iptables 中文man页面，比help更强的帮助介绍
NAMEiptables - IP包过滤器管理
总览
iptables -ADC 指定链的规则 [-A 添加 -D 删除 -C 修改]
iptables - RI
iptables -D chain rule num
iptables -LFZ 链名 [选项]
iptables - 指定链
iptables -P chain target
iptables -E old-chain-name new-chain-name
说明
Iptalbes 是用来设置、维护和检查Linux内核的IP包过滤规则的。
可以定义不同的表，每个表都包含几个内部的链，也能包含用户定义的链。每个链都是一个规则列表，对对应的包进行匹配：每条规则指定应当如何处理与之相匹配的包。这被称作'target'（目标），也可以跳向同一个表内的用户定义的链。
TARGETS
防火墙的规则指定所检查包的特征，和目标。如果包不匹配，将送往该链中下一条规则检查；如果匹配,那么下一条规则由目标值确定.该目标值可以是用户定义的链名,或是某个专用值,如ACCEPT[通过], DROP[删除], QUEUE[排队],或者 RETURN[返回]。
ACCEPT
表示让这个包通过。
DROP
表示将这个包丢弃。
QUEUE
表示把这个包传递到用户空间。
RETURN
表示停止这条链的匹配，到前一个链的规则重新开始。如果到达了一个内建的
链(的末端)，或者遇到内建链的规则是 RETURN，包的命运将由链准则指定的
目标决定。
TABLES
当前有三个表（哪个表是当前表取决于内核配置选项和当前模块)。
-t table
这个选项指定命令要操作的匹配包的表。如果内核被配置为自动加载模块，这时若模块没有加载，(系统)将尝试(为该表)加载适合的模块。
这些表如下：
filter
,这是默认的表，包含了内建的链INPUT（处理进入的包）、FORWORD（处理通过的包）和OUTPUT（处理本地生成的包）。
nat
这个表被查询时表示遇到了产生新的连接的包,由三个内建的链构成：PREROUTING
(修改到来的包)、OUTPUT（修改路由之前本地的包）、POSTROUTING
（修改准备出去的包）。
mangle
这个表用来对指定的包进行修改。它有两个内建规则：PREROUTING（修改路由之
前进入的包）和OUTPUT（修改路由之前本地的包）。
OPTIONS
这些可被iptables识别的选项可以区分不同的种类。
COMMANDS
这些选项指定执行明确的动作：若指令行下没有其他规定,该行只能指定一个选项. 对于长格式的命令和选项名,所用字母长度只要保证iptables能从其他选项中区分出该指令就行了。
-A -append
在所选择的链末添加一条或更多规则。当源（地址）或者/与 目的（地址）转换为多于一个(多个)地址时，这条规则会加到所有可能的地址(组合)后面。
-D -delete
从所选链中删除一条或更多规则。这条命令可以有两种方法：可以把被删除规则指定为链中的序号(第一条序号为1),或者指定为要匹配的规则。
-R -replace
从选中的链中取代一条规则。如果源（地址）或者/与 目的（地址）被转换为多地址，该命令会失败。规则序号从1开始。
-I -insert
根据给出的规则序号向所选链中插入一条或更多规则。所以，如果规则序号为1，规则会被插入链的头部。这也是不指定规则序号时的默认方式。
-L -list
显示所选链的所有规则。如果没有选择链，所有链将被显示。也可以和z选项一起使用，这时链会被自动列出和归零。精确输出受其它所给参数影响。
-F -flush
清空所选链。这等于把所有规则一个个的删除。
--Z -zero
把所有链的包及字节的计数器清空。它可以和 -L配合使用，在清空前察看计数器，请参见前文。
-N -new-chain
根据给出的名称建立一个新的用户定义链。这必须保证没有同名的链存在。
-X -delete-chain
删除指定的用户自定义链。这个链必须没有被引用，如果被引用，在删除之前你必须删除或者替换与之有关的规则。如果没有给出参数，这条命令将试着删除每个非内建的链。
-P -policy
设置链的目标规则。
-E -rename-chain
根据用户给出的名字对指定链进行重命名，这仅仅是修饰，对整个表的结构没有影响。 TARGETS参数给出一个合法的目标。只有非用户自定义链可以使用规则，而且内建链和用户自定义链都不能是规则的目标。
-h Help.
帮助。给出当前命令语法非常简短的说明。
参数
以下参数构成规则详述，如用于add、delete、replace、append 和 check命令。
-p -protocal [!]protocol
规则或者包检查(待检查包)的协议。指定协议可以是tcp、udp、icmp中的一个或者全部，也可以是数值，代表这些协议中的某一个。当然也可以使用在/etc/pro tocols中定义的协议名。在协议名前加上"!"表示相反的规则。数字0相当于所有 all。Protocol all会匹配所有协议，而且这是缺省时的选项。在和check命令结合时，all可以不被使用。
-s -source [!] address
指定源地址，可以是主机名、网络名和清楚的IP地址。mask说明可以是网络掩码或清楚的数字，在网络掩码的左边指定网络掩码左边”1”的个数，因此，mask 值为24等于255.255.255.0。在指定地址前加上"!"说明指定了相反的地址段。标志
--src 是这个选项的简写。
-d --destination [!] address
指定目标地址，要获取详细说明请参见 -s标志的说明。标志 --dst 是这个选项的简写。
-j --jump target
(-j 目标跳转)指定规则的目标；也就是说，如果包匹配应当做什么。目标可以是用户自定义链（不是这条规则所在的），某个会立即决定包的命运的专用内建目标，或者一个扩展（参见下面的EXTENSIONS）。如果规则的这个选项被忽略，那么匹配的过程不会对包产生影响，不过规则的计数器会增加。
-i -in-interface [!]
(i -进入的（网络）接口 [!][名称])这是包经由该接口接收的可选的入口名称，包通过该接口接收（在链INPUT、FORWORD和PREROUTING中进入的包）。当在接口名前使用"!"说明后，指的是相反的名称。如果接口名后面加上"+"，则所有以此接口名开头的接口都会被匹配。如果这个选项被忽略，会假设为"+"，那么将匹配任意接口。
-o --out-interface [!]
