chapter 14-16a

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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


Graph Theory and NetworksGraph Theory and Networks

Network Nodes

Network Links

Size of G: |E| = 10Order of G: |V| = 6


Graph Theory and NetworksGraph Theory and Networks

Weighted Digraph to Represent Link CostsWeighted Digraph to Represent Link Costs


Spanning TreesSpanning Trees


Dijkstra’s Link-State AlgorithmDijkstra’s Link-State Algorithm

Based on breadth-first searchRunning time order of |V|2


Bellman-Ford Distance Vector Bellman-Ford Distance Vector AlgorithmAlgorithm

Running time order of |V| x |E|


Ex: Dijkstra vs. Bellman-Ford Ex: Dijkstra vs. Bellman-Ford Least-cost routing algorithmsLeast-cost routing algorithms


Interior/Exterior Routing Interior/Exterior Routing Protocols Protocols

Hosth2

a

b

b

aaC

A

Bd c

A.a

A.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


Internet Routing ExampleInternet Routing Example


Routing TableRouting Table

Fixed vs. Adaptive Routing?


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)


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)


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


Open Shortest Path First Open Shortest Path First Protocol (Scale, Hierarchy)Protocol (Scale, Hierarchy)


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


Exterior RoutingExterior Routing

RIP

OSPFBGP


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 use preferred routes, providers (based on

policy)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)


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… ?


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 route send/withdraw route informationinformation

– keepalivekeepalive: : acknowledge or acknowledge or confirm relationshipconfirm relationship

– notificationnotification: error : error detecteddetected

chapter 14-16a

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