Chapter 14 Unicast Routing Protocols: RIP, OSPF, And BGP
Chapter 14Unicast Routing Protocols:RIP, OSPF, and BGPObjectivesUpon completion you will be able to: Distinguish between intra and interdomain routing Understand distance vector routing and RIP Understand link state routing and OSPF Understand path vector routing and BGP
IntroductionoAn internet is a combination of networks connectedby routersoHow to pass a packet from source to destination ?noWhich of the available pathways is the optimum pathway ?Depends on the metricnnMetric: a cost assigned for passing through a networkA router should choose the route with the smallest metric
Introduction (Cont.)oThe metric assigned to each network depends on thetype of protocolnRIP (Routing Information Protocol)oonTreat each network as equalThe cost of passing through each network is the same: one hopcountOpen Shortest Path First (OSPF)oAllow administrator to assign a cost for passing through anetwork based on the type of serviced requirednnFor example, maximum throughput or minimum delayBorder Gateway Protocol (BGP)oThe criterion is the policy, which can be set by the administrator
Introduction (Cont.)oRouting table can be static or dynamicnoAn internet needs dynamic routing tablesDynamic routing table is achieved by therouting protocols
14.1 INTRA- AND INTERDOMAINROUTINGRouting inside an autonomous system is referred to as intradomainrouting. Routing between autonomous systems is referred to asinterdomain routing.
Interior and Exterior RoutingoAn internet can be so largenoOne routing protocol cannot handle the task ofupdating routing table of all routersThus, an internet is divided into autonomoussystems (AS)nAS is a group of networks and routers under theauthority of a single administration
Intra- And Interdomain Routingointradomain routingnnnoRouting inside an autonomous systemEach AS can chose its own intradomain routingprotocolExamples: distance vector and link stateinterdomain routingnnnRouting between autonomous systemsOnly one interdomain routing protocol is usuallyused between ASsExamples: path vector
Figure 13-1Popular Routing ProtocolsThe McGraw-Hill Companies, Inc., 2000
Intradomain Routing AlgorithmsoDistance-vector routing algorithmnnoClassical Distributed Bellman-Ford algorithmRIP (Routing Information Protocol)Link-state routing algorithmnCentralized version of the shortest pathcomputationonEvery router has the whole “picture” of the internetOSPF (Open Shortest Path First)
ExampleoR1, R2, R3 and R4 use an intradomain and aninterdomain routing protocoloSolid thin linesnointradomain routing protocolBroken thick linesninterdomain routing protocol
Figure 13-2Autonomous SystemsThe McGraw-Hill Companies, Inc., 2000
14.2 DISTANCE VECTOR ROUTINGIn distance vector routing, the least cost route between any two nodes isthe route with minimum distance. In this protocol each node maintains avector (table) of minimum distances to every nodeThe topics discussed in this section include:InitializationSharingUpdatingWhen to ShareTwo-Node Loop InstabilityThree-Node Instability
Distance Vector RoutingoThe least cost route between any two nodes isthe route with minimum distance.oEach node maintains a vector (table) ofminimum distances to every node
Distance Vector Routing Tables
InitializationoAt the beginningnEach node can know only the distance betweenitself and its immediate neighborsnWe assume each node can send a message to theimmediate neighbors and find the distance
Initialization of Tables in DistanceVector Routing
SharingoIdea of distance vector routingnnoSharing of information between neighborsIn distance vector routing, each node shares itsrouting table with its immediate neighborsperiodically and when there is a changeHow much of the table must be shared ?nSend the entire table but contains only the firsttwo columnsoThe third column must be changed
UpdatingoooReceipt: a two-column table from a neighborAdd the cost between itself and the sending node toeach value in the second columnRepeat the following steps for each advertiseddestinationnIf (destination not in the routing table)onAdd the advertised information to the tableElseoIf (next-hop field is the same)noReplace retry in the table with the new advertised oneElsenIf (advertised hop count smaller than one in the table)oReplace entry in the routing table
Updating in Distance Vector RoutingReach A via C
When to ShareooThe table is sent both periodically and when there isa change in the tablePeriodic updatennoA node sends its routing table in a periodic updateNormally every 30 secondsTriggered updatennA node receives a table from a neighbor resulting inchanges in its own tableA node detects some failure in the neighboring linkswhich results in a distance change to infinity
