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 December 25, 2013 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 the 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.Sh INITIALIZATION AND CONTROL 65One special function, 66.Fn LibAliasInit , 67must always be called before any packet handling may be performed, and 68the returned instance pointer must be passed to all the other functions. 69Normally, the 70.Fn LibAliasSetAddress 71function is called afterwards, to set the default aliasing address. 72In addition, the operating mode of the packet aliasing engine can be 73customized by calling 74.Fn LibAliasSetMode . 75.Pp 76.Ft "struct libalias *" 77.Fn LibAliasInit "struct libalias *" 78.Bd -ragged -offset indent 79This function is used to initialize 80internal data structures. 81When called the first time, a 82.Dv NULL 83pointer should be passed as an argument. 84The following mode bits are always set after calling 85.Fn LibAliasInit . 86See the description of 87.Fn LibAliasSetMode 88below for the meaning of these mode bits. 89.Pp 90.Bl -item -offset indent -compact 91.It 92.Dv PKT_ALIAS_SAME_PORTS 93.It 94.Dv PKT_ALIAS_USE_SOCKETS 95.It 96.Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 97.El 98.Pp 99This function will always return the packet aliasing engine to the same 100initial state. 101The 102.Fn LibAliasSetAddress 103function is normally called afterwards, and any desired changes from the 104default mode bits listed above require a call to 105.Fn LibAliasSetMode . 106.Pp 107It is mandatory that this function be called at the beginning of a program 108prior to any packet handling. 109.Ed 110.Pp 111.Ft void 112.Fn LibAliasUninit "struct libalias *" 113.Bd -ragged -offset indent 114This function has no return value and is used to clear any 115resources attached to internal data structures. 116.Pp 117This function should be called when a program stops using the aliasing 118engine; amongst other things, it clears out any firewall holes. 119To provide backwards compatibility and extra security, it is added to 120the 121.Xr atexit 3 122chain by 123.Fn LibAliasInit . 124.Ed 125.Pp 126.Ft void 127.Fn LibAliasSetAddress "struct libalias *" "struct in_addr addr" 128.Bd -ragged -offset indent 129This function sets the source address to which outgoing packets from the 130local area network are aliased. 131All outgoing packets are re-mapped to this address unless overridden by a 132static address mapping established by 133.Fn LibAliasRedirectAddr . 134If this function has not been called, and no static rules match, an outgoing 135packet retains its source address. 136.Pp 137If the 138.Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 139mode bit is set (the default mode of operation), then the internal aliasing 140link tables will be reset any time the aliasing address changes. 141This is useful for interfaces such as 142.Xr ppp 8 , 143where the IP 144address may or may not change on successive dial-up attempts. 145.Pp 146If the 147.Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 148mode bit is set to zero, this function can also be used to dynamically change 149the aliasing address on a packet-to-packet basis (it is a low overhead call). 150.Pp 151It is mandatory that this function be called prior to any packet handling. 152.Ed 153.Pp 154.Ft unsigned int 155.Fn LibAliasSetMode "struct libalias *" "unsigned int flags" "unsigned int mask" 156.Bd -ragged -offset indent 157This function sets or clears mode bits 158according to the value of 159.Fa flags . 160Only bits marked in 161.Fa mask 162are affected. 163The following mode bits are defined in 164.In alias.h : 165.Bl -tag -width indent 166.It Dv PKT_ALIAS_LOG 167Enables logging into 168.Pa /var/log/alias.log . 169Each time an aliasing link is created or deleted, the log file is appended to 170with the current number of ICMP, TCP and UDP links. 171Mainly useful for debugging when the log file is viewed continuously with 172.Xr tail 1 . 173.It Dv PKT_ALIAS_DENY_INCOMING 174If this mode bit is set, all incoming packets associated with new TCP 175connections or new UDP transactions will be marked for being ignored 176.Fn ( LibAliasIn 177returns 178.Dv PKT_ALIAS_IGNORED 179code) 180by the calling program. 181Response packets to connections or transactions initiated from the packet 182aliasing host or local network will be unaffected. 183This mode bit is useful for implementing a one-way firewall. 184.It Dv PKT_ALIAS_SAME_PORTS 185If this mode bit is set, the packet-aliasing engine will attempt to leave 186the alias port numbers unchanged from the actual local port numbers. 187This can be done as long as the quintuple (proto, alias addr, alias port, 188remote addr, remote port) is unique. 189If a conflict exists, a new aliasing port number is chosen even if this 190mode bit is set. 191.It Dv PKT_ALIAS_USE_SOCKETS 192This bit should be set when the packet aliasing host originates network 193traffic as well as forwards it. 194When the packet aliasing host is waiting for a connection from an unknown 195host address or unknown port number (e.g.\& an FTP data connection), this 196mode bit specifies that a socket be allocated as a place holder to prevent 197port conflicts. 198Once a connection is established, usually within a minute or so, the socket 199is closed. 200.It Dv PKT_ALIAS_UNREGISTERED_ONLY 201If this mode bit is set, traffic on the local network which does not 202originate from unregistered address spaces will be ignored. 