VERDICT STATEMENT

~~~~~~~~~~~~~~~~~

The verdict statement alters control flow in the ruleset and issues policy decisions for packets.

[verse]

{*accept* | *drop* | *queue* | *continue* | *return*}

{*jump* | *goto*} 'chain'

*accept* and *drop* are absolute verdicts -- they terminate ruleset evaluation immediately.

[horizontal]

*accept*:: Terminate ruleset evaluation and accept the packet.

The packet can still be dropped later by another hook, for instance accept

in the forward hook still allows to drop the packet later in the postrouting hook,

or another forward base chain that has a higher priority number and is evaluated

afterwards in the processing pipeline.

*drop*:: Terminate ruleset evaluation and drop the packet.

The drop occurs instantly, no further chains or hooks are evaluated.

It is not possible to accept the packet in a later chain again, as those

are not evaluated anymore for the packet.

*queue*:: Terminate ruleset evaluation and queue the packet to userspace.

Userspace must provide a drop or accept verdict.  In case of accept, processing

resumes with the next base chain hook, not the rule following the queue verdict.

*continue*:: Continue ruleset evaluation with the next rule. This

 is the default behaviour in case a rule issues no verdict.

*return*:: Return from the current chain and continue evaluation at the

 next rule in the last chain. If issued in a base chain, it is equivalent to the

 base chain policy.

*jump* 'chain':: Continue evaluation at the first rule in 'chain'. The current

 position in the ruleset is pushed to a call stack and evaluation will continue

 there when the new chain is entirely evaluated or a *return* verdict is issued.

 In case an absolute verdict is issued by a rule in the chain, ruleset evaluation

 terminates immediately and the specific action is taken.

*goto* 'chain':: Similar to *jump*, but the current position is not pushed to the

 call stack, meaning that after the new chain evaluation will continue at the last

 chain instead of the one containing the goto statement.

.Using verdict statements

-------------------

# process packets from eth0 and the internal network in from_lan

# chain, drop all packets from eth0 with different source addresses.

filter input iif eth0 ip saddr 192.168.0.0/24 jump from_lan

filter input iif eth0 drop

-------------------

PAYLOAD STATEMENT

~~~~~~~~~~~~~~~~~

[verse]

'payload_expression' *set* 'value'

The payload statement alters packet content. It can be used for example to

set ip DSCP (diffserv) header field or ipv6 flow labels.

.route some packets instead of bridging

---------------------------------------

# redirect tcp:http from 192.160.0.0/16 to local machine for routing instead of bridging

# assumes 00:11:22:33:44:55 is local MAC address.

bridge input meta iif eth0 ip saddr 192.168.0.0/16 tcp dport 80 meta pkttype set unicast ether daddr set 00:11:22:33:44:55

-------------------------------------------

.Set IPv4 DSCP header field

---------------------------

ip forward ip dscp set 42

---------------------------

EXTENSION HEADER STATEMENT

~~~~~~~~~~~~~~~~~~~~~~~~~~

[verse]

'extension_header_expression' *set* 'value'

The extension header statement alters packet content in variable-sized headers.

This can currently be used to alter the TCP Maximum segment size of packets,

similar to TCPMSS.

.change tcp mss

---------------

tcp flags syn tcp option maxseg size set 1360

# set a size based on route information:

tcp flags syn tcp option maxseg size set rt mtu

---------------

LOG STATEMENT

~~~~~~~~~~~~~

[verse]

*log* [*prefix* 'quoted_string'] [*level* 'syslog-level'] [*flags* 'log-flags']

*log* *group* 'nflog_group' [*prefix* 'quoted_string'] [*queue-threshold* 'value'] [*snaplen* 'size']

*log level audit*

The log statement enables logging of matching packets. When this statement is

used from a rule, the Linux kernel will print some information on all matching

packets, such as header fields, via the kernel log (where it can be read with

dmesg(1) or read in the syslog).

In the second form of invocation (if 'nflog_group' is specified), the Linux

kernel will pass the packet to nfnetlink_log which will multicast the packet

through a netlink socket to the specified multicast group. One or more userspace

processes may subscribe to the group to receive the packets, see

libnetfilter_queue documentation for details.

In the third form of invocation (if level audit is specified), the Linux

kernel writes a message into the audit buffer suitably formatted for reading

with auditd. Therefore no further formatting options (such as prefix or flags)

are allowed in this mode.

