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documentation:examples:dropping_packets_at_high_rate

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Dropping packets at high rate

Goal

Using IPFW

Standard IP level configuration

The configuration file of an IPFW in standard mode is this one:

  • First rule is a blacklist of denied IP addresses
  • Second rule is to allow all the rest
  • Disabling the outgoing pfil(9) hook because we don't need to filter outgoing traffic
#!/bin/sh
set -eu
fwcmd="/sbin/ipfw"
${fwcmd} -f flush
${fwcmd} table blacklist destroy || true
${fwcmd} table blacklist create type addr
${fwcmd} table blacklist add 198.18.2.0/24
${fwcmd} add deny udp from table\(blacklist\) to any
${fwcmd} add pass ip from any to any
pfilctl unlink -o ipfw:default inet || true
pfilctl unlink -o ipfw:default6 inet6 || true

NIC level configuration

(A FreeBSD 13 / head) only feature.

Only iflib, vtnet, Mellanox and Chelsio drivers are “Pfil Memory Pointer Hooks” compliant.

The configuration file of an IPFW-at-NIC-level is this one:

  • First rule is a blacklist of denied IP addresses
  • Second rule is to allow all the rest
  • Removing pfil(9) from the IP level (in & out)
  • Enabling pfil(9) at NIC level (in only)
#!/bin/sh
set -eu
fwcmd="/sbin/ipfw"
${fwcmd} -f flush
${fwcmd} table blacklist destroy || true
${fwcmd} table blacklist create type addr
${fwcmd} table blacklist add 198.18.2.0/24
${fwcmd} add deny udp from table\(blacklist\) to any
${fwcmd} add pass ip from any to any
if pfilctl link -i ipfw:default-link cxl0; then
        pfilctl unlink -i ipfw:default inet || true
        pfilctl unlink -o ipfw:default inet || true
        pfilctl unlink -i ipfw:default6 inet6 || true
        pfilctl unlink -o ipfw:default6 inet6 || true
fi

Performance impact

Hardware:

  • Intel Xeon CPU E5-2697A v4 @ 2.60GHz (16 cores, 32 threads)
  • Input NIC (filtering): Chelsio T580-LP-CR (QSFP+ 40GBASE-SR4)
  • Output NIC: Mellanox ConnectX-4 MCX416A-CCAT (QSFP28 100GBASE-SR4)
  • FreeBSD 13.0-CURRENT r357572

Here is the rate of inet4 packets-per-second forwarded while dropping the 42Mpps of DDoS using the different configuration sets:

x ipfw-standard
+ ipfw-at-nic-level
+--------------------------------------------------------------------------+
|                                                                         +|
|                                                                         +|
|                                                                         +|
| x                                                                       +|
|xx xx                                                                    +|
||MA|                                                                      |
|                                                                         A|
+--------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   5     9902014.5      10004945     9940500.5     9949589.9     41823.097
+   5      12013847      12018302      12015790      12015667       1720.41
Difference at 95.0% confidence
        2.06608e+06 +/- 43167.6
        20.7655% +/- 0.523817%
        (Student's t, pooled s = 29598.4)

Using Chelsio's TCAM firewall

Chelsio NIC allows to configure hardware firewall with the use of cxgbetool(8): The linux user guide gives a lots more details than the FreeBSD user guide.

A Chelsio NIC is defined by its family name + id and the port id (if it's a 4 ports, port 0 to 4).

Example with only one Chelsio (t5nex0) with 2 ports (0 and 1)

# grep t.nex /var/run/dmesg.boot
t5nex0: <Chelsio T580-LP-CR> mem 0xf9300000-0xf937ffff,0xf8000000-0xf8ffffff,0xf9984000-0xf9985fff irq 40 at device 0.4 on pci4
cxl0: <port 0> on t5nex0
cxl1: <port 1> on t5nex0
t5nex0: PCIe gen3 x8, 2 ports, 66 MSI-X interrupts, 130 eq, 65 iq

Translating the firewall rule for the Chelsio:

  • Add a filter to drop packets incoming from Chelsio NIC 0 (t5nex0) port 0 matching source IP range 198.18.2.0/24
# cxgbetool t5nex0 filter 0 iport 0 sip 198.18.2.0/24 action drop
# cxgbetool t5nex0 filter list
 Idx     Hits FCoE Port      vld:VLAN  Prot MPS Frag                  DIP                  SIP     DPORT     SPORT Action
   0        0  0/0  0/7 0:0000/0:0000 00/00 0/0  0/0    00000000/00000000    c6120200/ffffff00 0000/0000 0000/0000 Drop

