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<pre>root@router0230:~# systemctl restart isc-dhcp-server.service</pre>
<pre>root@router0230:~# systemctl restart isc-dhcp-server.service</pre>


Damit Änderungen bei bereits aktivem Client wirksam werden, muss dieser sie neu anfordern.
Damit Änderungen bei bereits aktivem Client wirksam werden, muss dieser sie neu anfordern.

Version vom 26. September 2019, 15:04 Uhr

DHCP (Dynamic Host Configuration Protocol)

Allgemein

  • Erweiterung des Bootstrap-Protokolls (BOOTP)
  • Hintergrundprozess (Dienst/Daemon)
  • RFC 2131
  • Transport durch UDP
  • Standard-Ports:
    • IPv4: 67 (Server) 68 (Client)
    • IPv6: 547 (Server) 546 (Client)

Aufgabe

  • Clients automatisch in ein bestehendes Netz einbinden,
  • Übermittlung der Konfigurationsparameter...
    • IP-Adresse,
    • Netzmaske,
    • Gateway, die Brücke von einem ins andere Netz,
    • Rechnername,
    • Broadcast-Adresse,
    • Boot-Image für plattenlose Workstations,
    • NetBIOS Nameserver und Name Server (DNS)
    • Time- und NTP-Server, die für die Synchronisierung der Uhrzeit zuständig sind,

Betriebsmodi

  • dynamische Zuordnung:
  • automatische Zuordnung mit Lease-Time
Lease-Time: Festlegung wie lange eine IP-Adresse an Client „verliehen“ wird, bevor Client eine „Verlängerung“ beantragen muss
  • bei „Nicht-Verlängerung“ wird IP-Adresse frei und neu vergeben
  • automatische Zuordnung:
  • am DHCP-Server wird ein Bereich (range) von IP-Adressen definiert.
  • IP-Adressen werden automatisch an die MAC-Adressen von neuen DHCP-Clients zugewiesen und keinem anderen Host mehr zugewiesen
  • Zuweisungen sind permanent (siehe /var/lib/dhcpd.leases)
  • Neue Clients erhalten keine IP-Adresse, wenn Adressbereich vergeben, auch wenn IP-Adressen nicht aktiv genutzt werden
  • statische Zuordnung:
  • IP-Adressen werden MAC-Adressen fest zugeordnet; wichtig bei Port-Weiterleitungen oder wenn DHCP-Client Server-Dienste zur Verfügung stellt
kein „einfaches“ Einbinden von neuen Clients

Ablauf

DHCP Ablauf
  1. DHCP-DISCOVER: Client sucht per Broadcast nach DHCP-Server
  2. DHCP-OFFER: DHCP-Server bietet Client per Unicast Konfigurationsparameter der Schnittstelle an
  3. DHCP-REQUEST: Client fordert angebotene Konfigurationsparameter bei DHCP-Server an (z.B. Mietanfrage)
  4. DHCP-ACK: DHCP-Server sendet Konfigurationsparameter an Client


  • DHCP-NAK: Ablehnung einer DHCPREQUEST-Anforderung durch den DHCP-Server.
  • DHCP-DECLINE: Ablehnung durch den Client, da die IP-Adresse schon verwendet wird.
  • DHCP-RELEASE: Der Client gibt die eigene Konfiguration frei, damit die Parameter wieder für andere Clients zur Verfügung stehen.
  • DHCP-INFORM: Anfrage eines Clients nach weiteren Konfigurationsparametern, z. B. weil der Client eine statische IP-Adresse besitzt.

Einrichtung unter Linux/Debian am Beispiel "isc-dhcp-server"

Installation

root@router0230:~# apt install isc-dhcp-server

Konfiguration

/etc/dhcp/dhcpd.conf

  • Lease-Time in Sekunden
default-lease-time 600;
max-lease-time 7200;
  • Subnet-Blöcke
subnet 10.30.30.0 netmask 255.255.255.0
  • Range
range 10.30.30.10 10.30.30.99;
  • Options
option subnet-mask 255.255.255.0;
       option domain-name-servers 10.0.0.3, 10.0.0.4;
       option domain-name "raum102.itw";
       option domain-search "raum102.itw";
       option routers 10.30.30.1;
       option broadcast-address 10.30.30.255;

