978eb210d1
now completely consistent across all IP protocols and should be quite a bit faster. Use getprotoname() extensively, performed minor cleanups of admin utility. The admin utility could use a good kick in the pants. Basicly, these were the minimal changes I could make to the code to get it up to tollerable shape. There will be some future commits to clean up the basic architecture of the firewall code, and if I'm feeling ambitious, I may pull in changes like NAT from Linux and make the firewall hooks comletely generic so that a user can either load the ipfw module or the ipfilter module (cf Darren Reed). Discussed with: fenner & alex
353 lines
8.2 KiB
Groff
353 lines
8.2 KiB
Groff
.Dd July 20, 1996
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.Dt IPFW 8 SMM
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.Os FreeBSD
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.Sh NAME
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.Nm ipfw
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.Nd controlling utility for IP firewall
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.Sh SYNOPSIS
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.Nm
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.Ar file
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.Nm ipfw
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flush
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.Nm ipfw
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zero
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.Oo
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.Ar number
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.Oc
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.Nm ipfw
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delete
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.Ar number
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.Nm ipfw
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.Oo
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.Fl atN
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.Oc
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list
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.Nm ipfw
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add
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.Oo
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.Ar number
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.Oc
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.Ar action
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.Oo
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log
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.Oc
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.Ar proto
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from
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.Ar src
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to
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.Ar dst
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.Oo
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via
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.Ar name|ipno
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.Oc
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.Oo
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.Ar options
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.Oc
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.Sh DESCRIPTION
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If used as shown in the first synopsis line, the
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.Ar file
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will be read line by line and applied as arguments to the
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.Nm
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command.
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.Pp
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The
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.Nm
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code works by going through the rule-list for each packet,
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until a match is found.
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All rules have two associated counters, a packet count and
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a byte count.
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These counters are updated when a packet matches the rule.
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.Pp
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The rules are ordered by a ``line-number'' from 1 to 65534 that is used
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to order and delete rules. Rules are tried in increasing order, and the
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first rule that matches a packet applies.
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Multiple rules may share the same number and apply in
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the order in which they were added.
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.Pp
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If a rule is added without a number, it numbered 100 higher
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than the previous rule. If the highest defined rule number is
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greater than 65434, new rules are appended to the last rule.
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.Pp
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The delete operation deletes the first rule with number
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.Ar number ,
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if any.
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.Pp
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The list command prints out the current rule set.
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.Pp
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The zero operation zeroes the counters associated with rule number
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.Ar number .
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.Pp
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The flush operation removes all rules.
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.Pp
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One rule is always present:
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.Bd -literal -offset center
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65535 deny all from any to any
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.Ed
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This rule is the default policy, i.e., don't allow anything at all.
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Your job in setting up rules is to modify this policy to match your needs.
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.Pp
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The following options are available:
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.Bl -tag -width flag
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.It Fl a
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While listing, show counter values. This option is the only way to see
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accounting records.
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.It Fl t
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While listing, show last match timestamp.
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.It Fl N
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Try to resolve addresses and service names.
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.El
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.Pp
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.Ar action :
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.Bl -hang -offset flag -width 1234567890123456
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.It Nm allow
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Allow packets that match rule.
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The search terminates.
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.It Nm pass
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Same as allow.
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.It Nm accept
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Same as allow.
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.It Nm count
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Update counters for all packets that match rule.
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The search continues with the next rule.
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.It Nm deny
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Discard packets that match this rule.
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The search terminates.
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.It Nm reject
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Discard packets that match this rule, and try to send an ICMP notice.
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The search terminates.
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.It Nm divert port
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Divert packets that match this rule to the divert socket bound to port
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.Ar port .
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The search terminates.
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.El
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.Pp
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When a packet matches a rule with the
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.Nm log
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keyword, a message will be printed on the console.
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If the kernel was compiled with the
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.Nm IP_FIREWALL_VERBOSE_LIMIT
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option, then logging will cease after the number of packets
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specified by the option are recieved for that particular
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chain entry. Logging may then be re-enabled by clearing
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the packet counter for that entry.
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.Pp
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.Ar proto :
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.Bl -hang -offset flag -width 1234567890123456
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.It Nm ip
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All packets match.
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.It Nm all
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All packets match.
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.It Nm tcp
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Only TCP packets match.
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.It Nm udp
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Only UDP packets match.
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.It Nm icmp
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Only ICMP packets match.
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.It Nm <number|name>
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Only packets for the specified protocol matches (see
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.Pa /etc/protocols
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for a complete list).
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.El
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.Pp
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.Ar src
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and
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.Ar dst :
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.Pp
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.Bl -hang -offset flag
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.It <address/mask> [ports]
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.El
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.Pp
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The
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.Em <address/mask>
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may be specified as:
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.Bl -hang -offset flag -width 1234567890123456
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.It Ar ipno
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An ipnumber of the form 1.2.3.4.
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Only this exact ip number match the rule.
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.It Ar ipno/bits
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An ipnumber with a mask width of the form 1.2.3.4/24.
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In this case all ip numbers from 1.2.3.0 to 1.2.3.255 will match.
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.It Ar ipno:mask
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An ipnumber with a mask width of the form 1.2.3.4:255.255.240.0.
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In this case all ip numbers from 1.2.0.0 to 1.2.15.255 will match.
