Review of Networking Technologies
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Review of Networking Technologies Vahid Tabatabaee Fall 2007. References. Title: Internetworking with TCP/IP vol. I Principles, Protocols, and Architecture Author: Douglas E. Comer Publisher: Prentice-Hall

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Review of Networking Technologies

Vahid Tabatabaee

Fall 2007

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  • Title: Internetworking with TCP/IP vol. I Principles, Protocols, and Architecture

    Author: Douglas E. Comer

    Publisher: Prentice-Hall

  • Title: Network Processors Architectures, Protocols, and PlatformsAuthor: Panos C. LekkasPublisher: McGraw-Hill

  • Title Computer Networking: A Top-Down Approach

    Author: J.F. Kurose, K.W. Ross

    Publisher: Addison Wesley

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Connection Oriented Communication

  • Connection oriented communication forms a dedicated connection (circuit, path) between two points.

  • E.g. Telephone systems, ATM, Frame Relay

  • Potential Advantages:

    • Easier to make it reliable (note it is not necessarily more reliable).

    • Guaranteed/reserved bandwidth.

    • Identify flows by connection identifier rather than source/destination address (tag switching)

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Connection-less Communication

  • Data is segmented into packets.

  • Every packet has identification information that enables network hardware to send it to the specified destination.

  • E.g. Ethernet, Internet Protocol

  • Potential Advantages:

    • More efficient use of resources

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Network Hierarchy (3 layer)

  • Enterprise Network

    • Typical networks in companies, universities.

    • Based on Ethernet, Fast-Ethernet, WiFi.

    • Contains one or more LAN connecting PC, printers, servers

    • They can also have faster connections based on Gigabit Ethernet to connect to server and storage subsystems.

    • Gateway and customer access routers provide connection to the rest of the world

  • Access Network (provider network)

    • Aggregate customer traffic.

    • Send the aggregated traffic through a larger pipe into the WAN.

    • We have three kind of routers here:

      • Provider Edge Router (infamous last mile connection)

      • Provider core router

    • The typical speed range OC-3 and OC-48

  • WAN

    • Interconnect provide or career networks

    • The typical speed ranges between OC-12 and OC-192

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  • MAN are large network spanning a campus or city.

  • MAN (WAN) is generally less than (over) 30-50 Km.

  • WAN spans central office facilities, while a MAN starts and ends in a central office


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4 layer Network Hierarchy

  • Core Router Requirements:

    • OC-192 wire-speed IP routing and MPLS

    • VPN

    • Traffic Engineering

  • Edge Router Requirements:

    • Aggregate multiple access network interfaces

    • Access network uplinks can be GigE OC-12

    • Reliability

      • Redundant component

      • Hot pluggable line cards

    • Multiservice Providing Platform (MSSP)

      • TDM OC-3 to OC-192

      • GigE, 10GigE LAN, 10GigE WAN

      • SAN (Fibre Channel, …)

      • IP services

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Sprint Logical Topology

  • 18 IP routers with 36 bidirectional logical links

Source: A. Nucci, A. Sridharan, N. Taft, “The Problem of Synthetically Generating IP Traffic Matrices: Initial Recommendations”, ACM Computer Communication Review, vol. 35, no. 3, pp. 19-32 ,July 2005.

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Sprint WDM Technology

  • 36 OXC with 55 WDM fibers..

  • Wa = 40 OC-192 channels, Wb = 40 OC-48 channels, Wc = 40 OC-12 channels

Source: A. Nucci, A. Sridharan, N. Taft, “The Problem of Synthetically Generating IP Traffic Matrices: Initial Recommendations”, ACM Computer Communication Review, vol. 35, no. 3, pp. 19-32 ,July 2005.

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Ethernet Technology

  • Ethernet is the most popular LAN technology:

    • Shared media

    • Carrier Sense Multiple Access/ Collision Detection (CSMA/CD)

  • There are different variants of the Ethernet technology:

    • Coaxial

    • Thin wire

    • Twisted Pair (10Base-T)

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  • Data rate : 10Mbps

  • Broadcast, bus technology

  • Best effort delivery: Hardware provide no information to the sender that the packet is delivered


  • Max. Segment length: 100m

    • Repeaters relay electrical from one cable to another. At most two bridges between any two machines.