203Standard Class A, B and C unregistered addresses are: 204.Pp 20510.0.0.0 -> 10.255.255.255 (Class A subnet) 206172.16.0.0 -> 172.31.255.255 (Class B subnets) 207192.168.0.0 -> 192.168.255.255 (Class C subnets) 208.Pp 209This option is useful in the case that the packet aliasing host has both 210registered and unregistered subnets on different interfaces. 211The registered subnet is fully accessible to the outside world, so traffic 212from it does not need to be passed through the packet aliasing engine. 213.It Dv PKT_ALIAS_RESET_ON_ADDR_CHANGE 214When this mode bit is set and 215.Fn LibAliasSetAddress 216is called to change the aliasing address, the internal link table of the 217packet aliasing engine will be cleared. 218This operating mode is useful for 219.Xr ppp 8 220links where the interface address can sometimes change or remain the same 221between dial-up attempts. 222If this mode bit is not set, the link table will never be reset in the event 223of an address change. 224.It Dv PKT_ALIAS_PUNCH_FW 225This option makes 226.Nm 227.Dq punch holes 228in an 229.Xr ipfirewall 4 - 230based firewall for FTP/IRC DCC connections. 231The holes punched are bound by from/to IP address and port; it will not be 232possible to use a hole for another connection. 233A hole is removed when the connection that uses it dies. 234To cater to unexpected death of a program using 235.Nm 236(e.g.\& kill -9), 237changing the state of the flag will clear the entire firewall range 238allocated for holes. 239This clearing will also happen on the initial call to 240.Fn LibAliasSetFWBase , 241which must happen prior to setting this flag. 242.It Dv PKT_ALIAS_REVERSE 243This option makes 244.Nm 245reverse the way it handles incoming and outgoing packets, allowing it 246to be fed with data that passes through the internal interface rather 247than the external one. 248.It Dv PKT_ALIAS_PROXY_ONLY 249This option tells 250.Nm 251to obey transparent proxy rules only. 252Normal packet aliasing is not performed. 253See 254.Fn LibAliasProxyRule 255below for details. 256.It Dv PKT_ALIAS_SKIP_GLOBAL 257This option is used by 258.Pa ipfw_nat 259only. 260Specifying it as a flag to 261.Fn LibAliasSetMode 262has no effect. 263See section 264.Sx NETWORK ADDRESS TRANSLATION 265in 266.Xr ipfw 8 267for more details. 268.El 269.Ed 270.Pp 271.Ft void 272.Fn LibAliasSetFWBase "struct libalias *" "unsigned int base" "unsigned int num" 273.Bd -ragged -offset indent 274Set the firewall range allocated for punching firewall holes (with the 275.Dv PKT_ALIAS_PUNCH_FW 276flag). 277The range is cleared for all rules on initialization. 278.Ed 279.Pp 280.Ft void 281.Fn LibAliasSkinnyPort "struct libalias *" "unsigned int port" 282.Bd -ragged -offset indent 283Set the TCP port used by the Skinny Station protocol. 284Skinny is used by Cisco IP phones to communicate with 285Cisco Call Managers to set up voice over IP calls. 286If this is not set, Skinny aliasing will not be done. 287The typical port used by Skinny is 2000. 288.Ed 289.Sh PACKET HANDLING 290The packet handling functions are used to modify incoming (remote to local) 291and outgoing (local to remote) packets. 292The calling program is responsible for receiving and sending packets via 293network interfaces. 294.Pp 295Along with 296.Fn LibAliasInit 297and 298.Fn LibAliasSetAddress , 299the two packet handling functions, 300.Fn LibAliasIn 301and 302.Fn LibAliasOut , 303comprise the minimal set of functions needed for a basic IP masquerading 304implementation. 305.Pp 306.Ft int 307.Fn LibAliasIn "struct libalias *" "char *buffer" "int maxpacketsize" 308.Bd -ragged -offset indent 309An incoming packet coming from a remote machine to the local network is 310de-aliased by this function. 311The IP packet is pointed to by 312.Fa buffer , 313and 314.Fa maxpacketsize 315indicates the size of the data structure containing the packet and should 316be at least as large as the actual packet size. 317.Pp 318Return codes: 319.Bl -tag -width indent 320.It Dv PKT_ALIAS_OK 321The packet aliasing process was successful. 322.It Dv PKT_ALIAS_IGNORED 323The packet was ignored and not de-aliased. 324This can happen if the protocol is unrecognized, as for an ICMP message 325type that is not handled, or if incoming packets for new connections are being 326ignored (if the 327.Dv PKT_ALIAS_DENY_INCOMING 328mode bit was set using 329.Fn LibAliasSetMode ) . 330.It Dv PKT_ALIAS_UNRESOLVED_FRAGMENT 331This is returned when a fragment cannot be resolved because the header 332fragment has not been sent yet. 333In this situation, fragments must be saved with 334.Fn LibAliasSaveFragment 335until a header fragment is found. 336.It Dv PKT_ALIAS_FOUND_HEADER_FRAGMENT 337The packet aliasing process was successful, and a header fragment was found. 338This is a signal to retrieve any unresolved fragments with 339.Fn LibAliasGetFragment 340and de-alias them with 341.Fn LibAliasFragmentIn . 342.It Dv PKT_ALIAS_ERROR 343An internal error within the packet aliasing engine occurred. 344.El 345.Ed 346.Pp 347.Ft int 348.Fn LibAliasOut "struct libalias *" "char *buffer" "int maxpacketsize" 349.Bd -ragged -offset indent 350An outgoing packet coming from the local network to a remote machine is 351aliased by this function. 352The IP packet is pointed to by 353.Fa buffer , 354and 355.Fa maxpacketsize 356indicates the maximum packet size permissible should the packet length be 357changed. 358IP encoding protocols place address and port information in the encapsulated 359data stream which has to be modified and can account for changes in packet 360length. 