I'm using ip tuntap to create a tap interface, like this:
$ sudo ip tuntap add mode tap tap0
Afterwards, I set the interface up and address it with the common IP commands. I can see then my interface up and addressed with a simple ifconfig.
Now, I was told by a teacher that by creating a tap interface (named tap0 in that case), I would find a /dev/net/tap0 node, and that I would be able to write in it or to read it. However, I can't find it. I "just" have a /dev/net/tun.
Do I have to deal with this tun node, or am I supposed to really have a tap0 node?
It's been a long time since the question was asked, but I thought it would be a good idea to post an actual answer for future reference.
Tap interfaces, as well as tun interfaces, are virtual interfaces provided by the in-kernel TUN/TAP device driver. The only interface this driver provides initially is the character device /dev/net/tun mentioned in the question.
By issuing:
$ sudo ip tuntap add mode tap tap0
we instruct ip tuntap to create a network interface named tap0, which is accomplished using the proper ioctl(2) calls on the aforementioned device file /dev/net/tun, to communicate with the underlying TUN/TAP device driver, as we can observe in ip tuntap's source code.
One of these ioctl(2) calls (the one with TUNSETIFF option, which is called first) returns a file descriptor associated with the new virtual interface that was created and can be used by processes.
Summing it up:
Do I have to deal with this tun node, or am I supposed to really have a tap0 node?
The /dev/net/tun device file is only used as a starting point to create both tap and tun interfaces, by userspace utilities like iproute2. In the context of this question, there's no need to deal with it as ip tuntap does this job for us.
Any extra /dev/net/tap0 device files are not needed or expected to be created for the processes to use the tap interfaces.
you need to activate that link with command
ip link set dev tap0 up
after that you can use it.
Commented out all the items in /lib/systemd/network/99-default.link & rebooted.
All mac addresses (excepted phys adapter) are randomized again.
Related
ip link add link eth2 dev col0000000000a7 type macvlan mode bridge
I can't find this usage in the manual.
Is it a combination of two commands?
See this link for details
The ip command is used to assign an address to a network interface and/or configure network interface parameters on Linux operating systems. This command replaces old good and now deprecated ifconfig command on modern Linux distributions.
Looks like it is adding a bridging device to interface eth2.
Run $ ip a show eth2 would give you more info on that particular interface.
I have multiple devices with the same hardware mac address (in factory reset mode) that all call a tftp server in order to get a proper mac.
On the same nic, there would obviously be no way to differentiate the devices, however, i have one device per nic. I evaluated these options to use that fact:
SO_BINDTODEVICE
Binding the tftp server on each nic separately would probably still not give me a way to respond with a package to the sender, since linux' arp table would be confused about which nic to send that package out from.
net namespaces
Linux does not allow bringing physical interfaces into a net namespace. only veths, which again would need to be bridged on the 'host' side, which will probably not work with the same mac appearing on multiple physical nics.
Am i missing an option here?
I have this situation where I need to measure the bytes sent/received during its execution. The PC will have a normal ethernet interface (eth1) to interact with others in the network. I did a little research on linux network namespace and cgroups, given that, I came to this approach to do the measures.
create a new network namespace.
create a virtual ethernet pair of interfaces veth0 and veth1.
assign veth1 to the previously created namespace leaving veth0 on the default namespace.
configure the virtual interfaces and create a bridge between veth0 and eth1.
Given that, I will execute my process on the new namespace and assume the values from veth1 as the bytes sent/received for the process. I know that I can use iproute2 and bridge-utils for the above steps, but is it correct? or there is another way to do that kind of measure?
I want to build a MAC address spoofer that spits out a randomize mac address everytime my computer boots up. My question is how and from where do all my computer programs in linux pull up my MAC address. I know that my wi-fi network driver is responsible for telling my network card what to send, but from where does that driver get my MAC address? I also know that a MAC address is called a hardware address, however since it is possible to spoof MAC addresses, then it must only mean that the MAC address on my network card doesn't have to be used when sending information. I would like to know how this can be done as well.
Also when randomizing my MAC address this ought to work with all other programs such as my web-browser and whatever else that I use, which shouldn't be a problem since thats really an application layer ... not link layer
Thanks
The MAC address is usually stored in some kind of EEPROM on the network card. This address is read during initialization by the network adapter driver and used by the MAC layer when assembling/sending netowrk packets.
The MAC address used can be changed on the command line using "ifconfig" via the "hw" option:
hw class address
Set the hardware address of this interface, if the device driver
supports this operation. The keyword must be followed by the
name of the hardware class and the printable ASCII equivalent of
the hardware address. Hardware classes currently supported
include ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom
(AMPR NET/ROM).
ifconfig essentially uses the SIOCSIFHWADDR ioctl (see http://linux.die.net/man/7/netdevice) to set the MAC address.
In some cases it might even be possible to change the MAC address stored on the network adapter itself, see http://linux.die.net/man/8/ethtool - but I wouldn't recommend doing that.
The only thing that cares about your MAC address is the NIC itself. There should be no programs that use the MAC address (including browsers). Since MAC addresses are used on the physical layer -- that's the only thing that will read your MAC (such as routers, switches, etc).
To set the MAC address of your NIC you can use the ifconfig command: ifconfig eth0 hw ether ##:##:##:##:##:## (you might have to take your network down first, set it, and then bring it up. IE: ifconfig eth0 down; ifconfig eth0 hw ether ##:##:##:##:##:#; ifconfig eth0 up)
I want to determine if a network card is enabled, up, and plugged in. Basically, I want to know if the network card will work. I need this information from with a C++ program, and would like to display an error message when the network isn't working properly. If possible I would like to avoid using shell commands to determine this information.
You can look at /sys/class/net/eth0/operstate where eth0 is your interface to see if it's up.
Look at /sys/class/net/eth0/carrier to see if there is a carrier.
Though I guess executing ifconfig and friends will give you more compatibility to *BSDs.
open AF_NETLINK socket
bind it to sockaddr_nl with nl_groups = RTMGRP_LINK
send message RTM_GETLINK to kernel
make poll/epoll on socket to read RTM_NEWLINK and RTM_DELLINK messages
you will receive initial interfaces list and its changes in future
Remember, on Linux "everything" is a file.
The best way would be to use the approved kernel<->userspace communication, namely sysfs, mounted at /sys. Network devices are linked at /sys/class/net
If you wish to use the ioctl interface, look at man netdevice
How do you want to identify the network card? You might try taking a look at /etc/udev/rules.d/70-persistent-net.rules which maps hardware MAC addresses into nice names (like eth0).
Then, when you have the nicer name, you can run things like ethtool eth0 to determine if it is [physically] connected (last line), ifconfig eth0 to determine if it is up (look for "UP BROADCAST..."), and if it has an IP address.
I'm willing to guess there are automatic libraries for this though; have you looked around? I'm not sure if there's easily accessible code in NetworkManager, but that should be a good first place to look.
Run through the output of getifaddrs, you can use the link layer for the MAC address to identify an adapter and check the ifa_flags for IFF_UP. Use AF_NETLINK for notifications about interface changes.