NetworkPro on Quality of Service - MikroTik Wiki

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Applies to

RouterOS:

v2.9, v3, v4, v5

modified on 20 November 2011 at 20:02 36,477 views

NetworkPro on Quality of Service

Contents [hide]1 Theory

1.1 TCP control for QoS1.2 The TCP Window1.3 Control is Outbound1.4 QoS Packet Flow & Double Control1.5 HTB Queue Tree VS Simple Queue1.6 Guaranteeing Bandwidth with the HTB "Priority" Feature1.7 Guaranteeing Priority with the Limit-At setting1.8 Queue Type1.9 Queue Size1.10 Lends VS Borrows1.11 Adjusting the Max-Limit

2 QoS Example3 Test Setups4 Heads-up on Layer 2 devices, hidden buffers and performance degradation5 More Information6 Questions and Contradictions

TheoryLet's begin with some theory that I've accumulated over the years.It should save your life when dealing with Bandwidth Management and QoS.

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TCP control for QoSwikipedia.org/wiki/Bandwidth_management TCP rate control - artificially adjusting TCP window size as well ascontrolling the rate of ACKs being returned to the sender.

Note: The information at The Wikipedia.org website is considered inaccurate, biased, too general, or insecure

RouterOS HTB can adjust the TCP window by dropping packets out of the set bandwidth limit.

Note: The TCP ACKs should never be dropped! (refer to the example at the end of the article)

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More general information on TCP and the ACK packet: wikipedia.org/wiki/ACK_(TCP)

The TCP WindowA TCP window is the amount of data a sender can send on a particular TCP connection before it gets an acknowledgment(ACK packet) back from the receiver that it has gotten some of it.

For example if a pair of hosts are talking over a TCP connection that has a TCP window size of 64 KB (kilobytes), thesender can only send 64 KB of data and then it must stop and wait for an acknowledgment from the receiver that someor all of the data has been received. If the receiver acknowledges that all the data has been received then the sender isfree to send another 64 KB. If the sender gets back an acknowledgment from the receiver that it received the first 32 KB(which could happen if the second 32 KB was still in transit or it could happen if the second 32 KB got lost or dropped,shaped), then the sender could only send another 32 KB since it can't have more than 64 KB of unacknowledged data.

The primary reason for the window is congestion control. The whole network connection, which consists of the hosts atboth ends, the routers in between and the actual physical connections themselves (be they fiber, copper, satellite orwhatever) will have a bottleneck somewhere that can only handle data so fast. Unless the bottleneck is the sending speedof the transmitting host, then if the transmitting occurs too fast the bottleneck will be surpassed resulting in lost data. TheTCP window throttles the transmission speed down to a level where congestion and data loss do not occur.

Control is OutboundInbound traffic for router - traffic that hits routers' interfaces, no matter from what side - Internet or local - it will bereceived by interface no matter what, even malformed packets, and you cannot do anything with these. Outbound trafficfor router - traffic that goes out of routers' interfaces, no matter of direction, to your network or out of it. This is whereyou can set up queues and prioritize, and limit!

HTB allows us to work with the Outgoing traffic (the traffic that is leaving the router via any interface).

Example1: Client sends out 10Mbps UDP traffic - this traffic will get to the routers local interface, but in one of the HTBs(global-in, global-total, global-out or outgoing interface) it will be shaped to (lets say) 1Mbps. So only 1Mbps will leavethe router. But in the next second the client can send 10Mbps once again and we will shape them again.

Example2: Client sends out 10Mbps TCP traffic - this traffic will get to the routers local interface, but in one of the HTBs(global-in, global-total, global-out or outgoing interface) it will be shaped to (lets say) 1Mbps. So only 1Mbps will leavethe router. Source gets ACK replies only for 1Mbps of 10Mbps, so source, in the next second, will send a little more than1Mbps of TCP traffic. (due to TCP Window adjusting to our shaped bandwidth)

There are 4 ways we can look at a flow:1) client upload that router receives on the local interface2) client upload that router sends out to the Internet3) client download that router receives on the public interface4) client download that router sends out to the customer

1) and 3) - is Inbound traffic2) and 4) - is Outbound traffic

HTB can control 1) when its sent out as 2) and 3) when its sent out as 4)

Note: Connections can't be upload or download, packets are. For example TCP connections have traffic in bothdirections.

