Tc qdisc

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

After modifying the code, I loaded onto the kernel using the insmod command. Learn more. How to add a new qdisc in linux Ask Question. Asked 5 years, 5 months ago. Active 3 years, 7 months ago. Viewed 3k times.

Have you seen this: tldp. Active Oldest Votes. You have to create the module for your own. I would give you small instruction. However I am still facing the same error! I am getting the following message: open ". Since open ". I updated the answer so debug it with ltrace command.

tc qdisc

Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.

Socializing with co-workers while social distancing. Podcast Programming tutorials can be a real drag. Featured on Meta. Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Dark Mode Beta - help us root out low-contrast and un-converted bits. Related Hot Network Questions. Question feed. Stack Overflow works best with JavaScript enabled.The flexibility and control of Linux traffic control can be unleashed through the agency of the classful qdiscs.

Remember that the classful queuing disciplines can have filters attached to them, allowing packets to be directed to particular classes and subqueues. There are several common terms to describe classes directly attached to the root qdisc and terminal classes. Classess attached to the root qdisc are known as root classes, and more generically inner classes. Any terminal class in a particular queuing discipline is known as a leaf class by analogy to the tree structure of the classes.

Besides the use of figurative language depicting the structure as a tree, the language of family relationships is also quite common. HTB uses the concepts of tokens and buckets along with the class-based system and filter s to allow for complex and granular control over traffic.

With a complex borrowing modelHTB can perform a variety of sophisticated traffic control techniques. One of the easiest ways to use HTB immediately is that of shaping. This queuing discipline allows the user to define the characteristics of the tokens and bucket used and allows the user to nest these buckets in an arbitrary fashion. When coupled with a classifying scheme, traffic can be controlled in a very granular fashion. Below is example output of the syntax for HTB on the command line with the tc tool.

Although the syntax for tcng is a language of its own, the rules for HTB are the same. Unlike almost all of the other software discussed, HTB is a newer queuing discipline and your distribution may not have all of the tools and capability you need to use HTB. The kernel must support HTB; kernel version 2. One of the most common applications of HTB involves shaping transmitted traffic to a specific rate.

All shaping occurs in leaf classes.

Netdev 2.2: TC Workshop

No shaping occurs in inner or root classes as they only exist to suggest how the borrowing model should distribute available tokens. A fundamental part of the HTB qdisc is the borrowing mechanism. Children classes borrow tokens from their parents once they have exceeded rate.

As there are only two primary types of classes which can be created with HTB the following table and diagram identify the various possible states and the behaviour of the borrowing mechanisms.

This diagram identifies the flow of borrowed tokens and the manner in which tokens are charged to parent classes. In order for the borrowing model to work, each class must have an accurate count of the number of tokens used by itself and all of its children. For this reason, any token used in a child or leaf class is charged to each parent class until the root class is reached.

Any child class which wishes to borrow a token will request a token from its parent class, which if it is also over its rate will request to borrow from its parent class until either a token is located or the root class is reached.

Traffic Shaping with tc

So the borrowing of tokens flows toward the leaf classes and the charging of the usage of tokens flows toward the root class. Note in this diagram that there are several HTB root classes.

Each of these root classes can simulate a virtual circuit. An optional parameter with every HTB qdisc object, the default default is 0, which cause any unclassified traffic to be dequeued at hardware speed, completely bypassing any of the classes attached to the root qdisc.

Used to set the minimum desired speed to which to limit transmitted traffic. This can be considered the equivalent of a committed information rate CIRor the guaranteed bandwidth for a given leaf class. Used to set the maximum desired speed to which to limit the transmitted traffic. The borrowing model should illustrate how this parameter is used. This is the size of the rate bucket see Tokens and buckets. HTB will dequeue burst bytes before awaiting the arrival of more tokens.

This is the size of the ceil bucket see Tokens and buckets. HTB will dequeue cburst bytes before awaiting the arrival of more ctokens.Jump to navigation. Rigorously testing a network device or distributed service requires complex, realistic network test environments. Linux Traffic Control tc with Network Emulation netem provides the building blocks to create an impairment node that simulates such networks.

This three-part series describes how an impairment node can be set up using Linux Traffic Control. In the first postLinux Traffic control and its queuing disciplines were introduced. This second part shows which traffic control configurations are available to impair traffic and how to use them. The third and last part will describe how to get an impairment node up and running!

