traceroute
traceroute – print the route packets trace to network host
SYNOPSIS
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] [-D]
[-P proto] [–sport=port] [-M method] [-O mod_options]
[–mtu] [–back]
host [packet_len]
traceroute6 [options]
tcptraceroute [options]
lft [options]
DESCRIPTION
traceroute tracks the route packets taken from an IP network on their way to a given host. It utilizes the IP protocol’s time to live (TTL) field and attempts to elicit an ICMP TIME_EXCEEDED response from each gateway along the path to the host.
traceroute6 is equivalent to traceroute -6
tcptraceroute is equivalent to traceroute -T
lft , the Layer Four Traceroute, performs a TCP traceroute, like traceroute -T , but attempts to provide compatibility with the original such implementation, also called “lft”.
The only required parameter is the name or IP address of the destination host . The optional packet_len`gth is the total size of the probing packet (default 60 bytes for IPv4 and 80 for IPv6). The specified size can be ignored in some situations or increased up to a minimal value.
This program attempts to trace the route an IP packet would follow to some internet host by launching probe packets with a small ttl (time to
live) then listening for an ICMP “time exceeded” reply from a gateway.We start our probes with a ttl of one and increase by one until we get an ICMP “port unreachable” (or TCP reset), which means we got to the “host”, or hit a max (which defaults to 30 hops). Three probes (by default) are sent at each ttl setting and a line is printed showing the ttl, address of the gateway and round trip time of each probe. The address can be followed by additional information when requested. If the probe answers come from different gateways, the address of each responding system will be printed. If there is no response within a 5.0 seconds (default), an “*” (asterisk) is printed for that probe.
After the trip time, some additional annotation can be printed: !H, !N,or !P (host, network or protocol unreachable), !S (source route failed), !F (fragmentation needed), !X (communication administratively prohibited), !V (host precedence violation), !C (precedence cutoff in effect), or !<num> (ICMP unreachable span <num>). If almost all the probes result in some kind of unreachable, traceroute will give up and exit.
We don’t want the destination host to process the UDP probe packets, so the destination port is set to an unlikely value (you can change it with the -p flag). There is no such a problem for ICMP or TCP tracer‐ outing (for TCP we use half-open technique, which prevents our probes to be seen by applications on the destination host).
In the modern network environment the traditional traceroute methods can not be always applicable, because of widespread use of firewalls.Such firewalls filter the “unlikely” UDP ports, or even ICMP echoes.To solve this, some additional tracerouting methods are implemented(including tcp), see LIST OF AVAILABLE METHODS below. Such methods try to use particular protocol and source/destination port, in order to bypass firewalls (to be seen by firewalls just as a start of allowed type of a network session).
OPTIONS
–help Print help info and exit.
-4, -6 Explicitly force IPv4 or IPv6 tracerouting. 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, –icmp
Use ICMP ECHO for probes
-T, –tcp
Use TCP SYN for probes
-d, –debug
Enable socket level debugging (when the Linux kernel supports
it)
-F, –dont-fragment
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, –first=first_ttl
Specifies with what TTL to start. Defaults to 1.
-g gateway, –gateway=gateway
Tells traceroute to add an IP source routing option to the out going 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).
-i interface, –interface=interface
Specifies the interface through which traceroute should send packets. By default, the interface is selected according to the
routing table.
-m max_ttl, –max-hops=max_ttl
Specifies the maximum number of hops (max time-to-live value) traceroute will probe. The default is 30.
-N squeries, –sim-queries=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, –port=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 and others specifies just the (constant) destination port to connect. When using the tcptraceroute wrapper, -p speci fies the source port.
-t tos, –tos=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 precedence values, you have to be super user.
NOTES
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).
Reference
