From: Kyaw Khine (kkhine@register.com)
Date: Tue Nov 19 2002 - 19:04:26 GMT-3
Chuck,
Yes. It actually fixed my problems. So, modifying rate of 'host
unreachables' helps. (default is 1 reply every 500 milliseconds and I make
it lower, which might not be a good idea for ping floods.)
It is true that traceroute relies on TTL expired ICMPs for intermediate
routers along the path.
But, at final destination, it ends up with ICMP Destination Unreachable
(type 3) Port Unreachable (code 3).
Pls refer to
(ip icmp rate-limit unreachable command reference)
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr
as_r/1rfip1.htm#1068044
(how traceroute works)
http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration
_guide_chapter09186a008007f63a.html#xtocid6
(icmp type codes)
http://www.spirit.com/Resources/icmp.html
- Kyaw Khine
For those who don't want bother visiting CCO,
"
To identify the next hop, traceroute sends a UDP packet 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 reaches its destination, traceroute sets the
UDP destination interface in the datagram to a very large value which the
destination host is unlikely to be using. When a host receives a datagram
with an unrecognized interface number, it sends an ICMP port unreachable
error to the source. This message indicates to the traceroute facility that
it has reached the destination.
"
-----Original Message-----
From: Chuck Church [mailto:cchurch@optonline.net]
Sent: Tuesday, November 19, 2002 4:43 PM
To: Kyaw Khine; ccielab@groupstudy.com
Subject: Re: Lost packet in traceroute
Kyaw,
Did that actually fix your problem? According to the docs, it modifies
the rate that 'host unreachables' are sent. Traceroute relies on TTL
expired ICMPs
Chuck Church
CCIE #8776, MCNE, MCSE
----- Original Message -----
From: "Kyaw Khine" <kkhine@register.com>
To: <ccielab@groupstudy.com>
Sent: Tuesday, November 19, 2002 2:19 PM
Subject: RE: Lost packet in traceroute
> I found out the solution.
>
> Ip icmp rate-limit unreachable <time>
>
>
> -----Original Message-----
> From: Kyaw Khine
> Sent: Tuesday, November 19, 2002 1:55 PM
> To: 'ccielab@groupstudy.com'
> Subject: Lost packet in traceroute
>
>
> Hi Group,
>
> I'm seeing a packet drop when I traceroute to a neighbor router. It's
always
> like this that the middle packet is dropped.
>
> Tracing the route to
> 1 s4-0.core1.nyat.register.com (209.67.51.1) 4 msec * 4 msec
>
> Any thoughts what is going on?
>
>
> Thanks ..
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