A network namespace is logically another copy of the network
stack, with its own routes, firewall rules, and network devices.
By default a process inherits its network namespace from its
parent. Initially all the processes share the same default
network namespace from the init process.
By convention a named network namespace is an object at
/var/run/netns/NAME that can be opened. The file descriptor
resulting from opening /var/run/netns/NAME refers to the
specified network namespace. Holding that file descriptor open
keeps the network namespace alive. The file descriptor can be
used with the setns(2) system call to change the network
namespace associated with a task.
For applications that are aware of network namespaces, the
convention is to look for global network configuration files
first in /etc/netns/NAME/ then in /etc/. For example, if you
want a different version of /etc/resolv.conf for a network
namespace used to isolate your vpn you would name it
/etc/netns/myvpn/resolv.conf.
ip netns exec automates handling of this configuration, file
convention for network namespace unaware applications, by
creating a mount namespace and bind mounting all of the per
network namespace configure files into their traditional location
in /etc.
ip netns list - show all of the named network namespaces
This command displays all of the network namespaces in
/var/run/netns
ip netns add NAME - create a new named network namespace
If NAME is available in /var/run/netns this command
creates a new network namespace and assigns NAME.
ip netns attach NAME PID - create a new named network namespace
If NAME is available in /var/run/netns this command
attaches the network namespace of the process PID to NAME
as if it were created with ip netns.
ip [-all] netns delete [ NAME ] - delete the name of a network
namespace(s)
If NAME is present in /var/run/netns it is umounted and
the mount point is removed. If this is the last user of
the network namespace the network namespace will be freed
and all physical devices will be moved to the default one,
otherwise the network namespace persists until it has no
more users. ip netns delete may fail if the mount point is
in use in another mount namespace.
If -all option was specified then all the network
namespace names will be removed.
It is possible to lose the physical device when it was
moved to netns and then this netns was deleted with a
running process:
$ ip netns add net0
$ ip link set dev eth0 netns net0
$ ip netns exec net0 SOME_PROCESS_IN_BACKGROUND
$ ip netns del net0
and eth0 will appear in the default netns only after
SOME_PROCESS_IN_BACKGROUND will exit or will be killed. To
prevent this the processes running in net0 should be
killed before deleting the netns:
$ ip netns pids net0 | xargs kill
$ ip netns del net0
ip netns set NAME NETNSID - assign an id to a peer network
namespace
This command assigns a id to a peer network namespace.
This id is valid only in the current network namespace.
If the keyword "auto" is specified an available nsid will
be chosen. This id will be used by the kernel in some
netlink messages. If no id is assigned when the kernel
needs it, it will be automatically assigned by the kernel.
Once it is assigned, it's not possible to change it.
ip netns identify [PID] - Report network namespaces names for
process
This command walks through /var/run/netns and finds all
the network namespace names for network namespace of the
specified process, if PID is not specified then the
current process will be used.
ip netns pids NAME - Report processes in the named network
namespace
This command walks through proc and finds all of the
process who have the named network namespace as their
primary network namespace.
ip [-all] netns exec [ NAME ] cmd ... - Run cmd in the named
network namespace
This command allows applications that are network
namespace unaware to be run in something other than the
default network namespace with all of the configuration
for the specified network namespace appearing in the
customary global locations. A network namespace and bind
mounts are used to move files from their network namespace
specific location to their default locations without
affecting other processes.
If -all option was specified then cmd will be executed
synchronously on the each named network namespace even if
cmd fails on some of them. Network namespace name is
printed on each cmd executing.
ip netns monitor - Report as network namespace names are added
and deleted
This command watches network namespace name addition and
deletion events and prints a line for each event it sees.
ip netns list-id [target-nsid POSITIVE-INT] [nsid POSITIVE-INT] -
list network namespace ids (nsid)
Network namespace ids are used to identify a peer network
namespace. This command displays nsids of the current
network namespace and provides the corresponding iproute2
netns name (from /var/run/netns) if any.
The target-nsid option enables to display nsids of the
specified network namespace instead of the current network
namespace. This target-nsid is a nsid from the current
network namespace.
The nsid option enables to display only this nsid. It is a
nsid from the current network namespace. In combination
with the target-nsid option, it enables to convert a
specific nsid from the current network namespace to a nsid
of the target-nsid network namespace.
