Print help info and exit.
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.
Use ICMP ECHO for probes
Use TCP SYN for probes
Enable socket level debugging (when the Linux kernel supports it)
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.
Specifies with what TTL to start. Defaults to 1.
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 (most routers have disabled source routing for security reasons). In general, several gateway's is allowed (comma separated). For IPv6, the form of num,addr,addr... is allowed, where num is a route header type (default is type 2). Note the type 0 route header is now deprecated (rfc5095).
Specifies the interface through which traceroute should send packets. By default, the interface is selected according to the routing table.
Specifies the maximum number of hops (max time-to-live value) traceroute will probe. The default is 30.
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.
Do not try to map IP addresses to host names when displaying them.
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.
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.
Set the time (in seconds) to wait for a response to a probe (default 5.0 sec).
Sets the number of probe packets per hop. The default is 3.
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.
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.
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.
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 / ).
Perform AS path lookups in routing registries and print results directly after the corresponding addresses.
Print the version and exit.
There is a couple of additional options, intended for an advanced usage (another trace methods etc.):
Chooses the source port to use. Implies -N 1. Normally source ports (if applicable) are chosen by the system.
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).
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.
Use UDP to particular destination port for tracerouting (instead of increasing the port per each probe). Default port is 53 (dns).
Use UDPLITE for tracerouting (default port is 53).
Use raw packet of specified protocol for tracerouting. Default protocol is 253 (rfc3692).
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.
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' .
List Of Available Methods
In general, a particular traceroute method may have to be chosen by -M name, but most of the methods have their simple cmdline switches (you can see them after the method name, if present).
The traditional, ancient method of tracerouting. Used by default.
Probe packets are udp datagrams with so-called "unlikely" destination ports. The "unlikely" port of the first probe is 33434, then for each next probe it is incremented by one. Since the ports are expected to be unused, the destination host normally returns "icmp unreach port" as a final response. (Nobody knows what happens when some application listens for such ports, though).
This method is allowed for unprivileged users.
Most usual method for now, which uses icmp echo packets for probes.
If you can ping(8) the destination host, icmp tracerouting is applicable as well.
Well-known modern method, intended to bypass firewalls.
Uses the constant destination port (default is 80, http).
If some filters are present in the network path, then most probably any "unlikely" udp ports (as for default method) or even icmp echoes (as for icmp) are filtered, and whole tracerouting will just stop at such a firewall. To bypass a network filter, we have to use only allowed protocol/port combinations. If we trace for some, say, mailserver, then more likely -T -p 25 can reach it, even when -I can not.
This method uses well-known "half-open technique", which prevents applications on the destination host from seeing our probes at all. Normally, a tcp syn is sent. For non-listened ports we receive tcp reset, and all is done. For active listening ports we receive tcp syn+ack, but answer by tcp reset (instead of expected tcp ack), this way the remote tcp session is dropped even without the application ever taking notice.
There is a couple of options for tcp method:
Sets specified tcp flags for probe packet, in any combination.
Sets the flags field in the tcp header exactly to num.
Send syn packet with tcp flags ECE and CWR (for Explicit Congestion Notification, rfc3168)
Use the corresponding tcp header option in the outgoing probe packet.
Use current sysctl (/proc/sys/net/*) setting for the tcp header options above and ecn. Always set by default, if nothing else specified.
Use value of num for maxseg tcp header option (when syn).
Default options is syn,sysctl.
An initial implementation of tcp method, simple using connect(2) call, which does full tcp session opening. Not recommended for normal use, because a destination application is always affected (and can be confused).
Use udp datagram with constant destination port (default 53, dns).
Intended to bypass firewall as well.
Note, that unlike in tcp method, the correspond application on the destination host always receive our probes (with random data), and most can easily be confused by them. Most cases it will not respond to our packets though, so we will never see the final hop in the trace. (Fortunately, it seems that at least dns servers replies with something angry).
This method is allowed for unprivileged users.
Use udplite datagram for probes (with constant destination port, default 53).
This method is allowed for unprivileged users.
Set udplite send coverage to num.
raw -P proto
Send raw packet of protocol proto.
No protocol-specific headers are used, just IP header only.
Implies -N 1.
Use IP protocol proto (default 253).
To speed up work, normally several probes are sent simultaneously. On the other hand, it creates a "storm of packages", especially in the reply direction. Routers can throttle the rate of icmp responses, and some of replies can be lost. To avoid this, decrease the number of simultaneous probes, or even set it to 1 (like in initial traceroute implementation), i.e. -N 1
The final (target) host can drop some of the simultaneous probes, and might even answer only the latest ones. It can lead to extra "looks like expired" hops near the final hop. We use a smart algorithm to auto-detect such a situation, but if it cannot help in your case, just use -N 1 too.
For even greater stability you can slow down the program's work by -z option, for example use -z 0.5 for half-second pause between probes.
If some hops report nothing for every method, the last chance to obtain something is to use ping -R command (IPv4, and for nearest 8 hops only).