Subject: Re: [ippm] I-D Action:draft-ietf-ippm-tcp-throughput-tm-02.txt

From: Barry Constantine <[email-masked]>
Date: Tue, 8 Jun 2010 06:15:49 -0700

Ok Gilles,

Got that, a new version (-03) should soon be released and this will be incorporated.

Thanks,

Barry

Principal Member of Technical Staff

JDSU Communication Test (formerly Acterna)

Emerging Markets and Technology Research         

One Milestone Center Court                              

Germantown, MD 20876                                         

(W) 240-404-2227                                                

(C) 301-325-7069

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Gilles Forget
Sent: Tuesday, May 18, 2010 10:23 AM
To: [email-masked]; [email-masked]
Cc: [email-masked]
Subject: Re: [ippm] I-D Action:draft-ietf-ippm-tcp-throughput-tm-02.txt

Bonjour Barry,

I'm not sure about the first paragraph of the Path MTU section.
To be more specific, I think that the words between parentheses should be
replace by :
(at what packet length will fragmentation start to occur)

3.1. Determine Network Path MTU

   TCP implementations should use Path MTU Discovery techniques (PMTUD),
   but this technique does not always prove reliable in real world 
   situations.  Since PMTUD relies on ICMP messages (to inform the host
   that unfragmented transmission cannot occur), it's not always
   reliable since many network managers completely disable ICMP.

Thanks,
Gilles Forget, CCNP.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
[email-masked]
Sent: May-18-10 9:30 AM
To: [email-masked]
Cc: [email-masked]
Subject: [ippm] I-D Action:draft-ietf-ippm-tcp-throughput-tm-02.txt

A New Internet-Draft is available from the on-line Internet-Drafts
directories.
This draft is a work item of the IP Performance Metrics Working Group of the
IETF.

	Title           : TCP Throughput Testing Methodology
	Author(s)       : B. Constantine, et al.
	Filename        : draft-ietf-ippm-tcp-throughput-tm-02.txt
	Pages           : 19
	Date            : 2010-05-18

This memo describes a methodology for measuring sustained TCP throughput
performance in an end-to-end managed network environment.  
This memo is intended to provide a practical approach to help users validate
the TCP layer performance of a managed network, which should provide a
better indication of end-user application level experience.  
In the methodology, various TCP and network parameters are identified that
should be tested as part of the network verification at the TCP layer.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-ippm-tcp-throughput-tm-02.txt

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

Below is the data which will enable a MIME compliant mail reader
implementation to automatically retrieve the ASCII version of the
Internet-Draft.

_______________________________________________
ippm mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/ippm

---

From: Donald McLachlan <[email-masked]>
Date: Tue, 08 Jun 2010 11:00:36 -0400

Gilles and Barry,

Re: 3.1. Determine Network Path MTU

Gilles proposed:

I thought about e-mailing when Gilles first posted this comment.  
Actually, doesn't the ICMP message mean a packet was not transmitted 
because the DF bit was set and the packet size exceeded the MTU. 
Additionally, the ICMP message reports what the MTU size/limit is.

---

From: Barry Constantine <[email-masked]>
Date: Tue, 8 Jun 2010 08:14:32 -0700

So Donald,

Are you suggesting that the text remain as originally submitted?

Thanks,

Barry

Germantown, MD 20876                                         

(W) 240-404-2227                                                

(C) 301-325-7069

-----Original Message-----
From: Donald McLachlan [mailto:[email-masked]] 
Sent: Tuesday, June 08, 2010 11:01 AM
To: Barry Constantine; Gilles Forget
Cc: [email-masked]
Subject: Re: [ippm] I-D Action:draft-ietf-ippm-tcp-throughput-tm-02.txt

Gilles and Barry,

Gilles proposed:

---

From: "Gilles Forget" <[email-masked]>
Date: Tue, 8 Jun 2010 13:17:23 -0400

Donald and Barry,

Donald, you are absolutely right about the fact that the ICMP reply message
will indicate the MTU size. 

Barry, to me the confusion comes from the double negative in the sentence
"to inform the host that unfragmented transmission cannot occur".

