207 lines
8.5 KiB
Groff
207 lines
8.5 KiB
Groff
.Dd November 16, 1994
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.Dt IPFW(4)/IPACCT 4
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.Os
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.Sh NAME
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ipfirewall,ipfw - IP packets filter.
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ipaccounting,ipacct - IP packets/traffic accounting.
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.Sh SYNOPSIS
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#include <netinet/ip_fw.h>
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setsockopt(raw_socket,IPPROTO_IP,<ipfw/ipacct option>,
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<struct ip|struct ipfw>,<size>)
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Ipfw options:
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IP_FW_ADD_BLK - add entry to blocking chain.
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IP_FW_ADD_FWD - add entry to forwarding chain.
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IP_FW_CHK_BLK - check ip packet against blocking chain.
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IP_FW_CHK_FWD - check ip packet against forwarding chain.
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IP_FW_DEL_BLK - delete entry from blocking chain.
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IP_FW_DEL_FWD - delete entry from forwarding chain.
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IP_FW_FLUSH - flush all blocking & forwarding chain entries.
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IP_FW_POLICY - define default ipfw policy.
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Ipacct options:
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IP_ACCT_ADD - add entry to accounting chain.
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IP_ACCT_DEL - delete entry from accounting chain.
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IP_ACCT_FLUSH - flush all accounting chain entries.
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IP_ACCT_ZERO - zero all accounting chain entries.
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Ipfw/ipacct entry structure:
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#define IP_FW_MAX_PORTS 10
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struct ip_fw {
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struct ip_fw *next;
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struct in_addr src, dst;
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struct in_addr src_mask, dst_mask;
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u_short flags;
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u_short n_src_p, n_dst_p;
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u_short ports[IP_FW_MAX_PORTS];
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u_long p_cnt,b_cnt;
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}
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Flags values for "flags" field:
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IP_FW_F_ALL - The entry should match all IP packets.
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IP_FW_F_TCP - The entry should match TCP packets.
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IP_FW_F_UDP - The entry should match UDP packets.
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IP_FW_F_ICMP - The entry should match ICMP packets.
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IP_FW_F_KIND - Mask value to separate protocol kind.
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IP_FW_F_ACCEPT - This entry is accepting ( see below )
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IP_FW_F_SRNG - Source ports are range ( see below )
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IP_FW_F_DRNG - Destination ports are range ( see below )
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IP_FW_F_PRN - Print this entry ( see below )
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IP_FW_F_BIDIR - This acct entry is bidirectional ( see below )
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IP_FW_F_MASK - Mask to match all valid flag bits.
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Kernel symbols to kvm_nlist():
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struct ip_fw *ip_fw_blk_chain - chain of forwarding entries.
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struct ip_fw *ip_fw_fwd_chain - chain of blocking entries.
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int ip_fw_policy - default policy.
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struct ip_fw *ip_acct_chain - chain of accounting entries.
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Options in the kernel configuration file:
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IPFIREWALL - enable ipfirewall.
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IPFIREWALL_VERBOSE - enable firewall output ( see below )
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DEBUG_IPFIREWALL - enable extensive debugging output.
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IPACCT - enable ipaccounting.
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.Sh DESCRIPTION
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Ipfirewall (later ipfw) is a system facility,which allows filtering
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of incoming and/or forwarding packets on the protocol+source/destination
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adress/ports base.
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Ipaccounting (later ipacct) is a system facility,which allows counting
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of incoming,outgoing and forwarding traffic by packet/byte count.
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Basic idea is that every packet checked against number of entries
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in several chains.There are 3 chains:
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Blocking - this chain defines whenever packet should be accepted
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ever for local delivery or for forwarding.
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Forwarding - this chain defines whenever packet should be accepted
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for forwarding only.
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Accounting - this chain defines types of packets , which should be
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counted.
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Entries added to chains by means of setsockopt() call on RAW IP socket.
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Options to add/remove specific entries or to flush all entries described
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above. Value passed to setsockopt() is a value of struct ip_fw for
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entry. If entry added , it checked by such rules that when we start
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searching chain for matching entry the first matching is the best match,
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[ or at least one of them :^) ].
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That means:
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* First in chain entries with specific protocol and small ranges
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of src/dst adresses and ports.
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* Later going entries with wider ranges of ports and adresses.
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* Later entries matching every port for some adress range.
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* Later universal entries matching any protocol.
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While deleting entry , every entry which equal to that passed to
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setsockopt() will be removed.