Two-Node Loop InstabilityoA problem with distance vector routing is instabilitynoA network using this protocol can become unstableSee the following tablenn1. both node A and B know how to reach node X2. the link between A and X failson3a. If node A can send its routing table to B immediatelyonnnEverything is fine3b. However, if node B sends its routing table to A firstonNode A change its tableNode A assumes that B has found a way to reach X4. A sends its new update to B and B also update its routing table5. B sends its new update to A and so on until the cost reach infinity6. Then both A and B knows that the link is broken
Two-Node Instability
Two-Node Loop Instability (Cont.)oAs a result, during the time before cost reachesinfinitynnoA packet destined for X bounces between A and BCreate a two-node loop problemSolutionsnnnDefining infinitySplit horizonSplit horizon and poison reverse
Defining InfinityoRedefine infinity to a smaller numbernoMost implementation define the distance betweeneach node to be 1noShorten the time of instabilityDefine 16 as infinityAs a resultnnThe distance vector scheme cannot be used in large systemThe size of network, in each direction, can not exceed 15hops
Split HorizonooDo not flood the table through each interfaceand a router must distinguish betweendifferent interfaceIf a router received route updating messagefrom an interfacennThis same updated information must not be sentback through this interfaceSince the information has come from thesending one
Figure 13-14Split HorizonooB receives information about Net1 and Net2 through its leftinterfaceThis information is updated and passed on through the rightinterface but not to the leftThe McGraw-Hill Companies, Inc., 2000
Split Horizon (Cont.)oThus, in the figure of two-node instabilitynNode B eliminates the last line of its routing table beforeit sends to AonLater when A sends its routing table to BooNode A then keeps the value of infinity as the distance to XB then correct its routing tableThe system becomes stable after the first updatenBoth node A and B know that X is not reachable
Split Horizon and Poison ReverseoDrawback of split horizonnDistance vector uses a timeroonSince Node B eliminates the route to XooIf there is no news about a route within the timedurationDelete the routeNode A cannot decide it is due to split horizon orbecause B has not received any news about X recentlySolution: Split Horizon and Poison Reverse
Split Horizon and Poison ReverseooooA variation of split horizonsInformation received is used to update routing tableand then passed out to all interfaceHowever, a table entry is set to a metric of infinityas it’s come through and goes out interface are thesameFor examplennRouter B has received information about Net1 and Net2through its left interfaceThus, it sends information out about Net1 and Net2 with ametric of 16 to its left interface (assume 16 is infinity)
Figure 13-15Split Horizon and Poison ReverseThe McGraw-Hill Companies, Inc., 2000
Three-Node InstabilityooSplit Horizon and Poison Reverse cannot solve threenode instability1. A detects X is not reachableooo2. B updates its table but the packet to C is lost3. After a while, C sends to B its routing tableoooB is fooled and updates its routing table5. B sends its routing table to AooSends a packet to B and CA is fooled and updates its routing table6. A then sends its routing table to B and C7. The loop continues until the cost reach infinity
Three-Node Instability
14.3 RIPThe Routing Information Protocol (RIP) is an intradomain routingprotocol used inside an autonomous system. It is a very simple protocolbased on distance vector routing.The topics discussed in this section include:RIP Message FormatRequests and ResponsesTimers in RIPRIP Version 2Encapsulation
RIPoRIP: Routing Information ProtocolnoBased on distance vector routingDesign considerationsnnIn a AS, RIP deals with routers and networks (links)The destination in a routing table is a networkonnThe first column defines a network addressThe metric used in RIP is hop countInfinity is defined as 16oAny route in an AS cannot have more than 15 hops
Figure 14.8: Example of a Domain UsingRIP
