[Snort-users] gigabit nic?

snort-users snort-users at ...6527...
Tue Sep 10 17:35:04 EDT 2002

I've just recently finished deploying Linux based snort sensors and an ACID
console on my network, so I thought I'd send some of my findings back to the

After doing some GigE proof of concept work with a 3Com 3c996BT
(1000BT/copper) I've ended up using Intel Pro/1000 MF NICs (1000B-SX/fibre).
Both of these cards have "interrupt modularisation" and "TCP
Offload/checksum" features which means the CPU can actually keep up with the
data being thrown at it.  These cards also have 64bit,133MHz PCI/PCIX

During our original testing with a Dlink 4 port 100M card (33bit, 33MHz),
the sensor machine was receiving approx 8000 system interrupts per second
per 100M port.  The Pro 1000MF cards are delivering 5500 interrupts per
second per 1Gbit port.  Due to my network architechure I need to have both
of my SPAN ports arriving in the same box to be able to defragment as
required and not see "duplicate" alerts caused by dual path/equal cost
routing.  It should be noted however that Linux 2.4.18 is only able to
support a 33MHz PCI bus.

> using Intel Pro/1000F Server adapters, since all of our Gig
> infrastructure uses fiber.  The Linux driver support is good, and the

My sensor machine is a 1266MHz P3 with 256MB RAM and a (second, non disk
subsystem) 64bit PCI bus for the 2 Intel Pro/1000 MF cards (using the
excellent Intel e1000 driver module).  SCSI controller is an Ultra160
Adaptec.  File systems is using LVM.

options e1000 RxDescriptors=2048,2048 TxDescriptors=80,80

This is from /proc/net/PRO_LAN_Adapters/eth3.info

Rx_Packets                       2856981123
Rx_Errors                        4527
Rx_CSum_Offload_Good             143639510034
Rx_CSum_Offload_Errors           6886135

I think Rx_Packets is an unsigned 32bit counter, so I'm wrapping every 22
hours. Ish.

> kernel) keeps up with a 100Mbit sustained pipe, albeit with a somewhat
> tweaked ruleset.  I've seen the traffic on that link spike up to ~

1145 Option Chains linked into 138 Chain Headers

> 250Mbits, and Snort doesn't barf and I don't show dropped packets.

According to my core switches, I'm sending :

  output rate 248770000 bits/sec, 41521 packets/sec with Total output drops:
  output rate 300219000 bits/sec, 54450 packets/sec with Total output drops:

But this is a quiet time.  Sustained peaks of 700++Mbits are seen during the

Running one snort process and one barnyard process (alert).

  9:31am  up 28 days, 21:23,  3 users,  load average: 1.89, 1.93, 1.90
40 processes: 36 sleeping, 4 running, 0 zombie, 0 stopped
CPU states: 67.5% user, 32.4% system,  0.0% nice,  0.0% idle
Mem:   256108K av,  251296K used,    4812K free,       0K shrd,   54564K
Swap: 1052248K av,    2212K used, 1050036K free                   94252K

23942 snort     25   0 24068  22M  1204 R    99.8  9.1 11781m snort
 4621 snort     15   0  1656 1552   684 S     0.0  0.6  27:19 barnyard

 Snort analyzed -1369552896 out of -1641541576 packets,
 The kernel dropped -276243448(151.454%) packets
 Breakdown by protocol:                Action Stats:
     TCP: -2049327621 (84.632%)         ALERTS: 742392
     UDP: 525098514  (19.789%)         LOGGED: 457706
    ICMP: 69364820   (2.614%)          PASSED: 21064
     ARP: 17076640   (0.644%)
    IPv6: 0          (0.000%)
     IPX: 0          (0.000%)
   OTHER: 69000925   (2.600%)
 DISCARD: 816        (0.000%)
 Fragmentation Stats:
 Fragmented IP Packets: 3557042    (0.134%)
     Fragment Trackers: 1514704
    Rebuilt IP Packets: 73002
    Frag elements used: 146039
 Discarded(incomplete): 674577
    Discarded(timeout): 839974
   Frag2 memory faults: 142120
 TCP Stream Reassembly Stats:
         TCP Packets Used: 1092219664 (41.163%)
          Stream Trackers: 516056675
           Stream flushes: 314379316
            Segments used: 629265834
    Stream4 Memory Faults: 68267975


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