DHCP PROXY

DHCP Proxy For Deleting and Inserting Relayed Option 82 information

About

In environments like Cisco SD Access or Cisco ACI where option 82 is required, the DHCP server must support this by returning option 82 in its replies. If this is omitted the packets will never get back to the client because the network depends on this information for correct forwarding.

This proxy provides a fix by stripping the option 82 information in the request and re-inserting it in the offer, meaning the server is oblivious of this information.

The long time solution is to use a DHCP server that supports option 82, but this proxy is a feasable short time solution

This proxy can be used to manipulate other options as well, yet as of now it's only for option 82. Open an issue if you have any thoughts or ideas on how to further utilize or improve this proxy

Caveats

This proxy is in early development and is highly experimental, yet works as a charm if installed as described. A current major caveat is that there is little to none fault handling so if it catches an unknown it will CRASH. I'm currently working on improving this.

Installation

Install the proxy according to design

 DHCP Server <-> THIS_PROXY! <-> Relay Agent <-> DHCP Client
 Might work in other scenarios as well, but Ye Might Also Be Fecked!

Make sure git, python, pip and optionally virtualenv are installed on the platform of choice
```
 If not use "yum install " or "apt-get "  to fullfill these dependencies
```
Install scapy. Fret not, Scapy is a well-known packet manipulator used by Cisco Systems among others
```
 pip install scapy
```

Clone from Github

 git clone https://github.com/bentole/dhcpProxy.git

Create a file named settings.py and put it in the same directory as dhcpProxy.py. See Settings below
```
 vi settings.py or nano settings.py or whatever
```
Start the proxy
```
 python ./dhcpProxy.py
```
Change the relay information from pointing towards the dhcp server to point towards the proxy
```
 For Cisco routers : ip helper-address proxy_addr
```
Good luck, Chuck!

Settings

Copy & paste the below content and save it to settings.py. Just make sure it's placed in the same directory as the main scriptfile.

# the listener interface for the proxy
INT = 'ifname' 
# ip address of the listener interface
INT_IP = 'w.x.y.z' 
# ip address of the dhcp server
DHCP_SRV = 'w.x.y.z' 
# Log to the specified file or set to False for no logging
VERBOSE = True
LOGFILE = '/var/log/dhcpproxy.log' # Make sure this is placed in the correct logfolder

Install as service

Edit dhcpproxy.service and make sure that the file paths are correct

Put dhcpproxy.service file in the correct systemd folder

 On Centos: /usr/lib/systemd/system
 On Ubuntu: /etc/systemd/system
 Might be other locations as well, you'll figure it out.

Reload systemd to read the new service file
```
 sudo systemctl daemon-reload
```
Start the service
```
 sudo systemctl start dhcpproxy
```

Check status or stop

 sudo systemctl status dhcpproxy
 sudo systemctl stop dhcpproxy

Enable at startup
```
 sudo systemctl enable dhcpproxy
```
Puh, Done! Now tail the logfile to see what's going on
```
 tail -f /var/log/dhcpproxy.log
```