Interface Configuration and Management¶
ifupdown is the network interface manager for Cumulus Linux. Cumulus
Linux uses an updated version of this tool, ifupdown2.
For more information on network interfaces, see Switch Port Attributes.
Tip
By default, ifupdown is quiet; use the verbose option -v when
you want to know what is going on when bringing an interface down or up.
Basic Commands¶
To bring up an interface or apply changes to an existing interface, run:
cumulus@switch:~$ sudo ifup
To bring down a single interface, run:
cumulus@switch:~$ sudo ifdown
Tip
ifdown always deletes logical interfaces after bringing them down.
Use the --admin-state option if you only want to administratively
bring the interface up or down.
To see the link and administrative state, use the ip link show
command:
cumulus@switch:~$ ip link show dev swp1
3: swp1: mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 500
link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff
In this example, swp1 is administratively UP and the physical link is UP (LOWER_UP flag). More information on interface administrative state and physical state can be found in this knowledge base article.
To put an interface into an admin down state. The interface remains down
after any future reboots or applying configuration changes with
ifreload -a. For example:
cumulus@switch:~$ net add interface swp1 link down
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
These commands create the following configuration in the /etc/network/interfaces file:
auto swp1
iface swp1
link-down yes
ifupdown2 Interface Classes¶
ifupdown2 provides for the grouping of interfaces into separate
classes, where a class is a user-defined label that groups interfaces
sharing a common function (like uplink, downlink or compute). You
specify classes in the /etc/network/interfaces file.
The most common class is auto, which you configure like this:
auto swp1
iface swp1
You can add other classes using the allow prefix. For example, if you have multiple interfaces used for uplinks, you can make up a class called uplinks:
auto swp1
allow-uplink swp1
iface swp1 inet static
address 10.1.1.1/31
auto swp2
allow-uplink swp2
iface swp2 inet static
address 10.1.1.3/31
This allows you to perform operations on only these interfaces using the
--allow=uplinks option, or still use the -a options since these
interfaces are also in the auto class:
cumulus@switch:~$ sudo ifup --allow=uplinks
cumulus@switch:~$ sudo ifreload -a
If you are using management VRF, you can use the special interface class called mgmt, and put the management interface into that class.
The mgmt interface class is not supported if you are configuring Cumulus Linux using Network Command Line Utility - NCLU.
allow-mgmt eth0
iface eth0 inet dhcp
vrf mgmt
allow-mgmt mgmt
iface mgmt
address 127.0.0.1/8
vrf-table auto
All ifupdown2 commands (ifup, ifdown, ifquery, ifreload) can
take a class. Include the --allow=<class> option when you run the command.
For example, to reload the configuration for the management interface described
above, run:
cumulus@switch:~$ sudo ifreload --allow=mgmt
You can easily bring up or down all interfaces marked with the common auto
class in /etc/network/interfaces. Use the -a option. For further details,
see individual man pages for ifup(8), ifdown(8), ifreload(8).
To administratively bring up all interfaces marked auto, run:
cumulus@switch:~$ sudo ifup -a
To administratively bring down all interfaces marked auto, run:
cumulus@switch:~$ sudo ifdown -a
To reload all network interfaces marked auto, use the ifreload
command, which is equivalent to running ifdown then ifup, the
one difference being that ifreload skips any configurations that
didn’t change):
cumulus@switch:~$ sudo ifreload -a
Tip
Some syntax checks are done by default, however it may be safer to apply the configs only if the syntax check passes, using the following compound command:
cumulus@switch:~$ sudo bash -c "ifreload -s -a && ifreload -a"
Configure a Loopback Interface¶
Cumulus Linux has a loopback preconfigured in /etc/network/interfaces. When
the switch boots up, it has a loopback interface, called lo, which is up and
assigned an IP address of 127.0.0.1.
Tip
The loopback interface lo must always be specified in
/etc/network/interfaces and must always be up.
ifupdown Behavior with Child Interfaces¶
By default, ifupdown recognizes and uses any interface present on the system
— whether a VLAN, bond or physical interface — that is listed as a dependent of
an interface. You are not required to list them in the interfaces file unless
they need a specific configuration, for
MTU, link speed, and so forth. And if you need to
delete a child interface, you should delete all references to that interface from
the interfaces file.
