Charles
Charles Steinkuehler wrote:
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...> |
| I would expect the server to reduce the packet size accordingly but
| helas it does not. Am I just naive to expect M$ to follow or is it
| compulsory only to respect ICMP?
You have to have Path MTU discovery enabled:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/randz/protocol/path_mtu_discovery.asp
<quote>
# EnablePMTUBHDetect. This value adjusts the PMTU discovery algorithm to
attempt to detect noncompliant routers, also called PMTU black hole
routers. PMTU black hole detection is disabled by default but can be
enabled by adding this value to the registry key and setting it to 1.
# EnablePMTUDiscovery. This value enables or disables the PMTU discovery
mechanism, helping to diagnose problems with black hole routers. PMTU
discovery is enabled by default but can be disabled by adding this value
to the registry key and setting it to 0.
PMTU discovery is enabled so that the two sides of a conversation can
negotiate the most efficient MTU. When PMTU discovery is disabled, an
MSS of 536 bytes and an MTU of 540 bytes are used for all nonlocal
destination addresses.
</quote>
This definitely is not the case, as the address is non local and the
size is > 540
...and you have to enable the appropriate ICMP message to pass through all
routers involved (many folks just 'black hole' all ICMP traffic, and assume
there are no side effects, like broken Path MTU discovery).
The next hop router from the server generates the apropriate ICMP message.
NOTE: The MS page above indicates Microsoft is doing the proper thing with
Path MTU discovery, but that's for server 2003. IIRC, you had to
explicitly
enable PMTU discovery for older (ie: 2K & maybe XP) Microsoft systems
(motto: We can steal^h^h^h^h^h appropriate the BSD networking stack, but we
still don't know how to do TCP/IP...besides, who uses a WAN!?!).
Well .... yes.
thanks
Erich
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