CCNA (Part 3)

show interface status

a command used on switches to display the status of interfaces, including their operational state and basic configuration details (Port, Name, Status, Vlan, Duplex, Speed, and Type)

speed (speed/auto)

command to manually configure a switch interface to use a certain speed or to auto

duplex (half/full/auto)

command to manually configure a switch interface to use a certain type of duplexing

interface range (interfacetype+number - number)

a command to configure multiple interfaces at once

SW1(config-if-range)#

prompt that tells you are interface range mode

shutdown

command used to shutdown an interface or interface range

half duplex

the device cannot send and receive data at the same time. If it is receiving a frame, it must wait before sending a frame

full duplex

the device can send and receive data at the same time. It does not have to wait

Collision domain

a device connected to a hub. A network segment where data packets can collide with each other when sent simultaneously, leading to data loss or corruption

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

a network protocol used in Ethernet networks to manage access to the network medium and detect collisions.

Seed/duplex autonegotiation

a process used in Ethernet networking to automatically determine and set the optimal communication speed and duplex mode between two devices, ensuring compatibility and optimal performance

E

interface that runs only at 10

F

interface that runs at 10/100

G

interface that runs at 10/100/1000

10 or 100mbs

in disabled autonegotiation, switch will use half-duplex

1000mbs or higher

in disabled autonegotiation, switch will use full-duplex

Runts

an error found in "show interface (interface-id)" and are frames that are smaller than the minimum frame size of 64 bytes

Giants

an error found in "show interface (interface-id)" and are frames that are larger than the maximum frame size of 1518 bytes

CRC

an error found in "show interface (interface-id)" and are frames that have failed the CRC check (in the Ethernet FCS trailer)

Frame

an error found in "show interface (interface-id) and are frames that have an incorrect format (due to an error)

Input errors

a total of various counters (runts, giants, CRC, and frames) and is found in the "show interface (interface-id)"

Output errors

an error found in "show interface (interface-id)" and are frames the switch tried to send, but failed due to an error

Version

apart of the IPv4 header. 4 bits in length. Identifies the version of IP used. Vale is either IPv4=4 (0100) and IPv6=6 (0110)

IHL (Internet header length)

apart of the IPv4 header. 4 bits in length. Identifies the length of the header in 4-byte increments. Used because the final field of the IPv4 header (Options) is variable in length, so it displays the total length. Minimum value is 5 (empty Option field). Maximum value is 15

20 bytes

minimum IPv4 header length IHL=5. Options is empty

60 bytes

maximum IPv4 header length IHL=15. Options field is 40 bytes

DSCP (Differentiated Services Code Point)

apart of the IPv4 header. 6 bits in length. Used for QoS (Quality of Service). Used to prioritize delay-sensitive data (streaming voice, video, etc.)

ECN (Explicit congestion notification)

apart of the IPv4 header. 2 bits in length. Provide end-to-end (between two endpoints) notification of network congestion without dropping packets. Optional feature that requires both endpoints, as well as the underlying network infrastructure, to support it

Total length field

apart of the IPv4 header. Indicates the total length of the packet (L3 header + L4 segment). Measure in bytes (not 4-bytes increments like IHL). Minimum value of 20 (=IPv4 header with no encapsulated data). Maximum value of 65,535 (maximum 16-bit value)

Identifiaction

apart of the IPv4 header. Length is 16 bits. If a packet is fragmented due to being too large, this field is used to identify which packet the fragment belongs to. All fragments of the same packet will have their own IPv4 header with the same value in this field. Packets are fragmented if larger than the MTU (Maximum transmission unit)

MTU (Maximum transmission unit)

the largest size of a data packet that can be transmitted over a network protocol. Usually 1500 bytes

Flags

apart of the IPv4 header. 3 bits in length. Used to control/identify fragments. Bit 0: reserved, always set to 0. Bit 1: Don't fragment (DF bit), used to indicated a packet should not be fragmented. Bit 2: more fragments (MF bit), set to 1, if there are more fragments in the packet, set to 0 for the last fragment

DF Bit

found in the flag IPv4 header, when set, indicates that a packet should not be fragmented if its size exceeds the MTU of the network it is being sent over

MF bit

found in the flag of IPv4 header, if set to 1 there are more fragments. Set to 0 for the last fragment

Fragment offset

apart of the IPv4 header. 13 bits. Used to indicate the position of the fragment within the original, fragmented IP packet. Allow fragmented packets to reassembled even if the fragments arrive out of order.