Nach der Änderung der Konfiguration muss die dhcpd.conf erneut eingelesen werden. 

root@router0230:~# systemctl restart isc-dhcp-server.service


Damit Änderungen bei bereits aktivem Client wirksam werden, muss dieser sie neu anfordern.

bisherige Konfiguration verwerfen 

root@router0230:~# dhclient -r

neue Konfiguration anfordern 

root@router0230:~# dhclient

Fehlerauslesung

/var/log/syslog 

root@router0230:~# cat /var/log/syslog | grep "dhcp"

=> erst Ordner /var/lib/dhcpd erzeugen 

root@router0230:~# touch /var/lib/dhcpd

Dann Datei dhcpd.leases 

root@router0230:~# touch /var/lib/dhcpd/dhcpd.leases

Danach wird diese Daie erst beschrieben und kann ausgelesen werden. 

root@router0230:~# cat /var/lib/dhcpd/dhcpd.leases


Konfigurationsdatei auf Server

/etc/dhcp/dhcpd.conf 

dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
#option domain-name "example.org";
#option domain-name-servers ns1.example.org, ns2.example.org;

#default-lease-time 600;
#max-lease-time 7200;

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
#ddns-update-style none;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;
 
#No service will be given on this subnet, but declaring it helps the 
# DHCP server to understand the network topology.

#subnet 10.152.187.0 netmask 255.255.255.0 {
#}

# This is a very basic subnet declaration.

#subnet 10.254.239.0 netmask 255.255.255.224 {
#  range 10.254.239.10 10.254.239.20;
#  option routers rtr-239-0-1.example.org, rtr-239-0-2.example.org;
#}

# This declaration allows BOOTP clients to get dynamic addresses,
# which we don't really recommend.

#subnet 10.254.239.32 netmask 255.255.255.224 {
#  range dynamic-bootp 10.254.239.40 10.254.239.60;
#  option broadcast-address 10.254.239.31;
#  option routers rtr-239-32-1.example.org;
#}

# A slightly different configuration for an internal subnet.
subnet 10.30.30.0 netmask 255.255.255.0 {
       range 10.30.30.10 10.30.30.99;
       option subnet-mask 255.255.255.0;
       option domain-name-servers 10.0.0.3, 10.0.0.4;
       option domain-name "raum102.itw";
       option domain-search "raum102.itw";
       option routers 10.30.30.1;
       option broadcast-address 10.30.30.255;
       default-lease-time 600;
       max-lease-time 7200;
host user {
  hardware ethernet 00:1d:7d:c8:de:bd;
  fixed-address 10.30.30.5;
  option host-name "user";
}
host robert {
  hardware ethernet 74:27:ea:e1:b2:b4;
  fixed-address 10.30.30.6;
  option host-name "robert";
}
host meik {
  hardware ethernet 74:27:ea:cc:fe:a0;
  fixed-address 10.30.30.7;
  option host-name "meik";
}
host ufuk {
  hardware ethernet 74:27:ea:e1:ba:b1;
  fixed-address 10.30.30.8;
  option host-name "ufuk";
}
host tanja {
  hardware ethernet 74:27:ea:e1:b1:e4;
  fixed-address 10.30.30.9;
  option host-name "tanja";
}
}

Konfigurationsdatei auf Server

/etc/dhcp/dhcpd.conf 

# dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
#option domain-name "example.org";
#option domain-name-servers ns1.example.org, ns2.example.org;

#default-lease-time 600;
#max-lease-time 7200;

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
#ddns-update-style none;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# No service will be given on this subnet, but declaring it helps the 
# DHCP server to understand the network topology.