361Well known examples of such protocols are FTP and IRC DCC. 362.Pp 363Return codes: 364.Bl -tag -width indent 365.It Dv PKT_ALIAS_OK 366The packet aliasing process was successful. 367.It Dv PKT_ALIAS_IGNORED 368The packet was ignored and not aliased. 369This can happen if the protocol is unrecognized, or possibly an ICMP message 370type is not handled. 371.It Dv PKT_ALIAS_ERROR 372An internal error within the packet aliasing engine occurred. 373.El 374.Ed 375.Sh PORT AND ADDRESS REDIRECTION 376The functions described in this section allow machines on the local network 377to be accessible in some degree to new incoming connections from the external 378network. 379Individual ports can be re-mapped or static network address translations can 380be designated. 381.Pp 382.Ft struct alias_link * 383.Fo LibAliasRedirectPort 384.Fa "struct libalias *" 385.Fa "struct in_addr local_addr" 386.Fa "u_short local_port" 387.Fa "struct in_addr remote_addr" 388.Fa "u_short remote_port" 389.Fa "struct in_addr alias_addr" 390.Fa "u_short alias_port" 391.Fa "u_char proto" 392.Fc 393.Bd -ragged -offset indent 394This function specifies that traffic from a given remote address/port to 395an alias address/port be redirected to a specified local address/port. 396The parameter 397.Fa proto 398can be either 399.Dv IPPROTO_TCP 400or 401.Dv IPPROTO_UDP , 402as defined in 403.In netinet/in.h . 404.Pp 405If 406.Fa local_addr 407or 408.Fa alias_addr 409is zero, this indicates that the packet aliasing address as established 410by 411.Fn LibAliasSetAddress 412is to be used. 413Even if 414.Fn LibAliasSetAddress 415is called to change the address after 416.Fn LibAliasRedirectPort 417is called, a zero reference will track this change. 418.Pp 419If the link is further set up to operate with load sharing, then 420.Fa local_addr 421and 422.Fa local_port 423are ignored, and are selected dynamically from the server pool, as described in 424.Fn LibAliasAddServer 425below. 426.Pp 427If 428.Fa remote_addr 429is zero, this indicates to redirect packets from any remote address. 430Likewise, if 431.Fa remote_port 432is zero, this indicates to redirect packets originating from any remote 433port number. 434The remote port specification will almost always be zero, but non-zero 435remote addresses can sometimes be useful for firewalling. 436If two calls to 437.Fn LibAliasRedirectPort 438overlap in their address/port specifications, then the most recent call 439will have precedence. 440.Pp 441This function returns a pointer which can subsequently be used by 442.Fn LibAliasRedirectDelete . 443If 444.Dv NULL 445is returned, then the function call did not complete successfully. 446.Pp 447All port numbers should be in network address byte order, so it is necessary 448to use 449.Xr htons 3 450to convert these parameters from internally readable numbers to network byte 451order. 452Addresses are also in network byte order, which is implicit in the use of the 453.Fa struct in_addr 454data type. 455.Ed 456.Pp 457.Ft struct alias_link * 458.Fo LibAliasRedirectAddr 459.Fa "struct libalias *" 460.Fa "struct in_addr local_addr" 461.Fa "struct in_addr alias_addr" 462.Fc 463.Bd -ragged -offset indent 464This function designates that all incoming traffic to 465.Fa alias_addr 466be redirected to 467.Fa local_addr . 468Similarly, all outgoing traffic from 469.Fa local_addr 470is aliased to 471.Fa alias_addr . 472.Pp 473If 474.Fa local_addr 475or 476.Fa alias_addr 477is zero, this indicates that the packet aliasing address as established by 478.Fn LibAliasSetAddress 479is to be used. 480Even if 481.Fn LibAliasSetAddress 482is called to change the address after 483.Fn LibAliasRedirectAddr 484is called, a zero reference will track this change. 485.Pp 486If the link is further set up to operate with load sharing, then the 487.Fa local_addr 488argument is ignored, and is selected dynamically from the server pool, 489as described in 490.Fn LibAliasAddServer 491below. 492.Pp 493If subsequent calls to 494.Fn LibAliasRedirectAddr 495use the same aliasing address, all new incoming traffic to this aliasing 496address will be redirected to the local address made in the last function 497call. 498New traffic generated by any of the local machines, designated in the 499several function calls, will be aliased to the same address. 500Consider the following example: 501.Pp 502LibAliasRedirectAddr(la, inet_aton("192.168.0.2"), 503 inet_aton("141.221.254.101")); 504LibAliasRedirectAddr(la, inet_aton("192.168.0.3"), 505 inet_aton("141.221.254.101")); 506LibAliasRedirectAddr(la, inet_aton("192.168.0.4"), 507 inet_aton("141.221.254.101")); 508.Pp 509Any outgoing connections such as 510.Xr telnet 1 511or 512.Xr ftp 1 513from 192.168.0.2, 192.168.0.3 and 192.168.0.4 will appear to come from 514141.221.254.101. 515Any incoming connections to 141.221.254.101 will be directed to 192.168.0.4. 516.Pp 517Any calls to 518.Fn LibAliasRedirectPort 519will have precedence over address mappings designated by 520.Fn LibAliasRedirectAddr . 521.Pp 522This function returns a pointer which can subsequently be used by 523.Fn LibAliasRedirectDelete . 524If 525.Dv NULL 526is returned, then the function call did not complete successfully. 527.Ed 528.Pp 529.Ft int 530.Fo LibAliasAddServer 531.Fa "struct libalias *" 532.Fa "struct alias_link *link" 533.Fa "struct in_addr addr" 534.Fa "u_short port" 535.Fc 536.Bd -ragged -offset indent 537This function sets the 538.Fa link 539up for Load Sharing using IP Network Address Translation (RFC 2391, LSNAT). 