1.\"- 2.\" Copyright (c) 2001 Charles Mott <cm@linktel.net> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd June 22, 2011 29.Dt LIBALIAS 3 30.Os 31.Sh NAME 32.Nm libalias 33.Nd packet aliasing library for masquerading and network address translation 34.Sh SYNOPSIS 35.In sys/types.h 36.In netinet/in.h 37.In alias.h 38.Pp 39Function prototypes are given in the main body of the text. 40.Sh DESCRIPTION 41The 42.Nm 43library is a collection of functions for aliasing and de-aliasing of IP 44packets, intended for masquerading and network address translation (NAT). 45.Sh INTRODUCTION 46This library is a moderately portable set of functions designed to assist 47in the process of IP masquerading and network address translation. 48Outgoing packets from a local network with unregistered IP addresses can 49be aliased to appear as if they came from an accessible IP address. 50Incoming packets are then de-aliased so that they are sent to the correct 51machine on the local network. 52.Pp 53A certain amount of flexibility is built into the packet aliasing engine. 54In the simplest mode of operation, a many-to-one address mapping takes 55place between local network and the packet aliasing host. 56This is known as IP masquerading. 57In addition, one-to-one mappings between local and public addresses can 58also be implemented, which is known as static NAT. 59In between these extremes, different groups of private addresses can be 60linked to different public addresses, comprising several distinct 61many-to-one mappings. 62Also, a given public address and port can be statically redirected to a 63private address/port. 64.Pp 65The packet aliasing engine was designed to operate in user space outside 66of the kernel, without any access to private kernel data structure, but 67the source code can also be ported to a kernel environment. 68.Sh INITIALIZATION AND CONTROL 69One special function, 70.Fn LibAliasInit , 71must always be called before any packet handling may be performed and 72the returned instance pointer passed to all the other functions. 73Normally, the 74.Fn LibAliasSetAddress 75function is called afterwards, to set the default aliasing address. 76In addition, the operating mode of the packet aliasing engine can be 77customized by calling 78.Fn LibAliasSetMode . 79.Pp 80.Ft "struct libalias *" 81.Fn LibAliasInit "struct libalias *" 82.Bd -ragged -offset indent 83This function is used to initialize 84internal data structures. 85When called the first time, a 86.Dv NULL 87pointer should be passed as an argument. 88The following mode bits are always set after calling 89.Fn LibAliasInit . 90See the description of 91.Fn LibAliasSetMode 92below for the meaning of these mode bits. 93.Pp 94.Bl -item -offset indent -compact 95.It 96.Dv PKT_ALIAS_SAME_PORTS 97.It 98.Dv PKT_ALIAS_USE_SOCKETS 99.It 100.Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 101.El 102.Pp 103This function will always return the packet aliasing engine to the same 104initial state. 105The 106.Fn LibAliasSetAddress 107function is normally called afterwards, and any desired changes from the 108default mode bits listed above require a call to 109.Fn LibAliasSetMode . 110.Pp 111It is mandatory that this function be called at the beginning of a program 112prior to any packet handling. 113.Ed 114.Pp 115.Ft void 116.Fn LibAliasUninit "struct libalias *" 117.Bd -ragged -offset indent 118This function has no return value and is used to clear any 119resources attached to internal data structures. 120.Pp 121This functions should be called when a program stops using the aliasing 122engine; it does, amongst other things, clear out any firewall holes. 123To provide backwards compatibility and extra security, it is added to 124the 125.Xr atexit 3 126chain by 127.Fn LibAliasInit . 128.Ed 129.Pp 130.Ft void 131.Fn LibAliasSetAddress "struct libalias *" "struct in_addr addr" 132.Bd -ragged -offset indent 133This function sets the source address to which outgoing packets from the 134local area network are aliased. 135All outgoing packets are re-mapped to this address unless overridden by a 136static address mapping established by 137.Fn LibAliasRedirectAddr . 138If this function is not called, and no static rules match, an outgoing 139packet retains its source address. 140.Pp 141If the 142.Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 143mode bit is set (the default mode of operation), then the internal aliasing 144link tables will be reset any time the aliasing address changes. 145This is useful for interfaces such as 146.Xr ppp 8 , 147where the IP 148address may or may not change on successive dial-up attempts. 149.Pp 150If the 151.Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 152mode bit is set to zero, this function can also be used to dynamically change 153the aliasing address on a packet to packet basis (it is a low overhead call). 154.Pp 155It is mandatory that this function be called prior to any packet handling. 156.Ed 157.Pp 158.Ft unsigned int 159.Fn LibAliasSetMode "struct libalias *" "unsigned int flags" "unsigned int mask" 160.Bd -ragged -offset indent 161This function sets or clears mode bits 162according to the value of 163.Fa flags . 164Only bits marked in 165.Fa mask 166are affected. 167The following mode bits are defined in 168.In alias.h : 169.Bl -tag -width indent 170.It Dv PKT_ALIAS_LOG 171Enables logging into 172.Pa /var/log/alias.log . 173Each time an aliasing link is created or deleted, the log file is appended 174with the current number of ICMP, TCP and UDP links. 175Mainly useful for debugging when the log file is viewed continuously with 176.Xr tail 1 . 177.It Dv PKT_ALIAS_DENY_INCOMING 178If this mode bit is set, all incoming packets associated with new TCP 179connections or new UDP transactions will be marked for being ignored 180.Fn ( LibAliasIn 181returns 182.Dv PKT_ALIAS_IGNORED 183code) 184by the calling program. 185Response packets to connections or transactions initiated from the packet 186aliasing host or local network will be unaffected. 