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Cumulus Linux

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If you are using the current version of Cumulus Linux, the content on this page may not be up to date. The current version of the documentation is available here. If you are redirected to the main page of the user guide, then this page may have been renamed; please search for it there.

Configure SNMP

The most basic SNMP configuration requires you to:

  • Enable and start the snmpd service.
  • Specify one or more IP addresses on which the SNMP agent listens.
  • Specify either a username (for SNMPv3) or a read-only community string (a password, for SNMPv1 or SNMPv2c).

By default, the SNMP configuration has a listening address of localhost (127.0.0.1), which allows the agent (the snmpd service) to respond to SNMP requests originating on the switch itself. This is a secure method that allows checking the SNMP configuration without exposing the switch to outside attacks. For an external SNMP NMS to poll a Cumulus Linux switch, you must configure the snmpd service running on the switch to listen to one or more IP addresses on interfaces that have a link state UP.

Use the SNMPv3 username instead of the read-only community name. The SNMPv3 username does not expose the user credentials and can encrypt packet contents. However, SNMPv1 and SNMPv2c environments require read-only community passwords so that the snmpd daemon can respond to requests. The read-only community string enables you to poll various MIB objects on the device.

Basic Configuration

Before you can use SNMP, you need to enable and start the snmpd service, and configure a listening address.

cumulus@switch:~$ nv set service snmp-server enable on
cumulus@switch:~$ nv set service snmp-server listening-address localhost
cumulus@switch:~$ nv config apply

If you intend to run this service within a VRF, including the management VRF, follow these steps for configuring the service.

  1. Start the snmpd service:

    cumulus@switch:~$ sudo systemctl start snmpd.service

  2. Enable the snmpd service to start automatically after reboot:

    cumulus@switch:~$ sudo systemctl enable snmpd.service

    To enable the snmpd service to restart automatically after failure, create a file called /etc/systemd/system/snmpd.service.d/restart.conf and add the following lines:

    [Service]
Restart=always
RestartSec=60

  3. Edit the /etc/snmp/snmpd.conf file and add the IP address, protocol and port for snmpd to listen for incoming requests. You can use multiple lines to define multiple listening addresses or use a comma-separated list on a single line.

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
agentAddress 192.168.200.11@mgmt
agentAddress udp:66.66.66.66:161,udp:77.77.77.77:161,udp6:[2001::1]:161
...
  1. Run the sudo systemctl daemon-reload command.

Listening IP Addresses

The listening address is localhost by default so that the SNMP agent only responds to requests originating on the switch itself in the default VRF. To configure the switch to respond to requests sent to localhost in a mgmt VRF shell, see SNMP and VRFs. You can also configure listening only on the IPv6 localhost address. When using IPv6 addresses or localhost, you can use a readonly-community-v6 for SNMPv1 and SNMPv2c requests. For SNMPv3 requests, you can use the username command to restrict access. See Configure the SNMPv3 Username below.

The IP address must exist on an interface that has link UP on the switch where you use snmpd. By default, the IP address is udp:127.0.0.1:161, so snmpd only responds to requests (such as snmpwalk, snmpget, snmpgetnext) that originate from the switch. A wildcard setting of udp:161,udp6:161 forces snmpd to listen on all IPv4 and IPv6 interfaces for incoming SNMP requests.

You can configure multiple IP addresses and bind to a particular IP address within a particular VRF table.

To configure the listening IP addresses:

cumulus@switch:~$ nv set service snmp-server listening-address localhost
cumulus@switch:~$ nv set service snmp-server listening-address localhost-v6
cumulus@switch:~$ nv config apply

To configure the snmpd daemon to listen on all interfaces for either IPv4 or IPv6 UDP port 161 SNMP requests, run the following command, which removes all other individual IP addresses configured:

cumulus@switch:~$ nv set service snmp-server listening-address all
cumulus@switch:~$ nv set service snmp-server listening-address all-v6
cumulus@switch:~$ nv config apply

To configure snmpd to listen to a specific IPv4 or IPv6 address:

cumulus@switch:~$ nv set service snmp-server listening-address 192.168.200.11
cumulus@switch:~$ nv config apply

To configure snmpd to listen to multiple addresses for incoming SNMP queries, separate the addresses with a space:

cumulus@switch:~$ nv set service snmp-server listening-address 192.168.200.11 192.168.200.21
cumulus@switch:~$ nv config apply

Edit the /etc/snmp/snmpd.conf file and add the IP address, protocol and port for snmpd to listen for incoming requests. You can use multiple lines to define multiple listening addresses or use a comma-separated list on a single line.

