coredns/middleware/reverse

reverse

The reverse middleware allows CoreDNS to respond dynamicly to an PTR request and the related A/AAAA request.

Syntax

reverse NETWORK... {
    hostname TEMPLATE
    [ttl TTL]
    [fallthrough]

• NETWORK one or more CIDR formatted networks to respond on.
• hostname inject the IP and zone to an template for the hostname. Defaults to "ip-{IP}.{zone[1]}". See below for template.
• ttl defaults to 60
• fallthrough If zone matches and no record can be generated, pass request to the next middleware.

Template Syntax

The template for the hostname is used for generating the PTR for an reverse lookup and matching the forward lookup back to an IP.

{ip}

The {ip} symbol is required to make reverse work. For IPv4 lookups the "." is replaced with an "-", i.e.: 10.1.1.1 results in "10-1-1-1" With IPv6 lookups the ":" is removed, and any zero ranged are expanded, i.e.: "ffff::ffff" results in "ffff000000000000000000000000ffff"

{zone[i]}

The {zone[i]} symbol is optional and can be replaced by a fixed (zone) string. The zone will be matched by the zones listed in this configuration stanza. i needs to be replaced to the index of the configured listener zones, starting with 1.

Examples

arpa compute.internal {
    # proxy unmatched requests
    proxy . 8.8.8.8

    # answer requests for IPs in this networks
    # PTR 1.0.32.10.in-addr.arpa. 3600 ip-10-0-32-1.compute.internal.
    # A ip-10-0-32-1.compute.internal. 3600 10.0.32.1
    # v6 is also possible
    # PTR 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.d.f.ip6.arpa. 3600 ip-fd010000000000000000000000000001.compute.internal.
    # AAAA ip-fd010000000000000000000000000001.compute.internal. 3600 fd01::1
    reverse 10.32.0.0/16 fd01::/16 {
        # template of the ip injection to hostname, zone resolved to compute.internal.
        hostname ip-{ip}.{zone[2]}

        ttl 3600

        # Forward unanswered or unmatched requests to proxy # without this flag, requesting A/AAAA
        records on compute.internal. will end here.
        fallthrough
    }
}

32.10.in-addr.arpa.arpa arpa.company.org {

    reverse 10.32.0.0/16 {
        # template of the ip injection to hostname, zone resolved to arpa.company.org.
        hostname "ip-{ip}.v4.{zone[2]}"

        ttl 3600

        # fallthrough is not required, v4.arpa.company.org. will be only answered here
    }

    # cidr closer to the ip wins, so we can overwrite the "default"
    reverse 10.32.2.0/24 {
        # its also possible to set fix domain suffix
        hostname ip-{ip}.fix.arpa.company.org.

        ttl 3600
    }
}