EtherChannel & LACP

EtherChannel is Cisco’s implementation of Link Aggregation (LAG), bundling multiple physical links into one logical connection called a Port-Channel interface. Purpose Increased bandwidth Redundancy One STP link (prevents loops) Hardware limitations (ASIC) All member links must have the same speed Typically 16 interfaces supported – but only 8 active Maximum: 8 active links per Port-Channel […]

IPv6 Address Formats — Cheat Sheet

IPv6 address formats define the purpose and scope of an address – routing, local communication, multicast or special use. Address formats (what you must know) Type Prefix / format Scope Use Exam notes Global Unicast (GUA) 2000::/3 Global Normal routable IPv6 address The most used IPv6 address Link-Local FE80::/10 Link Neighbor Discovery, routing protocols Automatically […]

What is IPv6?

IPv6 is the next generation of IP, designed to replace IPv4 because IPv4 ran out of addresses and needs workarounds like NAT. 👉 IPv6 provides enough addresses for the whole planet, better routing and simpler network design. Basic facts Address length: 128 bits Notation: hexadecimal (0–9, a–f) Example: 2001:0db8:abcd:0012:0000:0000:0000:0001 → shortened 2001:db8:abcd:12::1 OSI layer: Layer […]

VLSM — Variable Length Subnet Masking

VLSM lets you use different subnet masks inside the same network, so IP space is utilized efficiently. Facts / key topics RFC: not a standalone RFC – part of the CIDR concept Layer 3 Requires classless routing protocols (OSPF, EIGRP, RIPv2, IS-IS, BGP) Does not work with classful routing (RIPv1, IGRP) Used in: enterprise LAN/WAN, […]

The IPv6 Header

The IPv6 header is a fixed 40-byte Layer 3 header designed for faster routing, better scalability and flexible extensions via Extension Headers (RFC 8200). Facts / key topics Standard / RFC: RFC 8200 · OSI layer: Layer 3 Header length: fixed 40 bytes (no options inside the header) Checksum: ❌ none (removed for performance) · […]

The IPv4 Header

The IPv4 header is a variable Layer 3 header (RFC 791, 20–60 bytes) containing everything a router uses to forward, fragment and deliver IPv4 packets. Facts / key topics Standard / RFC: RFC 791 · OSI layer: Layer 3 (Network) Header length: 20–60 bytes (20 bytes without options) Checksum: ✔ yes (header only) · Broadcast: […]

Encapsulation & Decapsulation

Encapsulation is the process where data is wrapped layer by layer with headers (and sometimes trailers) so it can be transmitted across the network; decapsulation is the reverse process on receipt. Facts / key topics OSI layers: L7 → L1 (encapsulation), L1 → L7 (decapsulation) Data units: L7–L5: Data · L4: Segment (TCP) / Datagram […]