Traffic control in Linux: classifiend and prioritizing traffic 2/2

According to the manual, tc uses the following rules for bandwidth definitions:

mbps = 1024 kbps = 1024 * 1024 bps => byte/s
mbit = 1024 kbit => kilo bit/s.
mb = 1024 kb = 1024 * 1024 b => byte
mbit = 1024 kbit => kilo bit.

Internally, the number is stored in bps and b.

When tc prints the rate, it uses following :

1Mbit = 1024 Kbit = 1024 * 1024 bps => byte/s

The kernel will honor the TOS field in the packets (Type Of Service), which is defined as:

TOS     Bits  Means                    Linux Priority    Band
------------------------------------------------------------
0x0     0     Normal Service           0 Best Effort     1
0x2     1     Minimize Monetary Cost   1 Filler          2
0x4     2     Maximize Reliability     0 Best Effort     1
0x6     3     mmc+mr                   0 Best Effort     1
0x8     4     Maximize Throughput      2 Bulk            2
0xa     5     mmc+mt                   2 Bulk            2
0xc     6     mr+mt                    2 Bulk            2
0xe     7     mmc+mr+mt                2 Bulk            2
0x10    8     Minimize Delay           6 Interactive     0
0x12    9     mmc+md                   6 Interactive     0
0x14    10    mr+md                    6 Interactive     0
0x16    11    mmc+mr+md                6 Interactive     0
0x18    12    mt+md                    4 Int. Bulk       1
0x1a    13    mmc+mt+md                4 Int. Bulk       1
0x1c    14    mr+mt+md                 4 Int. Bulk       1
0x1e    15    mmc+mr+mt+md             4 Int. Bulk       1

As an example, from the RFC 1349 we can see these definitions:

TELNET -> 1000 (8 in decimal) => minimize delay
FTP Control -> 1000 (8 in decimal) => minimize delay
FTP Data -> 0100 (4 in decimal) => maximize throughput

Modifying the TOS field on the traffic we can get our on line games to have priority over the rest of the network : (ok, perhaps some other uses? :)

# iptables -t mangle -N games
# iptables -t mangle -A games -p tcp -s <my playstation ip> -j RETURN
# iptables -t mangle -A games -j TOS --set-tos Maximize-Throughput
# iptables -t mangle -A games -j RETURN
# iptables -t mangle -A POSTROUTING -p tcp -m tos --tos Minimize-Delay -j games

Now, let's put the scenario that we have a Internet line connected to our eth0 with a bandwidth of 10 MBPS. We want to reserve 30% of it to browse internet, 30% for our ftp server and the rest for a online game which uses the port 20000. First we create the qdisc:

# tc qdisc add dev eth0 root handle 1: htb default 90

# tc class add dev eth0 parent 1: classid 1:1 htb rate 10000 kbit ceil 10000 kbit

(we set the root class as 10MBPS)

Next classes will have 30%, 30% and 40% of the bandwidth:

# tc class add dev eth0 parent 1:1 classid 1:10 htb rate 3000kbit ceil 10000kbit

# tc class add dev eth0 parent 1:1 classid 1:20 htb rate 3000kbit ceil 10000 kbit
# tc class add dev eth0 parent 1:1 classid 1:30 htb rate 4000kbit ceil 10000 kbit

Now we will use the Stochastic Fairness Queueing (SFQ) to settle the defined classes. We will use the recommended value of 10 seconds for the queue:

# tc qdisc add dev eth0 parent 1:10 handle 10: sfq perturb 10
# tc qdisc add dev eth0 parent 1:20 handle 20: sfq perturb 10
# tc qdisc add dev eth0 parent 1:30 handle 30: sfq perturb 10

To finish, we will use the tc to identify traffic for each class (explained in the previous post). Destination port to browse will be 80, source port for our FTP server is 20 and the destination port for the game is 20000:

# tc filter add dev eth0 parent 1:0 protocol ip u32 match ip dport 80 0xffff classid 1:10
# tc filter add dev eth0 parent 1:0 protocol ip u32 match ip sport 20 0xffff classid 1:20
# tc filter add dev eth0 parent 1:0 protocol ip u32 match ip dport 20000 0xffff classid 1:30

That's it. Is interesting to have a look to at the manual for other options like bursting, etc.