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Flush removes all entries.
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Every entry have several fields,by which packets matched:
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struct ip_fw *next - next entry in chain.(Set internally)
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struct in_addr src - source adress to be matched.
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struct in_addr src_mask - source adress mask.
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To match whole networks/subnets or adress groups
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mask bits should be zeroed here and also
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in src_mask field. Valuable bits should be set
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in src_mask field.
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struct in_addr dst - destination adress to be matched.
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struct in_addr dst_mask - destination adress mask.
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u_short flags - flags field.See exact description of flags meaning
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in description later.
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u_short n_src_p - number of source ports in "ports" array.
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u_short n_dst_p - number of destination ports in "ports" array.
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u_short ports[] - ports array.Overall length currently defined
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to reasonable maximum - 10,and could be changed.
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The packet's src port can ever match one of
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ports[0] ... ports[--n_src_p] numbers,or if
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flag IP_FW_F_SRNG set take port[0] as bottom
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range value and ports[1] as top one.n_src_p should
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be set to 2 then.If n_src_p equal to 0 , every port
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match. The same rules apply to packet's dst port,
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except that it matched against ports[n_src_p] ...
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... ports[n_src_p+n_dst_p--],or if IP_FW_F_DRNG set,
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range is ports[n_src_p] to ports[n_srcp++].
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u_long p_cnt - packets count for ipacct entries.
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u_long b_cnt - bytes count for ipacct entries.
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Packet matching proceeds in following way:
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a) If packet entry protocol set to ALL, see c).
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b) If entry protocol set to TCP/UDP/ICMP and packet protocol
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different - no match,if packet protocol and entry protocol
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same - continue.
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c) If source addres pattern does not equal to packets sources adress
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masked with src_mask , or destination pattern not equal to packets
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destination adress masked with dst_mask - no match.
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If they does and protocol set to ALL/ICMP - got match.
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If they does and protocol set to TCP/UDP - continue.
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d) If src port doesn't match or dst port doesn't match - all
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packet don't match. If they does - got match.
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In ipfw packet matched consequently against every chain entry.
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Search continues untill first matching entry found.If IP_FW_F_ACCEPT
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flag set - packet accepted.If it is not set - packet denied.
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If no matching entry found , all unmatched packets ever accepted or
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denied depending on global polici value. It can be set with
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IP_FW_POLICY raw socket option. Deny value is 0, other values
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(default 1) is accept.
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Entries can be added with IP_FW_F_PRN flag set.If kernel compiled
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with IPFIREWALL_VERBOSE option,packets matching this entries will
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be printed by kernel printf's.
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If some chain is empty,every packet accepted by this chain no
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matter what default policy is.
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To check whenever or not packet denied by some chain , checking
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options to setsockopt() can be issued. Then the argument is
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a buffer representing ip packet,thus it has to be
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struct ip + struct tcphdr .
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Then setsockopt() return value 0 on accept or another on deny.
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Ipaccounting entries added the same way as ipfw ones.Packet checked
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against all entries in chain and values of p_cnt and b_cnt in matching
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entries rised.p_cnt rises by 1 and b_cnt by ip_len value of ip packet.
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Thus all traffic size counted including IP headers.
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If IP_FW_F_BIDIR flag is set in accounting entry,packets counted are
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those which match entry in standart way along with packets which match
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entry while their source and destination addr/port pairs swapped.
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Zero option allows all accounting to be cleared.
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.Sh DIAGNOSTICS
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[EINVAL] The IP option field was improperly formed; an option
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field was shorter than the minimum value or longer than
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the option buffer provided.An structural error in
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ip_fw structure occured (n_src_p+n_dst_p too big,
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ports set for ALL/ICMP protocols etc.)
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.Sh SEE ALSO
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ip(4), setsockopt(2), kvm_nlist(3), kvm_read(3)
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.Sh BUGS
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Ipfw/ipacct facilities are new and , although serious bugs has
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been tracked,some less important ones expected.
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This man page also uncomplete bad styled.
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.Sh HISTORY
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Ipfw facility has been intitially written as package to BSDI
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by Daniel Boulet <danny@BouletFermat.ab.ca>.
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It has been havily modified and ported to FreeBSD 2.0
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by Ugen J.S.Antsilevich <ugen@NetVision.net.il>
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Ipacct facility written for FreeBSD 2.0
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by Ugen J.S.Antsilevich <ugen@NetVision.net.il>
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