# =============================================================================
# WUC Technologies — IPv4 Field Guide
# CLI cheat sheet: Multicast — 224.0.0.0/4
# Source: https://www.wuctechnologies.com/resources/field-guides/ipv4-address-analyzer/
# License: CC0 1.0 Public Domain (https://creativecommons.org/publicdomain/zero/1.0/)
# Released: 2026-05-22
#
# 224.0.0.0/4 = the entire IPv4 multicast range. Sub-divisions:
#   224.0.0.0/24     local-link, never forwarded by routers
#   224.0.1.0 – 238.255.255.255   internetwork control + globally scoped
#   239.0.0.0/8      administratively scoped (RFC 2365) — your enterprise
# =============================================================================

# -----------------------------------------------------------------------------
# Inspect multicast group membership on a host
# -----------------------------------------------------------------------------
# Show groups the host has joined on each interface:
ip -4 maddr show

# Equivalent classic syntax:
cat /proc/net/igmp

# -----------------------------------------------------------------------------
# Join / leave a multicast group manually (smcroute / mtest)
# -----------------------------------------------------------------------------
# Join a group (one-shot, requires smcroute):
sudo smcroutectl join eth0 239.1.1.1

# Leave it:
sudo smcroutectl leave eth0 239.1.1.1

# Alternative — Python one-liner to subscribe and read multicast packets:
python3 -c '
import socket, struct
g = "239.1.1.1"
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(("", 5000))
mreq = struct.pack("4sl", socket.inet_aton(g), socket.INADDR_ANY)
s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
while True: print(s.recv(2048))
'

# -----------------------------------------------------------------------------
# Send to a multicast group
# -----------------------------------------------------------------------------
# Using socat — send "hello" to 239.1.1.1:5000 with TTL 32:
echo "hello" | socat - UDP4-DATAGRAM:239.1.1.1:5000,ip-multicast-ttl=32

# Send from a specific interface:
echo "hello" | socat - UDP4-DATAGRAM:239.1.1.1:5000,ip-multicast-if=192.168.1.10

# -----------------------------------------------------------------------------
# Packet capture — multicast traffic only
# -----------------------------------------------------------------------------
sudo tcpdump -i any -nn 'multicast'

# Specific group:
sudo tcpdump -i eth0 -nn 'host 239.1.1.1'

# IGMP control plane (group join/leave signaling):
sudo tcpdump -i eth0 -nn -e 'igmp'

# -----------------------------------------------------------------------------
# Common well-known multicast addresses (link-local 224.0.0.0/24)
# -----------------------------------------------------------------------------
# 224.0.0.1       all hosts on the subnet
# 224.0.0.2       all routers on the subnet
# 224.0.0.5       OSPF — All OSPF routers (AllSPFRouters)
# 224.0.0.6       OSPF — All Designated Routers (AllDRouters)
# 224.0.0.9       RIPv2 routers
# 224.0.0.13      PIM routers
# 224.0.0.18      VRRP routers
# 224.0.0.22      IGMPv3
# 224.0.0.102     HSRPv2
# 224.0.0.251     mDNS (.local resolution)
# 239.255.255.250 SSDP / UPnP discovery

# These are NEVER forwarded by routers — they stay on the link. Firewalls
# that block multicast on a LAN break OSPF adjacencies, HSRP failover,
# Bonjour/mDNS, and UPnP service discovery silently.

# -----------------------------------------------------------------------------
# Router-side configuration (Cisco IOS reference)
# -----------------------------------------------------------------------------
# Enable PIM sparse mode globally:
# (config)# ip multicast-routing
# (config-if)# ip pim sparse-mode
#
# Configure an RP (Rendezvous Point):
# (config)# ip pim rp-address 10.1.1.1
#
# Show multicast routing table:
# # show ip mroute
#
# Show PIM neighbors:
# # show ip pim neighbor
#
# Show IGMP groups joined by hosts:
# # show ip igmp groups

# -----------------------------------------------------------------------------
# Address range reference
# -----------------------------------------------------------------------------
# 224.0.0.0/4     =  224.0.0.0  through  239.255.255.255
# Total addresses: 268,435,456 (entire former Class D space)
# Not routable on the public internet by default. Enterprise multicast
# deployments require explicit PIM, IGMP, and (across ASes) MSDP.
# =============================================================================