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tc: add a man page for u32 filter
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Signed-off-by: Phil Sutter <phil@nwl.cc>
This commit is contained in:
Phil Sutter
Stephen Hemminger
parent
fc7a72f1eb
commit
f15a23966f
663
man/man8/tc-u32.8
Normal file
663
man/man8/tc-u32.8
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.TH "Universal 32bit classifier in tc" 8 "25 Sep 2015" "iproute2" "Linux"
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.SH NAME
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u32 \- universal 32bit traffic control filter
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.SH SYNOPSIS
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.in +8
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.ti -8
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.BR tc " " filter " ... [ " handle
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.IR HANDLE " ] "
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.B u32
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.IR OPTION_LIST " [ "
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.B offset
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.IR OFFSET " ] [ "
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.B hashkey
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.IR HASHKEY " ] [ "
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.B classid
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.IR CLASSID " ] [ "
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.B divisor
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.IR uint_value " ] [ "
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.B order
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.IR u32_value " ] [ "
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.B ht
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.IR HANDLE " ] [ "
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.B sample
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.IR SELECTOR " [ "
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.B divisor
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.IR uint_value " ] ] [ "
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.B link
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.IR HANDLE " ] [ "
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.B indev
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.IR ifname " ] [ "
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.BR help " ]"
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.ti -8
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.IR HANDLE " := { "
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\fIu12_hex_htid\fB:\fR[\fIu8_hex_hash\fB:\fR[\fIu12_hex_nodeid\fR] | \fB0x\fIu32_hex_value\fR }
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.ti -8
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.IR OPTION_LIST " := [ " OPTION_LIST " ] " OPTION
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.ti -8
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.IR HASHKEY " := [ "
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.B mask
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.IR u32_hex_value " ] [ "
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.B at
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.IR 4*int_value " ]"
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.ti -8
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.IR CLASSID " := { "
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.BR root " | "
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.BR none " | "
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[\fIu16_major\fR]\fB:\fIu16_minor\fR | \fIu32_hex_value\fR }
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.ti -8
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.IR OFFSET " := [ "
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.B plus
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.IR int_value " ] [ "
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.B at
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.IR 2*int_value " ] [ "
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.B mask
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.IR u16_hex_value " ] [ "
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.B shift
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.IR int_value " ] [ "
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.BR eat " ]"
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.ti -8
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.IR OPTION " := { "
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.B match
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.IR SELECTOR " | "
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.B action
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.IR ACTION " } "
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.ti -8
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.IR SELECTOR " := { "
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.B u32
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.IR VAL_MASK_32 " | "
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.B u16
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.IR VAL_MASK_16 " | "
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.B u8
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.IR VAL_MASK_8 " | "
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.B ip
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.IR IP " | "
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.B ip6
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.IR IP6 " | { "
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.BR tcp " | " udp " } "
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.IR TCPUDP " | "
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.B icmp
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.IR ICMP " | "
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.B mark
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.IR VAL_MASK_32 " | "
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.B ether
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.IR ETHER " }"
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.ti -8
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.IR IP " := { { "
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.BR src " | " dst " } { " default " | " any " | " all " | "
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.IR ip_address " [ "
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.BR / " { "
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.IR prefixlen " | " netmask " } ] } " AT " | { "
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.BR dsfield " | " ihl " | " protocol " | " precedence " | "
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.BR icmp_type " | " icmp_code " } "
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.IR VAL_MASK_8 " | { "
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.BR sport " | " dport " } "
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.IR VAL_MASK_16 " | "
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.BR nofrag " | " firstfrag " | " df " | " mf " }"
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.ti -8
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.IR IP6 " := { { "
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.BR src " | " dst " } { " default " | " any " | " all " | "
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.IR ip6_address " [/" prefixlen " ] } " AT " | "
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.B priority
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.IR VAL_MASK_8 " | { "
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.BR protocol " | " icmp_type " | " icmp_code " } "
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.IR VAL_MASK_8 " | "
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.B flowlabel
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.IR VAL_MASK_32 " | { "
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.BR sport " | " dport " } "
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.IR VAL_MASK_16 " }"
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.ti -8
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.IR TCPUDP " := { "
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.BR src " | " dst " } "
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.I VAL_MASK_16
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.ti -8
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.IR ICMP " := { "
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.B type
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.IR VAL_MASK_8 " | "
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.B code
