Management VRF is a subset of Virtual Routing and Forwarding - 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 VRFs, the main routing table is the default table for the data plane switch ports. With management VRF, the switch uses a second table, mgmt, 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.
Cumulus Linux only supports eth0 (or eth1, depending on the switch platform) for out-of-band management. The Ethernet ports are software-only ports that are not hardware accelerated by
switchd. VLAN subinterfaces, bonds, bridges, and the front panel switch ports are not supported as OOB management interfaces.
In band management of Cumulus Linux is possible using loopbacks and SVIs (switch virtual interfaces).
Cumulus Linux enables Management VRF by default. 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 section contain a localhost loopback IPv4 address of 127.0.0.1/8 and IPv6 address of ::1/128. Management VRF must have an IPv6 address as well as an IPv4 address to work correctly. Adding the loopback address to the layer 3 domain of the management VRF prevents issues with applications that expect the loopback IP address to exist in the VRF, such as NTP.
Bring Up the Management VRF
If you take down the management VRF using
ifdown, to bring it back up you need to do one of two things:
- Run the
ifup --with-depends mgmtcommand
The following command example brings down the management VRF, then brings it back up with the
ifup --with-depends mgmt command:
cumulus@switch:~$ sudo ifdown mgmt cumulus@switch:~$ sudo ifup --with-depends mgmt
ifreload -a disconnects the session for any interface configured as auto.
Run Services within the Management VRF
At installation, the only two enabled services that run in the management VRF are NTP (
firstname.lastname@example.org) and netqd (
netqd@mgmt). However, you can run a variety of services within the management VRF instead of the default VRF. When you run a
systemd service inside the management VRF, that service runs only on eth0. You cannot configure the same service to run in both the management VRF and the default VRF; you must stop and disable the normal service with
You must disable the following services in the default VRF if you want to run them in the management VRF:
You can configure certain services (such as
snmpd) to use multiple routing tables, some in the management VRF, some in the default or additional VRFs. The kernel provides a
sysctl that allows a single instance to accept connections over all VRFs.
For TCP, connected sockets bind to the VRF on which the first packet arrives.
The following steps show how to enable the SNMP service to run in the management VRF. You can enable any of the services listed above, except for
dhcrelay (see DHCP Relays).
If SNMP is running, stop the service:
cumulus@switch:~$ sudo systemctl stop snmpd.service
Disable SNMP from starting automatically in the default VRF:
cumulus@switch:~$ sudo systemctl disable snmpd.service
Start SNMP in the management VRF:
cumulus@switch:~$ sudo systemctl start email@example.com
snmpd@mgmtso that it starts when the switch boots:
cumulus@switch:~$ sudo systemctl enable firstname.lastname@example.org
Verify that the SNMP service is running in the management VRF:
cumulus@switch:~$ ps aux | grep snmpd snmp 3083 0.1 1.9 35916 13292 ? Ss 21:07 0:00 /usr/sbin/snmpd -y -LS 0-4 d -Lf /dev/null -u snmp -g snmp -I -smux -p /run/snmpd.pid -f cumulus 3225 0.0 0.1 6076 884 pts/0 S+ 21:07 0:00 grep snmpd
Run the following command to show the process IDs associated with the management VRF:
cumulus@switch:~$ ip vrf pids mgmt 1149 ntpd 1159 login 1227 bash 16178 vi 948 dhclient 20934 sshd 20975 bash 21343 sshd 21384 bash 21477 ip
Run the following command to show the VRF association of the specified process:
cumulus@switch:~$ ip vrf identify 2055 mgmt
ip vrf help for additional
ip vrf commands.
Enable Polling with snmpd in a Management VRF
When you enable
snmpd to run in the management VRF, you need to specify that VRF so that
snmpd listens on eth0 in the management VRF; you can also configure
snmpd to listen on other ports. In Cumulus Linux, SNMP configuration is VRF aware so
snmpd can bind to multiple IP addresses each configured with a particular VRF (routing table). The
snmpd daemon responds to polling requests on the interfaces of the VRF on which the request comes in. For information about configuring SNMP version 1, 2c, and 3 Traps and (v3) Inform messages, refer to Simple Network Management Protocol - SNMP.
Duplicate IPv4 address detected, some interfaces may not be visible in IP-MIB displays after starting
snmpd in the management VRF. This is because the IP-MIB assumes that you cannot use the same IP address 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 does not impact the operation of the switch.
ping or traceroute on the Management VRF
By default, when you issue a
traceroute, the packet goes to the data plane network (the main routing table). To use
traceroute on the management network, use
ping -I mgmt or
traceroute -i mgmt. To select a source address within the management VRF, use the
-s flag for
cumulus@switch:~$ ping -I mgmt <destination-ip>
cumulus@switch:~$ sudo traceroute -i mgmt -s <source-ip> <destination-ip>
For additional information on using
traceroute, see Network Troubleshooting.
Run Services as a Non-root User
To run services in the management VRF as a non-root user, you need to create a custom service based on the original service file. The following example commands configure the SSH service to run in the management VRF as a non-root user.
