DGS-1510 Series Gigabit Ethernet SmartPro Switch CLI Reference Guide
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The traceroute command uses the TTL field in the IP header to cause routers and servers to
generate specific return messages. traceroute starts by sending a UDP datagram to the destination
host with the TTL field set to 1. If a router finds a TTL value of 1 or 0, it drops the datagram and sends
back an ICMP “time-exceeded” message to the sender. The traceroute facility determines the
address of the first hop by examining the source address field of the ICMP time-exceeded message.
To identify the next hop, traceroute again sends a UDP packet but this time with a TTL value of 2.
The first router decrements the TTL field by 1 and sends the datagram to the next router. The second
router sees a TTL value of 1, discards the datagram, and returns the time-exceeded message to the
source. This process continues until the TTL is incremented to a value large enough for the datagram
to reach the destination host (or until the maximum TTL is reached).
To determine when a datagram has reached its destination, traceroute sets the UDP destination port
in the datagram to a very large value that the destination host is unlikely to be using. When a host
receives a datagram with an unrecognized port number, it sends an ICMP “port unreachable” error to
the source. This message indicates to the traceroute facility that it has reached the destination.
Example
This example shows how to traceroute the host with IP address 211.21.180.1.
Switch#traceroute 211.21.180.1
10 ms 10.1.1.254
30 ms 192.168.249.134
30 ms 192.168.249.134
<10 ms 192.168.5.230
<10 ms 211.21.180.1
Trace complete.
Switch#
This example shows how to traceroute the host with IPv6 address
2001:238:f8a:77:7c10:41c0:6ddd:ecab.
Switch#traceroute 2001:238:f8a:77:7c10:41c0:6ddd:ecab
10 ms 1001:238:f8a:77:7c10:41c0:6ddd:ecab
Trace complete.
Switch#
36-3 ip helper-address
This command is used to add a target address for forwarding of UDP broadcast packets. Use the no
form of this command to remove the specified forwarding target address.
ip helper-address IP-ADDRESS
no ip helper-address [IP-ADDRESS]
Parameters
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