RIP Message FormatoCommand: 8-bitnoVersion: 8-bitnonDefine the family of the protocol usedTCP/IP: value is 2Network Address: 14 bytesnnnoDefine the RIP versionFamily: 16-bitnoThe type of message: request (1) or response (2)Defines the address of the destination network14 bytes for this field to be applicable to any protocolHowever, IP currently uses only 4 bytes, the rest are all 0sDistance: 32-bitnThe hop count from the advertising router to the destination network
Figure 13-6RIP Message FormatThe McGraw-Hill Companies, Inc., 2000
Requests and ResponseoRIP uses two type of messagesnoRequest and responseRequestnnSent by a router that has just come up or has sometime-out entriesCan ask specific entries or all entries
Figure 13-7Request MessagesThe McGraw-Hill Companies, Inc., 2000
Requests and Response (Cont.)oResponse: solicited or unsolicitednA solicited response: sent only in answer to arequestonContain information about the destination specified inthe corresponding requestAn unsolicited response: sent periodicallyoooEvery 30sContains information about the entire routing tableAlso called update packet
Example 1oFollowing Figure shows the update message sent from routerR1 to router R2 in Figure 14.8.noThe message is sent out of interface 130.10.0.2The message is prepared with the combination of splithorizon and poison reverse strategy in mind.nnRouter R1 has obtained information about networks 195.2.4.0,195.2.5.0, and 195.2.6.0 from router R2.When R1 sends an update message to R2,ooReplace the actual value of the hop counts for these three networks with16 (infinity) to prevent any confusion for R2.The figure also shows the table extracted from the message.nRouter R2 uses the source address of the IP datagram carrying theRIP message from R1 (130.10.02) as the next hop address.
Figure 14.11Solution to Example 1
Timers in RIPoRIP uses three timersnPeriodic timernExpiration timernGarbage collection timer
Figure 13-10RIP TimersThe McGraw-Hill Companies, Inc., 2000
Periodic TimeroPeriodic timernControl the advertising of regular update messagenAlthough protocol specifies 30 s, the workingmodel uses a random number between 25 and 35 soPrevent routers update simultaneously
Expiration TimerooGovern the validity of a routeSet to 180 s for a route when a router receives updateinformation for a routennoIf a new update for the route is received, the timer is resetIn normal operation, this occurs every 30 sIf timer goes off, the route is considered expirednThe hop count of the route is set to 16, which meansdestination is unreachable
Garbage Collection TimeroooooWhen a route becomes invalid, the router does notimmediately purge that route from its tableIt continues advertise the route with a metric value of16A garbage collection timer is set to 120 s for thatrouteWhen the count reaches zero, the route is purged fromthe tableAllow neighbors to become aware of the invalidity ofa route prior to purging
Example 2oooA routing table has 20 entries.It does not receive information about fiveroutes for 200 seconds.How many timers are running at this time?
SolutionoThe timers are listed below:nnnPeriodic timer: 1Expiration timer: 20 - 5 15Garbage collection timer: 5
RIP Version 2oDoes not augment the length of the messageof each entryoOnly replace those fields in version 1 thatwere filled with 0s with some new fields
RIP Version 2oNew fieldsnRouting Tag: carries information such as theautonomous system numberonSubnet mask: carries the subnet mask (or prefix)onEnable RIP to receive information from an exteriorrouting tableRIP2 support classless addressing and CIDRNext-hop address: show the address of the nexthop
Figure 13-16RIP-v2 FormatThe McGraw-Hill Companies, Inc., 2000
Classless AddressingoThe most important difference between thetwo versionsnoRIPv1 uses classful addressingnoclassful v.s. classless addressingThe only entry in the message format is thenetwork address (with a default mask)RIPv2 support classless addressingnAdds one filed for the subnet mask
AuthenticationooProtect the message against unauthorizedadvertisementThe first entry of the message is set aside forauthentication informationnFamily field FFFF16onAuthentication typeonNot used for routing information but for authenticationDefine the method used for authenticationAuthentication dataoContain the actual authentication data
Figure 13-17AuthenticationThe McGraw-Hill Companies, Inc., 2000
MulticastingoVersion 1 of RIP uses broadcasting to sendRIP message to every neighbornoAll the routers and the hosts receive the packetsRIP version 2nUses the multicast address 224.0.0.9 to multicastRIP message only to RIP routers in the network
EncapsulationoRIP message are encapsulated in UDP userdatagramoThe well-known port assigned to RIP in UDPis port 520