540LSNAT operates as follows. 541A client attempts to access a server by using the server virtual address. 542The LSNAT router transparently redirects the request to one of the hosts 543in the server pool, using a real-time load sharing algorithm. 544Multiple sessions may be initiated from the same client, and each session 545could be directed to a different host based on the load balance across server 546pool hosts when the sessions are initiated. 547If load sharing is desired for just a few specific services, the configuration 548on LSNAT could be defined to restrict load sharing to just the services 549desired. 550.Pp 551Currently, only the simplest selection algorithm is implemented, where a 552host is selected on a round-robin basis only, without regard to load on 553the host. 554.Pp 555First, the 556.Fa link 557is created by either 558.Fn LibAliasRedirectPort 559or 560.Fn LibAliasRedirectAddr . 561Then, 562.Fn LibAliasAddServer 563is called multiple times to add entries to the 564.Fa link Ns 's 565server pool. 566.Pp 567For links created with 568.Fn LibAliasRedirectAddr , 569the 570.Fa port 571argument is ignored and could have any value, e.g.\& htons(~0). 572.Pp 573This function returns 0 on success, \-1 otherwise. 574.Ed 575.Pp 576.Ft int 577.Fn LibAliasRedirectDynamic "struct libalias *" "struct alias_link *link" 578.Bd -ragged -offset indent 579This function marks the specified static redirect rule entered by 580.Fn LibAliasRedirectPort 581as dynamic. 582This can be used to e.g.\& dynamically redirect a single TCP connection, 583after which the rule is removed. 584Only fully specified links can be made dynamic. 585(See the 586.Sx STATIC AND DYNAMIC LINKS 587and 588.Sx PARTIALLY SPECIFIED ALIASING LINKS 589sections below for a definition of static vs.\& dynamic, 590and partially vs.\& fully specified links.) 591.Pp 592This function returns 0 on success, \-1 otherwise. 593.Ed 594.Pp 595.Ft void 596.Fn LibAliasRedirectDelete "struct libalias *" "struct alias_link *link" 597.Bd -ragged -offset indent 598This function will delete a specific static redirect rule entered by 599.Fn LibAliasRedirectPort 600or 601.Fn LibAliasRedirectAddr . 602The parameter 603.Fa link 604is the pointer returned by either of the redirection functions. 605If an invalid pointer is passed to 606.Fn LibAliasRedirectDelete , 607then a program crash or unpredictable operation could result, so 608care is needed when using this function. 609.Ed 610.Pp 611.Ft int 612.Fn LibAliasProxyRule "struct libalias *" "const char *cmd" 613.Bd -ragged -offset indent 614The passed 615.Fa cmd 616string consists of one or more pairs of words. 617The first word in each pair is a token and the second is the value that 618should be applied for that token. 619Tokens and their argument types are as follows: 620.Bl -tag -width indent 621.It Cm type encode_ip_hdr | encode_tcp_stream | no_encode 622In order to support transparent proxying, it is necessary to somehow 623pass the original address and port information into the new destination 624server. 625If 626.Cm encode_ip_hdr 627is specified, the original destination address and port are passed 628as an extra IP option. 629If 630.Cm encode_tcp_stream 631is specified, the original destination address and port are passed 632as the first piece of data in the TCP stream in the format 633.Dq Li DEST Ar IP port . 634.It Cm port Ar portnum 635Only packets with the destination port 636.Ar portnum 637are proxied. 638.It Cm server Ar host Ns Op : Ns Ar portnum 639This specifies the 640.Ar host 641and 642.Ar portnum 643that the data is to be redirected to. 644.Ar host 645must be an IP address rather than a DNS host name. 646If 647.Ar portnum 648is not specified, the destination port number is not changed. 649.Pp 650The 651.Ar server 652specification is mandatory unless the 653.Cm delete 654command is being used. 655.It Cm rule Ar index 656Normally, each call to 657.Fn LibAliasProxyRule 658inserts the next rule at the start of a linear list of rules. 659If an 660.Ar index 661is specified, the new rule will be checked after all rules with lower 662indices. 663Calls to 664.Fn LibAliasProxyRule 665that do not specify a rule are assigned rule 0. 666.It Cm delete Ar index 667This token and its argument MUST NOT be used with any other tokens. 668When used, all existing rules with the given 669.Ar index 670are deleted. 671.It Cm proto tcp | udp 672If specified, only packets of the given protocol type are matched. 673.It Cm src Ar IP Ns Op / Ns Ar bits 674If specified, only packets with a source address matching the given 675.Ar IP 676are matched. 677If 678.Ar bits 679is also specified, then the first 680.Ar bits 681bits of 682.Ar IP 683are taken as a network specification, and all IP addresses from that 684network will be matched. 685.It Cm dst Ar IP Ns Op / Ns Ar bits 686If specified, only packets with a destination address matching the given 687.Ar IP 688are matched. 689If 690.Ar bits 691is also specified, then the first 692.Ar bits 693bits of 694.Ar IP 695are taken as a network specification, and all IP addresses from that 696network will be matched. 697.El 698.Pp 699This function is usually used to redirect outgoing connections for 700internal machines that are not permitted certain types of internet 701access, or to restrict access to certain external machines. 