Working on an implementation of a split DNS design, I encountered an interesting bug in Cisco IOS: the ip dns view-group command works only on interfaces, but not on subinterfaces. As it’s a pure IP feature, there obviously no reason why it shouldn’t work on anything that has an IP address; obviously someone forgot to insert the correct entry in the parser tables.

Here’s a sample configuration session taken from a 7200-series router running IOS release 12.4(15)T5:

c7200(config)#ip dns view-list Test
c7200(cfg-dns-view-list)#interface Serial 1/0
c7200(config-if)#ip dns view-group Test
c7200(config-if)#encapsulation frame-relay
c7200(config-if)#interface Serial 1/0.1 point
c7200(config-subif)#ip dns view-group Test
                        ^
% Invalid input detected at '^' marker.