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Management VRF

Management VRF is a subset of VRF (virtual routing tables and forwarding) and provides a separation between the out-of-band management network and the in-band data plane network. For all VRFs, the main routing table is the default table for all of the data plane switch ports. With management VRF, a second table, mgmt, is used for routing through the Ethernet ports of the switch. The mgmt name is special cased to identify the management VRF from a data plane VRF. FIB rules are installed for DNS servers because this is the typical deployment case.

Cumulus Linux only supports eth0 as the management interface, or eth1, depending on the switch platform. The Ethernet ports are software-only parts that are not hardware accelerated by switchd. VLAN subinterfaces, bonds, bridges, and the front panel switch ports are not supported as management interfaces.

When management VRF is enabled, logins to the switch are set into the management VRF context. IPv4 and IPv6 networking applications (for example, Ansible, Chef, and apt-get) run by an administrator communicate out the management network by default. This default context does not impact services run through systemd and the systemctl command, and does not impact commands examining the state of the switch, such as the ip command to list links, neighbors, or routes.

The management VRF configurations in this chapter contain a localhost loopback IP address (127.0.0.1/8). Adding the loopback address to the L3 domain of the management VRF prevents issues with applications that expect the loopback IP address to exist in the VRF, such as NTP.

Enabling Management VRF

To enable management VRF on eth0, complete the following steps:

Example Management VRF Configuration

The example NCLU commands below create a VRF called mgmt:

The management VRF must be named mgmt to differentiate from a data plane VRF.

cumulus@switch:~$ net add vrf mgmt
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

The NCLU commands above create the following snippets in the /etc/network/interfaces file:

...
 
auto eth0
iface eth0 inet dhcp
    vrf mgmt
 
...
 
auto mgmt
iface mgmt
    address 127.0.0.1/8
    vrf-table auto
 
...

When you commit the change to add the management VRF, all connections over eth0 are dropped. This can impact any automation that might be running, such as Ansible or Puppet scripts.

Bringing the Management VRF Up after Downing It with ifdown

If you take down the management VRF using ifdown, to bring it back up you need to do one of two things:

  • Use ifup --with-depends <vrf>
  • Use ifreload -a

For example:

cumulus@switch:~$ sudo ifdown mgmt
cumulus@switch:~$ sudo ifup --with-depends mgmt

Running ifreload -a disconnects the session for any interface configured as auto.

Running Services within the Management VRF

You can run a variety of services within the management VRF instead of the default VRF. In most cases, you must stop and disable the instance running in the default VRF before you can start the service in the management VRF. This is because the instance running in the default VRF owns the port across all VRFs. The list of services that must be disabled in the default VRF are:

  • chef-client
  • collectd
  • dhcpd
  • dhcrelay
  • hsflowd
  • netq-agent
  • ntp
  • puppet
  • snmpd
  • snmptrapd
  • ssh
  • zabbix-agent

When you run a service inside the management VRF, that service runs only on eth0; it no longer runs on any switch port. However, you can keep the service running in the default VRF with a wildcard for agentAddress. This enables the service to run on all interfaces no matter which VRF, so you don’t have to run a different process for each VRF.

Some applications can work across all VRFs. The kernel provides a sysctl that allows a single instance to accept connections over all VRFs. For TCP, connected sockets are bound to the VRF on which the first packet is received. This sysctl is enabled for Cumulus Linux.

To enable a service to run in the management VRF, do the following. These steps use the NTP service, but you can use any of the services listed above, except for dhcrelay (discussed here) and hsflowd (discussed below).

  1. Configure the management VRF as described in the Enabling Management VRF section above.

  2. If NTP is running, stop the service:

    cumulus@switch:~$ sudo systemctl stop ntp.service

  3. Disable NTP from starting automatically in the default VRF:

    cumulus@switch:~$ sudo systemctl disable ntp.service

  4. Start NTP in the management VRF.

    cumulus@switch:~$ sudo systemctl start ntp@mgmt.service

  5. Enable ntp@mgmt so that it starts when the switch boots:

    cumulus@switch:~$ sudo systemctl enable ntp@mgmt.service

After you enable ntp@mgmt, you can verify that NTP peers are active:

cumulus@switch:~$ ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*38.229.71.1     204.9.54.119     2 u   42   64  377   31.275   -0.625   3.105
-104.131.53.252  209.51.161.238   2 u   47   64  377   16.381   -5.251   0.681
+45.79.10.228    200.98.196.212   2 u   44   64  377   42.998    0.115   0.585
+74.207.240.206  127.67.113.92    2 u   43   64  377   73.240   -1.623   0.320

Enabling Polling with snmpd in a Management VRF

When you enable snmpd to run in the management VRF, you need to specify that VRF with NCLU so that snmpd listens on eth0 in the management VRF; you can also configure snmpd to listen on other ports with the NCLU listening-address vrf command. As of CL 3.6, SNMP configuration is VRF aware so snmpd can bind to multiple IP addresses each configured with a particular VRFs (routing table). The snmpd daemon responds to polling requests on the interfaces of the VRF on which the request came in. SNMP version 1, 2c and 3 Traps and (v3) Inform messages can be configured with NCLU. See the chapter on SNMP management with NCLU for detailed instructions on how to configure SNMP with VRFs.

