IP(3)                                                       IP(3)

          ip, esp, gre, icmp, icmpv6, ipmux, rudp, tcp, udp, il -
          network protocols over IP

          bind -a #Ispec /net             /net/icmp
          /net/ipifc                      /net/icmpv6
          /net/ipifc/clone                /net/ipmux
          /net/ipifc/stats                /net/rudp
          /net/ipifc/n                    /net/tcp
          /net/ipifc/n/status             /net/udp
          /net/ipifc/n/ctl                /net/il
          ...                             /net/tcp/clone
          /net/arp                        /net/tcp/stats
          /net/bootp                      /net/tcp/n
          /net/iproute                    /net/tcp/n/data
          /net/ipselftab                  /net/tcp/n/ctl
          /net/log                        /net/tcp/n/local
          /net/ndb                        /net/tcp/n/remote
          /net/esp                        /net/tcp/n/status
          /net/gre                        /net/tcp/n/listen

         The ip device provides the interface to Internet Protocol
         stacks.  Spec is an integer starting from 0 identifying a
         stack.  Each stack implements IPv4 and IPv6.  Each stack is
         independent of all others: the only information transfer
         between them is via programs that mount multiple stacks.
         Normally a system uses only one stack.  However multiple
         stacks can be used for debugging new IP networks or imple-
         menting firewalls or proxy services.

         All addresses used are 16-byte IPv6 addresses.  IPv4
         addresses are a subset of the IPv6 addresses and both stan-
         dard ASCII formats are accepted.  In binary representation,
         all v4 addresses start with the 12 bytes, in hex:

              00 00 00 00 00 00 00 00 00 00 ff ff

       Configuring interfaces
         Each stack may have multiple interfaces and each interface
         may have multiple addresses.  The /net/ipifc directory con-
         tains a clone file, a stats file, and numbered subdirecto-
         ries for each physical interface.

         Opening the clone file reserves an interface.  The file
         descriptor returned from the open(2) will point to the con-
         trol file, ctl, of the newly allocated interface.  Reading
         ctl returns a text string representing the number of the

    IP(3)                                                       IP(3)

         interface.  Writing ctl alters aspects of the interface.
         The possible ctl messages are those described under Protocol
         directories below and these:

         bind ether path
                        Treat the device mounted at path as an Ether-
                        net medium carrying IP and ARP packets and
                        associate it with this interface.  The kernel
                        will dial(2) path!0x800, path!0x86DD and
                        path!0x806 and use the three connections for
                        IPv4, IPv6 and ARP respectively.

         bind pkt       Treat this interface as a packet interface.
                        Assume a user program will read and write the
                        data file to receive and transmit IP packets
                        to the kernel.  This is used by programs such
                        as ppp(8) to mediate IP packet transfer
                        between the kernel and a PPP encoded device.

         bind netdev path
                        Treat this interface as a packet interface.
                        The kernel will open path and read and write
                        the resulting file descriptor to receive and
                        transmit IP packets.

         bind loopback  Treat this interface as a local loopback.
                        Anything written to it will be looped back.

         unbind         Disassociate the physical device from an IP

         add local mask remote mtu proxy|trans
         try local mask remote mtu proxy|trans
                        Add a local IP address to the interface.  Try
                        adds the local address as a tentative address
                        if it's an IPv6 address.  The mask, remote,
                        mtu, proxy, and (Reg.)arguments are all
                        optional.  The default mask is the class mask
                        for the local address.  The default remote
                        address is local ANDed with mask. The default
                        mtu (maximum transmission unit) is 1514 for
                        Ethernet and 4096 for packet media.  The mtu
                        is the size in bytes of the largest packet
                        that this interface can send.  Specifying a
                        mtu of 0 will use the default.  Proxy, if
                        specified, means that this machine should
                        answer ARP requests for the remote address.
                        Ppp(8) does this to make remote machines
                        appear to be connected to the local Ethernet.
                        The trans argument enables source address
                        translation for packets routed to the

    IP(3)                                                       IP(3)

