On 4 dec 2008, at 14.05, Pekka Savola wrote:
On Wed, 3 Dec 2008, Anders Lindbäck wrote:
Mtr is even less usefull then that, in its default mode it does a
traceroute and then proceeds to ICMP Ping flood each IP in the
list generated by the traceroute, the result is usually completly
useless on WAN topologies due to asym-routing, ICMP node
protections by carriers and punting etc..
No, it doesn't try pinging the routers in the middle, at least not
anymore (I just re-checked with 0.71 and 0.75). I vaguely recall
behaviour like that in the past, however, so it's possible that
long time ago mtr did behave that way.
According to the 0.75 sorcecode ICMP is still the default prot used,
and the definition of MTR from bitwizards homepage disagress with you:
"mtr combines the functionality of the 'traceroute' and 'ping'
programs in a single network diagnostic tool.
As mtr starts, it investigates the network connection between the
host mtr runs on and a user-specified destination host. After it
determines the address of each network hop between the machines, it
sends a sequence ICMP ECHO requests to each one to determine the
quality of the link to each machine. As it does this, it prints
running statistics about each machine. For a preview take a look at
the screenshots."
Even if you use UDP/TCP or whatever, the return packet will be ICMP
and that will be ratelimited by any carrier worth there salt...
And using UDP will not really provide better results due to the
same thing, and IIRC Cisco from 12.0 has a standard setting of no
more then 1 ICMP Unreach per 500ms..
This is true and the point I was getting at, though I believe the
bucket is much larger in any recent software release (also in 12.0
series). Actually, 5 years ago, you could see spot Cisco routers
in "traceroute6" because they dropped the rate-limiter didn't
respond to the middle packet and it resulted in a star. The rate-
limiter has long since been fixed to be more lenient.
According to the 12.4T refrence it is still set to 1 packet / 500ms
as default, however changes where made to how you can controll this
in 12.4(2)T.
--
Pekka Savola "You each name yourselves king, yet the
Netcore Oy kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
------------------------------
Anders Lindbäck
[EMAIL PROTECTED]
