AROSTCP

AROSTCP -- Core Network Stack

This document covers the AmiTCP-derived core network stack: protocols, kernel infrastructure, BSD socket API (slots 1-50), IPv6 support, configuration services, and command-line utilities.

For Roadshow bsdsocket.library extensions (slots 51-138), see Roadshow TODO. For Miami compatibility library, see Miami TODO.

Last updated against codebase: March 2026.

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Core Protocol Support -- IMPLEMENTED

Protocol	Status	Key Files
IPv4	Complete	netinet/ip_input.c, ip_output.c, in.c, in_pcb.c
IPv6	Complete	netinet6/ip6_input.c, ip6_output.c, in6.c, in6_pcb.c
TCP (v4+v6)	Complete	netinet/tcp_input.c (2166), tcp_output.c (769), tcp_usrreq.c
UDP (v4+v6)	Complete	netinet/udp_usrreq.c, netinet6/udp6_usrreq.c
ICMP	Complete	netinet/ip_icmp.c
ICMPv6	Complete	netinet6/icmp6.c (548 lines)
Raw IP (v4+v6)	Complete	netinet/raw_ip.c
ARP	Complete	net/sana2arp.c

TCP Congestion Control & Modern Extensions -- IMPLEMENTED

The TCP stack implements modern congestion control algorithms, all enabled by default:

Feature	RFC	Status	Details
SACK (Selective ACK)	RFC 2018	Complete	Negotiation via TF_SACK_PERMIT, block parsing/generation, MAX_SACK_BLKS limit
NewReno Fast Recovery	RFC 3782	Complete	Partial ACK detection via snd_recover, TF_IN_FASTRECOV state tracking
ECN (Explicit Congestion Notification)	RFC 3168	Complete	CE codepoint detection, ECE/CWR handshake, IP ECT(0) marking

Defaults: tcp_do_sack = 1, tcp_do_newreno = 1 (both enabled in tcp_subr.c).

Key implementation points:

• SACK negotiation occurs during SYN exchange; SACK blocks are generated from the reassembly queue
• NewReno replaces legacy Reno -- a single packet loss in a window triggers partial ACK handling instead of full slow-start
• ECN negotiation uses TH_ECE|TH_CWR flags in SYN; congestion-experienced packets trigger ECE signaling to the sender

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Network Interface Layer -- IMPLEMENTED

Feature	Status	Key Files
SANA-II device integration	Complete	net/if_sana.c, sana2config.c (see note below)
Loopback interface	Complete	net/if_loop.c
Interface management	Complete	net/if.c
Routing table (radix tree)	Complete	net/route.c (611 lines), net/radix.c (710 lines)
PF_ROUTE routing socket	Complete	net/rtsock.c (886 lines)
BPF (packet capture/filter)	Complete	net/bpf.c (493 lines), net/bpf_filter.c (401 lines)
Packet filter framework	Complete	net/pfil.c (147 lines, conditional on ENABLE_PACKET_FILTER)
IP Filter / firewall	Complete	net/ipfilter.c (566 lines, rule engine, NAT support)

SANA-II Request Allocation: By default, sana2config.c allocates 16 I/O requests per interface (the original AmiTCP value). On non-m68k architectures, SANA2_LARGEREQALLOCS is automatically defined, enabling larger request pools for higher throughput.

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BSD Socket API (Slots 1-50) -- IMPLEMENTED

The core bsdsocket.library function table provides 50 slots for standard AmiTCP BSD socket operations. All are fully implemented.

