Chapter 4

Define Core routers(interior routers)

A router that directs data between networks within the same autonomous system.

Explain Header checksum[Fields in an IPv4 packet]

Allows the receiving host to calculate whether the IP header has been corrupted during transmission. If the checksum accompanying the message does not match the calculated checksum when the packet is received, the packet is presumed to be corrupt and is discarded.

Explain Checksum[ICMP packet]

Allows the receiving node to determine whether the ICMP packet became corrupted during transmission

Checksum[Fields of a TCP segment]

Allows the receiving node to determine whether the TCP segment became corrupted during transmission.

Acknowledgment number[Fields of a TCP segment]

Confirms receipt of data via a return message to the sender.

Explain Padding[Fields in an IPv4 packet]

Contains filler bits to ensure that the header is a multiple of 32 bits

Padding[Fields of a TCP segment]

Contains filler bits to ensure that the size of the TCP header is a multiple of 32 bits.

Layer 2 is also called

Frame

Flags[Fields of a TCP segment]

Identifies a collection of six 1-bit fields or flags that signal special conditions about other fields in the header.

Sequence number[Fields of a TCP segment]

Identifies the data segment's position in the stream of data segments being sent.

Explain Identification[Fields in an IPv4 packet]

Identifies the message to which a packet belongs and enables the receiving host to reassemble fragmented messages.

Traffic class[Fields in an IPv6 packet]

Identifies the packet's priority

Explain Total length[Fields in an IPv4 packet]

Identifies the total length of the IP packet, including the header and data, in bytes.

Next header[Fields in an IPv6 packet]

Identifies the type of header that immediately follows the IP packet header, usually TCP or UDP.

Explain Protocol[Fields in an IPv4 packet]

Identifies the type of protocol that will receive the packet (for example, TCP, UDP, or ICMP).

Explain Version[Fields in an IPv4 packet]

Identifies the version number of the protocol—for example, IPv4 or IPv6. The receiving workstation looks at this field first to determine whether it can read the incoming data. If it cannot, it will reject the packet.

Explain Fragment offset[Fields in an IPv4 packet]

Identifies where the packet fragment belongs in the series of incoming fragments.

PSH[TCP field flags]

If set to 1, data should be sent to an application without buffering

ACK[TCP field flags]

If set to 1, the Acknowledgment field earlier in the segment contains information for the receiver. If set to 0, the receiver will ignore the Acknowledgment field.

URG[TCP field flags]

If set to 1, the Urgent pointer field later in the segment contains information for the receiver. If set to 0, the receiver will ignore the Urgent pointer field.

FIN [TCP field flags]

If set to 1, the segment is the last in a sequence and the connection should be closed

SYN [TCP field flags]

If set to 1, the sender is requesting a synchronization of the sequence numbers between the two nodes. This code indicates that no payload is included in the segment, and the acknowledgment number should be increased by 1 in response.

RST[TCP field flags]

If set to 1, the sender is requesting that the connection be reset.

Explain Data[Fields in an IPv4 packet]

Includes the data originally sent by the source host, plus any headers from higher layers

Reserved[Fields of a TCP segment]

Indicates a field reserved for later use

Urgent pointer[Fields of a TCP segment]

Indicates a location in the data field where urgent data resides.

Sliding-window size (or window)[Fields of a TCP segment]

Indicates how many bytes the sender can issue to a receiver before acknowledgment is received

Explain Destination IP address[Fields in an IPv4 packet]

Indicates the IP address of the destination host.

Explain Source IP address[Fields in an IPv4 packet]

Indicates the IP address of the source host.

Destination address[Fields in an IPv6 packet]

Indicates the full IP address of the destination host.

Source address[Fields in an IPv6 packet]

Indicates the full IP address of the source host.

Explain IHL (Internet header length)[Fields in an IPv4 packet]

Indicates the length of the IP header in bytes. The header can be a minimum of 20 bytes to a maximum of 60 bytes in 4-byte increments.

TCP header length[Fields of a TCP segment]

Indicates the length of the TCP header in bytes

Explain TTL (Time to Live)[Fields in an IPv4 packet]

Indicates the maximum duration that the packet can remain on the network before it is discarded

Hop limit[Fields in an IPv6 packet]

Indicates the number of times the packet can be forwarded by routers on the network, similar to the TTL field in IPv4 packets.

Destination port[Fields of a TCP segment]

Indicates the port at the destination node

Source port [Fields of a TCP segment]

Indicates the port at the source node.

Payload length[Fields in an IPv6 packet]

Indicates the size of the payload, or data, carried by the packet.

Explain Code[ICMP packet]

Indicates the subtype of the message

Explain Type[ICMP packet]

Indicates the type of ICMP message

Explain Flags[Fields in an IPv4 packet]

Indicates whether a message is fragmented and, if it is fragmented, whether this packet is the last fragment

Version[Fields in an IPv6 packet]

Indicates which IP version the packet uses.

Flow label[Fields in an IPv6 packet]

Indicates which flow, or sequence of packets from one source to one or multiple destinations, the packet belongs to.

Explain DiffServ (Differentiated services)[Fields in an IPv4 packet]

Informs routers the level of precedence they should apply when processing the incoming packet.

What layer does a switch operate on?

Layer 2 - Data Link layer

What layer does a router operate on?

Layer 3 - Network Layer

What layer does a firewall operate on?

Layer 4 - Transport

Explain Options[Fields in an IPv4 packet]

May contain optional routing and timing information.

Layers 7, 6, and 5 when grouped is also called

Payload(data and instructions)

TCP Three-Way Handshake

SYN, SYN/ACK, ACK

Layer 4 is also called

Segment or datagram

UDP (User Datagram Protocol) field

Source port Destination port Length Checksum Data

Options[Fields of a TCP segment]

Specifies special options, such as the maximum segment size a network can handle

Explain Rest of header[ICMP packet]

Varies depending on message type and subtype

Summarize the TCP (Transmission Control Protocol) of Layer 4

connection-oriented—Before TCP transmits data, it ensures that a connection or session is established, similar to making sure someone is listening on the other end of a phone call before you start talking.( three-way handshake to establish a TCP connection) sequencing and checksums—In the analogy of a phone call, you might ask the other person if he can hear you clearly, and repeat a sentence as necessary. In the same vein, TCP sends a character string called a checksum; TCP on the destination host then generates a similar string flow control—You might slow down your talking over the phone if the other person needs a slower pace in order to hear every word and understand your message. TCP manages all these elements—the three-way handshake, checksums, sequencing, and flow control—by posting data to fields in the TCP header at the beginning of a TCP segment

UDP (User Datagram Protocol)

is an unreliable, connectionless protocol. The term unreliable does not mean that UDP can't be used reliably. Instead, it means that UDP does not guarantee delivery of data, and no connection is established by UDP before data is transmitted.

Layer 3 is also called

packets