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# DHCP
***SERVER SIDE:***
In my lab i will be using ubuntu server as my dhcp server and centos a sthe dhcp client
`sudo apt install isc-dhcp-server`
* *for recovery purposes*
`sudo mv dhcpd.conf dhcpd.conf.bak`
`sudo vim dhcpd.conf`
```bash
# Default lease time
default-lease-time 28800;
max-lease-time 86400;
# Home lab network
subnet 172.16.1.0 netmask 255.255.255.0 {
range 172.16.1.100 172.16.1.200;
option subnet-mask 255.255.255.0;
option routers 127.16.1.100;
option domain-name "homelab.lan";
option domain-name-servers ns1.homelab.lan;
}
```
{% hint style="info" %}
**Now i have to add a network interface inside my Vmware setting for ubuntu server machine**
{% endhint %}
A network interface with ens37 name has been added to this machine ( same thing to do for centos machine)
Netplan is responsible for network configuration in my machine:
`sudo vim /etc/netplan/00-installer-config.yaml`
```bash
# This is the network config written by 'subiquity'
network:
ethernets:
ens33:
addresses:
- 192.168.1.5/24
nameservers:
addresses:
- 8.8.8.8
search: []
routes:
- to: default
via: 192.168.1.1
ens37:
addresses:
- 172.16.1.100/24
nameservers:
addresses:
- 192.168.1.9
search: []
version: 2
```
As you can see, i have added a network interface configuration for ens37
> Note: I didn’t add a route to the gateway because this will issue a conflict between this interfaces Instead I am planning to use my ubuntu server as a router too and let the forwarding from ens37 to ens33 so any client that takes address from this interface will reach the internet via my home router (not ubuntu server = 192.168.1.1)
And you can see that i have put the default route for these clients to be the same interface that gives dhcp which is ens37=172.16.1.100
***Client Side:***
```bash
[k8s@k8s-manager ~]$ nmcli device status
DEVICE TYPE STATE CONNECTION
ens33 ethernet connected ens33
lo loopback connected (externally) lo
ens36 ethernet disconnected --
```
i am planning to use ens36 so i have to add it
`nmcli connection add con-name ens36 ifname ens36 type ethernet`
and VOILAA, ens36 will take ip address automatically since dhcp use broadcast
```bash
[k8s@k8s-manager ~]$ ifconfig ens36
ens36: flags=4163 mtu 1500
inet 172.16.1.102 netmask 255.255.255.0 broadcast 172.16.1.255
inet6 fe80::6f64:e247:657b:7b9f prefixlen 64 scopeid 0x20
ether 00:0c:29:66:54:2c txqueuelen 1000 (Ethernet)
RX packets 336 bytes 45221 (44.1 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 30 bytes 4538 (4.4 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
```
***Configure Routing***
Before we start configuring this, let me prove that ens36 can’t reach the internet:
```bash
[k8s@k8s-manager ~]$ ping -I ens36 google.com
PING google.com (216.58.212.110) from 172.16.1.102 ens36: 56(84) bytes of data.
From k8s-manager (172.16.1.102) icmp_seq=1 Destination Host Unreachable
From k8s-manager (172.16.1.102) icmp_seq=2 Destination Host Unreachable
From k8s-manager (172.16.1.102) icmp_seq=3 Destination Host Unreachable
From k8s-manager (172.16.1.102) icmp_seq=4 Destination Host Unreachable
From k8s-manager (172.16.1.102) icmp_seq=5 Destination Host Unreachable
From k8s-manager (172.16.1.102) icmp_seq=6 Destination Host Unreachable
^C
--- google.com ping statistics ---
7 packets transmitted, 0 received, +6 errors, 100% packet loss, time 6161ms
pipe 3
[k8s@k8s-manager ~]$ ping -I ens33 google.com
PING google.com (216.58.212.110) from 192.168.1.16 ens33: 56(84) bytes of data.
64 bytes from lhr35s06-in-f110.1e100.net (216.58.212.110): icmp_seq=1 ttl=115 time=29.2 ms
64 bytes from mrs09s12-in-f14.1e100.net (216.58.212.110): icmp_seq=2 ttl=115 time=28.3 ms
64 bytes from lhr35s06-in-f14.1e100.net (216.58.212.110): icmp_seq=3 ttl=115 time=29.4 ms
^C
--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 28.272/28.953/29.421/0.492 ms
```
Now let’s start setting up our machine to act like a router, matter of fact turn it into a router
* Enable IP Forwarding
Edit the **`/etc/sysctl.conf`** file and uncomment the following line
* Apply it :
```bash
touk@ubuntu-server:/etc/dhcp$ sudo sysctl -p
net.ipv4.ip_forward = 1
```
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