    • Bridges learn addresses and replicate the signal if needed. They isolate Ethernet segments from each other.

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Collision Detection and Recovery

  • It is possible that two transmitters send data simultaneously and collision happens.

  • Each transceiver monitors the cable to see if there is a coliision.

  • When it detects collision it aborts transmission and remain idle before trying again.

  • They use a binary exponential back-off policy.

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Ethernet Hardware Address

  • Ethernet defines a 48-bit addressing scheme.

  • Each hardware card has a unique address assigned to it.

  • Ethernet addresses are sometimes called hardware or physical addresses.

  • Interface card receives all packets, but only send to the host that are addressed to it.

  • Three types of address:

    • Physical address of one network interface.

    • The network broadcast address (all 1s)

    • Multicast address: some interfaces can be programmed to recognize multicast addresses.

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Alternating 0 and 1

Ethernet Frame Format

  • Ethernet frame size are between 64 and 1518 bytes (including header, data, and CRC).

  • There is also 12 byte gap between Ethernet frames.

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1 GigE and 10 GigE

  • It preserves compatibility with legacy software applications developed for running on 10BaseT.

  • The technology has been proposed both for LAN and MAN/WAN.

  • The jumbo frames can be up to 9000 bytes data.

  • 10 GigE is not based on the CSMA/CD technology anymore.

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Internet Architecture

  • Networks are connected by routers

  • Routers need to know about the topology of the internet beyond the networks to which they connect.

  • Routers use the destination network, not the destination host, when routing a packet.

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  • What is the exact form of Internet Addresses?

  • How Internet addresses are mapped to the Hardware addresses such as Ethernet addresses?

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Host Universal Identifiers

  • Host Identifiers are:

    • Names: specify what an object is.

    • Addresses: Where it is.

    • Routes: How to get there.

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Classes of IP Addresses

  • Each host has a unique 32 bit internet address.

  • Each address is a pair of (netid, hostid). -- -- -- -- --

  • is the loopback address in IP. ( to

  • – (zero addresses should not be used).

  • broadcast to all other nodes on the LAN

  • In general zeros mean this and ones mean all.

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Classless Inter-Domain Routing

  • It replaces the older system based on classes

  • Most sites were too big for class C and received class B number.

  • Depletion of class B addresses (~16,000 total)

  • It looks like a normal IP address but it ends with a slash and a number following it.

  • It facilitates routing by allowing blocks of addresses to be grouped together into single routing table entries.


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An example for CIDR

  • Different CIDR prefixes are used in different locations for routing

Outside MCI network

Inside MCI network

Inside ARS network

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Weaknesses in Internet Addressing

  • If a computer moves from one network to another, its IP address must change.

    • This is the main source of challenge for mobile IP.

  • The path used for hosts with multiple IP addresses (multi-homed hosts) depends on the address used.

  • If host B connection to network 1 fails, packets from host A that uses I3 address can not reach host B.

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Address Aggregation

Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

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More specific routes

Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

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Mapping Internet Address to Physical Address

  • Consider two machines A and B on the same network.

  • IA, IB are internet addresses and PA, PB are physical addresses of A and B respectively.

  • A wants to send a packet to B, but it only has IB address of B.

  • Address Resolution Protocol (ARP) resolves this problem for networks with static address and broadcast capability.

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  • Host A has an ARP cache of recently acquired IP-to-physical address bindings.

  • If IB is not in the cache, then A broadcasts an ARP request containing IB.

  • Host B responds with an ARP reply to A that contains (IB, PB). It also adds (IA, PA) to its own cache.

  • Sender A queues all packets destined to B until it receives ARP reply.

  • Expiring timer for the binding entries in the cache.

  • Resending the request (at least once) if did not get a reply.