                        interface.  Adding the special null-address
               or :: in local to a interface makes
                        the ip stack accept all incoming connections
                        regardless of the destination IP address.
                        This is used temporarily by ipconfig(8) to
                        accept DHCP answers when no IP address has
                        been assigned yet. This can also be used to
                        implement a NAT gateway by accepting all
                        incoming connections and proxying them with
                        trampoline(8) to a different ip stack.

         del local mask Delete a local IP address from an interface.

         mtu n          Set the maximum transfer unit for this device
                        to n. The mtu is the maximum size of the
                        packet including any medium-specific headers.

         speed n        Set the maximum transmit speed in bits per

         delay n        Set the maximum burst delay in milliseconds.
                        (Default is 40ms) When speed has been set and
                        packets in flight exceed the maximum burst
                        delay then packets send on the interface are
                        discarded until the load drops below the max-

         iprouting n    Allow (n is missing or non-zero) or disallow
                        (n is 0) forwarding packets between this
                        interface and others.

         reflect n      When forwarding, allow packets from this
                        interface to be echoed back on the same

         reassemble n   Reassemble IP fragments before forwarding to
                        this interface

         bridge         Enable bridging (see bridge(3)).

         promiscuous    Set the interface into promiscuous mode,
                        which makes it accept all incoming packets,
                        whether addressed to it or not.

         connect type   marks the Ethernet packet type as being in
                        use, if not already in use on this interface.
                        A type of -1 means `all' but appears to be a

         addmulti Media-addr
                        Treat the multicast Media-addr on this inter-
                        face as a local address.

    IP(3)                                                       IP(3)

         delmulti Media-addr
                        Delete the multicast address Media-addr from
                        this interface.

         scanbs         Make the wireless interface scan for base

         headersonly    Set the interface to pass only packet head-
                        ers, not data too.

         add6 v6addr pfx-len [onlink auto validlt preflt]
                        Add the local IPv6 address v6addr with prefix
                        length pfx-len to this interface.  See RFC
                        2461 §6.2.1 for more detail.  The remaining
                        arguments are optional:

                        onlink  flag: address is `on-link'
                        auto    flag: autonomous
                        validlt valid life-time in seconds
                        preflt  preferred life-time in seconds

         del6           Delete local IPv6 addresses that have expired
                        ther valid life-time.

         ra6 keyword value ...
                        Set IPv6 router advertisement (RA) parameter
                        keyword's value. Known keywords and the mean-
                        ings of their values follow.  See RFC 2461
                        §6.2.1 for more detail.  Flags are true iff

                        recvra     flag: receive and process RAs.
                        sendra     flag: generate and send RAs.
                        mflag      flag: ``Managed address configura-
                                   tion'', goes into RAs.
                        oflag      flag: ``Other stateful configura-
                                   tion'', goes into RAs.
                        maxraint   ``maximum time allowed between
                                   sending unsolicited multicast''
                                   RAs from the interface, in ms.
                        minraint   ``minimum time allowed between
                                   sending unsolicited multicast''
                                   RAs from the interface, in ms.
                        linkmtu    ``value to be placed in MTU
                                   options sent by the router.''
                                   Zero indicates none.
                        reachtime  sets the Reachable Time field in
                                   RAs sent by the router.  ``Zero
                                   means unspecified (by this
                        rxmitra    sets the Retrans Timer field in
                                   RAs sent by the router.  ``Zero

    IP(3)                                                       IP(3)

                                   means unspecified (by this
                        ttl        default value of the Cur Hop Limit
                                   field in RAs sent by the router.
                                   Should be set to the ``current
                                   diameter of the Internet.''
                                   ``Zero means unspecified (by this
                        routerlt   sets the Router Lifetime field of
                                   RAs sent from the interface, in
                                   ms.  Zero means the router is not
                                   to be used as a default router.

         Reading the interface's status file returns information
         about the interface. The first line is composed of white-
         space-separated fields, the first two fields are: device and
         maxmtu. Subsequent lines list the ip addresses assigned to
         that inferface. The colums are: ip address, network mask,
         network address and valid/preferred life times in millisec-
         onds. See readipifc in ip(2).