(-o --输出接口[名称])这是包经由该接口送出的可选的出口名称，包通过该口输出（在链FORWARD、OUTPUT和POSTROUTING中送出的包）。当在接口名前使用"!"说明后，指的是相反的名称。如果接口名后面加上"+"，则所有以此接口名开头的接口都会被匹配。如果这个选项被忽略，会假设为"+"，那么将匹配所有任意接口。
[!] -f, --fragment
( [!] -f --分片)这意味着在分片的包中，规则只询问第二及以后的片。自那以后由于无法判断这种把包的源端口或目标端口（或者是ICMP类型的），这类包将不能匹配任何指定对他们进行匹配的规则。如果"!"说明用在了"-f"标志之前，表示相反的意思。 TP -c, --set-counters PKTS BYTES This enables the administrater to initialize the packet and byte counters of a rule (during INSERT, APPEND, REPLACE operations)
其他选项
还可以指定下列附加选项：
-v --verbose
详细输出。这个选项让list命令显示接口地址、规则选项（如果有）和TOS （Type of Service）掩码。包和字节计数器也将被显示，分别用K、M、G (前缀)表示1000、1,000,000和1,000,000,000倍（不过请参看-x标志改变它），对于添加,插入,删除和替换命令，这会使一个或多个规则的相关详细信息被打印。
-n --numeric
数字输出。IP地址和端口会以数字的形式打印。默认情况下，程序试显示主机名、网络名或者服务（只要可用）。
-x -exact
扩展数字。显示包和字节计数器的精确值，代替用K,M,G表示的约数。这个选项仅能用于 -L 命令。
--line-numbers
当列表显示规则时，在每个规则的前面加上行号，与该规则在链中的位置相对应。
对应的扩展
iptables能够使用一些与模块匹配的扩展包。以下就是含于基本包内的扩展包，而且他们大多数都可以通过在前面加上!来表示相反的意思。
tcp
当 --protocol tcp 被指定,且其他匹配的扩展未被指定时,这些扩展被装载。它提供以下选项：
--source-port [!] ]
源端口或端口范围指定。这可以是服务名或端口号。使用格式端口：端口也可以指定包含的（端口）范围。如果首端口号被忽略，默认是"0"，如果末端口号被忽略，默认是"65535"，如果第二?龆丝诤糯笥诘谝桓觯?敲此?腔岜唤换弧Ｕ飧鲅∠羁梢允褂? --sport的别名。
--destionation-port [!] ]
目标端口或端口范围指定。这个选项可以使用 --dport别名来代替。
--tcp-flags [!] mask comp
匹配指定的TCP标记。第一个参数是我们要检查的标记，一个用逗号分开的列表，第二个参数是用逗号分开的标记表,是必须被设置的。标记如下：SYN ACK FIN
RST URG PSH ALL NONE。因此这条命令：iptables -A FORWARD -p tcp --tcp-flags SYN, ACK,
FIN, RST SYN只匹配那些SYN标记被设置而ACK、FIN和RST标记没有设置的包。
[!] --syn
只匹配那些设置了SYN位而清除了ACK和FIN位的TCP包。这些包用于TCP连接初始化时发出请求；例如，大量的这种包进入一个接口发生堵塞时会阻止进入的TCP连接，而出去的TCP连接不会受到影响。这等于 --tcp-flags SYN, RST, ACK SYN。如果 "--syn"前面有"!"标记，表示相反的意思。
--tcp-option [!] number
匹配设置了TCP选项的。
udp
当protocol udp 被指定,且其他匹配的扩展未被指定时,这些扩展被装载,它提供以下选项：
--source-port [!] ]
源端口或端口范围指定。详见 TCP扩展的--source-port选项说明。
--destination-port [!] ]
目标端口或端口范围指定。详见 TCP扩展的--destination-port选项说明。
icmp
当protocol icmp被指定,且其他匹配的扩展未被指定时,该扩展被装载。它提供以下选项：
--icmp-type [!] typename
这个选项允许指定ICMP类型，可以是一个数值型的ICMP?嘈停?蛘呤悄掣鲇擅??
iptables -p icmp -h
所显示的ICMP类型名。
mac
--mac-source [!] address
匹配物理地址。必须是XX:XX:XX:XX:XX这样的格式。注意它只对来自以太设备并进入PREROUTING、FORWORD和INPUT链的包有效。
limit
这个模块匹配标志用一个标记桶过滤器一一定速度进行匹配,它和LOG 目标结合使用来给出有限的登陆数.当达到这个极限值时,使用这个扩展包的规则将进行匹配.(除非使用了 ”!”标记)
--limit rate
最大平均匹配速率：可赋的值有'/second', '/minute', '/hour', or '/day'这样的单位，默认是3/hour。
--limit-burst number
待匹配包初始个数的最大值:若前面指定的极限还没达到这个数值,则概数字加1.默认值为5
multiport
这个模块匹配一组源端口或目标端口,最多可以指定15个端口。只能和-p tcp 或者 -p udp 连着使用。
--source-port ]
如果源端口是其中一个给定端口则匹配
--destination-port ]
如果目标端口是其中一个给定端口则匹配
--port ]
若源端口和目的端口相等并与某个给定端口相等,则匹配。
mark
这个模块和与netfilter过滤器标记字段匹配（就可以在下面设置为使用MARK标记）。
--mark value
匹配那些无符号标记值的包（如果指定mask，在比较之前会给掩码加上逻辑的标记）。
owner
此模块试为本地生成包匹配包创建者的不同特征。只能用于OUTPUT链，而且即使这样一些包（如ICMP ping应答）还可能没有所有者，因此永远不会匹配。
--uid-owner userid
如果给出有效的user id，那么匹配它的进程产生的包。
--gid-owner groupid
如果给出有效的group id，那么匹配它的进程产生的包。
--sid-owner seessionid
根据给出的会话组匹配该进程产生的包。
state
此模块，当与连接跟踪结合使用时，允许访问包的连接跟踪状态。
--state state
这里state是一个逗号分割的匹配连接状态列表。可能的状态是:INVALID 表示包是未知连接，ESTABLISHED表示是双向传送的连接，NEW表示包为新的连接，否则是非双向传送的，而RELATED表示包由新连接开始，但是和一个已存在的连接在一起，如FTP数据传送，或者一个ICMP错误。
unclean
此模块没有可选项，不过它试着匹配那些奇怪的、不常见的包。处在实验中。
tos
此模块匹配IP包首部的8位tos（服务类型）字段（也就是说，包含在优先位中）。
--tos tos
这个参数可以是一个标准名称，（用iptables -m tos -h 察看该列表），或者数值。
TARGET EXTENSIONS
iptables可以使用扩展目标模块：以下都包含在标准版中。
LOG
为匹配的包开启内核记录。当在规则中设置了这一选项后，linux内核会通过printk()打印一些关于全部匹配包的信息（诸如IP包头字段等）。
--log-level level
记录级别（数字或参看 syslog.conf(5)）。
--log-prefix prefix
在纪录信息前加上特定的前缀：最多14个字母长，用来和记录中其他信息区别。
--log-tcp-sequence
记录TCP序列号。如果记录能被用户读取那么这将存在安全隐患。
--log-tcp-options
记录来自TCP包头部的选项。
--log-ip-options
记录来自IP包头部的选项。
MARK
用来设置包的netfilter标记值。只适用于mangle表。
REJECT
作为对匹配的包的响应，返回一个错误的包：其他情况下和DROP相同。
此目标只适用于INPUT、FORWARD和OUTPUT链，和调用这些链的用户自定义链。这几个选项控制返回的错误包的特性：
--reject-with type
Type可以是icmp-net-unreachable、icmp-host-unreachable、icmp-port-nreachable、icmp-prot o-unreachable、 icmp-net-prohibited 或者
icmp-host-prohibited，该类型会返回相应的ICMP错误信息（默认是port-unreachable）。选项
echo-reply也是允许的；它只能用于指定ICMP
ping包的规则中，生成ping的回应。最后，选项tcp-reset可以用于在INPUT链中,或
