Help understanding iproute2 and tc scripts Post: 302552735

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Special Forums IP Networking Help understanding iproute2 and tc scripts Post 302552735 by shodg001 on Monday 5th of September 2011 10:09:08 AM

09-05-2011

Registered User

Help understanding iproute2 and tc scripts

Hi all,

I am new to linux routing and would like to keep a possible running dialog about some scripts I have been studying and what the different parts of them mean. We are using Openwrt backfire along with openvpn and Swyx as VoIP. My goal is to eventually implement some QoS using dsmark, but I want to understand what I am doing before I put anything into production.

Here is the first part of the script I have a question about:

# tc qdisc add dev eth0 handle ffff: ingress
# tc filter add dev eth0 parent ffff: protocol ip prop 1 u32 \ match ip protocol 17 0xff police rate 240kbit \ burst 15kb continue flowid :1

I think I comprehend everything except 'burst 15kb continue flowid :1'. What does that mean, and what is the point of it?

According to the author: opalsoft(.) net/qos/VoIP(.) htm

Our first ingress filter, priority 1, catchs UDP packets (UDP is protocol number 17) policing them up to 240kbits. Then we can manage with this 15 conversations of 16kbps each. Check your VoIP implementation to know the bandwidth requeriment per session and adjust your command according.

Now our valuable packets are in the outgoing queue *(What is the outgoing queue? out going as in the LAN side or WAN side?)*as fast as we can. For this side I suggest a prio queue to kick them asap to the outgoing interface (again which one is outgoing?); then something like this can help:

Here is the second part that is confusing:

# tc qdisc add dev eth1 root handle 1: prio
# tc filter add dev eth1 parent 1:0 protocol ip prio 1 \ handle 1 tcindex classid 1:1

Is this filter for stuff coming from the WAN to the LAN, the other way or both?
I am a bit confused on what constitutes ingress and egress. If the WAN (eth1) gets packets thats ingress, but then if eth1 sends the packets to eth0 (LAN) thats then egress?

Sorry to be long winded, but I think I need to chat a bit to work out all the stuff I read. Thank you in advance!

-Shawn

shodg001

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LEARN ABOUT OPENDARWIN

tc-route

Route classifier in tc(8)					       Linux						 Route classifier in tc(8)

NAME

       route - route traffic control filter

SYNOPSIS

       tc filter ... route [ from REALM | fromif TAG ] [ to REALM ] [ classid CLASSID ] [ action ACTION_SPEC ]

DESCRIPTION

       Match  packets  based  on routing table entries. This filter centers around the possibility to assign a realm to routing table entries. For
       any packet to be classified by this filter, a routing table lookup is performed and the returned realm is used to  decide  on  whether  the
       packet is a match or not.

OPTIONS

       action ACTION_SPEC
	      Apply an action from the generic actions framework on matching packets.

       classid CLASSID
	      Push matching packets into the class identified by CLASSID.

       from REALM
       fromif TAG
	      Perform source route lookups.  TAG is the name of an interface which must be present on the system at the time of tc invocation.

       to REALM
	      Match if normal (i.e., destination) routing returns the given REALM.

EXAMPLES

       Consider the subnet 192.168.2.0/24 being attached to eth0:

	      ip route add 192.168.2.0/24 dev eth0 realm 2

       The following route filter will then match packets from that subnet:

	      tc filter add ... route from 2 classid 1:2

       and pass packets on to class 1:2.

NOTES

       Due  to	implementation	details,  realm  values  must  be  in  a  range from 0 to 255, inclusive. Alternatively, a verbose name defined in
       /etc/iproute2/rt_realms may be given instead.

SEE ALSO

       tc(8), ip-route(8)

iproute2							    21 Oct 2015 					 Route classifier in tc(8)

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