187This mode bit is useful for implementing a one-way firewall. 188.It Dv PKT_ALIAS_SAME_PORTS 189If this mode bit is set, the packet aliasing engine will attempt to leave 190the alias port numbers unchanged from the actual local port numbers. 191This can be done as long as the quintuple (proto, alias addr, alias port, 192remote addr, remote port) is unique. 193If a conflict exists, a new aliasing port number is chosen even if this 194mode bit is set. 195.It Dv PKT_ALIAS_USE_SOCKETS 196This bit should be set when the packet aliasing host originates network 197traffic as well as forwards it. 198When the packet aliasing host is waiting for a connection from an unknown 199host address or unknown port number (e.g.\& an FTP data connection), this 200mode bit specifies that a socket be allocated as a place holder to prevent 201port conflicts. 202Once a connection is established, usually within a minute or so, the socket 203is closed. 204.It Dv PKT_ALIAS_UNREGISTERED_ONLY 205If this mode bit is set, traffic on the local network which does not 206originate from unregistered address spaces will be ignored. 207Standard Class A, B and C unregistered addresses are: 208.Bd -literal -offset indent 20910.0.0.0 -> 10.255.255.255 (Class A subnet) 210172.16.0.0 -> 172.31.255.255 (Class B subnets) 211192.168.0.0 -> 192.168.255.255 (Class C subnets) 212.Ed 213.Pp 214This option is useful in the case that packet aliasing host has both 215registered and unregistered subnets on different interfaces. 216The registered subnet is fully accessible to the outside world, so traffic 217from it does not need to be passed through the packet aliasing engine. 218.It Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 219When this mode bit is set and 220.Fn LibAliasSetAddress 221is called to change the aliasing address, the internal link table of the 222packet aliasing engine will be cleared. 223This operating mode is useful for 224.Xr ppp 8 225links where the interface address can sometimes change or remain the same 226between dial-up attempts. 227If this mode bit is not set, the link table will never be reset in the event 228of an address change. 229.It Dv PKT_ALIAS_PUNCH_FW 230This option makes 231.Nm 232`punch holes' in an 233.Xr ipfirewall 4 234based firewall for FTP/IRC DCC connections. 235The holes punched are bound by from/to IP address and port; it will not be 236possible to use a hole for another connection. 237A hole is removed when the connection that uses it dies. 238To cater to unexpected death of a program using 239.Nm 240(e.g.\& kill -9), 241changing the state of the flag will clear the entire firewall range 242allocated for holes. 243This will also happen on the initial call to 244.Fn LibAliasSetFWBase . 245This call must happen prior to setting this flag. 246.It Dv PKT_ALIAS_REVERSE 247This option makes 248.Nm 249reverse the way it handles incoming and outgoing packets, allowing it 250to be fed with data that passes through the internal interface rather 251than the external one. 252.It Dv PKT_ALIAS_PROXY_ONLY 253This option tells 254.Nm 255to obey transparent proxy rules only. 256Normal packet aliasing is not performed. 257See 258.Fn LibAliasProxyRule 259below for details. 260.It Dv PKT_ALIAS_SKIP_GLOBAL 261This option is used by 262.Pa ipfw_nat 263only. Specifying it as a flag to 264.Fn LibAliasSetMode 265has no effect. See section 266.Sx NETWORK ADDRESS TRANSLATION 267in 268.Xr ipfw 8 269for more details. 270.El 271.Ed 272.Pp 273.Ft void 274.Fn LibAliasSetFWBase "struct libalias *" "unsigned int base" "unsigned int num" 275.Bd -ragged -offset indent 276Set firewall range allocated for punching firewall holes (with the 277.Dv PKT_ALIAS_PUNCH_FW 278flag). 279The range will be cleared for all rules on initialization. 280.Ed 281.Pp 282.Ft void 283.Fn LibAliasSkinnyPort "struct libalias *" "unsigned int port" 284.Bd -ragged -offset indent 285Set the TCP port used by the Skinny Station protocol. 286Skinny is used by Cisco IP phones to communicate with 287Cisco Call Managers to set up voice over IP calls. 288If this is not set, Skinny aliasing will not be done. 289The typical port used by Skinny is 2000. 290.Ed 291.Sh PACKET HANDLING 292The packet handling functions are used to modify incoming (remote to local) 293and outgoing (local to remote) packets. 294The calling program is responsible for receiving and sending packets via 295network interfaces. 296.Pp 297Along with 298.Fn LibAliasInit 299and 300.Fn LibAliasSetAddress , 301the two packet handling functions, 302.Fn LibAliasIn 303and 304.Fn LibAliasOut , 305comprise minimal set of functions needed for a basic IP masquerading 306implementation. 307.Pp 308.Ft int 309.Fn LibAliasIn "struct libalias *" "char *buffer" "int maxpacketsize" 310.Bd -ragged -offset indent 311An incoming packet coming from a remote machine to the local network is 312de-aliased by this function. 313The IP packet is pointed to by 314.Fa buffer , 315and 316.Fa maxpacketsize 317indicates the size of the data structure containing the packet and should 318be at least as large as the actual packet size. 319.Pp 320Return codes: 321.Bl -tag -width indent 322.It Dv PKT_ALIAS_OK 323The packet aliasing process was successful. 324.It Dv PKT_ALIAS_IGNORED 325The packet was ignored and not de-aliased. 326This can happen if the protocol is unrecognized, possibly an ICMP message 327type is not handled or if incoming packets for new connections are being 328ignored (if 329.Dv PKT_ALIAS_DENY_INCOMING 330mode bit was set by 331.Fn LibAliasSetMode ) . 332.It Dv PKT_ALIAS_UNRESOLVED_FRAGMENT 333This is returned when a fragment cannot be resolved because the header 334fragment has not been sent yet. 335In this situation, fragments must be saved with 336.Fn LibAliasSaveFragment 337until a header fragment is found. 338.It Dv PKT_ALIAS_FOUND_HEADER_FRAGMENT 339The packet aliasing process was successful, and a header fragment was found. 