QoS Packet Flow & Double Control



Working with packets for bandwidth management is done in this order:

1. Mangle chain prerouting2. HTB global-in3. Mangle chain forward4. Mangle chain postrouting5. HTB global-out6. HTB out interface

So, in one router, you can do:

a) in #1+#2 - first marking & shaping, in #3+#5 - second marking & shapingb) in #1+#2 - first marking & shaping, in #3+#6 - second marking & shapingc) in #1+#2 - first marking & shaping, in #4+#5 - second marking & shapingd) in #1+#2 - first marking & shaping, in #4+#6 - second marking & shaping

In his presentation http://mum.mikrotik.com/presentations/CZ09/QoS_Megis.pdfJanis Megis says that creating priorities separately for each client is suicide - there is no hardware that can handle smallqueue tree for every user (if you have 1000 of them). So he has the next best thing, which is as close as possible to thedesired behavior.

The main Idea of the setup is to have two separate QoS steps:

1) In the first step we prioritize traffic, we are making sure that traffic with higher priority has more chance to get to thecustomers than traffic with lower priority.

Example: We have total of 100Mbps available, but clients at this particular moment would like to receive 10Mbps ofPriority=1 traffic, 20Mbps of Priority=4 and 150Mbps of Priority=8. Of course after our prioritization and limitation 80Mbpsof priority=8 will be dropped. And only 100Mbps total will get to the next step.

2) Next step is per-user limitation, we already have only higher priority traffic, but now we must make sure that someuser will not overuse it, so we have PCQ with limits.

This way we get virtually the same behavior as "per user prioritization".

So the plan is to mark by traffic type in prerouting and limit by traffic type in global-in. Then remark traffic by IPaddresses in forward and limit in global-out.

1) you need to mark all traffic, that would be managed by one particular Queue, at the same place (prerouting) 2) if you use global-total/in/out or Queue Simple or if you use Queue Tree and you do not mark connections first, youmust mark upload and download for every type of traffic separately4) if you do not use a simple PCQ, you must have a parent queue, that has max-limit and (lets say) parent=global-in, all



other queues parent=5) you need 2 sets of those queues - one for upload, one for download

Create packet marks in the mangle chain "Prerouting" for traffic prioritization in the global-in QueueLimitation for in mangle chain "forward" marked traffic can be placed in the "global-out" or interface queue

If queues will be placed in the interface queuesqueues on the public interface will capture only client uploadqueues on the local interface will capture only client's download

If queues will be placed in global-outdownload and upload will be limited together (separate marks needed)

Double Control is achieved with Queue Tree

HTB Queue Tree VS Simple QueueQueue Tree is an unidirectional queue in one of the HTBs. It is also The way to add a queue on a separate interface(parent:ether1/pppoe1..) - this way it is possible to ease mangle configuration - you don't need separate marks peroutgoing interface.Also it is possible to have double queuing, for example: prioritization of traffic in global-in or global-out, and limitationper client on the outgoing interface.

Note: If you have simple queues and queue tree in the same HTB - simple queues will get the traffic first, so theQueue Tree after that will not work.

Queue Tree is not ordered - all traffic passes it together, where as with Queue Simple - traffic is evaluated by each SimpleQueue, one by one, from top to bottom. If the traffic matches the Simple Queue - then its managed by it, otherwise itspassed down.

Each simple queue creates 3 separate queues:One in global-in ("direct" part)One in Global-out ('reverse" part)One in Global-total ('total" part)Simple queues are ordered - similar to firewall rulesfurther down = longer packet processingfurther down = smaller chance to get trafficso its necessary to reduce the number of queues

In the case of Simple Queues, the order is for 'catching traffic' (mangle) and the "priority" is the HTB feature.

http://wiki.mikrotik.com/wiki/Queue

Guaranteeing Bandwidth with the HTB "Priority" FeatureSee the official article http://wiki.mikrotik.com/wiki/Manual:HTB

We already know that limit-at (CIR) to all queues will be given out no matter what.