702.Ed 703.Pp 704.Ft struct alias_link * 705.Fo LibAliasRedirectProto 706.Fa "struct libalias *" 707.Fa "struct in_addr local_addr" 708.Fa "struct in_addr remote_addr" 709.Fa "struct in_addr alias_addr" 710.Fa "u_char proto" 711.Fc 712.Bd -ragged -offset indent 713This function specifies that any IP packet with protocol number of 714.Fa proto 715from a given remote address to an alias address will be 716redirected to a specified local address. 717.Pp 718If 719.Fa local_addr 720or 721.Fa alias_addr 722is zero, this indicates that the packet aliasing address as established 723by 724.Fn LibAliasSetAddress 725is to be used. 726Even if 727.Fn LibAliasSetAddress 728is called to change the address after 729.Fn LibAliasRedirectProto 730is called, a zero reference will track this change. 731.Pp 732If 733.Fa remote_addr 734is zero, this indicates to redirect packets from any remote address. 735Non-zero remote addresses can sometimes be useful for firewalling. 736.Pp 737If two calls to 738.Fn LibAliasRedirectProto 739overlap in their address specifications, then the most recent call 740will have precedence. 741.Pp 742This function returns a pointer which can subsequently be used by 743.Fn LibAliasRedirectDelete . 744If 745.Dv NULL 746is returned, then the function call did not complete successfully. 747.Ed 748.Sh FRAGMENT HANDLING 749The functions in this section are used to deal with incoming fragments. 750.Pp 751Outgoing fragments are handled within 752.Fn LibAliasOut 753by changing the address according to any applicable mapping set by 754.Fn LibAliasRedirectAddr , 755or the default aliasing address set by 756.Fn LibAliasSetAddress . 757.Pp 758Incoming fragments are handled in one of two ways. 759If the header of a fragmented IP packet has already been seen, then all 760subsequent fragments will be re-mapped in the same manner the header 761fragment was. 762Fragments which arrive before the header are saved and then retrieved 763once the header fragment has been resolved. 764.Pp 765.Ft int 766.Fn LibAliasSaveFragment "struct libalias *" "char *ptr" 767.Bd -ragged -offset indent 768When 769.Fn LibAliasIn 770returns 771.Dv PKT_ALIAS_UNRESOLVED_FRAGMENT , 772this function can be used to save the pointer to the unresolved fragment. 773.Pp 774It is implicitly assumed that 775.Fa ptr 776points to a block of memory allocated by 777.Xr malloc 3 . 778If the fragment is never resolved, the packet aliasing engine will 779automatically free the memory after a timeout period. 780[Eventually this function should be modified so that a callback function 781for freeing memory is passed as an argument.] 782.Pp 783This function returns 784.Dv PKT_ALIAS_OK 785if it was successful and 786.Dv PKT_ALIAS_ERROR 787if there was an error. 788.Ed 789.Pp 790.Ft char * 791.Fn LibAliasGetFragment "struct libalias *" "char *buffer" 792.Bd -ragged -offset indent 793This function can be used to retrieve fragment pointers saved by 794.Fn LibAliasSaveFragment . 795The IP header fragment pointed to by 796.Fa buffer 797is the header fragment indicated when 798.Fn LibAliasIn 799returns 800.Dv PKT_ALIAS_FOUND_HEADER_FRAGMENT . 801Once a fragment pointer is retrieved, it becomes the calling program's 802responsibility to free the dynamically allocated memory for the fragment. 803.Pp 804The 805.Fn LibAliasGetFragment 806function can be called sequentially until there are no more fragments 807available, at which time it returns 808.Dv NULL . 809.Ed 810.Pp 811.Ft void 812.Fn LibAliasFragmentIn "struct libalias *" "char *header" "char *fragment" 813.Bd -ragged -offset indent 814When a fragment is retrieved with 815.Fn LibAliasGetFragment , 816it can then be de-aliased with a call to 817.Fn LibAliasFragmentIn . 818The 819.Fa header 820argument is the pointer to a header fragment used as a template, and 821.Fa fragment 822is the pointer to the packet to be de-aliased. 823.Ed 824.Sh MISCELLANEOUS FUNCTIONS 825.Ft struct alias_link * 826.Fn AddLink "struct libalias *" "struct in_addr src_addr" "struct in_addr dst_addr" \ 827"struct in_addr alias_addr" "u_short src_port" "u_short dst_port" \ 828"int alias_param" "int link_type" 829.Bd -ragged -offset indent 830This function adds new state to the instance hash table. 831The dst_address and/or dst_port may be given as zero, which 832introduces some dynamic character into the link, since 833LibAliasSetAddress can change the address that is used. 834However, in the current implementation, such links can only be used 835for inbound (ext -> int) traffic. 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 CONCEPTUAL BACKGROUND 905This section is intended for those who are planning to modify the source 906code or want to create somewhat esoteric applications using the packet 907aliasing functions. 908.Pp 909The conceptual framework under which the packet aliasing engine operates 910is described here. 911Central to the discussion is the idea of an 912.Em aliasing link 913which describes the relationship for a given packet transaction between 914the local machine, aliased identity and remote machine. 915It is discussed how such links come into existence and are destroyed. 916.Ss ALIASING LINKS 917There is a notion of an 918.Em aliasing link , 919which is a 7-tuple describing a specific translation: 920.Bd -literal -offset indent 921(local addr, local port, alias addr, alias port, 922 remote addr, remote port, protocol) 923.Ed 924.Pp 925Outgoing packets have the local address and port number replaced with the 926alias address and port number. 927Incoming packets undergo the reverse process. 928The packet aliasing engine attempts to match packets against an internal 929table of aliasing links to determine how to modify a given IP packet. 