Skip to content

Ejercicio 1: Instalación y configuración DHCP

ENTREGA

Parte 1

Configuración de isc-dhcp-server

sudo apt update && sudo apt install isc-dhcp-server

En /etc/default/isc-dhcp-server:

  • Descomentar la línea: DHCPDv4_CONF=/etc/dhcp/dhcpd.conf
  • Especificar por qué interfaz escuchará y servirá IPs: INTERFACESv4="eth1"

En /etc/dhcp/dhcpd.conf: 

subnet 192.168.0.0 netmask 255.255.255.0 {
  range 192.168.0.100 192.168.0.110;
  option subnet-mask 255.255.255.0;
  option routers 192.168.0.1;
  option domain-name-servers 8.8.8.8, 8.8.4.4;
  max-lease-time 3600;
}

Reiniciar el servicio: 

sudo systemctl restart isc-dhcp-server

Parte 2

Mostrar lista de concesiones DHCP

sudo dhcp-lease-list --lease

To get manufacturer names please download http://standards.ieee.org/regauth/oui/oui.txt to /usr/local/etc/oui.txt
Use of uninitialized value $db_cand in -r at /usr/sbin/dhcp-lease-list line 77.
Reading leases from /var/lib/dhcp/dhcpd.leases
MAC                IP              hostname       valid until         manufacturer        
===============================================================================================
52:54:00:ac:7b:64  192.168.0.101   cliente        2021-10-18 18:21:40 -NA-

Parte 3

Configurar el cliente por DHCP

En /etc/network/interfaces configurar eth1 de la siguiente manera: 

auto eth1
iface eth1 inet dhcp

Pedimos configuración DHCP por eth1: 

sudo dhclient eth1

Parte 4

Hacer un ip a en cliente

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:b9:cb:6d brd ff:ff:ff:ff:ff:ff
    altname enp0s5
    altname ens5
    inet 192.168.121.68/24 brd 192.168.121.255 scope global dynamic eth0
       valid_lft 3534sec preferred_lft 3534sec
    inet6 fe80::5054:ff:feb9:cb6d/64 scope link
       valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:ac:7b:64 brd ff:ff:ff:ff:ff:ff
    altname enp0s6
    altname ens6
    inet 192.168.0.101/24 brd 192.168.0.255 scope global dynamic eth1
       valid_lft 3147sec preferred_lft 3147sec
    inet6 fe80::5054:ff:feac:7b64/64 scope link
       valid_lft forever preferred_lft forever

Parte 5

Servidor DHCP tiene que actuar como router NAT 

echo "1" > /proc/sys/net/ipv4/ip_forward
sudo modprobe iptable_nat
sudo iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE

Comprobación de resolución DNS en el cliente.

Mediante ping: 

vagrant@cliente:~$ ping www.example.org
PING www.example.org (93.184.216.34) 56(84) bytes of data.
64 bytes from 93.184.216.34 (93.184.216.34): icmp_seq=1 ttl=52 time=120 ms
64 bytes from 93.184.216.34 (93.184.216.34): icmp_seq=2 ttl=52 time=121 ms
^C
--- www.example.org ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 120.205/120.573/120.941/0.368 ms

Mediante dig: 

dig www.example.org

; <<>> DiG 9.16.15-Debian <<>> www.example.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6677
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.example.org.       IN  A

;; ANSWER SECTION:
www.example.org.    16060   IN  A   93.184.216.34

;; Query time: 24 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Mon Oct 18 19:07:53 UTC 2021
;; MSG SIZE  rcvd: 60
Cuando dig se usa sin especificar un DNS, hace la query con nuestro primer nameserver por defecto.
Utiliza 8.8.8.8, por lo que es una manera de comprobar si nuestra configuración DNS dada por el DHCP es correcta.

Escenario

  • Servidor DHCP
  • Cliente

Vagrantfile: 

Vagrant.configure("2") do |config|

config.vm.synced_folder ".", "/vagrant", disabled: true

  config.vm.define :servidor do |servidor|
    servidor.vm.box = "debian/bullseye64"
    servidor.vm.hostname = "servidor"
    servidor.vm.network :private_network,
      :libvirt__network_name => "ej1-dhcp",
      :libvirt__dhcp_enabled => false,
      :ip => "192.168.0.1",
      :libvirt__forward_mode => "veryisolated"
  end

  config.vm.define :cliente do |cliente|
    cliente.vm.box = "debian/bullseye64"
    cliente.vm.hostname = "cliente"
    cliente.vm.network :private_network,
      :libvirt__network_name => "ej1-dhcp",
      :libvirt__dhcp_enabled => false,
      :libvirt__forward_mode => "veryisolated"
  end

end

Realización

Comprobar la configuración de red del cliente

3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:ac:7b:64 brd ff:ff:ff:ff:ff:ff
    altname enp0s6
    altname ens6
    inet 192.168.0.101/24 brd 192.168.0.255 scope global dynamic eth1
       valid_lft 2910sec preferred_lft 2910sec
    inet6 fe80::5054:ff:feac:7b64/64 scope link
       valid_lft forever preferred_lft forever

Vemos que son correctos los parámetros:

  • Rango de IP
  • Máscara
  • Tiempo de concesión (ha pasado un rato desde que pedí configuración hasta que hice el copypaste, por eso el lifetime ha bajado)
vagrant@cliente:~$ ip r
default via 192.168.0.1 dev eth1
192.168.0.0/24 dev eth1 proto kernel scope link src 192.168.0.101
192.168.121.0/24 dev eth0 proto kernel scope link src 192.168.121.68

Vemos que ha surtido efecto el parámetro option routers

vagrant@cliente:~$ cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4

Vemos que ha surtido efecto el parámetro option domain-name-servers