自INPUT链调用的规则，只匹配TCP协议：将回应一个TCP
RST包。
TOS
用来设置IP包的首部八位tos。只能用于mangle表。
--set-tos tos
你可以使用一个数值型的TOS 值，或者用iptables -j TOS -h 来查看有效TOS名列表。
MIRROR
这是一个试验示范目标，可用于转换IP首部字段中的源地址和目标地址，再传送该包,并只适用于INPUT、FORWARD和OUTPUT链，以及只调用它们的用户自定义链。
SNAT
这个目标只适用于nat表的POSTROUTING链。它规定修改包的源地址（此连接以后所有的包都会被影响），停止对规则的检查，它包含选项：
--to-source <ipaddr>[-<ipaddr>][:port-port]
可以指定一个单一的新的IP地址，一个IP地址范围，也可以附加一个端口范围（只能在指定-p tcp 或者-p udp的规则里）。如果未指定端口范围，源端口中 512以下的（端口）会被安置为其他的512以下的端口；512到1024之间的端口会被安置为1024以下的，其他端口会被安置为1024或以上。如果可能，端口不会被修改。
--to-destiontion <ipaddr>[-<ipaddr>][:port-port]
可以指定一个单一的新的IP地址，一个IP地址范围，也可以附加一个端口范围（只能在指定-p tcp 或者-p
udp的规则里）。如果未指定端口范围，目标端口不会被修改。
MASQUERADE
只用于nat表的POSTROUTING链。只能用于动态获取IP（拨号）连接：如果你拥有静态IP 地址，你要用SNAT。伪装相当于给包发出时所经过接口的IP地址设置一个映像，当接口关闭连接会终止。这是因为当下一次拨号时未必是相同的接口地址（以后所有建立的连接都将关闭）。它有一个选项：
--to-ports <port>[-port>]
指定使用的源端口范围，覆盖默认的SNAT源地址选择（见上面）。这个选项只适用于指定了-p tcp或者-p udp的规则。
REDIRECT
只适用于nat表的PREROUTING和OUTPUT链，和只调用它们的用户自定义链。它修改包的目标IP地址来发送包到机器自身（本地生成的包被安置为地址127.0
--to-ports <port>[<port>]
指定使用的目的端口或端口范围：不指定的话，目标端口不会被修改。只能用于指定了-p tcp 或 -p udp的规则。
诊断
不同的错误信息会打印成标准错误：退出代码0表示正确。类似于不对的或者滥用的命令行参数错误会返回错误代码2，其他错误返回代码为1。
臭虫
检查还未完成。
COMPATIBILITY WITH IPCHAINS
与ipchains的兼容性
This iptables is very similar to ipchains by Rusty Russell. The main difference
is that the chains INPUT and OUTPUT are only traversed for packets coming into
the local host and originating from the local host respectively. Hence every
pack only passes through one of the three chains; previously a forwarded packet
would pass through all three. The other main difference is that -I refers to
input interface; -o refers to the output interface, and both are available for
packets entering the FORWARD chain. iptables is a pure packet filter when using
the default filter' table, with optional extension modules. This should
simplify much of the previous confusion over the combination of IP masquerading
and packet filtering seen previously. So the following options are handled
differently: -j MASQ -M -S -M -L There are several other chaines in iptables iptables和Rusty Russell的ipchains非常相似。主要区别是INPUT 链只用于进入本地主机的包,而OUTPUT只用于自本地主机生成的包。因此每个包只经过三个链的一个；以前转发的包会经过所有三个链。其他主要区别是 -i 引用进入接口；-o引用输出接口，两者都适用于进入FORWARD链的包。当和可选扩展模块一起使用默认过滤器表时，iptables是一个纯粹的包过滤器。这能大大减少以前对IP伪装和包过滤结合使用的混淆，所以以下选项作了不同的处理： -j MASQ -M -S -M -L 在iptables中有几个不同的链。
参见
iptables-HOWTO有详细的iptables用法,对netfilter-hacking-HOWTO也有详细的本质说明。
NAME
iptables - administration tool for IPv4 packet filtering and NAT
SYNOPSIS
iptables [-t table] - chain rule-specification
iptables [-t table] -I chain rule-specification
iptables [-t table] -R chain rulenum rule-specification
iptables [-t table] -D chain rulenum
iptables [-t table] -
iptables [-t table] -N chain
iptables [-t table] -X
iptables [-t table] -P chain target
iptables [-t table] -E old-chain-name new-chain-name
DESCRIPTION
Iptables is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user-defined chains.
Each chain is a list of rules which can match a set of packets. Each rule specifies what to do with a packet that matches. This is called a `target', which may be a jump to a user-defined chain in the same table.
TARGETS
A firewall rule specifies criteria for a packet, and a target. If the packet does not match, the next rule in the chain is the examined; if it does match, then the next rule is specified by the value of the target, which can be the name of a user-defined chain or one of the special values ACCEPT, DROP, QUEUE, or RETURN.
ACCEPT means to let the packet through. DROP means to drop the packet on the floor. QUEUE means to pass the packet to userspace (if supported by the kernel). RETURN means stop traversing this chain and resume at the next rule in the previous (calling) chain. If the end of a built-in chain is reached or a rule in a built-in chain with target RETURN is matched, the target specified by the chain policy determines the fate of the packet.
