· software-development

BT Internet: Non existent hosts mapping to

We have a test in our code which checks for unresolvable hosts and it started failing for me because instead of throwing an UnknownHostException from the following call:

InetAddress.getByName( "host.that.is.invalid" )

I was getting back a valid although unreachable host. When I called ping it was easier to see what was going on:

$ ping host.that.is.invalid
PING host.that.is.invalid ( 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2

As you can see, that hostname is resolving to '' which I thought was a bit weird but dig confirmed that this was happening:

$ dig host.that.is.invalid

; <<>> DiG 9.8.3-P1 <<>> host.that.is.invalid
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 30043
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;host.that.is.invalid.		IN	A

host.that.is.invalid.	300	IN	A

It turns out that BT have plugged into DNS searches and if one fails it redirects you to one of their pages instead - something I hadn't noticed before.

The site they direct you to is www.webaddresshelp.bt.com which contains a list of sponsored results for the search term 'host.that.is.invalid' in this case.

$ ping www.webaddresshelp.bt.com
PING www.webaddresshelp.bt.com ( 56 data bytes

Luckily this can be disabled by going to BT Web Address Help and then choosing to disable BT Web Address Help.

If we then wait a little bit for our DNS cache to clear the ping works as expected:

$ ping host.that.is.invalid
ping: cannot resolve host.that.is.invalid: Unknown host
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