is451e1review

B. stateless

d. Bus

b. Star

d. All of the above

b. Can use any amount of bandwidth available

a. Pipelined

b. To dynamically configure IP protocol on hosts

c. A specific process running on a network host

a. SMTP

a. Socket

b. 2

d. UDP because it provides faster timing/delivery

b. 25

b. Transport

a. UDP + (plus) reliability

a. IMAP

a. Iterative queries place less burden on a queried DNS server

d. To encode non-ASCII email

a. It reduces average response delay to clients

b. Usually runs for a specific period of time when needed

b. User agent

c. Separate different network functions

c. It can be used to always assign the same address to the same host

b. Allows persistent HTTP connections to used more efficiently

d. All of the above

e. A and c

d. Multiple objects can be transferred through the same connection

b. To have a different MAC and IP addresses than 2 physical routers

e. Both routers and VLANs

d. Only logical, but not physical topology will change

d. Layer 3 switch

d. High-speed link between internetworking devices

b. access

c. To provide fault-tolerance for the default gateway address for end stations

c. More end devices per segment are connected at faster speeds

Port

FTP

VRRP/HSRP

STP

IMAP

• 29 is equivalent to the port number
• Elm Street is equivalent to host number

• Core - in the middle
• Distribution
• Access -closer to the user

• Collision domain is on each switch port to prevent packets sent at the same time to collide with one another.
• Broadcast domain on a router to broadcast or send signal to hosts

• To exchange information about VLAN configuration
• VLAN info for VLANs spanning switches

• terms client and server indicate which side initiates contact
• Clients: communicate with server; must know which server to contact; contacts the server when needed; may terminate after interacting with the server; may have dynamic IP addresses; do not communicate directly with each other
• Server: always-on host; permanent IP address; Waits passively for client contact; server farms for scaling, server-class computers; handles multiple clients concurrently (threads of execution)

no always-on server; arbitrary end systems directly communicate; peers are intermittently connected and change IP addresses; example: Gnutella, Freenet, Bittorrent; Highly scalable but difficult to manage

• Skype: Centralized server: finding address of remote party; Client-client connection is direct (not through server)
• Instant messaging: Chatting between two users is P2P; Presence detection/location centralized: User registers its IP address with central server when it comes online; User contacts central server to find IP addresses of buddies

• Client process: process that initiates communication
• Server process: process that waits to be contacted

• Program running within a host
• Within same host, two processes communicate using inter-process communication (defined by OS)
• Processes in different hosts communicate by exchanging messages

• Allow for interoperability
• Standardized services independent of implementation
• e.g. HTTP, SMTP
• Proprietary protocols: For private communication, e.g. KaZaA

• 1. Data representation
• 2. Data Transfer

Process sends/receives messages to/from its socket

• to receive messages, process must have identifier; identifier includes both IP address and port numbers associated with process on host; e.g. HTTP server: 80; Mail server: 25
• Host device has unique 32-bit IP address

HTTP: port 80; FTP: port 20 data /21 control; DNS: port 53; DHCP: port 67 (server); SMTP: port 25

• Data loss: Some apps (e.g. audio) can tolerate some loss; Other apps (e.g. file transfer, telnet) require 100% reliable data transfer
• Timing: Some apps (e.g. Internet telephony, interactive games) require low delay to be "effective"
• Bandwidth: Some apps (e.g. multimedia) require minimum amount of bandwidth to be "effective"

• TCP service: connection-oriented; Point-to-point 1-to-1 connection; Stream interface; Sequence of individual bytes; Reliable transport; Flow control
• UDP service: Connectionless; Message-oriented communication; Unreliable (best effort) transfer; Many-to-many interaction
• Does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee

• SCTP (Stream Control Transmission Protocol): Message-oriented like UDP but … like TCP; Sequence of individual bytes; Reliable transport; Flow control; Multi-streaming; Multi-homing; Improved security
• DCCP (Datagram Congestion Control Protocol): Congestion control (like TCP) for unreliable communication (like UDP); Connection setup/teardown; Feature negotiation mechanism (variable features, such as Congestion control ID); Protection against corruption (checksum)

• HTTP: Hypertext transfer protocol: Web's application layer protocol
• HTTP is "stateless": server maintains no information about past clients requests

• client: browser that requests, receives, “displays” Web objects
• server: Web server sends objects in response to requests

• request, response
• HTTP request message:
• ASCII (human-readable format)

• At most one object is sent over a TCP connection; HTTP/1.0 uses nonpersistent HTTP
• Nonpersistent HTTP issues: requires 2 RTTs per object; OS overhead for each TCP connection; browsers often open parallel TCP connections to fetch referenced objects

