AS112 Explained

Denver IX operates an AS112 service for the peering fabric. This system provides anycast reverse DNS lookup for several prefixes, namely:


As these IP addresses are widely used for private networking, many end-user systems are configured to perform reverse DNS lookups for these address ranges. DNS lookups for these ranges should always be null-answered quickly, in order to make sure that DNS retransmits don’t occur (thereby overloading local DNS resolvers), and to prevent end-user systems from hanging due to DNS lookups.

AS112 services are provided around the world by a group of volunteers.

Connectivity to this service is available to all Denver IX members at no charge. To make use of this service, contact Denver IX operations and we will provision a BGP peering session on the AS112 server. Alternatively, this service is made available on all route servers without additional configuration.

Technical contact, NOC, and emergency contacts are the same as Denver IX Operations and can be reached via the Portal.

Technical Details

Denver IX operates the AS112 on a virtual machine using Bird 2 on Debian 9.x LTS.

Service conforms to rfc7534 (AS112 Nameserver Operations) and implements rfc7535 (AS112 Redirection Using DNAME). Queries are served over both IPv4 and IPv6.

Contact Denver IX Operations to arrange peering sessions. While the AS112 instance also peers with all Denver IX route servers, bilateral peering is recommended.

The peering addresses and looking glass for the AS112 service is as follows:

  • ASN: 112
  • IPv4:
  • IPv6: 2001:504:109::9