Glossary and Abbreviations

Last Updated: February 22, 2026

This document provides explanations of key terms and abbreviations related to Cilium. This glossary helps in understanding Cilium, eBPF, Kubernetes, and networking concepts.

Term Categories

Terms are classified into the following categories:

• Blue Cilium-related terms
• Orange eBPF-related terms
• Green Kubernetes-related terms
• Purple Networking-related terms
• White General terms

A

API (Application Programming Interface) - General

• A set of interface definitions that enable communication between applications

AWS ENI (Elastic Network Interface) - Networking

• Virtual network interface provided by Amazon Web Services
• Used in Cilium's AWS ENI IPAM mode

ARP (Address Resolution Protocol) - Networking

• Protocol that converts IP addresses to MAC addresses
• Essential protocol for communication in L2 networks

B

BGP (Border Gateway Protocol) - Networking

• Standard external gateway protocol used to exchange routing information on the Internet
• Can be used as native routing mode in Cilium

BPF (Berkeley Packet Filter) - eBPF

• Technology for packet filtering, predecessor to eBPF
• Originally developed for network packet capture

BPF Maps - eBPF

• Key-value stores used to store and retrieve data in eBPF programs
• Used for data sharing between user space and kernel space

C

CGroup (Control Group) - Kubernetes

• Linux kernel feature that limits and isolates resource usage of process groups
• Used for container resource limiting

CIDR (Classless Inter-Domain Routing) - Networking

• Method for IP address allocation and routing aggregation
• Example: 192.168.1.0/24 represents IP address range from 192.168.1.0 to 192.168.1.255

CNI (Container Network Interface) - Kubernetes

• Standard interface between container runtimes and network plugins
• Cilium is one of the CNI implementations

CoreDNS - Kubernetes

• DNS server commonly used in Kubernetes clusters
• Plays an important role in service discovery

CRD (Custom Resource Definition) - Kubernetes

• Method to define custom resources by extending the Kubernetes API
• Cilium uses CRDs to define network policies, etc.

Cilium - Cilium

• Open source networking, security, and observability solution based on eBPF
• Used as a Kubernetes CNI implementation

D

DNAT (Destination Network Address Translation) - Networking

• NAT type that modifies the destination IP address of packets
• Used for load balancing and port forwarding

DNS (Domain Name System) - Networking

• System that converts domain names to IP addresses
• Cilium supports DNS-based network policies

E

eBPF (extended Berkeley Packet Filter) - eBPF

• Technology that allows safe execution of programs within the Linux kernel
• Core technology used in Cilium

Endpoint - Cilium

• Workload unit to which network policies are applied in Cilium
• Generally corresponds to Kubernetes pods

Envoy - Cilium

• L7 proxy and service mesh component
• Used for L7 policy enforcement in Cilium

H

Hubble - Cilium

• Cilium's observability layer
• Tool for real-time monitoring and analysis of network flows

I

IPAM (IP Address Management) - Networking

• System responsible for allocating, tracking, and managing IP addresses
• Cilium supports multiple IPAM modes

IPsec - Networking

• Protocol suite that provides secure communication by encrypting IP packets
• Can be used for inter-node traffic encryption in Cilium

K

kube-proxy - Kubernetes

• Network proxy that implements Kubernetes service abstraction
• Cilium can replace kube-proxy

V

VXLAN (Virtual Extensible LAN) - Networking

• Network virtualization technology that overlays Layer 2 networks over Layer 3 networks
• One of Cilium's overlay networking modes

W

WireGuard - Networking

• Modern and fast VPN protocol
• Can be used for inter-node traffic encryption in Cilium

X

XDP (eXpress Data Path) - eBPF

• eBPF feature that processes packets at the network driver level
• Provides very high-performance packet processing

DaemonSet

• Kubernetes resource that runs a copy of a pod on all nodes

E

eBPF (extended Berkeley Packet Filter)

• Technology that allows safe execution of programs within the Linux kernel

Endpoint

• Network endpoint (generally a pod) to which network policies are applied in Cilium

Envoy

• Open source edge and service proxy used as L7 proxy and communication bus

F

FQDN (Fully Qualified Domain Name)

• Complete domain name of a host (e.g., www.example.com)

G

GENEVE (Generic Network Virtualization Encapsulation)

• Encapsulation protocol for network virtualization

gRPC (gRPC Remote Procedure Call)

• High-performance RPC (Remote Procedure Call) framework developed by Google

H

Hubble

• Cilium's network visibility and monitoring component

I

IPAM (IP Address Management)

• Planning, tracking, and management of IP addresses

IPsec (Internet Protocol Security)

• Protocol suite for IP communication security

Istio

• Open source platform that implements service mesh

K

Kafka

• Distributed streaming platform

kube-proxy

• Network proxy that implements Kubernetes service abstraction

Kubernetes

• Open source platform that automates deployment, scaling, and management of containerized applications

L

L2 (Layer 2)

• Data link layer of OSI model

L3 (Layer 3)

• Network layer of OSI model

L4 (Layer 4)

• Transport layer of OSI model

L7 (Layer 7)

• Application layer of OSI model

LoadBalancer

• Device or service that distributes traffic across multiple servers

M

MAC (Media Access Control) Address

• Unique identifier assigned to network interfaces

MTU (Maximum Transmission Unit)

• Maximum packet size that can be transmitted over a network

mTLS (mutual TLS)

• Extension of TLS where both client and server authenticate each other with certificates

N

NAT (Network Address Translation)

• Process of modifying IP address information in IP packets

NodePort

• Kubernetes service type that exposes a static port on each node's IP

O

OSI (Open Systems Interconnection) Model

• Conceptual model that classifies network communication into 7 abstract layers

Overlay Network

• Virtual network built on top of an existing network

P

Pod

• Smallest deployable computing unit in Kubernetes

Proxy

• Server that acts as intermediary between client and server

R

RBAC (Role-Based Access Control)

• Method for controlling access to system resources based on roles

S

Service

• Abstraction in Kubernetes that provides a stable endpoint for a set of pods

SNAT (Source Network Address Translation)

• NAT type that modifies the source IP address of packets

Socket

• Endpoint for inter-process communication over a network

T

TCP (Transmission Control Protocol)

• Connection-oriented transport protocol that provides reliable byte streams

TLS (Transport Layer Security)

• Cryptographic protocol that protects communication over networks

U

UDP (User Datagram Protocol)

• Connectionless transport protocol

V

VETH (Virtual Ethernet)

• Virtual ethernet device, typically created in pairs

VNI (VXLAN Network Identifier)

• 24-bit identifier that identifies VXLAN networks

VTEP (VXLAN Tunnel Endpoint)

• Endpoint responsible for encapsulation and decapsulation of VXLAN packets

VXLAN (Virtual Extensible LAN)

• Network virtualization technology that overlays Layer 2 networks over Layer 3 networks

W

WireGuard

• Modern, fast, and secure VPN tunnel protocol

X

XDP (eXpress Data Path)

• eBPF-based technology for very fast network packet processing

Quiz

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