Run the following command to create a custom service file in the
cumulus@switch:~$ sudo -E systemctl edit --full ssh.service
If a User directive exists under [Service], comment it out.
cumulus@switch:~$ sudo nano /etc/systemd/system/ssh.service ... [Service] #User=username ExecStart=/usr/local/bin/ssh agent -data-dir=/tmp/ssh -bind=192.168.0.11 ...
Modify the ExecStart line to
/usr/bin/ip vrf exec mgmt /sbin/runuser -u USER -- ssh:
... [Service] #User=username ExecStart=/usr/bin/ip vrf exec mgmt /sbin/runuser -u cumulus -- ssh ...
OSPF and BGP
FRR is VRF-aware and sends packets based on the switch port routing table. This includes BGP peering through loopback interfaces. BGP looks up routes in the default table. However, depending on how you redistribute your routes, you can perform the following modification.
Management VRF uses the mgmt table, including local routes. This does not affect route redistribution when you use 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 advertise to its neighbor.
This also creates a route on the neighbor device to the management network through the data plane.
NVIDIA recommends route maps to control advertised networks that you redistribute with the
redistribute connected command.
cumulus@switch:~$ nv set router policy route-map REDISTRIBUTE rule 10 match type ipv4 cumulus@switch:~$ nv set router policy route-map REDISTRIBUTE rule 10 match interface eth0 cumulus@switch:~$ nv set router policy route-map REDISTRIBUTE rule 10 action deny cumulus@switch:~$ nv set vrf default router bgp address-family ipv4-unicast redistribute connected route-map REDISTRIBUTE cumulus@switch:~$ nv config apply
cumulus@switch:$ sudo vtysh ... switch# configure terminal switch(config)# route-map REDISTRIBUTE-CONNECTED deny 10 switch(config-route-map)# match interface eth0 switch(config)# route-map REDISTRIBUTE-CONNECTED permit 100 switch(config-route-map)# exit switch(config)# router bgp switch(config-router)# address-family ipv4 unicast switch((config-router-af)# redistribute connected route-map REDISTRIBUTE-CONNECTED switch(config)# end switch# write memory switch# exit
The vtysh commands save the configuration in the
/etc/frr/frr.conf file. For example:
... router bgp 65101 bgp router-id 10.10.10.1 neighbor swp51 interface remote-as external neighbor swp52 interface remote-as external ! address-family ipv4 unicast network 10.1.10.0/24 network 10.10.10.1/32 redistribute connected route-map REDISTRIBUTE-CONNECTED maximum-paths 64 maximum-paths ibgp 64 exit-address-family ! route-map REDISTRIBUTE-CONNECTED deny 100 match interface eth0 ! route-map REDISTRIBUTE-CONNECTED permit 1000 ...
To limit SSH to listen on only the management VRF or to a specific IP address on the management VRF, see SSH and VRFs.
If you SSH to the switch through a switch port, SSH works as expected. If you need to SSH from the switch out of a switch port, use the
ip vrf exec default ssh <switch-port-ip-address>command. For example:
cumulus@switch:~$ sudo ip vrf exec default ssh 10.3.3.3
View the Routing Tables
When you use
ip route get to return information about a single route, the command resolves over the mgmt table by default. To show information about the route in the switching silicon, run this command:
cumulus@switch:~$ ip route get <ip-address>
To get the route for any VRF, run the
ip route get <ip-address> oif <vrf-name> command. For example, to show the route for the management VRF, run:
cumulus@switch:~$ ip route get <ip-address> oif mgmt
mgmt Interface Class
ifupdown2 uses interface classes 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.
You configure the management interface in the
/etc/network/interfaces file. The example below adds the management interface eth0 and the management VRF stanzas 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 address ::1/128 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
Management VRF and DNS
Cumulus Linux supports both DHCP and static DNS entries over management VRF through IP FIB rules, which it adds 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. You cannot specify the same DNS server address twice to associate it with different VRFs.
For example, to specify DNS servers and associate some of them with the management VRF, run the following commands:
cumulus@switch:~$ nv set service dns default server 192.0.2.1 cumulus@switch:~$ nv set service dns mgmt server 198.51.100.31 cumulus@switch:~$ nv set service dns mgmt server 203.0.113.13 cumulus@switch:~$ nv config apply
/etc/resolv.conf file to add the DNS servers and associate some of them with the management VRF. For example:
cumulus@switch:~$ sudo nano /etc/resolv.conf nameserver 192.0.2.1 nameserver 198.51.100.31 # vrf mgmt nameserver 203.0.113.13 # vrf mgmt
ifreload -a command to load the new configuration:
cumulus@switch:~$ ifreload -a
- Because FIB rules force DNS lookups out of the management interface, this can affect data plane ports if you use overlapping addresses. For example, when the switch learns the DNS server IP address over the management VRF, it creates a FIB rule for that IP address. When DHCP relay has the same IP address, the switch forwards any DHCP discover packet arriving on the front panel port out of the management interface (eth0) even though a route is present out the front-panel port.
- If you do not specify a DNS server and you lose in band connectivity, DNS does not work through the management VRF. Cumulus Linux does not assume all DNS servers are reachable through the management VRF.