CS610 - Computer Network
Course Page
Q & A
Short Question & Answers
Q82: Why organization does not use single router.
If there is no signal, how sever come to know there is communication arrived(3) by just guessing and after fixed time the sender can’t receive any response so the sender again sent he data so when he received any ACK than we know now the path is clear the ready to communicate with receiver.
Q83: What are two important principal that IP address hierarchy grantee?
Each 32-bit IP address is divided into two parts:
SUFFIX: It identifies an individual computer on the network.
PREFIX: It identifies the physical network to which the computers are attached.
Q84: Does OSPF share information within an area or it allow communication b/w area?
OSPF allows subdivision of Autonomous System into areas. The link-status information is propagated within an area. The routes are summarized before being propagated to another area. It reduces overhead (less broadcast traffic). Because it allows a manager to partition the routers and networks in an autonomous system into multiple areas, OSPF can scale to handle a larger number of routers than other IGPs.
Q85: Where should ICMP message be sent?
ICMP message is sent in response to incoming datagrams with problems. ICMP message is not sent for ICMP message.
Q86: How the TCP is reliable protocol?
Reliability is fundamental in a computer system. Software in the Internet must provide the same level of reliability as a computer system. Software must guarantee prompt and reliable communication without any loss, duplication, and change in the order.
Q87: Where the connection is orients service use connection identifier instead of full address?
The connection-oriented service paradigm for networking is similar to the manner in which telephones are used. This is given as follows: A caller dials a number of the destination. The telephone at the destination signals the arrival of a connection request. If the called person does not answer; the caller gives up after waiting for a timeout. If the called person does answer, then the connection is established. In data communication, as binary connection identifier is given to each of the two Parties to enable identification of the connection.
Q88: Summarize IP multicast semantics?
IP multicast group is anonymous in two ways:
1. Neither a sender nor a receiver knows the identity or the number of group members.
2. Routers and hosts do not know which applications will send a datagram to a group.
Q89: In internet routing how does a host join and leave the group?
A host sends a request to create, join, or leave a group to an immediate neighbor gateway. If the host requests creation of a group, a new network membership record is created by the serving gateway and distributed to all other gateways. If the host is the first on its network to join a group, or if the host is the last on its network to leave a group, the group's network membership record is updated in all gateways.
Q90: Why is internet multicast routing difficult?
Internet multicast routing is difficult because internet multicast allows arbitrary computer to join multicast group at any time. It allows arbitrary member to leave multicast group at any time. It also allows arbitrary computer to send message to a group (even if not a member).
Q91: Define Vector-Distance Algorithm.
Packet switches wait for next update message and they iterate through entries in message. If entry has shortest path to destination, insert source as next hop to destination and record distance as distance from next hop to destination plus distance from this switch to next hop.
Q92: What are the characteristic of border gateway protocol?
The characteristics of BGP follow:
• BGP is an exterior gateway protocol (EGP) used in routing in the Internet. It is an inter-
  domain routing protocol.
• BGP is a path vector routing protocol suited for strategic routing policies.
• BGP uses TCP Port 179 to establish connections with neighbors.
• BGPv4 implements CIDR.
• eBGP is for external neighbors. It's used between separate autonomous systems.
• iBGP is for internal neighbors. It's used within an AS.
• BGP uses several attributes in the routing-decision algorithm.
• BGP uses confederations and route reflectors to reduce BGP peering overhead.
• The MED (metric) attribute is used between autonomous systems to influence inbound
• Weight is used to influence the path of outbound traffic from a single router,
   configured locally.
Q93: How can a bridge know whether to forward frames?
The bridges configure themselves automatically to decide which bridge will forward broadcast frames and which bridge will not. The bridges communicate with each other on the network and use Distributed Spanning Tree (DST) algorithm to decide which bridge will not forward frames if a cycle occurs.

The bridge builds a list of MAC addresses on either side of the bridge. Therefore, it knows which packets should be forwarded to the other side and which should not. Most bridges are self-learning bridges. As soon as a frame arrives to a bridge, it extracts a source address from its header and automatically adds it in the list for that segment. In this way a bridge builds up address lists. In the example of a packet that uses a MAC address not in its table it can err on the side of caution by forwarding the packet.
Q94: What is the basic concept of Twice NAT (Network Address Translation)?
Twice NAT is another variant of NAT. it is used with site that runs server. In this process NAT box is connected to Domain Name.
Course Instructor

Mr. Hammad Khalid Khan
M.S Electrical Engineering
Oklahoma State University USA

Computer Networks & Internets with Internet Applications by Douglas E.Comer

Computer Networks by Andrew S. Tanenbaum

Networking: A Top-Down Approach Featuring the Internet by James F. Kurose and Keith W. Ross