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iptos(4) [osf1 man page]

iptos(4)						     Kernel Interfaces Manual							  iptos(4)

NAME
iptos - Defines the IP Type Of Service (TOS) for FTP and Telnet SYNOPSIS
/etc/iptos DESCRIPTION
The /etc/iptos file configures the Type Of Service (TOS) of the Internet Protocol (IP) used by FTP and Telnet. The TOS field in the Internet datagram is to specify how the datagram should be handled. It is a mechanism to allow control information to have precedence over data. Generally, protocols that are involved in direct interaction with a human should select low delay, while data transfers that involve large blocks of data need high throughput. Finally, high reliability is most important for datagram-based Internet management functions. In the Tru64 UNIX operating system, the ftp and telnet applications and the ftpd and telnetd daemons allow the configuring of TOS values. These applications check to see if the /etc/iptos file exists; if the file exists, the applications obtain the TOS value from the file and use that value to set the TOS field. If the /etc/iptos file does not exist, the applications default to the following TOS values recom- mended by RFC1060: Low delay High throughput Low delay Users who want to configure their own TOS values for the TOS field should provide the /etc/iptos file. Note Most IP routers do not differentiate based on TOS, and therefore providing values other than the default would have no affect. You should not change the default values for FTP and Telnet. Each entry should consist of a single line of the form: Application Proto TOS-bits aliases The entry fields contain the following information: The name of an application TOS entry. The protocol name for which the entry is appro- priate. The TOS value to be set for the entry. A list of aliases that exist for the entry. Items on an entry line are separated by any number of blanks, tabs, or combination of blanks and tabs. A number sign (#) indicates that the rest of the line is a comment and is not interpreted by routines that search the file. Blank lines in the file are ignored. Valid TOS entry names are ftp-control and ftp-data for FTP and telnet for Telnet. The TOS value for the entry should be one of the following hexadecimal numbers, corresponding to TOS bits: Low delay High throughput High reliability If you need to disable the use of TOS bits, because you are having troubling communicating with a TCP/IP host that doe not conform entirely with the IP specification, you can disable the TOS bits by using the the following settings in the /etc/iptos file: # # Format of this file: # Application Proto TOS-bits aliases # ftp-control tcp 0x0 ftp-data tcp 0x0 telnet tcp 0x0 EXAMPLES
The following example shows typical entries in the /etc/iptos file: # # Format of this file: # Application Proto TOS-bits aliases # ftp-control tcp 0x10 ftp-data tcp 0x08 telnet tcp 0x10 RELATED INFORMATION
RFC1060, ftp(1), telnet(1), ftpd(8), telnetd(8) delim off iptos(4)

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PRIO(8) 							       Linux								   PRIO(8)