340This is a signal to retrieve any unresolved fragments with 341.Fn LibAliasGetFragment 342and de-alias them with 343.Fn LibAliasFragmentIn . 344.It Dv PKT_ALIAS_ERROR 345An internal error within the packet aliasing engine occurred. 346.El 347.Ed 348.Pp 349.Ft int 350.Fn LibAliasOut "struct libalias *" "char *buffer" "int maxpacketsize" 351.Bd -ragged -offset indent 352An outgoing packet coming from the local network to a remote machine is 353aliased by this function. 354The IP packet is pointed to by 355.Fa buffer , 356and 357.Fa maxpacketsize 358indicates the maximum packet size permissible should the packet length be 359changed. 360IP encoding protocols place address and port information in the encapsulated 361data stream which has to be modified and can account for changes in packet 362length. 363Well known examples of such protocols are FTP and IRC DCC. 364.Pp 365Return codes: 366.Bl -tag -width indent 367.It Dv PKT_ALIAS_OK 368The packet aliasing process was successful. 369.It Dv PKT_ALIAS_IGNORED 370The packet was ignored and not aliased. 371This can happen if the protocol is unrecognized, or possibly an ICMP message 372type is not handled. 373.It Dv PKT_ALIAS_ERROR 374An internal error within the packet aliasing engine occurred. 375.El 376.Ed 377.Sh PORT AND ADDRESS REDIRECTION 378The functions described in this section allow machines on the local network 379to be accessible in some degree to new incoming connections from the external 380network. 381Individual ports can be re-mapped or static network address translations can 382be designated. 383.Pp 384.Ft struct alias_link * 385.Fo LibAliasRedirectPort 386.Fa "struct libalias *" 387.Fa "struct in_addr local_addr" 388.Fa "u_short local_port" 389.Fa "struct in_addr remote_addr" 390.Fa "u_short remote_port" 391.Fa "struct in_addr alias_addr" 392.Fa "u_short alias_port" 393.Fa "u_char proto" 394.Fc 395.Bd -ragged -offset indent 396This function specifies that traffic from a given remote address/port to 397an alias address/port be redirected to a specified local address/port. 398The parameter 399.Fa proto 400can be either 401.Dv IPPROTO_TCP 402or 403.Dv IPPROTO_UDP , 404as defined in 405.In netinet/in.h . 406.Pp 407If 408.Fa local_addr 409or 410.Fa alias_addr 411is zero, this indicates that the packet aliasing address as established 412by 413.Fn LibAliasSetAddress 414is to be used. 415Even if 416.Fn LibAliasSetAddress 417is called to change the address after 418.Fn LibAliasRedirectPort 419is called, a zero reference will track this change. 420.Pp 421If the link is further set up to operate for a load sharing, then 422.Fa local_addr 423and 424.Fa local_port 425are ignored, and are selected dynamically from the server pool, as described in 426.Fn LibAliasAddServer 427below. 428.Pp 429If 430.Fa remote_addr 431is zero, this indicates to redirect packets from any remote address. 432Likewise, if 433.Fa remote_port 434is zero, this indicates to redirect packets originating from any remote 435port number. 436Almost always, the remote port specification will be zero, but non-zero 437remote addresses can sometimes be useful for firewalling. 438If two calls to 439.Fn LibAliasRedirectPort 440overlap in their address/port specifications, then the most recent call 441will have precedence. 442.Pp 443This function returns a pointer which can subsequently be used by 444.Fn LibAliasRedirectDelete . 445If 446.Dv NULL 447is returned, then the function call did not complete successfully. 448.Pp 449All port numbers should be in network address byte order, so it is necessary 450to use 451.Xr htons 3 452to convert these parameters from internally readable numbers to network byte 453order. 454Addresses are also in network byte order, which is implicit in the use of the 455.Fa struct in_addr 456data type. 457.Ed 458.Pp 459.Ft struct alias_link * 460.Fo LibAliasRedirectAddr 461.Fa "struct libalias *" 462.Fa "struct in_addr local_addr" 463.Fa "struct in_addr alias_addr" 464.Fc 465.Bd -ragged -offset indent 466This function designates that all incoming traffic to 467.Fa alias_addr 468be redirected to 469.Fa local_addr . 470Similarly, all outgoing traffic from 471.Fa local_addr 472is aliased to 473.Fa alias_addr . 474.Pp 475If 476.Fa local_addr 477or 478.Fa alias_addr 479is zero, this indicates that the packet aliasing address as established by 480.Fn LibAliasSetAddress 481is to be used. 482Even if 483.Fn LibAliasSetAddress 484is called to change the address after 485.Fn LibAliasRedirectAddr 486is called, a zero reference will track this change. 487.Pp 488If the link is further set up to operate for a load sharing, then 489.Fa local_addr 490is ignored, and is selected dynamically from the server pool, as described in 491.Fn LibAliasAddServer 492below. 493.Pp 494If subsequent calls to 495.Fn LibAliasRedirectAddr 496use the same aliasing address, all new incoming traffic to this aliasing 497address will be redirected to the local address made in the last function 498call. 499New traffic generated by any of the local machines, designated in the 500several function calls, will be aliased to the same address. 501Consider the following example: 502.Bd -literal -offset indent 503LibAliasRedirectAddr(la, inet_aton("192.168.0.2"), 504 inet_aton("141.221.254.101")); 505LibAliasRedirectAddr(la, inet_aton("192.168.0.3"), 506 inet_aton("141.221.254.101")); 507LibAliasRedirectAddr(la, inet_aton("192.168.0.4"), 508 inet_aton("141.221.254.101")); 509.Ed 510.Pp 511Any outgoing connections such as 512.Xr telnet 1 513or 514.Xr ftp 1 515from 192.168.0.2, 192.168.0.3 and 192.168.0.4 will appear to come from 516141.221.254.101. 517Any incoming connections to 141.221.254.101 will be directed to 192.168.0.4. 518.Pp 519Any calls to 520.Fn LibAliasRedirectPort 521will have precedence over address mappings designated by 522.Fn LibAliasRedirectAddr . 523.Pp 524This function returns a pointer which can subsequently be used by 525.Fn LibAliasRedirectDelete . 526If 527.Dv NULL 528is returned, then the function call did not complete successfully. 