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2014-02-26 03:18:05
exam review is451

review for exam is451
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  1. Compare and contrast Client/Server and P2P
    application architectures.
    • Client/Server:-terms client and server indicate which side initiates contact
    • 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)
    • -client: -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
    • P2P application: no always-on server; arbitrary end systems directly communicate; peers are intermittently connected and change IP addresses;
    • example: Gnutella, Freenet; Highly scalable but difficult to manage
  2. Client process
    process that initiates communication
  3. Server process
    process that waits to be connected
  4. Sockets
    process sends/receives messages to/from its socket
  5. Know the TCP/UDP port numbers corresponding to the protocols discussed in class.
    • DNS port 53
    • email STMP port 25 TCP
    • file transfer FTP port 20 data/21 control TCP
    • web HTTP 80 TCP
    • DHCP 67(server)
    • remote terminal access Telnet TCP
    • streaming multimedia proprietary TCP or UDP
    • internet telephony proprietary typically UDP
  6. Understand the difference between using TCP and UDP transport and application requirements for a transport protocol (TCP or UDP).
    • 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
  7. Briefly describe newer transport protocols (SCTP and DCCP) and how they are different from TCP and UDP.
    • -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)
  8. HTTP
    • -(Hypertext transfer protocol): Web’s application layer protocol; client/server model; client: browser that requests, receives, “displays” Web objects; server: web server sends objects in response to requests; HTTP uses TCP: ;
    • -port 80
  9. HTTP – persistent vs non-persistent connections
    • -Nonpersistent HTTP: at most one object is sent over a TCP connection; HTTP/1.0 uses it;
    • -Persistent HTTP: multiple objects can be sent over single TCP connection between client and server; HTTP/1.1 uses it in default mode
  10. Stateless protocol
    -HTTP is “stateless”: server maintains no information about past client requests
  11. Pipelining
    • -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.
  12. FTP:
    -the file transfer protocol; transfer file to/from remote host; client/server model: client: side that initiates transfer (either to/from remote); server: remote host; ftp: RFC 959; ftp server: port 21 control, port 20 data
  13. Three component of electronic mail:
    -user agents; mail servers; SMTP: Simple Mail transfer protocol
  14. SMTP:
    • -Simple Mail transfer protocol; delivery/storage to receiver’s server; uses persistent connections; requires message (header & body)to be in 7-bit ASCII; SMTP server uses CRLF.CRLF to determine end of message; Comparison with HTTP: HTPP: pull; STMP: push; both have ASCII command/response interaction, status codes; HTTP: each object encapsulated in its own response msg; SMTP: multiple objects sent in multipart msg
    • -port 25
    • Push protocol, simple ASCII text only.
  15. MIME – attachments.
    -MIME: multimedia mail extension, RFC 2045, 2056
  16. Mail access protocols: IMAP, POP (compare and contrast)
    • IMAP
    • -(Internet Mail Access Protocol) [RFC 1730]; more features (more complex); manipulation of stored msgs on server; keep all messages in one place: the server; allows users to organize messages in folders; IMAP keeps user state across sessions: names of folders and mappings between message IDs and folder name
    • POP
    • -(Post Office Protocol) [RFC 1939]; authorization (agent > server) and download; POP3: 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
  17. HTTP-based access
    -ex. Hotmail, Yahoo! Mail, etc.
  18. 1 port/1 connection – in-band control connection.
  19. DNS:
    • -Domain Name System;
    • -distributed database implemented in hierarchy of many name servers;
    • -application-layer protocol host, routers, name servers to communicate to resolve names (address/name translation): note: core Internet function, implemented as application- layer protocol; complexity at network’s “edge”;
    • -port 53
    • -services: 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
    • -why not centralize DNS?: single point of failure; traffic volume; distant centralized database; maintenance; doesn’t scale!
  20. Distributed Hierarchical Database
    • -root DNS servers > com, org, edu DNS servers >,, DNS servers
    • -Root name servers > top-level domain servers > authoritative name servers
  21. DNS: Root name servers
    -Although we have referred to each of the 13 root name servers as if it were a single server, each "server" is actually a cluster of replicated servers, for both security and reliability purposes.
  22. Recursive vs Iterative queries.
    • -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; heavy load?
  23. DNS caching (speed vs accuracy)
    • -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
  24. -DHCP:
    • -Dynamic Host Configuration Protocol: DHCP – dynamically “leases” IP configuration information.
    • -dynamically allocates IP addresses and configuration options to hosts on a network
    • -based on BOOTP protocol
    • -port 67(server)
    • -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)
    • -non-routable, requires relay agents to route across subnets
  25. Different types of allocation.
    3 methods of allocation: manual, automatic, dynamic allocation
  26. manual 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
  27. automatic allocation
    -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.
  28. dynamic allocation
    -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.
  29. Understand basic topologies (bus, ring, star) and their scalability problems.
    -all are prone to scalability problems
  30. Compare and contrast physical and logical topologies.
  31. Understand difference between end devices and internetworking devices.
    • -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.
  32. Compare and contrast hub/bridge/switch/router/layer3 switch – how do they affect logical topology of the network.
  33. Hub
    -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
  34. Bridge
    -faster than a router because the decisions it makes are much simpler
  35. Switch
    • -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
  36. Router
    –connects switches to each other; operates at layer 3; comparatively smart, slow, expensive per port
  37. Layer3 switch
    -making the router a card in a Layer 2 switch, makes a single physical connection to the shared backplane of the switch
  38. Understand collision domain,
    -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
  39. broadcast domain.
    -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
  40. Understand ways to implement reliability/fault-tolerance:
    -Fault-tolerance-is art and science of building computing systems that continue to operate satisfactorily in the presence of faults.
  41. Layer2: Spanning tree- what is its purpose? How does it work?
    • -Spanning tree protocol: STP or IEEE 802.1d
    • -what is its purpose?
    • -eliminates loop and it activates redundant links for automated fault recovery; activates backup links and devices
    • -How does it work?
    • -
  42. Layer3: Address-based redundancy: HSRP and VRRP. How is it different from using dynamic routing protocols, like RIP or OSPF?
    • -HSRP: Hot Standby Router Protocol: A Cisco proprietary system
    • -VRRP: Virtual Router Redundancy Protocol: an open standard
    • -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
  43. What is a logical LAN segment?
    -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
  44. What is a spaghetti LAN?
    -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
  45. What is the 80/20 rule?
    • -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
  46. How are VLANs configured for membership:
    port-based, protocol-based; MAC-address based
  47. What is a Backbone?
    • -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
  48. What is a Collapsed Backbone?
    -To just interconnect several Ethernet segment or Token Rings via a single switch
  49. What is a Distributed Backbone?
    • -Just indicates more than one collapse point
    • -it distributes the backbone functions across a number of devices
  50. How can redundancy be achieved in a backbone?
    • -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.
  51. Hierarchical Design (HD) Model three layer
    -3 layers: access, distribution, core.
  52. access layer
    • -layer of hierarchical design 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
  53. distribution layer,
    • -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
  54. core layer
    • -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
  55. Elastic applications
    can use any amount of bandwidth available
  56. Transport layer port number identifies ...
    a specific process running on a network host
  57. How many TCP connections does FTP use?
    • 2
    • 20 data/ 21 control
  58. Interactive real-time applications prefer to use ...
    UDP because it provides faster timing/delivery
  59. STMP listens for client requests on port ...
  60. Addressing at the _ layer is implemented using host addresses.
  61. SCTP can be described as ...
    UDP + (plus) reliability