         The file iproute controls information about IP routing.
         When read, it returns one line per routing entry.  Each line
         contains eight white-space-separated fields: target address,
         target mask, address of next hop, flags, tag, interface num-
         ber, source address, source mask.  The entry used for rout-
         ing an IP packet is the one with the longest destination and
         source mask for which destination address ANDed with target
         mask equals the target and also the source ANDed with the
         source mask equals the source address.  The one-character
         flags are:

         4  IPv4 route
         6  IPv6 route
         i  local interface
         b  broadcast address
         u  local unicast address
         m  multicast route
         p  point-to-point route
         y  proxy ARP for this route
         t  network source address translation

         The tag is an arbitrary, up to 4 character, string.  It is
         normally used to indicate what routing protocol originated
         the route.

         Writing to /net/iproute changes the route table.  The mes-
         sages are:

         flush tag   Remove routes of the specified tag, or all

    IP(3)                                                       IP(3)

                     routes if tag is omitted.

         tag string  Associate the tag, string, with all subsequent
                     routes added via this file descriptor.

         add target mask nexthop

         add target mask nexthop interface

         add target mask nexthop source smask

         add target mask nexthop interface source smask

         add target mask nexthop flags interface source smask

         add target mask nexthop flags tag interface source smask.
                     Add the route to the table.  If one already
                     exists with the same target and mask, replace
                     it. The destination interface can be specified
                     as either the interface's /net/ipifc/n directory
                     number, a local IP address on the desired inter-
                     face, its bound device name or as - when unspec-
                     ified, in which case the interface will be
                     choosen based on the source and nexthop.

         del target mask

         del target mask nexthop

         del target mask source smask

         del target mask nexthop source smask

         del target mask nexthop interface source smask

         del target mask nexthop flags interface source smask

         del target mask nexthop flags tag interface source smask
                     Delete the matching route.

       Address resolution
         The file /net/arp controls information about address resolu-
         tion.  The kernel automatically updates the v4 ARP and v6
         Neighbour Discovery information for Ethernet interfaces.
         When read, the file returns one line per address containing
         the type of medium, the status of the entry (OK, WAIT), the
         IP address, the medium address and the IP address of the
         interface where the entry is valid.  Writing to /net/arp
         administers the ARP information.  The control messages are:

         add type IP-addr Media-addr Interface-IP-addr

    IP(3)                                                       IP(3)

                       Add an entry or replace an existing one for
                       the same IP address. The optional interface IP
                       address specifies the interface where the ARP
                       entry will be valid. This is needed for IPv6
                       link local addresses.

         del IP-addr   Delete an individual entry.

         flush         Remove all entries.

         garp IP-addr  Send a gratious ARP response for the specified
                       IP address.

         ARP entries do not time out.  The ARP table is a cache with
         an LRU replacement policy.  The IP stack listens for all ARP
         requests and, if the requester is in the table, the entry is
         updated.  Also, whenever a new address is configured onto an
         Ethernet, an ARP request is sent to help update the table on
         other systems.

         Currently, the only medium type is ether.

       Debugging and stack information
         If any process is holding /net/log open, the IP stack queues
         debugging information to it.  This is intended primarily for
         debugging the IP stack.  The information provided is
         implementation-defined; see the source for details.  Gener-
         ally, what is returned is error messages about bad packets.

         Writing to /net/log controls debugging.  The control mes-
         sages are:

         set arglist    Arglist is a space-separated list of items
                        for which to enable debugging.  The possible
                        items are: ppp, ip, fs, tcp, il, icmp, udp,
                        compress, ilmsg, gre, tcpwin, tcprxmt,
                        udpmsg, ipmsg, and esp.

         clear arglist  Arglist is a space-separated list of items
                        for which to disable debugging.

         only addr      If addr is non-zero, restrict debugging to
                        only those packets whose source or destina-
                        tion is that address.