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
agentAddress 192.168.200.11@mgmt
agentAddress udp:66.66.66.66:161,udp:77.77.77.77:161,udp6:[2001::1]:161
...

SNMP and VRFs

Cumulus Linux provides a listening address for VRFs together with trap and inform support. You can configure snmpd to listen to a specific IPv4 or IPv6 address on an interface within a particular VRF. With VRFs, identical IP addresses can exist in different VRF tables. This command restricts listening to a particular IP address within a particular VRF. If you do not provide a VRF name, Cumulus Linux uses the default VRF.

The following command configures snmpd to listen to IP address 10.10.10.10 on eth0, the management interface in the management VRF:

cumulus@switch:~$ nv set service snmp-server listening-address 10.10.10.10 vrf mgmt
cumulus@switch:~$ nv config apply

By default, snmpd does not cross VRF table boundaries. To listen on IP addresses in different VRF tables, use multiple listening-address commands each with a VRF name:

cumulus@switch:~$ nv set service snmp-server listening-address 10.10.10.10 vrf rocket
cumulus@switch:~$ nv set service snmp-server listening-address 10.10.10.20 vrf turtle
cumulus@switch:~$ nv config apply

By default, snmpd only responds to localhost requests in the default VRF. You can configure the switch to respond to requests sent to localhost in a mgmt VRF shell. To configure the snmpd daemon to listen on localhost in the mgmt VRF, run:

cumulus@switch:~$ nv set service snmp-server listening-address localhost vrf mgmt
cumulus@switch:~$ nv config apply

To bind to a particular IP address within a particular VRF table, edit the /etc/snmp/snmpd.conf file and append @ and the name of the VRF table to the IP address (for example, 192.168.200.11@mgmt).

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
agentAddress 192.168.200.11@mgmt
agentAddress udp:66.66.66.66:161,udp:77.77.77.77:161,udp6:[2001::1]:161
...

By default, snmpd only responds to localhost requests in the default VRF. You can configure the switch to respond to requests sent to localhost in a mgmt VRF shell. Edit the /etc/snmp/snmpd.conf file and add @mgmt to the agentaddress configuration:

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
agentaddress 127.0.0.1@mgmt
...

Then restart snmpd with the sudo systemctl restart snmpd command.

Configure the SNMPv3 Username

NVIDIA recommends you use an SNMPv3 username and password instead of the read-only community; SNMPv3 does not expose the password in the GetRequest and GetResponse packets and can also encrypt packet contents. You can configure multiple usernames for different user roles with different levels of access to various MIBs.

The default snmpd.conf file contains the default user _snmptrapusernameX. You cannot use this username for authentication. SNMP traps require this username.

You can authenticate the user in the following ways:

  • With no authentication password (if you specify auth-none)
  • With an MD5 password
  • With an SHA password

The following example command requires no authentication password for the user testusernoauth:

cumulus@switch:~$ nv set service snmp-server username testusernoauth auth-none
cumulus@switch:~$ nv config apply

The following example command configures MD5 authentication for the user limiteduser1:

cumulus@switch:~$ nv set service snmp-server username testuserauth auth-md5 myauthmd5password
cumulus@switch:~$ nv config apply

The following example command configures SHA authentication for the user limiteduser1:

cumulus@switch:~$ nv set service snmp-server username limiteduser1 auth-sha SHApassword1
cumulus@switch:~$ nv config apply

If you specify MD5 or SHA authentication, you can also specify an AES or DES encryption password to encrypt the contents of the request and response packets.

cumulus@switch:~$ nv set service snmp-server username testuserauth auth-md5 myauthmd5password encrypt-aes myencryptsecret
cumulus@switch:~$ nv config apply

