In my case, from a hardware UDP packets are sent to destination PC - 192.168.13.250 (45141) but MAC ID is FF:FF:FF:FF:FF:FF. Now I binded to that destination IP & port no using sockets. But I'm not able to receive UDP packets form PC using socket program. It is not coming out of recvfrom() call. Still it is waiting. If I change the MAC ID to destination PC MAC ID(00-12-d5-f6-3e-92) using hardware settings, then I'm able to receive UDP packets. Without changing the MAC ID, i.e, How to receive UDP packets from broadcast MAC ID. Any help would be highly appreciated. Thanks in advance. Following is the log from Wireshark.
With following UDP packets are not received (Wireshark)
Frame 3609 (7978 bytes on wire, 7978 bytes captured)
Ethernet II, Src: 0a:dc:0a:dc:0a:dc (0a:dc:0a:dc:0a:dc), Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Internet Protocol, Src: 192.168.13.25 (192.168.13.25), Dst: 192.168.13.250 (192.168.13.250)
User Datagram Protocol, Src Port: lbc-control (2780), Dst Port: 45141 (45141)
Data (7936 bytes)
With following UDP packets are received (Wireshark)
Frame 3609 (7978 bytes on wire, 7978 bytes captured)
Ethernet II, Src: 0a:dc:0a:dc:0a:dc (0a:dc:0a:dc:0a:dc), Dst: Broadcast (00:12:d5:f6:3e:92)
Internet Protocol, Src: 192.168.13.25 (192.168.13.25), Dst: 192.168.13.250 (192.168.13.250)
User Datagram Protocol, Src Port: lbc-control (2780), Dst Port: 45141 (45141)
Data (7936 bytes)
RFC 1122 section 3.3.6 states:
"When a host sends a datagram to a link-layer broadcast address, the IP destination address MUST be a legal IP broadcast or IP multicast address."
If you want your PC to receive the UDP packet with a broadcast MAC address, you should also be using a broadcast IP address.
Related
Hi my UDP Multicast is working but only 1 receiver is able to receive the data.
From my understanding, multicast send data via port number.
Can I have two device listening to the same port?
I'm capturing traffic with winpcap on a Windows machine that is also a network gateway, so I see packets with src mac, src ip, dst mac, and dst ip which are different from the gateway's mac and ip.
What I'm trying to do is redirect some of those packets to a listening server (for example, redirect all port 80 HTTP packets to a local HTTP server instead of their original destination, something similar to a captive portal).
My idea is to disable IP forwarding on the gateway so packets won't go out, and reinject the captured packets to the interface again with winpcap. However, the listening server ignores these packets.
I researched this issue, and found out that maybe it has something to do with Rx, Tx. Apparently, when you send packets with winpcap, listening for those packets on the same interface won't work because listening is on the Rx channel and sending is on the Tx channel.
Does anyone know any workaround for this issue?
My AutoIt script should receive UDP multicast packets sent to 239.255.250.250:9131. But it doesn't work and I see no option to specify a UDP multicast address for UDPBind().
UDPBind() in below code returns error 10049 (invalid address):
UDPStartup()
UDPBind("239.255.250.250", 9131)
While 1
$msg = UDPRecv($recv, 512)
If $msg <> "" Then
ConsoleWrite($msg)
EndIf
Sleep(100)
WEnd
How to listen for UDP multicast packets?
You must not bind to the multicast address. Bind is a local operation which sets the listening interface (on Windows) and port.
To receive multicast you need to:
Bind to the IP address of the interface and port you want to receiv mutlicast on. On Windows bind to the IP address on the selected interface. On Linux bind to 0.0.0.0.
Join the multicast group using the appropriate mechanisms.
Say for example, my machine is multi-homed and has two network interfaces:
Wireless LAN adapter WiFi : Ip: 10.20.19.140
Ethernet adapter Ethernet: Ip: 10.20.19.154
I create two UDP sockets one listening on (1) and other on (2). The i am assuming the interface is already assigned, then why do i need IP_MULTICAST_IF and IPV6_MULTICAST_IF?
The IP_MULTICAST_IF or IPV6_MULTICAST_IF settings tell your socket which interface to send its multicast packets on. It's a separate, independent setting from the interface that you bound your socket to with bind(), since bind() controls which interface(s) the socket receives multicast packets from.
(Granted, the BSD sockets API implementers could have made the assumption that a socket would always want to send packets out over the same interface it receives packets on, but that would make a number of use cases more difficult; for example, if you are using a single socket to receive multicast packets from all interfaces (via INADDR_ANY), then when sending a packet using that socket you'd still need a way to specify which multicast interface you want that packet to be sent over)
I recently turned on Windows Firewall logging on my computer and started tracking incoming and outgoing connections. Something curious about the logfiles is that I have noticed numerous UDP packets (in fact, it constitutes basically all of my incoming traffic) that don't have my host as destination or source showing up in the logs.
I thought this might be a implementation detail for UDP (the packets are hopping over my computer in the subnet) but Wikipedia'ing UDP didn't enlighten me any more, and I don't see why my computer should be forwarding these packets in the first place.
Any ideas?
Edit 1: Here is what a log file line with the mysterious UDP packet looks like:
2008-10-11 16:04:31 ALLOW UDP 18.243.7.218 239.255.255.250 49152 3702 0 - - - - - - - RECEIVE
Is 239.255.255.250 a broadcast address? Now that you mention it, the UDP packets I'm seeing have very specific destinations, basically 224.0.0.252, 239.255.255.250, 18.243.255.255. I also get phantom ICMP pings addressed to 224.0.0.1.
The packets addressed to IPs starting with 239 and 224 are multicast packets. This is a way to address traffic to a group of computers without broadcasting it to an entire network. It is used by various legitimate protocols.
224.0.0.252 is the address used by the Link Local Name Resolution protocol.
239.255.255.250 is the address used by the Simple Service Discovery Protocol.
224.0.0.1 is the all hosts address, used by your router to see who on your network is willing to participate in multicast conversations.
The ones addressed to 18.243.255.255 look like broadcasts, again this is used by many legitimate protocols such as Bonjour.
As recommended by Luka, a good protocol analyzer like Wireshark will tell you precisely what each of these packets are and what they contain.
It depends on the type of connection you are on.
On most cable modem ISP's you are basicly on the same LAN as your neigburs, and can usualy see some of their traffic (like brodcast).
Id recomend you install packet sniffer and see what is realy going on.
Good multiplatform packet sniffer is Wireshark
Hard to say without analyzing the log data, but they could be broadcast packets on the segment, in which case you're system would listen to them. This is possible in IPv4 and IPv6.
Your system should not be forwarding them unless it's set up to route, but it can certainly be listening to packets all the time (various network protocols use UDP).