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.IR VAL_MASK_8 " }"
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.ti -8
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.IR ETHER " := { "
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.BR src " | " dst " } "
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.IR ether_address " " AT
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.ti -8
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.IR VAL_MASK_32 " := " u32_value " " u32_hex_mask " [ " AT " ]"
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.ti -8
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.IR VAL_MASK_16 " := " u16_value " " u16_hex_mask " [ " AT " ]"
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.ti -8
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.IR VAL_MASK_8 " := " u8_value " " u8_hex_mask " [ " AT " ]"
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.ti -8
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.IR AT " := [ "
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.BR at " [ " nexthdr+ " ] "
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.IR int_value " ]"
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.SH DESCRIPTION
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The Universal/Ugly 32bit filter allows to match arbitrary bitfields in the
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packet. Due to breaking everything down to values, masks and offsets, It is
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equally powerful and hard to use. Luckily many abstracting directives are
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present which allow defining rules on a higher level and therefore free the
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user from having to fiddle with bits and masks in many cases.
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There are two general modes of invocation: The first mode creates a new filter
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to delegate packets to different destinations. Apart from the obvious ones,
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namely classifying the packet by specifying a
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.I CLASSID
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or calling an
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.BR action ,
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one may
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.B link
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one filter to another one (or even a list of them), effectively organizing
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filters into a tree-like hierarchy.
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Typically filter delegation is done by means of a hash table, which leads to the
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second mode of invocation: it merely serves to set up these hash tables. Filters
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can select a hash table and provide a key selector from which a hash is to be
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computed and used as key to lookup the table's bucket which contains filters for
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further processing. This is useful if a high number of filters is in use, as the
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overhead of performing the hash operation and table lookup becomes negligible in
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that case. Using hashtables with
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.B u32
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basically involves the following pattern:
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.IP (1) 4
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Creating a new hash table, specifying it's size using the
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.B divisor
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parameter and ideally a handle by which the table can be identified. If the
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latter is not given, the kernel chooses one on it's own, which has to be
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guessed later.
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.IP (2) 4
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Creating filters which link to the created table in
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.I (1)
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using the
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.B link
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parameter and defining the packet data which the kernel will use to calculate
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the
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.BR hashkey .
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.IP (3) 4
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Adding filters to buckets in the hash table from
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.IR (1) .
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In order to avoid having to know how exactly the kernel creates the hash key,
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there is the
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.B sample
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parameter, which gives sample data to hash and thereby define the table bucket
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the filter should be added to.
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.RE
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In fact, even if not explicitly requested
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.B u32
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creates a hash table for every
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.B priority
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a filter is being added with. The table's size is 1 though, so it is in fact
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merely a linked list.
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.SH VALUES
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Options and selectors require values to be specified in a specific format, which
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is often non-intuitive. Therefore the terminals in
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.I SYNOPSIS
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have been given descriptive names to indicate the required format and/or maximum
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allowed numeric value: Prefixes
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.IR u32 ", " u16 " and " u8
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indicate four, two and single byte unsigned values. E.g.
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.I u16
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indicates a two byte-sized value in range between 0 and 65535 (0xFFFF)
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inclusive. A prefix of
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.I int
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indicates a four byte signed value. A middle part of
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.I _hex_
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indicates that the value is parsed in hexadecimal format. Otherwise, the
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value's base is automatically detected, i.e. values prefixed with
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.I 0x
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are considered hexadecimal, a leading
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.I 0
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indicates octal format and decimal format otherwise. There are some values with
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special formatting as well:
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.IR ip_address " and " netmask
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are in dotted-quad formatting as usual for IPv4 addresses. An
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.I ip6_address
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is specified in common, colon-separated hexadecimal format. Finally,
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.I prefixlen
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is an unsigned, decimal integer value in range from 0 to the address width in
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bits (32 for IPv4 and 128 for IPv6).
