Man traceroute

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TRACEROUTE(1) Traceroute For Linux TRACEROUTE(1)

traceroute - print the route packets trace to network host

traceroute [-46dFITUnreAV] [-f first_ttl] [-g gate,...]
[-i device] [-m max_ttl] [-p port] [-s src_addr]
[-qnqueries] [-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]
traceroute6 [options]
lft [options]

traceroute tracks the route packets taken from an IP network on their way to agiven 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
lft is equivalent to traceroute -t

The only required parameter is the name or IP address of the destination host . The optional packet_len`gth is thetotal 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" replyfrom a gateway. We start our probes with a ttl of one and increase by one until we get an ICMP "port unreach‐
able" (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 befollowed 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 protocolunreachable), !S (source route failed), !F (frag‐
mentation needed), !X (communication administratively prohibited), !V (host precedence violation), !C (precedence cutoff in effect), or !<num> (ICMP
unreachable code <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 toprocess 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 tracerouting (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 cannot 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 byfirewalls just
as a start of allowed type of a network session).

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