529.Ed 530.Pp 531.Ft int 532.Fo LibAliasAddServer 533.Fa "struct libalias *" 534.Fa "struct alias_link *link" 535.Fa "struct in_addr addr" 536.Fa "u_short port" 537.Fc 538.Bd -ragged -offset indent 539This function sets the 540.Fa link 541up for Load Sharing using IP Network Address Translation (RFC 2391, LSNAT). 542LSNAT operates as follows. 543A client attempts to access a server by using the server virtual address. 544The LSNAT router transparently redirects the request to one of the hosts 545in server pool, selected using a real-time load sharing algorithm. 546Multiple sessions may be initiated from the same client, and each session 547could be directed to a different host based on load balance across server 548pool hosts at the time. 549If load share is desired for just a few specific services, the configuration 550on LSNAT could be defined to restrict load share for just the services 551desired. 552.Pp 553Currently, only the simplest selection algorithm is implemented, where a 554host is selected on a round-robin basis only, without regard to load on 555the host. 556.Pp 557First, the 558.Fa link 559is created by either 560.Fn LibAliasRedirectPort 561or 562.Fn LibAliasRedirectAddr . 563Then, 564.Fn LibAliasAddServer 565is called multiple times to add entries to the 566.Fa link Ns 's 567server pool. 568.Pp 569For links created with 570.Fn LibAliasRedirectAddr , 571the 572.Fa port 573argument is ignored and could have any value, e.g.\& htons(~0). 574.Pp 575This function returns 0 on success, \-1 otherwise. 576.Ed 577.Pp 578.Ft int 579.Fn LibAliasRedirectDynamic "struct libalias *" "struct alias_link *link" 580.Bd -ragged -offset indent 581This function marks the specified static redirect rule entered by 582.Fn LibAliasRedirectPort 583as dynamic. 584This can be used to e.g.\& dynamically redirect a single TCP connection, 585after which the rule is removed. 586Only fully specified links can be made dynamic. 587(See the 588.Sx STATIC AND DYNAMIC LINKS 589and 590.Sx PARTIALLY SPECIFIED ALIASING LINKS 591sections below for a definition of static vs.\& dynamic, 592and partially vs.\& fully specified links.) 593.Pp 594This function returns 0 on success, \-1 otherwise. 595.Ed 596.Pp 597.Ft void 598.Fn LibAliasRedirectDelete "struct libalias *" "struct alias_link *link" 599.Bd -ragged -offset indent 600This function will delete a specific static redirect rule entered by 601.Fn LibAliasRedirectPort 602or 603.Fn LibAliasRedirectAddr . 604The parameter 605.Fa link 606is the pointer returned by either of the redirection functions. 607If an invalid pointer is passed to 608.Fn LibAliasRedirectDelete , 609then a program crash or unpredictable operation could result, so it is 610necessary to be careful using this function. 611.Ed 612.Pp 613.Ft int 614.Fn LibAliasProxyRule "struct libalias *" "const char *cmd" 615.Bd -ragged -offset indent 616The passed 617.Fa cmd 618string consists of one or more pairs of words. 619The first word in each pair is a token and the second is the value that 620should be applied for that token. 621Tokens and their argument types are as follows: 622.Bl -tag -width indent 623.It Cm type encode_ip_hdr | encode_tcp_stream | no_encode 624In order to support transparent proxying, it is necessary to somehow 625pass the original address and port information into the new destination 626server. 627If 628.Cm encode_ip_hdr 629is specified, the original destination address and port are passed 630as an extra IP option. 631If 632.Cm encode_tcp_stream 633is specified, the original destination address and port are passed 634as the first piece of data in the TCP stream in the format 635.Dq Li DEST Ar IP port . 636.It Cm port Ar portnum 637Only packets with the destination port 638.Ar portnum 639are proxied. 640.It Cm server Ar host Ns Op : Ns Ar portnum 641This specifies the 642.Ar host 643and 644.Ar portnum 645that the data is to be redirected to. 646.Ar host 647must be an IP address rather than a DNS host name. 648If 649.Ar portnum 650is not specified, the destination port number is not changed. 651.Pp 652The 653.Ar server 654specification is mandatory unless the 655.Cm delete 656command is being used. 657.It Cm rule Ar index 658Normally, each call to 659.Fn LibAliasProxyRule 660inserts the next rule at the start of a linear list of rules. 661If an 662.Ar index 663is specified, the new rule will be checked after all rules with lower 664indices. 665Calls to 666.Fn LibAliasProxyRule 667that do not specify a rule are assigned rule 0. 668.It Cm delete Ar index 669This token and its argument MUST NOT be used with any other tokens. 670When used, all existing rules with the given 671.Ar index 672are deleted. 673.It Cm proto tcp | udp 674If specified, only packets of the given protocol type are matched. 675.It Cm src Ar IP Ns Op / Ns Ar bits 676If specified, only packets with a source address matching the given 677.Ar IP 678are matched. 679If 680.Ar bits 681is also specified, then the first 682.Ar bits 683bits of 684.Ar IP 685are taken as a network specification, and all IP addresses from that 686network will be matched. 687.It Cm dst Ar IP Ns Op / Ns Ar bits 688If specified, only packets with a destination address matching the given 689.Ar IP 690are matched. 691If 692.Ar bits 693is also specified, then the first 694.Ar bits 695bits of 696.Ar IP 697are taken as a network specification, and all IP addresses from that 698network will be matched. 699.El 700.Pp 701This function is usually used to redirect outgoing connections for 702internal machines that are not permitted certain types of internet 703access, or to restrict access to certain external machines. 704.Ed 705.Pp 706.Ft struct alias_link * 707.Fo LibAliasRedirectProto 708.Fa "struct libalias *" 709.Fa "struct in_addr local_addr" 710.Fa "struct in_addr remote_addr" 711.Fa "struct in_addr alias_addr" 712.Fa "u_char proto" 713.Fc 714.Bd -ragged -offset indent 715This function specifies that any IP packet with protocol number of 716.Fa proto 717from a given remote address to an alias address be 718redirected to a specified local address. 