--- /dev/null
+
+This documented is slightly dated but should give you idea of how things
+work.
+
+What is it?
+-----------
+
+An extension to the filtering/classification architecture of Linux Traffic
+Control.
+Up to 2.6.8 the only action that could be "attached" to a filter was policing.
+i.e you could say something like:
+
+-----
+tc filter add dev lo parent ffff: protocol ip prio 10 u32 match ip src \
+127.0.0.1/32 flowid 1:1 police mtu 4000 rate 1500kbit burst 90k
+-----
+
+which implies "if a packet is seen on the ingress of the lo device with
+a source IP address of 127.0.0.1/32 we give it a classification id of 1:1 and
+we execute a policing action which rate limits its bandwidth utilization
+to 1.5Mbps".
+
+The new extensions allow for more than just policing actions to be added.
+They are also fully backward compatible. If you have a kernel that doesnt
+understand them, then the effect is null i.e if you have a newer tc
+but older kernel, the actions are not installed. Likewise if you
+have a newer kernel but older tc, obviously the tc will use current
+syntax which will work fine. Of course to get the required effect you need
+both newer tc and kernel. If you are reading this you have the
+right tc ;->
+
+A side effect is that we can now get stateless firewalling to work with tc.
+Essentially this is now an alternative to iptables.
+I wont go into details of my dislike for iptables at times, but
+scalability is one of the main issues; however, if you need stateful
+classification - use netfilter (for now).
+
+This stuff works on both ingress and egress qdiscs.
+
+Features
+--------
+
+1) new additional syntax and actions enabled. Note old syntax is still valid.
+
+Essentially this is still the same syntax as tc with a new construct
+"action". The syntax is of the form:
+tc filter add <DEVICE> parent 1:0 protocol ip prio 10 <Filter description>
+flowid 1:1 action <ACTION description>*
+
+You can have as many actions as you want (within sensible reasoning).
+
+In the past the only real action was the policer; i.e you could do something
+along the lines of:
+tc filter add dev lo parent ffff: protocol ip prio 10 u32 \
+match ip src 127.0.0.1/32 flowid 1:1 \
+police mtu 4000 rate 1500kbit burst 90k
+
+Although you can still use the same syntax, now you can say:
+
+tc filter add dev lo parent 1:0 protocol ip prio 10 u32 \
+match ip src 127.0.0.1/32 flowid 1:1 \
+action police mtu 4000 rate 1500kbit burst 90k
+
+" generic Actions" (gact) at the moment are:
+{ drop, pass, reclassify, continue}
+(If you have others, no listed here give me a reason and we will add them)
++drop says to drop the packet
++pass says to accept it
++reclassify requests for reclassification of the packet
++continue requests for next lookup to match
+
+2)In order to take advantage of some of the targets written by the
+iptables people, a classifier can have a packet being massaged by an
+iptable target. I have only tested with mangler targets up to now.
+(infact anything that is not in the mangling table is disabled right now)
+
+In terms of hooks:
+*ingress is mapped to pre-routing hook
+*egress is mapped to post-routing hook
+I dont see much value in the other hooks, if you see it and email me good
+reasons, the addition is trivial.
+
+Example syntax for iptables targets usage becomes:
+tc filter add ..... u32 <u32 syntax> action ipt -j <iptables target syntax>
+
+example:
+tc filter add dev lo parent ffff: protocol ip prio 8 u32 \
+match ip dst 127.0.0.8/32 flowid 1:12 \
+action ipt -j mark --set-mark 2
+
+3) A feature i call pipe
+The motivation is derived from Unix pipe mechanism but applied to packets.
+Essentially take a matching packet and pass it through
+action1 | action2 | action3 etc.
+You could do something similar to this with the tc policer and the "continue"
+operator but this rather restricts it to just the policer and requires
+multiple rules (and lookups, hence quiet inefficient);
+
+as an example -- and please note that this is just an example _not_ The
+Word Youve Been Waiting For (yes i have had problems giving examples
+which ended becoming dogma in documents and people modifying them a little
+to look clever);
+
+i selected the metering rates to be small so that i can show better how
+things work.
+
+The script below does the following:
+- an incoming packet from 10.0.0.21 is first given a firewall mark of 1.
+
+- It is then metered to make sure it does not exceed its allocated rate of
+1Kbps. If it doesnt exceed rate, this is where we terminate action execution.
+
+- If it does exceed its rate, its "color" changes to a mark of 2 and it is
+then passed through a second meter.
+
+-The second meter is shared across all flows on that device [i am suprised
+that this seems to be not a well know feature of the policer; Bert was telling
+me that someone was writing a qdisc just to do sharing across multiple devices;
+it must be the summer heat again; weve had someone doing that every year around
+summer -- the key to sharing is to use a operator "index" in your policer
+rules (example "index 20"). All your rules have to use the same index to
+share.]
+
+-If the second meter is exceeded the color of the flow changes further to 3.
+
+-We then pass the packet to another meter which is shared across all devices
+in the system. If this meter is exceeded we drop the packet.
+
+Note the mark can be used further up the system to do things like policy
+or more interesting things on the egress.
