DANTED.CONF(5)

NAME
danted.conf - Dante server configuration file syntax

DESCRIPTION
The configuration file for the Dante server controls both access controls and logging. It is divided into three parts; server settings, rules, and routes.

Note that server settings must come before rules and routes.

A line can be commented out using the standard comment character #.

SERVER SETTINGS
The server settings control the generic behaviour of the server. Each keyword is separated from its value by a ':' character.

The following keywords are available:

clientmethod
    A list of acceptable authentication methods for client-rules, listed in order of preference. These are authentication methods that are to be checked immediately after the SOCKS client has connected to Dante, and before any socks-negotiation has started.

    Supported values are pam.address, pam.any, none, and rfc931 .

    For all methods the authentication will be based on solely on the IP-address of the client, possibly in combination with a rfc931 ("ident") lookup towards the host the client is running on.

    Any credentials provided during this pass will also be available for use in later socks-rules, when the socks-request from the client is evaluated.

    The default value for this keyword is all methods that may be necessary for the later socks-based authentication methods, as specified as values to the global socksmethod keyword. Normally you should not need to set this keyword, as Dante will set it to the correct value by it self.

compatibility
    With the sameport keyword, the server attempts to use the same port on the server's external side as the client used on the server's internal side. This is normally the default, but when this option is given it will be done with privileged ports also, meaning if a client connects to Dante from a privileged port, Dante will attempt to connect to the target destination from a privileged port too. There can be security issues involved with this, so normally this option should not be set.

    The draft-5.05 keyword will enable usage of parts of the socks v5-05 draft. The only feature from this draft that Dante supports is the "USECLIENTSPORT" extension. Note that there is a conflicting interpretation of this extension, so enabling it might prevent clients using the conflicting interpretation from working correctly. Only affects UDP.

cpu The CPU settings for the various type of Dante processes. Note that the possibility for configuring these settings depend on the platform Dante is running on. Not all platforms may provide support for these type of CPU settings.

    There are four process types: mother, negotiate, request, and io.

    The currently supported options are:

    schedule.<process type>: <scheduling policy>/<priority>.

    Example: cpu.schedule.mother: SCHED_FIFO/20 The above requests that the kernel schedules the mother process(es) using a first-in, first-out policy, at priority 20.

    The default is to not request any specific scheduling.

    mask.<process type>: <cpu id 1> [cpu id 1 ...]/any.

    Example: cpu.mask.mother: any Example: cpu.mask.io: 0 1

    The mask gives control over the CPU/cores on which the different process types will run. Specifying the default (all) allows the process type to run on any CPU id. Specifying one or more numeric CPU id limits the process to that set of CPUs.

    The cpu keywords (schedule and mask) should in most cases not be necessary. If they are to be used, the io processes are where most of the work is done and adjusting the priority or CPU usage is what is likely to have the most significant performance effect client performance and overhead from the server. The other processes are primarily used during connection/session establishment and changes to settings for the non-io process types will primarily affect these operations.

    The default is to not limit processes to any specific cpu.

debug
    Print debug info to the logs. The value sets the debug level.

errorlog
    This value can be set to receive only error-related logoutput. Note that this does not include client-specific errors, but only more serious "global" errors.

    The possible values are the same as for the logoutput keyword mentioned below.

    The intent is to have a special place that only serious errors are logged so that they can discovered quickly. The default is to not have any special place to log errors.

external
    The address to be used for outgoing connections. The address given may be either an IP address or an interface name. Can be given multiple times for different addresses.

external.log.<loglevel>.error
    See internal.log.<loglevel>.error. This option has an identical syntax and semantics, but applies to error related to the external interface side.

external.protocol
    By default Dante will use the address families specified and available, and there is no need to set this keyword.

    In some cases the operator may however wish to specify an address in a form that may include more than one address family, yet not wish for Dante to use all the address families available for that address form.

    This will typically happen if the operator wishes to specify that Dante should use the addresses on a network interface card which has both IPv4 and IPv6 addresses configured, yet the operator wishes Dante to only use one of these two address families. The operator can then specify the address family he wants Dante too look for when expanding the interface name for IP-addresses to use.

