improve documentation

tests/LINUX-MANAGEMENT.md

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+# Linux Management from the Centos Controller
+
+How to manage linux hosts with Ansible from the controller without the management network.
+
+On any or some distribution switch, enable IPv4 EIGRP dynamic routing for the management network:
+
+```bash
+conf t
+router eigrp 1
+  network 11.12.13.0
+```
+
+## Dynamic routing
+
+FRRouting should be installed on the centos controller.
+
+To load an EIGRP config:
+
+```bash
+vtysh -f /etc/frr/eigrpd.conf
+```
+
+To show learned routes:
+
+```bash
+vtysh -c "show ip route"
+```
+
+## Get linux hosts IP addresses from IOS DHCP servers
+
+```bash
+cat << EOF > dhcpleases.yaml
+- hosts: distribution
+  gather_facts: no
+  tasks:
+    - ios_command:
+        commands:
+          - show ip dhcp binding
+      register: output
+    - set_fact:
+        ip_list: "{{ output.stdout | regex_findall('[0-9]{1,3}\\\.[0-9]{1,3}\\\.[0-9]{1,3}\\\.[0-9]{1,3}') | list }}"
+    - debug:
+        msg: "{{ item }}"
+      loop: "{{ ip_list }}"
+      delegate_to: 127.0.0.1
+    - lineinfile:
+        line: "{{ item }},"
+        dest: ./linuxhosts
+        create: yes
+        state: present
+      loop: "{{ ip_list }}"
+      delegate_to: 127.0.0.1
+EOF
+
+ansible-playbook dhcpleases.yaml
+
+ansible -i "$(cat linuxhosts)" -u root -e ansible_password=testtest -m ping all
+```
+
+## Configure RHEL hosts with rhel-system-roles
+
+```bash
+yum -y install rhel-system-roles
+
+export ANSIBLE_ROLES_PATH=./roles:/usr/share/ansible/roles 
+
+export ANSIBLE_ROLES_PATH=./roles:/usr/share/ansible/roles >> $HOME/.bashrc
+
+cat << EOF > ./configure_rhel_ntp.yaml
+- hosts: all
+  vars:
+    timesync_ntp_servers:
+      - hostname: 192.168.1.1
+        pool: yes
+        iburst: yes
+    timesync_ntp_provider: ntp
+  roles:
+    - role: rhel-system-roles.timesync
+  tasks:
+    - package:
+        name:
+          - ntp-perl
+EOF
+
+ansible-playbook -i "$(cat linuxhosts)" -u root -e ansible_password=testtest configure_rhel_ntp.yaml
+```