+
+------------------ cut here -------------------------------
+#
+# Add an ingress qdisc on eth0
+tc qdisc add dev eth0 ingress
+#
+#if you see an incoming packet from 10.0.0.21
+tc filter add dev eth0 parent ffff: protocol ip prio 1 \
+u32 match ip src 10.0.0.21/32 flowid 1:15 \
+#
+# first give it a mark of 1
+action ipt -j mark --set-mark 1 index 2 \
+#
+# then pass it through a policer which allows 1kbps; if the flow
+# doesnt exceed that rate, this is where we stop, if it exceeds we
+# pipe the packet to the next action
+action police rate 1kbit burst 9k pipe \
+#
+# which marks the packet fwmark as 2 and pipes
+action ipt -j mark --set-mark 2 \
+#
+# next attempt to borrow b/width from a meter
+# used across all flows incoming on eth0("index 30")
+# and if that is exceeded we pipe to the next action
+action police index 30 mtu 5000 rate 1kbit burst 10k pipe \
+# mark it as fwmark 3 if exceeded
+action ipt -j mark --set-mark 3 \
+# and then attempt to borrow from a meter used by all devices in the
+# system. Should this be exceeded, drop the packet on the floor.
+action police index 20 mtu 5000 rate 1kbit burst 90k drop
+---------------------------------
+
+Now lets see the actions installed with
+"tc filter show parent ffff: dev eth0"
+
+-------- output -----------
+jroot# tc filter show parent ffff: dev eth0
+filter protocol ip pref 1 u32
+filter protocol ip pref 1 u32 fh 800: ht divisor 1
+filter protocol ip pref 1 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:15
+
+ action order 1: tablename: mangle hook: NF_IP_PRE_ROUTING
+ target MARK set 0x1 index 2
+
+ action order 2: police 1 action pipe rate 1Kbit burst 9Kb mtu 2Kb
+
+ action order 3: tablename: mangle hook: NF_IP_PRE_ROUTING
+ target MARK set 0x2 index 1
+
+ action order 4: police 30 action pipe rate 1Kbit burst 10Kb mtu 5000b
+
+ action order 5: tablename: mangle hook: NF_IP_PRE_ROUTING
+ target MARK set 0x3 index 3
+
+ action order 6: police 20 action drop rate 1Kbit burst 90Kb mtu 5000b
+
+ match 0a000015/ffffffff at 12
+-------------------------------
+
+Note the ordering of the actions is based on the order in which we entered
+them. In the future i will add explicit priorities.
+
+Now lets run a ping -f from 10.0.0.21 to this host; stop the ping after
+you see a few lines of dots
+
+----
+[root@jzny hadi]# ping -f 10.0.0.22
+PING 10.0.0.22 (10.0.0.22): 56 data bytes
+....................................................................................................................................................................................................................................................................................................................................................................................................................................................
+--- 10.0.0.22 ping statistics ---
+2248 packets transmitted, 1811 packets received, 19% packet loss
+round-trip min/avg/max = 0.7/9.3/20.1 ms
+-----------------------------
+
+Now lets take a look at the stats with "tc -s filter show parent ffff: dev eth0"
+
+--------------
+jroot# tc -s filter show parent ffff: dev eth0
+filter protocol ip pref 1 u32
+filter protocol ip pref 1 u32 fh 800: ht divisor 1
+filter protocol ip pref 1 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1
+5
+
+ action order 1: tablename: mangle hook: NF_IP_PRE_ROUTING
+ target MARK set 0x1 index 2
+ Sent 188832 bytes 2248 pkts (dropped 0, overlimits 0)
+
+ action order 2: police 1 action pipe rate 1Kbit burst 9Kb mtu 2Kb
+ Sent 188832 bytes 2248 pkts (dropped 0, overlimits 2122)
+
+ action order 3: tablename: mangle hook: NF_IP_PRE_ROUTING
+ target MARK set 0x2 index 1
+ Sent 178248 bytes 2122 pkts (dropped 0, overlimits 0)
+
+ action order 4: police 30 action pipe rate 1Kbit burst 10Kb mtu 5000b
+ Sent 178248 bytes 2122 pkts (dropped 0, overlimits 1945)
+
+ action order 5: tablename: mangle hook: NF_IP_PRE_ROUTING
+ target MARK set 0x3 index 3
+ Sent 163380 bytes 1945 pkts (dropped 0, overlimits 0)
+
+ action order 6: police 20 action drop rate 1Kbit burst 90Kb mtu 5000b
+ Sent 163380 bytes 1945 pkts (dropped 0, overlimits 437)
+
+ match 0a000015/ffffffff at 12
+-------------------------------
+
+Neat, eh?
+
+
+Wanna write an action module?
+------------------------------
+Its easy. Either look at the code or send me email. I will document at
+some point; will also accept documentation.
+
+TODO
+----
+
+Lotsa goodies/features coming. Requests also being accepted.
+At the moment the focus has been on getting the architecture in place.
+Expect new things in the spurious time i have to work on this
+(particularly around end of year when i have typically get time off
+from work).
+
git://git.onelab.eu / iproute2.git / blobdiff