This is a non-terminating statement, so the rule evaluation continues after

the packet is logged.

.log statement options

[options="header"]

|==================

|Keyword | Description | Type

|prefix|

Log message prefix|

quoted string

|level|

Syslog level of logging |

string: emerg, alert, crit, err, warn [default], notice, info, debug, audit

|group|

NFLOG group to send messages to|

unsigned integer (16 bit)

|snaplen|

Length of packet payload to include in netlink message |

unsigned integer (32 bit)

|queue-threshold|

Number of packets to queue inside the kernel before sending them to userspace |

unsigned integer (32 bit)

|==================================

.log-flags

[options="header"]

|==================

| Flag | Description

|tcp sequence|

Log TCP sequence numbers.

|tcp options|

Log options from the TCP packet header.

|ip options|

Log options from the IP/IPv6 packet header.

|skuid|

Log the userid of the process which generated the packet.

|ether|

Decode MAC addresses and protocol.

|all|

Enable all log flags listed above.

|==============================

.Using log statement

--------------------

# log the UID which generated the packet and ip options

ip filter output log flags skuid flags ip options

# log the tcp sequence numbers and tcp options from the TCP packet

ip filter output log flags tcp sequence,options

# enable all supported log flags

ip6 filter output log flags all

-----------------------

REJECT STATEMENT

~~~~~~~~~~~~~~~~

[verse]

____

*reject* [ *with* 'REJECT_WITH' ]

'REJECT_WITH' := *icmp type* 'icmp_code' |

                 *icmpv6 type* 'icmpv6_code' |

                 *icmpx type* 'icmpx_code' |

                 *tcp reset*

____

A reject statement 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

statement, ending rule traversal. This statement is only valid in the input,

forward and output chains, and user-defined chains which are only called from

those chains.

.different ICMP reject variants are meant for use in different table families

[options="header"]

|==================

|Variant |Family | Type

|icmp|

ip|

icmp_code

|icmpv6|

ip6|

icmpv6_code

|icmpx|

inet|

icmpx_code

|==================

For a description of the different types and a list of supported keywords refer

to DATA TYPES section above. The common default reject value is

*port-unreachable*. +

Note that in bridge family, reject statement is only allowed in base chains

which hook into input or prerouting.

COUNTER STATEMENT

~~~~~~~~~~~~~~~~~

A counter statement sets the hit count of packets along with the number of bytes.

[verse]

*counter* *packets* 'number' *bytes* 'number'

*counter* { *packets* 'number' | *bytes* 'number' }

CONNTRACK STATEMENT

~~~~~~~~~~~~~~~~~~~

The conntrack statement can be used to set the conntrack mark and conntrack labels.

[verse]

*ct* {*mark* | *event* | *label* | *zone*} *set* 'value'

The ct statement sets meta data associated with a connection. The zone id

has to be assigned before a conntrack lookup takes place, i.e. this has to be

done in prerouting and possibly output (if locally generated packets need to be

placed in a distinct zone), with a hook priority of -300.

.Conntrack statement types

[options="header"]

|==================

|Keyword| Description| Value

|event|

conntrack event bits |

bitmask, integer (32 bit)

|helper|

name of ct helper object to assign to the connection |

quoted string

|mark|

Connection tracking mark |

mark

|label|

Connection tracking label|

label

|zone|

conntrack zone|

integer (16 bit)

|==================

.save packet nfmark in conntrack

--------------------------------

ct mark set meta mark

--------------------------------

.set zone mapped via interface

------------------------------

table inet raw {

  chain prerouting {

      type filter hook prerouting priority -300;

      ct zone set iif map { "eth1" : 1, "veth1" : 2 }

  }

  chain output {

      type filter hook output priority -300;

      ct zone set oif map { "eth1" : 1, "veth1" : 2 }

  }

}

------------------------------------------------------

.restrict events reported by ctnetlink

--------------------------------------

ct event set new,related,destroy

--------------------------------------

META STATEMENT

~~~~~~~~~~~~~~

A meta statement sets the value of a meta expression. The existing meta fields

are: priority, mark, pkttype, nftrace. +

[verse]

*meta* {*mark* | *priority* | *pkttype* | *nftrace*} *set* 'value'

