V-272405

Discussion

Configuring hosts that run a BIND 9.x implementation to only accept DNS traffic on a DNS interface allows a system to be configured to segregate DNS traffic from all other host traffic. The TCP/IP stack in DNS hosts (stub resolver, caching/resolving/recursive name server, authoritative name server, etc.) could be subjected to packet flooding attacks (such as SYNC and smurf), resulting in disruption of communication. The use of a dedicated interface for DNS traffic allows for these threats to be mitigated by creating a means to limit what types of traffic can be processed using a host-based firewall solution.

Check Content

Verify that the BIND 9.x server is configured to use an interface that is configured to process only DNS traffic.

# ifconfig -a
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.1.252 netmask 255.255.255.0 broadcast 10.0.1.255
inet6 fd80::21c:d8ff:fab7:1dba prefixlen 64 scopeid 0x20<link>
ether 00:1a:b8:d7:1a:bf txqueuelen 1000 (Ethernet)
RX packets 2295379 bytes 220126493 (209.9 MiB)
RX errors 0 dropped 31 overruns 0 frame 0
TX packets 70507 bytes 12284940 (11.7 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1458
inet 10.0.0.5 netmask 255.255.255.0 broadcast 10.0.0.255
inet6 fe81::21c:a8bf:fad7:1dca prefixlen 64 scopeid 0x20<link>
ether 00:1d:d8:b5:1c:dd txqueuelen 1000 (Ethernet)
RX packets 39090 bytes 4196802 (4.0 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 93250 bytes 18614094 (17.7 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

If one of the interfaces listed is not dedicated to only process DNS traffic, this is a finding.