719.Pp 720If 721.Fa local_addr 722or 723.Fa alias_addr 724is zero, this indicates that the packet aliasing address as established 725by 726.Fn LibAliasSetAddress 727is to be used. 728Even if 729.Fn LibAliasSetAddress 730is called to change the address after 731.Fn LibAliasRedirectProto 732is called, a zero reference will track this change. 733.Pp 734If 735.Fa remote_addr 736is zero, this indicates to redirect packets from any remote address. 737Non-zero remote addresses can sometimes be useful for firewalling. 738.Pp 739If two calls to 740.Fn LibAliasRedirectProto 741overlap in their address specifications, then the most recent call 742will have precedence. 743.Pp 744This function returns a pointer which can subsequently be used by 745.Fn LibAliasRedirectDelete . 746If 747.Dv NULL 748is returned, then the function call did not complete successfully. 749.Ed 750.Sh FRAGMENT HANDLING 751The functions in this section are used to deal with incoming fragments. 752.Pp 753Outgoing fragments are handled within 754.Fn LibAliasOut 755by changing the address according to any applicable mapping set by 756.Fn LibAliasRedirectAddr , 757or the default aliasing address set by 758.Fn LibAliasSetAddress . 759.Pp 760Incoming fragments are handled in one of two ways. 761If the header of a fragmented IP packet has already been seen, then all 762subsequent fragments will be re-mapped in the same manner the header 763fragment was. 764Fragments which arrive before the header are saved and then retrieved 765once the header fragment has been resolved. 766.Pp 767.Ft int 768.Fn LibAliasSaveFragment "struct libalias *" "char *ptr" 769.Bd -ragged -offset indent 770When 771.Fn LibAliasIn 772returns 773.Dv PKT_ALIAS_UNRESOLVED_FRAGMENT , 774this function can be used to save the pointer to the unresolved fragment. 775.Pp 776It is implicitly assumed that 777.Fa ptr 778points to a block of memory allocated by 779.Xr malloc 3 . 780If the fragment is never resolved, the packet aliasing engine will 781automatically free the memory after a timeout period. 782[Eventually this function should be modified so that a callback function 783for freeing memory is passed as an argument.] 784.Pp 785This function returns 786.Dv PKT_ALIAS_OK 787if it was successful and 788.Dv PKT_ALIAS_ERROR 789if there was an error. 790.Ed 791.Pp 792.Ft char * 793.Fn LibAliasGetFragment "struct libalias *" "char *buffer" 794.Bd -ragged -offset indent 795This function can be used to retrieve fragment pointers saved by 796.Fn LibAliasSaveFragment . 797The IP header fragment pointed to by 798.Fa buffer 799is the header fragment indicated when 800.Fn LibAliasIn 801returns 802.Dv PKT_ALIAS_FOUND_HEADER_FRAGMENT . 803Once a fragment pointer is retrieved, it becomes the calling program's 804responsibility to free the dynamically allocated memory for the fragment. 805.Pp 806The 807.Fn LibAliasGetFragment 808function can be called sequentially until there are no more fragments 809available, at which time it returns 810.Dv NULL . 811.Ed 812.Pp 813.Ft void 814.Fn LibAliasFragmentIn "struct libalias *" "char *header" "char *fragment" 815.Bd -ragged -offset indent 816When a fragment is retrieved with 817.Fn LibAliasGetFragment , 818it can then be de-aliased with a call to 819.Fn LibAliasFragmentIn . 820The 821.Fa header 822argument is the pointer to a header fragment used as a template, and 823.Fa fragment 824is the pointer to the packet to be de-aliased. 825.Ed 826.Sh MISCELLANEOUS FUNCTIONS 827.Ft struct alias_link * 828.Fn AddLink "struct libalias *" "struct in_addr src_addr" "struct in_addr dst_addr" \ 829"struct in_addr alias_addr" "u_short src_port" "u_short dst_port" \ 830"int alias_param" "int link_type" 831.Bd -ragged -offset indent 832This function adds new state to instance hash table. 833Zero can be specified instead of dst_address and/or dst port. 834This makes link partially specified dynamic. 835However due to hashing method such links can be resolved on inbound (ext -> int) only. 836.Ed 837.Pp 838.Ft void 839.Fn LibAliasSetTarget "struct libalias *" "struct in_addr addr" 840.Bd -ragged -offset indent 841When an incoming packet not associated with any pre-existing aliasing link 842arrives at the host machine, it will be sent to the address indicated by a 843call to 844.Fn LibAliasSetTarget . 845.Pp 846If this function is called with an 847.Dv INADDR_NONE 848address argument, then all new incoming packets go to the address set by 849.Fn LibAliasSetAddress . 850.Pp 851If this function is not called, or is called with an 852.Dv INADDR_ANY 853address argument, then all new incoming packets go to the address specified 854in the packet. 855This allows external machines to talk directly to internal machines if they 856can route packets to the machine in question. 857.Ed 858.Pp 859.Ft int 860.Fn LibAliasCheckNewLink "struct libalias *" 861.Bd -ragged -offset indent 862This function returns a non-zero value when a new aliasing link is created. 863In circumstances where incoming traffic is being sequentially sent to 864different local servers, this function can be used to trigger when 865.Fn LibAliasSetTarget 866is called to change the default target address. 867.Ed 868.Pp 869.Ft u_short 870.Fn LibAliasInternetChecksum "struct libalias *" "u_short *buffer" "int nbytes" 871.Bd -ragged -offset indent 872This is a utility function that does not seem to be available elsewhere and 873is included as a convenience. 874It computes the internet checksum, which is used in both IP and 875protocol-specific headers (TCP, UDP, ICMP). 876.Pp 877The 878.Fa buffer 879argument points to the data block to be checksummed, and 880.Fa nbytes 881is the number of bytes. 882The 16-bit checksum field should be zeroed before computing the checksum. 883.Pp 884Checksums can also be verified by operating on a block of data including 885its checksum. 