Re: [fw-wiz] How does your firewall handle DNS messages > 512 octets?


Its a commercial of my own ;-)

But i use DJB's dnscache with some configuration wrappers that allow me to
control it the unified way. Actually the syntax is inherited from good old
fwtk, something like:

dnsctl: instances dnscache-lo dnscache-int
dnscache-lo: bind
dnscache-lo: default-servers some.where.outside
dnscache-lo: zone -servers some.where.inside
dnscache-lo: zone 10.IN-ADDR.ARPA -servers some.where.inside
dnscache-lo: permit-hosts
dnscache-int: bind

Unfortunately the license for DJB tools is quite restrictive, so i cannot
do much anomaly detection beyond what is available out of the box.

It does handle AAAA records ok, at least.

On Wed, Aug 30, 2006 at 03:01:00PM -0400, Dave Piscitello wrote:
Is this a commercial firewall or roll your own? If commercial which one?

Does your proxy do protocol anomaly detection? If yes, does it recognize
AAAA resource records or does it treat them as "out of compliance"?

ArkanoiD wrote:

Well, mine does cache/proxy so there is no packet size restriction
per se..

On Tue, Aug 29, 2006 at 03:13:34PM -0400, Dave Piscitello wrote:
Hi all,

I am trying to understand how different firewalls behave when they
receive a UDP datagram containing a DNS message that uses EDNS0 (RFC
2671) to support message sizes greater than the 512 maximum specified in
RFC 1035 (original DNS).


- does your firewall block/silently discard such messages by default?
- do you know the command to allow the message if blocked by default?

I've found dozens of claims that firewalls don't handle EDNS0 correctly,
but after a long search, I've only found URLs indicating that Firewall-1
and Pix block by default and have workarounds.

I'm curious whether SonicWall, Netscreen, Symantec, etc. behave
similarly. I'd also be curious to learn the behavior of IPS devices and
DNS proxies (Watchguard, WinProxy, etc).

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