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Chapter 14-16aChapter 14-16a
Internet RoutingInternet RoutingReviewReview
Chapter 14-16: Internet Routing Review2
Introduction Introduction Motivation:Motivation: Router performance is Router performance is
critical to overall performance and QoS critical to overall performance and QoS in the Internet and private in the Internet and private internetworks. Consider:internetworks. Consider:– selecting selecting best routes best routes (optimize delay, load)(optimize delay, load)– maintainingmaintaining routing tables (router overhead) routing tables (router overhead)– router-generated router-generated management trafficmanagement traffic
Topics:Topics:– Overview of Graph TheoryOverview of Graph Theory– Interior Routing ProtocolsInterior Routing Protocols– Exterior Routing ProtocolsExterior Routing Protocols
Chapter 14-16: Internet Routing Review3
Graph Theory and NetworksGraph Theory and Networks
Network Nodes
Network Links
Size of G: |E| = 10Order of G: |V| = 6
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Graph Theory and NetworksGraph Theory and Networks
Weighted Digraph to Represent Link CostsWeighted Digraph to Represent Link Costs
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Spanning TreesSpanning Trees
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Dijkstra’s Link-State AlgorithmDijkstra’s Link-State Algorithm
Based on breadth-first searchRunning time order of |V|2
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Bellman-Ford Distance Vector Bellman-Ford Distance Vector AlgorithmAlgorithm
Running time order of |V| x |E|
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Ex: Dijkstra vs. Bellman-Ford Ex: Dijkstra vs. Bellman-Ford Least-cost routing algorithmsLeast-cost routing algorithms
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Interior/Exterior Routing Interior/Exterior Routing Protocols Protocols
Hosth2a
b
ba
aC
A
Bd c
A.aA.c
C.bB.a
cb
Hosth1
Interior routingInterior routingwithin network within network
(AS) A(AS) A
ExteriorExterior routingroutingbetweenbetweennetworks networks A and BA and B
Interior routingInterior routingwithin network within network
(AS) B(AS) B
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Chapter 15Chapter 15
Interior Routing Interior Routing ProtocolsProtocols
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Internet Routing ExampleInternet Routing Example
Chapter 14-16: Internet Routing Review14
Routing TableRouting Table
Fixed vs. Adaptive Routing?
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Routing Information Routing Information Protocol (RIP)Protocol (RIP)Distance Vector AlgorithmDistance Vector Algorithm
– typically uses simple link delay count typically uses simple link delay count metricmetric
Small networksSmall networks– fast and simplefast and simple– max max hop counthop count = 15 (RIPv1) = 15 (RIPv1)
Adaptive Adaptive – updates sent approximately updates sent approximately every 30 every 30
secondsseconds– links are invalidated if no update in links are invalidated if no update in
180 seconds180 secondsUses UDPUses UDP transport (port 520) transport (port 520)
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RIP MessagesRIP Messages CommandCommand
– 1 for request1 for request– 2 for reply2 for reply
VersionVersion– 1: RIPv1, RFC 10581: RIPv1, RFC 1058– 2: RIP-2, RFC 17232: RIP-2, RFC 1723
Address Family IDAddress Family ID – always 2 for IP addressesalways 2 for IP addresses
IP addressIP address – non-zero network portionnon-zero network portion– zero host portionzero host portion
Cost MetricCost Metric – typically 1 (i.e. hop count)typically 1 (i.e. hop count)
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Open Shortest Path First Open Shortest Path First Protocol (OSPF)Protocol (OSPF)Link-State AlgorithmLink-State Algorithm
– Dijkstra’s AlgorithmDijkstra’s Algorithm– uses floodinguses flooding to advertise, request info to advertise, request info
Preferred for TCP/IP-based Preferred for TCP/IP-based internetsinternets– scale, TOS, hierarchy of areas, etc.scale, TOS, hierarchy of areas, etc.– multiple metrics… monetary cost, multiple metrics… monetary cost,
reliability, throughput, delay, arbitraryreliability, throughput, delay, arbitraryAdaptive Adaptive
– routers flood with new data when a routers flood with new data when a significant change occurssignificant change occurs
Sent as Sent as payload in IP datagrampayload in IP datagram
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Open Shortest Path First Open Shortest Path First Protocol (Scale, Hierarchy)Protocol (Scale, Hierarchy)
Chapter 14-16: Internet Routing Review19
OSPF MessagesOSPF Messages VersionVersion
– 2: current version2: current version TypeType
– 1: “Hello”, for discovery1: “Hello”, for discovery– 2: database structure2: database structure– 3: request link-state3: request link-state– 4: update link-state4: update link-state– 5: acknowledge update5: acknowledge update
Length of messageLength of message Router IDRouter ID
– unique in a single areaunique in a single area Area IDArea ID
– unique to an ASunique to an AS Internet checksumInternet checksum Authentication InfoAuthentication Info
– Type of authenticationType of authentication– 64 bit authentication 64 bit authentication
valuevalueOSPF HeaderOSPF Header
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Chapter 16aChapter 16a
Exterior Routing Exterior Routing ProtocolsProtocols
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Exterior RoutingExterior Routing
RIP
OSPFBGP
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Border Gateway Protocol Border Gateway Protocol (BGP-4)(BGP-4) Path Vector AlgorithmPath Vector Algorithm
– cost metrics not used or advertisedcost metrics not used or advertised– each router specifies a complete path to all each router specifies a complete path to all
other nodes (e.g., from node other nodes (e.g., from node AA to node to node ZZ = = AADFHKXDFHKXZZ))
Facilitates routing based on Facilitates routing based on policypolicy instead instead of cost metricsof cost metrics– use preferred routes, providers (based on policy)use preferred routes, providers (based on policy)– avoid competitors, poor performers, etc.avoid competitors, poor performers, etc.
Adaptive Adaptive – peers exchange updates peers exchange updates on demandon demand– nodes may choose not to nodes may choose not to participateparticipate
Uses TCP Uses TCP transport (port 179)transport (port 179)
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Border Gateway Protocol Border Gateway Protocol ExampleExample
A
B
C
W X
Y
legend:
customer network (Stub AS)
provider network
W, X, Y, A, B and C are networks Paths are specified as, for example:
Path (w, y) = wACy Path (x, y) = xCy
BGP routers advertise (update) only those routes that are specified by administrative policy would A advertise …ABx… or …ACx… ?
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BGP MessagesBGP MessagesCommon AttributesCommon Attributes MarkerMarker
– synchronization and synchronization and authentication authentication mechanismmechanism
Length of messageLength of message TypeType
– openopen: establish a : establish a neighbor relationshipneighbor relationship
– updateupdate: send/withdraw : send/withdraw route informationroute information
– keepalivekeepalive: : acknowledge or acknowledge or confirm relationshipconfirm relationship
– notificationnotification: error : error detecteddetected
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