Provided by: lft_2.2-4_amd64 bug

NAME

     lft — display the route packets take to a network host/socket; optionally show heuristic
     network information in transitu

SYNOPSIS

     lft [-d dport] [-s sport] [-m min] [-M max] [-a ahead] [-c scatter ms] [-t timeout ms]
         [-l min ttl] [-q ISN] [-D device] [-H ttl] [-i] [-n] [-E] [-N] [-A] [-T] [-S] [-V] [-v]
         [<gateway> <...>] host:dport

DESCRIPTION

     The Internet is a large and complex aggregation of network hardware, connected together by
     gateways.  Tracking the route one's packets follow (or finding the miscreant gateway that's
     discarding your packets) can be difficult.  (from traceroute(8))

     lft sends various TCP SYN and FIN probes (differing from Van Jacobson's UDP-based method)
     utilizing the IP protocol `time to live' field and attempts to elicit an ICMP TIME_EXCEEDED
     response from each gateway along the path to some host.  lft also listens for various TCP
     and ICMP messages along the way to assist network managers in ascertaining per-protocol
     heuristic routing information and can optionally retrieve various information about the
     networks it traverses.

     The only mandatory parameter is the destination host name or IP number.  Options toggle the
     display of more interesting data or change the variables of the trace itself.  The (-E)
     "smart" option tries several combinations in order to improve the chance of a successful
     trace.

     Other options are:

     -d dport
             Set dport as the destination TCP port of the probes LFT generates.  Default is 80.
             This option is useful to see if packets follow a different route based on protocol
             destination, a likely scenario when load balancers or proxies are involved.  This
             option may also bypass less sophisticated packet filter configurations.

     -s sport
             Set sport as the origin TCP port of the probes LFT generates.  Default is 53.  This
             option is useful to see if packets follow a different route based on protocol
             source. This option may also bypass less sophisticated packet filter configurations.

     -m min  Set min as the minimum number of probes to send per host.  Default is 1 unless
             "smart" (-E) mode is used.

     -M max  Set max as the maximum number of probes to send per host.  Default is 5.

     -a ahead
             Set ahead as the number of hops forward to query before waiting for a response.
             Default is 5.

     -c scatter ms
             Set scatter ms as the minimum number of milliseconds to wait between sending probes.
             Default is 20.

     -t timeout ms
             Set timeout ms as the maximum number of milliseconds to wait before assuming a probe
             was lost/discarded.  Default is 1000.

     -l min ttl
             Set min tll as the minimum TTL (time-to-live) on outgoing probes (essentially, the
             first hop in the line that you want to display).  Default is 1.

     -q ISN  Set ISN as the ISN (initial sequence number) of the first probe.  If unset, one will
             be automatically generated.

     -D device
             Set device as the network device or IP address to be used.  (e.g., "en1")  If unset,
             one will be automagically selected by default.

     -H ttl  Set ttl as the maximum TTL, essentially the maximum route traversal distance in
             hops.  Default is 30.

     -i      Disable "stop" on ICMP other than TTL expired.

     -n      Print addresses numerically rather than symbolically and numerically.  Disables use
             of the DNS resolver completely.

     -E      Enable use of the "smart" engine which tries FIN/SYN/etc tables to improve the
             chance of a successful trace.  The engine also displays other useful information
             such as stateful inspection firewalls it finds along the way.

     -N      Enable lookup and display of network names (e.g., [GNTY-NETBLK-4]).  This option
             queries various registries of network address allocation such as ARIN.

     -A      Enable lookup and display of of AS (autonymous system) numbers (e.g., [1]).  This
             option queries various registries of network address allocation such as ARIN.

     -T      Enable display of LFT's execution timer.  This option places timers on the trace
             itself and on lookups and name resolution to show where LFT is spending its time,
             waiting on resolvers, or processing trace packets.

     -S      Suppress display of the real-time status bar.  This option makes LFT show its
             completed trace output only, no-frills.

     -V      Verbose output.  Mostly debug garbage.  Likely too verbose for regular use.

     -v      Display version information, then exit().

