Subject: Ping6 utility issue:-

From: niviya vijayan <[email-masked]>
Date: Mon, 3 May 2010 16:13:31 +0530

Hi All,

I am using linux os version 2.6.10 and i have an mtu configured 1500 .When i
do a ping6 request  with size 1800 and DF bit set as yes, i could see a
fragmentation happening eventhough DF bit is set. As per my understanding ,
Ping6 request has to be dropped.Correct me if am wrong.Did anyone face
this issue anytime before?

Looking forward to hear from you...

Regards,
Niviya

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From: Mark Andrews <[email-masked]>
Date: Mon, 03 May 2010 21:40:32 +1000

> Looking forward to hear from you...

Fragmentation and DF are not mutually exclusive.  DF says don't
fragment when forwarding.  When you are originating the packet
you are not forwarding.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]

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From: niviya vijayan <[email-masked]>
Date: Mon, 3 May 2010 17:34:52 +0530

Hi Mark,

Thanks for your reply. But for ipv6, fragmentation will happen at the host
side.Intermediate routers will not do it and depending on the path MTU
packets are fragmented at the initiator side. so while originating packets
itself will do fragmentation.. Since the packets are sent with DF set as
one, packets has to be dropped there itself.

If I am wrong, Please give some more explanation.

Thanks In advance,
Niviya

---

From: Mohacsi Janos <[email-masked]>
Date: Mon, 3 May 2010 17:03:49 +0200 (CEST)

On Mon, 3 May 2010, niviya vijayan wrote:

> Hi All,
>  
> I am using linux os version 2.6.10 and i have an mtu configured 1500 .When i do a ping6 request  with size 1800 and DF bit set as
> yes, i could see a fragmentation happening eventhough DF bit is set. As per my understanding , Ping6 request has to be
> dropped.Correct me if am wrong.Did anyone face this issue anytime before?

Can you send packet capture from originating and reciver side?

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From: Hagen Paul Pfeifer <[email-masked]>
Date: Mon, 3 May 2010 20:46:24 +0200

>If I am wrong, Please give some more explanation.

With the -M option you actual disable the PMTUD mechanism, not IP
fragmentation at all. This means that no dynamic mechanism is involved, on the
contrary, the MTU size of the outgoing interface is used. Standard is to enable
path MTU discovery.

~3 month ago there where a interesting discussion on the netdev mailinglist,
maybe you should grep the netdev archive for some background information.

Cheers, Hagen

-- 
Hagen Paul Pfeifer <[email-masked]>  ||  http://jauu.net/
Telephone: +49 174 5455209           ||  Key Id: 0x98350C22
Key Fingerprint: 490F 557B 6C48 6D7E 5706 2EA2 4A22 8D45 9835 0C22
Always in motion, the future is.

---

From: Hagen Paul Pfeifer <[email-masked]>
Date: Mon, 3 May 2010 23:20:09 +0200

>>If I am wrong, Please give some more explanation.

Small addendum: RFC 3542 specify a socket option (11.2.) called IPV6_DONTFRAG,
maybe this is the option you are searching for:

		This specification defines a mechanism to turn off the automatic
		inserting of a fragment header for UDP and raw sockets.  This can be
		enabled using the IPV6_DONTFRAG socket option.

Linux does *not* implement this option. ;-)

Cheers, Hagen

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From: niviya vijayan <[email-masked]>
Date: Tue, 4 May 2010 10:34:24 +0530

On Mon, May 3, 2010 at 8:33 PM, Mohacsi Janos <[email-masked]> wrote:

>> I am using linux os version 2.6.10 and i have an mtu configured 1500 .When
>> i do a ping6 request  with size 1800 and DF bit set as
>> yes, i could see a fragmentation happening eventhough DF bit is set. As
>> per my understanding , Ping6 request has to be
> I cannot share the packets captured.But I could see the packets getting
> fragmented eventhough DF bit set from the originator side.Is there any open
> issues reported for this in linux? Is there any web page, where I can find
> all the linux bugs related to ipv6/ ping6 ?
>
>>

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From: Brian Haley <[email-masked]>
Date: Tue, 04 May 2010 10:37:17 -0400

> Linux does *not* implement this option. ;-)

It will in 2.6.35 :)

http://marc.info/?l=linux-netdev&m=127205848417786&w=2

BTW, Linux-specific networking questions should be sent to
either [email-masked] (general questions) or
[email-masked] (development).

-Brian