CCNA Automation flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

OSI Layer 3

The network layer, responsible for logical addressing (IP) and routing packets between networks; routers operate primarily at this layer using destination IP addresses.

TCP three-way handshake

Connection setup using SYN, SYN-ACK, and ACK segments; establishes sequence numbers and confirms both endpoints are reachable before data transfer begins.

Private IPv4 ranges

RFC 1918 blocks 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are not routable on the public Internet and require NAT for external communication.

Usable hosts formula

For a subnet with h host bits, usable addresses = 2^h - 2, subtracting the network and broadcast addresses; a /24 provides 254 usable hosts.

ARP purpose

Address Resolution Protocol maps a known IPv4 address to a MAC address on the local segment by broadcasting a request and receiving a unicast reply.

Ethernet MTU

Default maximum transmission unit is 1500 bytes of payload; frames smaller than 64 bytes are runts and frames larger than the MTU are fragmented or dropped.

802.1Q trunk tag

A 4-byte tag inserted into Ethernet frames to identify VLAN membership; contains a 12-bit VLAN ID supporting up to 4094 usable VLANs.

Native VLAN

The VLAN whose frames traverse a trunk untagged; both ends of an 802.1Q trunk must agree on the native VLAN to avoid misforwarding and VLAN hopping.

STP root bridge election

The switch with the lowest bridge ID (priority then MAC address) becomes root; default priority is 32768 and can be lowered to force election.

PortFast and BPDU Guard

PortFast skips STP listening/learning on edge ports for fast host connectivity; BPDU Guard err-disables a PortFast port if it receives a BPDU.

EtherChannel

Bundles multiple physical links into one logical link for increased bandwidth and redundancy; member interfaces must share speed, duplex, and VLAN settings.

CAPWAP tunnels

Protocol between lightweight APs and a wireless LAN controller; control traffic uses UDP 5246 and data traffic uses UDP 5247, optionally with DTLS encryption.

Longest prefix match

Router forwarding rule that selects the route with the most specific mask (highest prefix length) when multiple routes match a destination address.

Administrative distance

Trustworthiness value of a route source; lower is preferred. Defaults: connected 0, static 1, EIGRP 90, OSPF 110, RIP 120.

OSPF cost metric

Calculated as reference bandwidth divided by interface bandwidth; default reference is 100 Mbps, so a 100 Mbps link costs 1 and a 10 Mbps link costs 10.

OSPF neighbor states

Progression is Down, Init, 2-Way, ExStart, Exchange, Loading, Full; routers reach Full adjacency with the DR and BDR, and 2-Way with other DROTHERs.

HSRP

Cisco first-hop redundancy protocol where an active and standby router share a virtual IP and MAC; the standby takes over if the active fails.

Floating static route

A static route configured with an administrative distance higher than the primary route, so it is installed only if the primary route fails.

PAT overload

Port Address Translation maps many inside private addresses to one public IP by translating source ports; configured with the overload keyword on a NAT statement.

DHCP DORA process

Client discovery sequence: Discover (broadcast), Offer (server), Request (client selects offer), Acknowledge (server confirms lease); uses UDP 67 and 68.

DHCP relay

The ip helper-address command on a router interface forwards client DHCP broadcasts as unicast to a DHCP server on another subnet.

Syslog severity levels

Eight levels from 0 Emergency (most severe) to 7 Debugging (least severe); lower numbers indicate higher severity and are logged when the threshold is set.

DSCP EF

Expedited Forwarding, DSCP value 46, is the recommended marking for voice traffic; it provides low latency, low jitter, and assured bandwidth treatment.

NTP stratum

Indicates distance from the reference clock: stratum 0 is the clock itself, stratum 1 is directly attached, and each additional hop increases the stratum number.

Standard ACL placement

Standard ACLs filter only source IP addresses and should be placed close to the destination to avoid blocking traffic intended for other networks.

Extended ACL placement

Extended ACLs filter source, destination, protocol, and port; place them close to the source to drop unwanted traffic early and conserve bandwidth.

Port security violation modes

Protect drops offending frames silently; restrict drops and logs with a counter increment; shutdown err-disables the port and is the default mode.

DHCP snooping

Switch feature that classifies ports as trusted or untrusted and drops DHCP server messages arriving on untrusted ports, preventing rogue DHCP servers.

TACACS+ versus RADIUS

TACACS+ uses TCP 49 and encrypts the entire payload, separating AAA functions; RADIUS uses UDP 1812/1813 and encrypts only the password.

REST API methods

GET reads, POST creates, PUT replaces, PATCH updates partially, and DELETE removes resources; responses use status codes such as 200, 201, 400, and 404.

NETCONF and YANG

NETCONF is an XML-based configuration protocol over SSH port 830; YANG is the data modeling language that defines the structure of data exchanged.

Ansible characteristics

Agentless configuration management tool that connects over SSH, uses YAML playbooks, and is idempotent, so repeated runs produce the same end state.