IPv6 mtu restriction

[Bill Davidsen]

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.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot