Linux Traffic Control

Transcription

1 Linux Traffic Control Author: Ivan Delchev Course: Networks and Distributed Systems Seminar Instructor: Prof. Juergen Schoenwaelder International University Bremen, Spring 2006

2 Processing of Network Data Fig. 1: Processing of network data by the linux kernel [2] Packets arrive via an input interface Input Traffic Control (policing) Input De-Multiplexing determine whether packet is for local node "Forwarding" selects the output interface, the next hop etc. Output Traffic Control Device driver picks up packets and emits them on the network.

3 Definition of Traffic Control(TC) Sets of queuing systems and mechanisms by which packets are received and transmitted on a router Determine which packets to accept and at what rate on the input of an interface Determine which packets to transmit in what order and at what rate on the output of an interface

4 Why Use Traffic Control? Lack of differentiation between types of flows. Traffic control allows an administrator to queue packets differently based on attributes of the packets leading to: More predictable usage of network resources Less volatile contention for network resources

5 Common Traffic Control Solutions Limit total bandwidth to a known rate Limit the bandwidth of a particular user Reserve bandwidth for a particular application Prefer latency sensitive traffic Ensure that a particular type of traffic is dropped

6 Terms Queue a buffer containing a finite number of items waiting for an action or service. Typically FIFO. Flow - a distinct connection or conversation between two hosts. Any unique set of packets between two hosts can be regarded as a flow. Token - A particular message or bit pattern that signifies permission to transmit. Bucket - type of data buffer, containing a number of tokens

7 Traditional Elements of TC Shaping - delay packets to meet a desired rate. Scheduling - arrange and/or rearrange packets for output Classifying - sort or separate traffic into queues for different treatment Policing - measure and limit traffic in a particular queue Dropping - discard an entire packet, flow or classification Marking - a mechanism by which a packet is altered.

8 Classless Queuing Disciplines 1 Fig. 2 FIFO Fast queuing discipline[1] Classless qdisc - a qdisc with no configurable internal subdivisions FIFO (pfifo and bfifo) no shaping or rearranging of packets. FIFO Fast(pfifo_fast) default for all interfaces. Provides three different bands (individual FIFOs) for separating traffic.

9 Classless Queuing Disciplines 2 Fig. 3 Stochastic Fair Queuing [1] Stochastic Fair Queuing(SFQ) Goal - fairly distribute opportunity to transmit data among flows Uses a hash function to separate the traffic Dequeue queues in a round-robin fashion Perturb hash function periodically to avoid unfairness

10 Classless Queuing Disciplines 3 Token Bucket Filter(TBF) Goal - shape/limit traffic transmitted on an interface Generate tokens at a desired rate Send packets only if there are sufficient tokens available. Fig. 4 Token Bucket Filter [1]

11 Classful Queuing Disciplines 1 Fig. 5: Example of a queuing discipline containing filters and classes [2] Classful qdiscs can contain filters and classes Filters distinguish among different classes of packets and process each class in a specific way e.g. pass to different internal class object The queuing discipline on the respective class takes care

12 Classful Queuing Disciplines 2 Hierarchical Token Bucket(HTB) HTB is an arbitrary number of token buckets arranged in a hierarchy User can define the characteristics of the tokens and buckets used and to nest these buckets in an arbitrary fashion. rate - sets the guaranteed bandwidth available for a given class ( tokens bucket) ceil - sets the maximum bandwidth that class is allowed to consume. ( ctokens bucket)

13 Classful Queuing Disciplines 3 HTB Contd. Fig. 6 Hierarchical link-sharing structure using HTB [2] Use one physical link to simulate several slower links and send different kinds of traffic on different simulated links

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15 References [1] [2]