Re: IPV6 Doubt

AFAIK, PMTUD has no need for TCP.
And is not directly related to MSS tinkering, other than that being a
band-aid fix for the overzealous security admins filtering all ICMP
messages and breaking PMTUD.

You may read http://www.nil.com/ipcorner/IP_Fragmentation/ by Ivan
Pepelnjak for a nice writeup on the subject.

-Carlos

Joe Astorino @ 07/06/2011 20:29 -0300 dixit:
> My thought originally was it may have to do with the idea that TCP can retransmit segments while UDP does not but I could be wrong. Maybe someone else knows definitively.
>
>
> Sent from my Verizon Wireless BlackBerry
>
> Regards,
>
> Joe Astorino
> CCIE #24347
>
> "He not busy being born is busy dying" - Dylan
>
> -----Original Message-----
> From: Carlos G Mendioroz <tron_at_huapi.ba.ar>
> Date: Tue, 07 Jun 2011 20:23:46
> To: <joeastorino1982_at_gmail.com>
> Cc: Routing Freak<routingfreak_at_gmail.com>; Cisco certification<ccielab_at_groupstudy.com>
> Subject: Re: IPV6 Doubt
>
> But you said it made sense... :)
>
> Joe Astorino @ 07/06/2011 20:15 -0300 dixit:
>> That is what it states in the document I posted. Check it out
>>
>>
>> Sent from my Verizon Wireless BlackBerry
>>
>> Regards,
>>
>> Joe Astorino
>> CCIE #24347
>>
>> "He not busy being born is busy dying" - Dylan
>>
>> -----Original Message-----
>> From: Carlos G Mendioroz <tron_at_huapi.ba.ar>
>> Date: Tue, 07 Jun 2011 20:06:52
>> To: Joe Astorino<joeastorino1982_at_gmail.com>
>> Cc: Routing Freak<routingfreak_at_gmail.com>; Cisco certification<ccielab_at_groupstudy.com>
>> Subject: Re: IPV6 Doubt
>>
>> Joe,
>> why do you think that PMTUD is only possible under TCP ?
>> All it takes is sending oversized packets with DF, and waiting for
>> someone to tell back "no go". Any IP packet can do that, or am I missing
>> something ?
>> -Carlos
>>
>> Joe Astorino @ 07/06/2011 12:29 -0300 dixit:
>>> From reading this document it seems that path MTU discovery (PMTUD) is a way
>>> for routers to determine the maximum IP MTU they can use along a path.
>>> Seems it is only possible for TCP traffic according to the doc which makes
>>> sense because if you send a TCP segment and it is higher than the outgoing
>>> MTU at some point along the path, you should get an ICMP message back saying
>>> so and be able to retransmit that segment. "ip tcp path-mtu-discovery"
>>> seems to be the same basic concept but for router initiated traffic.
>>>
>>> Now, for IPv6 I believe that the PMTUD function is moved off of the routers
>>> and on to the hosts but basically that is how I read things here.
>>>
>>> http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml#t4
>>>
>>> HTH
>>>
>>>
>>> On Tue, Jun 7, 2011 at 11:04 AM, Routing Freak <routingfreak_at_gmail.com>wrote:
>>>
>>>> Hi fellows,
>>>> I am searching for a command to enable path mtu discovery in IPV6.
>>>> I want to know the difeerence between ip mtu discovery and ip tcp path mtu
>>>> discovery
>>>>
>>>> Can some one point out the difference.
>>>>
>>>>
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>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net