send TCP fall back DNS queries with dnspython

Here’s how to send TCP fallback DNS queries with dnspython.

dnspython supports TCP fallback since version 1.10.

just referred to http://www.bortzmeyer.org/dnspython.html.

many thanks.

Looking into the code also helps me understand dns.resolver.Resolver.

http://www.dnspython.org/docs/1.10.0/html/dns.resolver-pysrc.html

install dnspython on ubuntu 13.04

# tail -1 /etc/lsb-release DISTRIB_DESCRIPTION="Ubuntu 13.04" # uname -ri 3.8.0-25-generic x86_64 # apt-get install python-dnspython –y

[ enable EDN0 ]

# cat enable_edns0.py -n # cat -n enable_edns0.py     1  #!/usr/bin/env python     2     3  import dns.resolver     4     5  myresolver = dns.resolver.Resolver(configure=False)     6  myresolver.use_edns(0,0,4096)     7  myresolver.nameservers = ['192.168.10.200']     8  result = myresolver.query('www.foo.bar','a',source="192.168.10.100")     9  for i in result:    10          print i

use_edns(0,0,4096)

enable edns0 = 0 , disable edns0 =  -1 ,

edns version

payload size

capture data when dnspython sending a query to the DNS server.

Queries        www.foo.bar: type A, class IN            Name: www.foo.bar            Type: A (Host address)            Class: IN (0x0001)    Additional records        <Root>: type OPT            Name: <Root>            Type: OPT (EDNS0 option)            UDP payload size: 4096            Higher bits in extended RCODE: 0x0            EDNS0 version: 0            Z: 0x0            Data length: 0

[ disable EDNS0 ]

# cat disable_edns0.py -n     1  #!/usr/bin/env python     2     3  import dns.resolver     4     5  myresolver = dns.resolver.Resolver(configure=False)     6  myresolver.use_edns(-1,0,4096)     7  myresolver.nameservers = ['192.168.10.200']     8  result = myresolver.query('www.foo.bar','a',tcp=False,source="192.168.10.100",source_port=50000)     9  for i in result:    10          print i

or you can disable edns0 by just removing the line “use_edns ..” .

cap data (  dnspython to DNS server )

Queries        www.foo.bar: type A, class IN            Name: www.foo.bar            Type: A (Host address)            Class: IN (0x0001)

[ send only TCP queries without sending UDP queries ]

# cat -n send_TCP_queries.py     1  #!/usr/bin/env python     2     3  import dns.resolver     4     5  myresolver = dns.resolver.Resolver(configure=False)     6  myresolver.use_edns(0,0,4096)     7  myresolver.nameservers = ['192.168.10.200']     8  result = myresolver.query('www.foo.bar','a',tcp=True,source="192.168.10.100")     9  for i in result:    10          print i

nice tool!