    Valid values for this keyword are: ipv4 and ipv6, indicating that Dante should only use the IPv4 address family or only the IPv6 address family, respectively. The default is to use both families, if available.

    A corresponding keyword exists for the internal side (see internal.protocol).

external.rotation
    If more than one external address is given, this governs which of the given addresses is selected as the source address for outgoing connections/packets. Note that regardless of which external rotation value is used, all external addresses that are to be used must be listed via the external keyword first.

    Valid values are none (the default), route, and same-same.

    none indicates the first address on the list of external addresses should be used.

    route indicates the kernels routing table should be consulted to find out what the source address for a given destination will be, and might require you to set user.privileged to root. Note that route might create problems for ftp-clients using active ftp if the Dante bind extension is enabled for the ftp-client.

    same-same indicates the source address for a given destination should be the same address as the Dante server accepted the clients connection on.

internal
    The internal addresses. Connections will only be accepted on these addresses. The address given may be either an IP address or an interface name.

internal.log.<loglevel>.error
    Specifies that certain system call failures, listed as symbolic errno values, or certain dns failures, listed as symbolic libresolv failure-codes, should be logged, possibly an extra time, at the log-level log-level.

    Note that this only applies to errors on the internal interface side only.

    A corresponding keyword exists for the external side (see external.log).

    In addition to the standard errno and getaddrinfo(3) error symbols, the following special symbols are accepted:

    no-route
        Any error related to no route.

    dns-any
        Any error related to DNS/hostname-resolving.

    system-any
        Any system error. I.e., any errno value.

internal.protocol
    See external.protocol. This option has an identical syntax and semantics, but applies to the internal interface, for addresses to listen to connections from clients on.

libwrap.hosts_access
    If the server is compiled with libwrap support, determines whether the hosts_access() function should be used for access control. When enabled by setting this value to yes, the libwrap library determines if TCP connections or UDP packets should be immediately dropped or not, typically by consulting /etc/hosts.allow and /etc/hosts.deny. These checks are applied to all traffic, before the rule processing starts. The default value is no (disabled).

logoutput
    This value controls where the server sends logoutput. It can be set to syslog[/facility], stdout, stderr, a filename, or a combination. The default is nowhere. Note that if errorlog is also set, there will be a overlap between what is logged there (errors only), and what will be logged here (errors, and everything else).

socksmethod
    A list of acceptable authentication methods for socks-rules, listed in order of preference. It is thus important that you specify these in the desired order, normally with the more secure methods first.

    Supported values are bsdauth, gssapi, none, pam.any, pam.address, pam.username, rfc931, and username,

    If a method is not set in this list it will never be selected. The default is no methods, which means all socks-requests will be blocked.

    See the section on AUTHENTICATION METHODS for an explanation of the different methods and their meaning.

srchost
    This keyword allows you to configure a few options that relate to the srchost, i.e., the host the Dante server accepts the connections from.

    With the nodnsmismatch keyword, the server will not accept connections from addresses having a mismatch between DNS IP address and hostname. Default is to accept them.

    With the nodnsunknown keyword, the server will not accept connections from addresses without a DNS record. Default is to accept them.

    With the checkreplyauth keyword, the server will check that the authentication on bind-replies and udp-replies matches that which is set in the rule and global socksmethod. Normally, authentication is not desired on replies, as they are replies sent to the socks-clients from non-socks clients, and thus only a limited set of authentication methods are possible.

    The methods possible for TCP are the methods not involving the socks protocol in any way, and are listed in the clientmethod section previously mentioned. For UDP-replies, no methods can be used.

    Default is not to check the authentication on replies.

timeout.connect
    The number of seconds the server will wait for a connect initiated on behalf of the socks-client to complete. The default is 30. Setting it to 0 will use the systems default.

timeout.io
    The number of seconds an established connection can be idle. The default is 0, meaning forever. See also the "-n" option in the danted(8) manpage.

    Individual timeouts can be set for TCP and UDP by suffixing io with ".<protocolname>", i.e. timeout.io.tcp or timeout.io.udp.