Priority is responsible for distribution of remaining parent queues traffic to child queues so that they are able to reachmax-limit

Note: Although no one nowhere talks about it, my conclusion is that this "reaching of max-limit" gives time to eachleaf in a round-robin manner. Where as the tests show that reaching of limit-at is a process that will give betterperformance to priority traffic.

Queue with higher priority will reach its max-limit before the queue with lower priority. 8 is the lowest priority, 1 is thehighest.



Make a note that priority only works:

for leaf queues - priority in inner queue have no meaning.if max-limit is specified (not 0)

"Priority" feature (1..8) : Prioritize one child queue over other child queue. Does not work on parent queues (if queue hasat least one child). One is the highest, eight is the lowest priority. Child queue with higher priority will have chance toreach its limit-at before child with lower priority (confirmed) and after that child queue with higher priority will havechance to reach its max-limit before child with lower priority.

Note: The "Priority" feature has nothing to do with the "bursts" HTB feature .

Guaranteeing Priority with the Limit-At settingPriority traffic will have better performance in its limit-at than in between limit-at and max-limit. Currently for me thismeans, although no one nowhere talks about it, that a leaf with higher "priority" setting is given more transmission timewhen the bandwidth its trying to consume is within its limit-at.

A queue tree with all default-small leaf queues, will degrade performance by 10ms on a leaf queue that has more trafficthan whats configured in its limit-at. If traffic is within this limit-at - performance is OK - no additional delays could benoticed. No information about this could be seen from any columns inside WinBox - Bytes, Packets, Dropped, Lends,Borrows, Queued Bytes, Queued Packets. Changing to Queue Type "default" (50 packets) did not increase the delay anddid not change it noticably.

Queue TypeQueue type applies only to Child queues. It doesn't matter what queue type you set for the parent. The parent is onlyused to set the max-limit and to group the leaf queues.

My tests show that PCQ by dst-port for example will have better results than default and default-small. SFQ as thewireless default- as well. So much in fact that I would never use a FIFO queue again. I wonder why its the default onEthernet. I guess its because FIFO uses as little resources as possible.

Note: PCQ may not be optimized for high speeds like 20m, 90m... when used in combination with multiple gateways.More testing will be done soon.

More information:http://wiki.mikrotik.com/wiki/Queue#Queue_Types

Queue Sizehttp://wiki.mikrotik.com/wiki/Manual:Queue_Size

Lends VS Borrowsa Lend happens when the packet is treated as limit-ata Borrow happens when the packet is between limit-at and max-limit

Adjusting the Max-LimitWithout setting the max-limit properly, the HTB Queue Tree will not drop enough low-priority packets, so the bandwidthcontrol would be lost. In order to have Control - we must set the max-limit to a lower value - 99.99% to 85% of thetested throuput of the bottleneck.Also to keep control our limi-ats combined must not be more than the max-limit.

I know it bugs you to set only 80% of your available bandwidth in these fields but this is required. There will be a



bottleneck somewhere in the system and QoS can only work if the bottleneck is in your router where it has some control.The goal is to force the bottleneck to be in your router as opposed to some random location out on the wire over whichyou have no control.

The situation can become confusing because most ISPs offer only "Best effort" service which means they don't actuallyguarantee any level of service to you. Fortunately there is usually a minimum level that you receive on a consistent basisand you must set your QoS limits below this minimum. The problem is finding this minimum. For this reason start with80% of your measured speed and try things for a couple of days. If the performance is acceptable you can start to inchyour levels up. But I warn you that if you go even 5% higher than you should be your QoS will totally stop working (justtoo high) or randomly stop working (high when your ISP is slow). This can lead to a lot of confusion on your part so takemy advice and get it working first by conservatively setting these speeds and then optimize later..

QoS ExampleUpload QoS for ADSL, tested and seems working good enough. Can be easily adapted and upgraded for allneeds - up/down, ADSL or dedicated optic.