TABLES
There are currently three independent tables (which tables are present at any time depends on the kernel configuration options and which modules are present).
-t, --table table
This option specifies the packet matching table which the command should operate on. If the kernel is configured with automatic module loading, an attempt will be made to load the appropriate module for that table if it is not already there.
The tables are as follows:
filter:
This is the default table (if no -t option is passed). It contains the built-in chains INPUT (for packets coming into the box itself), FORWARD (for packets being routed through the box), and OUTPUT (for locally-generated packets).
nat:
This table is consulted when a packet that creates a new connection is encountered. It consists of three built-ins: PREROUTING (for altering packets as soon as they come in), OUTPUT (for altering locally-generated packets before routing), and POSTROUTING (for altering packets as they are about to go out).
mangle:
This table is used for specialized packet alteration. Until kernel 2.4.17 it had two built-in chains: PREROUTING (for altering incoming packets before routing) and OUTPUT (for altering locally-generated packets before routing). Since kernel 2.4.18, three other built-in chains are also supported: INPUT (for packets coming into the box itself), FORWARD (for altering packets being routed through the box), and POSTROUTING (for altering packets as they are about to go out).
OPTIONS
The options that are recognized by iptables can be divided into several different groups.
COMMANDS
These options specify the specific action to perform. Only one of them can be specified on the command line unless otherwise specified below. For all the long versions of the command and option names, you need to use only enough letters to ensure that iptables can differentiate it from all other options.
-A, --append chain rule-specification
Append one or more rules to the end of the selected chain. When the source and/or destination names resolve to more than one address, a rule will be added for each possible address combination.
-D, --delete chain rule-specification
-D, --delete chain rulenum
Delete one or more rules from the selected chain. There are two versions of this command: the rule can be specified as a number in the chain (starting at 1 for the first rule) or a rule to match.
-I, --insert chain rule-specification
Insert one or more rules in the selected chain as the given rule number. So, if the rule number is 1, the rule or rules are inserted at the head of the chain. This is also the default if no rule number is specified.
-R, --replace chain rulenum rule-specification
Replace a rule in the selected chain. If the source and/or destination names resolve to multiple addresses, the command will fail. Rules are numbered starting at 1.
-L, --list
List all rules in the selected chain. If no chain is selected, all chains are listed. As every other iptables command, it applies to the specified table (filter is the default), so NAT rules get listed by
iptables -t nat -n -L
Please note that it is often used with the -n option, in order to avoid long reverse DNS lookups. It is legal to specify the -Z (zero) option as well, in which case the chain(s) will be atomically listed and zeroed. The exact output is affected by the other arguments given. The exact rules are suppressed until you use
iptables -L -v
-F, --flush
Flush the selected chain (all the chains in the table if none is given). This is equivalent to deleting all the rules one by one.
-Z, --zero
Zero the packet and byte counters in all chains. It is legal to specify the -L, --list (list) option as well, to see the counters immediately before they are cleared. (See above.)
-N, --new-chain chain
Create a new user-defined chain by the given name. There must be no target of that name already.
-X, --delete-chain
Delete the optional user-defined chain specified. There must be no references to the chain. If there are, you must delete or replace the referring rules before the chain can be deleted. If no argument is given, it will attempt to delete every non-builtin chain in the table.
-P, --policy chain target
Set the policy for the chain to the given target. See the section TARGETS for the legal targets. Only built-in (non-user-defined) chains can have policies, and neither built-in nor user-defined chains can be policy targets.
-E, --rename-chain old-chain new-chain
Rename the user specified chain to the user supplied name. This is cosmetic, and has no effect on the structure of the table.
-h
Help. Give a (currently very brief) description of the command syntax.
PARAMETERS
The following parameters make up a rule specification (as used in the add, delete, insert, replace and append commands).
-p, --protocol [!] protocol
The protocol of the rule or of the packet to check. The specified protocol can be one of tcp, udp, icmp, or all, or it can be a numeric value, representing one of these protocols or a different one. A protocol name from /etc/protocols is also allowed. A "!" argument before the protocol inverts the test. The number zero is equivalent to all. Protocol all will match with all protocols and is taken as default when this option is omitted.
-s, --source [!] address
Source specification. Address can be either a network name, a hostname (please note that specifying any name to be resolved with a remote query such as DNS is a really bad idea), a network IP address (with /mask), or a plain IP address. The mask can be either a network mask or a plain number, specifying the number of 1's at the left side of the network mask. Thus, a mask of 24 is equivalent to 255.255.255.0. A "!" argument before the address specification inverts the sense of the address. The flag --src is an alias for this option.
-d, --destination [!] address
Destination specification. See the description of the -s (source) flag for a detailed description of the syntax. The flag --dst is an alias for this option.
-j, --jump target
This specifies the target of the rule; i.e., what to do if the packet matches it. The target can be a user-defined chain (other than the one this rule is in), one of the special builtin targets which decide the fate of the packet immediately, or an extension (see EXTENSIONS below). If this option is omitted in a rule, then matching the rule will have no effect on the packet's fate, but the counters on the rule will be incremented.
-i, --in-interface [!] name
Name of an interface via which a packet was received (only for packets entering the INPUT, FORWARD and PREROUTING chains). When the "!" argument is used before the interface name, the sense is inverted. If the interface name ends in a "+", then any interface which begins with this name will match. If this option is omitted, any interface name will match.
-o, --out-interface [!] name
Name of an interface via which a packet is going to be sent (for packets entering the FORWARD, OUTPUT and POSTROUTING chains). When the "!" argument is used before the interface name, the sense is inverted. If the interface name ends in a "+", then any interface which begins with this name will match. If this option is omitted, any interface name will match.
[!] -f, --fragment
This means that the rule only refers to second and further fragments of fragmented packets. Since there is no way to tell the source or destination ports of such a packet (or ICMP type), such a packet will not match any rules which specify them. When the "!" argument precedes the "-f" flag, the rule will only match head fragments, or unfragmented packets.
-c, --set-counters PKTS BYTES
This enables the administrator to initialize the packet and byte counters of a rule (during INSERT, APPEND, REPLACE operations).
OTHER OPTIONS
The following additional options can be specified:
-v, --verbose
Verbose output. This option makes the list command show the interface name, the rule options (if any), and the TOS masks. The packet and byte counters are also listed, with the suffix 'K', 'M' or 'G' for 1000, 1,000,000 and 1,000,000,000 multipliers respectively (but see the -x flag to change this). For appending, insertion, deletion and replacement, this causes detailed information on the rule or rules to be printed.