    Individual timeouts can also be set within rules, using the same syntax. The timeout set in the rule will then override the default timeouts for clients matching the rule.

timeout.negotiate
    The number of seconds a client can spend negotiating with the Dante server for a socks session before Dante will close the connection to the client. The default is 30. Set it to 0 for forever, though that is strongly discouraged.

timeout.tcp_fin_wait
    The timeout for the equivalent of TCP's FIN-WAIT-2. The default is 0, which means use the systems default (normally, no timeout).

udp.connectdst
    Enables or disables whether the server should attempt connecting UDP sockets to the destination. Valid values are yes and no.

    The default is yes, which improves UDP performance, but may not be compatible with some UDP-based application protocols as it means the server can only receive packets from the destination address.

    The socket will only remain connected as long as the client only sends UDP packets to one destination address. If packets are sent to multiple destinations the socket will no longer remain connected and replies can be received from any destination.

Userids
    On platforms providing a privilege-model supported by Dante, the Dante server does not use userid-switching via the seteuid(2) system call. On other platforms, it is prudent to set the userid to be used by the Dante server to appropriate values. The Dante server can use two different userids, or three if compiled with libwrap support. They are as follows:

user.privileged
    Username which will be used for doing privileged operations. If you need special privileges to read the danted.conf file or to write the danted.pid file (you can create it manually before starting danted), have anything in your configuration that requires binding privileged TCP/UDP ports (ports below 1024), or use some sort of password-based authentication, this probably needs to be set to root.

    If not, you can probably set it to the same value as user.unprivileged.

user.unprivileged
    User which the server runs as most of the time. This should be an id with as little privileges as possible. It is recommended that a separate userid is created for this purpose.

user.libwrap
    User used to execute libwrap commands. Normally this should be the same as user.unprivileged

MODULES
The following modules are supported by Dante. Modules are purchased separately from Inferno Nettverk A/S and may add extra functionality that is not needed by most users. See the Dante homepage for more information.

bandwidth
    The bandwidth module gives control over how much bandwidth the Dante server uses on behalf of different clients or to different targets.

redirect
    The redirect module gives you control over what addresses the server will use on behalf of the clients, as well as allowing you to redirect client requests to a different addresses.

SOCKET OPTIONS

The server has support for setting a large number of low-level socket options on both incoming and outgoing traffic. Most users will not need to set any of these options, but some might want to do it, to enable special network features, or to perform various experiments.

Options can be set globally as defaults for all traffic, or be set in the access control rules to only affect clients and targets matching the given rule.

The socket options that are available vary between platforms, so during configuration and building of the server the options that are available will be determined. Currently, the following options should be detected, when available, for the specified protocol levels:

    SOCKET
        so_bindany, so_broadcast, so_debug, so_dontroute, so_jumbo, so_keepalive, so_oobinline, so_priority, so_rcvbuf, so_rcvbufforce, so_rcvlowat, so_sndbuf, so_sndbufforce, so_sndlowat, so_useloopback

    TCP tcp_cork, tcp_cwnd, tcp_init_cwnd, tcp_keepcnt, tcp_keepidle, tcp_keepintvl, tcp_linger2, tcp_maxrt, tcp_maxseg, tcp_md5sig, tcp_nodelay, tcp_noopt, tcp_nopush, tcp_sack_enable, tcp_stdurg, tcp_syncnt, tcp_window_clamp

    UDP udp_cork

    IP  ip_auth_level, ip_dontfrag, ip_esp_network_level, ip_esp_trans_level, ip_freebind, ip_ipcomp_level, ip_minttl, ip_mtu_discover, ip_portrange, ip_recvtos, ip_tos, ip_ttl

The syntax for setting socket options is as follows:

<direction>.<level>.<option>: <value>

The value field corresponds to the value that the socket option should be set to. For many socket options this is an integer value. The level and option values correspond to the socket names and protocol levels listed above. Both should be in lower-case.

