To capture flow data instruct tcpdump to write to a file (-s 1500 -w
/tmp/mycapture.cap), leave it on for a while and then open it in wireshark.
Select "Decode as" cflow in wireshark. It may still not display the full
payload if it doesn't capture a template file, which is sent periodically
(as quick as every second, or as slow as once in 30 minutes - it depends).
On Tue, Jul 24, 2012 at 7:33 PM, cedric.delaunay
<cedric.delau...@gmail.com>wrote:
> Hi,
> Thanks for your answers.
>
> I'll try to upgrade nfsen and nfdump to lastest versions (currently 1.3.5
> and 1.6.1p1)
>
> I can't see how to capture the flows as a tcpdump on collector's machine
> won't give me packets content. Am I wrong ? Any Idea howto ? Maybe with
> "-E" option on nfcapd but data are already interpreted...
> I'm unable to read data like
> 00:05:00:1e:06:32:4d:c0:50:0e:c8:44:00:9e:61:4e:03:22:64:3a:2a:2a:00:00:26:71:a5:50:81:14:5e:1b:00:00:00:00:00:00:00:00:00:00:00:04:00:00:00:ae:06:30:e2:78:06:30
> ;)
>
> I will see when I'll be back thursday.
> Bye
>
>
> Le 24/07/2012 17:22, Jan Pazdera a écrit :
>
> Hi,
>
> this can sometimes happen, if the exporter shifts its system time, for
> example during NTP time correction. Try to check, whether the exporter does
> this or not and if so, turn it off to see, if this is the reason.
>
> The problem is connected with nfcapd > v1.6. When it detects a time shift,
> it performs a time correction, which sometimes leads to overflow.
>
> Regards,
> Jan
>
> Jan Pazdera <pazdera at invea.cz>
> INVEA-TECH a.s.
> U Vodarny 2965/2, 61600 Brno, Czech Republic
> Tel: +420 511 205 251www.invea-tech.com
> Key 0x89F62F78: 41A7 28C2 C624 FBD1 E236 6827 42EB 3694 89F6 2F78
>
>
>
> On 24.7.2012 17:05, Adrian Popa wrote:
>
> I guess a packet capture of those flows might help determine if they are
> sent with this duration timestamp incorrectly set, or if nfcapd interprets
> them incorrectly.
> Peter will be able to tell you more.
>
> On Tue, Jul 24, 2012 at 6:00 PM, Adrian Popa <adrian.popa...@gmail.com>wrote:
>
>> Usually the network device which sends flows (the router) will expire
>> flows based on flow termination or on a specific timeout value. For Cisco
>> you can set timeouts for active flows to force them to expire even if there
>> is still traffic (useful in case of a DOS attack).
>> I don't remember the commands but I can look them up if you need them.
>>
>> I don't think nfcapd can do anything about this - the timestamps you are
>> getting look like a bug - it looks awfully close to 4294967296 - which is
>> 2^32. So I would suspect a variable overflow somewhere. Negative time
>> perhaps, with a positive int?
>>
>>
>> On Tue, Jul 24, 2012 at 5:02 PM, cedric.delaunay <
>> cedric.delau...@gmail.com> wrote:
>>
>>> Hi all,
>>> One small question before holidays.
>>>
>>> As we know, flow expiration on the exporter runs if no packet comes in a
>>> flow or if a "end of session" tcp flag is detected.
>>> Then the exporter will inform nfcapd in an udp packet.
>>>
>>> What's happens if this packet is lost on the network ? Will nfsen never
>>> see that this flow has expired ?
>>> I found flows with duration up to 4 000 000 000 ms and only 1 flow.
>>> here a example anonymized :
>>>
>>> Date flow start Duration Proto Src IP Addr:Port
>>> Dst IP Addr:Port Packets Bytes Flows
>>> 2012-07-24 10:59:54.007 2.000 UDP 113.107.214.100:61918 ->
>>> 216.67.102.45:2122 1 131 1
>>> 2012-07-24 10:59:54.007 2.000 UDP 216.67.102.45:2122 ->
>>> 113.107.214.100:61918 1 305 1
>>> 2012-07-24 10:59:59.007 3.000 UDP 62.252.190.196:123 ->
>>> 61.192.94.167:123 4 304 1
>>> 2012-07-24 10:59:59.007 3.000 UDP 61.192.94.167:123 ->
>>> 62.252.190.196:123 4 304 1
>>> 2012-06-04 17:59:57.711 4294966.296 UDP 113.107.184.123:27057 ->
>>> 216.67.102.45:2122 1 126 1
>>> 2012-06-04 17:59:57.711 4294966.296 UDP 216.67.102.45:2122 ->
>>> 113.107.184.123:27057 1 309 1
>>> 2012-07-24 11:32:08.008 116.000 TCP 113.107.219.116:36157 ->
>>> 218.185.100.221:80 7 730 1
>>> 2012-07-24 11:32:08.008 116.000 TCP 218.185.100.221:80 ->
>>> 113.107.219.116:36157 5 1764 1
>>> 2012-07-24 11:54:54.008 9.000 TCP 113.107.79.246:38264 ->
>>> 242.194.34.210:25 3 156 1
>>> 2012-07-24 11:59:59.008 1.000 UDP 62.252.190.196:123 ->
>>> 61.192.94.167:123 4 304 1
>>> 2012-07-24 11:59:59.008 1.000 UDP 61.192.94.167:123 ->
>>> 62.252.190.196:123 4 304 1
>>> IP addresses anonymized
>>> Summary: total flows: 11, total bytes: 4737, total packets: 35, avg bps:
>>> 0, avg pps: 0, avg bpp: 135
>>> Time window: 2012-06-04 17:59:57 - 2012-07-24 12:00:00
>>> Total flows processed: 3783450, Blocks skipped: 0, Bytes read: 196757126
>>> Sys: 1.618s flows/second: 2337262.1 Wall: 1.612s flows/second: 2345863.0
>>>
>>>
>>> All flows with duration > 4000000000 started the same day : 2012-04-06
>>>
>>> Am I wrong if I think this should not happen ?
>>> Could a packet loss be the reason of my problem ? What else if not ?
>>> Is there a way to force nfcapd to expire flows for which he recieves no
>>> more information ?
>>>
>>> The exporter is a Packetfilter firewall running on OpenBSD with pflow
>>> enabled.
>>> Thanks
>>>
>>>
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>>
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