-n, --numeric
Numeric output. IP addresses and port numbers will be printed in numeric format. By default, the program will try to display them as host names, network names, or services (whenever applicable).
-x, --exact
Expand numbers. Display the exact value of the packet and byte counters, instead of only the rounded number in K's (multiples of 1000) M's (multiples of 1000K) or G's (multiples of 1000M). This option is only relevant for the -L command.
--line-numbers
When listing rules, add line numbers to the beginning of each rule, corresponding to that rule's position in the chain.
--modprobe=command
When adding or inserting rules into a chain, use command to load any necessary modules (targets, match extensions, etc).
MATCH EXTENSIONS
iptables can use extended packet matching modules. These are loaded in two ways: implicitly, when -p or --protocol is specified, or with the -m or --match options, followed by the matching module name; after these, various extra command line options become available, depending on the specific module. You can specify multiple extended match modules in one line, and you can use the -h or --help options after the module has been specified to receive help specific to that module.
The following are included in the base package, and most of these can be preceded by a ! to invert the sense of the match.
addrtype
This module matches packets based on their address type. Address types are used within the kernel networking stack and categorize addresses into various groups. The exact definition of that group depends on the specific layer three protocol.
The following address types are possible:
UNSPEC
an unspecified address (i.e. 0.0.0.0) UNICAST an unicast address LOCAL a local address BROADCAST a broadcast address ANYCAST an anycast packet MULTICAST a multicast address BLACKHOLE a blackhole address UNREACHABLE an unreachable address PROHIBIT a prohibited address THROW FIXME NAT FIXME XRESOLVE FIXME
--src-type type
Matches if the source address is of given type
--dst-type type
Matches if the destination address is of given type
ah
This module matches the SPIs in AH header of IPSec packets.
--ahspi [!] spi[:spi]
childlevel
This is an experimental module. It matches on whether the packet is part of a master connection or one of its children (or grandchildren, etc). For instance, most packets are level 0. FTP data transfer is level 1.
--childlevel [!] level
condition
This matches if a specific /proc filename is '0' or '1'.
--condition [!] filename
Match on boolean value stored in /proc/net/ipt_condition/filename file
connmark
This module matches the netfilter mark field associated with a connection (which can be set using the CONNMARK target below).
--mark value
Matches packets in connections with the given mark value (if a mask is specified, this is logically ANDed with the mark before the comparison).
connrate
This module matches the current transfer rate in a connection.
--connrate [!] :
Match against the current connection transfer rate being within 'from' and 'to' bytes per second. When the "!" argument is used before the range, the sense of the match is inverted.
conntrack
This module, when combined with connection tracking, allows access to more connection tracking information than the "state" match. (this module is present only if iptables was compiled under a kernel supporting this feature)
--ctstate state
Where state is a comma separated list of the connection states to match. Possible states are INVALID meaning that the packet is associated with no known connection, ESTABLISHED meaning that the packet is associated with a connection which has seen packets in both directions, NEW meaning that the packet has started a new connection, or otherwise associated with a connection which has not seen packets in both directions, and RELATED meaning that the packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error. SNAT A virtual state, matching if the original source address differs from the reply destination. DNAT A virtual state, matching if the original destination differs from the reply source.
--ctproto proto
Protocol to match (by number or name)
--ctorigsrc [!] address
Match against original source address
--ctorigdst [!] address
Match against original destination address
--ctreplsrc [!] address
Match against reply source address
--ctrepldst [!] address
Match against reply destination address
--ctstatus [,...]
Match against internal conntrack states
--ctexpire time[:time]
Match remaining lifetime in seconds against given value or range of values (inclusive)
dscp
This module matches the 6 bit DSCP field within the TOS field in the IP header. DSCP has superseded TOS within the IETF.
--dscp value
Match against a numeric (decimal or hex) value .
--dscp-class DiffServ Class
Match the DiffServ class. This value may be any of the BE, EF, AFxx or CSx classes. It will then be converted into it's according numeric value.
dstlimit
This module allows you to limit the packet per second (pps) rate on a per destination IP or per destination port base. As opposed to the `limit' match, every destination ip / destination port has it's own limit.
--dstlimit avg
Maximum average match rate (packets per second unless followed by /sec /minute /hour /day postfixes).
--dstlimit-mode mode
The limiting hashmode. Is the specified limit per dstip, dstip-dstport tuple, srcip-dstip tuple, or per srcipdstip-dstport tuple.
--dstlimit-name name
Name for /proc/net/ipt_dstlimit/* file entry
[--dstlimit-burst burst]
Number of packets to match in a burst. Default: 5
[--dstlimit-htable-size size]
Number of buckets in the hashtable
[--dstlimit-htable-max max]
Maximum number of entries in the hashtable
[--dstlimit-htable-gcinterval interval]
Interval between garbage collection runs of the hashtable (in miliseconds). Default is 1000 (1 second).
[--dstlimit-htable-expire time
After which time are idle entries expired from hashtable (in miliseconds)? Default is 10000 (10 seconds).
ecn
This allows you to match the ECN bits of the IPv4 and TCP header. ECN is the Explicit Congestion Notification mechanism as specified in RFC3168
--ecn-tcp-cwr
This matches if the TCP ECN CWR (Congestion Window Received) bit is set.
--ecn-tcp-ece
This matches if the TCP ECN ECE (ECN Echo) bit is set.
--ecn-ip-ect num
This matches a particular IPv4 ECT (ECN-Capable Transport). You have to specify a number between `0' and `3'.
esp
This module matches the SPIs in ESP header of IPSec packets.
--espspi [!] spi[:spi]
fuzzy
This module matches a rate limit based on a fuzzy logic controller
--lower-limit number
Specifies the lower limit (in packets per second).
--upper-limit number
Specifies the upper limit (in packets per second).
helper
This module matches packets related to a specific conntrack-helper.
--helper string
Matches packets related to the specified conntrack-helper.
string can be "ftp" for packets related to a ftp-session on default port. For other ports append -portnr to the value, ie. "ftp-2121".
Same rules apply for other conntrack-helpers.
icmp
This extension is loaded if `--protocol icmp' is specified. It provides the following option:
--icmp-type [!] typename
This allows specification of the ICMP type, which can be a numeric ICMP type, or one of the ICMP type names shown by the command
iptables -p icmp -h
iprange
This matches on a given arbitrary range of IPv4 addresses
[!]--src-range ip-ip
Match source IP in the specified range.
