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List:       fedora-list
Subject:    Re: IPv6 mtu restriction
From:       Robert Moskowitz <rgm () htt-consult ! com>
Date:       2014-03-27 23:37:07
Message-ID: 5334B623.4060209 () htt-consult ! com
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On 03/27/2014 07:28 PM, Bill Davidsen wrote:
> Robert Moskowitz wrote:
>>
>> On 03/27/2014 03:40 PM, Rick Stevens wrote:
>>> On 03/27/2014 09:50 AM, Robert Moskowitz issued this missive:
>>>> This is from a Fedora 20 client testing to a Centos 6.5 server.
>>>>
>>>> I can do a ping6 with no problems, but I cannot 'ssh -6' to the server
>>>> (ssh -4 works).  I have reason to suspect the challenge is in my PPPoE
>>>> link with a restricted MTU size that v6's PMTU is not working right 
>>>> with.
>>>>
>>>> So my question is:  Is there a way to specify the MTU size for things
>>>> like ssh (and http) to use?
>>>
>>> The odds are that your PPoE stuff has problems with IPV6 addressing (as
>>> many things do). I really doubt the MTU has anything to do with it
>>> since MTU sets the maximum size of a packet and has nothing to do with
>>> the addressing mechanisms. You could have a router that doesn't like
>>> big packets, but that would affect both IPV4 and IPV6.
>>
>> ping6 works in both directions no problem.  Addressing is right.  I 
>> actually
>> have my own /48 allocation here.
>>
>> It seems to be something with the firewall.
>>
>>
> You can set the myu using the route command (or ip, if that's what you 
> know). The option is mss, used to set the payload size, when mtu 
> discovery doesn't work due to firewall. See 'man route' mss section 
> for some discussion.
>

AH, I was looking in the wrong man pages.  Thanks.  Need to know this 
for the future.


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