Slot	Function	Slot	Function
1	socket	26	ReleaseCopyOfSocket
2	bind	27	Errno
3	listen	28	SetErrnoPtr
4	accept	29	Inet_NtoA
5	connect	30	inet_addr
6	sendto	31	Inet_LnaOf
7	send	32	Inet_NetOf
8	recvfrom	33	Inet_MakeAddr
9	recv	34	inet_network
10	shutdown	35	gethostbyname
11	setsockopt	36	gethostbyaddr
12	getsockopt	37	getnetbyname
13	getsockname	38	getnetbyaddr
14	getpeername	39	getservbyname
15	IoctlSocket	40	getservbyport
16	CloseSocket	41	getprotobyname
17	WaitSelect	42	getprotobynumber
18	SetSocketSignals	43	Syslog
19	getdtablesize	44	Dup2Socket
20	ObtainSocket	45	sendmsg
21	ReleaseSocket	46	recvmsg
22	ReleaseCopyOfSocket	47	gethostname
23	Errno	48	gethostid
24	SetErrnoPtr	49	SocketBaseTagList
25	ObtainSocket	50	GetSocketEvents

Implementation files: api/amiga_libcalls.c (address conversion), api/gethostnamadr.c (name resolution), api/getxbyy.c (service/protocol/network lookups), kern/uipc_socket.c + uipc_socket2.c (socket core).

SO_REUSEPORT vs SO_REUSEADDR Semantics

BSD-standard behavior is implemented in netinet/in_pcb.c:

• Multicast addresses: SO_REUSEADDR is treated as SO_REUSEPORT (allows full duplication)
• Unicast addresses: SO_REUSEPORT required on both sockets for shared binds
• This matches FreeBSD/macOS semantics; differs from Linux where SO_REUSEADDR alone enables UDP port sharing

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IPv6 Control Plane -- IMPLEMENTED

IPPROTO_IPV6 Socket Options -- FUNCTIONAL

ip6_ctloutput() in netinet6/in6_proto.c (lines 261-508) implements real option handling with backing kernel state for both PRCO_SETOPT and PRCO_GETOPT.

• IPV6_JOIN_GROUP -- calls in6_joingroup_inp() -> in6_addmulti() -> MLD report
• IPV6_LEAVE_GROUP -- calls in6_leavegroup_inp() -> in6_delmulti() -> MLD done
• IPV6_MULTICAST_IF -- sets im6o->im6o_multicast_ifp
• IPV6_MULTICAST_HOPS -- sets im6o->im6o_multicast_hlim (validated 0-255 or -1)
• IPV6_MULTICAST_LOOP -- sets im6o->im6o_multicast_loop
• IPV6_V6ONLY -- sets inp->in6p_v6only
• IPV6_RECVPKTINFO -- sets/clears IN6P_PKTINFO flag
• IPV6_TCLASS -- sets inp->in6p_tclass
• IPV6_UNICAST_HOPS -- sets inp->in6p_hops
• IPV6_HOPLIMIT -- NOT HANDLED (get/set hop limit ancillary data)

NDP (Neighbor Discovery Protocol) -- IMPLEMENTED

Feature	Status	Key Files
Neighbor Discovery	Complete	netinet6/nd6.c (1007 lines), nd6_nbr.c (750), nd6_rtr.c (906)
DAD (Duplicate Address Detection)	Complete	netinet6/nd6.c (nd6_dad_start/timer)
SLAAC (Stateless Auto-config)	Complete	netinet6/nd6_rtr.c (RA processing, prefix handling)
Router Discovery	Complete	netinet6/nd6_rtr.c (RS/RA)

IPv6 Multicast -- IMPLEMENTED

Full multicast stack with MLD protocol support.

• Per-socket IPv6 group membership list (struct ip6_moptions, max 20 groups)
• Per-interface multicast group table (struct in6_multi linked list, in6_multihead)
• MLD (Multicast Listener Discovery) -- MLDv1 per RFC 2710 (netinet6/mld6.c, 386 lines)
  • Query/Report/Done message handling
  • Per-group state machine (IDLE/LAZY/SLEEPING/AWAKENING)
  • Report timer with random delay
  • Report suppression on hearing other reports
  • Unsolicited reports on join, Done on leave
  • ff02::1 (all-nodes) exemption per RFC 2710 Section 6
• SANA-II multicast MAC registration (sana_add_mcast6 / sana_del_mcast6)
• IPv6 multicast output (ip6_output.c -- interface selection, hop limit, loopback)

IoctlSocket() -- IPv6 Ioctls -- IMPLEMENTED

IPv6 address management ioctls are handled in in6_control():