14.4 LINK STATE ROUTINGIn link state routing, if each node in the domain has the entire topologyof the domain, the node can use Dijkstra’s algorithm to build a routingtable.The topics discussed in this section include:Building Routing Tables
Figure 14.15Concept of link state routing
Link State RoutingoFrom Figure 14.15nEach node uses the same topology to create arouting tablenBut the routing table for each node is uniqueoLike a city map
Link State RoutingoAssumption of link state routingnAlthough the global topology knowledge is notclear and each node has partial knowledgeonIt knows the state (type, condition, cost) of its linkHowever, the while topology can be compiledfrom the partial knowledge of each nodeoSee the Figure 14.16
Figure 14.16oooLink state knowledgeEach node has a partial knowledge of the networkThere is an overlap in the knowledgeThe overlap guarantees the creation of a common topologynA picture of the whole domain for each node
Building Routing TablesoFor sets of actions in link state routingnCreation of the states of the links by each nodeonnnCalled the link state packet or LSPDissemination of LSPs to every other router,called flooding, in an efficient and reliable wayFormation of a shorten path tree for each nodeCalculation of a routing table based on theshortest path tree
Creation of Link State Packet (LSP)oAssume a LSP carriesnnThe node identityThe list of linksonA sequence numberonBoth are needed to make the topologyDistinguishes new LSPs from old onesAgeoPrevent old LSPs from remaining in the domain for along time
Creation of Link State Packet (LSP)oLSP are generated on two occasionsnWhen there is a change in the topology of thedomainonQuickly inform any node to update its topologyOn a periodic basisooThe period is much longer compared to the distancevector routing60 minutes or 2 hours
Flooding of LSPsoFlooding: the LSP must be disseminated to all other nodes inthe domainnoNot only to its neighborsRulesnnThe creating node sends a copy of the LSP out of each interfaceAll receiving nodes compare the incoming one with the copy it mayalready haveoIf the newly LSP is older than the one it has by checking sequencenumbernoDiscard the LSPElsennDiscard the old LSPSends a copy of it out of each interface except the incoming one
Formation of Shortest Path Tree:Dijkstra Algorithm
Figure 14.18Example of formation of shortest path tree
Calculation of Routing Table fromShortest Path TreeoExample:
14.5 OSPFThe Open Shortest Path First (OSPF) protocol is an intradomain routingprotocol based on link state routing. Its domain is also an autonomoussystem.The topics discussed in this section include:AreasMetricTypes of LinksGraphical RepresentationOSPF PacketsLink State Update PacketOther PacketsEncapsulation
AreasoOSPF divides an autonomous system into areasnTo handle routing efficiently and in a timely manneroA collection of networks, hosts, and routers allcontained within an autonomous systemoThus, an autonomous system can be divided intomany different areasoAll networks inside an area must be connected
Areas (Cont.)oRouters inside an area flood the area withrouting informationoAt the border of an area, special routers calledarea border routersnSummarize the information about the area andsent it to other areas
Areas (Cont.)oAmong the area inside an autonomous systemis a special area called backbonenoAll of the areas inside an AS must be connectedto the backboneThe routers inside the backbone are called thebackbone routersnA backbone router can also be an area borderrouter
Areas (Cont.)oIf the connectivity between a backbone and anarea is brokennoA virtual link must be created by theadministrationEach area has an area identificationnThe area identification of the backbone is zero
Figure 13-18Areas in an Autonomous SystemThe McGraw-Hill Companies, Inc., 2000
MetricsooOSPF allows the administrator to assign acost, called the metric, to each routeMetric can be based on a type of servicennoMinimum delayMaximum throughputA router can have multiple routing tablesnEach based on a different type of service
Types of LinksoIn OSPF, a connection is called a linkoFour types of linksnnnnPoint-to-pointTransientStubVirtual
Figure 13-19Types of LinksThe McGraw-Hill Companies, Inc., 2000
Point-to-Point LinkooConnect two routers without any other host or routerin these two routersExamplennoGraphically representationnnoTelephone lineT-lineThe routers are represented by nodesThe link is represented by a bidirectional edgeThe metricnUsually the same at the two ends
Figure 13-20Point-to-Point LinkThe McGraw-Hill Companies, Inc., 2000