TTL (time to live)

apart of the IPv4 header. 8 bits. Used to prevent infinite loops. A router will drop if set to 0. Indicates a "hop count": each time the packet arrives at a router, the router decreases the value by 1. Recommend value is 64

Protocol

apart of the IPv4 header. 8 bits. Indicates the protocol of the encapsulated L4 PDU. 6 for TCP, 17 for UDP, 1 for ICMP, 89 for OSPF

6

protocol value for TCP (IPv4 header)

17

protocol value for UDP (IPv4 header)

1

protocol value for ICMP (IPv4 header)

89

protocol value of OSPF (dynamic routing protocol) (IPv4)

Header checksum

apart of IPv4 header. A calculated checksum used to check for errors in the IPv4 header. When a router receives a packet, it calculates the checksum of the header and compares it to the one in this field of the header. If they do not match, the router drops the packet.

Options

apart of IPv4 header. 0-320 bits. Rarely used. If the IHL field is greater than 5, it means that this field is present

Routing

the process that routers use to determine the path that IP packets should take over a network to reach their destination

Routing table

a data table stored in a router or a networked computer that lists the routes to particular network destinations, specifying the next hop for data packets to reach their destination

Dynamic routing

a network technique where routers update routing information automatically, allowing them to adapt to changing network conditions and find the best paths for data packets to reach their destinations

Static routing

a network technique where network routes are manually configured by a network administrator, specifying fixed paths for data packets to reach their destinations

next-hop

the next router in the path to the destination

show ip route

command to display the IP routing table, showing the routes the router knows about and how it will forward packets to different destinations

codes legend

found in "show ip route" command and lists the different protocols which router can use to learn routes

local(L)

code used in "show ip route" and is a route to the actual IP address configured on the interface (with a /32 netmask). Router receives for itself

Connected (C)

code used in "show ip route" and is a route to the network interface is connected to (with the actual netmask configured on the interface)

/32

means all 32 bits in an IPv4 address is filed and they can't change

Most specific

refers to the route entry in the routing table that matches the destination address of a packet most precisely, based on its subnet mask or prefix length

Default gateway

a network device, typically a router, that servers as an entry and exit point for traffic between a local network and external or remote networks. A route to 0.0.0.0/0 (a route that includes everything)

Default route

the least specific route possible, because it includes all IP addresses. 0.0.0.0/0 = 4,294,967,296 IP addresses

Two-way reachability

refers to the configuration where two routers have static routes to each other's networks, ensuring that traffic can flow in both directions between the networks they connect

ip route (ip-address)(netmask)(next-hop)

used to manually configure static IP routes in the router's routing table, specifying the destination network, subnet mask, and next-hop IP address or exit interface for the route

ip route (ip-address)(netmask)(exit-interface)

command used to manually configure a static route in the router's routing table. It specifies the destination network's IP address, the subnet mask, and the exit interface or next-hop IP address for the route

Proxy ARP

used with exit-interface static routes. A technique used in computer networks where a device, usually a router, answers ARP request on behalf of another device that is not on the same subnet. It allows devices on a subnet to communicate with device on other subnets as if they were on the same subnet, by having the router respond to ARP request for the remote devices with its own MAC address

ip route 0.0.0.0 0.0.0.0 (ip address)

a command used to configure a default route, which tells the router to send all traffic with unknown destinations to the specified next-hop IP address

* - candidate default

output of the "show ip route" command that indicates that there is a candidate default route in the routing table. This means that the router is configured to used to default route (0.0.0.0/0) for routing packets to destination for which it does not have a specific route