930Both the IP header and protocol dependent headers are modified as necessary. 931Aliasing links are created and deleted as necessary according to network 932traffic. 933.Pp 934Protocols can be TCP, UDP or even ICMP in certain circumstances. 935(Some types of ICMP packets can be aliased according to sequence or ID 936number which acts as an equivalent port number for identifying how 937individual packets should be handled.) 938.Pp 939Each aliasing link must have a unique combination of the following five 940quantities: alias address/port, remote address/port and protocol. 941This ensures that several machines on a local network can share the 942same aliasing IP address. 943In cases where conflicts might arise, the aliasing port is chosen so that 944uniqueness is maintained. 945.Ss STATIC AND DYNAMIC LINKS 946Aliasing links can either be static or dynamic. 947Static links persist indefinitely and represent fixed rules for translating 948IP packets. 949Dynamic links come into existence for a specific TCP connection or UDP 950transaction or ICMP ECHO sequence. 951For the case of TCP, the connection can be monitored to see when the 952associated aliasing link should be deleted. 953Aliasing links for UDP transactions (and ICMP ECHO and TIMESTAMP requests) 954work on a simple timeout rule. 955When no activity is observed on a dynamic link for a certain amount of time 956it is automatically deleted. 957Timeout rules also apply to TCP connections which do not open or close 958properly. 959.Ss PARTIALLY SPECIFIED ALIASING LINKS 960Aliasing links can be partially specified, meaning that the remote address 961and/or remote port are unknown. 962In this case, when a packet matching the incomplete specification is found, 963a fully specified dynamic link is created. 964If the original partially specified link is dynamic, it will be deleted 965after the fully specified link is created, otherwise it will persist. 966.Pp 967For instance, a partially specified link might be 968.Bd -literal -offset indent 969(192.168.0.4, 23, 204.228.203.215, 8066, 0, 0, tcp) 970.Ed 971.Pp 972The zeros denote unspecified components for the remote address and port. 973If this link were static it would have the effect of redirecting all 974incoming traffic from port 8066 of 204.228.203.215 to port 23 (telnet) 975of machine 192.168.0.4 on the local network. 976Each individual telnet connection would initiate the creation of a distinct 977dynamic link. 978.Ss DYNAMIC LINK CREATION 979In addition to aliasing links, there are also address mappings that can be 980stored within the internal data table of the packet aliasing mechanism. 981.Bd -literal -offset indent 982(local addr, alias addr) 983.Ed 984.Pp 985Address mappings are searched when creating new dynamic links. 986.Pp 987All outgoing packets from the local network automatically create a dynamic 988link if they do not match an already existing fully specified link. 989If an address mapping exists for the outgoing packet, this determines 990the alias address to be used. 991If no mapping exists, then a default address, usually the address of the 992packet aliasing host, is used. 993If necessary, this default address can be changed as often as each individual 994packet arrives. 995.Pp 996The aliasing port number is determined such that the new dynamic link does 997not conflict with any existing links. 998In the default operating mode, the packet aliasing engine attempts to set 999the aliasing port equal to the local port number. 1000If this results in a conflict, then port numbers are randomly chosen until 1001a unique aliasing link can be established. 1002In an alternate operating mode, the first choice of an aliasing port is also 1003random and unrelated to the local port number. 1004.Sh MODULAR ARCHITECTURE (AND Xr ipfw 4 Sh SUPPORT) 1005One of the latest improvements to 1006.Nm 1007was to make its support 1008for new protocols independent from the rest of the library, giving it 1009the ability to load/unload support for new protocols at run-time. 1010To achieve this feature, all the code for protocol handling was moved 1011to a series of modules outside of the main library. 1012These modules are compiled from the same sources but work in 1013different ways, depending on whether they are compiled to work inside a kernel 1014or as part of the userland library. 1015.Ss LIBALIAS MODULES IN KERNEL LAND 1016When compiled for the kernel, 1017.Nm 1018modules are plain KLDs recognizable with the 1019.Pa alias_ 1020prefix. 1021.Pp 1022To add support for a new protocol, load the corresponding module. 1023For example: 1024.Pp 1025.Dl "kldload alias_ftp" 1026.Pp 1027When support for a protocol is no longer needed, its module can be unloaded: 1028.Pp 1029.Dl "kldunload alias_ftp" 1030.Ss LIBALIAS MODULES IN USERLAND 1031Due to the differences between kernel and userland (no KLD mechanism, 1032many different address spaces, etc.), we had to change a bit how to 1033handle module loading/tracking/unloading in userland. 1034.Pp 1035While compiled for a userland 1036.Nm , 1037all the modules are plain libraries, residing in 1038.Pa /usr/lib , 1039and recognizable with the 1040.Pa libalias_ 1041prefix. 1042.Pp 1043There is a configuration file, 1044.Pa /etc/libalias.conf , 1045with the following contents (by default): 1046.Bd -literal -offset indent 1047/usr/lib/libalias_cuseeme.so 1048/usr/lib/libalias_ftp.so 1049/usr/lib/libalias_irc.so 1050/usr/lib/libalias_nbt.so 1051/usr/lib/libalias_pptp.so 1052/usr/lib/libalias_skinny.so 1053/usr/lib/libalias_smedia.so 1054.Ed 1055.Pp 1056This file contains the paths to the modules that 1057.Nm 1058will load. 1059To load/unload a new module, just add its path to 1060.Pa libalias.conf 1061and call 1062.Fn LibAliasRefreshModules 1063from the program. 