Transient LinkoA network with several routers attached to itnoData can enter through any of the routers andleave through any routerExamplenAll LANs and some WANs with two or morerouters
Transient Link (Cont.)oGraphically representationnFigure b in the next slide. However, it isoNot efficient: each router need to advertise theneighborhood of four other routersnoFor a total of 20 advertisementNot realistic: there is no single network (link)between each pair of routersnThere should be only one network that serves as a crossroadbetween all five routers
Transient Link (Cont.)oReality: each router should be connected to everyrouter through one single networknnThe network is represented by a nodeHowever, network is not a machineooCannot function as a routerSolution: one of the routers acts as a single networknThis router has a dual purpose: a true router and adesignated routerooThe link is represented as a bidirectional edgeFigure c in the next slide
Figure 13-21Transient LinkThe McGraw-Hill Companies, Inc., 2000
Stub LinkoA network that is connected to only one routernooData packet enter and leave through this only one routerA special case of transient networkGraphically representationnnnThe router as a nodeThe designated router as the networkNote, the link is only one-directionalooFrom the router to the networkBecause the network is the end point in the graph representationnSee the following third slides
Figure 13-22Stub LinkThe McGraw-Hill Companies, Inc., 2000
Virtual LinkoWhen the link between two routers is brokennThe administrator may create a virtual pathbetween them using a longer path and may gothrough several routers
Figure 14.24Example of an AS and its graphical representation in OSPF
Types of PacketsoOSPF uses five different packetsnnnnHello packetDatabase description packetLink state request packetLink state update packetooooonRouter linkNetwork linkSummary link to networkSummary link to AS boundary routerExternal linkLink state acknowledgment packet
Figure 13-33Types of OSPF PacketsThe McGraw-Hill Companies, Inc., 2000
Common HeaderoAll OSPF packets share the same headernVersion: 8-bitonType: 8-bitonThe type of the packetMessage length: 16-bitonThe version of the OSPF protocol. Currently, it is 2The length of the total message including the headerSource router IP address: 32-bitoThe IP address of the router that sends the packet
Figure 13-34OSPF Common HeaderThe McGraw-Hill Companies, Inc., 2000
Common Header (Cont.)nArea identification: 32-bitonChecksum: 16-bitonError detection on the entire packet excluding the authenticationtype and authentication data fieldAuthentication type: 16-bitoonThe area within which the routing take placeDefine the authentication method used in this area0: none, 1: passwordAuthentication: 64-bitooThe actual value of the authentication dataFilled with 0 if type 0; eight-character password if type 1
Link State Update PacketoooUsed by a router to advertise the state of itslinksEach update packet may contain severaldifferent LSAs (List State Advertisement)Packet formatnnNumber of link state advertisements: 32-bitLink state advertisementooThere are five different LSAs, as discussed beforeAll have the same general header, but different bodies
Figure 14.27Link state update packet
LSA General HeaderoLink state age: the number of seconds elapsedsince this message was first generatednnnLSA goes from router to router, i.e., floodingWhen a router create a message, age 0When each successive router forwards this messageooEstimate the transmit time and add it to the age fieldE flag: if 1, the area is a stub areani.e., an area that is connected to the backbone areaby only one path
LSA General Header (Cont.)ooT flag: if 1, the router can handle multipletypes of serviceLink state typennnnn1: router link2: network link3: summary link to network4: summary link to AS boundary router5: external link
LSA General Header (Cont.)oLink state ID: depend on the type of linknnnnnRouter link: IP address of the routerNetwork link: IP address of the designated routerSummary link to network: address of the networkSummary link to AS boundary router: IP addressof the AS boundary routerExternal link: address of the external network
LSA General Header (Cont.)oAdvertisement router:noLink state sequence number:noSequence number assigned to each link state updatemessageLink state checksum:noIP address of the router advertising this messageA special checksum algorithm: Fletcher’s checksumLength:nTotal packet length
Figure 13-39LSA General HeaderThe McGraw-Hill Companies, Inc., 2000
