Please login to your router:
Vigor 130
User name: admin
Password: admin
OR
Vigor 120
User name: admin
Password: blank (no password)
Step 1:
Create a firewall filter under default data filter by following the snapshot.
Name it as Block Reddit and click the active checkbox.
Step 2:
Add a Filter data and click on filter 2.
Use the following configuration:
Direction: LAN to WAN
Source: Any
Destination: Select range
198.41.208.100-198.41.208.200(This is the range of reddit.com public IP list)
Service Type: Any
Filter: Block Immediately
Step3:
Repeat step 2 and create a filter 3, change the address range
Direction: LAN to WAN
Source: Any
Destination: Select range
198.41.209.100-198.41.209.200(This is the range of reddit.com public IP list)
Service Type: Any
Filter: Block Immediately
Confirm by browsing to reddit.com
This will block only reddit.com and allow the rest of the traffic.
Reddit.com is a https website, please note that the same method can be used to block any https website by putting the correct range of their Public IPs and using the filter block.