         The file /net/ndb can be read or written by programs.  It is
         normally used by ipconfig(8) to leave configuration informa-
         tion for other programs such as dns and cs (see ndb(8)).
         /net/ndb may contain up to 1024 bytes.

         The file /net/ipselftab is a read-only file containing all

    IP(3)                                                       IP(3)

         the IP addresses considered local.  Each line in the file
         contains three white-space-separated fields: IP address,
         usage count, and flags.  The usage count is the number of
         interfaces to which the address applies.  The flags are the
         same as for routing entries.

       Protocol directories
         The ip device supports IP as well as several protocols that
         run over it: TCP, UDP, RUDP, ICMP, IL, GRE, and ESP.  TCP
         and UDP provide the standard Internet protocols for reliable
         stream and unreliable datagram communication.  RUDP is a
         locally-developed reliable datagram protocol based on UDP.
         ICMP is IP's catch-all control protocol used to send low
         level error messages and to implement ping(8). GRE is a gen-
         eral encapsulation protocol.  ESP is the encapsulation pro-
         tocol for IPsec.  IL provides a reliable datagram service
         for communication between Plan 9 machines but is now depre-

         Each protocol is a subdirectory of the IP stack.  The top
         level directory of each protocol contains a clone file, a
         stats file, and subdirectories numbered from zero to the
         number of connections opened for this protocol.

         Opening the clone file reserves a connection.  The file
         descriptor returned from the open(2) will point to the con-
         trol file, ctl, of the newly allocated connection.  Reading
         ctl returns a text string representing the number of the
         connection.  Connections may be used either to listen for
         incoming calls or to initiate calls to other machines.

         A connection is controlled by writing text strings to the
         associated ctl file.  After a connection has been estab-
         lished data may be read from and written to data.  A connec-
         tion can be actively established using the connect message
         (see also dial(2)). A connection can be established pas-
         sively by first using an announce message (see dial(2)) to
         bind to a local port and then opening the listen file (see
         dial(2)) to receive incoming calls.

         The following control messages are supported:

         connect ip-address!port!r local
                      Establish a connection to the remote ip-address
                      and port. If local is specified, it is used as
                      the local port number.  If local is not speci-
                      fied but !r is, the system will allocate a
                      restricted port number (less than 1024) for the
                      connection to allow communication with Unix
                      login and exec services.  Otherwise a free port
                      number starting at 5000 is chosen.  The connect

    IP(3)                                                       IP(3)

                      fails if the combination of local and remote
                      address/port pairs are already assigned to
                      another port.

         announce [ip-address!]port
                      Set the local IP address and port number and
                      accept calls there.  If ip-address is left out,
                      accept calls on any address.  If port is 0, a
                      port is automatically choosen that is not yet
                      announced.  If the address is `*', accept calls
                      on any address.  If port is `*', accept calls
                      on any port.  If port is `*', and the address
                      is left out, accept calls on any address and
                      port.  Announce fails if the connection is
                      already announced.

         bind [ip-address!]port
                      Set the local IP address and port number like
                      for a server connection similar to the announce
                      command.  If ip-address is left out, an address
                      is automatically selected.  If port is 0, a
                      port is automatically choosen that is not yet
                      announced.  This command has no actual effect,
                      beyond remembering the parameters and possibly
                      selecting an unused port.  The commands
                      announce and connect reset both the local
                      address and the port according to their own
                      parameters.  This command also does not reserve
                      the IP address and port, another connection can
                      use them, even while they are registered in a
                      connection by this command.  This exists to
                      support emulation of BSD sockets by the APE
                      libraries (see pcc(1)) and is not otherwise

         ttl n        Set the time to live IP field in outgoing pack-
                      ets to n.

         tos n        Set the service type IP field in outgoing pack-
                      ets to n.

         ignoreadvice Don't break (UDP) connections because of ICMP

         addmulti ifc-ip [ mcast-ip ]
                      Treat ifc-ip on this multicast interface as a
                      local address.  If mcast-ip is present, use it
                      as the interface's multicast address.

         delmulti ip  Delete the address ip from this multicast

    IP(3)                                                       IP(3)

         Port numbers must be in the range 1 to 32767.