The previous post introduced Linux traffic control and the queuing disciplines that define its behavior.

tc qdisc

It also described what the default qdisc configuration of a Linux interface looks like. Finally, it showed how this default configuration can be replaced by a hierarchy of custom queuing disciplines. Our goal is still to create an Impairment Node device that manipulates traffic between two of its Ethernet interfaces eth0 and eth1while managing it from a third interface e. To impair traffic leaving interface eth0we replace the default root queuing discipline with one of our own.

Note that for a symmetrical impairment, the same must be done on the other interface eth1! Deleting a custom configuration using tc qdisc del actually replaces it with the default. Caveat : It is important to note that Traffic Control uses quite odd units. This means that one kbps equals bytes per second instead of the expected bits per second. On the other hand, kibibit for data and kibibit per second for data rate are both represented by the unit kbit.

To limit the outgoing traffic on an interface, we can use the Token Bucket Filter or tbf qdisc man pageread morepicture. These tokens are refreshed at the desired output rate. Tokens are saved up in a bucket of limited size, so smaller bursts of traffic can still be handled at a higher rate. This qdisc is typically used to impose a soft limit on the traffic, which allows limited burst to be sent at line rate, while still respecting the specified rate on average.

Allows burst s of up to 32kbit to be sent at maximum rate. Packets accumulating a latency of over ms due to the rate limitation are dropped. Using extra options we can limit the peak rate at which bursts themselves are handled. In other words, we can configure the speed at which the bucket gets emptied read morepicture.Definition at line of file qdisc.

Here is the caller graph for this function:. The configuration of the qdisc is derived from the attributes of the specified qdisc. After sending, the function will wait for the ACK or an eventual error message to be received and will therefore block until the operation has been completed. Here is the call graph for this function:. Allocates a new qdisc cache and fills it with a list of all configured qdiscs on all network devices. Queueing Disciplines Traffic Control. Build a netlink message requesting the addition of a qdisc.

Add qdisc. In this case, it is the responsibility of the caller to handle any error messages returned. Returns 0 on success or a negative error code. Build netlink message requesting the update of a qdisc.

Update qdisc. Build netlink message requesting the deletion of a qdisc. Delete qdisc. The message is constructed out of the following attributes: ifindex and parent handle optional, must match if provided kind optional, must match if provided All other qdisc attributes including all qdisc type specific attributes are ignored.

Note It is not possible to delete default qdiscs. Allocate a cache and fill it with all configured qdiscs. Parameters sk Netlink socket result Pointer to store the created cache Allocates a new qdisc cache and fills it with a list of all configured qdiscs on all network devices.

Search qdisc by interface index and parent. Returns pointer to qdisc inside the cache or NULL if no match was found. Search qdisc by interface index and handle. Call a callback for each child class of a qdisc deprecated Deprecated: Use of this function is deprecated, it does not allow to handle the out of memory situation that can occur. Call a callback for each filter attached to the qdisc deprecated Deprecated: Use of this function is deprecated, it does not allow to handle the out of memory situation that can occur.

Build a netlink message requesting the update of a qdisc. Change attributes of a qdisc. Generated on Tue Jan 21 for libnl by 1. Fast Prio. Fair Queue CoDel. Ingress qdisc.

Network Emulator. Call a callback for each child class of a qdisc deprecated More Call a callback for each filter attached to the qdisc deprecated MoreFor any host connected to a network, there is the possibility of network congestion. The network bandwidth is always limited.

As the data flow on a network link increases, a time comes when the quality of service QoS gets degraded. New connections are blocked and the network throughput deteriorates. The incoming and outgoing packets are queued before these are received or transmitted respectively. The queue for incoming packets is known as the ingress queue. Similarly, the queue for outgoing packets is called the egress queue. We have more control over the egress queue as it has packets generated by our host.

We can re-order these packets in the queue, effectively favoring some packets over the rest. The ip -s link command gives the queue capacity qlen in number of packets.