886If the checksum is valid, 887.Fn LibAliasInternetChecksum 888will return zero. 889.Ed 890.Pp 891.Ft int 892.Fn LibAliasUnaliasOut "struct libalias *" "char *buffer" "int maxpacketsize" 893.Bd -ragged -offset indent 894An outgoing packet, which has already been aliased, 895has its private address/port information restored by this function. 896The IP packet is pointed to by 897.Fa buffer , 898and 899.Fa maxpacketsize 900is provided for error checking purposes. 901This function can be used if an already-aliased packet needs to have its 902original IP header restored for further processing (e.g.\& logging). 903.Ed 904.Sh AUTHORS 905.An Charles Mott Aq cm@linktel.net , 906versions 1.0 - 1.8, 2.0 - 2.4. 907.An Eivind Eklund Aq eivind@FreeBSD.org , 908versions 1.8b, 1.9 and 2.5. 909Added IRC DCC support as well as contributing a number of architectural 910improvements; added the firewall bypass for FTP/IRC DCC. 911.An Erik Salander Aq erik@whistle.com 912added support for PPTP and RTSP. 913.An Junichi Satoh Aq junichi@junichi.org 914added support for RTSP/PNA. 915.An Ruslan Ermilov Aq ru@FreeBSD.org 916added support for PPTP and LSNAT as well as general hacking. 917.An Paolo Pisati Aq piso@FreeBSD.org 918made the library modular, moving support for all 919protocols (except for IP, TCP and UDP) to external modules. 920.Sh ACKNOWLEDGMENTS 921Listed below, in approximate chronological order, are individuals who 922have provided valuable comments and/or debugging assistance. 923.Bd -ragged -offset indent 924.An -split 925.An Gary Roberts 926.An Tom Torrance 927.An Reto Burkhalter 928.An Martin Renters 929.An Brian Somers 930.An Paul Traina 931.An Ari Suutari 932.An Dave Remien 933.An J. Fortes 934.An Andrzej Bialecki 935.An Gordon Burditt 936.Ed 937.Sh CONCEPTUAL BACKGROUND 938This section is intended for those who are planning to modify the source 939code or want to create somewhat esoteric applications using the packet 940aliasing functions. 941.Pp 942The conceptual framework under which the packet aliasing engine operates 943is described here. 944Central to the discussion is the idea of an 945.Em aliasing link 946which describes the relationship for a given packet transaction between 947the local machine, aliased identity and remote machine. 948It is discussed how such links come into existence and are destroyed. 949.Ss ALIASING LINKS 950There is a notion of an 951.Em aliasing link , 952which is a 7-tuple describing a specific translation: 953.Bd -literal -offset indent 954(local addr, local port, alias addr, alias port, 955 remote addr, remote port, protocol) 956.Ed 957.Pp 958Outgoing packets have the local address and port number replaced with the 959alias address and port number. 960Incoming packets undergo the reverse process. 961The packet aliasing engine attempts to match packets against an internal 962table of aliasing links to determine how to modify a given IP packet. 963Both the IP header and protocol dependent headers are modified as necessary. 964Aliasing links are created and deleted as necessary according to network 965traffic. 966.Pp 967Protocols can be TCP, UDP or even ICMP in certain circumstances. 968(Some types of ICMP packets can be aliased according to sequence or ID 969number which acts as an equivalent port number for identifying how 970individual packets should be handled.) 971.Pp 972Each aliasing link must have a unique combination of the following five 973quantities: alias address/port, remote address/port and protocol. 974This ensures that several machines on a local network can share the 975same aliasing IP address. 976In cases where conflicts might arise, the aliasing port is chosen so that 977uniqueness is maintained. 978.Ss STATIC AND DYNAMIC LINKS 979Aliasing links can either be static or dynamic. 980Static links persist indefinitely and represent fixed rules for translating 981IP packets. 982Dynamic links come into existence for a specific TCP connection or UDP 983transaction or ICMP ECHO sequence. 984For the case of TCP, the connection can be monitored to see when the 985associated aliasing link should be deleted. 986Aliasing links for UDP transactions (and ICMP ECHO and TIMESTAMP requests) 987work on a simple timeout rule. 988When no activity is observed on a dynamic link for a certain amount of time 989it is automatically deleted. 990Timeout rules also apply to TCP connections which do not open or close 991properly. 992.Ss PARTIALLY SPECIFIED ALIASING LINKS 993Aliasing links can be partially specified, meaning that the remote address 994and/or remote port are unknown. 995In this case, when a packet matching the incomplete specification is found, 996a fully specified dynamic link is created. 997If the original partially specified link is dynamic, it will be deleted 998after the fully specified link is created, otherwise it will persist. 999.Pp 1000For instance, a partially specified link might be 1001.Bd -literal -offset indent 1002(192.168.0.4, 23, 204.228.203.215, 8066, 0, 0, tcp) 1003.Ed 1004.Pp 1005The zeros denote unspecified components for the remote address and port. 1006If this link were static it would have the effect of redirecting all 1007incoming traffic from port 8066 of 204.228.203.215 to port 23 (telnet) 1008of machine 192.168.0.4 on the local network. 1009Each individual telnet connection would initiate the creation of a distinct 1010dynamic link. 1011.Ss DYNAMIC LINK CREATION 1012In addition to aliasing links, there are also address mappings that can be 1013stored within the internal data table of the packet aliasing mechanism. 1014.Bd -literal -offset indent 1015(local addr, alias addr) 1016.Ed 1017.Pp 1018Address mappings are searched when creating new dynamic links. 1019.Pp 1020All outgoing packets from the local network automatically create a dynamic 1021link if they do not match an already existing fully specified link. 1022If an address mapping exists for the outgoing packet, this determines 1023the alias address to be used. 1024If no mapping exists, then a default address, usually the address of the 1025packet aliasing host, is used. 1026If necessary, this default address can be changed as often as each individual 1027packet arrives. 