I am using Debian 6.0 and net-snmp 5.4.3. I have a question relating to capturing IP address and MAC address for ethernet interfaces exist on the system. In my SNMP agent, I have to figure out how many system ethernet interfaces are exist and update their IP and MAC address in a table. I have looked at pre installed mibs and found that IP-MIB contains a table for system ethernet IP addresses but I couldn't find the source to check how it is implemented. Could you please suggest me how can I implement this functionality or where I can find some further infromation?
Thanks,
Ravi
Someone may suggest a better way, but if not here's a solution of last resort. You can call out to ifconfig to get the data as text and then parse the results.
Related
for my project i have to fetch all devices name & their ip address which are connected in same network.
How to get the names and ips of all devices on my local network? somewhat similar to post but i have to use c code & this post is for ios only.
I know that ARP protocol use to map ip address with the mac address but exactly don't know how to scan all the ip's from there.
My aim is to get the output without any command line tool as nmap & arp command are also there which will give the network ip addresses but not in a proper way.
Can anybody tell me the way i can get all these details with or without code that would be really helpful.
Thanks,
you can socket raw c, Create two threads
Thread 1: ping all machines using ICMP.
Thread 2: Caputre all data comming to your interface (ex: eth0) then filter only ARP response.
I want to send a packet to another machine but with a different MAC address in the ethernet header. For this I am using raw sockets in C and creating my own ethernet header so that I can set the source MAC as desired. The trouble is that I am not sure what destination MAC address to fill in the header. I know the IP of the destination machine but not the MAC. Even if I knew, I don't want to hardcode this MAC.
One option I see is that my machine would know the MAC in its ARP table and I could read it and get the MAC address and fill it in. But doing this before sending each packet is overhead. I could read it once and keep using but what if some day the destination machine gets replaced. The admin would assign the same IP address to the new machine but the MAC address would be different. Probably when the new machine boots up, it would send a Gratuitous ARP and my machine would update its ARP table. But my program wouldn't know this. My program would keep sending packets with old MAC.
I feel I am missing something very basic. Thoughts?
What you are seeing here is the same problem that everyone faces, who tries to implement a network stack.
You have several options:
If the packet is a reply packet, then just use the MAC address of the from address
You can maintain an own arp-table and send a arp request if the entry in your table is missing or outdated. Parse arp replies and update your table accordingly. Packets to be sent without a valid arp table entry have to be queued. This is the most elegant, but also a very demanding option.
You can simply send the packet to the MAC of your local router. It will forward the packet to the correct host specified in the IP header. If your local router employs protocols like vrrp, hsrp or gblp, then the MAC address is always the same and doesn't change, even if your router is replaced.
You can read the MAC address from /proc/net/arp or with ioctl(SIOCGARP, ...);, but the entry for the IP you are looking for might not be present, if your host hasn't tried to communicate with it recently. You could, of course, send a dummy packet with sendto(); to that host before reading the arp table.
If you describe in more detail what you are planning to do, the suggestions might get better.
You can set the MAC address for the device with SIOCSIFHWADDR ioctl request. The manual for netdevice is a good starting point for this.
I have TBS6905 DVB-S2 PCIe card and its configured in Ubuntu 14.
And I have to find MAC address of all adapters because my application will do Blind Scan for all four adapters at the same time.
And index of these adapters will change after reboot.
So I have to find MAC address and set static start and end frequency to particular adapter device using C language.
What I tried:
- I checked dmesg but I did get MAC address(while I have also Prof 7500 DVB-S2, in that dvb card I can find MAC address using dmesg).
- And I also checked udevadm command, but no luck yet.
Thank you.
https://unix.stackexchange.com/questions/147278/how-does-ubuntu-14-04-achieve-persistent-eth-interfaces
The persistent eth interface rule for udev, you can probably grab from another version or distro.
The MAC address is visible for shell scripts if you run commands like ifconfig.
We can give static Index to particular DVB device using udev rules.
Example1 and
Example2
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.
Please don't criticise the solution. It's not my design and yes, it sucks.
On a computer running Linux, and using C, we need to verify that a TCP connection made to a process is from the same machine. Doing it by IP address is problematic since the OS is generating two IP addresses and the process only knows one. Anyway, verifying by IP address is a bit poor.
We want to do the verification by comparing the "remote" MAC address to the local MAC address. We already get the local MAC address. All I need to know is how to get the "remote" MAC address. It's in the packet that gets sent when forming the connection (and in all subsequent ones too). How do we drag it out of the ethernet layer?
Before anyone says this again, I KNOW you cannot get the MAC address of the remote host if it's not on the same subnet/LAN. That's fine. Presumably we'll get something like 00:00:00:00:00:00 and since that is different to the local MAC address it will be different - just what we want.
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So, to summarise, we have a TCP connection socket fd, we've received a data packet, how do we then find the MAC address of the remote host, the MAC address that was in the packet's header?
If I understand correctly, you are not trying to tell remote machines apart, but to use the idea that the source and destination MAC would match on traffic sent from a machine to itself in order to allow only local traffic.
This seems rather roundabout, and has been pointed out, insecure.
A somewhat better idea might be to have the TCP client listen only on the loopback interface (127.0.0.1) and not on INADDR_ANY. Or go a step further and use a unix-domain socket instead of a TCP one (a common method used by X servers today to prevent the possibility of remote connections)
The MAC address of a live same-subnet TCP connection will almost certainly be in the ARP cache.
On Linux, you could examine the ARP cache by looking in /proc/net/arp. Here is what it looks like on my Ubuntu box:
aix#aix:~$ cat /proc/net/arp
IP address HW type Flags HW address Mask Device
10.0.0.32 0x1 0x2 00:1e:4f:f5:be:dc * eth0
10.10.10.1 0x1 0x2 00:1f:6c:3e:02:e3 * eth0
There's probably some callable API that you could use to get to the same data if you're averse to parsing the pseudo-file.
How about configuring a firewall (internal or external) to block or MAC-filter external traffic on the port in question?
A loopback connection (whether it's over the loopback interface or some other interface) it not routed over any ethernet device and therefore does not have a MAC address associated with it.
I suggest you just use getsockname and getpeername to get the local and remote IP address and compare that they are equal. That will work without any a priori knowledge of the configured IP addresses of your system.
Further, if you want to be IPv4/v6 agnostic, you could use getnameinfo with the NI_NUMERIC flag to convert both addresses to numeric string representations and strcmp them.