Tree Structured Internet(c. 1990) Stanford NSFNET backbone ISU BARRNET MidNet … regional W estnet regional regional Berkeley P ARC UNL UNM KU NCAR UA Autonomous Systems CS565 Internetworking

The Global Internet We know How to internetwork(heterogeneous) IP scalability Routers don’t need to know about every host Need to know about all the networks Ten of thousands of networks CS565 Internetworking

Scaling Two related scaling issues Scalability of routing Minimize # of network numbers in routing protocols Minimize # of entries in the routing tables Address utilization Minimize the usage rate of IP addresses Classless routing CS565 Internetworking

Making Routing Scale Need efficient Hierarchical Addressing Reduce the # of network numbers assigned Inefficient use of Hierarchical Address Space class C with 2 hosts (2/254 = 0.78% efficient) class B with 256 hosts (256/65534 = 0.39% efficient) 7 24 (a) Network Host 14 16 Any network with > 255 hosts (b) 1 Network Host 21 8 (c) 1 1 Network Host CS565 Internetworking

Subnetting Split a single IP network number into several subnets Add another level to address/routing hierarchy: subnet Subnet masks enable physical networks to share the same subnet number Subnets visible only within site, world sees single network Network number Host number Class B address Subnet mask (255.255.255.0) Subnetted address 111111111111111111111111 00000000 Host ID Subnet ID Configure each node with a subnet mask Hosts now configured with IP address and subnet address CS565 Internetworking

Subnet Example Forwarding table at router R1 Subnet mask: 255.255.255.128 Subnet number: 128.96.34.0 128.96.34.15 128.96.34.1 H1 R1 128.96.34.130 Subnet number: 128.96.34.128 128.96.34.129 128.96.34.139 R2 H2 128.96.33.1 128.96.33.14 Subnet mask: 255.255.255.0 Subnet number: 128.96.33.0 H3 Forwarding table at router R1 Subnet Number Subnet Mask Next Hop 128.96.34.0 255.255.255.128 interface 0 128.96.34.128 255.255.255.128 interface 1 128.96.33.0 255.255.255.0 R2 CS565 Internetworking

Datagram Forwarding Algorithm D = destination IP address for each entry (SubnetNum, SubnetMask, NextHop) D1 = SubnetMask & D if D1 = SubnetNum if NextHop is an interface deliver datagram directly to D else deliver datagram to NextHop Use a default router if nothing matches Not necessary for all 1s in subnet mask to be contiguous Can put multiple subnets on one physical network Subnets not visible from the rest of the Internet CS565 Internetworking

Chapter 4 “There is more than one network” Point-to-point links Shared media Switches Goal – connect these things together Heterogeneity Scale Routing(connection of nodes) Addressing Introduce the Internet Protocol(IP) CS565 Internetworking

Internet, internet or internetwork Concatenation of Networks Protocol Stack R2 R1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7 R3 H8 Routers/Gateways R1 ETH FDDI IP TCP R2 PPP R3 H1 H8 CS565 Internetworking

Service Model the services that are to be provided from host-to-host IP provides Datagram data delivery service Connectionless (datagram-based) / full dest Best-effort delivery (unreliable service) packets are lost packets are delivered out of order duplicate copies of a packet are delivered packets can be delayed for a long time CS565 Internetworking

Datagram Datagram format Version-IP e.g. IPv4, IPv6 Hlen-Header length TOS-Type Of Service TTL-Time To Live Protocol-UDP/TCP V ersion HLen TOS Length Ident Flags Offset TTL Protocol Checksum SourceAddr DestinationAddr Options (variable) Pad (variable) 4 8 16 19 31 Data Assigned at 32-bit Boundary CS565 Internetworking

Fragmentation and Reassembly Each network has some Maximum Transmission Unit(MTU) – largest IP datagram that it can carry in a frame. Strategy fragment when necessary (MTU < Datagram) try to avoid fragmentation at source host re-fragmentation is possible when travel to a different network fragments are self-contained datagrams delay reassembly until destination host do not recover from lost fragments CS565 Internetworking

Global Addresses All hosts attached to the same network have the same network field The host field unique Routers have two interfaces R2 R1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7 R3 H8 CS565 Internetworking

Datagram Forwarding How do IP routers forward datagrams? Strategy (main points) every datagram contains destination’s address if directly connected to destination network, then forward to host(i.e. same network number) if not directly connected to destination network, then forward to some router(next hop router-host selected) Hosts = 1 interface, routers >= 2 interfaces forwarding table maps network number into next hop each host has a default router each router maintains a forwarding table CS565 Internetworking