1028.Pp 1029The aliasing port number is determined such that the new dynamic link does 1030not conflict with any existing links. 1031In the default operating mode, the packet aliasing engine attempts to set 1032the aliasing port equal to the local port number. 1033If this results in a conflict, then port numbers are randomly chosen until 1034a unique aliasing link can be established. 1035In an alternate operating mode, the first choice of an aliasing port is also 1036random and unrelated to the local port number. 1037.Sh MODULAR ARCHITECTURE (AND Xr ipfw 4 Sh SUPPORT) 1038One of the latest improvements to 1039.Nm 1040was to make its support 1041for new protocols independent from the rest of the library, giving it 1042the ability to load/unload support for new protocols at run-time. 1043To achieve this feature, all the code for protocol handling was moved 1044to a series of modules outside of the main library. 1045These modules are compiled from the same sources but work in 1046different ways, depending on whether they are compiled to work inside a kernel 1047or as part of the userland library. 1048.Ss LIBALIAS MODULES IN KERNEL LAND 1049When compiled for the kernel, 1050.Nm 1051modules are plain KLDs recognizable with the 1052.Pa alias_ 1053prefix. 1054.Pp 1055To add support for a new protocol, load the corresponding module. 1056For example: 1057.Pp 1058.Dl "kldload alias_ftp" 1059.Pp 1060When support for a protocol is no longer needed, its module can be unloaded: 1061.Pp 1062.Dl "kldunload alias_ftp" 1063.Ss LIBALIAS MODULES IN USERLAND 1064Due to the differences between kernel and userland (no KLD mechanism, 1065many different address spaces, etc.), we had to change a bit how to 1066handle module loading/tracking/unloading in userland. 1067.Pp 1068While compiled for a userland 1069.Nm , 1070all the modules are plain libraries, residing in 1071.Pa /usr/lib , 1072and recognizable with the 1073.Pa libalias_ 1074prefix. 1075.Pp 1076There is a configuration file, 1077.Pa /etc/libalias.conf , 1078with the following contents (by default): 1079.Bd -literal -offset indent 1080/usr/lib/libalias_cuseeme.so 1081/usr/lib/libalias_ftp.so 1082/usr/lib/libalias_irc.so 1083/usr/lib/libalias_nbt.so 1084/usr/lib/libalias_pptp.so 1085/usr/lib/libalias_skinny.so 1086/usr/lib/libalias_smedia.so 1087.Ed 1088.Pp 1089This file contains the paths to the modules that 1090.Nm 1091will load. 1092To load/unload a new module, just add its path to 1093.Pa libalias.conf 1094and call 1095.Fn LibAliasRefreshModules 1096from the program. 1097In case the application provides a 1098.Dv SIGHUP 1099signal handler, add a call to 1100.Fn LibAliasRefreshModules 1101inside the handler, and everytime you want to refresh the loaded modules, 1102send it the 1103.Dv SIGHUP 1104signal: 1105.Pp 1106.Dl "kill -HUP <process_pid>" 1107.Ss MODULAR ARCHITECURE: HOW IT WORKS 1108The modular architecture of 1109.Nm 1110works similar whether it is running inside the 1111kernel or in userland. 1112From 1113.Pa alias_mod.c : 1114.Bd -literal 1115/* Protocol and userland module handlers chains. */ 1116LIST_HEAD(handler_chain, proto_handler) handler_chain ... 1117\&... 1118SLIST_HEAD(dll_chain, dll) dll_chain ... 1119.Ed 1120.Pp 1121.Va handler_chain 1122keep tracks of all the protocol handlers loaded, while 1123.Va ddl_chain 1124takes care of userland modules loaded. 1125.Pp 1126.Va handler_chain 1127is composed of 1128.Vt "struct proto_handler" 1129entries: 1130.Bd -literal 1131struct proto_handler { 1132 u_int pri; 1133 int16_t dir; 1134 uint8_t proto; 1135 int (*fingerprint)(struct libalias *la, 1136 struct ip *pip, struct alias_data *ah); 1137 int (*protohandler)(struct libalias *la, 1138 struct ip *pip, struct alias_data *ah); 1139 LIST_ENTRY(proto_handler) entries; 1140}; 1141.Ed 1142.Pp 1143where: 1144.Bl -inset 1145.It Va pri 1146is the priority assigned to a protocol handler, lower 1147is better. 1148.It Va dir 1149is the direction of packets: ingoing or outgoing. 1150.It Va proto 1151says at which protocol this packet belongs: IP, TCP or UDP. 1152.It Va fingerprint 1153points to the fingerprint function while protohandler points 1154to the protocol handler function. 1155.El 1156.Pp 1157The 1158.Va fingerprint 1159function has the double of scope of checking if the 1160incoming packet is found and if it belongs to any categories that this 1161module can handle. 1162.Pp 1163The 1164.Va protohandler 1165function actually manipulates 1166the packet to make 1167.Nm 1168correctly NAT it. 1169.Pp 1170When a packet enters 1171.Nm , 1172if it meets a module hook, 1173.Va handler_chain 1174is searched to see if there is an handler that matches 1175this type of a packet (it checks protocol and direction of packet), then if 1176more than one handler is found, it starts with the module with 1177the lowest priority number: it calls the 1178.Va fingerprint 1179function and interprets the result. 1180.Pp 1181If the result value is equal to 0 then it calls the protocol handler 1182of this handler and returns. 1183Otherwise, it proceeds to the next eligible module until the 1184.Va handler_chain 1185is exhausted. 1186.Pp 1187Inside 1188.Nm , 1189the module hook looks like this: 1190.Bd -literal -offset indent 1191struct alias_data ad = { 1192 lnk, 1193 &original_address, 1194 &alias_address, 1195 &alias_port, 1196 &ud->uh_sport, /* original source port */ 1197 &ud->uh_dport, /* original dest port */ 1198 256 /* maxpacketsize */ 1199}; 1200 1201\&... 1202 1203/* walk out chain */ 1204err = find_handler(IN, UDP, la, pip, &ad); 1205.Ed 1206.Pp 1207All data useful to a module are gathered together in an 1208.Vt alias_data 1209structure, then 1210.Fn find_handler 1211is called. 