For this example, swp1 and swp2 below do not need an entry in the interfaces
file. The following stanzas defined in /etc/network/interfaces provide the
exact same configuration:
| With Child Interfaces Defined | Without Child Interfaces Defined |
|---|---|
auto swp1
iface swp1
auto swp2
iface swp2
auto bridge
iface bridge
bridge-vlan-aware yes
bridge-ports swp1 swp2
bridge-vids 1-100
bridge-pvid 1
bridge-stp on
|
auto bridge
iface bridge
bridge-vlan-aware yes
bridge-ports swp1 swp2
bridge-vids 1-100
bridge-pvid 1
bridge-stp on
|
Bridge in Traditional Mode - Example¶
For this example, swp1.100 and swp2.100 below do not need an entry in
the interfaces file. The following stanzas defined in
/etc/network/interfaces provide the exact same configuration:
For more information on the bridge in traditional mode vs the bridge in VLAN-aware mode, please read this knowledge base article.
ifupdown2 Interface Dependencies¶
ifupdown2 understands interface dependency relationships. When
ifup and ifdown are run with all interfaces, they always run
with all interfaces in dependency order. When run with the interface
list on the command line, the default behavior is to not run with
dependents. But if there are any built-in dependents, they will be
brought up or down.
To run with dependents when you specify the interface list, use the
--with-depends option. --with-depends walks through all
dependents in the dependency tree rooted at the interface you specify.
Consider the following example configuration:
auto bond1
iface bond1
address 100.0.0.2/16
bond-slaves swp29 swp30
auto bond2
iface bond2
address 100.0.0.5/16
bond-slaves swp31 swp32
auto br2001
iface br2001
address 12.0.1.3/24
bridge-ports bond1.2001 bond2.2001
bridge-stp on
Using ifup --with-depends br2001 brings up all dependents of br2001:
bond1.2001, bond2.2001, bond1, bond2, bond1.2001, bond2.2001, swp29,
swp30, swp31, swp32.
cumulus@switch:~$ sudo ifup --with-depends br2001
Similarly, specifying ifdown --with-depends br2001 brings down all
dependents of br2001: bond1.2001, bond2.2001, bond1, bond2, bond1.2001,
bond2.2001, swp29, swp30, swp31, swp32.
cumulus@switch:~$ sudo ifdown --with-depends br2001
Warning
As mentioned earlier, ifdown2 always deletes logical interfaces
after bringing them down. Use the --admin-state option if you only
want to administratively bring the interface up or down. In terms of the
above example, ifdown br2001 deletes br2001.
To guide you through which interfaces will be brought down and up, use
the --print-dependency option to get the list of dependents.
Use ifquery --print-dependency=list -a to get the dependency list of
all interfaces:
cumulus@switch:~$ sudo ifquery --print-dependency=list -a
lo : None
eth0 : None
bond0 : ['swp25', 'swp26']
bond1 : ['swp29', 'swp30']
bond2 : ['swp31', 'swp32']
br0 : ['bond1', 'bond2']
bond1.2000 : ['bond1']
bond2.2000 : ['bond2']
br2000 : ['bond1.2000', 'bond2.2000']
bond1.2001 : ['bond1']
bond2.2001 : ['bond2']
br2001 : ['bond1.2001', 'bond2.2001']
swp40 : None
swp25 : None
swp26 : None
swp29 : None
swp30 : None
swp31 : None
swp32 : None
To print the dependency list of a single interface, use:
cumulus@switch:~$ sudo ifquery --print-dependency=list br2001
br2001 : ['bond1.2001', 'bond2.2001']
bond1.2001 : ['bond1']
bond2.2001 : ['bond2']
bond1 : ['swp29', 'swp30']
bond2 : ['swp31', 'swp32']
swp29 : None
swp30 : None
swp31 : None
swp32 : None
To print the dependency information of an interface in dot format:
cumulus@switch:~$ sudo ifquery --print-dependency=dot br2001
/* Generated by GvGen v.0.9 (http://software.inl.fr/trac/wiki/GvGen) */
digraph G {
compound=true;
node1 [label="br2001"];
node2 [label="bond1.2001"];
node3 [label="bond2.2001"];
node4 [label="bond1"];
node5 [label="bond2"];
node6 [label="swp29"];
node7 [label="swp30"];
node8 [label="swp31"];
node9 [label="swp32"];
node1->node2;
node1->node3;
node2->node4;
node3->node5;
node4->node6;
node4->node7;
node5->node8;
node5->node9;
}
You can use dot to render the graph on an external system where
dot is installed.
