Traceroute

Description

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Installation

$ apt-get install traceroute

Usage

Basic syntax

$ traceroute [-46dFITUnreAV] [-f first_ttl] [-g gate,...]
             [-i device] [-m max_ttl] [-p port] [-s src_addr]
             [-q nqueries] [-N squeries] [-t tos]
             [-l flow_label] [-w waittime] [-z sendwait]
             [-UL] [-P proto] [--sport=port] [-M method] [-O mod_options]
             [--mtu] [--back]
             host [packet_len]

Options

Standard options

--help

Print help info and exit.

-4, -6

Explicitly force IPv4 or IPv6 traceouting. By default, the program will try to resolve the name given, and choose the appropriate protocol automatically.

If resolving a host name returns both IPv4 and IPv6 addresses, traceroute will use IPv4.

-I

Use ICMP ECHO for probes

-T

Use TCP SYN for probes

-d

Enable socket level debugging (when the Linux kernel supports it)

-F

Do not fragment probe packets. (For IPv4 it also sets DF bit, which tells intermediate routers not to fragment remotely as well).

Varying the size of the probing packet by the packet_len command line parameter, you can manually obtain information about the MTU of individual network hops. The --mtu option (see below) tries to do this automatically.

Note that non-fragmented features (like -F or --mtu) work properly since the Linux kernel 2.6.22 only. Before that version, IPv6 was always fragmented, IPv4 could use the once the discovered final mtu only (from the route cache), which can be less than the actual mtu of a device.

-f <first_ttl>

Specifies with what TTL to start. Defaults to 1.

-g <gateway>

Tells traceroute to add an IP source routing option to the outgoing packet that tells the network to route the packet through the specified gateway. Not very useful, because most routers have disabled source routing for security reasons.

-i <interface>

Specifies the interface through which traceroute should send packets. By default, the interface is selected according to the routing table.

-m <max_ttl>

Specifies the maximum number of hops (max time-to-live value) traceroute will probe.

The default is 30.

-N squeries

Specifies the number of probe packets sent out simultaneously. Sending several probes concurrently can speed up traceroute considerably. The default value is 16.

Note that some routers and hosts can use ICMP rate throttling. In such a situation specifying too large number can lead to loss of some responses.

-n

Do not try to map IP addresses to host names when displaying them.

-p <port>

For UDP tracing, specifies the destination port base traceroute will use (the destination port number will be incremented by each probe).

For ICMP tracing, specifies the initial icmp sequence value (incremented by each probe too).

For TCP specifies just the (constant) destination port to connect.

-t <tos>

For IPv4, set the Type of Service (TOS) and Precedence value. Useful values are 16 (low delay) and 8 (high throughput). Note that in order to use some TOS precendence values, you have to be super user.

For IPv6, set the Traffic Control value.

-w waittime

Set the time (in seconds) to wait for a response to a probe (default 5.0 sec).

-q <nqueries>

Sets the number of probe packets per hop. The default is 3.

-r

Bypass the normal routing tables and send directly to a host on an attached network.

If the host is not on a directly-attached network, an error is returned. This option can be used to ping a local host through an interface that has no route through it.

-s <source_addr>

Chooses an alternative source address. Note that you must select the address of one of the interfaces. By default, the address of the outgoing interface is used.

-z <sendwait>

Minimal time interval between probes (default 0). If the value is more than 10, then it specifies a number in milliseconds, else it is a number of seconds (float point values allowed too). Useful when some routers use rate-limit for icmp messages.

-e

Show ICMP extensions (rfc4884). The general form is CLASS/TYPE: followed by a hexadecimal dump. The MPLS (rfc4950) is shown parsed, in a form: MPLS:L=label,E=exp_use,S=stack_bottom,T=TTL (more objects separated by / ).

-A

Perform AS path lookups in routing registries and print results directly after the corresponding addresses.

-V

Print the version and exit.

Advanced options

There is a couple of additional options, intended for an advanced usage (another trace methods etc.):

--sport=port

Chooses the source port to use. Implies -N 1. Normally source ports (if applicable) are chosen by the system.

-M <method>

Use specified method for traceroute operations. Default traditional udp method has name default, icmp (-I) and tcp (-T) have names icmp and tcp respectively. Method-specific options can be passed by -O. Most methods have their simple shortcuts, (-I means -M icmp, etc).

-O <option>

Specifies some method-specific option. Several options are separated by comma (or use several -O on cmdline). Each method may have its own specific options, or many not have them at all. To print information about available options, use -O help.

-U

Use UDP to particular destination port for tracerouting (instead of increasing the port per each probe). Default port is 53 (dns).

-UL

Use UDPLITE for tracerouting (default port is 53).

-P protocol

Use raw packet of specified protocol for tracerouting. Default protocol is 253 (rfc3692).

--mtu

Discover MTU along the path being traced. Implies -F -N 1. New mtu is printed once in a form of F=NUM at the first probe of a hop which requires such mtu to be reached. (Actually, the correspond "frag needed" icmp message normally is sent by the previous hop).

Note that some routers might cache once the seen information on a fragmentation. Thus you can receive the final mtu from a closer hop. Try to specify an unusual tos by -t, this can help for one attempt (then it can be cached there as well). See -F option for more info.

--back

Print the number of backward hops when it seems different with the forward direction. This number is guessed in assumption that remote hops send reply packets with initial ttl set to either 64, or 128 or 255 (which seems a common practice). It is printed as a negate value in a form of '-NUM'.

Available methods

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Example

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