• SIOCGIFADDR_IN6 -- get IPv6 interface address
• SIOCAIFADDR_IN6 -- add/configure IPv6 interface address
• SIOCDIFADDR_IN6 -- delete IPv6 interface address
• SIOCGIFDSTADDR_IN6 -- get destination address (point-to-point)
• SIOCGIFNETMASK_IN6 -- get network mask
• SIOCGLIFADDR -- enumerate addresses (used by getifaddrs)

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Configuration & Services -- IMPLEMENTED

Feature	Status	Key Files
DHCPv4 client	Complete	kern/amiga_dhcp.c (external dhclient launcher)
DHCPv6 client	Complete	kern/amiga_dhcp.c (conditional on INET6 && DHCP6)
Network database	Complete	kern/amiga_netdb.c
ARexx interface	Complete	kern/amiga_rexx.c
GUI configuration	Complete	kern/amiga_gui.c
Logging / debug	Complete	kern/amiga_log.c, kern/subr_prf.c
RC file configuration	Complete	kern/amiga_rc.c, amiga_config.c

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Firewall Preferences Application -- IMPLEMENTED

A Zune/MUI preferences application at AROS/workbench/prefs/firewall/ provides a GUI for managing IP filter and NAT rules.

Feature	Description
Filter rules editor	Add, edit, remove, reorder IP filter rules (ipf.rules)
NAT rules editor	Add, edit, remove NAT/redirect rules (ipnat.rules)
Sub-window editing	Rule parameters edited in separate pop-up windows with Use/Cancel
Theme-aware buttons	Probes for THEME:Images/Gadgets/ icons; falls back to text buttons
Locale support	Full FlexCat catalog localization (49 string entries)
PrefsEditor subclass	Integrates with AROS Prefs framework (Save/Use/Cancel semantics)

Configuration files: Reads/writes ENV:AROSTCP/ipf.rules and ENV:AROSTCP/ipnat.rules, with ENVARC copies for persistence.

Source files: main.c, fweditor.c (MUI editor class), filter.c (filter rule I/O), nat.c (NAT rule I/O), prefsdata.c (orchestration), locale.c, args.c.

Utility	Location
arp	common/C/arp.c
ifconfig	common/C/ifconfig.c
ping	common/C/ping.c
route	common/C/route.c
netstat	common/C/netstat/ (inet, inet6, route, if, mbuf stats)
traceroute	common/C/traceroute/
nslookup	common/C/nslookup/ (interactive mode)
hostname	common/C/hostname.c
resolve	common/C/resolve.c
logger	common/C/logger.c
whoami	common/C/whoami.c
ipf	common/C/ipf/ (IP Filter rule management)
ipnat	common/C/ipnat/ (NAT rule management)
ip	common/C/ip/ (iproute2-style network tool, see below)

The ip Command

The ip utility (v1.0) provides a Linux iproute2-inspired command-line interface for network management on AROS, adapted to the BSD/SANA-II kernel APIs.

Usage: ip [-V] [-s] [-d] [-r] [-f family] [-4|-6|-0] OBJECT [COMMAND]

Object	Aliases	Description
link	l	Display/manage network interfaces (flags, MTU, state, link-layer addresses)
addr	address, a	Display/manage interface addresses (IPv4 + IPv6 with prefix lengths)
route	r	Display routing tables (parsed from kernel routing messages)
neigh	neighbor, n	Display neighbor cache (ARP for IPv4, NDP for IPv6)
maddr	maddress	Display multicast group memberships
mroute		Display multicast routing cache
rule	ru	Policy routing rules (stub -- AROS lacks RPDB)
netns		Network namespaces (stub -- AROS lacks namespaces)

Source files: ip.c (main dispatcher), ip_link.c, ip_addr.c, ip_route.c, ip_neigh.c, ip_maddr.c, ip_stub.c, ip_util.c (formatting helpers).