The message Duplicate IPv4 address detected, some interfaces may not be visible in IP-MIB displays after starting snmpd in the mgmt VRF. This is because the IP-MIB assumes the same IP address cannot be used twice on the same device; the IP-MIB is not VRF aware. This message is a warning that the SNMP IP-MIB detects overlapping IP addresses on the system; it does not indicate a problem and is non-impacting to the operation of the switch.

Enabling hsflowd

If you are using sFlow to monitor traffic in the management VRF, you need to complete the following steps to enable sFlow.

  1. Add the hsflowd process to the systemd configuration file in /etc/vrf. Edit the /etc/vrf/systemd.conf file with a text editor.

    cumulus@switch:~$ sudo nano /etc/vrf/systemd.conf 
# Systemd-based services that are expected to be run in a VRF context.
#
# If changes are made to this file run systemctl daemon-reload
# to re-generate systemd files.
chef-client
collectd
dhcpd
dhcrelay
hsflowd  <<< Add this line
ntp
puppet
snmpd
snmptrapd
ssh
zabbix-agent

  2. Stop the hsflowd daemon if it is running:

    cumulus@switch:~$ sudo systemctl stop hsflowd.service

  3. Disable hsflowd to ensure it does not start in the default VRF if the system is rebooted:

    cumulus@switch:~$ sudo systemctl disable hsflowd.service

  4. Run the daemon-reload command:

    cumulus@switch:~$ sudo systemctl daemon-reload

  5. Start hsflowd in the the management VRF:

    cumulus@switch:~$ sudo systemctl start hsflowd@mgmt.service

  6. Enable hsflowd@mgmt so it starts when the switch boots:

    cumulus@switch:~$ sudo systemctl enable hsflowd@mgmt.service

  7. Verify that the hsflowd service is running in the management VRF:

    cumulus@switch:~$ ps aux | grep flow
root      7294  0.0  0.4  81320  2108 ?        Ssl  22:22   0:00 /usr/sbin/hsflowd
cumulus   7906  0.0  0.4  12728  2056 pts/0    S+   22:34   0:00 grep flow
cumulus@switch:~$ vrf task identify 7294
mgmt

Using ping or traceroute

By default, when you issue a ping or traceroute, the packet is sent to the dataplane network (the main routing table). To use ping or traceroute on the management network, use the -I flag for ping and -i for traceroute.

cumulus@switch:~$ ping -I mgmt

Or:

cumulus@switch:~$ sudo traceroute -i mgmt

Running Services as a Non-root User

Sometimes you may want to run services in the management VRF as a non-root user. To do so, you need to create a custom service based on the original service file.

  1. Copy the original service file to its new name and store the file in /etc/systemd/system.

    cumulus@switch:~$ sudo cp /lib/systemd/system/myservice.service /etc/systemd/system/myservice.service

  2. If there is a User directive, comment it out. If it exists, you can find it under [Service].

    cumulus@switch:~$ sudo nano /etc/systemd/system/myservice.service 
     
[Unit]
Description=Example
Documentation=https://www.example.io/
     
[Service]
#User=username
ExecStart=/usr/local/bin/myservice agent -data-dir=/tmp/myservice -bind=192.168.0.11
     
[Install]
WantedBy=multi-user.target

  3. Modify the ExecStart line to /usr/bin/vrf exec mgmt /sbin/runuser -u USER -- COMMAND. For example, to have the cumulus user run the foocommand:

    [Unit]
Description=Example
Documentation=https://www.example.io/
     
[Service]
#User=username
ExecStart=/usr/bin/vrf task exec mgmt /sbin/runuser -u cumulus -- foocommand
     
[Install]
WantedBy=multi-user.target

  4. Save and exit the file.

    ^O
^X
cumulus@switch:~$

  5. Reload the service so the changes take effect:

    cumulus@switch:~$ sudo systemctl daemon-reload

OSPF and BGP

In general, no changes are required for either BGP or OSPF. FRRouting is VRF-aware and automatically sends packets based on the switch port routing table. This includes BGP peering via loopback interfaces. BGP does routing lookups in the default table. However, depending on how your routes are redistributed, you might want to perform the following modification.

Redistributing Routes in Management VRF

Management VRF uses the mgmt table, including local routes. It does not affect how the routes are redistributed when using routing protocols such as OSPF and BGP.

