type (hello, database description, link-state request and response, link-state acknowledgement) • Router ID (source) • Source area ID (0.0.0.0 for backbone) • upper-level data Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  22. Additional OSPF features • LSA are sent every 30 minutes • authentication (MD5 algorithm) • equal-cost, multipath routing (round-robin algorithm) • load balancing: distributing traffic equally among routes • routing based on upper-layer type-of-service (TOS) requests (delay, low throughput, and high reliability bits in IP headers) • VLSMs support Advantages of link state over distance vector: • Faster convergence than distance vector • Easier to discover network topology, troubleshoot network • Can do better source-routing with link-stateType & Quality-of-service routing (multiple route tables) possible Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  23. Border Gateway Protocol • BGP is replacing EGP • routing between ASs • BGP provides a mechanism that allows non-core routers to learn routes from core routers so that they can choose optimal backbone routes • distance vector protocol • keep-alive messages every 30 seconds • BGP usesTCP - reliable delivery B AS5 A BGP C OSPF, RIP BGP BGP BGP AS1 RIP AS3 RIP AS4 AS2 IGRP RIP Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  24. BGP-4 features Three types of routing: interautonomous system routing intra-autonomous system routing (between two or more BGP routers located within the same autonomous system, ex. in university building) pass-through autonomous system routing (virtual channels) BGP B IGP AS BGP C Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

  25. BGP-4 features (cont'd) • AS has the responsibility of advertising reachability info to other ASs. • Received routing info is retained and not inserted into routing table until incremental update. • Routers send only the portion of their routing table that has changed, not the whole table every session. • The best route is chosen on path attributes, for example, administrative preferences based on political, organizational, or security considerations in the routing decisionas well as number of autonomous systems through which the path passes, stability, speed, delay, or cost. Petrozavodsk State University, Alex Moschevikin, 2003 NET TECHNOLOGIES

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