Sloved - Re: IPv6 mtu restriction

[Robert Moskowitz]

On 03/27/2014 03:40 PM, poma wrote:
> On 27.03.2014 20:35, Robert Moskowitz wrote:
>> On 03/27/2014 12:50 PM, Robert Moskowitz wrote:
>>> 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?
>> I was told that:
>>
>> To figure out where I could put new MTU values:
>> “find /sys |grep mtu”
>>
>> To set the MTU for my eth0, as root:
>> “echo 1300 > /sys/devices/pci0000:00/0000:00:03.0/0000:02:00.0/net/eth0/mtu”
>>
>> "ifconfig eth0" reports an MTU of 1300 now.
>>
>>
>> And this works.  But it is not my problem.  Still not getting a TCP connection.  Going to have to check with wireshark.  Maybe it will help me...
>>
> Considering how much data you've provided us. :)

I was told elsewhere that my ipv6 problem was an mtu path discovery 
problem.  Try forcing my mtu so that it will get through whatever path 
(claim PPPoE link is the problem).  So, all I was asking was how to set 
the mtu for a tcp connection.  I asked here and on the list where I was 
testing the ipv6 app.  There someone said, not be app, but by interface, 
and showed how he did it.  So that is the story to now.  But a 1300 mtu 
still does not work.  So fire up wireshark.  I think it is a firewall 
problem.  SO I will go away again and look at the firewall.....