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Sometimes values need to be dividable by a certain number. In that case a name
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of the form
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.I N*val
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was chosen, indicating that
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.I val
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must be dividable by
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.IR N .
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Or the other way around: the resulting value must be a multiple of
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.IR N .
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.SH OPTIONS
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.B U32
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recognizes the following options:
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.TP
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.BI handle " HANDLE"
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The handle is used to reference a filter and therefore must be unique. It
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consists of a hash table identifier
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.B htid
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and optional
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.B hash
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(which identifies the hash table's bucket) and
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.BR nodeid .
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All these values are parsed as unsigned, hexadecimal numbers with length 12bits
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(
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.BR htid " and " nodeid )
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or 8bits (
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.BR hash ).
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Alternatively one may specify a single, 32bit long hex number which contains
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the three fields bits in concatenated form. Other than the fields themselves, it
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has to be prefixed by
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.BR 0x .
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.TP
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.BI offset " OFFSET"
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Set an offset which defines where matches of subsequent filters are applied to.
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Therefore this option is useful only when combined with
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.BR link " or a combination of " ht " and " sample .
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The offset may be given explicitly by using the
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.B plus
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keyword, or extracted from the packet data with
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.BR at .
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It is possible to mangle the latter using
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.BR mask " and/or " shift
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keywords. By default, this offset is recorded but not implicitly applied. It is
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used only to substitute the
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.B nexthdr+
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statement. Using the keyword
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.B eat
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though inverses this behaviour: the offset is applied always, and
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.B nexthdr+
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will fall back to zero.
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.TP
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.BI hashkey " HASHKEY"
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Spefify what packet data to use to calculate a hash key for bucket lookup. The
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kernel adjusts the value according to the hash table's size. For this to work,
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the option
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.B link
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must be given.
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.TP
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.BI classid " CLASSID"
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Classify matching packets into the given
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.IR CLASSID ,
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which consists of either 16bit
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.BR major " and " minor
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numbers or a single 32bit value combining both.
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.TP
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.BI divisor " u32_value"
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Specify a modulo value. Used when creating hash tables to define their size or
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for declaring a
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.B sample
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to calculate hash table keys from. Must be a power of two with exponent not
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exceeding eight.
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.TP
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.BI order " u32_value"
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A value to order filters by, ascending. Conflicts with
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.B handle
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which serves the same purpose.
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.TP
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.BI sample " SELECTOR"
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Used together with
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.B ht
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to specify which bucket to add this filter to. This allows one to avoid having
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to know how exactly the kernel calculates hashes. The additional
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.B divisor
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defaults to 256, so must be given for hash tables of different size.
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.TP
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.BI link " HANDLE"
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Delegate matching packets to filters in a hash table.
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.I HANDLE
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is used to only specify the hash table, so only
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.BR htid " may be given, " hash " and " nodeid
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have to be omitted. By default, bucket number 0 will be used and can be
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overridden by the
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.B hashkey
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option.
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.TP
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.BI indev " ifname"
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Filter on the incoming interface of the packet. Obviously works only for
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forwarded traffic.
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.TP
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.BI help
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Print a brief help text about possible options.
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.SH SELECTORS
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Basically the only real selector is
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.B u32 .
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All others merely provide a higher level syntax and are internally translated
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into
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.B u32 .
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.TP
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.BI u32 " VAL_MASK_32"
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.TQ
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.BI u16 " VAL_MASK_16"
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.TQ
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.BI u8 " VAL_MASK_8"
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Match packet data to a given value. The selector name defines the sample length
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to extract (32bits for
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.BR u32 ,
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16bits for
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.B u16
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and 8bits for
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.BR u8 ).
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Before comparing, the sample is binary AND'ed with the given mask. This way
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uninteresting bits can be cleared before comparison. The position of the sample
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is defined by the offset specified in
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.IR AT .
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.TP
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.BI ip " IP"
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.TQ
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.BI ip6 " IP6"
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Assume packet starts with an IPv4 (
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.BR ip )
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or IPv6 (
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.BR ip6 )
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header.
