Title: ICND1 / Networking Fundamentals

Q: 802.3z is what IEEE Standard
A: 1000BASE-LX, 5km

Q: 802.3ab is what IEEE Standard
A: 1000BASE-T, Gigabit Ethernet

Q: 802.3an is what IEEE Standard
A: 10GBASE-T, 10 Gigabit Ethernet

Q: As a rule, Ethernet NIC transmitters use the pair connected to pins _______; the NIC receivers use a pair of wires at pin positions _______. LAN switches, knowing those facts about what Ethernet NICs do, do the opposite: Their receivers use the wire pair at pins _______, and their transmitters use the wire pair at pins _______.
A: 1 and 2,
3 and 6,
1 and 2,
3 and 6,

Q: PCs, Routers, and WAPs transmit on pins ______, while Hubs and Switches transmit on pins _______.
A: 1 and 2,
3 and 6

Q: What is missing from the Ethernet Frame?
A: Preamble: The preamble of an Ethernet packet consists of a 56-bit (seven-byte) pattern of alternating 1 and 0 bits, allowing devices on the network to easily synchronize their receiver clocks, which is followed by the SFD (start frame delimiter) to mark a new incoming frame.

Q: What is missing from the Ethernet Frame?
A: SFD/Start Frame Delimiter: the eight-bit (one-byte) value marking the end of the preamble, which is the first field of an Ethernet packet, and indicating the beginning of the Ethernet frame. The SFD is designed to break the bit pattern of the preamble and signal the start of the actual frame.

Q: What is missing from the Ethernet Frame?
A: Destination MAC address

Q: What is missing from the Ethernet Frame?
A: Source MAC Address

Q: What is missing from the Ethernet Frame?
A: Protocol Type Field

Q: What is missing from the Ethernet Frame?
A: The Frame Check Sequence (FCS); a four-octet cyclic redundancy check (CRC) that allows detection of corrupted data within the entire frame as received on the receiver side.

Q: What is missing from the IPv4 Header?
A: Version: The first header field in an IP packet is the four-bit version field. For IPv4, this has a value of 4 (hence the name IPv4).

Q: What is missing from the IPv4 Header?
A: Internet Header Length (IHL): The second field (4 bits) is the Internet Header Length (IHL), which is the number of 32-bit words in the header. Since an IPv4 header may contain a variable number of options, this field specifies the size of the header (this also coincides with the offset to the data). The minimum value for this field is 5 (RFC 791), which is a length of 5×32 = 160 bits = 20 bytes. Being a 4-bit value, the maximum length is 15 words (15×32 bits) or 480 bits = 60 bytes.

Q: What is missing from the IPv4 Header?
A: Differentiated Services Code Point (DSCP): Originally defined as the Type of service (ToS) field. This field is now defined by RFC 2474 for Differentiated services (DiffServ). New technologies are emerging that require real-time data streaming and therefore make use of the DSCP field. An example is Voice over IP (VoIP), which is used for interactive data voice exchange.

Q: What is missing from the IPv4 Header?
A: Total Length: This 16-bit field defines the entire packet size, including header and data, in bytes. The minimum-length packet is 20 bytes (20-byte header + 0 bytes data) and the maximum is 65,535 bytes — the maximum value of a 16-bit word. All hosts are required to be able to reassemble datagrams of size up to 576 bytes, but most modern hosts handle much larger packets. Sometimes subnetworks impose further restrictions on the packet size, in which case datagrams must be fragmented. Fragmentation is handled in either the host or router in IPv4.

Q: What is missing from the IPv4 Header?
A: Identification: This field is an identification field and is primarily used for uniquely identifying the group of fragments of a single IP datagram. Some experimental work has suggested using the ID field for other purposes, such as for adding packet-tracing information to help trace datagrams with spoofed source addresses,[11] but RFC 6864 now prohibits any such use.

Q: What is missing from the IPv4 Header?
A: Flags: A three-bit field follows and is used to control or identify fragments. They are (in order, from high order to low order):
bit 0: Reserved; must be zero.[note 1]
bit 1: Don't Fragment (DF)
bit 2: More Fragments (MF)
If the DF flag is set, and fragmentation is required to route the packet, then the packet is dropped. This can be used when sending packets to a host that does not have sufficient resources to handle fragmentation. It can also be used for Path MTU Discovery, either automatically by the host IP software, or manually using diagnostic tools such as ping or traceroute. For unfragmented packets, the MF flag is cleared. For fragmented packets, all fragments except the last have the MF flag set. The last fragment has a non-zero Fragment Offset field, differentiating it from an unfragmented packet.

Q: What is missing from the IPv4 Header?
A: Fragment Offset: The fragment offset field, measured in units of eight-byte blocks (64 bits), is 13 bits long and specifies the offset of a particular fragment relative to the beginning of the original unfragmented IP datagram. The first fragment has an offset of zero. This allows a maximum offset of (213 – 1) × 8 = 65,528 bytes, which would exceed the maximum IP packet length of 65,535 bytes with the header length included (65,528 + 20 = 65,548 bytes).

Q: What is missing from the IPv4 Header?
A: Time To Live (TTL): An eight-bit time to live field helps prevent datagrams from persisting (e.g. going in circles) on an internet. This field limits a datagram's lifetime. It is specified in seconds, but time intervals less than 1 second are rounded up to 1. In practice, the field has become a hop count—when the datagram arrives at a router, the router decrements the TTL field by one. When the TTL field hits zero, the router discards the packet and typically sends an ICMP Time Exceeded message to the sender.
The program traceroute uses these ICMP Time Exceeded messages to print the routers used by packets to go from the source to the destination.

Q: What is missing from the IPv4 Header?
A: Protocol: This field defines the protocol used in the data portion of the IP datagram. The Internet Assigned Numbers Authority maintains a list of IP protocol numbers which was originally defined in RFC 790.