Router Link LSAoDefine the link of a true routeroA true router uses this advertisement toannounce information aboutnnAll of its linksWhat is at the other side of the links (neighbors)
Figure 14.29Router link
Router Link LSA (Cont.)oFormatnLink ID:onLink data:onDefine the metrics for the default type of service (TOS 0)TOS:onThe number of type of services announced for each linkMetric for TOS 0:onFour different types of links are defined based on the type of network, see Table14.2Number of types of services (TOS)onGive additional information about the link, also depend on the type of link, seeTable 14.2Link type:onDepend on the type of link, see Table 14.2Define the type of serviceMetric:oDefine the metric for the corresponding TOS
Figure 14.30Router link LSA
Table 14.2 Link types, link identification, and link data
Example 3Give the router link LSA sent by router 10.24.7.9in Figure 14.31.oThis router has three linksnnoTwo of type 1 (point-to-point)One of type 3 (stub network)Figure 14.32 shows the router link LSAThe McGraw-Hill Companies, Inc., 2000
Figure 14.31Example 3
Figure 14.32Solution to Example 3
Network Link LSAoooDefine the links of a networkA designed router, on behalf of the transientnetwork, distributes this type of LSA packetAnnounce the existence of all of the routersconnected to the networknSee Fig. 14.33
Network Link LSA (Cont.)oFormatnNetwork maskonDefine the network maskAttached routeroDefine the IP addresses of all attached routers
Figure 14.33Network link
Figure 14.34Network link advertisement format
Example 4Give the network link LSA in the followingFigure.The McGraw-Hill Companies, Inc., 2000
SolutionThe network, for which the network link advertises,has three routers attached. The LSA shows themask and the router addresses. See Figure 14.36.The McGraw-Hill Companies, Inc., 2000
Figure 14.36Solution to Example 4
Example 5In Figure 14.37, which router(s) sends out router link LSAs?See Next SlideSolutionAll routers advertise router link LSAs.a. R1 has two links, N1 and N2.b. R2 has one link, N1.c. R3 has two links, N2 and N3.
Figure 14.37Example 5 and Example 6
Example 6In Figure 14.37, which router(s) sends out the network linkLSAs?SolutionAll three network must advertise network links:a. Advertisement for N1 is done by R1 because it is the onlyattached router and therefore the designated router.b. Advertisement for N2 can be done by either R1, R2, or R3,depending on which one is chosen as the designated router.c. Advertisement for N3 is done by R3 because it is the onlyattached router and therefore the designated router.
Summary Link to Network LSAoRouter link and network link advertisementsnoBut a router must also know about the networksoutside its areanoFlood the area with information inside an areaThe area border routers provide this informationAn area border router is active in more than one areannnReceive router link and network link advertisementsCreate a router table for each areaProvide one area’s information to other areas by thesummary link to network advertisement
ExampleoR1 is an area border router and has tworouting tablesnOne for area 1 and one for area 0oR1 will flood area 1 with information abouthow to reach a network located in area 0oR2 plays the same role
Figure 14.38Summary link to network
Summary Link to Network LSA (Cont.)oThe LSA consists of only network mask and metric for eachtype of servicennoEach advertisement announces only one networknoNot include the network addressSince the IP address of the advertising router is in the headerIf more than one network, a separate advertisement must be issued foreachFormatnnNetwork maskTOS:onType of serviceMetric:oMetric for the type of service defined in the TOS field
Figure 13-46Summary Link to Network LSAThe McGraw-Hill Companies, Inc., 2000
Summary Link to AS Boundary RouterLSAooooPrevious advertisement lets every router know thecost to reach all of the networks inside the ASBut, how to reach a network outside an AS?A router must know how to reach the autonomousboundary router firstThe summary link to AS boundary router providesthis informationnThe area border routers flood their area with thisinformation
Figure 13-29Summary Link to AS Boundary Router LSAThe McGraw-Hill Companies, Inc., 2000
Summary Link to AS Boundary RouterLSA (Cont.)oAnnounce the route to an AS boundary routernnoDefine the network to which the AS boundaryrouter is attachedThe area border routers flood their area with thisLASFormatnThe same as the summary link to network LSA
Figure 14.41Summary link to AS boundary router LSA