To check the packet dropping rate, this a small script will be used:

#!/bin/sh
set -euf -o pipefail
if [ $# -eq 0 ]; then
        echo "Need Chelsio nexus name (examble: t5nex0)"
                echo "List of Nexus detected:"
                grep t.nex /var/run/dmesg.boot || true
        exit 1
fi
VALUE=$(cxgbetool $1 filter list  | awk '{if (NR!=1) {print $2}}')
echo "Filter hit rate"
while true; do
 sleep 1
 NEW_VALUE=$(cxgbetool $1 filter list  | awk '{if (NR!=1) {print $2}}')
 RATE=$((NEW_VALUE - VALUE))
 VALUE=${NEW_VALUE}
 echo ${RATE}
done

And its output during the 42Mpps DDoS:

# /tmp/cxgbe-filter-rate.sh t5nex0
32361520
32365722
32368802
32492850
32494303
32434792
32398556

The script report an hardware dropping rate of 32Mpps: Where are the other 10Mpps ?

Let's read the Chelsio default firmware configuration file of our T5 family NIC:

        # TCAM has 8K cells; each region must start at a multiple of 128 cell.
        # Each entry in these categories takes 4 cells each.  nhash will use the
        # TCAM iff there is room left (that is, the rest don't add up to 2048).
        nroute = 32
        nclip = 32
        nfilter = 1008
        nserver = 512
        nhash = 524288

And we can display the current value applied:

#  sysctl -n dev.t5nex.0.misc.devlog | grep -w le
        12           576921      INFO       RES  le configuration: nentries 2048 route 32 clip 32 filter 1440 server 416 active 128 hash 0 nserversram 0
        16           619796      INFO       RES  le initialization: nentries 2048 route 32 clip 32 filter 1440 server 416 active 128 hash 0 nserversram 0

To improve the TCAM performance for a filtering usage, all unused “regions” will be disabled to kept only the route and filter.

For that we need to download a default TCAM firmware configuration file for our T5 NIC to edit its parameters and load it into the NIC

# fetch -o /etc/t5fw.txt 'https://svnweb.freebsd.org/base/head/sys/dev/cxgbe/firmware/t5fw_cfg_hashfilter.txt?view=co'
# sed -i "" -e "s/nclip.*/nclip = 0/" /etc/t5fw.txt
# sed -i "" -e "s/nfilter.*/nfilter = 2000/" /etc/t5fw.txt
# sed -i "" -e "s/nserver.*/nserver = 0/" /etc/t5fw.txt
# sed -i "" -e "s/nhash.*/nhash = 0/" /etc/t5fw.txt
# echo 'hw.cxgbe.config_file="flash"' >> /boot/loader.conf.local
# cxgbetool t5nex0 loadcfg /etc/t5fw.txt

Check the new tuned parameters:

# sysctl -n dev.t5nex.0.misc.devlog | grep -w le
        12           690716      INFO       RES  le configuration: nentries 2048 route 32 clip 32 filter 1024 server 0 active 960 hash 0 nserversram 0

We confirm that server|hash are at 0,

Now the packet drop rate by the TCAM firewall match the generator's 42Mpps:

# /tmp/cxgbe-filter-rate.sh t5nex0
42218564
42147194
42229442
42171263
42210128
42165602
42165483
42223090

And the firewall able to forward all packets without being too busy in the same time:

[root@firewall]~# netstat -ihw 1
           input        (Total)           output
   packets  errs idrops      bytes    packets  errs      bytes colls
       46M     0  5.0k       2.7G        14M     0       801M     0
       46M     0  2.6k       2.7G        14M     0       801M     0
       46M     0  2.1k       2.8G        14M     0       801M     0
       45M     0   515       2.7G        14M     0       801M     0
       46M     0  1.7k       2.7G        14M     0       801M     0
       46M     0   422       2.7G        14M     0       801M     0
       46M     0  3.9k       2.7G        14M     0       801M     0
[root@firewall]~# nstat -I cxl0
 InMpps  OMpps InGbs   OGbs err  TCP Est  %CPU syscalls    csw irq     GBfree
 45.60   0.00  23.35   0.00 1553      1   67.15    393 3168947 1728658 123.75
 45.56   0.00  23.33   0.00 4497      1   66.87    398 3171213 1729358 123.75
 45.53   0.00  23.31   0.00 12418     1   66.76    372 3182570 1734057 123.75
 45.52   0.00  23.31   0.00 9215      1   65.43    371 3183916 1735372 123.75
documentation/examples/dropping_packets_at_high_rate.1581084309.txt.gz · Last modified: 2020/02/07 15:05 by olivier

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