DNS Relay Configuration

Overview

DNS relay is used to forward DNS request and reply packets between the DNS client and DNS server. In the network where DNS relay is used, the DNS client sends DNS request packets to the DNS relay. The DNS relay forwards request packets to the DNS server and sends reply packets to the DNS client, and domain resolution is realized.

Configuration

Topology

Figure 34. DNS relay configuration

Linux Configuration on the DNS client

  1. sudo ifconfig enp4s0f0 4.4.4.2/24
  2. sudo ifconfig enp4s0f0 inet6 add fd02::2/16
  3. echo nameserver fd02::1 >> /etc/resolv.conf
  4. echo nameserver 4.4.4.1 >> /etc/resolv.conf

Linux Configuration on the DNS server

  1. sudo ifconfig enp3s0f0 1.1.1.2/24
  2. sudo ifconfig enp3s0f0 inet6 add fd01::2/16

  3. Install and configure BIND9:

    Maximum of 10 bind9 instances is supported.

    1. apt-get -y update && apt install -y bind9

    2. Configure 'forwarders' section in the /etc/bind/named.conf.options file like this:

      Copy 
          forwarders  { 8.8.8.8;  2001:4860:4860::8888; };

DNS Relay Router

#configure terminal

Enter configure mode

(config)#ip dns relay address 1.1.1.2

Set the IPv4 address of a DNS server

(config)#ipv6 dns relay address fd01::2

Set the IPv6 address of a DNS server

(config)#commit

Commit the configuration

(config)#interface xe44

Enter interface mode (interface connected to client)

(config-if)#ip address 4.4.4.1/24

Assign an IPv4 address to the interface

(config-if)#ip dns relay

Set the interface as a DNS relay client-facing IPv4 port

(config-if)#ipv6 address fd02::1/16

Assign an IPv6 address to the interface

(config-if)#ipv6 dns relay

Set the interface as a DNS relay client-facing IPv6 port

(config-if)#commit

Commit the configuration

(config)#interface xe1

Enter interface mode (interface connected to server)

(config-if)#ip address 1.1.1.1/24

Assign an IPv4 address to the interface

(config-if)#ip dns relay uplink

Set the interface as a DNS relay server-facing IPv4 port

(config-if)#ipv6 address fd01::1/16

Assign an IPv6 address to the interface

(config-if)#ipv6 dns relay uplink

Set the interface as a DNS relay server-facing IPv6 port

(config-if)#commit

Commit the configuration

(config)#exit

Exit configure mode

Validation

Copy 
#sh run dns relay
!
ip dns relay address 1.1.1.2
!
ipv6 dns relay address fd01::2
!
interface xe1
 ip dns relay uplink
 ipv6 dns relay uplink
!
interface xe44
 ip dns relay
 ipv6 dns relay
!
#show running-config interface xe1
!
interface xe1
 ip address 1.1.1.1/24
 ipv6 address fd01::1/16
 ip dns relay uplink
 ipv6 dns relay uplink
!
#show running-config interface xe44
!
interface xe44
 ip address 4.4.4.1/24
 ipv6 address fd02::1/16
 ip dns relay
 ipv6 dns relay
!

Verify DNS Query result on DNS client machine:

Copy 
[root@localhost ~]# host google.com
google.com has address 172.217.160.238
google.com has IPv6 address 2404:6800:4002:804::200e
google.com mail is handled by 40 alt3.aspmx.l.google.com.
google.com mail is handled by 10 aspmx.l.google.com.
google.com mail is handled by 50 alt4.aspmx.l.google.com.
google.com mail is handled by 30 alt2.aspmx.l.google.com.
google.com mail is handled by 20 alt1.aspmx.l.google.com.