• Multiple objects can be sent over single TCP connection between client and server; HTTP/1.1 uses persistent connections in default mode
• server leaves connection open after sending response; subsequent HTTP messages between same client/server sent over open connection

client issues new request only when previous response has been received; one RTT for each referenced object

default in HTTP/1.1; client sends requests as soon as it encounters a referenced object; as little as one RTT for all the referenced objects; two types of HTTP messages: request, response; HTTP request message: ASCII (human-readable format)

• A persistent connection where a client doesn’t wait for a response from an HTTP server before issuing a new request
• Is an implementation technique where multiple instructions are overlapped in execution.
• The computer pipeline is divided in stages. Each stage completes a part of an instruction in parallel. The stages are connected one to the next to form a pipe - instructions enter at one end, progress through the stages, and exit at the other end.
• Pipelining does not decrease the time for individual instruction execution. Instead, it increases instruction throughput. The throughput of the instruction pipeline is determined by how often an instruction exits the pipeline

• FTP: the file transfer protocol: transfer file to/from remote host
• FTP server: port 21; data 20, control 21
• FTP uses 2 ports/2 connections for data and commands
• Control connection: "out-of-band"
• Maintains "state": current directory, earlier authentication
• Separate control, data connections
• FTP client contacts FTP server at port 21, specifying TCP as transport protocol; Client obtains authorization over control connection; Client browses remote directory by sending commands over control connection.; When server receives a command for a file transfer, the server opens a TCP data connection to client; After transferring one file, server closes connection.; Server opens a second TCP data connection to transfer another file.

• client: side that initiates transfer (either to/from remote)
• server: remote host

• User agents
• Mail servers
• Simple mail transfer protocol: SMTP

• Composing, editing, reading mail messages
• Outgoing, incoming messages stored on server

• Mailbox contains incoming messages for user
• Message queue of outgoing (to be sent) mail messages
• SMTP protocol between mail servers to send email messages

• Simple mail transfer protocol: SMTP
• protocol for exchanging email msgs
• SMTP uses persistent connections
• SMTP server uses CRLF.CRLF to determine end of message
• Push protocol, simple ASCII text only.

• client: sending mail server
• “server”: receiving mail server

• HTTP: pull, SMTP: push
• Both have ASCII command/response interaction, status codes
• SMTP requires message (header & body) to be in 7-bit ASCII
• HTTP: each object encapsulated in its own response msg
• SMTP: multiple objects sent in multipart msg

• MIME: multimedia mail extension
• Additional lines in msg header declare MIME content types

• SMTP: delivery/storage to receiver's server
• Mail access protocol: retrieval from server: POP: Post Office Protocol; IMAP: Internet Mail Access Protocol
• HTTP: Hotmail, Yahoo! Mail, etc.

• Post Office Protocol
• Authorization (agent <--> server) and download
• Usually uses "download and delete" mode
• Bob cannot re-read email if he changes client
• "Download-and-keep": copies of messages on different clients
• POP3 is stateless across sessions

• Internet Mail Access Protocol
• More features (more complex)
• Manipulation of stored msgs on server
• Keep all messages in one place: the server
• Allows user to organize messages in folders
• IMAP keeps user state across sessions: Names of folders and mappings between message IDs and folder name

• Distributed database implemented in hierarchy of many name servers
• Application-layer protocol host, routers, name servers to communicate to resolve names (address/name translation)

• Hostname to IP address translation
• Host aliasing: Canonical and alias names
• Mail server aliasing
• Load distribution: Replicated Web servers: set of IP addresses for one canonical name

• single point of failure
• traffic volume
• distant centralized database
• maintenance
• doesn’t scale!

• Root DNS servers --> com DNS servers --> yahoo.com DNS servers
• Root name servers:
• Top-level domain (TLD) servers:
• Authoritative DNS servers:

• Network solutions maintains servers for com TLD
• Educause for edu TLD

Can be maintained by organization or service provider

• Does not strictly belong to hierarchy
• Each ISP (residential ISP, company, university) has one: Also called “default name server”
• When a host makes a DNS query, query is sent to its local DNS server: Acts as a proxy, forwards query into hierarchy.

