Slide 1Review of Networking Technologies
References
Author: Douglas E. Comer
Author: Panos C. Lekkas
Author: J.F. Kurose, K.W. Ross
Publisher: Addison Wesley
Connection Oriented Communication
E.g. Telephone systems, ATM, Frame Relay
Potential Advantages:
Easier to make it reliable (note it is not necessarily more reliable).
Guaranteed/reserved bandwidth.
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Connection-less Communication
Every packet has identification information that enables network hardware to send it to the specified destination.
E.g. Ethernet, Internet Protocol
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Network Hierarchy (3 layer)
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
WAN
The typical speed ranges between OC-12 and OC-192
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Conceptual Hierarchy of Networks
LAN/MAN/WAN
Source:
MAN
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
Source:
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4 layer Network Hierarchy
VPN
Access network uplinks can be GigE OC-12
Reliability
SAN (Fibre Channel, …)
Sprint Logical Topology
18 IP routers with 36 bidirectional logical links
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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
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Ethernet Technology
Shared media
There are different variants of the Ethernet technology:
Coaxial
10Base-T
Data rate : 10Mbps
Broadcast, bus technology
Best effort delivery: Hardware provide no information to the sender that the packet is delivered
Source:
http://www.webclasses.net/Courses/Intro/6.1/demo/units/unit02/sec04b.html
Max. Segment length: 100m
Repeaters relay electrical from one cable to another. At most two bridges between any two machines.
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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
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:
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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.
10101011
1 GigE and 10 GigE
It preserves compatibility with legacy software applications developed for running on 10BaseT.
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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.
Cloud
Questions
What is the exact form of Internet Addresses?
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Host Universal Identifiers
Host Identifiers are:
Addresses: Where it is.
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Classes of IP Addresses
Each address is a pair of (netid, hostid).
127.0.0.1 is the loopback address in IP. (127.0.0.0 to 127.255.255.255)
0.0.0.0 – 0.255.255.255 (zero addresses should not be used).
255.255.255.255 broadcast to all other nodes on the LAN
In general zeros mean this and ones mean all.
0.0.0.0 --127.255.255.255
128.0.0.0 --191.255.255.255
192.0.0.0 --223.255.255.255
224.0.0.0 --239.255.255.255
240.0.0.0 --255.255.255.255
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.
Source:
http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing
An example for CIDR
Different CIDR prefixes are used in different locations for routing
Outside MCI network
Inside MCI network
Inside ARS network
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.


Address Aggregation
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More specific routes
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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.
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ARP
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.
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RARP
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.
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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).
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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:
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Direct Delivery
Sender encapsulates the datagram in a single physical frame.
Binds the destination IP address to a physical hardware address using ARP (if needed).
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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:
Question:
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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.
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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 0.0.0.0/0
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 192.168.20.19, but the second
one with larger prefix number is used.
Source: Wikipedia
Example: Route Selection in Cisco Routers
This example is based on the “Route Selection in Cisco Routers, Document ID: 8651 available at:
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.
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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
Routing Table Entry Update
EIGRP, OSPF, RIP, IGRP
All 4 process learned various routes to 192.168.24.0/24 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
Default Administrative Distances
Prefix Lengths
EIGRP (internal): 192.168.32.0 / 26
RIP: 192.168.32.0 / 24
OSPF: 192.168.32.0 / 19
ALL these routes will be installed in the routing table, since they have different prefix length.
Routing Table:
....
A packet destined for 192.168.32.1 is forwarded to 10.1.1.1, which has the longest prefix match (26 bits verses 24 or 19 bits).
A packet destined for 192.168.32.100 is forwarded to 10.1.1.2, because it does NOT fall within 192.168.32.0/26 (192.168.32.0—192.168.32.63).
But it falls within the 192.168.32.0/24 destination (192.168.32.0-192.168.32.255)
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Forwarding Decision Process
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.
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DHCP architecture
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
Source:http://www.windowsitpro.com/Files/5181/Figure_02.gif
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
Source:http://www.windowsitpro.com/Files/5181/Figure_01.gif
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.
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Mobile Network Architecture
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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.
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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
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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.
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Indirect Forwarding
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Encapsulation and Decapsulation
Home agent encapsulates packets
Foreign agent decapsulates packets
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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.
Enterprise Network
Access Network