To redistribute the routes in your network, use the redistribute connected command under BGP or OSPF. This enables the directly-connected network out of eth0 to be advertised to its neighbor.

This also creates a route on the neighbor device to the management network through the data plane, which might not be desired.

Cumulus Networks recommends you always use route maps to control the advertised networks redistributed by the redistribute connected command. For example, you can specify a route map to redistribute routes in this way (for both BGP and OSPF):

cumulus@leaf01:~$ net add routing route-map REDISTRIBUTE-CONNECTED deny 100 match interface eth0
cumulus@leaf01:~$ net add routing route-map REDISTRIBUTE-CONNECTED permit 1000

These commands produce the following configuration snippet in the /etc/frr/frr.conf file:

<routing protocol> 
redistribute connected route-map REDISTRIBUTE-CONNECTED
 
route-map REDISTRIBUTE-CONNECTED deny 100
 match interface eth0
!
route-map REDISTRIBUTE-CONNECTED permit 1000

Using SSH within a Management VRF Context

If you SSH to the switch through a switch port, SSH works as expected. If you need to SSH from the device out of a switch port, use vrf exec default ssh <ip_address_of_swp_port>. For example:

cumulus@switch:~$ sudo vrf exec default ssh 10.23.23.2 10.3.3.3

Viewing the Routing Tables

When you look at the routing table with ip route show, you are looking at the switch port (main) table. You can also see the dataplane routing table with net show route vrf main.

To look at information about eth0 (the management routing table), use net show route vrf mgmt.

cumulus@switch:~$ net show route vrf mgmt
default via 192.168.0.1 dev eth0
 
cumulus@switch:~$ net show route
default via 10.23.23.3 dev swp17  proto zebra  metric 20
10.3.3.3 via 10.23.23.3 dev swp17
10.23.23.0/24 dev swp17  proto kernel  scope link  src 10.23.23.2
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.11

Viewing a Single Route

If you use ip route get to return information about a single route, the command resolves over the mgmt table by default. To obtain information about the route in the switching silicon, use:

cumulus@switch:~$ net show route <addr>

To get the route for any VRF, run the following command:

cumulus@switch:~$ net show route vrf mgmt <addr>

Using the mgmt Interface Class

In ifupdown2, interface classes are used to create a user-defined grouping for interfaces. The special class mgmt is available to separate the management interfaces of the switch from the data interfaces. This allows you to manage the data interfaces by default using ifupdown2 commands. Performing operations on the mgmt interfaces requires specifying the --allow-mgmt option, which prevents inadvertent outages on the management interfaces. Cumulus Linux by default brings up all interfaces in both the auto (default) class and the mgmt interface class when the switch boots.

The management VRF interface class is not supported if you are configuring Cumulus Linux using NCLU.

You configure the management interface in the /etc/network/interfacesfile. In the example below, the management interface, eth0 and the management VRF stanzas are added to the mgmt interface class:

auto lo
iface lo inet loopback 
 
allow-mgmt eth0
iface eth0 inet dhcp
    vrf mgmt
  
allow-mgmt mgmt
iface mgmt
    address 127.0.0.1/8
    vrf-table auto

When you run ifupdown2 commands against the interfaces in the mgmt class, include --allow=mgmt with the commands. For example, to see which interfaces are in the mgmt interface class, run:

cumulus@switch:~$ ifquery l --allow=mgmt
eth0
mgmt

To reload the configurations for interfaces in the mgmt class, run:

cumulus@switch:~$ sudo ifreload --allow=mgmt

You can still bring the management interface up and down using ifup eth0 and ifdown eth0.

Management VRF and DNS

Cumulus Linux supports both DHCP and static DNS entries over management VRF through IP FIB rules. These rules are added to direct lookups to the DNS addresses out of the management VRF.

For DNS to use the management VRF, the static DNS entries must reference the management VRF in the /etc/resolv.conf file. For example:

nameserver 192.0.2.1
nameserver 198.51.100.31 # vrf mgmt
nameserver 203.0.113.13 # vrf mgmt

Nameservers configured through DHCP are updated automatically, Statically configured nameservers (configured in the /etc/resolv.conf file) only get updated when you run ifreload -a.

Because DNS lookups are forced out of the management interface using FIB rules, this might affect data plane ports if overlapping addresses are used. For example, when the DNS server IP address is learned over the management VRF, a FIB rule is created for that IP address. When DHCP relay is configured for the same IP address, a DHCP discover packet received on the front panel port is forwarded out of the management interface (eth0) even though a route is present out the front-panel port.

Incompatibility with cl-ns-mgmt

Management VRF has replaced the management namespace functionality in Cumulus Linux. The management namespace feature (used with the cl-ns-mgmt utility) has been deprecated, and the cl-ns-mgmt command has been removed.