1212The 1213.Fn find_handler 1214function is responsible for walking out the handler 1215chain, it receives as input parameters: 1216.Bl -tag -width indent 1217.It Fa IN 1218direction 1219.It Fa UDP 1220working protocol 1221.It Fa la 1222pointer to this instance of libalias 1223.It Fa pip 1224pointer to a 1225.Vt "struct ip" 1226.It Fa ad 1227pointer to 1228.Vt "struct alias_data" 1229(see above) 1230.El 1231.Pp 1232In this case, 1233.Fn find_handler 1234will search only for modules registered for 1235supporting INcoming UDP packets. 1236.Pp 1237As was mentioned earlier, 1238.Nm 1239in userland is a bit different, cause 1240care has to be taken of module handling too (avoiding duplicate load of 1241module, avoiding module with same name, etc.) so 1242.Va dll_chain 1243was introduced. 1244.Pp 1245.Va dll_chain 1246contains a list of all userland 1247.Nm 1248modules loaded. 1249.Pp 1250When an application calls 1251.Fn LibAliasRefreshModules , 1252.Nm 1253first unloads all the loaded modules, then reloads all the modules listed in 1254.Pa /etc/libalias.conf : 1255for every module loaded, a new entry to 1256.Va dll_chain 1257is added. 1258.Pp 1259.Va dll_chain 1260is composed of 1261.Vt "struct dll" 1262entries: 1263.Bd -literal 1264struct dll { 1265 /* name of module */ 1266 char name[DLL_LEN]; 1267 /* 1268 * ptr to shared obj obtained through 1269 * dlopen() - use this ptr to get access 1270 * to any symbols from a loaded module 1271 * via dlsym() 1272 */ 1273 void *handle; 1274 struct dll *next; 1275}; 1276.Ed 1277.Bl -inset 1278.It Va name 1279is the name of the module 1280.It Va handle 1281is a pointer to the module obtained through 1282.Xr dlopen 3 1283.El 1284Whenever a module is loaded in userland, an entry is added to 1285.Va dll_chain , 1286then every protocol handler present in that module 1287is resolved and registered in 1288.Va handler_chain . 1289.Ss HOW TO WRITE A MODULE FOR LIBALIAS 1290There is a module (called 1291.Pa alias_dummy.[ch] ) 1292in 1293.Nm 1294that can be used as a skeleton for future work, here we analyse some parts of that 1295module. 1296From 1297.Pa alias_dummy.c : 1298.Bd -literal 1299struct proto_handler handlers [] = {{666, IN|OUT, UDP|TCP, 1300 &fingerprint, &protohandler}}; 1301.Ed 1302.Pp 1303The variable 1304.Va handlers 1305is the 1306.Dq "most important thing" 1307in a module 1308cause it describes the handlers present and lets the outside world use 1309it in an opaque way. 1310.Pp 1311It must ALWAYS be present in every module, and it MUST retain 1312the name 1313.Va handlers , 1314otherwise attempting to load a module in userland will fail and 1315complain about missing symbols: for more information about module 1316load/unload, please refer to 1317.Fn LibAliasRefreshModules , 1318.Fn LibAliasLoadModule 1319and 1320.Fn LibAliasUnloadModule 1321in 1322.Pa alias.c . 1323.Pp 1324.Va handlers 1325contains all the 1326.Vt proto_handler 1327structures present in a module. 1328.Bd -literal 1329static int 1330mod_handler(module_t mod, int type, void *data) 1331{ 1332 int error; 1333 1334 switch (type) { 1335 case MOD_LOAD: 1336 error = 0; 1337 attach_handlers(handlers); 1338 break; 1339 case MOD_UNLOAD: 1340 error = 0; 1341 detach_handlers(handlers; 1342 break; 1343 default: 1344 error = EINVAL; 1345 } 1346 return (error); 1347} 1348.Ed 1349When running as KLD, 1350.Fn mod_handler 1351register/deregister the module using 1352.Fn attach_handlers 1353and 1354.Fn detach_handlers , 1355respectively. 1356.Pp 1357Every module must contain at least 2 functions: one fingerprint 1358function and a protocol handler function. 1359.Bd -literal 1360#ifdef _KERNEL 1361static 1362#endif 1363int 1364fingerprint(struct libalias *la, struct ip *pip, struct alias_data *ah) 1365{ 1366 1367\&... 1368} 1369 1370#ifdef _KERNEL 1371static 1372#endif 1373int 1374protohandler(struct libalias *la, struct ip *pip, 1375 struct alias_data *ah) 1376{ 1377 1378\&... 1379} 1380.Ed 1381and they must accept exactly these input parameters. 1382.Ss PATCHING AN APPLICATION FOR USERLAND LIBALIAS MODULES 1383To add module support into an application that uses 1384.Nm , 1385the following simple steps can be followed. 1386.Bl -enum 1387.It 1388Find the main file of an application 1389(let us call it 1390.Pa main.c ) . 1391.It 1392Add this to the header section of 1393.Pa main.c , 1394if not already present: 1395.Pp 1396.Dl "#include <signal.h>" 1397.Pp 1398and this just after the header section: 1399.Pp 1400.Dl "static void signal_handler(int);" 1401.It 1402Add the following line to the init function of an application or, 1403if it does not have any init function, put it in 1404.Fn main : 1405.Pp 1406.Dl "signal(SIGHUP, signal_handler);" 1407.Pp 1408and place the 1409.Fn signal_handler 1410function somewhere in 1411.Pa main.c : 1412.Bd -literal -offset indent 1413static void 1414signal_handler(int sig) 1415{ 1416 1417 LibAliasRefreshModules(); 1418} 1419.Ed 1420.Pp 1421Otherwise, if an application already traps the 1422.Dv SIGHUP 1423signal, just add a call to 1424.Fn LibAliasRefreshModules 1425in the signal handler function. 1426.El 1427For example, to patch 1428.Xr natd 8 1429to use 1430.Nm 1431modules, just add the following line to 1432.Fn RefreshAddr "int sig __unused" : 1433.Pp 1434.Dl "LibAliasRefreshModules()" 1435.Pp 1436recompile and you are done. 1437.Ss LOGGING SUPPORT IN KERNEL LAND 1438When working as KLD, 1439.Nm 1440now has log support that 1441happens on a buffer allocated inside 1442.Vt "struct libalias" 1443(from 1444.Pa alias_local.h ) : 1445.Bd -literal 1446struct libalias { 1447 ... 1448 1449 /* log descriptor */ 1450#ifdef KERNEL_LOG 1451 char *logDesc; /* 1452 * ptr to an auto-malloced 1453 * memory buffer when libalias 1454 * works as kld 1455 */ 1456#else 1457 FILE *logDesc; /* 1458 * ptr to /var/log/alias.log 1459 * when libalias runs as a 1460 * userland lib 1461 */ 1462#endif 1463 1464 ... 1465} 1466.Ed 1467so all applications using 1468.Nm 1469will be able to handle their 1470own logs, if they want, accessing 1471.Va logDesc . 1472Moreover, every change to a log buffer is automatically added to 1473.Xr syslog 3 1474with the 1475.Dv LOG_SECURITY 1476facility and the 1477.Dv LOG_INFO 1478level. 1479