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uk.telecom.broadband (UK broadband) (uk.telecom.broadband) Discussion of broadband services, technology and equipment as provided in the UK. Discussions of specific services based on ADSL, cable modems or other broadband technology are also on-topic. Advertising is not allowed.

Request for someone with Zen and IPv6



 
 
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  #21  
Old April 3rd 20, 11:41 AM posted to uk.telecom.broadband
Brian Gregory[_2_]
external usenet poster
 
Posts: 86
Default Request for someone with Zen and IPv6

On 03/04/2020 02:45, Andy Burns wrote:
Richard Tobin wrote:

For some reason typing that made me consider the possibility that it
was an MTU problem, and bingo! setting the MTU to 1492 or less on the
client machine makes it work.* I notice that 1492 is the MTU of the
PPPoE interface of the router.

I'll look into it further tomorrow.


See if you have an option for baby-jumbo packets, I need that on my
PPPoE interface with plusnet (not IPv6 related).


A quick Google search suggests many people cannot find a way to make
pfSense do this

An alternative fix for the problem /might/ be to enable MSS clamping if
that option is available and set it to 1452 for IPv4 and 1432 for IPv6.

--
Brian Gregory (in England).
  #22  
Old April 3rd 20, 12:28 PM posted to uk.telecom.broadband
Andy Burns[_5_]
external usenet poster
 
Posts: 546
Default Request for someone with Zen and IPv6

Brian Gregory wrote:

Andy Burns wrote:

See if you have an option for baby-jumbo packets


A quick Google search suggests many people cannot find a way to make
pfSense do this


sorry I can't help, I'm on openWRT.

An alternative fix for the problem /might/ be to enable MSS clamping if
that option is available and set it to 1452 for IPv4 and 1432 for IPv6.


Any reason path MTU discovery can't work it out for itself? If it were
IPv4 I'd be wondering about ICMP fragmentation-needed packets going
missing, it seems rfc8201 is "more complicated" ...
  #23  
Old April 3rd 20, 05:11 PM posted to uk.telecom.broadband
Brian Gregory[_2_]
external usenet poster
 
Posts: 86
Default Request for someone with Zen and IPv6

On 03/04/2020 12:28, Andy Burns wrote:
Brian Gregory wrote:

Andy Burns wrote:

See if you have an option for baby-jumbo packets


A quick Google search suggests many people cannot find a way to make
pfSense do this


sorry I can't help, I'm on openWRT.

An alternative fix for the problem /might/ be to enable MSS clamping
if that option is available and set it to 1452 for IPv4 and 1432 for
IPv6.


Any reason path MTU discovery can't work it out for itself?* If it were
IPv4 I'd be wondering about ICMP fragmentation-needed packets going
missing, it seems rfc8201 is "more complicated" ...


It should be automatic and from Richard says I presume it is working for
most IPv6 sites, just not this one. So I presume something is wrongly
configured at the server end with this particular site. Setting up MSS
clamping in your router or gateway is something I've seen people suggest
helps when path MTU discovery isn't working correctly. Some people even
set it to lower values like 1412 and 1392 just to try and make sure that
no matter when is wrong at the remote end it will still work even if the
MTU is even more restricted at some point along the route.

--
Brian Gregory (in England).
  #24  
Old April 3rd 20, 08:04 PM posted to uk.telecom.broadband
grinch
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Posts: 99
Default Request for someone with Zen and IPv6

Evening Ladies and Gents ,just tried a simple test from my phone. I can
get to the site from the 3 data network ,but not the Zen network. Tried
twice and get the same result on both occasions.

  #25  
Old April 3rd 20, 09:12 PM posted to uk.telecom.broadband
Brian Gregory[_2_]
external usenet poster
 
Posts: 86
Default Request for someone with Zen and IPv6

On 03/04/2020 20:04, grinch wrote:
Evening Ladies and Gents ,just tried a simple test from my phone. I can
get to the site from the 3 data network ,but not the Zen network. Tried
twice and get the same result on both occasions.


Is your MTU below 1500 like Richard's?

--
Brian Gregory (in England).
  #26  
Old April 4th 20, 09:50 AM posted to uk.telecom.broadband
grinch
external usenet poster
 
Posts: 99
Default Request for someone with Zen and IPv6

On 03/04/2020 21:12, Brian Gregory wrote:
On 03/04/2020 20:04, grinch wrote:
Evening Ladies and Gents ,just tried a simple test from my phone. I
can get to the site from the 3 data network ,but not the Zen network.
Tried twice and get the same result on both occasions.