I think, we all agree on the inefficiency of packet fragmentation and that
is why we need to find the path MTU before we do any throughput testing.

May I suggest "to inform the host about the MTU size".

I just want to avoid the double negative.

Thanks,
Gilles. 

-----Original Message-----
From: Donald McLachlan [mailto:[email-masked]] 
Sent: June-08-10 11:01 AM
To: Barry Constantine; Gilles Forget
Cc: [email-masked]
Subject: Re: [ippm] I-D Action:draft-ietf-ippm-tcp-throughput-tm-02.txt

Gilles and Barry,

Gilles proposed:

	I'm not sure about the first paragraph of the Path MTU section.
	To be more specific, I think that the words between parentheses
should be
	replace by :
	(at what packet length will fragmentation start to occur)

> From: [email-masked] [mailto:[email-masked]] On Behalf Of
Gilles Forget

---

From: Donald McLachlan <[email-masked]>
Date: Wed, 09 Jun 2010 10:04:00 -0400

Hi Barry,

Maybe I'm being pedantic but in the original text I did not like the 
double "since"s, and the double "reliable"s, and I thought the text 
(even with Gilles' comment) did not describe the PMTUD / ICMP 
interaction very accurately.

I think either one assumes the reader understands the interaction 
between PMTUD and ICMP or one assumes the reader does not.  In the first 
case, I think the paragraph could be shorter and clearer:

     TCP implementations should use Path MTU Discovery techniques (PMTUD).
     PMTUD relies on ICMP 'need to frag' messages to learn the path MTU.
     Unfortunately, because many network managers naively completely
     disable ICMP, this technique does not always prove reliable in real
     world situations.

[ Note: I also added the work naively. ]

In the second case, I think the paragraph needs more details.  In this 
case maybe the following text is better:

     TCP implementations should use Path MTU Discovery techniques (PMTUD).
     PMTUD relies on ICMP 'need to frag' messages to learn the path MTU.
     When a device has a packet to send which has the Don't Fragment (DF)
     bit in the IP header set and the packet is larger than the Maximum
     Transmission Unit (MTU) of the next hop link, the packet is dropped
     and the device sends an ICMP 'need to frag' message back to the host
     that originated the packet. The ICMP 'need to frag' message includes
     the next hop MTU which PMTUD uses to tune the TCP Maximum Segment
     Size (MSS). Unfortunately, because many network managers naively
     completely disable ICMP, this technique does not always prove reliable
     in real world situations.

Personally I prefer the shorter version.

Don

---

From: Donald McLachlan <[email-masked]>
Date: Wed, 09 Jun 2010 10:04:21 -0400

Hi Barry,

[ Note: I also added the word naively. ]

Don

---

From: Alexander Zimmermann <[email-masked]>
Date: Wed, 09 Jun 2010 16:38:24 +0200

Hi Folks,

sorry for hijacking your discussion...
Your section 3.1. says:

   PMTUD relies on ICMP...

This is not completely true since with RFC4821, we can discover the PMTU
without ICMP too. Maybe it's not a bad idea to include some words about
this fact into the paragraph.

Just my 2c.

Alex

---

From: Barry Constantine <[email-masked]>
Date: Wed, 9 Jun 2010 08:33:51 -0700

Alexander, your feedback and Donald's are most welcome!

Let me sort through these comments and try to come up with a paragraph that satisfies all.

-03 version is coming out soon and I will make the changes in this version.

Again, thanks for your comments and appreciate more in any other sections that you can review.

Thanks,

Barry

Germantown, MD 20876                                         

(W) 240-404-2227                                                

(C) 301-325-7069

-----Original Message-----
From: Alexander Zimmermann [mailto:[email-masked]] 
Sent: Wednesday, June 09, 2010 10:38 AM
To: Donald McLachlan
Cc: Barry Constantine; [email-masked]
Subject: Re: [ippm] I-D Action:draft-ietf-ippm-tcp-throughput-tm-02.txt

Hi Folks,

Just my 2c.

Alex