DHCP

• DHCP Grundlagen

Einrichten eines DHCP-Servers auf Debian

Installation

• apt install isc-dhcp-server

Konfiguration der aktiven Netzwerkkarten

• Zusätzlich wird hier die zu benutzende Daemon-Konfiguration angegeben
• vim /etc/default/isc-dhcp-server

DHCPDv4_CONF=/etc/dhcp/dhcpd.conf
INTERFACESv4="interface_1 interface_2"

Konfiguration der zu vergebenden Netzwerkparameter

• vim /etc/dhcp/dhcpd.conf

option domain-name "lab100.it";
option domain-name-servers 10.0.100.254;
default-lease-time 600;
max-lease-time 7200;
authoritative;

# Subnet der ersten angegeben Netzwerkkarte
subnet 10.0.100.0 netmask 255.255.255.0 {
    range 10.0.100.50 10.0.100.100;
    option routers 10.0.100.1;
}

# Subnet der zweiten angegeben Netzwerkkarte
subnet 192.168.0.0 netmask 255.255.255.0 {
    range 192.168.0.50 192.168.0.100;
    option routers 192.168.0.1;
}

# Feste IP-Adresse für eine bestimmte MAC-Adresse
host controller {
    hardware ethernet fe:fe:fe:fe:fe:fe;
    fixed-address 192.168.0.2;
    option routers 192.168.0.1;
}

• Dienst mit der neuen Konfiguration starten und überprüfen
• systemctl restart isc-dhcp-server
• systemctl status isc-dhcp-server

Logs

• tail -f -n 100 /var/log/syslog | grep dhcp

Apr 20 09:20:42 fw dhcpd[3217]: DHCPREQUEST for 10.0.100.51 (10.0.100.1) from be:98:60:d1:af:88 via ens19: wrong network.
Apr 20 09:20:42 fw dhcpd[3217]: DHCPNAK on 10.0.100.51 to be:98:60:d1:af:88 via ens19
Apr 20 09:20:43 fw dhcpd[3217]: reuse_lease: lease age 1 (secs) under 25% threshold, reply with unaltered, existing lease for 10.0.10.50
Apr 20 09:20:43 fw dhcpd[3217]: DHCPDISCOVER from be:98:60:d1:af:88 (archiso) via ens19
Apr 20 09:20:43 fw dhcpd[3217]: DHCPOFFER on 10.0.10.50 to be:98:60:d1:af:88 (archiso) via ens19
Apr 20 09:20:43 fw dhcpd[3217]: reuse_lease: lease age 1 (secs) under 25% threshold, reply with unaltered, existing lease for 10.0.10.50
Apr 20 09:20:43 fw dhcpd[3217]: DHCPREQUEST for 10.0.10.50 (10.0.10.1) from be:98:60:d1:af:88 (archiso) via ens19
Apr 20 09:20:43 fw dhcpd[3217]: DHCPACK on 10.0.10.50 to be:98:60:d1:af:88 (archiso) via ens19
Apr 20 09:22:27 fw dhcpd[3217]: DHCPDISCOVER from fe:fe:fe:fe:fe:fe via ens20
Apr 20 09:22:27 fw dhcpd[3217]: DHCPOFFER on 192.168.0.2 to fe:fe:fe:fe:fe:fe via ens20
Apr 20 09:22:27 fw dhcpd[3217]: DHCPREQUEST for 192.168.0.2 (192.168.0.1) from fe:fe:fe:fe:fe:fe via ens20
Apr 20 09:22:27 fw dhcpd[3217]: DHCPACK on 192.168.0.2 to fe:fe:fe:fe:fe:fe via ens20
Apr 20 09:23:41 fw dhcpd[3217]: DHCPDISCOVER from 76:54:06:7a:bd:48 via ens20
Apr 20 09:23:42 fw dhcpd[3217]: DHCPOFFER on 192.168.0.50 to 76:54:06:7a:bd:48 (archiso) via ens20
Apr 20 09:23:42 fw dhcpd[3217]: uid lease 192.168.0.50 for client 76:54:06:7a:bd:48 is duplicate on 192.168.0.0/24
Apr 20 09:23:42 fw dhcpd[3217]: DHCPREQUEST for 192.168.0.53 (192.168.0.1) from 76:54:06:7a:bd:48 via ens20
Apr 20 09:23:42 fw dhcpd[3217]: DHCPACK on 192.168.0.53 to 76:54:06:7a:bd:48 (archiso) via ens20
Apr 20 09:25:07 fw dhcpd[3217]: DHCPRELEASE of 192.168.0.53 from 76:54:06:7a:bd:48 (archiso) via ens20 (found)
Apr 20 09:28:03 fw dhcpd[3217]: DHCPREQUEST for 192.168.0.51 from 5e:12:1a:8d:b8:b6 via ens20
Apr 20 09:28:03 fw dhcpd[3217]: DHCPACK on 192.168.0.51 to 5e:12:1a:8d:b8:b6 (debian) via ens20
Apr 20 09:32:14 fw dhcpd[3217]: DHCPREQUEST for 192.168.0.51 from 5e:12:1a:8d:b8:b6 (debian) via ens20
Apr 20 09:32:14 fw dhcpd[3217]: DHCPACK on 192.168.0.51 to 5e:12:1a:8d:b8:b6 (debian) via ens20

DHCP Anfragen über die Kommandozeile

• apt install isc-dhcp-common
• Bei den folgenden Befehlen kann man auch eine spezifische Netzwerkkarte angeben

neue IP-Adresse anfragen

• dhclient

Lease der IP-Adresse verlängern

• dhclient -r