Is your MTU below 1500 like Richard's?


From my Cisco 867 routers config

ipv6 enable
ipv6 mtu 1492
!
interface Dialer0
mtu 1492
ip address negotiated

ip virtual-reassembly in
encapsulation ppp
ip tcp adjust-mss 1452



I should have added I can get to it via Zen's IPv4 ,works just fine if I
disable IPv6 on my PFsense firewall.

The above config is what Cisco recommend for dual stack, MTU wise. Also
anecdotal evidence after 20 years as a network engineer has told me that
an MTU of 1492 for PPP does not usually cause issues even when firewalls
block ICMP and break Path MTU. Please remember this is a rule of thumb
not a set in stone fact.

Most modern internet trunk links are some form/speed of Ethernet and an
MTU of less than 1500 should work,most of the time.

This explains the theory,that I cant be bothered typing out myself

https://www.sonicwall.com/support/kn...0505851231244/
  #27  
Old April 4th 20, 10:05 AM posted to uk.telecom.broadband
Andy Burns[_5_]
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Posts: 546
Default Request for someone with Zen and IPv6

grinch wrote:

Most modern internet trunk links are some form/speed of Ethernet and an
MTU of less than 1500 should work,most of the time.


But occasionally you find one server (like the NIH one?) that
inexplicably gets upset if it's not exactly 1500 bytes

Handy test site, I've only used it with IPv4, you can achieve the same
with ping -f (or -M do) and various -l (or -s) sizes

http://www.letmecheck.it/mtu-test.php
  #28  
Old April 4th 20, 11:45 AM posted to uk.telecom.broadband
grinch
external usenet poster
 
Posts: 99
Default Request for someone with Zen and IPv6

On 04/04/2020 10:05, Andy Burns wrote:
grinch wrote:

Most modern internet trunk links are some form/speed of Ethernet and
an MTU of less than 1500 should work,most of the time.


But occasionally you find one server (like the NIH one?) that
inexplicably gets upset if it's not exactly 1500 bytes

Handy test site, I've only used it with IPv4, you can achieve the same
with ping -f (or -M do) and various -l (or -s) sizes

http://www.letmecheck.it/mtu-test.php


Only problem with your theory is I can use the site via IPv4 no problem
at all IPv6 does not work at all.

My MTU settings are the same for both IP versions. Also I, for security
reasons, block incoming ICMP so no path mtu and don't see any issues
normally,even with IPv6. I have been like this for 3 years.

As MTU is a layer 2 why would you have different settings for different
layer 4 protocols? I'm sure its possible but why would you do it ?

I think this is an IPv6 ICMP required issue. I am going to have a play
this afternoon to prove or disprove my theory,I am hardly busy at the
moment for obvious reasons.
  #29  
Old April 4th 20, 12:04 PM posted to uk.telecom.broadband
Richard Tobin
external usenet poster
 
Posts: 295
Default Request for someone with Zen and IPv6

In article ,
grinch wrote:

Only problem with your theory is I can use the site via IPv4 no problem
at all IPv6 does not work at all.


Well that's to be expected. IPv4 will fragment and reassemble
packets; IPv6 doesn't do that because v6 hosts are supposed to
determine the MTU and not exceed it.

-- Richard
  #30  
Old April 4th 20, 01:45 PM posted to uk.telecom.broadband
grinch
external usenet poster
 
Posts: 99
Default Request for someone with Zen and IPv6

On 04/04/2020 12:04, Richard Tobin wrote:
In article ,
grinch wrote:

Only problem with your theory is I can use the site via IPv4 no problem
at all IPv6 does not work at all.


Well that's to be expected. IPv4 will fragment and reassemble
packets; IPv6 doesn't do that because v6 hosts are supposed to
determine the MTU and not exceed it.

-- Richard

Agreed ,but with such a small MTU such as mine 1492 I would have thought
it would not be an issue ,clearly I was wrong. It does not normally
cause issue but this is the exception which proves the rule as the
saying goes.

As an experiment I created an IPv6 WAN to LAN rule for all ICMP and
turned of the anti ICMP ACL on my router temporarily. Made no difference
at all so put it back on. Proved I could ping the router using v4 from
the 3 data network which is normally blocked. I don't get v6 from 3 so
not a proper test really.

I know that my network setup is wrong but it keeps some of the hackers
at bay, but I have seen the IPv6 address in my firewalls blocked logs,
even the hackers are upgrading to v6.
 




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