         Several files report the status of a connection.  The remote
         and local files contain the IP address and port number for
         the remote and local side of the connection.  The status
         file contains protocol-dependent information to help debug
         network connections.  On receiving and error or EOF reading
         or writing the data file, the err file contains the reason
         for error.

         A process may accept incoming connections by open(2)ing the
         listen file.  The open will block until a new connection
         request arrives.  Then open will return an open file
         descriptor which points to the control file of the newly
         accepted connection.  This procedure will accept all calls
         for the given protocol.  See dial(2).

         TCP connections are reliable point-to-point byte streams;
         there are no message delimiters.  A connection is determined
         by the address and port numbers of the two ends.  TCP ctl
         files support the following additional messages:

         hangup       close down this TCP connection

         close        graceful hangup

         keepalive n  turn on keep alive messages.  N, if given, is
                      the milliseconds between keepalives (default

         checksum n   emit TCP checksums of zero if n is zero; other-
                      wise, and by default, TCP checksums are com-
                      puted and sent normally.

         tcpporthogdefense onoff
                      onoff of `on' enables the TCP port-hog defense
                      for all TCP connections; onoff of `off' dis-
                      ables it.  The defense is a solution to
                      hijacked systems staking out ports as a form of
                      denial-of-service attack.  To avoid stateless
                      TCP conversation hogs, ip picks a TCP sequence
                      number at random for keepalives.  If that num-
                      ber gets acked by the other end, ip shuts down
                      the connection.  Some firewalls, notably ones
                      that perform stateful inspection, discard such
                      out-of-specification keepalives, so connections
                      through such firewalls will be killed after
                      five minutes by the lack of keepalives.


    IP(3)                                                       IP(3)

         UDP connections carry unreliable and unordered datagrams.  A
         read from data will return the next datagram, discarding
         anything that doesn't fit in the read buffer.  A write is
         sent as a single datagram.

         By default, a UDP connection is a point-to-point link.
         Either a connect establishes a local and remote address/port
         pair or after an announce, each datagram coming from a dif-
         ferent remote address/port pair establishes a new incoming
         connection.  However, many-to-one semantics is also possi-

         If, after an announce, the message `headers' is written to
         ctl, then all messages sent to the announced port are
         received on the announced connection prefixed with the cor-
         responding structure, declared in <ip.h>:

              typedef struct Udphdr Udphdr;
              struct Udphdr
                   uchar     raddr[16];     /* V6 remote address */
                   uchar     laddr[16];     /* V6 local address */
                   uchar     ifcaddr[16];   /* V6 interface address (receive only) */
                   uchar     rport[2]; /* remote port */
                   uchar     lport[2]; /* local port */

         Before a write, a user must prefix a similar structure to
         each message.  The system overrides the user specified local
         port with the announced one.  If the user specifies an
         address that isn't a unicast address in /net/ipselftab, that
         too is overridden.  Since the prefixed structure is the same
         in read and write, it is relatively easy to write a server
         that responds to client requests by just copying new data
         into the message body and then writing back the same buffer
         that was read.

         In this case (writing `headers' to the ctl file), no listen
         nor accept is needed; otherwise, the usual sequence of
         announce, listen, accept must be executed before performing
         I/O on the corresponding data file.

         RUDP is a reliable datagram protocol based on UDP, currently
         only for IPv4.  Packets are delivered in order.  RUDP does
         not support listen.  One must write either `connect' or
         `announce' followed immediately by `headers' to ctl.