#subnet 10.152.187.0 netmask 255.255.255.0 {
#}

# This is a very basic subnet declaration.

#subnet 10.254.239.0 netmask 255.255.255.224 {
#  range 10.254.239.10 10.254.239.20;
#  option routers rtr-239-0-1.example.org, rtr-239-0-2.example.org;
#}

# This declaration allows BOOTP clients to get dynamic addresses,
# which we don't really recommend.

#subnet 10.254.239.32 netmask 255.255.255.224 {
#  range dynamic-bootp 10.254.239.40 10.254.239.60;
#  option broadcast-address 10.254.239.31;
#  option routers rtr-239-32-1.example.org;
#}

# A slightly different configuration for an internal subnet.
subnet 10.30.30.0 netmask 255.255.255.0
       range 10.30.30.10 10.30.30.99;
       option subnet-mask 255.255.255.0;
       option domain-name-servers 10.0.0.3, 10.0.0.4;
       option domain-name "raum102.itw";
       option domain-search "raum102.itw";
       option routers 10.30.30.1;
       option broadcast-address 10.30.30.255;
       default-lease-time 600;
       max-lease-time 7200;
}

# Hosts which require special configuration options can be listed in
# host statements.   If no address is specified, the address will be
# allocated dynamically (if possible), but the host-specific information
# will still come from the host declaration.
#host passacaglia {
#  hardware ethernet 0:0:c0:5d:bd:95;
#  filename "vmunix.passacaglia";
#  server-name "toccata.example.com";
#}

# Fixed IP addresses can also be specified for hosts.   These addresses
# should not also be listed as being available for dynamic assignment.
# Hosts for which fixed IP addresses have been specified can boot using
# BOOTP or DHCP.   Hosts for which no fixed address is specified can only
# be booted with DHCP, unless there is an address range on the subnet
# to which a BOOTP client is connected which has the dynamic-bootp flag
# set.
#host fantasia {
#  hardware ethernet 08:00:07:26:c0:a5;
#  fixed-address fantasia.example.com;
#}

# You can declare a class of clients and then do address allocation
# based on that.   The example below shows a case where all clients
# in a certain class get addresses on the 10.17.224/24 subnet, and all
# other clients get addresses on the 10.0.29/24 subnet.

#class "foo" {
#  match if substring (option vendor-class-identifier, 0, 4) = "SUNW";
#}

#shared-network 224-29 {
#  subnet 10.17.224.0 netmask 255.255.255.0 {
#    option routers rtr-224.example.org;
#  }
#  subnet 10.0.29.0 netmask 255.255.255.0 {
#    option routers rtr-29.example.org;
#  }
#  pool {
#    allow members of "foo";
#    range 10.17.224.10 10.17.224.250;
#  }
#  pool {
#    deny members of "foo";
#    range 10.0.29.10 10.0.29.230;
#  }
#}

Konfigurationsdatei auf Client

/etc/dhcp/dhclient.conf 

# Configuration file for /sbin/dhclient.
#
# This is a sample configuration file for dhclient. See dhclient.conf's 
#       man page for more information about the syntax of this file 
#       and a more comprehensive list of the parameters understood by 
#       dhclient.
#
# Normally, if the DHCP server provides reasonable information and does
#       not leave anything out (like the domain name, for example), then
#       few changes must be made to this file, if any.
#

option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;

send host-name = gethostname();
request subnet-mask, broadcast-address, time-offset, routers,
        domain-name, domain-name-servers, domain-search, host-name,
        dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,
        netbios-name-servers, netbios-scope, interface-mtu,
        rfc3442-classless-static-routes, ntp-servers;

#send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;
#send dhcp-lease-time 3600;
#supersede domain-name "fugue.com home.vix.com";
#prepend domain-name-servers 127.0.0.1;
#require subnet-mask, domain-name-servers;
#timeout 60;
#retry 60;
#reboot 10;
#select-timeout 5;
#initial-interval 2;
#script "/sbin/dhclient-script";
#media "-link0 -link1 -link2", "link0 link1";
#reject 192.33.137.209;

#alias {
#  interface "eth0";
#  fixed-address 192.5.5.213;
#  option subnet-mask 255.255.255.255;
#}

#lease {
#  interface "eth0";
#  fixed-address 192.33.137.200;
#  medium "link0 link1";
#  option host-name "andare.swiftmedia.com";
#  option subnet-mask 255.255.255.0;
#  option broadcast-address 192.33.137.255;
#  option routers 192.33.137.250;
#  option domain-name-servers 127.0.0.1;
#  renew 2 2000/1/12 00:00:01;
#  rebind 2 2000/1/12 00:00:01;
#  expire 2 2000/1/12 00:00:01;
#}
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