[!]--dst-range ip-ip
Match destination IP in the specified range.
length
This module matches the length of a packet against a specific value or range of values.
--length length[:length]
limit
This module matches at a limited rate using a token bucket filter. A rule using this extension will match until this limit is reached (unless the `!' flag is used). It can be used in combination with the LOG target to give limited logging, for example.
--limit rate
Maximum average matching rate: specified as a number, with an optional `/second', `/minute', `/hour', or `/day' suffix; the default is 3/hour.
--limit-burst number
Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5.
mac
--mac-source [!] address
Match source MAC address. It must be of the form XX:XX:XX:XX:XX:XX. Note that this only makes sense for packets coming from an Ethernet device and entering the PREROUTING, FORWARD or INPUT chains.
mark
This module matches the netfilter mark field associated with a packet (which can be set using the MARK target below).
--mark value
Matches packets with the given unsigned mark value (if a mask is specified, this is logically ANDed with the mask before the comparison).
mport
This module matches a set of source or destination ports. Up to 15 ports can be specified. It can only be used in conjunction with -p tcp or -p udp.
--source-ports port[,port[,port...]]
Match if the source port is one of the given ports. The flag --sports is a convenient alias for this option.
--destination-ports port[,port[,port...]]
Match if the destination port is one of the given ports. The flag --dports is a convenient alias for this option.
--ports port[,port[,port...]]
Match if the both the source and destination ports are equal to each other and to one of the given ports.
multiport
This module matches a set of source or destination ports. Up to 15 ports can be specified. It can only be used in conjunction with -p tcp or -p udp.
--source-ports port[,port[,port...]]
Match if the source port is one of the given ports. The flag --sports is a convenient alias for this option.
--destination-ports port[,port[,port...]]
Match if the destination port is one of the given ports. The flag --dports is a convenient alias for this option.
--ports port[,port[,port...]]
Match if the both the source and destination ports are equal to each other and to one of the given ports.
nth
This module matches every `n'th packet
--every value
Match every `value' packet
[--counter num]
Use internal counter number `num'. Default is `0'.
[--start num]
Initialize the counter at the number `num' insetad of `0'. Most between `0' and `value'-1.
[--packet num]
Match on `num' packet. Most be between `0' and `value'-1.
owner
This module attempts to match various characteristics of the packet creator, for locally-generated packets. It is only valid in the OUTPUT chain, and even this some packets (such as ICMP ping responses) may have no owner, and hence never match.
--uid-owner userid
Matches if the packet was created by a process with the given effective user id.
--gid-owner groupid
Matches if the packet was created by a process with the given effective group id.
--pid-owner processid
Matches if the packet was created by a process with the given process id.
--sid-owner sessionid
Matches if the packet was created by a process in the given session group.
--cmd-owner name
Matches if the packet was created by a process with the given command name. (this option is present only if iptables was compiled under a kernel supporting this feature)
physdev
This module matches on the bridge port input and output devices enslaved to a bridge device. This module is a part of the infrastructure that enables a transparent bridging IP firewall and is only useful for kernel versions above version 2.5.44.
--physdev-in name
Name of a bridge port via which a packet is received (only for packets entering the INPUT, FORWARD and PREROUTING chains). If the interface name ends in a "+", then any interface which begins with this name will match. If the packet didn't arrive through a bridge device, this packet won't match this option, unless '!' is used.
--physdev-out name
Name of a bridge port via which a packet is going to be sent (for packets entering the FORWARD, OUTPUT and POSTROUTING chains). If the interface name ends in a "+", then any interface which begins with this name will match. Note that in the nat and mangle OUTPUT chains one cannot match on the bridge output port, however one can in the filter OUTPUT chain. If the packet won't leave by a bridge device or it is yet unknown what the output device will be, then the packet won't match this option, unless
--physdev-is-in
Matches if the packet has entered through a bridge interface.
--physdev-is-out
Matches if the packet will leave through a bridge interface.
--physdev-is-bridged
Matches if the packet is being bridged and therefore is not being routed. This is only useful in the FORWARD and POSTROUTING chains.
pkttype
This module matches the link-layer packet type.
--pkt-type
random
This module randomly matches a certain percentage of all packets.
--average percent
Matches the given percentage. If omitted, a probability of 50% is set.
realm
This matches the routing realm. Routing realms are used in complex routing setups involving dynamic routing protocols like BGP.
--realm [!]value
Matches a given realm number (and optionally mask).
state
This module, when combined with connection tracking, allows access to the connection tracking state for this packet.
--state state
Where state is a comma separated list of the connection states to match. Possible states are INVALID meaning that the packet could not be identified for some reason which includes running out of memory and ICMP errors which don't correspond to any known connection, ESTABLISHED meaning that the packet is associated with a connection which has seen packets in both directions, NEW meaning that the packet has started a new connection, or otherwise associated with a connection which has not seen packets in both directions, and RELATED meaning that the packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error.
tcp
These extensions are loaded if `--protocol tcp' is specified. It provides the following options:
--source-port [!] port[:port]
Source port or port range specification. This can either be a service name or a port number. An inclusive range can also be specified, using the format port:port. If the first port is omitted, "0" is assumed; if the last is omitted, "65535" is assumed. If the second port greater then the first they will be swapped. The flag --sport is a convenient alias for this option.
--destination-port [!] port[:port]
Destination port or port range specification. The flag --dport is a convenient alias for this option.
--tcp-flags [!] mask comp
Match when the TCP flags are as specified. The first argument is the flags which we should examine, written as a comma-separated list, and the second argument is a comma-separated list of flags which must be set. Flags are: SYN ACK FIN RST URG PSH ALL NONE. Hence the command
iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
will only match packets with the SYN flag set, and the ACK, FIN and RST flags unset.
[!] --syn
Only match TCP packets with the SYN bit set and the ACK and RST bits cleared. Such packets are used to request TCP connection initiation; for example, blocking such packets coming in an interface will prevent incoming TCP connections, but outgoing TCP connections will be unaffected. It is equivalent to --tcp-flags SYN,RST,ACK SYN. If the "!" flag precedes the "--syn", the sense of the option is inverted.
--tcp-option [!] number
Match if TCP option set.
--mss value[:value]
Match TCP SYN or SYN/ACK packets with the specified MSS value (or range), which control the maximum packet size for that connection.
tcpmss
This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time.