A meta statement sets meta data associated with a packet. +

.Meta statement types

[options="header"]

|==================

|Keyword| Description| Value

|priority |

TC packet priority|

tc_handle

|mark|

Packet mark |

mark

|pkttype |

packet type |

pkt_type

|nftrace |

ruleset packet tracing on/off. Use *monitor trace* command to watch traces|

0, 1

|==========================

LIMIT STATEMENT

~~~~~~~~~~~~~~~

[verse]

____

*limit rate* [*over*] 'packet_number' */* 'TIME_UNIT' [*burst* 'packet_number' *packets*]

*limit rate* [*over*] 'byte_number' 'BYTE_UNIT' */* 'TIME_UNIT' [*burst* 'byte_number' 'BYTE_UNIT']

'TIME_UNIT' := *second* | *minute* | *hour* | *day*

'BYTE_UNIT' := *bytes* | *kbytes* | *mbytes*

____

A limit statement matches at a limited rate using a token bucket filter. A rule

using this statement will match until this limit is reached. It can be used in

combination with the log statement to give limited logging. The optional

*over* keyword makes it match over the specified rate.

.limit statement values

[options="header"]

|==================

|Value | Description | Type

|packet_number |

Number of packets |

unsigned integer (32 bit)

|byte_number |

Number of bytes |

unsigned integer (32 bit)

|========================

NAT STATEMENTS

~~~~~~~~~~~~~~

[verse]

____

*snat to* 'address' [*:*'port'] ['PRF_FLAGS']

*snat to* 'address' *-* 'address' [*:*'port' *-* 'port'] ['PRF_FLAGS']

*snat* { *ip* | *ip6* } *to* 'address' *-* 'address' [*:*'port' *-* 'port'] ['PR_FLAGS']

*dnat to* 'address' [*:*'port'] ['PRF_FLAGS']

*dnat to* 'address' [*:*'port' *-* 'port'] ['PR_FLAGS']

*dnat* { *ip* | *ip6* } *to* 'address' [*:*'port' *-* 'port'] ['PR_FLAGS']

*masquerade to* [*:*'port'] ['PRF_FLAGS']

*masquerade to* [*:*'port' *-* 'port'] ['PRF_FLAGS']

*redirect to* [*:*'port'] ['PRF_FLAGS']

*redirect to* [*:*'port' *-* 'port'] ['PRF_FLAGS']

'PRF_FLAGS' := 'PRF_FLAG' [*,* 'PRF_FLAGS']

'PR_FLAGS'  := 'PR_FLAG' [*,* 'PR_FLAGS']

'PRF_FLAG'  := 'PR_FLAG' | *fully-random*

'PR_FLAG'   := *persistent* | *random*

____

The nat statements are only valid from nat chain types. +

The *snat* and *masquerade* statements specify that the source address of the

packet should be modified. While *snat* is only valid in the postrouting and

input chains, *masquerade* makes sense only in postrouting. The dnat and

redirect statements are only valid in the prerouting and output chains, they

specify that the destination address of the packet should be modified. You can

use non-base chains which are called from base chains of nat chain type too.

All future packets in this connection will also be mangled, and rules should

cease being examined.

The *masquerade* statement is a special form of snat which always uses the

outgoing interface's IP address to translate to. It is particularly useful on

gateways with dynamic (public) IP addresses.

The *redirect* statement is a special form of dnat which always translates the

destination address to the local host's one. It comes in handy if one only wants

to alter the destination port of incoming traffic on different interfaces.

When used in the inet family (available with kernel 5.2), the dnat and snat

statements require the use of the ip and ip6 keyword in case an address is

provided, see the examples below.

Before kernel 4.18 nat statements require both prerouting and postrouting base chains

to be present since otherwise packets on the return path won't be seen by

netfilter and therefore no reverse translation will take place.

.NAT statement values

[options="header"]

|==================

|Expression| Description| Type

|address|

Specifies that the source/destination address of the packet should be modified.

You may specify a mapping to relate a list of tuples composed of arbitrary

expression key with address value. |

ipv4_addr, ipv6_addr, e.g. abcd::1234, or you can use a mapping, e.g. meta mark map { 10 : 192.168.1.2, 20 : 192.168.1.3 }

|port|

Specifies that the source/destination address of the packet should be modified. |

port number (16 bit)

|===============================

.NAT statement flags

[options="header"]

|==================

|Flag| Description

|persistent |

Gives a client the same source-/destination-address for each connection.

|random|

In kernel 5.0 and newer this is the same as fully-random.