• iterative query: contacted server replies with name of server to contact (referral)
• “I don’t know this name, but ask this server”
• recursive query: puts burden of name resolution on contacted name server

• once (any) name server learns mapping, it caches mapping
• cache entries timeout (disappear) after some time
• TLD servers typically cached in local name servers: thus root name servers not often visited
• Caching optimizes DSN query response times

• DHCP: Dynamic Host Configuration Protocol - dynamically “leases” IP configuration information
• -dynamically allocates IP addresses and configuration options to hosts on a network
• Based on BOOTP protocol
• Non-routable, requires relay agents to route across subnets
• in dynamic allocation addresses are “leased” to hosts temporarily. (the duration of lease can vary depending on traffic and number of addresses available for a certain number of clients)

Manual allocation, automatic allocation, dynamic allocation

• the network administrator on the DHCP server manually configures the client's IP address in the server.
• When the client workstation makes the request for an IP address, the server looks at the MAC address (Media Access Control address; manufacture's unique address of the network card) and assigns the client the manually set IP address.

• the DHCP client workstation is assigned an IP address when it first contacts the DHCP server.
• In this method the IP address is randomly assigned and is not set in the server.
• The IP address is permanently assigned to the DHCP client and is not reused by another DHCP client.

• the DHCP server assigns an IP address to a requesting client workstation on a temporary basis.
• The IP address is leased to the DHCP client for a specified duration of time.
• When this lease expires, the IP address is revoked from the client and the client is required to surrender the address.
• If the DHCP client still needs an IP address to perform its functions, it can request another IP address.
• Addresses are “leased” to hosts temporarily. (The duration of lease can vary depending on traffic and number of addresses available for a certain number of clients)

• all are prone to scalability problems
• What is the current most used topology? Why?
• Compare and contrast physical and logical topologies.

• Faster CPUs
• Faster Operating Systems
• Network-intensive applications

• Bandwidth (not shared)
• VLANs
• Security

• End devices are the devices that care about Layer 7. End devices run applications, request data from one another, present information to humans, or control machinery; most importantly, end devices should never perform network functions
• An internetwork is a collection of individual networks, connected by intermediate networking devices, that functions as a single large network. Internetworking refers to the industry, products, and procedures that meet the challenge of creating and administering internetworks

the central device aggregates the traffic from every device and broadcasts it back out to all other devices, letting them decide for themselves packet by packet what they should pay attention to

faster than a router because the decisions it makes are much simpler

• the central device could act as a switch and selectively send traffic only where it is intended to go
• connects end points to the network, operates at layer 2, fast, not as smart inexpensive per port

• connects switches to each other; operates at layer 3; comparatively smart, slow, expensive per port
• Routers use Layer 3 information to make routing decisions (routing tables) and choose the “optimal” path
• Routers use routing protocols (e.g. OSPF, BGP) to exchange updates/routing info
• Routers filter broadcasts and multicasts, switches don’t – can create broadcast storm
• Routers create separate broadcast domains
• Switches don’t have network (host) addresses, routers do.
• Routers modify destination’s physical (not network) address

making the router a card in a Layer 2 switch, makes a single physical connection to the shared backplane of the switch

• Is an area of the network where you have two station stand at the same time boom there's a collision and that happen if you have a HUB … switch … collision domain to a port of a switch so collision domain when a device and a switch
• Collision domain is on each switch port to prevent packets sent at the same time to collide with one another.

• The area in the network where broadcast … so with a switch we're eliminated, we have multiple collision domain … we still have one large broadcast domain … we switches the router now we have smaller broadcast domain
• Broadcast domain on a router to broadcast or send signal to hosts

Fault-tolerance-art and science of building computing systems that continue to operate satisfactorily in the presence of faults.

• STP: Spanning Tree Protocol or IEEE 802.1d
• eliminates loop and it activates redundant links for automated fault recovery; activates backup links and devices
• Is a Layer 2 protocol designed to run on bridges and switches.
• The main purpose of spanning tree is to prevent loops from forming in a switched network.

• HSRP: Hot Standby Router Protocol: A Cisco proprietary system
• VRRP: Virtual Router Redundancy Protocol: an open standard
• Both of these protocols work by allowing end devices to send packets to a default gateway IP address that exists on both routers.
• However, end devices actually send their packets to the Layer 2 address associated with that default gateway IP address in their ARP cache.
• They don't use the default gateway address directly.
• When the backup router takes over for the primary router's default gateway functions, it must adopt both the IP address and the Layer 2 MAC address.
• Both VRRP and HSRP have quick and efficient methods of making this change.
• When one router fails, the other takes over and the end stations on that segment are not even aware that a problem has occurred.

• They reroute traffic through the backup link
• OSPF: Open Shortest Path First: router protocol, a host that obtains a change to a routing table or detects a change in the network immediately multicasts the information to all other hosts in the network so that all will have the same routing table information.
• RIP: Routing Information Protocol: for route updates. RIP calculates the best route based on hop count.