1064In case the application provides a 1065.Dv SIGHUP 1066signal handler, add a call to 1067.Fn LibAliasRefreshModules 1068inside the handler, and everytime you want to refresh the loaded modules, 1069send it the 1070.Dv SIGHUP 1071signal: 1072.Pp 1073.Dl "kill -HUP <process_pid>" 1074.Ss MODULAR ARCHITECURE: HOW IT WORKS 1075The modular architecture of 1076.Nm 1077works similar whether it is running inside the 1078kernel or in userland. 1079From 1080.Pa alias_mod.c : 1081.Bd -literal 1082/* Protocol and userland module handlers chains. */ 1083LIST_HEAD(handler_chain, proto_handler) handler_chain ... 1084\&... 1085SLIST_HEAD(dll_chain, dll) dll_chain ... 1086.Ed 1087.Pp 1088.Va handler_chain 1089keeps track of all the protocol handlers loaded, while 1090.Va ddl_chain 1091tracks which userland modules are loaded. 1092.Pp 1093.Va handler_chain 1094is composed of 1095.Vt "struct proto_handler" 1096entries: 1097.Bd -literal 1098struct proto_handler { 1099 u_int pri; 1100 int16_t dir; 1101 uint8_t proto; 1102 int (*fingerprint)(struct libalias *la, 1103 struct ip *pip, struct alias_data *ah); 1104 int (*protohandler)(struct libalias *la, 1105 struct ip *pip, struct alias_data *ah); 1106 TAILQ_ENTRY(proto_handler) link; 1107}; 1108.Ed 1109.Pp 1110where: 1111.Bl -inset 1112.It Va pri 1113is the priority assigned to a protocol handler; lower priority 1114is better. 1115.It Va dir 1116is the direction of packets: ingoing or outgoing. 1117.It Va proto 1118indicates to which protocol this packet belongs: IP, TCP or UDP. 1119.It Va fingerprint 1120points to the fingerprint function while protohandler points 1121to the protocol handler function. 1122.El 1123.Pp 1124The 1125.Va fingerprint 1126function has the dual role of checking if the 1127incoming packet is found, and if it belongs to any categories that this 1128module can handle. 1129.Pp 1130The 1131.Va protohandler 1132function actually manipulates 1133the packet to make 1134.Nm 1135correctly NAT it. 1136.Pp 1137When a packet enters 1138.Nm , 1139if it meets a module hook, 1140.Va handler_chain 1141is searched to see if there is an handler that matches 1142this type of a packet (it checks protocol and direction of packet). 1143Then, if more than one handler is found, it starts with the module with 1144the lowest priority number: it calls the 1145.Va fingerprint 1146function and interprets the result. 1147.Pp 1148If the result value is equal to 0 then it calls the protocol handler 1149of this handler and returns. 1150Otherwise, it proceeds to the next eligible module until the 1151.Va handler_chain 1152is exhausted. 1153.Pp 1154Inside 1155.Nm , 1156the module hook looks like this: 1157.Bd -literal -offset indent 1158struct alias_data ad = { 1159 lnk, 1160 &original_address, 1161 &alias_address, 1162 &alias_port, 1163 &ud->uh_sport, /* original source port */ 1164 &ud->uh_dport, /* original dest port */ 1165 256 /* maxpacketsize */ 1166}; 1167 1168\&... 1169 1170/* walk out chain */ 1171err = find_handler(IN, UDP, la, pip, &ad); 1172.Ed 1173.Pp 1174All data useful to a module are gathered together in an 1175.Vt alias_data 1176structure, then 1177.Fn find_handler 1178is called. 1179The 1180.Fn find_handler 1181function is responsible for walking the handler 1182chain; it receives as input parameters: 1183.Bl -tag -width indent 1184.It Fa IN 1185direction 1186.It Fa UDP 1187working protocol 1188.It Fa la 1189pointer to this instance of libalias 1190.It Fa pip 1191pointer to a 1192.Vt "struct ip" 1193.It Fa ad 1194pointer to 1195.Vt "struct alias_data" 1196(see above) 1197.El 1198.Pp 1199In this case, 1200.Fn find_handler 1201will search only for modules registered for 1202supporting INcoming UDP packets. 1203.Pp 1204As was mentioned earlier, 1205.Nm 1206in userland is a bit different, as 1207care must be taken in module handling as well (avoiding duplicate load of 1208modules, avoiding modules with same name, etc.) so 1209.Va dll_chain 1210was introduced. 1211.Pp 1212.Va dll_chain 1213contains a list of all userland 1214.Nm 1215modules loaded. 1216.Pp 1217When an application calls 1218.Fn LibAliasRefreshModules , 1219.Nm 1220first unloads all the loaded modules, then reloads all the modules listed in 1221.Pa /etc/libalias.conf : 1222for every module loaded, a new entry is added to 1223.Va dll_chain . 1224.Pp 1225.Va dll_chain 1226is composed of 1227.Vt "struct dll" 1228entries: 1229.Bd -literal 1230struct dll { 1231 /* name of module */ 1232 char name[DLL_LEN]; 1233 /* 1234 * ptr to shared obj obtained through 1235 * dlopen() - use this ptr to get access 1236 * to any symbols from a loaded module 1237 * via dlsym() 1238 */ 1239 void *handle; 1240 struct dll *next; 1241}; 1242.Ed 1243.Bl -inset 1244.It Va name 1245is the name of the module. 1246.It Va handle 1247is a pointer to the module obtained through 1248.Xr dlopen 3 . 1249.El 1250Whenever a module is loaded in userland, an entry is added to 1251.Va dll_chain , 1252then every protocol handler present in that module 1253is resolved and registered in 1254.Va handler_chain . 1255.Ss HOW TO WRITE A MODULE FOR LIBALIAS 1256There is a module (called 1257.Pa alias_dummy.[ch] ) 1258in 1259.Nm 1260that can be used as a skeleton for future work. 1261Here we analyse some parts of that module. 