  • In most technologies a single type value is used for ARP frames.

    • In Ethernet type field of (0806)16 is for ARP messages.

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  • A machine uses Reverse Address Resolution Protocol (RARP) to get its IP address from the server at the startup.

  • The server has a list of IP addresses of the machines.

  • Machine uses its physical address to communicate on the network.

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IP Packet (Datagram) delivery

  • The maximum size of an IP datagram is 216 octets.

  • It is more efficient to carry each IP packet in a network frame (encapsulation).

  • Each technology has a different maximum frame size

    • Ethernet 1500 octets

    • FDDI 4470 octets

  • IP chooses a appropriate initial datagram size.

  • Fragmentation is the process of dividing larger packets into smaller ones to adhere to the network Maximum Transfer Unit (MTU).

  • Destination uses the Identification, Flags, and Fragment offset to reassembly the packet.

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Time To Live field

  • Time To Live field specifies how long a packet is allowed to be in the Internet.

  • The source sets the maximum time that the datagram should survive.

  • Each router decrement this field by one when it process the packet.

  • To take into account buffering delay, each router records arrival time and decrement the field by seconds that packet stays in the router.

  • When TTL reaches zero, the router discards the packet.

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IP routing

  • Direct Delivery:

    Transmission of packets from one machine across a SINGLE physical network to another.

  • Indirect Delivery:

    Destination is not connected directly to the network of the sender, hence sender should pass the packet to a router for delivery.

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Direct Delivery

  • Does not involve the router.

  • Sender encapsulates the datagram in a single physical frame.

  • Binds the destination IP address to a physical hardware address using ARP (if needed).

  • How does the sender know if the destination is directly connected to the same network?

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Indirect Delivery

  • Host (sender):

    Encapsulates the datagram in a physical network frame and send it to a router attached to the network.

  • Router:

    Extracts the encapsulated datagram,

    Decides the next router to send the datagram to.

    Encapsulates the Datagram for transmission over the next network.

  • Question:

    How a router and host decide next router to send the datagram to?

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IP Routing Table

  • Every host and router has a routing table

  • Routing table has information about destination and how to reach them.

  • We can not have a separate entry for every possible destination.

  • First refinement: We can have a single entry for all hosts connected to the same network and only check the netid part of the internet address.

  • Second refinement: We only need to keep the information for the next hop not the entire path for each destination.

  • All next hop routers listed in router M routing table must lie on networks to which M connects directly.

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Routing Table

  • Longest Prefix Match:

    • Recall that in CIDR more than one table entry may match the destination address.

    • The one with largest prefix number is used for routing.

    • Routing Table Entries:



  • Default Routes:

    • A default route is used by a router or a server when no other known route works for a packet destination address.

    • The default route in CIDR is

    • Hosts and routers in an organization generally point the default route towards the router that has connection to a network service provider

Both entries match the destination

address, but the second

one with larger prefix number is used.


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Example: Route Selection in Cisco Routers

  • This example is based on the “Route Selection in Cisco Routers, Document ID: 8651 available at:

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Routing Table

There are three process involved in building and maintaining the routing table:

  • Various Routing Process, which run a routing protocol such as:

    • Enhanced Interior Gateway Routing Protocol (EIGRP)

    • Border Gateway Protocol (BGP)

    • Intermediate System-to-Intermediate System (IS-IS)

    • Open Shortest Path First (OSPF)

  • The routing table, which accepts information from routing process and replies to requests from the forwarding process.

  • The forwarding process, which requests information from the routing table for packet forwarding.

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Building the Routing Table

Main considerations in building the routing table:

  • Administrative Distance: This indicates how much we trust source of the route.

  • Metric: This is a measure used by the routing protocol to calculate the best path to a given destination.

  • Prefix length

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Routing Table Entry Update

Assume there are four routing process running:


  • All 4 process learned various routes to and each has chosen its best path to that network using its internal metrics and process.

  • Each routing process attempts to install their route in the routing table.

