2013_Routing_protocols (1131233), страница 2
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Copy the matching bit and add the rest zero bits.Supernet - group of major network addresses summarized as single network.7RIP version 2Features:• classless• next-hop addresses are included in updates• multicasting instead of broadcasting (takes up less bandwidth and less processing of non-RIP devices)• authentication option available (accepting packets from devices with the same password)• holddown and other timers, triggered updates, split horizon, poisoning• auto-summarizing by default as in RIPv1 (can be disabled)RIPv2 message format:– command (request/responce)– version– address family id (2 for IP, 0 for requesting full table)– route tag– subnet mask– next hop address (used to identify a better hext-hop address than router address) (0.0.0.0refers to the best next-hop address)– IP routes (25 maximum) + metricThe routing tableSource network types:• directly connected• static routes• dynamic protocolsLevel 1 route is a route with subnet mask equal or less than the classful mask of network address.
Suchroutes can function as:• default route - static route with the address 0.0.0.0/0• supernet route (mask less than classful)• network route (mask is equal to classful)Ultimate route includes:• either a next-hop IP address• and/or an exit interface8Parent route doesn't contain any next-hop IP address or exit interface. It is automatically created whena route with a greater mask than the classful mask is entered into the routing table.Level 2 route - route that is a subnet of a classful network address.Parent route can be subnetted or variably subnetted (VLSM).Routing behaviour (not the same as protocols) (affects lookup process only):• classful• classlessRoute lookup process:1.
Examining 1 level routes.(a) If the best match is ultimate route then forward.(b) Otherwise (parent route) continue.2. Examining child routes.(a) If there is a match then forward.(b) Otherwise continue.3. If classful behavior then drop. If classless behavior then continue searching supernets , includingthe default route, with less match.4. Forward if there is a match.5. Drop.EIGRPFeatures:• distance vector• authentication allowed• auto-summarizing by defaultMessage format:1.
Data link frame header2. IP packet header3. EIGRP packet header4. Type/length/values (TLV) typesEIGRP packet header fields:• opcode– update– query and reply– reply9– hello• autonomous system (AS) number - number to track multiple EIGRP instancesTLV:• parameters– weights for composite metric (only bandwidth and delay by default, equally weighted)– hold timer (time for neighbors to wait before considering the advertising router down)• IP internal (used for advertising routes within an AS)– delay (sum of delays from src to dst in units of 10 microseconds)– bandwidth (lowest configured bandwidth of any interface along the route)– subnet mask (prefix length)– destination address (24bits + additional 32bits if needed)• IP external (used for importing external routes into routing process)EIGRP is capable of several different routing protocols IP, IPX, AppleTalk using protocol-dependentmodules (PDM).Reliable Transport Protocol (RTP) - protocol for exchanging information packets.
Can send packetseither multicast or unicast.Packet types:• hello (discover neighbors and form adjacency) (multicast unreliable delivery)• update (propagate routing information is sent only when necessary and to routers that need it)(multicast or unicast dependent on quantity)• acknowledgement (when reliable delivery is used; contain a nonzero ack number) (always unicast)• query and reply (used by DUAL; always reliable delivery) (queries are multicast, responses areunicast)Hello's are sent every 5 seconds (60 on slow connections).Holdtime is three times the hello interval.DUAL finite state machine (FSM) track all routes, uses efficient loop-free least cost path.Wildcard mask - inverse subnet mask.Null0 is included as a child route if:• There is at least one EIGPR-learned subnet.• Auto-summarizing is enabled.Null0 is always selected if there is no match regardless the classless behavior.Metric consists of:• bandwidth (link characteristic)• delay (set by administrator)• reliability (probability of fail)10• load (amount of traffic utilizing a link)($EIGRP metric =10.000.000bandwidth kbps+sum of delays10)∗ 256$Diffusing update algorithm (DUAL) (uses topology table and neighbor table to build the routing table):• Successor - neighboring router that is used for packet forwarding and is the least-cost to the destination network).• Feasible distance (FD) - the lowest calculated metric to reach the destination.• Feasible successor (FS) - neighbor who has a loop-free backup path to the same network as successor by satisfying the FC.• Reported distance (RD) - total metric along a path to destination (neighbor's FD).• Feasibility condition (FC) is met when a neighbor's RD is less than the local router FD.Topology table holds information about the successor, FD and any FS with their RD.Passive state means that DUAL is not performing computations.Link-state protocolsDijkstra's algorithm (shortest path first).Routing process:1.
