Automate your legacy network with ansible

You manage a lot of network devices, but you are alone or you don’t have time. Ansible can help you to manage your change on your whole network very quickly based on your own template. In this article we will use Cisco Nexus 9K.

You have a new DNS server, syslog server etc and you need to modify hundred switches. No worries, with ansible it can be very simple.

First you should create at least two files. The first one will be your inventory and contains your switches. The second will be your playbook.

The first thing is to create a service account for ansible in your switches. This account could be centralize or local. In the following I’ll provide my password in cleartext. Of course, it’s not recommended and you should prefer ssh-key.

On my virtual nexus 9k, I only configured my account and my management IP address.

My topology contains :

  • Nexus-1 : IP 10.0.100.99, name: AGG1
  • Nexus-2 : IP 10.0.100.100, name: ACC1
  • Nexus-3 : IP 10.0.100.101, name: ACC2
switch(config-if)# sh run 

!Command: show running-config
!Running configuration last done at: Sat Mar 21 18:28:03 2020
!Time: Sat Mar 21 18:29:45 2020

version 9.3(2) Bios:version  
[..]
username ansible password 5 $5$.FhD0kmO$4PJV/HKJN5ul9aK7160ii.1WQ3s9pjh2QCRL7x7l
EU/  role network-admin
username ansible passphrase  lifetime 99999 warntime 14 gracetime 3
ip domain-lookup

[..]
interface mgmt0
  vrf member management
  ip address 10.0.100.100/24
line console
line vty

The inventory file will be the following. We can use two formats: YAML or INI. This one will use the INI format. This file contains a group named N9K with three switches.

[N9K]
AGR1 ansible_host=10.0.100.99  ansible_port=22
ACC1  ansible_host=10.0.100.100 ansible_port=22
ACC2  ansible_host=10.0.100.101 ansible_port=22

[N9K:vars]
ansible_user=ansible
ansible_password=@ns1b!E.
ansible_connection=network_cli
ansible_network_os=nxos
ansible_python_interpreter="/usr/bin/env python"

The following file uses the YAML format. This first playbook is very simple and contains one task to configure the switch hostname.

---
- name: Setup Nexus Devices

  hosts: all
  connection: local
  gather_facts: False


  tasks:

    - name: configure hostname
      nxos_config:
        lines: hostname {{ inventory_hostname }}
        save_when: modified

Now I’ll verify my playbook, before apply the changes. This command uses the option -i to specify which file should be use as inventory and –check to simulate the changes.

root@09cf326cc275:/ansible/NXOS# ansible-playbook -i inventory-home playbook-home.yaml --check

PLAY [Setup Nexus Devices] ***********************************************************************************************************************

TASK [configure hostname] ************************************************************************************************************************
[WARNING]: Skipping command `copy running-config startup-config` due to check_mode.  Configuration not copied to non-volatile storage
terpreter_discovery.html for more information.
changed: [ACC1]
changed: [AGR1]
changed: [ACC2]

PLAY RECAP ***************************************************************************************************************************************
ACC1                       : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
ACC2                       : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
AGR1                       : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 

Now I’ll do the same without the option –check and my Nexus device should be configured. You can see the message copy running is not there.

root@09cf326cc275:/ansible/NXOS# ansible-playbook -i inventory-home playbook-home.yaml        

PLAY [Setup Nexus Devices] ***********************************************************************************************************************

TASK [configure hostname] ************************************************************************************************************************

changed: [ACC1]
changed: [AGR1]
changed: [ACC2]

PLAY RECAP ***************************************************************************************************************************************
ACC1                       : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
ACC2                       : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
AGR1                       : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

Fantastic, my nexus have been configured !! With the command show accounting log, you can verify the command injected by ansible. In my playbook, I added the line save_when: modified to save the configuration after the changes.