To print the dependency information of the entire interfaces file:
cumulus@switch:~$ sudo ifquery --print-dependency=dot -a >interfaces_all.dot
Subinterfaces¶
On Linux an interface is a network device, and can be either a
physical device like switch port (such as swp1), or virtual, like a VLAN
(vlan100). A VLAN subinterface is a VLAN device on an interface, and
the VLAN ID is appended to the parent interface using dot (.) VLAN
notation. For example, a VLAN with ID 100 that is a subinterface of swp1
is named swp1.100 in Cumulus Linux. The dot VLAN notation for a VLAN
device name is a standard way to specify a VLAN device on Linux. Many
Linux configuration tools, most notably ifupdown2 and its
predecessor ifupdown, recognize such a name as a VLAN interface
name.
A VLAN subinterface only receives traffic tagged for that VLAN, so swp1.100 only receives packets tagged with VLAN 100 on switch port swp1. Similarly, any transmits from swp1.100 result in tagging the packet with VLAN 100.
For an MLAG deployment, the peerlink interface that connects the two switches in the MLAG pair has a VLAN subinterface named 4094 by default, provided you configured the subinterface with Network Command Line Utility - NCLU. The peerlink.4094 subinterface only receives traffic tagged for VLAN 4094.
ifup and Upper (Parent) Interfaces¶
When you run ifup on a logical interface (like a bridge, bond or
VLAN interface), if the ifup resulted in the creation of the logical
interface, by default it implicitly tries to execute on the interface’s
upper (or parent) interfaces as well. This helps in most cases,
especially when a bond is brought down and up, as in the example below.
This section describes the behavior of bringing up the upper interfaces.
Consider this example configuration:
auto br100
iface br100
bridge-ports bond1.100 bond2.100
auto bond1
iface bond1
bond-slaves swp1 swp2
If you run ifdown bond1, ifdown deletes bond1 and the VLAN
interface on bond1 (bond1.100); it also removes bond1 from the bridge
br100. Next, when you run ifup bond1, it creates bond1 and the VLAN
interface on bond1 (bond1.100); it also executes ifup br100 to add
the bond VLAN interface (bond1.100) to the bridge br100.
As you can see above, implicitly bringing up the upper interface helps, but there can be cases where an upper interface (like br100) is not in the right state, which can result in warnings. The warnings are mostly harmless.
If you want to disable these warnings, you can disable the implicit
upper interface handling by setting skip_upperifaces=1 in
/etc/network/ifupdown2/ifupdown2.conf.
With skip_upperifaces=1, you will have to explicitly execute
ifup on the upper interfaces. In this case, you will have to run
ifup br100 after an ifup bond1 to add bond1 back to bridge
br100.
Note
Although specifying a subinterface like swp1.100 and then running
ifup swp1.100 will also result in the automatic creation of the swp1
interface in the kernel, Cumulus Networks recommends you specify the
parent interface swp1 as well. A parent interface is one where any
physical layer configuration can reside, such as link-speed 1000 or
link-duplex full.
It’s important to note that if you only create swp1.100 and not swp1,
then you cannot run ifup swp1 since you did not specify it.
Configure IP Addresses¶
IP addresses are configured with the net add interface command.
