On Thu, Sep 10, 2009 at 10:07 AM, Jon D <rekcahp...@gmail.com> wrote:
> I've never paid enough attention. When youguys do a tracert to your
> wan links, is it normal to get a timeout somewhere along the way, like
> maybe right after your border router?

  It depends.

  Traceroute works by crafting packets with a deliberately low TTL and
sending them to the target you specify.  It starts with a TTL of one,
so the first hop should expire the packet and return an ICMP "Time
Exceeded" message to the source (your node).  Traceroute reports the
sender of that ICMP message to you, increments the TTL to two, and
tries again.  It repeats that until it gets a response from the target
(or hits the hop limit, 30 by default).

  If any given hop fails to send ICMP "Time Exceeded" messages, you'll
see a timeout at that hop, but hops past it will work.  Typically
looks something like this:

1   <1ms   <1ms   <1ms   foo
2   *   *   *   Request timed out
3   5 ms   5 ms   5 ms   bar
4   7 ms   6 ms   7 ms   baz

  If any given hop fails to *forward* ICMP "Time Exceeded" messages,
then you'll traceroute returns up to that hop, and then timeouts from
that point forward.  For example:

1   <1ms   <1ms   <1ms   foo
2   5 ms   5 ms   5 ms   bar
3   7 ms   6 ms   7 ms   baz
4   *   *   *   Request timed out
5   *   *   *   Request timed out

  Some routers don't generate or forward "Time Exceeded" messages like
they should.  Sometimes that's due to brain damaged
design/implementation by the router manufacturer.  Other times it's
because a brain damaged operator thinks ICMP is a virus, rather than
an essential part of IP.  (Such people are IWF -- Idiot With

> ... traffic is getting through despite the timeout ...

  That almost certainly means the traceroute timeout for a single hop
is spurious and should be ignored.

> ... I see some high latency ...

  You want to see where the latency is coming from.  Compare the
latency between hops.  Large increases across two hops narrow the
problem down to there.

-- Ben

~ Finally, powerful endpoint security that ISN'T a resource hog! ~
~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/>  ~

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