[!] --mss value[:value]
Match a given TCP MSS value or range.
time
This matches if the packet arrival time/date is within a given range. All options are facultative.
--timestart value
Match only if it is after `value' (Inclusive, format: HH:MM ; default 00:00).
--timestop value
Match only if it is before `value' (Inclusive, format: HH:MM ; default 23:59).
--days listofdays
Match only if today is one of the given days. (format: Mon,Tue,Wed,Thu,Fri,Sat,Sun ; default everyday)
--datestart date
Match only if it is after `date' (Inclusive, format: YYYY[:MM[:DD[:hh[:mm[:ss]]]]] ; h,m,s start from 0 ; default to 1970)
--datestop date
Match only if it is before `date' (Inclusive, format: YYYY[:MM[:DD[:hh[:mm[:ss]]]]] ; h,m,s start from 0 ; default to 2037)
tos
This module matches the 8 bits of Type of Service field in the IP header (ie. including the precedence bits).
--tos tos
The argument is either a standard name, (use
iptables -m tos -h
to see the list), or a numeric value to match.
ttl
This module matches the time to live field in the IP header.
--ttl-eq ttl
Matches the given TTL value.
--ttl-gt ttl
Matches if TTL is greater than the given TTL value.
--ttl-lt ttl
Matches if TTL is less than the given TTL value.
udp
These extensions are loaded if `--protocol udp' is specified. It provides the following options:
--source-port [!] port[:port]
Source port or port range specification. See the description of the --source-port option of the TCP extension for details.
--destination-port [!] port[:port]
Destination port or port range specification. See the description of the --destination-port option of the TCP extension for details.
unclean
This module takes no options, but attempts to match packets which seem malformed or unusual. This is regarded as experimental.
TARGET EXTENSIONS
iptables can use extended target modules: the following are included in the standard distribution.
BALANCE
This allows you to DNAT connections in a round-robin way over a given range of destination addresses.
--to-destination ipaddr-ipaddr
Address range to round-robin over.
CLASSIFY
This module allows you to set the skb->priority value (and thus classify the packet into a specific CBQ class).
--set-class MAJOR:MINOR
Set the major and minor class value.
CLUSTERIP
This module allows you to configure a simple cluster of nodes that share a certain IP and MAC address without an explicit load balancer in front of them. Connections are statically distributed between the nodes in this cluster.
--new
Create a new ClusterIP. You always have to set this on the first rule for a given ClusterIP.
--hashmode mode
Specify the hashing mode. Has to be one of sourceip, sourceip-sourceport, sourceip-sourceport-destport
--clustermac mac
Specify the ClusterIP MAC address. Has to be a link-layer multicast address
--total-nodes num
Number of total nodes within this cluster.
--local-node num
Local node number within this cluster.
--hash-init rnd
Specify the random seed used for hash initialization.
CONNMARK
This module sets the netfilter mark value associated with a connection
--set-mark mark
Set connection mark. If a mask is specified then only those bits set in the mask is modified.
--save-mark [--mask mask]
Copy the netfilter packet mark value to the connection mark. If a mask is specified then only those bits are copied.
--restore-mark [--mask mask]
Copy the connection mark value to the packet. If a mask is specified then only those bits are copied. This is only valid in the mangle table.
DNAT
This target is only valid in the nat table, in the PREROUTING and OUTPUT chains, and user-defined chains which are only called from those chains. It specifies that the destination address of the packet should be modified (and all future packets in this connection will also be mangled), and rules should cease being examined. It takes one type of option:
--to-destination ipaddr[-ipaddr][:port-port]
which can specify a single new destination IP address, an inclusive range of IP addresses, and optionally, a port range (which is only valid if the rule also specifies -p tcp or -p udp). If no port range is specified, then the destination port will never be modified.
You can add several --to-destination options. If you specify more than one destination address, either via an address range or multiple --to-destination options, a simple round-robin (one after another in cycle) load balancing takes place between these adresses.
DSCP
This target allows to alter the value of the DSCP bits within the TOS header of the IPv4 packet. As this manipulates a packet, it can only be used in the mangle table.
--set-dscp value
Set the DSCP field to a numerical value (can be decimal or hex)
--set-dscp-class class
Set the DSCP field to a DiffServ class.
ECN
This target allows to selectively work around known ECN blackholes. It can only be used in the mangle table.
--ecn-tcp-remove
Remove all ECN bits from the TCP header. Of course, it can only be used in conjunction with -p tcp.
LOG
Turn on kernel logging of matching packets. When this option is set for a rule, the Linux kernel will print some information on all matching packets (like most IP header fields) via the kernel log (where it can be read with dmesg or syslogd(8)). This is a "non-terminating target", i.e. rule traversal continues at the next rule. So if you want to LOG the packets you refuse, use two separate rules with the same matching criteria, first using target LOG then DROP (or REJECT).
--log-level level
Level of logging (numeric or see syslog.conf(5)).
--log-prefix prefix
Prefix log messages with the specified prefix; up to 29 letters long, and useful for distinguishing messages in the logs.
--log-tcp-sequence
Log TCP sequence numbers. This is a security risk if the log is readable by users.
--log-tcp-options
Log options from the TCP packet header.
--log-ip-options
Log options from the IP packet header.
MARK
This is used to set the netfilter mark value associated with the packet. It is only valid in the mangle table. It can for example be used in conjunction with iproute2.
--set-mark mark
MASQUERADE
This target is only valid in the nat table, in the POSTROUTING chain. It should only be used with dynamically assigned IP (dialup) connections: if you have a static IP address, you should use the SNAT target. Masquerading is equivalent to specifying a mapping to the IP address of the interface the packet is going out, but also has the effect that connections are forgotten when the interface goes down. This is the correct behavior when the next dialup is unlikely to have the same interface address (and hence any established connections are lost anyway). It takes one option:
--to-ports port[-port]
This specifies a range of source ports to use, overriding the default SNAT source port-selection heuristics (see above). This is only valid if the rule also specifies -p tcp or -p udp.
MIRROR
This is an experimental demonstration target which inverts the source and destination fields in the IP header and retransmits the packet. It is only valid in the INPUT, FORWARD and PREROUTING chains, and user-defined chains which are only called from those chains. Note that the outgoing packets are NOT seen by any packet filtering chains, connection tracking or NAT, to avoid loops and other problems.
NETMAP
This target allows you to statically map a whole network of addresses onto another network of addresses. It can only be used from rules in the nat table.
