Re: DNS ACL ?

[Richard C Lewis <mrlew1 () earthlink net>]

Whenever a DNS server returns a response of over 512 bytes it will set
the Truncation bit to tell the requesting server to reissue the same
query over a Virtual Circuit (TCP connection). This is normally seen
with requests for web server information for large server farms. If you
block TCP/53 to your DNS server you *MAY* not experience any problems,
but the problems will likely occur on the requesting side of someone
seeking your information. If you do not have a lot of systems with the
same name on multiple IP addresses or multiple CNAMES or a large mail
server farm you *MAY* come out okay. Just keep in mind that your DNS
system will not be functioning the way it *should* be... but then we
wouldn't have a need for security professionals if everything did what
it *should*...

You can limit your exposure by reducing who can perform zone transfers
via the allow-transfer option and use the query-source option to control
the port used for your outgoing queries. Coupled with router/firewall
ACLs you can serious limit the TCP connections to your DNS server.
> --- Begin Message ---
>
>
> From: John Hally <JHally () epnet com>
>
> Date: Fri, 11 Nov 2005 08:35:06 -0500
>
> Hello All,
>
>  
>
> I need a sanity check regarding DNS ACLs.  For external facing DNS servers
> you need to allow only udp/53 inbound, correct?  I know tcp/53 is used for
> zone transfers and requests/replies greater than a certain size, but they
> shouldn't typically happen for general dns queries correct?  
>
>  
>
> Thanks in advance!
>
>
>
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Audit your website security with Acunetix Web Vulnerability Scanner: 

Hackers are concentrating their efforts on attacking applications on your 
website. Up to 75% of cyber attacks are launched on shopping carts, forms, 
login pages, dynamic content etc. Firewalls, SSL and locked-down servers are 
futile against web application hacking. Check your website for vulnerabilities 
to SQL injection, Cross site scripting and other web attacks before hackers do! 
Download Trial at:

http://www.securityfocus.com/sponsor/pen-test_050831
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