Q: What is missing from the IPv4 Header?
A: Header Checksum: The 16-bit checksum field is used for error-checking of the header. When a packet arrives at a router, the router calculates the checksum of the header and compares it to the checksum field. If the values do not match, the router discards the packet. Errors in the data field must be handled by the encapsulated protocol. Both UDP and TCP have checksum fields. When a packet arrives at a router, the router decreases the TTL field. Consequently, the router must calculate a new checksum.

Q: What is missing from the IPv4 Header?
A: Source address: This field is the IPv4 address of the sender of the packet. Note that this address may be changed in transit by a network address translation device.

Q: What is missing from the IPv4 Header?
A: Destination address: This field is the IPv4 address of the receiver of the packet. As with the source address, this may be changed in transit by a network address translation device.

Q: What is missing from the TCP Header?
A: Source port (16 bits)

Q: What is missing from the TCP Header?
A: Destination port (16 bits)

Q: What is missing from the TCP Header?
A: Sequence number (32 bits)
has a dual role:
If the SYN flag is set (1), then this is the initial sequence number. The sequence number of the actual first data byte and the acknowledged number in the corresponding ACK are then this sequence number plus 1.
If the SYN flag is clear (0), then this is the accumulated sequence number of the first data byte of this segment for the current session.

Q: What is missing from the TCP Header?
A: Acknowledgment number (32 bits)
if the ACK flag is set then the value of this field is the next sequence number that the receiver is expecting. This acknowledges receipt of all prior bytes (if any). The first ACK sent by each end acknowledges the other end's initial sequence number itself, but no data.

Q: What is missing from the TCP Header?
A: Data offset (4 bits)
specifies the size of the TCP header in 32-bit words. The minimum size header is 5 words and the maximum is 15 words thus giving the minimum size of 20 bytes and maximum of 60 bytes, allowing for up to 40 bytes of options in the header. This field gets its name from the fact that it is also the offset from the start of the TCP segment to the actual data.

Q: What is missing from the TCP Header?
A: Reserved (3 bits)
for future use and should be set to zero

Q: What is missing from the TCP Header?
A: Flags (9 bits) (aka Control bits)
contains 9 1-bit flags
NS (1 bit) – ECN-nonce concealment protection (experimental: see RFC 3540).
CWR (1 bit) – Congestion Window Reduced (CWR) flag is set by the sending host to indicate that it received a TCP segment with the ECE flag set and had responded in congestion control mechanism (added to header by RFC 3168).
ECE (1 bit) – ECN-Echo has a dual role, depending on the value of the SYN flag. It indicates:
If the SYN flag is set (1), that the TCP peer is ECN capable.
If the SYN flag is clear (0), that a packet with Congestion Experienced flag in IP header set is received during normal transmission (added to header by RFC 3168).
URG (1 bit) – indicates that the Urgent pointer field is significant
ACK (1 bit) – indicates that the Acknowledgment field is significant. All packets after the initial SYN packet sent by the client should have this flag set.
PSH (1 bit) – Push function. Asks to push the buffered data to the receiving application.
RST (1 bit) – Reset the connection
SYN (1 bit) – Synchronize sequence numbers. Only the first packet sent from each end should have this flag set. Some other flags and fields change meaning based on this flag, and some are only valid for when it is set, and others when it is clear.
FIN (1 bit) – No more data from sender

Q: What is missing from the TCP Header?
A: Window size (16 bits)
the size of the receive window, which specifies the number of window size units (by default, bytes) (beyond the segment identified by the sequence number in the acknowledgment field) that the sender of this segment is currently willing to receive (see Flow control and Window Scaling)

Q: What is missing from the TCP Header?
A: Checksum (16 bits)
The 16-bit checksum field is used for error-checking of the header and data

Q: What is missing from the TCP Header?
A: Urgent pointer (16 bits)
if the URG flag is set, then this 16-bit field is an offset from the sequence number indicating the last urgent data byte

Q: Ports 67,68
Protocol: ______
Application: ______
A: UDP,
DHCP

Q: Port 20
Protocol: ______
Application: ______
A: TCP,
FTP Data

Q: Ports 21
Protocol: ______
Application: ______
A: TCP,
FTP Control

Q: Ports 53
Protocol: ______
Application: ______
A: UDP & TCP,
DNS

Q: Ports 69
Protocol: ______
Application: ______
A: UDP,
TFTP

Q: Ports 161
Protocol: ______
Application: ______
A: UDP,
SNMP

Q: Ports 443
Protocol: ______
Application: ______
A: TCP,
SSL

Q: All switches can use normal-range VLANs with values from ____ to ____.
Only some switches can use extended-range VLANs with VLAN IDs from ___ to ___.
A: 1 to 1005,
1005 to 4094

Q: dynamic __________:
Initiates negotation messages and responds to negotiation messages to dynamically choose whether to statrt using trunking
A: desirable

Q: dynamic __________:
Passively waits to receive trunk negotation messages, at which point the switch will respond and negotiate whether to use trunking.
A: auto

Q: Which two commands will display the current IP address and basic Layer 1 and 2 status of an interface? (Choose two.)
A. router#show version
B. router#show ip interface
C. router#show protocols
D. router#show controllers
E. router#show running-config
A: C,D

Q: Which two privileged mode Cisco IOS commands can be used to determine a Cisco router chassis serial number? (Choose two)
A. show inventory
B. show flash:filesys
C. dir flash:|include chassis
D. show diag
E. show controllers
A: A,D

Q: Which command helps a network administrator to manage memory by displaying flash memory and NVRAM utilization?
A. show secure
B. show file systems
C. show flash
D. show version
A: B