In earlier kernels the port mapping will be randomized using a seeded MD5

hash mix using source and destination address and destination port.

|fully-random|

If used then port mapping is generated based on a 32-bit pseudo-random algorithm.

|=============================

.Using NAT statements

---------------------

# create a suitable table/chain setup for all further examples

add table nat

add chain nat prerouting { type nat hook prerouting priority 0; }

add chain nat postrouting { type nat hook postrouting priority 100; }

# translate source addresses of all packets leaving via eth0 to address 1.2.3.4

add rule nat postrouting oif eth0 snat to 1.2.3.4

# redirect all traffic entering via eth0 to destination address 192.168.1.120

add rule nat prerouting iif eth0 dnat to 192.168.1.120

# translate source addresses of all packets leaving via eth0 to whatever

# locally generated packets would use as source to reach the same destination

add rule nat postrouting oif eth0 masquerade

# redirect incoming TCP traffic for port 22 to port 2222

add rule nat prerouting tcp dport 22 redirect to :2222

# inet family:

# handle ip dnat:

add rule inet nat prerouting dnat ip to 10.0.2.99

# handle ip6 dnat:

add rule inet nat prerouting dnat ip6 to fe80::dead

# this masquerades both ipv4 and ipv6:

add rule inet nat postrouting meta oif ppp0 masquerade

------------------------

TPROXY STATEMENT

~~~~~~~~~~~~~~~~

Tproxy redirects the packet to a local socket without changing the packet header

in any way. If any of the arguments is missing the data of the incoming packet

is used as parameter. Tproxy matching requires another rule that ensures the

presence of transport protocol header is specified.

[verse]

*tproxy to* 'address'*:*'port'

*tproxy to* {'address' | *:*'port'}

This syntax can be used in *ip/ip6* tables where network layer protocol is

obvious. Either IP address or port can be specified, but at least one of them is

necessary.

[verse]

*tproxy* {*ip* | *ip6*} *to* 'address'[*:*'port']

*tproxy to :*'port'

This syntax can be used in *inet* tables. The *ip/ip6* parameter defines the

family the rule will match. The *address* parameter must be of this family.

When only *port* is defined, the address family should not be specified. In

this case the rule will match for both families.

.tproxy attributes

[options="header"]

|=================

| Name | Description

| address | IP address the listening socket with IP_TRANSPARENT option is bound to.

| port | Port the listening socket with IP_TRANSPARENT option is bound to.

|=================

.Example ruleset for tproxy statement

-------------------------------------

table ip x {

    chain y {

        type filter hook prerouting priority -150; policy accept;

        tcp dport ntp tproxy to 1.1.1.1

        udp dport ssh tproxy to :2222

    }

}

table ip6 x {

    chain y {

       type filter hook prerouting priority -150; policy accept;

       tcp dport ntp tproxy to [dead::beef]

       udp dport ssh tproxy to :2222

    }

}

table inet x {

    chain y {

        type filter hook prerouting priority -150; policy accept;

        tcp dport 321 tproxy to :ssh

        tcp dport 99 tproxy ip to 1.1.1.1:999

        udp dport 155 tproxy ip6 to [dead::beef]:smux

    }

}

-------------------------------------

SYNPROXY STATEMENT

~~~~~~~~~~~~~~~~~~

This statement will process TCP three-way-handshake parallel in netfilter

context to protect either local or backend system. This statement requires

connection tracking because sequence numbers need to be translated.