AGR1# show accounting log | last 10
Sat Mar 21 18:45:42 2020:type=stop:id=10.0.100.150@pts/2:user=ansible:cmd=shell terminated because the ssh session closed
Sat Mar 21 18:49:11 2020:type=start:id=10.0.100.150@pts/2:user=ansible:cmd=
Sat Mar 21 18:49:12 2020:type=update:id=10.0.100.150@pts/2:user=ansible:cmd=terminal length 0 (SUCCESS)
Sat Mar 21 18:49:12 2020:type=update:id=10.0.100.150@pts/2:user=ansible:cmd=terminal width 511 (SUCCESS)
Sat Mar 21 18:49:20 2020:type=update:id=10.0.100.150@pts/2:user=ansible:cmd=configure terminal ; hostname AGR1 (SUCCESS)
Sat Mar 21 18:49:26 2020:type=update:id=10.0.100.150@pts/2:user=ansible:cmd=Performing configuration copy.
Sat Mar 21 18:49:36 2020:type=start:id=vsh.bin.13650:user=admin:cmd=
Sat Mar 21 18:49:52 2020:type=update:id=10.0.100.150@pts/2:user=ansible:cmd=copy running-config startup-config (SUCCESS)
Sat Mar 21 18:49:53 2020:type=stop:id=10.0.100.150@pts/2:user=ansible:cmd=shell terminated because the ssh session closed
Sat Mar 21 18:52:35 2020:type=update:id=console0:user=admin:cmd=terminal width 511 (SUCCESS)

Now you can imagine the next step. You can add your syslog server for example.

    - name: configure syslog server
      nxos_config:
        lines:
          - logging server 10.0.100.42 4 use-vrf management facility local7
          - logging timestamp milliseconds
        save_when: modified

Before the change:

AGR1(config)# logging timestamp milliseconds ^C
AGR1(config)# sh logging 

Logging console:                enabled (Severity: critical)
Logging monitor:                enabled (Severity: notifications)
Logging linecard:               enabled (Severity: notifications)
Logging timestamp:              Seconds
Logging source-interface :      disabled
Logging rate-limit:             enabled
Logging server:                 disabled
Logging origin_id :             disabled
Logging RFC :                   disabled
Logging logflash:               enabled (Severity: notifications)
Logging logfile:                enabled
        Name - messages: Severity - notifications Size - 4194304

[..]

After the change:

AGR1(config)# 2020 Mar 21 18:58:48 AGR1 %$ VDC-1 %$  %SYSLOG-2-SYSTEM_MSG: Attempt to configure logging server with: hostname/IP 10.0.100.42,severity 4,port 514,facility local7 - syslogd
AGR1(config)# sh logging 

Logging console:                enabled (Severity: critical)
Logging monitor:                enabled (Severity: notifications)
Logging linecard:               enabled (Severity: notifications)
Logging timestamp:              Milliseconds
Logging source-interface :      disabled
Logging rate-limit:             enabled
Logging server:                 enabled
{10.0.100.42}
        This server is temporarily unreachable
        server severity:        warnings
        server facility:        local7
        server VRF:             management
        server port:            514
Logging origin_id :             disabled
Logging RFC :                   disabled
Logging logflash:               enabled (Severity: notifications)
Logging logfile:                enabled
        Name - messages: Severity - notifications Size - 4194304
[..]
root@09cf326cc275:/ansible/NXOS# ansible-playbook -i inventory-home playbook-home.yaml

PLAY [Setup Nexus Devices] ***********************************************************************************************************************

TASK [configure hostname] ************************************************************************************************************************

ok: [ACC1]
ok: [AGR1]
ok: [ACC2]

TASK [configure syslog server] *******************************************************************************************************************
changed: [ACC1]
changed: [ACC2]
changed: [AGR1]

PLAY RECAP ***************************************************************************************************************************************
ACC1                       : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
ACC2                       : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
AGR1                       : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

I can be useful to manage your access-list. Imagine you install a new server for the monitoring and you need to update one entry. This time we will use another module named nxos_acl.