1262From 1263.Pa alias_dummy.c : 1264.Bd -literal 1265struct proto_handler handlers[] = { 1266 { 1267 .pri = 666, 1268 .dir = IN|OUT, 1269 .proto = UDP|TCP, 1270 .fingerprint = fingerprint, 1271 .protohandler= protohandler, 1272 }, 1273 { EOH } 1274}; 1275.Ed 1276.Pp 1277The variable 1278.Va handlers 1279is the 1280.Dq "most important thing" 1281in a module 1282since it describes the handlers present and lets the outside world use 1283it in an opaque way. 1284.Pp 1285It must ALWAYS be present in every module, and it MUST retain 1286the name 1287.Va handlers , 1288otherwise attempting to load a module in userland will fail and 1289complain about missing symbols: for more information about module 1290load/unload, please refer to 1291.Fn LibAliasRefreshModules , 1292.Fn LibAliasLoadModule 1293and 1294.Fn LibAliasUnloadModule 1295in 1296.Pa alias.c . 1297.Pp 1298.Va handlers 1299contains all the 1300.Vt proto_handler 1301structures present in a module. 1302.Bd -literal 1303static int 1304mod_handler(module_t mod, int type, void *data) 1305{ 1306 int error; 1307 1308 switch (type) { 1309 case MOD_LOAD: 1310 error = LibAliasAttachHandlers(handlers); 1311 break; 1312 case MOD_UNLOAD: 1313 error = LibAliasDetachHandlers(handlers); 1314 break; 1315 default: 1316 error = EINVAL; 1317 } 1318 return (error); 1319} 1320.Ed 1321When running as KLD, 1322.Fn mod_handler 1323registers/deregisters the module using 1324.Fn LibAliasAttachHandlers 1325and 1326.Fn LibAliasDetachHandlers , 1327respectively. 1328.Pp 1329Every module must contain at least 2 functions: one fingerprint 1330function and a protocol handler function. 1331.Bd -literal 1332#ifdef _KERNEL 1333static 1334#endif 1335int 1336fingerprint(struct libalias *la, struct ip *pip, struct alias_data *ah) 1337{ 1338 1339\&... 1340} 1341 1342#ifdef _KERNEL 1343static 1344#endif 1345int 1346protohandler(struct libalias *la, struct ip *pip, 1347 struct alias_data *ah) 1348{ 1349 1350\&... 1351} 1352.Ed 1353and they must accept exactly these input parameters. 1354.Ss PATCHING AN APPLICATION FOR USERLAND LIBALIAS MODULES 1355To add module support into an application that uses 1356.Nm , 1357the following simple steps can be followed. 1358.Bl -enum 1359.It 1360Find the main file of an application 1361(let us call it 1362.Pa main.c ) . 1363.It 1364Add this to the header section of 1365.Pa main.c , 1366if not already present: 1367.Pp 1368.Dl "#include <signal.h>" 1369.Pp 1370and this just after the header section: 1371.Pp 1372.Dl "static void signal_handler(int);" 1373.It 1374Add the following line to the init function of an application or, 1375if it does not have any init function, put it in 1376.Fn main : 1377.Pp 1378.Dl "signal(SIGHUP, signal_handler);" 1379.Pp 1380and place the 1381.Fn signal_handler 1382function somewhere in 1383.Pa main.c : 1384.Bd -literal -offset indent 1385static void 1386signal_handler(int sig) 1387{ 1388 1389 LibAliasRefreshModules(); 1390} 1391.Ed 1392.Pp 1393Otherwise, if an application already traps the 1394.Dv SIGHUP 1395signal, just add a call to 1396.Fn LibAliasRefreshModules 1397in the signal handler function. 1398.El 1399For example, to patch 1400.Xr natd 8 1401to use 1402.Nm 1403modules, just add the following line to 1404.Fn RefreshAddr "int sig __unused" : 1405.Pp 1406.Dl "LibAliasRefreshModules()" 1407.Pp 1408recompile and you are done. 1409.Ss LOGGING SUPPORT IN KERNEL LAND 1410When working as KLD, 1411.Nm 1412now has log support that 1413happens on a buffer allocated inside 1414.Vt "struct libalias" 1415(from 1416.Pa alias_local.h ) : 1417.Bd -literal 1418struct libalias { 1419 ... 1420 1421 /* log descriptor */ 1422#ifdef KERNEL_LOG 1423 char *logDesc; /* 1424 * ptr to an auto-malloced 1425 * memory buffer when libalias 1426 * works as kld 1427 */ 1428#else 1429 FILE *logDesc; /* 1430 * ptr to /var/log/alias.log 1431 * when libalias runs as a 1432 * userland lib 1433 */ 1434#endif 1435 1436 ... 1437} 1438.Ed 1439so all applications using 1440.Nm 1441will be able to handle their 1442own logs, if they want, accessing 1443.Va logDesc . 1444Moreover, every change to a log buffer is automatically added to 1445.Xr syslog 3 1446with the 1447.Dv LOG_SECURITY 1448facility and the 1449.Dv LOG_INFO 1450level. 1451.Sh AUTHORS 1452.An Charles Mott Aq cm@linktel.net , 1453versions 1.0 - 1.8, 2.0 - 2.4. 1454.An Eivind Eklund Aq eivind@FreeBSD.org , 1455versions 1.8b, 1.9 and 2.5. 1456Added IRC DCC support as well as contributing a number of architectural 1457improvements; added the firewall bypass for FTP/IRC DCC. 1458.An Erik Salander Aq erik@whistle.com 1459added support for PPTP and RTSP. 1460.An Junichi Satoh Aq junichi@junichi.org 1461added support for RTSP/PNA. 1462.An Ruslan Ermilov Aq ru@FreeBSD.org 1463added support for PPTP and LSNAT as well as general hacking. 1464.An Gleb Smirnoff Aq glebius@FreeBSD.org 1465ported the library to kernel space. 1466.An Paolo Pisati Aq piso@FreeBSD.org 1467made the library modular, moving support for all 1468protocols (except for IP, TCP and UDP) to external modules. 1469.Sh ACKNOWLEDGEMENTS 1470Listed below, in approximate chronological order, are individuals who 1471have provided valuable comments and/or debugging assistance. 1472.Bd -ragged -offset indent 1473.An -split 1474.An Gary Roberts 1475.An Tom Torrance 1476.An Reto Burkhalter 1477.An Martin Renters 1478.An Brian Somers 1479.An Paul Traina 1480.An Ari Suutari 1481.An Dave Remien 1482.An J. Fortes 1483.An Andrzej Bialecki 1484.An Gordon Burditt 1485.Ed 1486