Datagram Forwarding Example (R2) Network Number Next Hop 1 1 R3 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7 R3 H8 Example (R2) Network Number Next Hop 1 R3 2 R1 3 interface 1 4 interface 0 1 Routers/Gateways CS565 Internetworking

Bridges, Switches, and Routers Confusion? Bridges Link-level to forward frames from one link to another to create extended LANs Switches Network-level to forward packets from one link to another to create packet-switched networks Routers Internet-level to forward datagrams from network to another Bridges/Switches (above the physical below the internet) CS565 Internetworking

IP Mapping IP datagrams contain IP addresses Physical interface only understands the addressing specific to its link-level(i.e. Ethernet, Token-Ring, etc) Problem – how to put the two together? Solution – have each host maintain a table of address pairs. CS565 Internetworking

ARP - Address Translation Map IP addresses into physical addresses destination host next hop router ARP cache or ARP table ARP (Address Resolution Protocol) table of IP to physical address bindings dynamically created broadcast request if IP address not in table target machine responds with its link-level and physical address table entries are discarded if not refreshed CS565 Internetworking

Routing For VC’s (one-off setup) For datagrams, every packet must be routed Regardless, switches and routers must Look at destination port Determine the output port best suited transmission CS565 Internetworking

Routing & Forwarding Routing tables are constructed as precursors to forwarding table construction Routing algorithms Map Ntwk #s to NHs Optimized for changes in topology Forwarding tables Ntwk #s, Output interfaces, MAC address of NH Optimized to look up Ntwk #s CS565 Internetworking

Routing & Forwarding Routing Table Network NH (NextHop) 10 171.29.222.38 Forwarding table Network Int MAC Address 10 if0 8:0:2 B:E 4:B:1:2 CS565 Internetworking

Routing Domain What is a routing domain? it is a matter of graph theory hosts, switches, routers, or networks network links w/associated costs CS565 Internetworking

Routing Protocol How to store the shortest paths? calculate and store in non-volatile memory? Nope! Node/link failures not handled Node/link additions not handled Edge costs do not change Run routing protocols among nodes instead Distance vector and link state CS565 Internetworking

Distance Vector(Bellman-Ford) Each node maintains a set of triples (Destination, Cost, NextHop) Exchange updates directly connected neighbors periodically (on the order of several seconds) whenever table changes (called triggered update) Each update is a list of pairs: (Destination, Cost) Update local table if receive a “better” route smaller cost came from next-hop Refresh existing routes; delete if they time out CS565 Internetworking

Distance Vector Destination Cost NextHop Destination Cost NextHop B 1 B C 1 C D E 1 E F 1 F G Destination Cost NextHop B 1 B C 1 C D 2 C E 1 E F 1 F G 2 F With no topological changes Only a few exchanges for completion Realization of routing tables at nodes is called convergence The beauty - no one node is responsible for being the central authority CS565 Internetworking

Routing Updates Two circumstances under which a node sends an update Periodic updates (I’m alive!) Triggered updates (recipient) CS565 Internetworking

Routing Protocols Interior Gateway Protocols(IGP) Distance Vector Updates based upon directly connected neighbors Destination, cost, and NH (NextHop) Count-to-Infinity RIP Link State Updates communicated through network CS565 Internetworking

Routing Information Protocol(RIP) Probably the most used routing protocol today Example distance vector protocol RIP send advertisements every 30 seconds Routers also send updates when it receives an update from another router All link costs = 1 Minimum hop route Valid distance = 1 16() CS565 Internetworking

Link State Routing Strategy Link State Packet (LSP) send to all nodes (not just neighbors) information about directly connected links (but not entire routing table) Reliable flooding of Link State Packet (LSP) Each node then has complete topology of network Apply any shortest path algorithm (e.g. Dijkstra) to find the shortest route Link State Packet (LSP) id of the node that created the LSP cost of link to each directly connected neighbor sequence number (SEQNO) time-to-live (TTL) for this packet CS565 Internetworking

OSPF Open Shortest Path First (OSPF) Most commonly used type of LSP CS565 Internetworking

Distance Vector vs. Link State Each node talks to only its directly connected neighbors all other nodes via LSP(Flooding) It relays everything it knows – distance to all other nodes only the costs of its directly connected links CS565 Internetworking