使用 Python 的 socket.gethostbyaddr() 时遇到困难

Question

我试图在python中使用socket.gethostbyaddr()反转dns的ip列表，该列表为某些值返回'未知主机'，但使用dig为相同的ip返回主机名。此外，dig似乎比使用python模块快得多，有什么具体原因吗?

import socket
# This returns 'Unknown Host' 
name, alias, addresslist = socket.gethostbyaddr('114.143.51.197')

Answer 1

From comments…

而dig -x 114.143.51.197+short给了我主机名。

对不起，你错了。114.143.51.197没有PTR记录……因此socket.gethostbyaddr()应该抛出一个错误…为了正确地处理这个用例，添加一个try/except子句来捕获socket.herror

>>> def dns_ptr_lookup(addr):
...     try:
...         return socket.gethostbyaddr(addr)
...     except socket.herror:
...         return None, None, None
...
>>> # At this time, 4.2.2.2 has a valid PTR
>>> name,alias,addresslist = dns_ptr_lookup('4.2.2.2')
>>> print(name)
vnsc-bak.sys.gtei.net
>>>
>>> # At this time, 114.143.51.197 does NOT have a valid PTR
>>> name,alias,addresslist = dns_ptr_lookup('114.143.51.197')
>>> print(name)
None
>>>

DNS反向查找114.143.51.197…注意，它没有一个有效的PTR记录

[mpenning@Bucksnort ~]$ dig @8.8.8.8 -x 114.143.51.197
; <<>> DiG 9.6-ESV-R4 <<>> @8.8.8.8 -x 114.143.51.197
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 4735
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;197.51.143.114.in-addr.arpa.   IN      PTR
;; AUTHORITY SECTION:
114.in-addr.arpa.       1800    IN      SOA     ns1.apnic.net. read-txt-record-of-zone-first-dns-admin.apnic.net. 17812 7200 1800 604800 172800
;; Query time: 182 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Tue Nov 22 05:11:36 2011
;; MSG SIZE  rcvd: 134
[mpenning@Bucksnort ~]$ python
Python 2.5.2 (r252:60911, Jan 24 2010, 14:53:14)
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import socket
>>> socket.gethostbyaddr('114.143.51.197')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
socket.herror: (1, 'Unknown host')
>>>

一个有效的PTR记录应该是这样的…

[mpenning@Bucksnort ~]$ dig -x 4.2.2.2
; <<>> DiG 9.6-ESV-R4 <<>> -x 4.2.2.2
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61856
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 1
;; QUESTION SECTION:
;2.2.2.4.in-addr.arpa.          IN      PTR
;; ANSWER SECTION:
2.2.2.4.in-addr.arpa.   86400   IN      PTR     vnsc-bak.sys.gtei.net.
;; AUTHORITY SECTION:
2.4.in-addr.arpa.       86400   IN      NS      dnsauth2.sys.gtei.net.
2.4.in-addr.arpa.       86400   IN      NS      dnsauth1.sys.gtei.net.
2.4.in-addr.arpa.       86400   IN      NS      dnsauth3.sys.gtei.net.
;; ADDITIONAL SECTION:
dnsauth1.sys.gtei.net.  1800    IN      A       4.2.49.2
;; Query time: 308 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Nov 22 05:10:16 2011
;; MSG SIZE  rcvd: 158
[mpenning@Bucksnort ~]$ python
Python 2.5.2 (r252:60911, Jan 24 2010, 14:53:14)
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import socket
>>> socket.gethostbyaddr('4.2.2.2')
('vnsc-bak.sys.gtei.net', [], ['4.2.2.2'])
>>>