learning about directly connected networks (detecting that interface is up)2. saying hello to neighbors on directly connected networks3. building link-state packet (LSP) containing the state of directly connected links4. flooding LSP to all neighbors, who then store it in database5. using database to construct a complete map of the topology and compute the best path to eachdestination networkLSP includes:• interface IP and subnet mask• type of network (ethernet, point-to-point)• link cost• any neighbor routers on that link• sequence number and aging info (help to manage flooding and to keep the database up-to-time)Unlike distance vector protocols, SPF is calculated after the flooding is complete.LSPs are sent when:• initial startup• topology changeOverall advantages:11• building a topological map• fast convergence• event-driven updates• hierarchical design (concept of areas)IS-IS is mainly used by ISPs and carriers.OSPFFeatures:• link-state routing protocol• AD 110• authentication is allowedMessage format:1.
Data link frame header2. IP packet header3. OSPF packet header4. OSPF packet type-specific dataPacket types:• hello• database description (DBD) (check for database synchronization between routers)• link state request (LSR) (request for specific database records)• link state update (LSU) (reply to LSR)• link state acknowledgment (LSAck) (confirm receipt of the LSU)Usage of hello packets:• discover neighbors and establish adjacencies• advertise parameters on which routers must agree to become neighbors• elect designated router (DR) and backup DR (BDR) on multiaccess networksOSPF packet fields:• type (hello, DD, LSR, LSU, LSAck)• router ID• area ID• network mask (associated with sending interface)12• hello interval• router priority• DR ID if any• BDR ID if any• list of neighbors (IDs)Hello interval - time before hellos (10s on multiaccess and point-to-point, 30 on non-broadcast multiaccess segments e.g.
frame relay).Dead interval - time to wait until neighbor is considered down if there is no hellos. 4 times the hellointerval.To establish connection network type, dead and hello intervals must be the same.DR is responsible for updating all other routers when a change occurs in the multiaccess network.LSA contains route information for destination networks.Each router has link-state database containing LSAs from neighbors.OSPF area - group of routers that share link-state info.Multiarea is used for isolating unstable networks and for storing smaller databases.How to choose router ID:1. configured IP address2.
if not, choose highest IP of any loopbacks3. if not, highest active IP of any physical interfaceRouter ID is chosen with first 'network' command and changes only if ospf process is killed.Flapping link - network that cycles between up and down.SPF shedule delay - 5 seconds delay after receiving an LSU before running SPF. Used to minimize flapping link problem.Hold time - 10 seconds delay between rerunning SPF.Retransmit interval is time before repeated advertisement is sent if there was no ack).$OSPF Cisco metric =108bps $The cost of OSPF route is accumulated value from one router to the destination.Multiaccess network - network with more than 2 devices on the same shared media (e.g. ethernet LAN).OSPF network types:• point-to-point• broadcast multiaccess• nonbroadcast multiaccess (NBMA)• point-to-multipoint• virtual linksChallenges in multiaccess networks:• creation of multiple adjacencies $Total adjacencies =13n(n−1)$2• extensive flooding of LSAs (the problem is to introduce each device to other devices)DR and BDR are chosen to solve flooding problem (only in multiaccess).1.
DR is a router with highest interface priority.2. BDR is a router second highest interface priority.3. If priorities are equal ther compare by router IDs.4. Other router are marked as DROther.Neighbor states:• full• 2way (two drothers form adjacency)DR remains RD until:• DR fails• OSPF process on it fails• multiaccess interface on it failsRouters with priority 0 will never be DR or BDR.Autonomous system boundary router (ASBR) is located between OSPF routing domain and non-OSPFnetwork.OSPF area types:• Backbone area forms the kernel. It should distribute routing information between non-backboneareas.• Standard area is created by default.
It receives link updates, summary routes and external routes.• Stub area don't receive information about external routes but receives it from other areas.• Totally stubbed area don'r receive information from other areas. Cannot contain ASBR.LSA types:1. router link state update2. network link state3.
summary network LSA4. ASBR summary5. AS external6. + some other ...14.
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