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Rakeesh

join:2011-10-30
Mesa, AZ
Reviews:
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reply to NormanS

Re: [AZ] Huge latency and packet loss issues in the Valley Area

Traceroute is just a standard ICMP echo (aka ping command) only we start the TTL in the IP header at just 1, and then increment it each time to find successive hops.

For those who don't know, the TTL is a value that decreased by one each time it passes through a router (aka a hop). When the value reaches zero, the router where it hit zero will send a return packet indicating that the TTL expired in transit, which includes its own IP address. This is done to mitigate downtime caused by routing loops. A side effect is that it allows traceroute to identify all of the hops between you and the destination (otherwise routers are invisible.)

Many routers are configured to ignore ICMP echo requests however, so when one lands at their interface with an expired TTL they just discard the packet and don't return a notice that it was discarded. This is typically done for security reasons rather than performance reasons. If your destination host also ignores ICMP echo, (All versions of Windows Server that I have used are configured to do this by default, by the way) you'll never know exactly how many hops it takes to get to your destination, so traceroute will just keep counting up until it reaches the max number of hops you specify (windows defaults to 30 IIRC).