Re: no bug in tcng; tc kbit v. tcng kbps [LARTC] was tcng error

["lartc@manchotnetworks.net" <lartc@manchotnetworks.net>]

hi martin,


On Thu, 2003-11-27 at 20:58, Martin A. Brown wrote:
> Hello Charles,
> 
>  : after slicing and dicing, i found that i had cut and pasted bad syntax,
>  : so i have solved the problem posted in my first message.
> 
> Where did you find the original (I'm hoping it's not one of mine).  If so,
> let me know, and I'll fix it.
indeed, i used some of your examples as well as those included in the
tcng/examples-ng directory, and wshaper.htb to create the following
(i'll post it now as it is untested but functioning less or more)

#define DEVICE eth0
#define DOWNLINK 1024 
#define UPLINK 512 

#include "fields.tc"
#include "ports.tc"

dev DEVICE {
    ingress {
        $policer = SLB( cir DOWNLINK kBps, cbs 60kB, mpu 0b );
        class (<>) if SLB_ok($policer);
        drop if 1;
    }

    egress {
        class (<$high>) if tcp_ACK || 
                           ip_proto = IPPROTO_ICMP ||
                           ip_tos = 0x10 ||
                           tcp_dport = PORT_SSH ||
                           tcp_dport = 8080 ||
                           tcp_dport = 18082 ||
                           tcp_dport = 18083;


        class (<$medium>) if tcp_dport = PORT_HTTP ||
                             tcp_dport = PORT_SMTP ; 

        class (<$low>) if 1;

        htb () {
            class (rate UPLINK bps, burst 6kB) {
                $high = class (prio 1, rate UPLINK kBps)
                    { sfq (perturb 10 sec); };
                $medium = class (prio 2, rate (0.9*UPLINK)kBps)
                    { sfq (perturb 10 sec); };
                $low = class (prio 3, rate (0.8*UPLINK) kBps)
                    { sfq (perturb 10 sec); };
            }
        }
    }
}


>   [ example snipped ]
> 
>  : notice that the UPLINK of 512 kbps (arguably 524288 bps) has been
>  : incorrectly calculated as 64000 bps
> 
> You have not actually found a bug, but rather a historical strangeness
> about the Linux traffic control system.  For reasons of which I'm
> ignorant, the syntax for the "tc" command uses bps for bytes/second.  So,
> 64000 bytes/second is actually 512 kilobits/second ("512 kbps" in common
> usage), but is 512 kbit to the "tc" tool.  Here's a brief chart:
> 
>                       tc syntax       tcng syntax
>                   +----------------+----------------+
>      bytes/second |      bps       |      Bps       |
>       bits/second |      bit       |      bps       |
>  kilobytes/second |     kbps       |     kBps       |
>   kilobits/second |     kbit       |     kbps       |
>                   +----------------+----------------+
> 
> Note that the tcng syntax is exactly the same sort of syntax we use in
> general when discussing speed of WAN links.  "It's a 512 kbps line" means
> it's 512 kilobits per second, but this would be 64000 bytes per second if
> we were writing a "tc" command line.
ah ha -- thanks for this!!!! much clearer now ... perhaps this table is
worthy of inclusion in the howto or a compatibility option in tcng?

curious also on your experience with ingress -- i noticed that using a
Single Leaky Bucket, and playing with the cbs parameter can dramatically
(obviously) affect the ingress policing. is there a general rule of
thumb in calculating the cbs size based on the cir?

cheers

charles




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