Example IP Address Configuration¶
The following commands configure three IP addresses for swp1: two IPv4 addresses, and one IPv6 address.
cumulus@switch:~$ net add interface swp1 ip address 12.0.0.1/30
cumulus@switch:~$ net add interface swp1 ip address 12.0.0.2/30
cumulus@switch:~$ net add interface swp1 ipv6 address 2001:DB8::1/126
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
These commands create the following code snippet:
auto swp1
iface swp1
address 12.0.0.1/30
address 12.0.0.2/30
address 2001:DB8::1/126
Note
You can specify both IPv4 and IPv6 addresses for the same interface.
For IPv6 addresses, you can create or modify the IP address for an interface using either “::” or “0:0:0” notation. Both of the following examples are valid:
cumulus@switch:~$ net add bgp neighbor 2620:149:43:c109:0:0:0:5 remote-as internal
cumulus@switch:~$
cumulus@switch:~$ net add interface swp1 ipv6 address 2001:DB8::1/126
Note
The address method and address family are added by NCLU when needed, specifically when you are creating DHCP or loopback interfaces.
auto lo
iface lo inet loopback
To show the assigned address on an interface, use ip addr show:
cumulus@switch:~$ ip addr show dev swp1
3: swp1: mtu 1500 qdisc pfifo_fast state UP qlen 500
link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff
inet 192.0.2.1/30 scope global swp1
inet 192.0.2.2/30 scope global swp1
inet6 2001:DB8::1/126 scope global tentative
valid_lft forever preferred_lft forever
Specify IP Address Scope¶
ifupdown2 does not honor the configured IP address scope setting in
/etc/network/interfaces, treating all addresses as global. It does
not report an error. Consider this example configuration:
auto swp2
iface swp2
address 35.21.30.5/30
address 3101:21:20::31/80
scope link
When you run ifreload -a on this configuration, ifupdown2
considers all IP addresses as global.
cumulus@switch:~$ ip addr show swp2
5: swp2: mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 74:e6:e2:f5:62:82 brd ff:ff:ff:ff:ff:ff
inet 35.21.30.5/30 scope global swp2
valid_lft forever preferred_lft forever
inet6 3101:21:20::31/80 scope global
valid_lft forever preferred_lft forever
inet6 fe80::76e6:e2ff:fef5:6282/64 scope link
valid_lft forever preferred_lft forever
To work around this issue, configure the IP address scope:
cumulus@switch:~$ net add interface swp6 post-up ip address add 71.21.21.20/32 dev swp6 scope site
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
These commands create the following code snippet in the /etc/network/interfaces file:
auto swp6
iface swp6
post-up ip address add 71.21.21.20/32 dev swp6 scope site
Now it has the correct scope:
cumulus@switch:~$ ip addr show swp6
9: swp6: mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 74:e6:e2:f5:62:86 brd ff:ff:ff:ff:ff:ff
inet 71.21.21.20/32 scope site swp6
valid_lft forever preferred_lft forever
inet6 fe80::76e6:e2ff:fef5:6286/64 scope link
valid_lft forever preferred_lft forever
Purge Existing IP Addresses on an Interface¶
By default, ifupdown2 purges existing IP addresses on an interface.
If you have other processes that manage IP addresses for an interface,
you can disable this feature including the address-purge setting in
the interface’s configuration.
cumulus@switch:~$ net add interface swp1 address-purge no
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
These commands create the following configuration snippet in the
/etc/network/interfaces file:
CDATA[auto swp1
iface swp1
address-purge no
Note
Purging existing addresses on interfaces with multiple iface stanzas
is not supported. Doing so can result in the configuration of multiple
addresses for an interface after you change an interface address and
reload the configuration with ifreload -a. If this happens, you must
shut down and restart the interface with ifup and ifdown, or
manually delete superfluous addresses with
ip address delete specify.ip.address.here/mask dev DEVICE. See also
the Caveats and Errata section below for some cautions about using
multiple iface stanzas for the same interface.