The direction keywords is used to specify whether the socket option should be set for traffic on the internal or the external interface and can have the values internal and external. For example, to set the IP_TOS socket option on outgoing traffic, the following syntax can be used:

external.ip.ip_tos: 0x10

In this example, the argument value (0x10) is specified as a hex value. For some of the socket options the value can also be set symbolically. Currently this is possible for the following options, with the listed values:

    ip_portrange
        ip_portrange_default, ip_portrange_low, ip_portrange_high

The IP_TOS socket option also supports this, but handling this option is somewhat complicated by the same bits having different meanings in different RFCs. Handling this is done with a subfield that indicates the type of argument that should be used. The following subfields are defined and should be added to the name of the socket option as specified below:

    ip_tos.dscp
        af11 af12 af13 af21 af22 af23 af31 af32 af33 af41 af42 af43 cs0 cs1 cs2 cs3 cs4 cs5 cs6 cs7 ef

    ip_tos.prec
        netcontrol internetcontrol critic_ecp flashoverride flash immediate priority routine

    ip_tos.tos
        lowdelay throughput reliability

When numerical arguments are given to subfields, the values are shifted to apply only to the subfield bit range. The following example shows the different ways of setting IP_TOS to lowdelay on external traffic:

external.ip.ip_tos:     0x10       #base value, numerically
external.ip.ip_tos.tos: 0x08       #subfield, numerically
external.ip.ip_tos.tos: lowdelay   #subfield, symbolically

The first value sets the value directly, the second sets only the TOS bits, which are shifted relative to the base value. The final line sets the TOS value symbolically.

This functionality gives a large amount of control over socket options, but it should not be used without some understanding of how the kernel allows the socket option to be set, and the limitations that apply when the socket options are set as either defaults or in rules.

Setting a socket option in a client pass or socks-rules will cause any defaults to be overridden. Global options are set before bind() is called on internal sockets, or before connect() is called on external sockets. Options set in client rules are also applied before bind() is called on the internal socket, but cannot be set for the external socket. For socks-rules, both external and internal options can be set, but because the socks-request must be interpreted before the rules can be evaluated, socket options can only be set on internal sockets after the connection has been received.

Some socket options must be set before a connection has been established, while others can only be set after a connection has been established. Others can be set at any time.

Socket options that are not listed above can also be set by specifying the socket option name numerically, for example:

external.ip.10: 0x12

In this example the socket option corresponding to the value 10 will be set. These numbers are platform dependent but can typically be determined by looking at the appropriate system header files. Specifying options numerically might result in some warnings, but allows any socket option to be specified, as long as it takes a numerical argument. This is not the recommended approach for setting socket options, but represents a simple way of setting socket options that are not directly supported by the server, such as local kernel extensions.

AUTHENTICATION METHODS
The Dante server supports the following authentication methods. Some installations of Dante may support only a subset of these, depending on platform support.

none
    This method requires no form of authentication.

username
    This method requires the client to provide a username and password. This information must match the username and password given in the system password file.

gssapi
    This method requires the setup of a Kerberos environment and can provide strong encryption and authentication, depending on the gssapi settings you choose.

rfc931
    This method requires the host the socks client runs on to provide a rfc931 ("ident") username for the client. This username match a username given in the system password file.

pam.address
    IP-based (rhosts) PAM authentication.

pam.any
    Will try to match against any type of PAM authentication, depending on the information that is currently available. Normally of limited use, and you should instead set the pam-based method(s) you actually want.

pam.username
    Username/password-based PAM authentication. Similar to the method username, but the information is passed to the PAM subsystem for authentication, rather than Dante using the system password file directly. When using PAM, be wary of memory leakages and other bugs in the external PAM library Dante will have to use on your platform.

bsdauth
    This method requires the available client data to be verified by the BSD Authentication system. Similar to the method username, but passed to the BSD authentication system instead.

ADDRESSES
Each address field can consist of an IP address (and where required, a netmask, separated from the IP address by a '/' sign), a hostname, a domainname (designated so by the leading '.'), or an interface name.

An IP address can be given on on IPv4 form, IPv6 form, or as the special value 0/0, which matches all IP addresses, be they IPv4 or IPv6. The latter is intended for use in rules that should match both IPv4 and IPv6 clients or targets.

Each address, except the external address, can include an optional port specifier.

RULES
There are two sets of rules and they work at different levels. Rules prefixed with client are checked first and are used to see if the client is allowed to connect to the Dante server. We call them "client-rules". These rules will start with client pass for a rule that allows the client, or client block for a rule that blocks the client.

