driver.net.proto.arp¶

ARP (Address Resolution Protocol) implementation with cache.

Overview¶

This unit implements ARP over Ethernet (hardware type $0001, protocol type $0800). It maintains an in-memory ARP cache as a linked list, handles incoming ARP requests and replies, generates outgoing requests and gratuitous announcements, and provides IP-to-MAC resolution for use by higher protocol layers.

Dependencies¶

driver.net
driver.net.types
driver.net.util
driver.net.proto.eth2
syslog
terminal

Types¶

TARPCacheRecord¶

Linked-list node in the ARP cache:

Field	Type	Description
`mac`	`TMACAddress`	Resolved MAC address
`ip`	`TIPv4Address`	Corresponding IP address
`Next`	`^TARPCacheRecord`	Next cache entry, or `nil`

Functions and Procedures¶

register¶

procedure register;

Registers ARP as a promiscuous handler for EtherType $0806 via driver.net.proto.eth2.registerTypePromisc.

recv¶

procedure recv(ctx: PPacketContext);

Processes an incoming ARP frame. Updates the cache with the sender's MAC/IP pair. If the ARP operation is a request targeting our IPv4 address, constructs and sends a reply.

send¶

procedure send(op: uint16; target_mac: TMACAddress; target_ip: TIPv4Address);

Builds a TARPHeader and transmits it via driver.net.proto.eth2.send to the specified destination.

sendGratuitous¶

procedure sendGratuitous;

Sends a gratuitous ARP announcement (operation=reply, target=our own IP) to the broadcast MAC. Used to update other hosts' caches after IP configuration changes.

sendRequest¶

procedure sendRequest(target_ip: TIPv4Address);

Sends an ARP request asking who owns target_ip.

sendRequestGateway¶

procedure sendRequestGateway;

Convenience wrapper that sends an ARP request for the configured default gateway IP.

resolveIP¶

function resolveIP(ip: TIPv4Address; out mac: TMACAddress): boolean;

Looks up ip in the cache. Returns true and fills mac on a hit. On a miss, sends an ARP request and returns false; the caller must retry after allowing time for a reply.

IPv4ToMAC¶

function IPv4ToMAC(ip: TIPv4Address): TMACAddress;

Cache lookup returning the MAC for the given IP, or NULL_MAC if not found.

MACToIIPv4¶

function MACToIIPv4(mac: TMACAddress): TIPv4Address;

Reverse cache lookup returning the IP for the given MAC, or NULL_IP if not found.

terminal_command_arp¶

procedure terminal_command_arp(args: string);

Terminal command handler. With no arguments, dumps the full ARP cache. With an IP address argument, sends an ARP request for that IP.

Notes¶

The cache is an unbounded singly-linked list; entries are never expired in this implementation.
ARP replies to requests are sent with the sender and target fields swapped from the incoming request.