Topic Path: Symbol Reference > Classes > TIdTraceRoute Class > TIdTraceRoute Methods > Trace Method
TIdTraceRoute.Trace Method

Performs route tracing to the system Host or IP Address.

procedure Trace;

Trace is a method used to launch the ICMP probe that performs route tracing to the system specified in the Host or IPAddr properties. 

TIdTraceRoute utilizes the IP protocol 'time to live' field and attempts to elicit an ICMP TIME_EXCEEDED response from each gateway along the path to some host. 

TIdTraceRoute uses the Host or IPAddr specified for the client as the destination host name or IP number. 

TIdTraceRoute attempts to trace the route an IP packet would follow to some internet host by launching UDP probe packets with a small ttl (time to live) then listening for an ICMP "time exceeded" reply from a gateway. The probe is initialized with a ttl value of one, and increased by one until we get an ICMP "port unreachable" (which means we got to "host") or hit a max (which defaults to 30 hops). If the probe answers come from different gateways, the address of each responding system will be provided using the OnReply event handler. 

Use the OnReply event handler to access the response from the ping probe. 

Use ResolveHostNames to indicate if IP addresses are converted to host names for use in the OnReply event handler.

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