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.IR IP / IP6
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then allows to match various header fields:
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.RS
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.TP
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.BI src " ADDR"
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.BI dst " ADDR"
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Compare Source or Destination Address fields against the value of
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.IR ADDR .
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The reserved words
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.BR default ", " any " and " all
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effectively match any address. Otherwise an IP address of the particular
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protocol is expected, optionally suffixed by a prefix length to match whole
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subnets. In case of IPv4 a netmask may also be given.
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.TP
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.BI dsfield " VAL_MASK_8"
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IPv4 only. Match the packet header's DSCP/ECN field. Synonyms to this are
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.BR tos " and " precedence .
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.TP
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.BI ihl " VAL_MASK_8"
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IPv4 only. Match the Internet Header Length field. Note that the value's unit is
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32bits, so to match a packet with 24byte header length
|
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.I u8_value
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has to be 6.
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.TP
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.BI protocol " VAL_MASK_8"
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Match the Protocol (IPv4) or Next Header (IPv6) field value, e.g. 6 for TCP.
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.TP
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.BI icmp_type " VAL_MASK_8"
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.TQ
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.BI icmp_code " VAL_MASK_8"
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Assume a next-header protocol of icmp or ipv6-icmp and match Type or Code
|
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field values. This is dangerous, as the code assumes minimal header size for
|
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IPv4 and lack of extension headers for IPv6.
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.TP
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.BI sport " VAL_MASK_16"
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.TQ
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.BI dport " VAL_MASK_16"
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Match layer four source or destination ports. This is dangerous as well, as it
|
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assumes a suitable layer four protocol is present (which has Source and
|
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Destination Port fields right at the start of the header and 16bit in size).
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Also minimal header size for IPv4 and lack of IPv6 extension headers is assumed.
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.TP
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.B nofrag
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.TQ
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.B firstfrag
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.TQ
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.B df
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.TQ
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.B mf
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IPv4 only, check certain flags and fragment offset values. Match if the packet
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is not a fragment
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.RB ( nofrag ),
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the first fragment
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.RB ( firstfrag ),
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if Don't Fragment
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.RB ( df )
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or More Fragments
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.RB ( mf )
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bits are set.
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.TP
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.BI priority " VAL_MASK_8"
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IPv6 only. Match the header's Traffic Class field, which has the same purpose
|
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and semantics of IPv4's ToS field since RFC 3168: upper six bits are DSCP, the
|
||||
lower two ECN.
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.TP
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||||
.BI flowlabel " VAL_MASK_32"
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IPv6 only. Match the Flow Label field's value. Note that Flow Label itself is
|
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only 20bytes long, which are the least significant ones here. The remaining
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upper 12bytes match Version and Traffic Class fields.
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.RE
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.TP
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.BI tcp " TCPUDP"
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.TQ
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.BI udp " TCPUDP"
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Match fields of next header of protocol TCP or UDP. The possible values for
|
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.I TCPDUP
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are:
|
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.RS
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||||
.TP
|
||||
.BI src " VAL_MASK_16"
|
||||
Match on Source Port field value.
|
||||
.TP
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||||
.BI dst " VALMASK_16"
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Match on Destination Port field value.
|
||||
.RE
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||||
.TP
|
||||
.BI icmp " ICMP"
|
||||
Match fields of next header of protocol ICMP. The possible values for
|
||||
.I ICMP
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are:
|
||||
.RS
|
||||
.TP
|
||||
.BI type " VAL_MASK_8"
|
||||
Match on ICMP Type field.
|
||||
.TP
|
||||
.BI code " VAL_MASK_8"
|
||||
Match on ICMP Code field.
|
||||
.RE
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||||
.TP
|
||||
.BI mark " VAL_MASK_32"
|
||||
Match on netfilter fwmark value.
