Cisco ENNA 300-445 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; maps to the Internet layer of the TCP/IP model.

Default Ethernet MTU

1500 bytes of payload for standard Ethernet, excluding the 14-byte header and 4-byte FCS; jumbo frames raise this to roughly 9000 bytes.

Private IPv4 ranges

10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are non-routable on the internet and require NAT for external access.

Usable hosts formula

For a subnet with h host bits, usable host addresses equal 2^h minus 2, subtracting the network address and the directed broadcast address.

TCP handshake order

SYN, SYN-ACK, then ACK. This three-way handshake establishes sequence numbers and confirms both endpoints are reachable before data transfer.

Native VLAN on trunk

The single VLAN whose frames cross an 802.1Q trunk untagged. Both ends must match, or a native VLAN mismatch occurs and traffic may leak between VLANs.

DTP desirable plus auto

A dynamic desirable port actively requests a trunk, so pairing it with a dynamic auto port results in a trunk link. Auto paired with auto stays access.

STP root bridge election

The switch with the lowest bridge ID wins, where bridge ID combines the 2-byte priority (default 32768) and the 6-byte MAC address.

BPDU Guard behavior

If a PortFast-enabled access port receives a BPDU, BPDU Guard places the port in err-disabled state, preventing loops from unauthorized switches.

LACP active mode

An LACP mode that actively sends negotiation frames. Pairing active with active or active with passive forms an EtherChannel; passive with passive does not.

CAPWAP ports

The protocol between access points and wireless LAN controllers uses UDP 5246 for control traffic and UDP 5247 for encapsulated data traffic.

Administrative distance order

Lower AD is preferred: connected 0, static 1, eBGP 20, EIGRP 90, OSPF 110, RIP 120, iBGP 200. AD breaks ties between different routing sources.

Longest prefix match

The router forwards using the most specific matching route, meaning the entry with the longest subnet mask wins regardless of administrative distance.

OSPF default cost formula

Cost equals reference bandwidth divided by interface bandwidth, with the reference defaulting to 100 Mbps. A 10 Mbps link costs 10; a 100 Mbps link costs 1.

OSPF stuck in ExStart

Neighbors stuck in ExStart or Exchange usually indicate an MTU mismatch on the link. OSPF requires identical interface MTU values to reach Full state.

EIGRP feasible successor

A backup route whose reported distance is lower than the current feasible distance of the successor; it can be used immediately without recomputation.

HSRP virtual MAC v1

HSRP version 1 uses 0000.0c07.acXX, where XX is the group number in hex. Version 2 uses 0000.0c9f.fXXX for larger group support.

PAT overload

Port Address Translation maps many inside local addresses to one inside global address, tracking sessions by source port number.

DHCP DORA sequence

Discover, Offer, Request, Acknowledge. The client broadcasts Discover, the server offers an address, the client requests it, and the server confirms the lease.

Syslog severity 5

Severity level 5 is notice. Levels run 0 emergency through 7 debug, and configuring a trap level sends that level plus all numerically lower, more severe levels.

SNMP trap port

SNMP agents send unsolicited notifications to a manager on UDP 162, while managers poll agents for information on UDP 161.

SLAAC EUI-64

The interface identifier is built from the 48-bit MAC by inserting FFFE in the middle and flipping the universal/local bit of the first byte.

TACACS+ versus RADIUS

TACACS+ uses TCP 49 and encrypts the full payload with per-command authorization; RADIUS uses UDP and encrypts only the password field.

Port security violation shutdown

The default violation mode. A port receiving traffic from an unauthorized MAC is placed in err-disabled state and requires manual or errdisable recovery.

DHCP snooping trusted port

Ports facing the DHCP server or uplink are trusted and may carry DHCP server replies; untrusted access ports may only send client requests.

Dynamic ARP Inspection

DAI validates ARP packets against the DHCP snooping binding table, dropping replies that do not match a known IP-to-MAC binding on untrusted ports.

Extended ACL placement

Extended ACLs filter by source, destination, protocol, and port, so they are placed close to the source to drop unwanted traffic early.

IPsec ESP protocol number

Encapsulating Security Payload uses IP protocol 50 and provides confidentiality plus integrity; AH uses protocol 51 and provides integrity only.

JSON syntax essentials

JSON uses double-quoted keys, colons, commas, and braces for objects or brackets for arrays; it supports strings, numbers, booleans, null, objects, and arrays.

REST HTTP 404

The Not Found status code means the requested resource URI does not exist on the server; 401 means authentication is required or failed.

NETCONF transport and port

NETCONF runs over SSH on TCP 830, encodes messages in XML, and supports operations such as get-config, edit-config, and commit against datastores.

Idempotent automation

An operation is idempotent when repeating it produces the same end state without additional changes, a core property of declarative configuration tools.