Specify User Commands¶
You can specify additional user commands in the interfaces file. As
shown in the example below, the interface stanzas in
/etc/network/interfaces can have a command that runs at pre-up, up,
post-up, pre-down, down, and post-down:
cumulus@switch:~$ net add interface swp1 post-up /sbin/foo bar
cumulus@switch:~$ net add interface ip address 12.0.0.1/30
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
These commands create the following configuration in the
/etc/network/interfaces file:
auto swp1
iface swp1
address 12.0.0.1/30
post-up /sbin/foo bar
Any valid command can be hooked in the sequencing of bringing an interface up or down, although commands should be limited in scope to network-related commands associated with the particular interface.
For example, it wouldn’t make sense to install some Debian package on
ifup of swp1, even though that is technically possible. See
man interfaces for more details.
Warning
If your post-up command also starts, restarts or reloads any
systemd service, you must use the --no-block option with
systemctl. Otherwise, that service or even the switch itself may
hang after starting or restarting.
For example, to restart the dhcrelay service after bringing up VLAN
100, first run:
cumulus@switch:~$ net add vlan 100 post-up systemctl --no-block restart dhcrelay.service
cumulus@switch:~$ net commit
These commands create the following configuration in the
/etc/network/interfaces file:
auto bridge
iface bridge
bridge-vids 100
bridge-vlan-aware yes
auto vlan100
iface vlan100
post-up systemctl --no-block restart dhcrelay.service
vlan-id 100
vlan-raw-device bridge
Source Interface File Snippets¶
Sourcing interface files helps organize and manage the interfaces
file. For example:
cumulus@switch:~$ cat /etc/network/interfaces
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
iface eth0 inet dhcp
source /etc/network/interfaces.d/bond0
The contents of the sourced file used above are:
cumulus@switch:~$ cat /etc/network/interfaces.d/bond0
auto bond0
iface bond0
address 14.0.0.9/30
address 2001:ded:beef:2::1/64
bond-slaves swp25 swp26
Use Globs for Port Lists¶
NCLU supports globs to define port lists (that is, a range of ports).
The glob keyword is implied when you specify bridge ports and bond
slaves:
cumulus@switch:~$ net add bridge bridge ports swp1-4,6,10-12
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
Tip
While you must use commas to separate different ranges of ports in the NCLU command, the /etc/network/interfaces file renders the list of ports individually, as in the example output below.
These commands produce the following snippet in the
/etc/network/interfaces file:
...
auto bridge
iface bridge
bridge-ports swp1 swp2 swp3 swp4 swp6 swp10 swp11 swp12
bridge-vlan-aware yes
auto swp1
iface swp1
auto swp2
iface swp2
auto swp3
iface swp3
auto swp4
iface swp4
auto swp6
iface swp6
auto swp10
iface swp10
auto swp11
iface swp11
auto swp12
iface swp12
Use Templates¶
ifupdown2 Mako-style templates. The Mako
template engine is run over the interfaces file before parsing.
Use the template to declare cookie-cutter bridges in the interfaces file:
%for v in [11,12]:
auto vlan${v}
iface vlan${v}
address 10.20.${v}.3/24
bridge-ports glob swp19-20.${v}
bridge-stp on
%endfor
And use it to declare addresses in the interfaces file:
%for i in [1,12]:
auto swp${i}
iface swp${i}
address 10.20.${i}.3/24
Note
Regarding Mako syntax, use square brackets ([1,12]) to specify a
list of individual numbers (in this case, 1 and 12). Use range(1,12)
to specify a range of interfaces.
Tip
You can test your template and confirm it evaluates correctly by running
mako-render /etc/network/interfaces.
Tip
For more examples of configuring Mako templates, read this `knowledge base article https://support.cumulusnetworks.com/hc/en-us/articles/202868023>`_.
To comment out content in Mako templates, use double hash marks (##). For example:
## % for i in range(1, 4):
## auto swp${i}
## iface swp${i}
## % endfor
##
Run ifupdown Scripts under /etc/network/ with ifupdown2¶
Unlike the traditional ifupdown system, ifupdown2 does not run
scripts installed in /etc/network/*/ automatically to configure
network interfaces.