     Any hosts listed after these options and before the final host will comprise the loose
     source route.  Since network operators have security concerns with regard to the use of
     source routing, don't expect the LSRR options to do much for you in most public network
     environments.

EXAMPLES

     A sample use and output might be:

     [edge.lax]$ lft -S 4.2.2.2

     Hop  LFT trace to vnsc-bak.sys.gtei.net (4.2.2.2):80/tcp
      1   ln-gateway.centergate.com (206.117.161.1) 0.5ms
      2   isi-acg.ln.net (130.152.136.1) 2.3ms
      3   isi-1-lngw2-atm.ln.net (130.152.180.21) 2.5ms
      4   gigabitethernet5-0.lsanca1-cr3.bbnplanet.net (4.24.4.249) 3.0ms
      5   p6-0.lsanca1-cr6.bbnplanet.net (4.24.4.2) 3.4ms
      6   p6-0.lsanca2-br1.bbnplanet.net (4.24.5.49) 3.3ms
      7   p15-0.snjpca1-br1.bbnplanet.net (4.24.5.58) 10.9ms
      8   so-3-0-0.mtvwca1-br1.bbnplanet.net (4.24.7.33) 11.1ms
      9   p7-0.mtvwca1-dc-dbe1.bbnplanet.net (4.24.9.166) 11.0ms
     10   vlan40.mtvwca1-dc1-dfa1-rc1.bbnplanet.net (128.11.193.67) 11.1ms
     **   [neglected] no reply packets received from TTLs 11 through 20
     **   [4.2-3 BSD bug] the next gateway may errantly reply with reused TTLs
     21   [target] vnsc-bak.sys.gtei.net (4.2.2.2) 11.2ms

     The (-S) option was used to suppress the real-time status bar for clean output.  LFT's "**"
     notifiers in between hops 10 and 21 represent additional useful information: the first is a
     "[neglected]" indicator that lets us know that none of the probes sent with the TTLs
     indicated elicited responses.  This could be for a variety of reasons, but the cause of this
     specific occurrence is described in the next informative message which indicates that this
     is likely the result of a bug in the 4.[23] BSD network code (and its derivatives):  BSD 4.x
     (x < 3) sends an unreachable message using whatever TTL remains in the original datagram.
     Since, for gateways, the remaining TTL is zero, the ICMP "time exceeded" is guaranteed to
     not make it back to us.  LFT does its best to identify this condition rather than print lots
     and lots of hops that don't exist (trying to reach a high enough TTL).

     Now, using the smart engine option:

     [edge.lax]$ lft -E -S 4.2.2.1

     Hop  LFT trace to vnsc-pri.sys.gtei.net (4.2.2.1):80/tcp
      1   ln-gateway.centergate.com (206.117.161.1) 0.5/0.5ms
      2   isi-acg.ln.net (130.152.136.1) 2.1/2.3ms
      3   isi-1-lngw2-atm.ln.net (130.152.180.21) 2.6/7.1ms
      4   gigabitethernet5-0.lsanca1-cr3.bbnplanet.net (4.24.4.249) 6.1/3.9ms
     **   [firewall] the next gateway may statefully inspect packets
      5   p0-0-0.lsanca1-csr1.bbnplanet.net (4.24.4.10) 155.4/3.7ms
      6   [target] vnsc-pri.sys.gtei.net (4.2.2.1) 22.6/3.7/*/*/*/*/*ms

     In the scenario above, the smart engine was able to identify a stateful, packet-inspecting
     firewall in the path.  Another example with more options:

