For my project, I need some way to know which multicast group a packet was originally sent to when it's received by my client. I've considered maintaining a map of sockets to multicast groups and identifying them this way, but surely there's some way to get the address from the datagram?
To listen, I'm currently using:
# Initialise socket for IPv6 datagrams
sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
# Allows address to be reused
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
# Binds to all interfaces on the given port
sock.bind(('', 8080))
# Allow messages from this socket to loop back for development
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_LOOP, True)
# Construct message for joining multicast group
mreq = struct.pack("16s15s".encode('utf-8'), socket.inet_pton(socket.AF_INET6, "ff02::abcd:1"), (chr(0) * 16).encode('utf-8'))
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)
data, addr = sock.recvfrom(1024)
and to send:
# Create ipv6 datagram socket
sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
# Allow own messages to be sent back (for local testing)
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_LOOP, True)
sock.sendto("hello world".encode('utf-8'), ("ff02::abcd:1", 8080))
Which works, but the address when received is that of the sending machine. How can I see the multicast group it was sent to?
Thanks!
You only joined multicast group address "ff02::abcd:1". Therefore, any packet that is received on the socket must have been sent to that multicast address.
Related
I have a linux network interface that IPv6 multicast traffic is arriving on. There are both ICMPv6 packets and UDP packets arriving for the same multicast group.
I'm trying to receive the UDP traffic. The code below is in Python but I don't believe this is important; the Python library here is a pretty thin wrapper around the BSD sockets API. This is what I'm doing:
import socket
import struct
import select
import ipaddress
# .packet is a byte array
mcast_group = ipaddress.IPv6Address("ff22:5eea:675c:d1fc:17c::1").packed
address = ipaddress.IPv6Address("...ipv6 global scope address of interface...")
sock = socket.socket(socket.AF_INET6, socket.SOCK_RAW, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
group = struct.pack("16s i",
mcast_group,
3 #Interface ID
)
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, group)
sock.bind((address.compressed, 0, 0, 0))
recv_socks, _, _ = select.select([sock], [], [], 10)
if recv_socks:
print("Received packet")
With the code above, I appear to be receiving both the UDP and ICMPv6 packets. If I change the second parameter to socket.socket() from socket.SOCK_RAW to socket.SOCK_DGRAM then I receive no packets at all.
I've confirmed that both packet types are arriving on that interface, addressed to that multicast group, using wireshark.
There is something here that I've fundamentally not understood about socket(). Shouldn't specifying IPPROTO_UDP mean that I only get UDP packets? Shouldn't specifying SOCK_DGRAM still allow UDP packets through?
The Linux kernel is 4.9 on aarch64, in case that's important.
Eventually figured this out. Here's the correct way of doing this:
import socket
import struct
import select
import ipaddress
# .packet is a byte array
mcast_group = ipaddress.IPv6Address("ff22:5eea:675c:d1fc:17c::1")
address = ipaddress.IPv6Address("...ipv6 global scope address of interface...")
port_no = 5555
interface_idx = 3
sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
group = struct.pack("16s i",
mcast_group.packed,
3 #Interface ID
)
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, group)
sock.bind((str(mcast_group), port_no, 0, interface_idx))
recv_socks, _, _ = select.select([sock], [], [], 10)
if recv_socks:
print("Received packet")
Important differences from the code in the question:
UDP (SOCK_DGRAM) sockets need to be bound to a port number. AFAICT this is why I was getting ICMP traffic as well as UDP with SOCK_RAW and no traffic at all with SOCK_DGRAM.
Instead of binding the socket to a unicast address on the interface of interest, bind it to the multicast group but use the interface index as the scope_id (the fourth in the address tuple passed to socket.bind()).
Which address should I write, if I want that my server listens to 5-6 specific ip addresses?
I want my server to listen only to these addresses, and all of them, not just one.
import socket
ADDRESS = ('127.0.0.1', 5555) /**here**
serverSock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
serverSock.bind(ADDRESS)
(data, addr) = serverSock.recvfrom(65535)
I have an application that meeds to:
talks in UDP
support optionally disabling multicast.
treat multicast message the same way as unicast message but with few restrictions
I thought I should use same UDP socket to receive both unicast and multicast datagrams.