|
||||
.TP
|
||||
.BI ether " ETHER"
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||||
Match on ethernet header fields. Possible values for
|
||||
.I ETHER
|
||||
are:
|
||||
.RS
|
||||
.TP
|
||||
.BI src " ether_address" " " AT
|
||||
.TQ
|
||||
.BI dst " ether_address" " " AT
|
||||
Match on source or destination ethernet address. This is dangerous: It assumes
|
||||
an ethernet header is present at the start of the packet. This will probably
|
||||
lead to unexpected things if used with layer three interfaces like e.g. tun or
|
||||
ppp.
|
||||
.SH EXAMPLES
|
||||
.RS
|
||||
.EX
|
||||
tc filter add dev eth0 parent 999:0 prio 99 protocol ip u32 \\
|
||||
match ip src 192.168.8.0/24 classid 1:1
|
||||
.EE
|
||||
.RE
|
||||
|
||||
This attaches a filter to the qdisc identified by
|
||||
.BR 999:0.
|
||||
It's priority is
|
||||
.BR 99 ,
|
||||
which affects in which order multiple filters attached to the same
|
||||
.B parent
|
||||
are consulted (the lower the earlier). The filter handles packets of
|
||||
.B protocol
|
||||
type
|
||||
.BR ip ,
|
||||
and
|
||||
.BR match es
|
||||
if the IP header's source address is within the
|
||||
.B 192.168.8.0/24
|
||||
subnet. Matching packets are classified into class
|
||||
.BR 1.1 .
|
||||
The effect of this command might be surprising at first glance:
|
||||
|
||||
.RS
|
||||
.EX
|
||||
filter parent 1: protocol ip pref 99 u32
|
||||
filter parent 1: protocol ip pref 99 u32 \\
|
||||
fh 800: ht divisor 1
|
||||
filter parent 1: protocol ip pref 99 u32 \\
|
||||
fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1 \\
|
||||
match c0a80800/ffffff00 at 12
|
||||
.EE
|
||||
.RE
|
||||
|
||||
So parent
|
||||
.B 1:
|
||||
is assigned a new
|
||||
.B u32
|
||||
filter, which contains a hash table of size 1 (as the
|
||||
.B divisor
|
||||
indicates). The table ID is
|
||||
.BR 800 .
|
||||
The third line then shows the actual filter which was added above: it sits in
|
||||
table
|
||||
.B 800
|
||||
and bucket
|
||||
.BR 0 ,
|
||||
classifies packets into class ID
|
||||
.B 1:1
|
||||
and matches the upper three bytes of the four byte value at offset
|
||||
.B 12
|
||||
to be
|
||||
.BR 0xc0a808 ,
|
||||
which is 192, 168 and 8.
|
||||
|
||||
Now for something more complicated, namely creating a custom hash table:
|
||||
|
||||
.RS
|
||||
.EX
|
||||
tc filter add dev eth0 prio 99 handle 1: u32 divisor 256
|
||||
.EE
|
||||
.RE
|
||||
|
||||
This creates a table of size 256 with handle
|
||||
.B 1:
|
||||
in priority
|
||||
.BR 99 .
|
||||
The effect is as follows:
|
||||
|
||||
.RS
|
||||
.EX
|
||||
filter parent 1: protocol all pref 99 u32
|
||||
filter parent 1: protocol all pref 99 u32 fh 1: ht divisor 256
|
||||
filter parent 1: protocol all pref 99 u32 fh 800: ht divisor 1
|
||||
.EE
|
||||
.RE
|
||||
|
||||
So along with the requested hash table (handle
|
||||
.BR 1: ),
|
||||
the kernel has created his own table of size 1 to hold other filters of the same
|
||||
priority.
|
||||
|
||||
The next step is to create a filter which links to the created hash table:
|
||||
|
||||
.RS
|
||||
.EX
|
||||
tc filter add dev eth0 parent 1: prio 1 u32 \\
|
||||
link 1: hashkey mask 0x0000ff00 at 12 \\
|
||||
match ip src 192.168.0.0/16
|
||||
.EE
|
||||
.RE
|
||||
|
||||
The filter is given a lower priority than the hash table itself so
|
||||
.B u32
|
||||
consults it before manually traversing the hash table. The options
|
||||
.BR link " and " hashkey
|
||||
determine which table and bucket to redirect to. In this case the hash key
|
||||
should be constructed out of the second byte at offset 12, which corresponds to
|
||||
an IP packet's third byte of the source address field. Along with the
|
||||
.B match
|
||||
statement, this effectively maps all class C networks below 192.168.0.0/16 to
|
||||
different buckets of the hash table.