You can restrict a user to a particular OID tree. The OID can be either a string of decimal numbers separated by periods or a unique text string that identifies an SNMP MIB object. The MIBs that Cumulus Linux includes are in the /usr/share/snmp/mibs/ directory. If the MIB you want to use does not install by default, you can install it with the latest Debian snmp-mibs-downloader package.

cumulus@switch:~$ nv set service snmp-server username testuserauth auth-md5 myauthmd5password encrypt-aes myaessecret oid 1.3.6.1.2.1.1
cumulus@switch:~$ nv config apply

You can restrict a user to a predefined view:

cumulus@switch:~$ nv set service snmp-server username testuserauth auth-md5 myauthmd5password encrypt-aes myaessecret view rocket
cumulus@switch:~$ nv config apply

The example below defines five users, each with a different combination of authentication and encryption:

cumulus@switch:~$ nv set service snmp-server username user1 auth-none
cumulus@switch:~$ nv set service snmp-server username user2 auth-md5 user2password
cumulus@switch:~$ nv set service snmp-server username user3 auth-md5 user3password encrypt-des user3encryption
cumulus@switch:~$ nv set service snmp-server username user666 auth-sha user666password encrypt-aes user666encryption
cumulus@switch:~$ nv set service snmp-server username user999 auth-md5 user999password encrypt-des user999encryption
cumulus@switch:~$ nv set service snmp-server username user1 auth-none oid 1.3.6.1.2.1
cumulus@switch:~$ nv set service snmp-server username user3 auth-sha testshax encrypt-aes testaesx oid 1.3.6.1.2.1
cumulus@switch:~$ nv config apply

Three directives define an internal SNMPv3 username that you need for snmpd to retrieve information and send built-in traps or for traps you configure with the monitor command (see below):

  • createuser is the default SNMPv3 username.
  • iquerysecName is the default SNMPv3 username you use when making internal queries to retrieve monitored expressions, either to evaluate the monitored expression or build a notification payload. These internal queries always use SNMPv3, even if you query the agent using SNMPv1 or SNMPv2c. The iquerysecname directive only defines which user to use.
  • rouser is the username for these SNMPv3 queries.

Edit the /etc/snmp/snmpd.conf file and add the createuser, iquerysecName, rouser commands. The following example configuration configures snmptrapusernameX as the username using the createUser command.

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
createuser snmptrapusernameX
iquerysecname snmptrapusernameX
rouser snmptrapusernameX
...

The example below defines five users, each with a different combination of authentication and encryption:

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
# simple no auth user
#createuser user1

# user with MD5 authentication
#createuser user2 MD5 user2password

# user with MD5 for auth and DES for encryption
#createuser user3 MD5 user3password DES user3encryption

# user666 with SHA for authentication and AES for encryption
createuser user666 SHA user666password AES user666encryption

# user999 with MD5 for authentication and DES for encryption
createuser user999 MD5 user999password DES user999encryption

# restrict users to certain OIDs
# (Note: creating rouser or rwuser will give
# access regardless of the createUser command above. However,
# createUser without rouser or rwuser will not provide any access).
rouser user1 noauth 1.3.6.1.2.1
rouser user2 auth 1.3.6.1.2.1
rwuser user3 priv 1.3.6.1.2.1
rwuser user666
rwuser user999
...

The following example shows a more advanced but slightly more secure method of configuring SNMPv3 users without creating cleartext passwords:

  1. Install the net-snmp-config script that is in the libsnmp-dev package:

    cumulus@switch:~$ sudo -E apt-get update
cumulus@switch:~$ sudo -E apt-get install libsnmp-dev

  2. Stop the snmpd daemon:

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

  3. Use the net-snmp-config command to create two users, one with MD5 and DES, and the next with SHA and AES.

The minimum password length is eight characters and the arguments -a and -x have different meanings in net-snmp-config than snmpwalk.

cumulus@switch:~$ sudo net-snmp-config --create-snmpv3-user -a md5authpass -x desprivpass -A MD5 -X DES userMD5withDES
cumulus@switch:~$ sudo net-snmp-config --create-snmpv3-user -a shaauthpass -x aesprivpass -A SHA -X AES userSHAwithAES
cumulus@switch:~$ sudo systemctl start snmpd.service

This adds a createUser command in /var/lib/snmp/snmpd.conf. Do not edit this file by hand unless you are removing usernames. You can edit this file and restrict access to certain parts of the MIB by adding noauth, auth or priv to allow unauthenticated access, require authentication, or to enforce use of encryption.

