# tracepath

## NAME



           tracepath - traces path to a network host discovering MTU along
           this path
    


## SYNOPSIS



    
           **tracepath**[**-4**] [**-6**] [**-n**] [**-b**] [**-l** _pktlen_] [**-m** _max_hops_] [**-p** _port_]
                     [**-V**] {destination}
    


## DESCRIPTION



           It traces the network path to _destination_ discovering MTU along
           this path. It uses UDP port _port_ or some random port. It is
           similar to **traceroute**. However, it does not require superuser
           privileges and has no fancy options.
    
           **tracepath -6** is a good replacement for **traceroute6** and classic
           example of application of Linux error queues. The situation with
           IPv4 is worse, because commercial IP routers do not return enough
           information in ICMP error messages. Probably, it will change, when
           they are updated. For now it uses Van Jacobson's trick, sweeping a
           range of UDP ports to maintain trace history.
    


## OPTIONS



           **-4**
               Use IPv4 only.
    
           **-6**
               Use IPv6 only.
    
           **-n**
               Print primarily IP addresses numerically.
    
           **-b**
               Print both: Host names and IP addresses.
    
           **-l**
               Sets the initial packet length to _pktlen_ instead of 65535 for
               **IPv4** or 128000 for **IPv6**.
    
           **-m**
               Set maximum hops (or maximum TTLs) to _max_hops_ instead of 30.
    
           **-p**
               Sets the initial destination port to use.
    
           **-V**
               Print version and exit.
    


## OUTPUT



               root@mops:~ # tracepath -6 3ffe:2400:0:109::2
                1?: [LOCALHOST]                              pmtu 1500
                1:  dust.inr.ac.ru                   0.411ms
                2:  dust.inr.ac.ru        asymm  1   0.390ms pmtu 1480
                2:  3ffe:2400:0:109::2               463.514ms reached
                    Resume: pmtu 1480 hops 2 back 2
    
           The first column shows the TTL of the probe, followed by colon.
           Usually the value of TTL is obtained from the reply from the
           network, but sometimes it does not contain the necessary
           information and we have to guess it. In this case the number is
           followed by ?.
    
           The second column shows the network hop which replied to the
           probe. It is either the address of the router or the word
           [LOCALHOST], if the probe was not sent to the network.
    
           The rest of the line shows miscellaneous information about the
           path to the corresponding network hop. It contains the value of
           RTT, and additionally it can show Path MTU when it changes. If the
           path is asymmetric or the probe finishes before it reaches the
           prescribed hop, the number of hops in return direction is shown
           next to the keyword "asymm". This information is not reliable,
           e.g. the third line shows asymmetry of 1. This is because the
           first probe with TTL of 2 was rejected at the first hop due to
           Path MTU Discovery.
    
           The last line summarizes information about all the paths to the
           destination. It shows detected Path MTU, amount of hops to the
           destination and our guess about the number of hops from the
           destination to us, which can be different when the path is
           asymmetric.
    


## HANDLING ERRORS



           In case of errors **tracepath** prints short error code.
           ┌─────────────┬──────────────┬────────────────────┐
           │ **Output** │ **Code** │ **Meaning** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **!A** │ **EACCES** │ **Communication** │
           │             │              │ **administratively** │
           │             │              │ **prohibited** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **!H** │ **EHOSTUNREACH** │ **Destination host** │
           │             │              │ **unreachable** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **!N** │ **ENETUNREACH** │ **Destination** │
           │             │              │ **network** │
           │             │              │ **unreachable** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **!P** │ **EPROTO** │ **Destination** │
           │             │              │ **protocol** │
           │             │              │ **unreachable** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **pmtu N** │ **EMSGSIZE** │ **Message too long** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **reached** │ **ECONNREFUSED** │ **Connection refused** │
           ├─────────────┼──────────────┼────────────────────┤
           │             │ **ETIMEDOUT** │ **Connection timed** │
           │             │              │ **out** │
           ├─────────────┼──────────────┼────────────────────┤
           │ **NET ERROR N** │              │ **Any other error** │
           └─────────────┴──────────────┴────────────────────┘
    


## SECURITY



           No security issues.
    
           This lapidary deserves to be elaborated.  **tracepath** is not a
           privileged program, unlike **traceroute** , **ping** and other beasts of
           their kind.  **tracepath** may be executed by everyone who has enough
           access to the network to send UDP datagrams to the desired
           destination using the given port.
    


## AVAILABILITY



           **tracepath** is part of _iputils_ package.
    


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