         Unlike TCP, the reboot of one end of a connection does not
         force a closing of the connection.  Communications will
         resume when the rebooted machine resumes talking.  Any unac-
         knowledged packets queued before the reboot will be lost.  A

    IP(3)                                                       IP(3)

         reboot can be detected by reading the err file.  It will
         contain the message

              hangup address!port

         where address and port are of the far side of the connec-
         tion.  Retransmitting a datagram more than 10 times is
         treated like a reboot: all queued messages are dropped, an
         error is queued to the err file, and the conversation

         RUDP ctl files accept the following messages:

         headers               Corresponds to the `headers' format of
         hangup IP port        Drop the connection to address IP and
         randdrop [ percent ]  Randomly drop percent of outgoing
                               packets.  Default is 10%.

         ICMP is a datagram protocol for IPv4 used to exchange con-
         trol requests and their responses with other machines' IP
         implementations.  ICMP is primarily a kernel-to-kernel pro-
         tocol, but it is possible to generate `echo request' and
         read `echo reply' packets from user programs.

         ICMPv6 is the IPv6 equivalent of ICMP.  If, after an
         announce, the message `headers' is written to ctl, then
         before a write, a user must prefix each message with a cor-
         responding structure, declared in <ip.h>:

               *  user level icmpv6 with control message "headers"
              typedef struct Icmp6hdr Icmp6hdr;
              struct Icmp6hdr {
                   uchar     unused[8];
                   uchar     laddr[IPaddrlen];   /* local address */
                   uchar     raddr[IPaddrlen];   /* remote address */

         In this case (writing `headers' to the ctl file), no listen
         nor accept is needed; otherwise, the usual sequence of
         announce, listen, accept must be executed before performing
         I/O on the corresponding data file.

         IL is a reliable point-to-point datagram protocol that runs
         over IPv4.  Like TCP, IL delivers datagrams reliably and in
         order. Also like TCP, a connection is determined by the

    IP(3)                                                       IP(3)

         address and port numbers of the two ends.  Like UDP, each
         read and write transfers a single datagram.

         IL is efficient for LANs but doesn't have the congestion
         control features needed for use through the Internet.  It is
         no longer necessary, except to communicate with old stan-
         dalone fs(4) file servers.  Its use is now deprecated.

         GRE is the encapsulation protocol used by PPTP.  The kernel
         implements just enough of the protocol to multiplex it.  Our
         implementation encapsulates in IPv4, per RFC 1702.  Announce
         is not allowed in GRE, only connect.  Since GRE has no port
         numbers, the port number in the connect is actually the 16
         bit eproto field in the GRE header.

         Reads and writes transfer a GRE datagram starting at the GRE
         header.  On write, the kernel fills in the eproto field with
         the port number specified in the connect message.

         ESP is the Encapsulating Security Payload (RFC 1827, obso-
         leted by RFC 4303) for IPsec (RFC 4301).  We currently
         implement only tunnel mode, not transport mode.  It is used
         to set up an encrypted tunnel between machines.  Like GRE,
         ESP has no port numbers.  Instead, the port number in the
         connect message is the SPI (Security Association Identifier
         (sic)).  IP packets are written to and read from data.  The
         kernel encrypts any packets written to data, appends a MAC,
         and prefixes an ESP header before sending to the other end
         of the tunnel.  Received packets are checked against their
         MAC's, decrypted, and queued for reading from data.  In the
         following, secret is the hexadecimal encoding of a key,
         without a leading `0x'.  The control messages are:

         esp alg secret  Encrypt with the algorithm, alg, using
                         secret as the key.  Possible algorithms are:
                         null, des_56_cbc, des3_cbc, and eventually
                         aes_128_cbc, and aes_ctr.

         ah alg secret   Use the hash algorithm, alg, with secret as
                         the key for generating the MAC.  Possible
                         algorithms are: null, hmac_sha1_96,
                         hmac_md5_96, and eventually aes_xcbc_mac_96.

         header          Turn on header mode.  Every buffer read from
                         data starts with 4 unused bytes, and the
                         first 4 bytes of every buffer written to
                         data are ignored.

         noheader        Turn off header mode.

    IP(3)                                                       IP(3)

       IP packet filter
         The directory /net/ipmux looks like another protocol direc-
         tory.  It is a packet filter built on top of IP.  Each num-
         bered subdirectory represents a different filter.  The con-
         nect messages written to the ctl file describe the filter.
         Packets matching the filter can be read on the data file.
         Packets written to the data file are routed to an interface
         and transmitted.