# udp_multicast_recv.py
# Python version used: 3.9.1
import socket
import struct
host = "224.1.1.1"
# host = "0.0.0.0"
listen_all = True
port = 5683
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
if listen_all:
s.bind(("", port))
else:
s.bind((host, port))
mreq = struct.pack("4sl", socket.inet_aton(host), socket.INADDR_ANY)
s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
data = None
print("Listening")
while True:
# data, addr = s.recvfrom(1024)
data, ancdata, msg_flags, addr = s.recvmsg(1024)
print(addr, ":", data, ancdata, msg_flags)
# udp_multicast_send.py
import socket
dest = "224.1.1.1"
dest = "192.168.86.188"
port = 5683
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.sendto("Hello world".encode(), (dest, port))
I soon noticed I need a way to distinguish multicast datagram from unicast datagram. But I was unable to find a solution nor related question on how to achieve this on the internet.
Hence the question: When receiving UDP datagram from same socket, is there a way to tell whether datagram is unicast or multicast?
There is a script that opens a socket and read from it the multicast (from Multicast in Python)
import socket
import struct
MCAST_GRP = '224.1.1.1'
MCAST_PORT = 1234
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(('', MCAST_PORT))
mreq = struct.pack("4sl", socket.inet_aton(MCAST_GRP), socket.INADDR_ANY)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
while True:
print sock.recv(10240)
Everything is fine as long as I do not run parallel to the same script to another multicast group, but the ports are the same, for example
rtp://224.1.1.1:1234
rtp://224.1.1.2:1234
After starting the second script starts mess - the first script sees packets for the second and the second to first.
I tried to do as a mcast.py - a similar result.
Why is this happening and how to cure?
UPD Fix
-sock.bind(('', MCAST_PORT))
+sock.bind((MCAST_GRP, MCAST_PORT))
An application listening to all incoming connections on a port will get all messages to that port, no matter which application initiated multicast group membership. To mitigate this, have every application listen to the multicast address it's expecting data from, by specifying it as the first argument in the address tupel given to bind.
This following is a straightforward IPv4 UDP broadcast, followed by listening on all interfaces.
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, True)
sock.bind(("", 1337))
sock.sendto("hello world", ("255.255.255.255", 1337))
while True:
data, addr = sock.recvfrom(0x100)
print "received from {0}: {1!r}".format(addr, data)
I want to adjust this to send and receive both IPv4 and IPv6.
I've poked around and read as much as I can and believe the following is roughly the route I need to take:
Create an IPv6 socket.
Add the socket to a link or site local multicast group.
Send the UDP packets to the multicast address for the group in use.
Further info I have is that I may need to bind to several interfaces, and tell the socket using setsockopt() that it should also receive multicast packets. Lastly getaddrinfo() can be used across the board to gracefully "drop back" to IPv4 where IPv6 isn't available.
I have much of this implemented, but stumble primarily on the multicasting parts. A complete code example in Python, or vivid description of the constants and addresses needed are preferred.
Here's a link to python mcast demo, does both IPv4 and IPv6.
I'm currently asking a question over here that involves getting the multicast address of a received message, but the source code answers your question!
To listen:
# Initialise socket for IPv6 datagrams
sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
# Allows address to be reused
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
# Binds to all interfaces on the given port
sock.bind(('', 8080))
# Allow messages from this socket to loop back for development
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_LOOP, True)
# Construct message for joining multicast group
mreq = struct.pack("16s15s".encode('utf-8'), socket.inet_pton(socket.AF_INET6, "ff02::abcd:1"), (chr(0) * 16).encode('utf-8'))
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)
data, addr = sock.recvfrom(1024)
and to send:
# Create ipv6 datagram socket
sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
# Allow own messages to be sent back (for local testing)
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_LOOP, True)
sock.sendto("hello world".encode('utf-8'), ("ff02::abcd:1", 8080))
This is for python3.6, with python 2.7 I don't think the encodes are necessary. Also in the struct.pack line, I've seen variations of "16s15s" such as "4s", but I don't know what it is and what I have worked for me!