[Pdns-users] [Help] Increase DNS UDP Message Size

[Đức Vinh Hồ]

Hi all,
My website is using PDNS round robin with too many servers pointed to 1
domain name. I mean:

     Name                                  Type                 Content
    abc.com                                A                   X.X.X.1
    abc.com                                A                   X.X.X.2
.....
    abc.com                                A                   X.X.X.50
.....

Couple of days ago, my boss complain me that sometime, he can't access the
website at night.
After many research, i found that a DNS message carried in UDP
*cannot*exceed 512 bytes.
When a UDP DNS message exceeds 512 octets/bytes, the *TRUNCATED* bit is
included in the response, indicating to the client/resolver that not all of
the answers were returned, and they should re-query using a TCP DNS
message. I thinks my DNS round robin records is too large. And that is the
main cause of my problem

So, can you show me how to increase the PDNS UDP message size, or some
solution to make sure PDNS ok

Otherwise, I check in my PDNS log, here many error phrase:


Nov 12 14:01:44 my-server pdns[23075]: Received a malformed qdomain from
74.125.191.19, '*%**20*abc.com <http://20abc.com> <http://20abc.com>':
sending servfail
Nov 12 14:01:54 my-server pdns[23075]: Received a malformed qdomain from
74.125.191.26, '*%**20*abc.com <http://20abc.com> <http://20abc.com>':
sending servfail
Nov 12 14:01:54 my-server pdns[23075]: Received a malformed qdomain from
74.125.191.17, '*%**20*abc.com <http://20abc.com> <http://20abc.com>':
sending servfail

Nov 12 14:02:14 my-server pdns[23075]: Received a malformed qdomain from
74.125.191.20, 'xyz*,.*com': sending servfail
Nov 12 14:02:24 my-server pdns[23075]: Received a malformed qdomain from
74.125.191.26, ''xyz*,.*com': sending servfail
Nov 12 14:02:24 my-server pdns[23075]: Received a malformed qdomain from
74.125.191.16, ''xyz*,.*com': sending servfail

After some check, i found that range IP 74.125.191.x is from google server,
but i think there are some mistake here, because my website domain is
abc.com, not *%20*abc.com (%20 = space)
And other of my company website is xyz.com, not xyz*,.*com

Can someone help me to explain what is the log mean !
Thanks you so much,
Regards,
Vinh Ho
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