• They're different from dynamic routing protocols because they don't get confuse with multiple route, router you got protocol, like RIP or OSPF to update each other on what their route look like how to get token of the network
• HSRP and VRRP are require to create redundancy for the default gateway for the end coast

• A VLAN is a switched network that is logically segmented on an organizational basis, by functions, project teams, or applications rather than on a physical or geographical basis
• VLANs consist of end systems that are members of a single logical broadcast domain.
• A VLAN has no physical proximity constraints for the broadcast domain
• A VLAN can span various pieces of network equipment that support VLAN trunking protocols between them
• Without a router, hosts in 1 VLAN can’t communicate with hosts in another VLAN

• VLANs break networks into smaller broadcast domains
• VLANs provide security
• Easier network management
• Well-behaved VLANs usually follow 80/20 network design rule

• Trunk – high-speed connection between internetworking devices
• Switches use Trunking protocol to exchange information about VLAN configuration (e.g. IEEE 802.1Q, Cisco’s ISL)
• With trunking, tags are added to all the frames traveling on the trunk

Is when you have many, many different ports and many different source combine to a VLAN so what you end doing there is creating a lot of traffic between the switches maintaining that VLAN a lot of overhead traffic and in addition to the normal traffic you now have all those packet that are tagged with VLAN information, so spaghetti VLAN create a extra load extra traffic on the trunk between the switches

• Keep loads down on routers that direct your VLAN-to-VLAN traffic
• -80% of your traffic is local and 20% need to cross the Core
• The majority of the traffic stay within the segment and only some of the traffic crosses over
• -The less traffic that has to cross through the Core, the happier and less congested it will be

• By port – each port must belong to only 1 VLAN
• In a port based VLAN, the administrator assigns each port of a switch to a VLAN.
• For example, ports 6-10 might be assigned to the Manufacturing VLAN, ports 1-4 to the Sales VLAN and ports 4-6 to the Accounts VLAN.
• The main drawback of VLANs defined by port is that the systems manager must reconfigure VLAN membership when a user moves from one port to another.

• By protocol – single port can support more than 1 VLAN
• VLANs based on Layer 3 information take into account protocol type (IP, NetBIOS) and Layer 3 addresses in determining VLAN membership.
• One of the main benefits of this method is that users can physically move their workstation without having to reconfigure their workstation's network address.
• The shortcoming of VLANs based on Layer 3 is the slow performance.

• By a user-defined value – e.g. MAC address
• In MAC address-based VLANs, membership is defined by the source or destination MAC.
• The main advantage of this model is that the switch doesn't need to be reconfigured when a user makes a move to a different port.
• The main problem with MAC address-based VLANs is that a single MAC address cannot easily be a member of multiple VLANs.

• Why is the old rule of bridging on campus and routing off being changed?  
• -refer to a high-capacity part of the network that collects traffic from many smaller segments.
• -it can gather traffic from several remote LANs onto a network backbone that connects to a central computer room

To just interconnect several Ethernet segment or Token Rings via a single switch

• -Just indicates more than one collapse point
• -it distributes the backbone functions across a number of devices

• -the switch can suffer a failure affecting any one port without having to flip the entire backbone of the network from one switch to the other: suffer a single port failure
• -Minimizing the impact to the rest of the network when this happens will result in a more stable network.

• Understand 3 layers: access, distribution, core; what is the major function for each layer/level?
• The 80/20 rule is most applicable to what layer?

• From Hierarchical Design (HD) Model
• -end stations are connected here
• -exist primarily to give a place for these end devices to connect to the network
• -it’s need to give a high port density with a low cost per port
• The access layer provides the first level of access to the network. Layer 2 switching, security, and QoS reside at this layer.

• From Hierarchical Design (HD) Model
• -is what allows the network to spread out the distributed backbone
• -distributes data form the Core out to the Access Levels of the network
• -exists to connect the Access and Core Levels
• aggregates wiring closets and provides policy enforcement.
• When Layer 3 protocols are used at this layer, a business can experience benefits such as load balancing, fast convergence, and scalability.
• This layer also provides first hop default gateway redundancy to end stations.

• From Hierarchical Design (HD) Model
• -Central servers are connected here
• -performs the main traffic switching functions, directing packets from one part of the network to another
• -it’s more important to have high throughput devices with a few high-speed ports
• is the backbone of the network.
• This layer is designed to be fast converging, highly reliable, and stable.
• Also designed with Layer 3 protocols, the core provides load balancing, fast convergence, and scalability.

• Central routing: router is at the center
• Distributed routing