Tracerouting in MPLS Networks
Tracerouting is a special tool that is widely used because it is so powerful. Soon you will learn how tracerouting behaves in an MPLS network, but to understand this, you must first understand how tracerouting works in an IP network.
Tracerouting in an IP Network
In Cisco IOS, when you issue the traceroute command on a router, it sends probes to the particular destination IP address that you specify. The probes sent out are UDP packets with a high destination UDP port. The first probe sent out has its IP TTL set to 1, the second probe has its IP TTL set to 2, and so on. In Cisco IOS, the high destination UDP port is a number that is greater than 30,000. Because the first probe sent out has a TTL of 1, the TTL of ...