It is recommended that the client-rules do not use hostnames but only IP-addresses, both for security and performance reasons. These rules operate at the TCP level.

The other rules, which we call "socks-rules", are prefixed with socks and operate at the socks protocol level.

These rules will start with socks pass for a rule that allows the client, or socks block for a rule that blocks the client.

These rules are only checked if the client connection has been allowed by the client-rules. The socks-rules are used to evaluate the socks request that the client sends.

While it is less important that these rules use only IP-addresses, provided the client-rules have been configured to only allow access from a pre-defined range of client IP-addresses, it is still recommended.

Both set of rules include a pass or deny keyword. The pass/deny keyword determines whether connections matching the rule are to be passed through or be blocked.

Both the client-rules and the socks-rules also specify a from/to address pair which gives the addresses the rule will match.

In both contexts, from refers to the clients address, i.e., the address the client is connecting to the Dante server from. The to address however refers to different things depending on whether it is used in a client-rule or in a socks-rule.

In the client-rule context, to means the address the request is accepted on, i.e., a address the Dante server listens on.

In the socks-rule context, to means the client's destination address, as expressed in the client's socks request. I.e., the address the Dante server should connect to (for TCP sessions) or send packets to (for UDP session) on behalf of the client.

Both set of rules are evaluated on a "first match is best match" basis. That means, the first rule matched for a particular client or socks request is the rule that will be used.

In addition to the addresses there is a set of optional keywords which can be given. There are two forms of keywords; conditions and actions. For each rule, all conditions are checked and if they match the request, all actions are executed.

The list of condition keywords is: clientcompatibility, clientmethod, command, from, group, socksmethod, protocol, proxyprotocol, to, user.

The list of action keywords is: bandwidth, libwrap, log, session, redirect, timeout.connect, timeout.negotiate, timeout.io, timeout.tcp_fin_wait, and udp.portrange.

The format and content of the keyword as used in client-rules or socks-rules is identical, but client-rules can contain only a subset of the keyword that socks-rules may contain.

    The contents of a client-rule can be:

bandwidth
    The clients matching this rule will all share the given amount of bandwidth, measured in bytes per second. Requires the bandwidth module.

clientcompatibility
    Enables certain options for compatibility with broken clients. Valid values are: necgssapi, for compatibility with clients implementing GSSAPI the NEC socks way.

from
    The rule applies to requests coming from the specified address.

group
    The user must belong to one of the groups given as value.

    Note that if gssapi-based authentication is used, the username as provided to the Dante server normally includes the Kerberos domain. The name must be listed on the same form here and in the system groupfile (usually /etc/passwd) if it is to be used.

gssapi.enctype
    Which encryption to enforce for GSSAPI-authenticated communication. Possible values are clear, integrity, or confidentiality. The default is to accept whatever the client offers except clear, as clear is not part of the SOCKS GSSAPI standard.

gssapi.keytab
    Value for keytab to use. The default is "FILE:/etc/danted.keytab".

gssapi.servicename
    Which servicename to use when involving GSSAPI. Default is "rcmd".

libwrap
    The server will pass the specified parameter line to libwrap for execution.

log Used to control logging. Accepted keywords are connect, disconnect, data, error, ioop, and tcpinfo. The default is no logging.

session
    Control the max number of sessions or session establishment rate. See below for details.

clientmethod
    Require that the connection be "authenticated" using one of the given clientmethods.

pam.servicename
    Which servicename to use when involving pam. Default is "danted".

port
    Parameter to from, to and via. Accepts the keywords eq/=, neq/!=, ge/>=, le/<=, gt/>, lt/< followed by a number. A port range can also be given as "port <start #> - <end #>", which will match all port numbers within the range <start #> and <end #>.

    The default is to match all ports.

redirect
    The source and/or destination can be redirected using the redirect statement. Requires the redirect module.

