mirror of https://github.com/hashicorp/consul
232 lines
7.1 KiB
Markdown
232 lines
7.1 KiB
Markdown
---
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layout: "docs"
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page_title: "Forwarding"
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sidebar_current: "docs-guides-forwarding"
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description: |-
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By default, DNS is served from port 53. On most operating systems, this requires elevated privileges. Instead of running Consul with an administrative or root account, it is possible to instead forward appropriate queries to Consul, running on an unprivileged port, from another DNS server.
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---
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# Forwarding DNS
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By default, DNS is served from port 53. On most operating systems, this
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requires elevated privileges. Instead of running Consul with an administrative
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or root account, it is possible to instead forward appropriate queries to Consul,
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running on an unprivileged port, from another DNS server.
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In this guide, we will demonstrate forwarding from [BIND](https://www.isc.org/downloads/bind/)
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as well as [dnsmasq](http://www.thekelleys.org.uk/dnsmasq/doc.html).
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For the sake of simplicity, BIND and Consul are running on the same machine in this example,
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but this is not required.
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It is worth mentioning that, by default, Consul does not resolve DNS
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records outside the `.consul.` zone unless the
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[recursors](/docs/agent/options.html#recursors) configuration option
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has been set. As an example of how this changes Consul's behavior,
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suppose a Consul DNS reply includes a CNAME record pointing outside
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the `.consul` TLD. The DNS reply will only include CNAME records by
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default. By contrast, when `recursors` is set and the upstream resolver is
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functioning correctly, Consul will try to resolve CNAMEs and include
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any records (e.g. A, AAAA, PTR) for them in its DNS reply.
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### BIND Setup
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First, you have to disable DNSSEC so that Consul and BIND can communicate.
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Here is an example of such a configuration:
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```text
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options {
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listen-on port 53 { 127.0.0.1; };
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listen-on-v6 port 53 { ::1; };
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directory "/var/named";
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dump-file "/var/named/data/cache_dump.db";
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statistics-file "/var/named/data/named_stats.txt";
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memstatistics-file "/var/named/data/named_mem_stats.txt";
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allow-query { localhost; };
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recursion yes;
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dnssec-enable no;
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dnssec-validation no;
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/* Path to ISC DLV key */
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bindkeys-file "/etc/named.iscdlv.key";
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managed-keys-directory "/var/named/dynamic";
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};
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include "/etc/named/consul.conf";
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```
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### Zone File
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Then we set up a zone for our Consul managed records in consul.conf:
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```text
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zone "consul" IN {
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type forward;
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forward only;
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forwarders { 127.0.0.1 port 8600; };
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};
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```
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Here we assume Consul is running with default settings and is serving
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DNS on port 8600.
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### Dnsmasq Setup
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Dnsmasq is typically configured via a `dnsmasq.conf` or a series of files in
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the `/etc/dnsmasq.d` directory. In Dnsmasq's configuration file
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(e.g. `/etc/dnsmasq.d/10-consul`), add the following:
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```text
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# Enable forward lookup of the 'consul' domain:
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server=/consul/127.0.0.1#8600
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# Uncomment and modify as appropriate to enable reverse DNS lookups for
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# common netblocks found in RFC 1918, 5735, and 6598:
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#rev-server=0.0.0.0/8,127.0.0.1#8600
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#rev-server=10.0.0.0/8,127.0.0.1#8600
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#rev-server=100.64.0.0/10,127.0.0.1#8600
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#rev-server=127.0.0.1/8,127.0.0.1#8600
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#rev-server=169.254.0.0/16,127.0.0.1#8600
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#rev-server=172.16.0.0/12,127.0.0.1#8600
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#rev-server=192.168.0.0/16,127.0.0.1#8600
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#rev-server=224.0.0.0/4,127.0.0.1#8600
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#rev-server=240.0.0.0/4,127.0.0.1#8600
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```
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Once that configuration is created, restart the `dnsmasq` service.
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Additional useful settings in `dnsmasq` to consider include (see
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[`dnsmasq(8)`](http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html)
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for additional details):
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```
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# Accept DNS queries only from hosts whose address is on a local subnet.
