[98334] in North American Network Operators' Group
Re: Seeking Comcast Contact: need to troubleshoot packet loss and/or asymmetric routing issue between Comcast & Onvoy
daemon@ATHENA.MIT.EDU (Duane Waddle)
Fri Aug 3 00:22:06 2007
Date: Thu, 2 Aug 2007 22:51:52 -0500
From: "Duane Waddle" <duane.waddle@gmail.com>
To: nanog@merit.edu
In-Reply-To: <11896.1186108384@turing-police.cc.vt.edu>
Errors-To: owner-nanog@merit.edu
------=_Part_51695_7164430.1186113112534
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
On 8/2/07, Valdis.Kletnieks@vt.edu <Valdis.Kletnieks@vt.edu> wrote:
>
>
>
> AIX 5.2 and earlier supported it for UDP (we're getting out of the AIX
> business, so I can't speak to what 5.3 does). Basically, it would send
> out a
> gratuitous 64K ICMP Echo Request with DF set, and waited to see what came
> back.
AIX 5.3 changes the whole PMTU scheme to work more like the RFCs and not
depend on out of band ICMP packets.
From http://www.ibm.com/developerworks/aix/library/au-aix5l-me.html :
PMTU discovery in AIX 5L Version 5.3
The current Path Maximum Transmission Unit (PMTU) discovery implementation
uses ICMP Echo Request and ICMP Echo Reply packets to discover PMTU. Some
system administrators set up their firewall to drop ICMP Echo packets,
resulting in the above method of PMTU discovery to fail. The PMTU discovery
mechanism in AIX 5L Version 5.3 is implemented with TCP packets and UDP
datagram instead of ICMP Echo packets.
------=_Part_51695_7164430.1186113112534
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
<br><br><div><span class="gmail_quote">On 8/2/07, <b class="gmail_sendername"><a href="mailto:Valdis.Kletnieks@vt.edu">Valdis.Kletnieks@vt.edu</a></b> <<a href="mailto:Valdis.Kletnieks@vt.edu">Valdis.Kletnieks@vt.edu</a>
> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br><br>AIX 5.2 and earlier supported it for UDP (we're getting out of the AIX
<br>business, so I can't speak to what 5.3 does). Basically, it would send out a<br>gratuitous 64K ICMP Echo Request with DF set, and waited to see what came back.</blockquote><div><br>AIX 5.3 changes the whole PMTU scheme to work more like the RFCs and not depend on out of band ICMP packets.
<br><br>From <a href="http://www.ibm.com/developerworks/aix/library/au-aix5l-me.html">http://www.ibm.com/developerworks/aix/library/au-aix5l-me.html</a> :<br><br>PMTU discovery in AIX 5L Version 5.3 <br>
The current Path Maximum Transmission Unit (PMTU) discovery
implementation uses ICMP Echo Request and ICMP Echo Reply packets to
discover PMTU. Some system administrators set up their firewall to drop
ICMP Echo packets, resulting in the above method of PMTU discovery to
fail. The PMTU discovery mechanism in AIX 5L Version 5.3 is implemented
with TCP packets and UDP datagram instead of ICMP Echo packets.<br></div><br></div>
------=_Part_51695_7164430.1186113112534--