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.El
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.Pp
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With the TCP and UDP
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.Em protocols ,
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an optional
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.Em port
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may be specified as:
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.Pp
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.Bl -hang -offset flag
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.It Ns {port|port-port} Ns Op ,port Ns Op ,...
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.El
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.Pp
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Service names (from
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.Pa /etc/services )
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may not be used instead of a numeric port value.
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Also, note that a range may only be specified as the first value,
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and the port list is limited to
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.Nm IP_FW_MAX_PORTS
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(as defined in /usr/src/sys/netinet/ip_fw.h)
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ports.
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.Pp
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If ``via''
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.Ar name
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is specified, only packets received via or on their way out of an interface
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matching
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.Ar name
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will match this rule.
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.Pp
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If ``via''
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.Ar ipno
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is specified, only packets received via or on their way out of an interface
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having the address
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.Ar ipno
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will match this rule.
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.Pp
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.Ar options :
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.Bl -hang -offset flag -width 1234567890123456
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.It frag
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Matches if the packet is a fragment and this is not the first fragment
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of the datagram.
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.It in
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Matches if this packet was on the way in.
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.It out
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Matches if this packet was on the way out.
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.It ipoptions Ar spec
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Matches if the IP header contains the comma separated list of
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options specified in
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.Ar spec .
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The supported IP options are:
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.Nm ssrr
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(strict source route),
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.Nm lsrr
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(loose source route),
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.Nm rr
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(record packet route), and
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.Nm ts
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(timestamp).
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The absence of a particular option may be denoted
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with a ``!''.
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.It established
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Matches packets that have the RST or ACK bits set.
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TCP packets only.
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.It setup
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Matches packets that have the SYN bit set but no ACK bit.
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TCP packets only.
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.It tcpflags Ar spec
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Matches if the TCP header contains the comma separated list of
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flags specified in
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.Ar spec .
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The supported TCP flags are:
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.Nm fin ,
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.Nm syn ,
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.Nm rst ,
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.Nm psh ,
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.Nm ack ,
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and
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.Nm urg .
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The absence of a particular flag may be denoted
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with a ``!''.
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.It icmptypes Ar types
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Matches if the ICMP type is in the list
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.Ar types .
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The list may be specified as any combination of ranges
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or individual types separated by commas.
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.El
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.Sh CHECKLIST
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Here are some important points to consider when designing your
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rules:
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.Bl -bullet -hang -offset flag -width 1234567890123456
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.It
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Remember that you filter both packets going in and out.
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Most connections need packets going in both directions.
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.It
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Remember to test very carefully.
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It is a good idea to be near the console when doing this.
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.It
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Don't forget the loopback interface.
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.El
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.Sh FINE POINTS
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There is one kind of packet that the firewall will always discard,
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that is an IP fragment with a fragment offset of one.
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This is a valid packet, but it only has one use, to try to circumvent
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firewalls.
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.Pp
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If you are logged in over a network, loading the LKM version of
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.Nm
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is probably not as straightforward as you would think.
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I recommend this command line:
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.Bd -literal -offset center
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modload /lkm/ipfw_mod.o && \e
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ipfw add 32000 allow all from any to any
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.Ed
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Along the same lines, doing an
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.Bd -literal -offset center
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ipfw flush
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.Ed
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in similar surroundings is also a bad idea.
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.Sh PACKET DIVERSION
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A divert socket bound to the specified port will receive all packets diverted
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to that port; see
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.Xr divert 4 .
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If no socket is bound to the destination port, or if the kernel
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wasn't compiled with divert socket support, diverted packets are dropped.
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.Sh EXAMPLES
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This command adds an entry which denies all tcp packets from
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.Em hacker.evil.org
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to the telnet port of
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.Em wolf.tambov.su
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from being forwarded by the host:
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.Pp
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.Dl ipfw add deny tcp from hacker.evil.org to wolf.tambov.su 23
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.Pp
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This one disallows any connection from the entire hackers network to
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my host:
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.Pp
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.Dl ipfw addf deny all from 123.45.67.0/24 to my.host.org
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.Pp
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Here is good usage of list command to see accounting records:
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.Pp
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.Dl ipfw -at l
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.Pp
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or in short form
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.Pp
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.Dl ipfw -a l
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.Pp
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This rule diverts all incoming packets from 192.168.2.0/24 to divert port 5000:
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.Pp
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.Dl ipfw divert 5000 all from 192.168.2.0/24 to any in
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.Sh SEE ALSO
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.Xr divert 4 ,
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.Xr ip 4 ,
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.Xr ipfirewall 4 ,
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.Xr protocols 5 ,
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.Xr services 5 ,
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.Xr reboot 8 ,
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.Xr syslogd 8
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.Sh BUGS
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.Pp
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.Em WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!
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.Pp
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This program can put your computer in rather unusable state. When
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using it for the first time, work on the console of the computer, and
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do
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.Em NOT
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do anything you don't understand.
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.Pp
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When manipulating/adding chain entries, service and protocol names are
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not accepted.
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.Sh AUTHORS
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Ugen J. S. Antsilevich,
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Poul-Henning Kamp,
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Alex Nash,
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Archie Cobbs.
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API based upon code written by Daniel Boulet for BSDI.
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.Sh HISTORY
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.Nm
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first appeared in FreeBSD 2.0.
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