         A filter is a semicolon-separated list of relations.  Each
         relation describes a portion of a packet to match.  The pos-
         sible relations are:

         ver=n            the IP version must be n.

         proto=n          the IP protocol number must be n.

         data[n:m]=expr   bytes n through m following the IP header
                          must match expr.

         iph[n:m]=expr    bytes n through m of the IP packet header
                          must match expr.

         ifc=expr         the packet must have been received on an
                          interface whose address matches expr.

         src=expr         The source address in the packet must match

         dst=expr         The destination address in the packet must
                          match expr.

         Expr is of the form:





         If a mask is given, the relevant field is first ANDed with
         the mask.  The result is compared against the value or list
         of values for a match.  In the case of ifc, dst, and src the
         value is a dot-formatted IP address and the mask is a dot-
         formatted IP mask.  In the case of data, iph and proto, both
         value and mask are strings of 2 hexadecimal digits repre-
         senting 8-bit values.

         A packet is delivered to only one filter.  The filters are

    IP(3)                                                       IP(3)

         merged into a single comparison tree.  If two filters match
         the same packet, the following rules apply in order (here
         '>' means is preferred to):

         1)   protocol > data > source > destination > interface

         2)   lower data offsets > higher data offsets

         3)   longer matches > shorter matches

         4)   older > younger

         So far this has just been used to implement a version of
         OSPF in Inferno and 6to4 tunnelling.

         The stats files are read only and contain statistics useful
         to network monitoring.

         Reading /net/ipifc/stats returns a list of 19 tagged and
         newline-separated fields representing:
           forwarding status (0 and 2 mean foourtwpaurtdipnagckoeftfs,
                1 means on)                output packets discarded
           default TTL                     output packets with no route
           input packets                   timed out fragments in reassembly queue
           input header errors             requested reassemblies
           input address errors            successful reassemblies
           packets forwarded               failed reassemblies
           input packets for unknown protocoslusccessful fragmentations
           input packets discarded         unsuccessful fragmentations
           input packets delivered to higherfrlaegvmeelntpsroctroecaotlesd

        Reading /net/icmp/stats returns a list of 26 tagged and
        newline-separated fields representing:
          messages received               messages sent
          bad received messages           transmission errors
          unreachables received           unreachables sent
          time exceededs received         time exceededs sent
          input parameter problems receivedinput parameter problems sent
          source quenches received        source quenches sent
          redirects received              redirects sent
          echo requests received          echo requests sent
          echo replies received           echo replies sent
          timestamps received             timestamps sent
          timestamp replies received      timestamp replies sent
          address mask requests received  address mask requests sent
          address mask replies received   address mask replies sent

       Reading /net/tcp/stats returns a list of 11 tagged and
       newline-separated fields representing:
         maximum number of connections
         total outgoing calls

  IP(3)                                                       IP(3)

         total incoming calls          segments retransmitted
         number of established connectiornestrtannusmmbietrtoifmecouurtrsently established connections
       segments received               bad received segments
       segments sent                   transmission failures

      Reading /net/udp/stats returns a list of 4 tagged and
      newline-separated fields representing:
        datagrams received              malformed datagrams received
        datagrams received for bad portsdatagrams sent

     Reading /net/il/stats returns a list of 6 tagged and
     newline-separated fields representing:
       checksum errors                 retransmitted messages
       header length errors            duplicate messages
       out of order messages           duplicate bytes

     Reading /net/gre/stats returns a list of 1 tagged number
       header length errors

     dial(2), ip(2), bridge(3), ndb(6), listen(8)
     /lib/rfc/rfc2460  IPv6
     /lib/rfc/rfc4291  IPv6 address architecture
     /lib/rfc/rfc4443  ICMPv6


     Ipmux has not been heavily used and should be considered
     experimental.  It may disappear in favor of a more tradi-
     tional packet filter in the future.