    - name: configure SNMP-ACCESS-LIST
      nxos_acl:
        name: ACL_SNMP-ReadOnly
        seq: "10"
        action: permit
        proto: udp
        src: 10.0.100.42/32
        dest: any
        state: present

Now we have the ACL configured on all switches. When the module exists, prefer to use the specific module.

root@09cf326cc275:/ansible/NXOS# ansible-playbook -i inventory-home playbook-home.yaml

PLAY [Setup Nexus Devices] ***********************************************************************************************************************

TASK [configure hostname] ************************************************************************************************************************

ok: [ACC1]
ok: [AGR1]
ok: [ACC2]

TASK [configure syslog server] *******************************************************************************************************************
changed: [ACC1]
changed: [ACC2]
changed: [AGR1]

TASK [configure SNMP-ACCESS-LIST] ****************************************************************************************************************
changed: [ACC1]
changed: [ACC2]
changed: [AGR1]

PLAY RECAP ***************************************************************************************************************************************
ACC1                       : ok=3    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
ACC2                       : ok=3    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
AGR1                       : ok=3    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 
AGR1(config)# sh ip access-lists ACL_SNMP-ReadOnly

IP access list ACL_SNMP-ReadOnly
        10 permit udp 10.0.100.42/32 any
--
ACC1(config)# sh ip access-lists ACL_SNMP-ReadOnly

IP access list ACL_SNMP-ReadOnly
	10 permit udp 10.0.100.42/32 any
--
ACC2# sh ip access-lists ACL_SNMP-ReadOnly

IP access list ACL_SNMP-ReadOnly
        10 permit udp 10.0.100.42/32 any 

This module is idempotent. Now we will update the ACL with a second entry. The documentation is here.

    - name: configure SNMP-ACCESS-LIST
      nxos_acl:
        name: ACL_SNMP-ReadOnly
        seq: "10"
        action: permit
        proto: udp
        src: 10.0.100.42/32
        dest: any
        state: present

    - name: configure SNMP-ACCESS-LIST
      nxos_acl:
        name: ACL_SNMP-ReadOnly
        seq: "20"
        action: permit
        proto: udp
        src: 10.0.100.43/32
        dest: any
        state: present
root@09cf326cc275:/ansible/NXOS# ansible-playbook -i inventory-home playbook-home.yaml

PLAY [Setup Nexus Devices] ***********************************************************************************************************************

TASK [configure hostname] ************************************************************************************************************************
changed: [ACC1]
changed: [AGR1]
changed: [ACC2]

TASK [configure syslog server] *******************************************************************************************************************
changed: [ACC1]
changed: [ACC2]
changed: [AGR1]

TASK [configure SNMP-ACCESS-LIST] ****************************************************************************************************************
ok: [ACC1]
ok: [AGR1]
ok: [ACC2]

TASK [configure SNMP-ACCESS-LIST] ****************************************************************************************************************
changed: [ACC1]
changed: [AGR1]
changed: [ACC2]

PLAY RECAP ***************************************************************************************************************************************
ACC1                       : ok=4    changed=3    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
ACC2                       : ok=4    changed=3    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
AGR1                       : ok=4    changed=3    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
AGR1(config)# sh ip access-lists ACL_SNMP-ReadOnly

IP access list ACL_SNMP-ReadOnly
        10 permit udp 10.0.100.42/32 any 
        20 permit udp 10.0.100.43/32 any

and they update the last entry with a new IP address.

    - name: configure SNMP-ACCESS-LIST
      nxos_acl:
        name: ACL_SNMP-ReadOnly
        seq: "10"
        action: permit
        proto: udp
        src: 10.0.100.42/32
        dest: any
        state: present

    - name: configure SNMP-ACCESS-LIST
      nxos_acl:
        name: ACL_SNMP-ReadOnly
        seq: "20"
        action: permit
        proto: udp
        src: 10.0.100.44/32
        dest: any
        state: present
root@09cf326cc275:/ansible/NXOS# ansible-playbook -i inventory-home playbook-home.yaml

PLAY [Setup Nexus Devices] ***********************************************************************************************************************

TASK [configure hostname] ************************************************************************************************************************
changed: [ACC1]
changed: [ACC2]
changed: [AGR1]

TASK [configure syslog server] *******************************************************************************************************************
changed: [ACC1]
changed: [AGR1]
changed: [ACC2]

TASK [configure SNMP-ACCESS-LIST] ****************************************************************************************************************
ok: [ACC1]
ok: [AGR1]
ok: [ACC2]

TASK [configure SNMP-ACCESS-LIST] ****************************************************************************************************************
changed: [ACC1]
changed: [AGR1]
changed: [ACC2]

PLAY RECAP ***************************************************************************************************************************************
ACC1                       : ok=4    changed=3    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
ACC2                       : ok=4    changed=3    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
AGR1                       : ok=4    changed=3    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 
AGR1(config)# sh ip access-lists ACL_SNMP-ReadOnly

IP access list ACL_SNMP-ReadOnly
        10 permit udp 10.0.100.42/32 any 
        20 permit udp 10.0.100.44/32 any

You can image a lot of scenario now, and apply your change very quickly.

