These domains point to servers that maintain a list of IP addresses with bad reputations. Servers get listed for network misuse such as spamming, brute force attacks, and scraping bots.

In this section, you’ll learn how to add or remove custom domains. If your company has a DNS with an updated list of dangerous or forbidden IP addresses that you want to block, this is where to configure it.

Preloaded Domain List #

The bottom section shows the preloaded domains maintained and updated by the Relianoid Team. When these domains are used, your load balancer queries them first. Ensure these DNS are reachable from your load balancing appliance.

The Custom Domain List section allows you to add, delete, or edit custom domains. Each added domain should be a DNSBL (domain name server block list).

DNSBL queries #

When a mail server receives a connection and checks the client against a DNSBL (e.g., sbl.spamhaus.org), it follows these steps:

• 1. Takes the client’s IP address (e.g., 172.168.42.23) and reverses the octets to 23.42.168.172.
• 2. Appends the DNSBL’s domain name: 23.42.168.172.sbl.spamhaus.org.
• 3. Looks up this name in the DNS as an A record. This returns an address if the client is listed, or an NXDOMAIN code if the client is not listed.

Optionally, if the client is listed, it looks up the name as a TXT record. Most DNSBLs provide the reason for listing in the TXT records.

Looking up an address in a DNSBL is similar to a reverse DNS lookup, but a DNSBL uses the A record type and a forward domain (e.g., dnsbl.example.net) rather than the reverse domain in-addr.arpa.