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Kernel Source File Reference

kern/ (Core Kernel)

File	Description
amiga_main.c	Stack initialization & main event loop
uipc_socket.c	Socket creation/management core logic
uipc_socket2.c	Socket additional operations & queuing
uipc_domain.c	Protocol domain/family registration
uipc_mbuf.c	Memory buffer (mbuf) allocation & manipulation
kern_malloc.c	Kernel memory allocator
kern_subr.c	Kernel subroutines (sleep, wakeup, etc.)
kern_synch.c	Amiga-specific synchronization primitives
amiga_config.c	Configuration file parsing for network setup
amiga_netdb.c	Name database (hosts, services) caching
amiga_time.c	Time management & timers
amiga_log.c	Logging subsystem
amiga_rexx.c	ARexx command interface
amiga_dhcp.c	DHCP client implementation (v4 + v6)
amiga_cx.c	Commodities Exchange interface
amiga_gui.c	GUI components for configuration
accesscontrol.c	Access control lists
subr_prf.c	Printf-style formatting utilities

netinet/ (IPv4 Core)

File	Description
in_proto.c	IPv4 protocol family/domain initialization
ip_input.c	IPv4 packet reception & routing
ip_output.c	IPv4 packet transmission & fragmentation
ip_icmp.c	ICMP (ping, error messages)
in_pcb.c	Protocol control blocks (TCP/UDP connection state)
in_cksum.c	IPv4/TCP checksum calculation
in_cksum_sse2.c	Optimized SSE2 checksum
in.c	IPv4 address utilities & interface configuration
tcp_input.c	TCP segment reception & state machine (2166 lines; SACK/NewReno/ECN)
tcp_output.c	TCP segment transmission (769 lines; SACK option generation, ECN marking)
tcp_usrreq.c	TCP user request processing
tcp_subr.c	TCP support routines (511 lines; default enables for SACK/NewReno)
tcp_timer.c	TCP retransmit & keepalive timers (314 lines)
tcp_debug.c	TCP debug tracing
udp_usrreq.c	UDP datagram handling
raw_ip.c	Raw IPv4 socket support

netinet6/ (IPv6)

File	Description
ip6_input.c	IPv6 packet reception & routing (273 lines)
ip6_output.c	IPv6 packet transmission, multicast output (298 lines)
in6.c	IPv6 address management, ioctls, multicast (788 lines)
in6_pcb.c	IPv6 PCB bind/connect/lookup (223 lines)
in6_proto.c	IPv6 protocol switch, ip6_ctloutput (512 lines)
in6_cksum.c	IPv6 checksum calculation
in6_cksum_sse2.c	Optimized SSE2 IPv6 checksum
icmp6.c	ICMPv6 echo, parameter problem, time exceeded (548 lines)
nd6.c	Neighbor cache, NUD, ND option parsing (1007 lines)
nd6_nbr.c	NS/NA processing, DAD (750 lines)
nd6_rtr.c	RS/RA processing, SLAAC, prefix management (906 lines)
mld6.c	MLDv1 multicast listener discovery (386 lines)
udp6_usrreq.c	UDP over IPv6

net/ (Generic Network Layer)

File	Description
if.c	Network interface management
if_sana.c	SANA-II device driver integration
if_loop.c	Loopback interface
route.c	Routing table management (611 lines)
rtsock.c	PF_ROUTE routing socket (886 lines)
radix.c	Radix tree for route lookups (710 lines)
raw_cb.c	Raw socket control blocks
raw_usrreq.c	Raw socket user requests
netisr.c	Network interrupt scheduler
sana2arp.c	ARP (Address Resolution Protocol)
sana2config.c	SANA-II device configuration (16 reqs default; larger with SANA2_LARGEREQALLOCS)
sana2copybuff.c	Buffer copying utilities
sana2perror.c	SANA-II error reporting
bpf.c	Berkeley Packet Filter, packet capture (493 lines)
bpf_filter.c	BPF packet filtering VM/interpreter (401 lines)
pfil.c	Packet filter hooks framework (147 lines)
ipfilter.c	IP packet filtering rules engine (566 lines)

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Core Stack Remaining Backlog

1. Implement IPV6_HOPLIMIT socket option (ancillary data for received hop limit)