--to address
Network address to map to. The resulting address will be constructed in the following way: All 'one' bits in the mask are filled in from the new `address'. All bits that are zero in the mask are filled in from the original address.
NOTRACK
This target disables connection tracking for all packets matching that rule.
It can only be used in the
raw table.
REDIRECT
This target is only valid in the nat table, in the PREROUTING and OUTPUT chains, and user-defined chains which are only called from those chains. It alters the destination IP address to send the packet to the machine itself (locally-generated packets are mapped to the 127.0.0.1 address). It takes one option:
--to-ports port[-port]
This specifies a destination port or range of ports to use: without this, the destination port is never altered. This is only valid if the rule also specifies -p tcp or -p udp.
REJECT
This is used to send back an error packet in response to the matched packet: otherwise it is equivalent to DROP so it is a terminating TARGET, ending rule traversal. This target is only valid in the INPUT, FORWARD and OUTPUT chains, and user-defined chains which are only called from those chains. The following option controls the nature of the error packet returned:
--reject-with type
The type given can be
icmp-net-unreachable
icmp-host-unreachable
icmp-port-unreachable
icmp-proto-unreachable
icmp-net-prohibited
icmp-host-prohibited or
icmp-admin-prohibited (*)
which return the appropriate ICMP error message (port-unreachable is the default). The option tcp-reset can be used on rules which only match the TCP protocol: this causes a TCP RST packet to be sent back. This is mainly useful for blocking ident (113/tcp) probes which frequently occur when sending mail to broken mail hosts (which won't accept your mail otherwise).
(*) Using icmp-admin-prohibited with kernels that do not support it will result in a plain DROP instead of REJECT
ROUTE
This is used to explicitly override the core network stack's routing decision. mangle table.
--oif ifname
Route the packet through `ifname' network interface
--iif ifname
Change the packet's incoming interface to `ifname'
--gw IP_address
Route the packet via this gateway
--continue
Behave like a non-terminating target and continue traversing the rules. Not valid in combination with `--iif'
SNAT
This target is only valid in the nat table, in the POSTROUTING chain. It specifies that the source address of the packet should be modified (and all future packets in this connection will also be mangled), and rules should cease being examined. It takes one type of option:
--to-source ipaddr[-ipaddr][:port-port]
which can specify a single new source IP address, an inclusive range of IP addresses, and optionally, a port range (which is only valid if the rule also specifies -p tcp or -p udp). If no port range is specified, then source ports below 512 will be mapped to other ports below 512: those between 512 and 1023 inclusive will be mapped to ports below 1024, and other ports will be mapped to 1024 or above. Where possible, no port alteration will occur.
You can add several --to-source options. If you specify more than one source address, either via an address range or multiple --to-source options, a simple round-robin (one after another in cycle) takes place between these adresses.
TCPMSS
This target allows to alter the MSS value of TCP SYN packets, to control the maximum size for that connection (usually limiting it to your outgoing interface's MTU minus 40). Of course, it can only be used in conjunction with -p tcp.
This target is used to overcome criminally braindead ISPs or servers which block ICMP Fragmentation Needed packets. The symptoms of this problem are that everything works fine from your Linux firewall/router, but machines behind it can never exchange large packets:
1)
Web browsers connect, then hang with no data received.
2)
Small mail works fine, but large emails hang.
3)
ssh works fine, but scp hangs after initial handshaking.
Workaround: activate this option and add a rule to your firewall configuration like:
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
-j TCPMSS --clamp-mss-to-pmtu
--set-mss value
Explicitly set MSS option to specified value.
--clamp-mss-to-pmtu
Automatically clamp MSS value to (path_MTU - 40).
These options are mutually exclusive.
TOS
This is used to set the 8-bit Type of Service field in the IP header. It is only valid in the mangle table.
--set-tos tos
You can use a numeric TOS values, or use
iptables -j TOS -h
to see the list of valid TOS names.
TRACE
This target has no options. It just turns on packet tracing for all packets that match this rule.
TTL
This is used to modify the IPv4 TTL header field. The TTL field determines how many hops (routers) a packet can traverse until it's time to live is exceeded.
Setting or incrementing the TTL field can potentially be very dangerous,
so it should be avoided at any cost.
Don't ever set or increment the value on packets that leave your local network!
mangle table.
--ttl-set value
Set the TTL value to `value'.
--ttl-dec value
Decrement the TTL value `value' times.
--ttl-inc value
Increment the TTL value `value' times.
ULOG
This target provides userspace logging of matching packets. When this target is set for a rule, the Linux kernel will multicast this packet through a netlink socket. One or more userspace processes may then subscribe to various multicast groups and receive the packets. Like LOG, this is a "non-terminating target", i.e. rule traversal continues at the next rule.
--ulog-nlgroup nlgroup
This specifies the netlink group (1-32) to which the packet is sent. Default value is 1.
--ulog-prefix prefix
Prefix log messages with the specified prefix; up to 32 characters long, and useful for distinguishing messages in the logs.
--ulog-cprange size
Number of bytes to be copied to userspace. A value of 0 always copies the entire packet, regardless of its size. Default is 0.
--ulog-qthreshold size
Number of packet to queue inside kernel. Setting this value to, e.g. 10 accumulates ten packets inside the kernel and transmits them as one netlink multipart message to userspace. Default is 1 (for backwards compatibility).
DIAGNOSTICS
Various error messages are printed to standard error. The exit code is 0 for correct functioning. Errors which appear to be caused by invalid or abused command line parameters cause an exit code of 2, and other errors cause an exit code of 1.
BUGS
Bugs? What's this? ;-) Well... the counters are not reliable on sparc64.
COMPATIBILITY WITH IPCHAINS
This iptables is very similar to ipchains by Rusty Russell. The main difference is that the chains INPUT and OUTPUT are only traversed for packets coming into the local host and originating from the local host respectively. Hence every packet only passes through one of the three chains (except loopback traffic, which involves both INPUT and OUTPUT chains); previously a forwarded packet would pass through all three.
The other main difference is that -i refers to the input interface; -o refers to the output interface, and both are available for packets entering the FORWARD chain.
iptables is a pure packet filter when using the default `filter' table, with optional extension modules. This should simplify much of the previous confusion over the combination of IP masquerading and packet filtering seen previously. So the following options are handled differently:
-j MASQ
-M -S
-M -L
There are several other changes in iptables.
SEE ALSO
iptables-save(8), iptables-restore(8), ip6tables(8), ip6tables-save(8), ip6tables-restore(8).
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