[verse]

*synproxy* [*mss* 'mss_value'] [*wscale* 'wscale_value'] ['SYNPROXY_FLAGS']

.synproxy statement attributes

[options="header"]

|=================

| Name | Description

| mss | Maximum segment size announced to clients. This must match the backend.

| wscale | Window scale announced to clients. This must match the backend.

|=================

.synproxy statement flags

[options="header"]

|=================

| Flag | Description

| sack-perm |

Pass client selective acknowledgement option to backend (will be disabled if

not present).

| timestamp |

Pass client timestamp option to backend (will be disabled if not present, also

needed for selective acknowledgement and window scaling).

|=================

.Example ruleset for synproxy statement

---------------------------------------

Determine tcp options used by backend, from an external system

              tcpdump -pni eth0 -c 1 'tcp[tcpflags] == (tcp-syn|tcp-ack)'

                  port 80 &

              telnet 192.0.2.42 80

              18:57:24.693307 IP 192.0.2.42.80 > 192.0.2.43.48757:

                  Flags [S.], seq 360414582, ack 788841994, win 14480,

                  options [mss 1460,sackOK,

                  TS val 1409056151 ecr 9690221,

                  nop,wscale 9],

                  length 0

Switch tcp_loose mode off, so conntrack will mark out-of-flow packets as state INVALID.

              echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose

Make SYN packets untracked.

	table ip x {

		chain y {

			type filter hook prerouting priority raw; policy accept;

			tcp flags syn notrack

		}

	}

Catch UNTRACKED (SYN  packets) and INVALID (3WHS ACK packets) states and send

them to SYNPROXY. This rule will respond to SYN packets with SYN+ACK

syncookies, create ESTABLISHED for valid client response (3WHS ACK packets) and

drop incorrect cookies. Flags combinations not expected during  3WHS will not

match and continue (e.g. SYN+FIN, SYN+ACK). Finally, drop invalid packets, this

will be out-of-flow packets that were not matched by SYNPROXY.

    table ip foo {

            chain z {

                    type filter hook input priority filter; policy accept;

                    ct state { invalid, untracked } synproxy mss 1460 wscale 9 timestamp sack-perm

                    ct state invalid drop

            }

    }

The outcome ruleset of the steps above should be similar to the one below.

	table ip x {

		chain y {

			type filter hook prerouting priority raw; policy accept;

	                tcp flags syn notrack

		}

		chain z {

			type filter hook input priority filter; policy accept;

	                ct state { invalid, untracked } synproxy mss 1460 wscale 9 timestamp sack-perm

		        ct state invalid drop

	        }

	}

---------------------------------------

FLOW STATEMENT

~~~~~~~~~~~~~~

A flow statement allows us to select what flows you want to accelerate

forwarding through layer 3 network stack bypass. You have to specify the

flowtable name where you want to offload this flow.

*flow add @*'flowtable'

QUEUE STATEMENT

~~~~~~~~~~~~~~~

This statement passes the packet to userspace using the nfnetlink_queue handler.

The packet is put into the queue identified by its 16-bit queue number.

Userspace can inspect and modify the packet if desired. Userspace must then drop

or re-inject the packet into the kernel. See libnetfilter_queue documentation

for details.

[verse]

____

*queue* [*num* 'queue_number'] [*bypass*]

*queue* [*num* 'queue_number_from' - 'queue_number_to'] ['QUEUE_FLAGS']

'QUEUE_FLAGS' := 'QUEUE_FLAG' [*,* 'QUEUE_FLAGS']

'QUEUE_FLAG'  := *bypass* | *fanout*

____

.queue statement values

[options="header"]

|==================

|Value | Description | Type

|queue_number |

Sets queue number, default is 0. |

unsigned integer (16 bit)

|queue_number_from |

Sets initial queue in the range, if fanout is used. |

unsigned integer (16 bit)

|queue_number_to |

Sets closing queue in the range, if fanout is used. |

unsigned integer (16 bit)

|=====================

.queue statement flags

[options="header"]

|==================

|Flag | Description

|bypass |

Let packets go through if userspace application cannot back off. Before using

this flag, read libnetfilter_queue documentation for performance tuning recommendations.

|fanout |

Distribute packets between several queues.

|===============================

DUP STATEMENT

~~~~~~~~~~~~~

The dup statement is used to duplicate a packet and send the copy to a different

destination.

[verse]

*dup to* 'device'

*dup to* 'address' *device* 'device'

.Dup statement values

[options="header"]

|==================

|Expression | Description | Type

|address |

Specifies that the copy of the packet should be sent to a new gateway.|

ipv4_addr, ipv6_addr, e.g. abcd::1234, or you can use a mapping, e.g. ip saddr map { 192.168.1.2 : 10.1.1.1 }

|device |

Specifies that the copy should be transmitted via device. |

string

|===================

.Using the dup statement

------------------------

# send to machine with ip address 10.2.3.4 on eth0

ip filter forward dup to 10.2.3.4 device "eth0"

# copy raw frame to another interface

netdetv ingress dup to "eth0"

dup to "eth0"

# combine with map dst addr to gateways

dup to ip daddr map { 192.168.7.1 : "eth0", 192.168.7.2 : "eth1" }

-----------------------------------

FWD STATEMENT

~~~~~~~~~~~~~

The fwd statement is used to redirect a raw packet to another interface. It is

only available in the netdev family ingress hook. It is similar to the dup

statement except that no copy is made.