Ansible basic commands

Check hosts in the inventory :

ansible@Deb-Master:~/base$ ansible all --list-hosts
   hosts (1):
     client1

Get list of modules

ansible@Deb-Master:~/base$ /usr/local/bin/ansible-doc -l | egrep ^(aci|mso)
 [WARNING]: win_template parsing did not produce documentation.
 [WARNING]: template parsing did not produce documentation.
 aci_l3out                                                     Manage Layer 3 Outside (L3Out) objects (l3ext:Out)
 aci_interface_policy_cdp                                      Manage CDP interface policies (cdp:IfPol)
 aci_maintenance_group_node                                    Manage maintenance group nodes
 mso_site                                                      Manage sites
 aci_intf_policy_fc                                            Manage Fibre Channel interface policies (fc:IfPol)
 aci_filter_entry                                              Manage filter entries (vz:Entry)
 mso_schema_site_vrf                                           Manage site-local VRFs in schema template
 mso_schema_site_anp_epg_staticleaf                            Manage site-local EPG static leafs in schema template
 aci_intf_policy_port_channel                                  Manage port channel interface policies (lacp:LagPol)
 mso_schema_template_filter_entry                              Manage filter entries in schema templates
 aci_aaa_user_certificate                                      Manage AAA user certificates (aaa:UserCert)
 aci_switch_policy_leaf_profile                                Manage switch policy leaf profiles (infra:NodeP)
 aci_interface_policy_lldp                                     Manage LLDP interface policies (lldp:IfPol)
 mso_schema_template_externalepg                               Manage external EPGs in schema templates
 aci_tenant_span_src_group                                     Manage SPAN source groups (span:SrcGrp)
 aci_access_port_block_to_access_port                          Manage port blocks of Fabric interface policy leaf profile interface selectors (infra:HPortS, infra:PortBlk)
 aci_epg_to_contract                                           Bind EPGs to Contracts (fv:RsCons, fv:RsProv)
 aci_access_port_to_interface_policy_leaf_profile              Manage Fabric interface policy leaf profile interface selectors (infra:HPortS, infra:RsAccBaseGrp, infra:PortBlk)
 aci_firmware_source                                           Manage firmware image sources (firmware:OSource)
 aci_tenant_action_rule_profile                                Manage action rule profiles (rtctrl:AttrP)
[..]

The documentation for a specific module

ansible@Deb-Master:~/base$ /usr/local/bin/ansible-doc  aci_tenant
   ACI_TENANT (/usr/local/lib/python2.7/dist-packages/ansible/modules/network/aci/aci_tenant.py) 
    Manage tenants on Cisco ACI fabrics. 
 This module is maintained by an Ansible Partner
 OPTIONS (= is mandatory):
 certificate_name
     The X.509 certificate name attached to the APIC AAA user used for signature-based authentication.
     If a private_key' filename was provided, this defaults to the private_key' basename, without extension.
     If PEM-formatted content was provided for private_key', this defaults to the username' value.
     (Aliases: cert_name)[Default: (null)]
     type: str
 description
     Description for the tenant.
     (Aliases: descr)[Default: (null)]
     type: str 
 = host
         IP Address or hostname of APIC resolvable by Ansible control host.
         (Aliases: hostname)
         type: str
 output_level
     Influence the output of this ACI module.
      normal' means the standard output, incl. current' dict
      info' adds informational output, incl. previous', proposed' and sent' dicts
     debug' adds debugging output, incl. filter_string', method',response', status' and url' information
     (Choices: debug, info, normal)[Default: normal]
     type: str 
[..]