The snmpd daemon reads the information from the /var/lib/snmp/snpmd.conf file and then removes the line (so that Cumulus Linux does not store the master password for that user) and replaces it with the key it derives (using the EngineID). The key is a localized key so that if someone steals the password, they cannot use it to access other agents. To remove the two users userMD5withDES and userSHAwithAES, stop the snmpd daemon and edit the /var/lib/snmp/snmpd.conf file. Remove the lines containing the username, then restart the snmpd daemon as in step 3 above.

Configure an SNMP View Definition

To restrict MIB tree exposure, you can define a view for an SNMPv3 username or community password, and a host from a restricted subnet. In doing so, any SNMP request with that username and password must have a source IP address within the configured subnet.

You can define a specific view multiple times and fine tune to provide or restrict access using the included or excluded command to specify branches of certain MIB trees.

By default, the snmpd.conf file contains many views within the systemonly view.

cumulus@switch:~$ nv set service snmp-server viewname cumulusOnly included .1.3.6.1.4.1.40310
cumulus@switch:~$ nv set service snmp-server viewname cumulusCounters included .1.3.6.1.4.1.40310.2
cumulus@switch:~$ nv set service snmp-server readonly-community simplepassword access any view cumulusOnly
cumulus@switch:~$ nv set service snmp-server username testusernoauth auth-none view cumulusOnly
cumulus@switch:~$ nv set service snmp-server username limiteduser1 auth-md5 md5password1 encrypt-aes myaessecret view cumulusCounters
cumulus@switch:~$ nv config apply

Edit the /etc/snmp/snmpd.conf file and add the view command.

rocommunity uses the systemonly view to create a password that can only access these branches of the OID tree.

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
view systemonly included .1.3.6.1.2.1.1
view systemonly included .1.3.6.1.2.1.2
view systemonly included .1.3.6.1.2.1.3
...

Configure the Community String

Cumulus Linux disables snmpd authentication for SNMPv1 and SNMPv2c by default. To enable authentication, provide a password (community string) for SNMPv1 or SNMPv2c environments so that the snmpd daemon can respond to requests. By default, this provides access to the full OID tree for such requests, regardless of their source. Cumulus Linux does not set a default password so snmpd does not respond to any requests that arrive unless you set the read-only community password.

For SNMPv1 and SNMPv2c, you can specify a read-only community string. For SNMPv3, you can specify a read-only or a read-write community string (as long as you are not using the preferred username method; see above).

You can specify a source IP address token to restrict access to only that a host or network.

You can also specify a view to restrict the subset of the OID tree.

The following example configuration:

  • Sets the read-only community string to simplepassword for SNMP requests.
  • Restricts requests to only those that come from hosts in the 192.168.200.10/24 subnet.
  • Restricts viewing to the mysystem view, which you define with the view command.
cumulus@switch:~$ nv set service snmp-server viewname mysystem included 1.3.6.1.2.1.1
cumulus@switch:~$ nv set service snmp-server readonly-community simplepassword access 192.168.200.10/24 view mysystem
cumulus@switch:~$ nv config apply

This example creates a read-only community password showitall that allows access to the entire OID tree for requests originating from any source IP address.

cumulus@switch:~$ nv set service snmp-server readonly-community showitall access any
cumulus@switch:~$ nv config apply

To enable the community string, provide a community string, then set:

  • rocommunity or rwcommunity: rocommunity is for a read-only community; rwcommunity is for read-write access. Specify one or the other.
  • public: The plain text password or community string.

NVIDIA strongly recommends you change this password to something else.

