I have a Linux machine that is connected directly to a Raspberry Pi via an Ethernet cable. Is there a way to programmatically in C get the Raspberry Pi's MAC address based on which Ethernet port on my computer it is connected to (eth0, eth1 etc...)
For instance, say I have two Raspberry Pi's, one connected to eth0 and another to eth1. I would like to get the MAC address of only the Pi that is connected to eth0. How would I do that?
Depending on do you know the ip address of the Pi, there are two cases:
The Pi has IP address and are known to your program, you can just send any data to it, e.g. an ICMP PING packet, the networking stack will send out ARP requests for the address, and when the Pi respond with its MAC address, you can get it from the ARP table, which can be viewed by the command arp -n.
The Pi's IP is not known, then you send a broadcast packet through the connected interface, eth0 in this case, for example, ping -b -I eth0 255.255.255.255, the Pi will also respond with its MAC address, and you can get it from the local arp table.
Now for how to do this in programmatic way, you can send the packet using raw sockets, and read arp table through parsing the proc entry /proc/net/arp.
Related
I have two interfaces in my Linux system - eth0 and eth1. I have opened a raw socket on eth0 and I am listening on it for incoming packets. When a packet comes from eth0, I forward it to eth1 after changing the ethernet header (specifically destination MAC to eth1's MAC address). The packet should now be accepted by the interface and sent to the kernel for further processing and eventually to the application waiting for it. But for some reason the packet reaches eth1 (as I can see from wireshark) but the application does not receive it (the application is ping and I don't see the ping reply).
How do I send the packet to eth1 such that it is accepted and sent upstream to the kernel?
There is probably a misunderstanding here:
If you send a packet through a raw socket on an interface, in your case eth1, it will not be treated as local to the kernel, regardless of its mac-address, but will leave the interface to the network (with its own mac-address as destination). This is what you observe with wireshark.
If you want the packet to be processed by your kernel, send it to the lo-interface (Loopback-interface), which is specifically for that purpose.
I'm writing a C program on Linux machine that needs convert data from UART port to ETH and send it to the ETH port. In order to do so, I build a UDP packet with a given payload (in a SKB from UART) and send it to another machine (win7) on a given destination IP via the ETH port.
I do the following all on Linux machine:
"Learn" the other machine (win7) MAC address, from receive packets.
Allocate a new SKB and copy all the given UART SKB data to the new SKB
Build ETH, IP and UDP headers with correct data
Send the UDP packet that I built to the network by 'netif_rx(MsgSkb);' command.
Now, when I write in the ETH header the local port MAC address, I get an error on the Linux machine:
net_ratelimit: 167 callbacks suppressed
br0: received packet on mb_radio with own address as source address
br0: received packet on mb_radio with own address as source address
br0: received packet on mb_radio with own address as source address
br0: received packet on mb_radio with own address as source address
When I write in the ETH header a junk MAC address as 00:01:02:03:04:05, all works OK.
In both the cases, I checked and verified in the destination machine (win7) with a sniffer (Wireshark) that all the packet that I send from the Linux machine are received OK with the MAC address that I wrote.
How can I write the packet to leave the Linux machine with the correct MAC address?
Thank ahead for your help and advice,
-yaron.
Need to send messages on PC without configured IP using MAC address in C language as a reply on PC's broadcast message. I suppose I should work with ethernet-header and use some (linux) kernel's structures and subroutines, however I couldn't find good links and samples about my question.
Example of sending a raw Ethernet frame in Linux:
https://gist.github.com/austinmarton/1922600
I am trying to find out mac address of a machine in a switched environment after sending it a raw packet. I am trying to implement traceroute command . I want to know when i receive a ICMP time exceeded message how can I extract the mac address of that machine . I am a new to network programming so am confused what socket call will help me to extract the mac address.
Thanks .
No, you can not extract MAC address from ICMP reply.
You can only determine MAC addresses of linked machines next to you. In ICMP(tracert) you can just find out the IP address of target or middle machine.
If you want to detect MAC addresses, you should use ARP protcols where it's applicable in local networks not Internet.
ICMP protocol starts after IPv4 header[1] and MAC addresses is related to physical/link layer. In low level layers the MAC addresses will transparent from top level layers such as network(IP) or Transmission,...
To determining MAC addresses, you should use Raw sockets or PCAP SDKs to access lower layers of network programming. (I say again, these are not useful over Internet)
Like Masoud M said, you can only get the MAC address of machines that are on your local network. That said, you can parse the output the arp command to find the MAC address given the IP address of a machine one your local network.
In general, on internet, you don't even know the media a host is using for transmitting packets. Let's suppose a remote host is conected over a serial rs-232-C link with PPP protocol. It doesn't have a mac address. This also happens for example if the host uses a token ring interface or frame relay link. This makes determining the remote mac addresses of hosts a local issue completely. Normally, when you get a packet from a remote site over ethernet, the source mac addres you get in the packet is the one of the last router that links you to the internet, not the one of the original host that sent the IP packet. In the RFC on IP over avian carriers (rfc1149, rfc2549 and rfc6214) the media used for transmission doesn't allow to use mac addresses (the link address, if somewhat feasible on a pidgeon could be, would be its name)
If you want to read about traceroute on ethernet network of switches, perhaps you had to have a look at the IEEE802.1ag, that has an specification to do tracerouting over switches (tracelink service) but I think is far over the scope of this answer.
I have a need for some C or C++ code, compilable under Linux, to be able to take a list of IP addresses of some arbitrary number of remote hosts machines and obtain a ethernet MAC address for each one. These host machines may be on the same subnet or they could be on a different subnet behind a router. Its OK if the MAC address of some or all of the remote hosts is the address of the interface on the router. Ultimately, I want to hand off the IP address and MAC address to an FPGA who will use these pieces of information to format and send UDP/IP packets over ethernet to the hosts. Obviously, the FPGA will also be given its own MAC address and IP address to fill in the source MAC and source IP addresses in the packets.
Is there some code I can be pointed to that can create and broadcast ARP packets to these remote machines and receive back the ARP response packets such that the destination MAC addresses can be extracted?
Part of what you want to do requires some raw socket programming.
http://mixter.void.ru/rawip.html
The source for the linux arp command will give the rest of what you need. Here's a link:
http://www.comp.nus.edu.sg/~cs4236/readings/out/html/arp_8c-source.html
I recommend looking into arping which is doing a somewhat identical job. It takes IPs and MACs and tries to receive additional informationen. Or justs pings them.
http://freshmeat.net/projects/arping/