To enable or disable ifupdown2 scripting, edit the
addon_scripts_support line in the
/etc/network/ifupdown2/ifupdown2.conf file. 1 enables scripting
and 2 disables scripting. The following example enables scripting.
cumulus@switch:~$ sudo nano /etc/network/ifupdown2/ifupdown2.conf
# Support executing of ifupdown style scripts.
# Note that by default python addon modules override scripts with the same name
addon_scripts_support=1
ifupdown2 sets the following environment variables when executing
commands:
$IFACErepresents the physical name of the interface being processed; for example,br0orvxlan42. The name is obtained from the/etc/network/interfacesfile.$LOGICALrepresents the logical name (configuration name) of the interface being processed.$METHODrepresents the address method; for example, loopback, DHCP, DHCP6, manual, static, and so on.$ADDRFAMrepresents the address families associated with the interface, formatted in a comma-separated list; for example,"inet,inet6".
Add Descriptions to Interfaces¶
You can add descriptions to the interfaces configured in
/etc/network/interfaces by using the alias keyword.
The following commands create an alias for swp1:
cumulus@switch:~$ net add interface swp1 alias hypervisor_port_1
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit
These commands create the following code snippet:
auto swp1
iface swp1
alias hypervisor_port_1
You can query the interface description using NCLU:
cumulus@switch$ net show interface swp1
Name MAC Speed MTU Mode
-- ---- ----------------- ------- ----- ---------
UP swp1 44:38:39:00:00:04 1G 1500 Access/L2
Alias
-----
hypervisor_port_1
Interface descriptions also appear in the SNMP OID IF-MIB::ifAlias.
Note
Aliases are limited to 256 characters.
To show the interface description (alias) for all interfaces on the
switch, run the net show interface alias command. For example:
cumulus@switch:~$ net show interface alias
State Name Mode Alias
----- ------------- ------------- ------------------
UP bond01 LACP
UP bond02 LACP
UP bridge Bridge/L2
UP eth0 Mgmt
UP lo Loopback loopback interface
UP mgmt Interface/L3
UP peerlink LACP
UP peerlink.4094 SubInt/L3
UP swp1 BondMember hypervisor_port_1
UP swp2 BondMember to Server02
...
To show the interface description for all interfaces on the switch in
JSON format, run the net show interface alias json command.
Caveats and Errata¶
While ifupdown2 supports the inclusion of multiple iface stanzas
for the same interface, Cumulus Networks recommends you use a single
iface stanza for each interface, if possible.
There are cases where you must specify more than one iface stanza
for the same interface. For example, the configuration for a single
interface can come from many places, like a template or a sourced file.
If you do specify multiple iface stanzas for the same interface,
make sure the stanzas do not specify the same interface attributes.
Otherwise, unexpected behavior can result.
For example, swp1 is configured in two places:
cumulus@switch:~$ cat /etc/network/interfaces
source /etc/network/interfaces.d/speed_settings
auto swp1
iface swp1
address 10.0.14.2/24
As well as /etc/network/interfaces.d/speed_settings
cumulus@switch:~$ cat /etc/network/interfaces.d/speed_settings
auto swp1
iface swp1
link-speed 1000
link-duplex full
ifupdown2 correctly parses a configuration like this because the
same attributes are not specified in multiple iface stanzas.
And, as stated in the note above, you cannot purge existing addresses on
interfaces with multiple iface stanzas.
ifupdown2 and sysctl¶
For sysctl commands in the pre-up, up, post-up,
pre-down, down, and post-down lines that use the $IFACE
variable, if the interface name contains a dot (.), ifupdown2 does
not change the name to work with sysctl. For example, the interface name
bridge.1 is not converted to bridge/1.
Long Interface Names¶
The Linux kernel limits interface names to 15 characters in length and
cannot have a number as the first character. Longer interface names can
result in errors. To work around this issue, remove the interface from
the /etc/network/interfaces file, then restart the
networking.service.
cumulus@switch:~$ sudo vi /etc/network/interfaces
cumulus@switch:~$ sudo systemctl restart networking.service