  • The one with lowest administrative distance (EIGRP here) can install its route in the routing table

  • Other routes may be used as backup routes

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Prefix Lengths

  • Assume the three routing process have received these routes:

    • EIGRP (internal): / 26

    • RIP: / 24

    • OSPF: / 19

  • ALL these routes will be installed in the routing table, since they have different prefix length.

  • Routing Table:


    D via

    R via

    O via


A packet destined for is forwarded to, which has the longest prefix match (26 bits verses 24 or 19 bits).

A packet destined for is forwarded to, because it does NOT fall within (—

But it falls within the destination (

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Dynamic Host Configuration Protocol (DHCP)

  • The router IP addresses are typically configured manually, often remotely with a network management tool.

  • Host addresses is typically configured using the DHCP protocol.

  • DHCP can give a host the same IP address each time it connects to the network or assign a temporary IP address that will be different each time the host connects to the network

  • DHCP also provides additional information such as subnet mask, address of the first hop router (default gateway) and address of the local DNS server.

  • DHCP is also used commonly in residential access networks and in wireless LANs.

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DHCP architecture

  • DHCP is a client-server protocol

  • Newly arriving hosts are clients

  • DHCP server has the information requested by the clients

  • Subnets may have a DHCP server

  • If there is no server in a subnet, a DHCP relay agent knows the address of a DHCP server for that network


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DHCP 4-step process

  • DHCP server discovery: Newly arriving host sends DHCPDISCOVER message a UDP packet to port 67. This message is broadcasted.

  • DHCP sservers respond with DHCPOFFER, which is again broadcasted. The message cotains the transaction ID, the proposed IP address, the network mask, lease time.

  • The client will choose one server offer and respond to that server with a DHCPrequest message.

  • The server responds with DHCPACK

When the renewal timer expires

When the rebinding timer expires


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Mobility Management

  • Home Network: The permanent home of a mobile node.

  • Home Agent: The entity within the home network that performs the mobility management functions.

  • Foreign Network: The network where the mobile node is currently residing.

  • Foreign Agent: The entity in the foreign network that help the mobile node with the mobility management functions.

  • Correspondent: The entity that wants to communicate with the mobile node

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Mobile Network Architecture

Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

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Addressing (Naïve Approach)

  • Foreign Network advertises to its neighbors that it has a highly specific route to the mobile node permanent IP address.

  • When mobile node leaves one foreign network and joins another the new foreign network, the new foreign agent would advertise that it has a specific route and the old one eould withdraw its routing information.

  • Drawback: Scalability; it completely destroys the hierarchical structure of IP addresses.

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Addressing for mobile

  • Foreign agent is located at the edge of the foreign network.

  • Foreign agent creates a care-of address (COA) for the mobile node, with the network portion of the COA matching that of the foreign network.

  • Note that there are two addresses for the mobile node:

    • Permanent address

    • Foreign address

  • The foreign agent informs the home agent that the mobile node is in its network and has the given COA.

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Indirect Routing to a Mobile Node

  • The correspondent addresses the packet to the mobile node’s permanent address.

  • The packet is first routed to the mobile node home agent.

  • The home agent forwards the packet to a mobile node in two steps:

    • The packet is first forwarded to the foreign agent using the COA

    • From the foreign agent to the mobile node.

  • Mobile node can address directly its packets to the correpondent.

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Indirect Forwarding

Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

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Encapsulation and Decapsulation

  • Home agent encapsulates packets

  • Foreign agent decapsulates packets

Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

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Network Layer Functionality to Support Mobility

  • Mobile Node to Foreign Agent: The mobile node registers with the foreign agent and deregisters when it leaves the network.

  • Foreign Agent to Home Agent: Foreign agent registers the mobile node ‘s COA with the home agent. Does it need to deregister the COA when the mobile node leaves its network?

  • Home Agent Packet Encapsulation: Encapsulation and forwarding of the original packets within a packet with the COA address

  • Foreign Agent Decapsulation: Extraction of the correspondent’s original packet and forwarding of it to the mobile node.