|
||||
|
||||
Filters for certain subnets can be created like so:
|
||||
|
||||
.RS
|
||||
.EX
|
||||
tc filter add dev eth0 parent 1: prio 99 u32 \\
|
||||
ht 1: sample u32 0x00000800 0x0000ff00 at 12 \\
|
||||
match ip src 192.168.8.0/24 classid 1:1
|
||||
.EE
|
||||
.RE
|
||||
|
||||
The bucket is defined using the
|
||||
.B sample
|
||||
option: In this case, the second byte at offset 12 must be 0x08, exactly. In
|
||||
this case, the resulting bucket ID is obviously 8, but as soon as
|
||||
.B sample
|
||||
selects an amount of data which could exceed the
|
||||
.BR divisor ,
|
||||
one would have to know the kernel-internal algorithm to deduce the destination
|
||||
bucket. This filter's
|
||||
.B match
|
||||
statement is redundant in this case, as the entropy for the hash key does not
|
||||
exceed the table size and therefore no collisions can occur. Otherwise it's
|
||||
necessary to prevent matching unwanted packets.
|
||||
|
||||
Matching upper layer fields is problematic since IPv4 header length is variable
|
||||
and IPv6 supports extension headers which affect upper layer header offset. To
|
||||
overcome this, there is the possibility to specify
|
||||
.B nexthdr+
|
||||
when giving an offset, and to make things easier there are the
|
||||
.BR tcp " and " udp
|
||||
matches which use
|
||||
.B nexthdr+
|
||||
implicitly. This offset has to be calculated in beforehand though, and the only
|
||||
way to achieve that is by doing it in a separate filter which then links to the
|
||||
filter which wants to use it. Here is an example of doing so:
|
||||
|
||||
.RS
|
||||
.EX
|
||||
tc filter add dev eth0 parent 1:0 protocol ip handle 1: \\
|
||||
u32 divisor 1
|
||||
tc filter add dev eth0 parent 1:0 protocol ip \\
|
||||
u32 ht 1: \\
|
||||
match tcp src 22 FFFF \\
|
||||
classid 1:2
|
||||
tc filter add dev eth0 parent 1:0 protocol ip \\
|
||||
u32 ht 800: \\
|
||||
match ip protocol 6 FF \\
|
||||
match ip firstfrag \\
|
||||
offset at 0 mask 0f00 shift 6 \\
|
||||
link 1:
|
||||
.EE
|
||||
.RE
|
||||
|
||||
This is what is being done: In the first call, a single element sized hash table
|
||||
is created so there is a place to hold the linked to filter and a known handle
|
||||
.RB ( 1: )
|
||||
to reference to it. The second call then adds the actual filter, which pushes
|
||||
packets with TCP source port 22 into class
|
||||
.BR 1:2 .
|
||||
Using
|
||||
.BR ht ,
|
||||
it is moved into the hash table created by the first call. The third call then
|
||||
does the actual magic: It matches IPv4 packets with next layer protocol 6 (TCP),
|
||||
only if it's the first fragment (usually TCP sets DF bit, but if it doesn't and
|
||||
the packet is fragmented, only the first one contains the TCP header), and then
|
||||
sets the offset based on the IP header's IHL field (right-shifting by 6
|
||||
eliminates the offset of the field and at the same time converts the value into
|
||||
byte unit). Finally, using
|
||||
.BR link ,
|
||||
the hash table from first call is referenced which holds the filter from second
|
||||
call.
|
||||
.SH SEE ALSO
|
||||
.BR tc (8),
|
||||
.br
|
||||
.BR cls_u32.txt " at " http://linux-tc-notes.sourceforge.net/
|
||||
Loading…
Reference in New Issue
Block a user