    The syntax of the redirect statement is as follows:

    redirect from: ADDRESS

    See the redirect manual for detailed information.

socksmethod
    If the client offers more than one authentication method, Dante will select the method to use based on the order the methods are listed here. Valid values are the same as in the global socksmethod line. Normally there will be no need to set this keyword in a client-rule, but if it is set and the client offers none of the methods listed, the client will be blocked at this stage.

timeout.negotiate
    See the global timeout.negotiate option.

to  The rule applies to requests going to the address given as value.

user
    The user must match one of the names given as value. If no user value is given for a rule requiring usernames, the effect will be the same as listing every user in the password file.

    Note that if gssapi-based authentication is used, the username as provided to the Dante server normally includes the Kerberos domain. The name must be listed on the same form here if it is to be used.

    The contents of a socks-rule can be:

bandwidth
    The clients matching this rule will all share the given amount of bandwidth, measured in bytes per second. Requires the bandwidth module.

bsdauth.stylename
    The name of the BSD authentication style to use. The default is to not specify a value, causing the default system style to be used.

command
    The rule applies to the given commands. Valid commands are bind, bindreply, connect, udpassociate and udpreply. Can be used instead of, or to complement, protocol. The default is all commands valid for the protocols allowed by the rule.

from
    The rule applies to requests coming from the address given as value.

group
    The user must belong to one of the groups given as value.

libwrap
    The server will pass the line to libwrap for execution.

log Used to control logging. Accepted keywords are connect, disconnect, data, ioop, and tcpinfo.

session
    Control the max number of sessions or session establishment rate. See

socksmethod
    Require that the connection be established using one of the given authentication methods. A method normally refers to the socks client part of the rule, and thus authenticates the client, and not the target destination (see checkreplyauth for information about authentication the target destination). Valid values are the same as in the global socksmethod line.

pam.servicename
    What servicename to use when involving pam. Default is "danted".

port
    Parameter to from, to and via. Accepts the keywords eq/=, neq/!=, ge/>=, le/<=, gt/>, lt/< followed by a number. A portrange can also be given as "port <start #> - <end #>", which will match all port numbers within the range <start #> and <end #>.

    The default is all ports.

protocol
    The rule applies to the given protocols. Valid values are tcp and udp. The default is all supported protocols that can apply to the given commands.

proxyprotocol
    The rule applies to requests using the given proxy protocol. Valid proxy protocols are socks_v4 and socks_v5. The default is all supported proxy protocols.

redirect
    The source and/or destination can be redirected using the redirect statement. Requires the redirect module.

    The syntax of the redirect statement is as follows:

    redirect from: ADDRESS

    redirect to: ADDRESS

    The semantics of from and to vary according to command. See the redirect manual for detailed information.

timeout.connect
    See the global timeout.connect option.

timeout.io
    See the global timeout.io option.

timeout.tcp_fin_wait
    See the global timeout.tcp_fin_wait option.

to  The rule applies to requests going to or using the address given as value. Note that the meaning of this address is affected by command.

udp.portrange
    The argument to this keyword is two port numbers, separated by a dash ('-'). They specify the UDP port-range that will be used between the socks-client and the Dante-server for UDP packets. Note that this has no relation to the UDP port-range used between the Dante-server and external, non-socks, clients/servers.

user
    The user must match one of the names given as value. If no user value is given for a rule requiring usernames, the effect will be the same as listing every user in the password file.

SESSION
The session keyword can be used any any rule to limit the number of active sessions and the rate at which they are established. There are two main commands for this; session.max, that controls the max number of sessions that can be matched, and session.throttle, that controls the connection rate. These commands can be applied both for the total limit for all matching clients and can be set as global defaults or in any of the rule types. The session.max keyword takes a number corresponding to the highest number of allowed simultaneous connections as an argument. The session.throttle keyword takes two number separated by a slash character, with the first representing the number of connections and the latter a time duration in seconds. If more than the specified number of connections are received in the specified number of seconds, additional connections will be dropped.

Stateful session tracking on a per IP-address basis is also supported. For stateful tracking, the limits apply to each connection with a matching IP-address, with the session.state.key keyword is used to control how the IP-address is determined. Currently two values are supported, from and hostid. The former causes the limit to be applied to all hosts with the same source IP-address and the latter to all TCP connections with the same hostid value. If a hostid value is used, the session.state.key.hostindex keyword can be used to choose which of the to hostid values are used, with the first value being the default.

