[nsp] NetFlow through a firewall?

[Temkin, David]

Thanks.  My thought exactly, but I know my security team will ask the
question, so I figured I'd try to be armed with something :-)

-----Original Message-----
From: Gert Doering [mailto:gert at greenie.muc.de] 
Sent: Wednesday, May 07, 2003 2:58 PM
To: Temkin, David
Cc: cisco-nsp at puck.nether.net
Subject: Re: [nsp] NetFlow through a firewall?


Hi,

On Wed, May 07, 2003 at 02:46:22PM -0400, Temkin, David wrote:
> Has anyone sucessfully passed NetFlow traffic through a firewall?  If 
> anyone has any pointers (ie, how to do this securely...) I'd love to 
> hear them.

It's not trivial, as NetFlow is source-spoofeable UDP.

On the other hand - the worst thing that people can do is send you faked
accounting records (which the flow sequence number checks should catch) and
maybe crash your netflow software.

It should be fairly safe if you make sure you don't permit source spoofed
UDP packets (with a source IP of your routers) from "outside", and then
permit only those sources through your firewall.

gert


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