Another solution for Redhat Linux that works without additional scripting:
Add the following lines to /etc/sysctl.conf:
net.ipv4.neigh.default.gc_thresh3 = 4096
net.ipv4.neigh.default.gc_thresh2 = 2048
net.ipv4.neigh.default.gc_thresh1 = 1024
Regards,
-Slif
Bob McLaren wrote:
> Holy arp entries Batman!!! You fixed it!!!
>
> I have had this exact same problem since early March! I had already
> given up on it! Bless you both...
>
> BTW
> Just to add my two cents and try to help out, here are the commands I
> used on my RedHat 7.1 system to write the kernel variables
>
> /sbin/sysctl -w net.ipv4.neigh.default.gc_thresh3 = 4096
> /sbin/sysctl -w net.ipv4.neigh.default.gc_thresh2 = 2048
> /sbin/sysctl -w net.ipv4.neigh.default.gc_thresh1 = 1024
>
> Regards,
> Bob
>
> joeclifton_at_bellsouth.net wrote:
>
>> David,
>> I did some research, and found the following entries in my system log
>> (/var/log/messages)kernel:
>> Neighbour table overflow
>> NET: 1067 messages suppressed
>>
>> This is definitely an arp table overflow, so I fully concur with your
>> findings.
>>
>> Here is how I fixed it....well, at least temporarily:
>>
>> by allocating more ram for the arp table:
>> echo 1024 > /proc/sys/net/ipv4/neigh/default/gc_thresh1
>> echo 2048 > /proc/sys/net/ipv4/neigh/default/gc_thresh2
>> echo 4096 > /proc/sys/net/ipv4/neigh/default/gc_thresh3
>>
>> I'm not sure if these will be there when I reboot, if not, I will have
>> to find out where I can set those on each boot, or permanently.
>>
>> I have tested this while scanning an entire /16 subnet, then I tried
>> it in 2 console windows, while simultaneously scanning 2 /16
>> subnets.....knock on wood...it is working thus far.
>> Hope this helps you!
>>
>> joe
>>
>> On Wed, 2004-04-14 at 13:35, David G. Cheney wrote:
>>
>> 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.--dgc
>>
>> joeclifton_at_bellsouth.net wrote:> Any help is appreciated.
>>
>>
>>>> My Command line: > > nmap -sP -PI -oA ping-10.10.0.0 10.10.0.0/16> >
>>>> 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> > er
>>>> ror #2> RTTVAR > > > 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....> > joe> > >
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Received on Apr 14 2004
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