  • default allows connections from any system.
  • localhost allows requests only from the local host. A restricted source can either be a specific hostname (or address), or a subnet, represented as IP/MASK (like 10.10.10.0/255.255.255.0), or IP/BITS (like 10.10.10.0/24), or the IPv6 equivalents.
  • -V restricts viewing to a specific view. For example, systemonly is one SNMP view. This is a user-defined value.

Edit the /etc/snmp/snmpd.conf file and add the community string.

In the following example, the first line sets the read-only community string to turtle for SNMP requests sourced from the 192.168.200.10/24 subnet and restricts viewing to the systemonly view defined with the -V option. The second line creates a read-only community string that allows access to the entire OID tree from any source IP address.

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
rocommunity turtle 192.168.200.10/24 -V systemonly
rocommunity cumuluspassword
...

Restart snmpd for the changes to take effect:

cumulus@switch:~$ systemctl restart snmpd.service

Configure System Settings

You can configure system settings for the SNMPv2 MIB. The following example commands set:

  • The system physical location for the node in the SNMPv2-MIB system table (the syslocation).
  • The username and email address of the contact person for this managed node (the syscontact).
  • An administratively assigned name for the managed node (the sysname).

To set the system physical location for the node in the SNMPv2-MIB system table:

cumulus@switch:~$ nv set service snmp-server system-location my-private-bunker
cumulus@switch:~$ nv config apply

To set the username and email address of the contact person for this managed node:

cumulus@switch:~$ nv set service snmp-server system-contact myemail@example.com
cumulus@switch:~$ nv config apply

To set an administratively assigned name for the managed node, run the following command. Typically, this is the fully qualified domain name of the node.

cumulus@switch:~$ nv set service snmp-server system-name CumulusBox-1,543,567
cumulus@switch:~$ nv config apply

Edit the /etc/snmp/snmpd.conf file and add the following configuration:

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
...
syscontact myemail@example.com
syslocation My-private-bunker
sysname CumulusBox-1,543,567
...

Enable SNMP Support for FRR

SNMP supports routing MIBs in FRR. If you are running Linux commands to configure the switch, you need to configure AgentX (ASX) access in FRR.

The NVUE nv set service snmp-server enable on command automatically configures AgentX (ASX) access in FRR; you do not need to run any additional commands.

  1. Enable AgentX:

    cumulus@switch:~$ sudo vtysh
...
switch# configure terminal
switch(config)# agentx
switch(config)# end
switch# write memory
switch# exit

  2. If your SNMP view restricts MIB access, expose the following MIBs for the protocols you are using:

    • For the BGP4 MIB, allow access to 1.3.6.1.2.1.15
    • For the OSPF MIB, allow access to 1.3.6.1.2.1.14
    • For the OSPFV3 MIB, allow access to 1.3.6.1.2.1.191

To verify the configuration, you can run snmpwalk.

cumulus@switch:~$ sudo snmpwalk -v2c -cpublic localhost 1.3.6.1.2.1.14

Enable the .1.3.6.1.2.1 Range

The snmpd.conf file in Cumulus Linux does not include certain MIBs by default. This results in some default views on common network tools (like librenms) to return less than optimal data. To include more MIBs, enable the complete .1.3.6.1.2.1 range. The default SNMPv3 configuration includes:

  • ENTITY-MIB
  • ENTITY-SENSOR MIB
  • Parts of the BRIDGE-MIB and Q-BRIDGE-MIBs

This configuration grants access to a large number of MIBs, including all SNMPv2-MIB, which shows more data than you expect. In addition to being a security vulnerability, it consumes more CPU resources.

To enable the .1.3.6.1.2.1 range, make sure the view commands include the required MIB objects.

Set up the Custom MIBs on the NMS

You do not need to change the /etc/snmp/snmpd.conf file on the switch to support the custom MIBs. The file includes the following lines by default and provides support for both the Cumulus Counters and the Cumulus Resource Query MIBs.

cumulus@switch:~$ cat /etc/snmp/snmpd.conf
...
sysObjectID 1.3.6.1.4.1.40310
pass_persist .1.3.6.1.4.1.40310.1 /usr/share/snmp/resq_pp.py
pass_persist .1.3.6.1.4.1.40310.2 /usr/share/snmp/cl_drop_cntrs_pp.py
...

