Fragmentation Routers & sending host Only sending host Configuration Manual or DHCP Stateless Auto-configuration (SLAAC) or DHCPv6 Header Size 20-60 bytes Fixed 40 bytes

IPv6 Advantages & Limitations over IPv4

Advantages: Vast address space, improved routing efficiency due to simplified header, enhanced security (IPsec built-in), better support for mobile devices, auto-configuration.
Limitations: Transition complexity (IPv4-IPv6 coexistence), lack of universal backward compatibility, increased header size (though often offset by efficiency), slower adoption rate.

Address Resolution Protocol (ARP)

Definition: ARP is a protocol used to map an IP address to a physical MAC address on a local area network (LAN).

How it works:

A host (Sender) wants to send data to another host (Receiver) on the same LAN but only knows the Receiver's IP address.
The Sender checks its ARP cache. If the MAC address is found, it uses it.
If not found, the Sender broadcasts an ARP Request packet to all devices on the LAN. This packet contains the Sender's IP and MAC, and the Receiver's IP.
All devices on the LAN receive the ARP Request. Only the Receiver whose IP matches the request replies.
The Receiver sends an ARP Reply packet directly to the Sender. This packet contains the Receiver's IP and MAC address.
The Sender receives the ARP Reply, updates its ARP cache with the Receiver's MAC address, and can now send data directly to the Receiver.

Example: Host A (IP: $192.168.1.10$, MAC: AAAA) wants to send data to Host B (IP: $192.168.1.20$, MAC: BBBB).

Host A checks ARP cache, no entry for $192.168.1.20$.
Host A broadcasts ARP Request: "Who has $192.168.1.20$? Tell $192.168.1.10$ (AAAA)".
Host B receives the request and replies: "I am $192.168.1.20$ (BBBB)".
Host A receives the reply, adds entry "$192.168.1.20 \rightarrow$ BBBB" to its cache, and sends data to BBBB.

ICMPv4 vs. ICMPv6

Internet Control Message Protocol (ICMP) is used for sending error messages and operational information indicating, for example, that a requested service is not available or that a host or router could not be reached.

Feature	ICMPv4	ICMPv6 (ICMP for IPv6)
Associated IP	IPv4	IPv6
Purpose	Error reporting, diagnostics	Error reporting, diagnostics, Neighbor Discovery, Multicast Listener Discovery
Key Messages	Echo Request/Reply (ping), Destination Unreachable, Time Exceeded, Redirect	Echo Request/Reply, Destination Unreachable, Packet Too Big, Time Exceeded, Parameter Problem, Router Solicitation/Advertisement, Neighbor Solicitation/Advertisement, Multicast Listener Query/Report/Done
ARP equivalent	Separate ARP protocol	Integrated into Neighbor Discovery Protocol (NDP) via Neighbor Solicitation/Advertisement messages
IGMP equivalent	Separate IGMP protocol	Integrated into Multicast Listener Discovery (MLD) messages