If the queue is full and more packets come; these are discarded and are not transmitted. The ingress queue has packets which have been sent to us by other hosts. We can not reorder them; the only thing we can do is to drop some packets, indicating network congestion by not sending the TCP ACK to the sending host. The sending host gets the hint and slows down transmission of packets to us. For UDP packets, this does not work. Shaping involves delaying the transmission of packets to meet a certain data rate.

This is the way we ensure that the output data rate does not exceed the desired value. Shapers can also smooth out the bursts in traffic. Shaping is done at egress. Scheduling is deciding which packet would be transmitted next.This page is meant as a quick reference for how to use these tools, and as admittedly elementary validation for how accurate each function may or may not be.

I was able to test how accurate this was with a simple ping test. I would have expected a need for a larger sample set, but this shows that the tool is fairly accurate in this regard. An optional correlation may also be added I did not test this. This causes the random number generator to be less random and can be used to emulate packet burst losses. So if you had:. These numbers suggest there is a small amount of overhead to the delay injection. So I ran the test again with a larger value to verify that the overhead is fixed, rather than a percentage.

These numbers look good, suggesting that the amount of overhead for delayed packets is minimal, being noticeable on the low end only. The other explanation could be that our delay is limited by the clock resolution of the kernel, and 3ms is an invalid interval.

But based on these tests, I conclude that adding fixed delay is accurate enough for testing purposes. Note that this is an approximation, not a true statistical correlation. However, it is more common to use a distribution to describe the delay variation. The tc tool includes several tables to specify a non-uniform distribution normal, pareto, paretonormal. Again, I would conclude that the approximation is just that, an approximation. This should be good enough for testing purposes.

When using the limit parameter with a token bucket filter, it specifies the number of bytes that can be queued waiting for tokens. From the man page:. You can also specify this the other way around by setting the latency parameter, which specifies the maximum amount of time a packet can sit in the TBF. The latter calculation takes into account the size of the bucket, the rate and possibly the peakrate if set.

tc(8) - Linux man page

These two parameters are mutually exclusive. Unfortunately, the netem discipline does not include rate control. The first command sets up our root qdisc with a handle named which is equivalent to 1: since the minor number of a qdisc is always 0 and a packet delay of ms.

The second command creates a child class with 1: as the parent since has the same major number. This child class could now be referenced using its handle,and its children would be, etc. The buffer value tells us the size of the bucket in bytes. A little more info on the buffer parameter, from the man page:. Size of the bucket, in bytes. This is the maximum amount of bytes that tokens can be available for instantaneously. In general, larger shaping rates require a larger buffer.

If your buffer is too small, packets may be dropped because more tokens arrive per timer tick than fit in your bucket. The minimum buffer size can be calculated by dividing the rate by HZ. Controlling the rate with tc is by far the most complicated feature. Ok, so now you can shape outgoing traffic! But what if you only want to shape traffic on a certain port, or traffic going to a particular IP address? With filters, you can do just that.Installation TC bundled with iproute2 package in Debian.

Using queueing we control the data flow. In a router you might want control the traffic distributing inside your network.

tc qdisc

Several queueing disciplines qdisc can be used with tc. Choose a qdisc based on your requirements. Simple Classless Queueing Disciplines It has no configurable internal subdivisions.

The classless queueing disciplines accept data, then reschedule, delay or drop based on queueing disciplines qdisc. TBF for details. It changes its hashing algorithm within an interval. No single session will able to dominate outgoing bandwidth. SFQ for details. Testing Classless Queueing To check the status run: tc -s -d qdisc show dev eth1 To remove it: tc qdisc del dev eth1 root Classful Queueing Disciplines It helps to set different kinds of traffic priority. Classful Queueing for details.

HTB manual from devik for details. Video streaming will get the lowest priority. Creating root 1: and using HTB default 6 means follow if no rule matched tc qdisc add dev eth1 root handle 1: htb default 6 tc class add dev eth1 parent 1: classid htb rate 2mbit ceil 2mbit Creating leaf class prio represents priority, and 0 means high priority tc class add dev eth1 parent classid htb rate 1mbit ceil 1.

Priority low - prio 5. You can get the IP address using "iptraf" tool tc class add dev eth1 parent classid htb rate 0. Wiki Login. Hosting provided by Metropolitan Area Network Darmstadt.

thoughts on “Tc qdisc

Leave a Reply

Your email address will not be published. Required fields are marked *