Limits are evaluated first for client rules, then for hostid rules, and finally for socks rules. By default, a limit set in a matching client rule will be used also any subsequent matching hostid or socks rules, unless either of these rules also have session limit keywords. This session inheritance can be disabled in client and hostid rules, causing them to only apply in the rule in which they appear. This is done by setting the session.inheritable to no.

The session keywords must be set in a rule (either client, hostid, or socks), setting them globally is not supported.

TRAFFIC MONITORING

The Dante server can be configured to monitor the traffic passing through it, and trigger alarms based on the observed network traffic.

The alarms are specified in so-called monitors. These objects have the same general format as the rules Dante uses for access control and enable perform passive monitoring of network traffic, or the lack of network traffic.

The following example shows the general monitor syntax, specifying a monitor without any monitoring operations:

     monitor {
      from: 0.0.0.0/0 to: www.example.org port = 80
      protocol: tcp
     }

A monitor can include many of the same keywords that are available in the Dante ACL rules. The following subset is currently supported:

    from
        Normally specifies what SOCKS client addresses/networks to monitor.

    to  Normally specifies what target addresses/networks to monitor.

    protocol
        Can be used to restrict monitoring to a certain protocol (TCP, UDP or both). Note: only TCP should be used for now.

    hostid
        Can be used to restrict monitoring to only clients with a specific hostid value set.

    hostindex
        Used along with the hostid keyword to control which of the two possible hostid values will be used when matching.

NOTE: It is currently recommended that the protocol keyword is always specified and set to tcp because there is currently only limited support for monitoring of UDP traffic, and testing of UDP traffic monitoring has not been done.

The main function of monitors is to provide a container for one or more alarms, which are specified using a new set of keywords not available for other rules. Alarms specify a condition that will cause Dante to log a warning if the condition is triggered.

Active TCP sessions will at most match one monitor, but multiple alarms can be specified in a single monitor. This makes it possible to specify multiple sets of conditions for the same TCP sessions, depending on what network interface the traffic is transferred on and whether the traffic is being received or transmitted.

Alarms can trigger as a result of periods of no or little data being transmitted, or a large numbers of TCP connections disconnecting during a short period of time, or for other reasons. See below for a complete list of what conditions alarms can be enabled for.

  Data alarms
Adding an alarm.data keyword to a monitor will result in warnings being logged if there are periods with too little network traffic.

Dante has four network paths and data alarms can be configured independently for each of them:

    internal.alarm.data.recv
        Data received on Dante's internal interface (data sent from the SOCKS clients to Dante).

    internal.alarm.data.send
        Data sent out on Dante's internal interface (data sent from Dante to the SOCKS clients).

    external.alarm.data.recv
        Data received on Dante's external interface (data sent from the target servers to Dante).

    external.alarm.data.send
        Data sent out on Dante's external interface (data sent from Dante to the target servers).

The data.alarm keyword takes two parameters: a byte count and a duration in seconds. The alarm will trigger if the specified number of seconds pass with only the specified number of bytes (or less) being transmitted.

The syntax is as follows:

internal.alarm.data.recv: DATALIMIT in INTERVAL

The DATALIMIT is a number that specifies the byte limit. The INTERVAL is a number that specifies the duration. If only DATALIMIT bytes (or less) have been transferred during a period of INTERVAL seconds, an alarm will trigger in Dante.

Data alarms trigger when a period of data idleness has been detected. Once a data alarm has triggered it will remain active until it is cleared. A warning will be logged when the alarm triggers and than again when the alarm condition is cleared. In between these two points no warnings related to this alarm will be logged. This avoids repeating the same alarm/warning multiple times during network problems that last for an extended amount of time. When the alarm is cleared, Dante will also include information about how long the alarm condition lasted.

A data alarm can be cleared in two ways; automatically, once enough data has been transferred in a short enough amount of time, or manually, by sending the Dante server a SIGHUP signal. A SIGHUP will cause all active alarms to be cleared. No log messages indicating that the alarms have cleared will be logged when alarms are cleared in this way.

