Glossary
Terms drawn directly from the job description, defined the way you would define them in an interview.
APIPA — The 169.254.x.x address a host self-assigns when DHCP fails. Seeing one means "DHCP did not work", not "the network is down".
ARP — The protocol that maps an IPv4 address to a MAC address on the local segment. If ARP fails, traffic cannot leave the subnet.
Broadcast domain — The set of devices that receive a broadcast frame. A flat switch has one; each VLAN has its own.
Collision domain — The set of devices whose transmissions can collide. A hub has one, a switch has one per port.
Caching DNS server — A resolver that stores answers for its TTL to reduce lookup traffic.
DHCP (DORA) — Discover, Offer, Request, Acknowledge. The automatic configuration protocol; hands out address, mask, gateway, DNS and lease.
DSCP — Differentiated Services Code Point. A QoS marker that determines priority on a marked VLAN, used to keep voice traffic ahead of file transfers.
EDR — Endpoint Detection and Response. Behaviour-based endpoint protection with investigation tooling, as opposed to signature-only antivirus.
GPO — Group Policy Object. A collection of user and computer settings applied by Active Directory link.
HR — High Availability — In virtualisation, clustering hosts so VMs restart elsewhere on failure.
Kerberos — AD's ticket-based authentication. The client gets a TGT then a service ticket; the password never crosses the network after logon.
Loopback processing — The GPO setting deciding whether user or computer policy wins when a user logs on to a shared machine.
NAT / PAT — Network Address Translation. PAT is the many-to-one form using ports, and it is what lets a whole office share one public address.
NTFS permissions — File-system level access control. Combined with share permissions, the more restrictive wins.
OU — Organisational Unit. A container that Group Policy links to and permissions can be delegated at.
Patch ring — A staged rollout: test, then pilot, then production, with defined reboot windows.
RPO — Recovery Point Objective. The maximum tolerable data loss, measured in time.
RTO — Recovery Time Objective. The maximum tolerable downtime.
SNMP — Simple Network Management Protocol. Port 161 for polling, 162 for traps. How switches and APs report health.
Scope (DHCP) — A pool of addresses a server hands out, with options such as gateway, DNS and lease duration.
SMB — Server Message Block. File and printer sharing. Port 445 today, and the propagation path for WannaCry-class ransomware.
Spanning Tree (STP) — The protocol preventing layer-two loops, which would otherwise cause a broadcast storm.
Subnet mask — Splits an address into network and host portions. In CIDR, the prefix length is the number of network bits.
TACACS+ / RADIUS — AAA protocols. Centralise authentication, authorisation and accounting for network devices — what makes 802.1X campus Wi-Fi possible.
TLS / SSL — Transport encryption. TLS 1.2 or 1.3 only; SSL and TLS 1.0 are obsolete and usually fail compliance.
Trunk port — A switch port carrying several VLANs, tagged 802.1Q.
VLAN — Virtual LAN. Logical segmentation of a switch into separate broadcast domains, without extra hardware.
Wildcard mask — The inverse of a subnet mask, used in ACLs to express which bits to match.
WSUS — Windows Server Update Services. A Microsoft patch server that downloads, approves and stages updates for managed machines.
3-2-1 backup rule — Three copies, two media types, one offsite. The baseline that survives ransomware.
802.1X — Port-based network access control. Authenticate the device on the switch port before it gets network access.
DRS — Distributed Resource Scheduler. VMware's feature that rebalances VMs across hosts by load.
vSAN — Virtual SAN. Storage virtualised across an ESXi cluster so virtualisation does not depend on local disks.