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#local-service
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# Don't poll /etc/resolv.conf for changes.
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#no-poll
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# Don't read /etc/resolv.conf. Get upstream servers only from the command
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# line or the dnsmasq configuration file (see the "server" directive below).
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#no-resolv
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# Specify IP address(es) of other DNS servers for queries not handled
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# directly by consul. There is normally one 'server' entry set for every
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# 'nameserver' parameter found in '/etc/resolv.conf'. See dnsmasq(8)'s
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# 'server' configuration option for details.
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#server=1.2.3.4
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#server=208.67.222.222
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#server=8.8.8.8
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# Set the size of dnsmasq's cache. The default is 150 names. Setting the
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# cache size to zero disables caching.
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#cache-size=65536
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```
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### Testing
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First, perform a DNS query against Consul directly to be sure that the record exists:
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```text
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[root@localhost ~]# dig @localhost -p 8600 master.redis.service.dc-1.consul. A
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; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.32.amzn1 <<>> @localhost master.redis.service.dc-1.consul. A
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; (1 server found)
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;; global options: +cmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11536
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;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
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;; QUESTION SECTION:
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;master.redis.service.dc-1.consul. IN A
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;; ANSWER SECTION:
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master.redis.service.dc-1.consul. 0 IN A 172.31.3.234
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;; Query time: 4 msec
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;; SERVER: 127.0.0.1#53(127.0.0.1)
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;; WHEN: Wed Apr 9 17:36:12 2014
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;; MSG SIZE rcvd: 76
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```
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Then run the same query against your BIND instance and make sure you get a
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valid result:
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```text
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[root@localhost ~]# dig @localhost -p 53 master.redis.service.dc-1.consul. A
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; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.32.amzn1 <<>> @localhost master.redis.service.dc-1.consul. A
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; (1 server found)
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;; global options: +cmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11536
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;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
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;; QUESTION SECTION:
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;master.redis.service.dc-1.consul. IN A
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;; ANSWER SECTION:
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master.redis.service.dc-1.consul. 0 IN A 172.31.3.234
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;; Query time: 4 msec
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;; SERVER: 127.0.0.1#53(127.0.0.1)
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;; WHEN: Wed Apr 9 17:36:12 2014
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;; MSG SIZE rcvd: 76
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```
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If desired, verify reverse DNS using the same methodology:
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```text
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[root@localhost ~]# dig @127.0.0.1 -p 8600 133.139.16.172.in-addr.arpa. PTR
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; <<>> DiG 9.10.3-P3 <<>> @127.0.0.1 -p 8600 133.139.16.172.in-addr.arpa. PTR
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; (1 server found)
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;; global options: +cmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3713
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;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
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;; WARNING: recursion requested but not available
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;; QUESTION SECTION:
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;133.139.16.172.in-addr.arpa. IN PTR
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;; ANSWER SECTION:
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133.139.16.172.in-addr.arpa. 0 IN PTR consul1.node.dc1.consul.
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;; Query time: 3 msec
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;; SERVER: 127.0.0.1#8600(127.0.0.1)
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;; WHEN: Sun Jan 31 04:25:39 UTC 2016
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;; MSG SIZE rcvd: 109
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[root@localhost ~]# dig @127.0.0.1 +short -x 172.16.139.133
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consul1.node.dc1.consul.
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```
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### Troubleshooting
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If you don't get an answer from your DNS server (e.g. BIND, Dnsmasq) but you
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do get an answer from Consul, your best bet is to turn on your DNS server's
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query log to see what's happening.
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For BIND:
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```text
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[root@localhost ~]# rndc querylog
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[root@localhost ~]# tail -f /var/log/messages
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```
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The log may show errors like this:
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```text
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error (no valid RRSIG) resolving
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error (no valid DS) resolving
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```
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This indicates that DNSSEC is not disabled properly.
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If you see errors about network connections, verify that there are no firewall
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or routing problems between the servers running BIND and Consul.
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For Dnsmasq, see the `log-queries` configuration option and the `USR1`
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signal.
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