External Link LSAoHow a router inside an AS know which networks areavailable outside the AS ?noThe AS boundary routers floods the autonomoussystem with the cost of each network outside the ASnoThe external link advertisement provides this informationUsing a routing table created by an exterior routingprotocolNotably, each advertisement announces one singlenetworknSeparate announcements are made if more than onenetwork exists Announce all the networks outside the AS
External Link LSAooUse to announce all of the networks outsidethe ASFormat: similar to the summary link to ASboundary router LSA but add two fieldsnForwarding addressonMay define a forward router than can provide a betterroute to the destinationExternal route tagoUsed by other protocol, but not by OSPF
Figure 13-48External Link LSAThe McGraw-Hill Companies, Inc., 2000
Other PacketsoNot used as LSA but are essential to the OSPFnHello messagenDatabase description messagenLink state request packetnLink state acknowledgment packet
Hello MessageoOSPF uses the hello message tonnoCreate neighborhood relationshipsTest the reachability of neighborsFirst step in link state routingnIt must first greet its neighbors
Figure 13-35Hello PacketThe McGraw-Hill Companies, Inc., 2000
Hello Packet FormatoNetwork mask: 32-bitnoHello interval: 16-bitnoDefine the number of seconds between hello messageE flag: 1-bitnoDefine the network mask of the network over which thehello message is sentIf it is set, the area is a stub areaT flag: 1-bitnIf it is set, the router supports multiple metrics
Hello Packet Format (Cont.)oPrioritynnnnThe priority of the router. Used for the selectionof the designated routerThe router with the highest priority is chosen asthe designated routerThe router with the second highest priority ischosen as the backup designated routerIf it is 0, the router never wants to be a designatedor backup designated router
Hello Packet Format
Two-Node Loop Instability o A problem with distance vector routing is instability n A network using this protocol can become unstable o See the following table n 1. both node A and B know how to reach node X n 2. the link between A and X fails o Node A change its table n 3a. If node A can send its routing table to B immediately
Contents iv Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide, Release 7.x Unicast RIB 1-10 Adjacency Manager 1-11 Unicast Forwarding Distribution Module 1-11 FIB 1-12 Hardware Forwarding 1-12 Software Forwarding 1-12 Summary of Layer 3 Unicast Routing Features 1-12 IPv4 and IPv6 1-13 IP Services 1-13 OSPF 1-13 EIGRP 1-13 IS-IS 1-14 BGP 1-14 RIP 1-14 Static Routing 1-14
[3] The IPv6 Unicast space encompasses the entire IPv6 address range with the exception of FF00::/8. [RFC4291] IANA unicast address assignments are currently limited to the IPv6 unicast address range of 2000::/3. IANA assignments from this block are registered in the IANA registry: iana-ipv6-unicast-address-assignments.
This chapter describes the Cisco NX-OS unicast routing show commands available on the Cisco Nexus 3548 switch. 2 Cisco Nexus 3548 Switch NX-OS Unicast Routing Command Reference OL-27852-01 . Examples This example shows how to display an entry in the BGP table: switch# show bgp ipv4 multicast Related Commands
IPv6 Address Type Unicast An IPv6 unicast address is an identifier for a single interface, on a single node. A packet that is sent to a unicast address is delivered to the interface identified by that address. The Cisco IOS XE software supports the following IPv6 unicast address types: Aggregatable Global Address, page 5
37-2 Catalyst 3560 Switch Software Configuration Guide OL-8553-07 Chapter 37 Configuring IP Unicast Routing Understanding IP Routing † Configuring Protocol-Independent Features, page 37-86 † Monitoring and Maintaining the IP Network, page 37-100 Note When configuring routing parameters on the switch and to allocate system resources to maximize the .
Part One: Heir of Ash Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26 Chapter 27 Chapter 28 Chapter 29 Chapter 30 .
IPv6 Unicast Addresses Structure of an IPv6 Global Unicast Address A global unicast address has three parts: Global routing prefix - network, portion of the address that is assigned by the provider. Typically /48. Subnet ID - Used to subnet within an organization. Interface ID - equivalent to the host portion of an IPv4 address.
TO KILL A MOCKINGBIRD. Contents Dedication Epigraph Part One Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Part Two Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18. Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26
