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Re: Buffer space Problems
From: "David G. Cheney" <dgc () rocketfiber com>
Date: Wed, 14 Apr 2004 10:35:24 -0700

I believe this isn't just an nmap problem.

I have encountered similar problems useing a home grown scanner similar to fping on FreeBSD. The buffer starvation in my case is related to the arp table growing to hundreds of thousands of entries. In FreeBSD 4.8 there was a known denial of service vulnerability based on this behavior, and where it was claimed to have been fixed the problem still occurs when it is the local arp daemon making the requests.

My workaround was pretty ugly. I resorted to flushing the arp table every couple of thousand probes. This solves the problem on FreeBSD (btw. 5.2.1 still has this issue). I'm guessing that Linux has some similar issues.

I personally don't think it should be the task of the user space application (i.e. scanner) to deal with resource starvation issues like this, but to be fair to the various kernels a scanner is not a typical load.

If anyone has an alternate solution I would love to hear it.


joeclifton () bellsouth net wrote:

Any help is appreciated. My Command line:
nmap -sP -PI -oA ping-

Obvisouly, I am running out of buffer space somewhere, but where is my question, and is there a solution, except to 
reduce the size of the subnet being scanned.  I first tired -T4, and backed it all the way down to -T1, with almost no 
difference.  I get lots of hosts returned as being up, then it starts giving me the error below.  I have tried 
different size subnets, and the largest I can scan with out geting the error is /22.

I sometimes get an error similar to #2 below. (can;t remember the whole thing, and forgot to copy it.)

I scan a lot of large subnets, and would like to ge this resolved.
Is there another way to throttle back, besides the timing option?  I hate having to do 20 or 25 smaller scans, then 
cat'ing them together.

error #1

sendto in sendpingquery returned -1 (should be 8)!
sendto: No buffer space available

error #2

My versions:

nmap version 3.48
Linux xxx.xxxx.org 2.4.22-1.2174.nptl #1 Wed Feb 18 16:38:32 EST 2004 i686 i686 i386 GNU/Linux   (Fedora Core 1)

Thanks again for any help....


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