You need to copy several files to the NMS server for it to recognize the custom Cumulus MIB.

  • /usr/share/snmp/mibs/Cumulus-Snmp-MIB.txt
  • /usr/share/snmp/mibs/Cumulus-Counters-MIB.txt
  • /usr/share/snmp/mibs/Cumulus-Resource-Query-MIB.txt

Pass Persist Scripts

The pass persist scripts in Cumulus Linux use the pass_persist extension to Net-SNMP. The scripts are in /usr/share/snmp and include:

  • bgp4_pp.py
  • bridge_pp.py
  • cl_drop_cntrs_pp.py
  • cl_poe_pp.py
  • entity_pp.py
  • entity_sensor_pp.py
  • ieee8023_lag_pp.py
  • resq_pp.py
  • snmpifAlias_pp.py
  • sysDescr_pass.py

Cumulus Linux enables all the scripts by default except for bgp4_pp.py, which FRR uses.

Disable SNMP

To disable SNMP, run the nv unset service snmp-server enable command:

cumulus@switch:~$ nv unset service snmp-server enable
cumulus@switch:~$ nv config apply

When you disable SNMP, the FRR service restarts, which might impact traffic.

Example Configuration

The following example configuration:

  • Enables an SNMP agent to listen on all IPv4 addresses with a community string password.
  • Sets the trap destination host IP address.
  • Creates several types of SNMP traps.
cumulus@switch:~$ nv set service snmp-server listening-address all
cumulus@switch:~$ nv set service snmp-server readonly-community tempPassword access any
cumulus@switch:~$ nv set service snmp-server trap-destination 1.1.1.1 community-password mypassword version 2c
cumulus@switch:~$ nv set service snmp-server trap-link-up check-frequency 15
cumulus@switch:~$ nv set service snmp-server trap-link-down check-frequency 10
cumulus@switch:~$ nv set service snmp-server trap-snmp-auth-failures
cumulus@switch:~$ nv config apply

Edit the /etc/snmp/snmpd.conf file and apply the following configuration (add every line starting with a +):

cumulus@switch:~$ sudo nano /etc/snmp/snmpd.conf
+agentaddress udp:161
agentxperms 777 777 snmp snmp
agentxsocket /var/agentx/master
+authtrapenable 1
createuser _snmptrapusernameX
iquerysecname _snmptrapusernameX
+load 7.45 5.14 0
master agentx
monitor -r 60 -o laNames -o laErrMessage "laTable" laErrorFlag != 0
+monitor CumulusLinkDOWN -S -r 10 -o ifName -o ifIndex -o ifAdminStatus -o ifOperStatus ifOperStatus == 2
+monitor CumulusLinkUP -S -r 15 -o ifName -o ifIndex -o ifAdminStatus -o ifOperStatus ifOperStatus != 2
pass -p 10 1.3.6.1.2.1.1.1 /usr/share/snmp/sysDescr_pass.py
pass_persist 1.2.840.10006.300.43 /usr/share/snmp/ieee8023_lag_pp.py
pass_persist 1.3.6.1.2.1.17 /usr/share/snmp/bridge_pp.py
pass_persist 1.3.6.1.2.1.31.1.1.1.18 /usr/share/snmp/snmpifAlias_pp.py
pass_persist 1.3.6.1.2.1.47 /usr/share/snmp/entity_pp.py
pass_persist 1.3.6.1.2.1.99 /usr/share/snmp/entity_sensor_pp.py
pass_persist 1.3.6.1.4.1.40310.1 /usr/share/snmp/resq_pp.py
pass_persist 1.3.6.1.4.1.40310.2 /usr/share/snmp/cl_drop_cntrs_pp.py
pass_persist 1.3.6.1.4.1.40310.3 /usr/share/snmp/cl_poe_pp.py
+rocommunity neteng default
+rocommunity tempPassword default
rouser _snmptrapusernameX
+syslocation leaf01
sysobjectid 1.3.6.1.4.1.40310
sysservices 72
+trap2sink 1.1.1.1 mypassword

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