NAME
PRIO - Priority qdisc SYNOPSIS
tc qdisc ... dev dev ( parent classid | root) [ handle major: ] prio [ bands bands ] [ priomap band band band... ] [ estimator interval timeconstant ] DESCRIPTION
The PRIO qdisc is a simple classful queueing discipline that contains an arbitrary number of classes of differing priority. The classes are dequeued in numerical descending order of priority. PRIO is a scheduler and never delays packets - it is a work-conserving qdisc, though the qdiscs contained in the classes may not be. Very useful for lowering latency when there is no need for slowing down traffic. ALGORITHM
On creation with 'tc qdisc add', a fixed number of bands is created. Each band is a class, although is not possible to add classes with 'tc qdisc add', the number of bands to be created must instead be specified on the command line attaching PRIO to its root. When dequeueing, band 0 is tried first and only if it did not deliver a packet does PRIO try band 1, and so onwards. Maximum reliability packets should therefore go to band 0, minimum delay to band 1 and the rest to band 2. As the PRIO qdisc itself will have minor number 0, band 0 is actually major:1, band 1 is major:2, etc. For major, substitute the major num- ber assigned to the qdisc on 'tc qdisc add' with the handle parameter. CLASSIFICATION
Three methods are available to PRIO to determine in which band a packet will be enqueued. From userspace A process with sufficient privileges can encode the destination class directly with SO_PRIORITY, see socket(7). with a tc filter A tc filter attached to the root qdisc can point traffic directly to a class with the priomap Based on the packet priority, which in turn is derived from the Type of Service assigned to the packet. Only the priomap is specific to this qdisc. QDISC PARAMETERS
bands Number of bands. If changed from the default of 3, priomap must be updated as well. priomap The priomap maps the priority of a packet to a class. The priority can either be set directly from userspace, or be derived from the Type of Service of the packet. Determines how packet priorities, as assigned by the kernel, map to bands. Mapping occurs based on the TOS octet of the packet, which looks like this: 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | | | | |PRECEDENCE | TOS |MBZ| | | | | +---+---+---+---+---+---+---+---+ The four TOS bits (the 'TOS field') are defined as: Binary Decimal Meaning ----------------------------------------- 1000 8 Minimize delay (md) 0100 4 Maximize throughput (mt) 0010 2 Maximize reliability (mr) 0001 1 Minimize monetary cost (mmc) 0000 0 Normal Service As there is 1 bit to the right of these four bits, the actual value of the TOS field is double the value of the TOS bits. Tcpdump -v -v shows you the value of the entire TOS field, not just the four bits. It is the value you see in the first column of this table: TOS Bits Means Linux Priority Band ------------------------------------------------------------ 0x0 0 Normal Service 0 Best Effort 1 0x2 1 Minimize Monetary Cost 0 Best Effort 1 0x4 2 Maximize Reliability 0 Best Effort 1 0x6 3 mmc+mr 0 Best Effort 1 0x8 4 Maximize Throughput 2 Bulk 2 0xa 5 mmc+mt 2 Bulk 2 0xc 6 mr+mt 2 Bulk 2 0xe 7 mmc+mr+mt 2 Bulk 2 0x10 8 Minimize Delay 6 Interactive 0 0x12 9 mmc+md 6 Interactive 0 0x14 10 mr+md 6 Interactive 0 0x16 11 mmc+mr+md 6 Interactive 0 0x18 12 mt+md 4 Int. Bulk 1 0x1a 13 mmc+mt+md 4 Int. Bulk 1 0x1c 14 mr+mt+md 4 Int. Bulk 1 0x1e 15 mmc+mr+mt+md 4 Int. Bulk 1 The second column contains the value of the relevant four TOS bits, followed by their translated meaning. For example, 15 stands for a packet wanting Minimal Monetary Cost, Maximum Reliability, Maximum Throughput AND Minimum Delay. The fourth column lists the way the Linux kernel interprets the TOS bits, by showing to which Priority they are mapped. The last column shows the result of the default priomap. On the command line, the default priomap looks like this: 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 This means that priority 4, for example, gets mapped to band number 1. The priomap also allows you to list higher priorities (> 7) which do not correspond to TOS mappings, but which are set by other means. This table from RFC 1349 (read it for more details) explains how applications might very well set their TOS bits: TELNET 1000 (minimize delay) FTP Control 1000 (minimize delay) Data 0100 (maximize throughput) TFTP 1000 (minimize delay) SMTP Command phase 1000 (minimize delay) DATA phase 0100 (maximize throughput) Domain Name Service UDP Query 1000 (minimize delay) TCP Query 0000 Zone Transfer 0100 (maximize throughput) NNTP 0001 (minimize monetary cost) ICMP Errors 0000 Requests 0000 (mostly) Responses <same as request> (mostly) CLASSES
PRIO classes cannot be configured further - they are automatically created when the PRIO qdisc is attached. Each class however can contain yet a further qdisc. BUGS
Large amounts of traffic in the lower bands can cause starvation of higher bands. Can be prevented by attaching a shaper (for example, tc- tbf(8) to these bands to make sure they cannot dominate the link. AUTHORS
Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>, J Hadi Salim <hadi@cyberus.ca>. This manpage maintained by bert hubert <ahu@ds9a.nl> iproute2 16 December 2001 PRIO(8)
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