*fwd to* 'device'

SET STATEMENT

~~~~~~~~~~~~~

The set statement is used to dynamically add or update elements in a set from

the packet path. The set setname must already exist in the given table and must

have been created with one or both of the dynamic and the timeout flags. The

dynamic flag is required if the set statement expression includes a stateful

object. The timeout flag is implied if the set is created with a timeout, and is

required if the set statement updates elements, rather than adding them.

Furthermore, these sets should specify both a maximum set size (to prevent

memory exhaustion), and their elements should have a timeout (so their number

will not grow indefinitely) either from the set definition or from the statement

that adds or updates them. The set statement can be used to e.g. create dynamic

blacklists.

[verse]

{*add* | *update*} *@*'setname' *{* 'expression' [*timeout* 'timeout'] [*comment* 'string'] *}*

.Example for simple blacklist

-----------------------------

# declare a set, bound to table "filter", in family "ip". Timeout and size are mandatory because we will add elements from packet path.

nft add set ip filter blackhole "{ type ipv4_addr; flags timeout; size 65536; }"

# whitelist internal interface.

nft add rule ip filter input meta iifname "internal" accept

# drop packets coming from blacklisted ip addresses.

nft add rule ip filter input ip saddr @blackhole counter drop

# add source ip addresses to the blacklist if more than 10 tcp connection requests occurred per second and ip address.

# entries will timeout after one minute, after which they might be re-added if limit condition persists.

nft add rule ip filter input tcp flags syn tcp dport ssh meter flood size 128000 { ip saddr timeout 10s limit rate over 10/second} add @blackhole { ip saddr timeout 1m } drop

# inspect state of the rate limit meter:

nft list meter ip filter flood

# inspect content of blackhole:

nft list set ip filter blackhole

# manually add two addresses to the set:

nft add element filter blackhole { 10.2.3.4, 10.23.1.42 }

-----------------------------------------------

MAP STATEMENT

~~~~~~~~~~~~~

The map statement is used to lookup data based on some specific input key.

[verse]

____

'expression' *map* *{* 'MAP_ELEMENTS' *}*

'MAP_ELEMENTS' := 'MAP_ELEMENT' [*,* 'MAP_ELEMENTS']

'MAP_ELEMENT'  := 'key' *:* 'value'

____

The 'key' is a value returned by 'expression'.

// XXX: Write about where map statement can be used (list of statements?)

.Using the map statement

------------------------

# select DNAT target based on TCP dport:

# connections to port 80 are redirected to 192.168.1.100,

# connections to port 8888 are redirected to 192.168.1.101

nft add rule ip nat prerouting dnat tcp dport map { 80 : 192.168.1.100, 8888 : 192.168.1.101 }

# source address based SNAT:

# packets from net 192.168.1.0/24 will appear as originating from 10.0.0.1,

# packets from net 192.168.2.0/24 will appear as originating from 10.0.0.2

nft add rule ip nat postrouting snat to ip saddr map { 192.168.1.0/24 : 10.0.0.1, 192.168.2.0/24 : 10.0.0.2 }

------------------------

VMAP STATEMENT

~~~~~~~~~~~~~~

The verdict map (vmap) statement works analogous to the map statement, but

contains verdicts as values.

[verse]

____

'expression' *vmap* *{* 'VMAP_ELEMENTS' *}*

'VMAP_ELEMENTS' := 'VMAP_ELEMENT' [*,* 'VMAP_ELEMENTS']

'VMAP_ELEMENT'  := 'key' *:* 'verdict'

____

.Using the vmap statement

-------------------------

# jump to different chains depending on layer 4 protocol type:

nft add rule ip filter input ip protocol vmap { tcp : jump tcp-chain, udp : jump udp-chain , icmp : jump icmp-chain }

------------------------