wiki-grav/pages/02.linux/14.dhcp-server-and-routing/default.en.md

---
title: 'DHCP Server and Routing'
---

[toc]
## Installation
`# apt install isc-dhcp-server`  

## Configuration
Edit `/etc/default/isc-dhcp-server`  
`INTERFACESv4="(interface 1) (interface 2)"`  

Edit `/etc/dhcp/dhcpd.conf` to set a subnet  
```
subnet (netaddress) netmask (subnetmask) {
    range (first dhcp) (last dhcp);
    option subnet-mask (subnetmask);
    option routers (gateway);
    option domain-name "(name)";
    option domain-name-servers (dns server);
}
```

Edit `/etc/network/interfaces`  
```
auto (interface)
iface (interface) inet static
    address (address)
    network (netaddress)
    netmask (netmask)
    broadcast (broadcast)
```

Enable the interface  
`# ifup (interface)`  

Restart DHCP Server  
`# systemctl restart isc-dhcp-server.service`  

### Enable routing
`# echo "net.ipv4.ip_forward=1" >> /etc/sysctl.d/80-forwarding.conf`  
`# sysctl -p /etc/sysctl.d/80-forwarding.conf`  

`# iptables -t nat -A POSTROUTING -o (WAN interface) -j MASQUERADE`  
`# iptables -A FORWARD -i (LAN interface) -j ACCEPT`  

Make iptables permanent  
Select `Yes` during the installation to save current rules  
`# apt install iptables-persistent`  

### Enable DHCP-managed fixed IP address
```
host (hostname) {
  hardware ethernet (mac);
  fixed-address (ip address);
}
```

### Dynamic DNS
*Needs a supported DNS like BIND or PowerDNS*  
[Configure your DNS server to accept updates](https://wiki.realstickman.net/e/en/linux/services/powerdns)  
Add the following snippet to your `/etc/dhcp/dhcpd.conf` file  
How to generate the key is also described in the DNS article  
```

ddns-updates on;
ddns-update-style interim;
update-static-leases on;

ddns-domainname "testpdns";
ddns-rev-domainname "in-addr.arpa.";

key "(keyname)" {
    algorithm hmac-md5;
    secret "(key)";
};

zone testpdns {
    primary 127.0.0.1;
    key (keyname);
}

zone 7.168.192.in-addr.arpa. {
    primary 127.0.0.1;
    key (keyname);
}

```

## Client
DHCP Request  
`# dhclient -v`  

Release IP  
`# dhclient -v -r`