coredns/middleware/reverse

reverse

The reverse middleware allows CoreDNS to respond dynamic 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[0]}". 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}

This symbol is required to work. V4 network replaces the "." with an "-". 10.1.1.1 results in "10-1-1-1" V6 network removes the ":" and fills the zeros. "ffff::ffff" results in "ffff000000000000000000000000ffff"

{zone[i]}

This symbol is optional to use and can be replaced by a fix zone string. The zone will be matched by the configured listener on the server block key. i needs to be replaced to the index of the configured listener zones, starting with 0.

arpa.:53 domain.com.:8053 will resolve zone{0} to arpa. and zone{1} to domain.com.

Examples

# Serve on port 53
# match arpa. and compute.internal. to resolv reverse and forward lookup 
.arpa.:53 compute.internal.:53 {
    # 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[1]}

        # set time-to-live of the RR
        ttl 3600

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

    # cache with ttl timeout
    cache
}

# Serve on port 53
# listen only on the specific network
32.10.in-addr.arpa.arpa.:53 arpa.company.org.:53 {

    reverse 10.32.0.0/16 {
        # template of the ip injection to hostname, zone resolved to arpa.company.org.
        hostname "ip-{ip}.v4.{zone[1]}"

        # set time-to-live of the RR
        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.

        # set time-to-live of the RR
        ttl 3600
    }

    # cache with ttl timeout
    cache
}