Once an alarm has been cleared, it can trigger again if enough data is not being transferred.

Note that data alarms will trigger regardless of whether there are active sessions matching the monitor or not; if enough data is not being transmitted or received, a data alarm will trigger. Alarms will trigger also shortly after server startup, if the Dante server does not receive sufficient traffic to prevent the alarms from triggering.

Note that the message indicating that an alarm has cleared is not logged if the alarm was cleared due to a SIGHUP signal being received.

  Disconnect alarms
The disconnect alarms are related to connection disconnects and by using the alarm.disconnect keyword the Dante server can log warnings based on the number and rate of terminated connections.

There are two variants of the alarm keyword, one for the internal network interface, between the SOCKS clients and Dante, and one for the external interface, between the Dante server and the target servers:

    internal.alarm.disconnect
        Connections between SOCKS clients and the Dante server.

    external.alarm.disconnect
        Connections between the Dante server and target servers.

Each alarm keyword takes three parameters, a minimum count, a ratio value, and a time interval. The following format is used:

internal.alarm.disconnect: MINCOUNT/RATIO in INTERVAL

The MINCOUNT is the minimum number of connections that must be disconnected for the alarm to trigger. The RATIO is used together with the MINCOUNT to express the number of connections, relative to the total number of connections that have existed in the time period, that must be disconnected for the alarm to trigger. The INTERVAL is the time in seconds within which the disconnects must occur for the alarm to trigger.

To set values that are useful, some knowledge about the expected amount of network traffic and number of sessions is required. If the rate of disconnects, as a percentage, is lower than the ratio specified, an alarm will not trigger. Conversely, if the MINCOUNT is set too low, alarms might trigger too frequently because only a small number of disconnects might be sufficient to achieve the required number of disconnects and disconnect ratio at times when there are only a few active sessions.

Only connections that are terminated on the specified interface are counted, i.e., an external.alarm.disconnect alarm will only trigger for connections that are terminated on the network interface between the Dante server and the target server, either by the target server closing the connection to Dante or by Dante receiving a fatal network error from that side of the connection (e.g., a TCP RST packet).

Connections that are closed on the internal interface (by the SOCKS clients) will not count towards a disconnect alarm on the external side. Likewise, connections closed by target servers will not count towards a disconnect alarm on the internal side.

A practical consequence of this is that if a large number of connections are simultaneously closed by both the client and the target server, each connection will only be counted as a disconnect on one of the sides; either the external side or the internal side, depending on which side closes the connection first.

Alarms trigger each time a sufficient number disconnects occur. Each sufficiently large burst of disconnects will result in an alarm, but normally at most one warning per alarm will be logged during each time interval, though this might change in a later version of Dante.

Separate alarms are produced for each distinct alarm keyword when multiple alarms are specified in a monitor rule.

ROUTES
The routes are specified with a route keyword. Inside a pair of curly braces ({}) a set of keywords control the behavior of the route. See dante.conf(5) for a description. This is used to perform so-called "server-chaining", where one socks-server connects to another socks-server further upstream.

The syntax for these routes is the same as the routes used by the client. Please see dante.conf(5) for information about the route syntax.

There are however some special things one need to be aware of regarding serverchaining and routes specified for the server:

    At present serverchaining is only supported for the tcp connect command.

    If the route specifies that a username/password-method should be offered to the upstream proxy, Dante will forward the username/password received from its own client to the foreign upstream proxy, meaning the upstream proxy will receive the user's username and password in cleartext from Dante.

    At present serverchaining does not scale well in Dante and should not be used for anything but minimal client loads.

EXAMPLES
See the example/ directory in the distribution.

FILES
/etc/danted.conf   Dante server configuration file.
/etc/passwd       systemfile used when doing standard username/password
                  authentication.

AUTHORS
For inferno Nettverk A/S:
   Michael Shuldman
   Karl-Andre' Skevik

SEE ALSO
danted(8), dante.conf(5), hosts_access(5)

Information about new releases and other related issues can be found on the Dante WWW home page: http://www.inet.no/dante/

Information about commercial support can be found on the Dante WWW support page: http://www.inet.no/dante/support.html