     [edge.lax]$ lft -S -A -T -m 2 -d 80 -s 53 www.yahoo.com

     Hop  LFT trace to w9.scd.yahoo.com (66.218.71.88):80/tcp
      1   [AS226] ln-gateway.centergate.com (206.117.161.1)  1 ms
      2   [AS226] isi-acg.ln.net (130.152.136.1)  2 ms
      3   [AS226] isi-1-lngw2-atm.ln.net (130.152.180.21)  3 ms
      4   [AS1] gigether5-0.lsanca1-cr3.bbnplanet.net (4.24.4.249)  3 ms
      5   [AS1] p6-0.lsanca1-cr6.bbnplanet.net (4.24.4.2)  5 ms
      6   [AS1] p6-0.lsanca2-br1.bbnplanet.net (4.24.5.49)  3 ms
      7   [AS1] p1-0.lsanca2-cr2.bbnplanet.net (4.25.112.1)  3 ms
      8   [AS16852] pos4-0.core1.LosAngeles1.Level3.net (209.0.227.57)  3 ms
      9   [AS3356] so-4-0-0.mp1.LosAngeles1.Level3.net (209.247.10.193)  3 ms
     10   [AS3356] so-3-0-0.mp2.SanJose1.Level3.net (64.159.1.130)  11 ms
     11   [AS3356] gige10-0.ipcolo4.SanJose1.Level3.net (64.159.2.42)  11 ms
     12   [AS3356] cust-int.level3.net (64.152.81.62)  52 ms
     13   [AS10310] vl17.bas2.scd.yahoo.com (66.218.64.150)  53 ms
     14   [AS10310] w9.scd.yahoo.com (66.218.71.88) [target]  54 ms

     LFT's trace took 5.23 seconds.  Resolution required 3.58 seconds.

     And why not request netblock lookups?

     [edge.lax]$ lft -S -N www.microsoft.com

     Hop  LFT trace to www.us.microsoft.com (207.46.197.113):80/tcp
      1   [LOS-NETTOS-BLK4] ln-gateway.centergate.com (206.117.161.1)  2 ms
      2   [LOS-NETTOS] isi-acg.ln.net (130.152.136.1)  3 ms
      3   [LOS-NETTOS] isi-1-lngw2-pos.ln.net (130.152.80.30)  5 ms
      4   [GNTY-4-0] gigether5-0.lsanca1-cr3.bbnplanet.net (4.24.4.249)  4 ms
      5   [GNTY-4-0] p6-0.lsanca1-cr6.bbnplanet.net (4.24.4.2)  3 ms
      6   [GNTY-4-0] p6-0.lsanca2-br1.bbnplanet.net (4.24.5.49)  3 ms
      7   [GNTY-4-0] p15-0.snjpca1-br1.bbnplanet.net (4.24.5.58)  10 ms
      8   [GNTY-4-0] p9-0.snjpca1-br2.bbnplanet.net (4.24.9.130)  11 ms
      9   [GNTY-4-0] so-1-0-0.sttlwa2-br1.bbnplanet.net (4.0.3.229)  27 ms
     10   [GNTY-4-0] so-0-0-0.sttlwa1-hcr1.bbnplanet.net (4.24.11.202)  28 ms
     11   [GNTY-4-0] so-7-0-0.sttlwa1-hcr2.bbnplanet.net (4.24.10.234)  28 ms
     12   [GNTY-4-0] p1-0.sttlwa1-cr2.bbnplanet.net (4.24.10.241)  29 ms
     13   [GNTY-4-0] p2-0.msseattle.bbnplanet.net (4.25.89.6)  32 ms
     14   [MICROSOFT-GLOBAL-NET] 207.46.154.9  32 ms
     15   [MICROSOFT-GLOBAL-NET] 207.46.155.17  33 ms
     16   [MICROSOFT-GLOBAL-NET] 207.46.129.51 [prohibited]  35 ms

Running LFT as a non-root user

     As distributed by Debian, lft can only be run by the root user.  To allow regular users to
     run lft, the sysadmin needs to read the file /usr/share/doc/lft/HOWTO-UsersLFT.txt and
     follow the instructions in that file.

AUTHOR

     Nils McCarthy, Victor Oppleman, Ugen Antsilevitch, and other helpers around the world.  The
     source is currently maintained and administered by MainNerve, Inc.

REPORTING BUGS

     To report bugs, send e-mail to <lft-bugs@mainnerve.com>

SEE ALSO

     traceroute(8), netstat(1), whois(1)

HISTORY

     The lft command first appeared in 1998 as 'fft'.  Renamed as a result of confusion with fast
     fourier transforms, lft stands for 'layer four trace.'