/ip firewall mangleadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_1_Up dst-port=80,443 packet-size=0-666 protocol=tcp tcp-flags=syn comment=QoSadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_1_Up dst-port=80,443 packet-size=0-123 protocol=tcp tcp-flags=ackadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_1_Up dst-port=53,123 protocol=udpadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_2_Up dst-port=80,443 connection-bytes=0-1000000 protocol=tcpadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_2_Up dst-port=110,995,143,993,25,20,21 packet-size=0-666 protocol=tcp tcp-flags=synadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_2_Up dst-port=110,995,143,993,25,20,21 packet-size=0-123 protocol=tcp tcp-flags=ackadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_3_Up packet-size=0-666 protocol=tcp tcp-flags=synadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_3_Up packet-size=0-123 protocol=tcp tcp-flags=ackadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_4_Up dst-port=110,995,143,993,25,20,21 protocol=tcpadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_4_Up dst-port=80,443 connection-bytes=1000000-0 protocol=tcpadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_8_Up p2p=all-p2padd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_7_Upadd action=mark-packet chain=postrouting out-interface=ADSL1 passthrough=no new-packet-mark=QoS_2_Up src-port=8291 comment=WinBox

/queue treeadd max-limit=666K name=QoS_ADSL1_Up parent=ADSL1add name=QoS_1 packet-mark=QoS_1_Up parent=QoS_ADSL1_Up priority=1add name=QoS_2 packet-mark=QoS_2_Up parent=QoS_ADSL1_Up priority=2add name=QoS_3 packet-mark=QoS_3_Up parent=QoS_ADSL1_Up priority=3add name=QoS_7 packet-mark=QoS_7_Up parent=QoS_ADSL1_Up priority=7add name=QoS_8 packet-mark=QoS_8_Up parent=QoS_ADSL1_Up priority=8add name=QoS_4 packet-mark=QoS_4_Up parent=QoS_ADSL1_Up priority=4

Note: This Mangle setup does not take into account any DSCP values of incoming traffic. To use the DSCP values -they must be recognised and the packets marked with the according packet-mark. This would help with VoIPapplications for example



Note: This Mangle setup will not catch most BitTorrent traffic. To catch that and put it in priority 8, you should useLayer 7 matchers. Some torrent traffic will still be unrecognized since BT inc takes care to hide their protocols betterwith each version. To improve overall QoS consider using latest versions of BT inc torrent clients across your networkbecause of the TP .

Note: To optimize Mangle rules for less CPU consumption, you should try to mark connections first with connectionstate new, then mark the packets of the marked connections. Also try implementing the passthrough optionManual:IP/Firewall/Mangle

Note: This HTB Queue Tree should be upgraded to a structure like Example 3 in the HTB article . Otherwise if left asshown, the leafs will be treated in a round-robin manner which could degrade performance for priority traffic. Butmost notably - traffic from the lower priorities would not even have a chance and will be dropped. Still this exampleworks beautifully in production.

Note: To fix traceroute - ICMP needs to have priority, for example 4.

Note: Recommended queue sizes are small.

Test SetupsTo study packet queues one can use a couple of RouterOS machines. One with packet queues and the other to generatetraffic with Bandwidth Test. If sniffer is needed - the built-in is used.

So far testing with VMWare has shown wrong resulst with TCP. I have achieved correct behaviour with live RouterBOARDSas well as with Oracle VM VirtualBox.



This screenshot shows the easiest test scenario.First addresses are assigned to ether1 - 192.168.56.55/24, 192.168.56.56/32 to 59/32Then packets are marked in prerouting by their dst addressAfter that a Queue Tree is built as shown, with one leaf per packet mark.So when generating traffic with the bandwidth test and with ping tools to one of the different IPs, you will be simulatingyour different priority traffic.Then its up to ones need and imagination to experiment.



In the picture you can see an example laboratory setup. This graphic diagram I made for my MSc thesis presentation.

Heads-up on Layer 2 devices, hidden buffers and performance degradationMake sure Flow Control is turned off on everything that passes Ethernet frames - switches, ports, devices.Avoid using QoS or priority on cheap switches due to limitations in the level of control over the queues on those devices.

More InformationHead of Line blocking http://wiki.mikrotik.com/wiki/Category:QoShttp://www.mikrotik.com/testdocs/ros/3.0/qos/queue.phphttp://en.wikipedia.org/wiki/Quality_of_Service

Questions and ContradictionsIf you have found a contradiction and if you have a question - please ask in the forum. http://forum.mikrotik.com/

Category: QoS

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