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Message 31 of 57

Re: How do I re-enable IPv6 on my HH6?

@smf22: I think perhaps I didn't understand your reply then. You wrote:

> "If I leave the Ubiquiti running it simply renews the lease after 7 days as per the T1 timer in the DHCPv6 PD reply, and the prefix doesn't change. If I manually renew the lease it actually performs a DHCPv6 release and immediate renew, but again I'm not seeing a change. I think the change only comes after a reboot of the router, but I need to verify that."

I understood that to mean that despite lease expiry and renewal, it was giving you the same IPv6 prefix as before. From what you wrote, nothing short of a CPE reboot forces address reassignment for you. (This would make sense, since all TCP sessions and firewall statefulness are lost on reboot, so at least on the hub there is nothing left relying on a previous source endpoint that will break on IP change.)

But I guess that's not what you meant?

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Message 32 of 57

Re: How do I re-enable IPv6 on my HH6?

@smf22

For clarification most of the IP changes were due to my intervention.

From 6 December to 14 February inclusive, the IP change was down to me removing the FritzBox from the line to test other hardware.  Either 29 November or 2 October were down to a BT network fault, can't remember which one.  So we're down to 3 BT initiated changes over the period 25 June to 21 February, so not as bad as it may look.

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Message 33 of 57

Re: How do I re-enable IPv6 on my HH6?

@MorgaineD: No you understood correctly. Periodic lease renewal works fine and I maintain the same address, but seem to get a new address when the router is rebooted.

 

I checked the DHCP Unique Identifier (DUID) sent before and after a reboot and this doesn't change, so the upstream delegating router / DHCPv6 server should be able to uniquely identify the client and assign the same prefix.

 

What I can see when my router reboots is that it sends a DHCPv6 Release, and so presumably the BT delegating router puts the prefix back in the pool never to be seen by my router again.

 

@Liam_: It's not bad, but it's not great. At the end of the day it means that despite there being no shortage of addresses, we'll still have to run dynamic DNS for any services at home that we want to access when out and about.

 

Regards

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Message 34 of 57

Re: How do I re-enable IPv6 on my HH6?

@smf22: Well the simple answer is, don't reboot the CPE. 😛

 

None of my equipment here gets power cycled except on power failure, and the comms equipment not even then because it's on a dedicated comms UPS.  If BT's IPv6 is as well behaved as you describe then I'm looking forward to saying very nice things about it! 😄

 

Conversely, I will not be saying nice things if open TCP sessions are broken because the prefix of their source address has unilaterally been changed by some ISP that thinks IPv6 has the same need for address sharing as IPv4.  Open TCP streams stuck in limbo is not merely an annoyance, it's an absolute fault in the TCP/IP networking infrastructure, and never under any circumstances is it operationally normal.

 

I expect that such worries won't actually materialize.  Your observations suggest that all is (fairly) well.

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Message 35 of 57

Re: How do I re-enable IPv6 on my HH6?

I generally don't reboot the CPE.... unless as I've been doing since getting IPv6, I'm having a play to understand it better. That's (one) of the great things about third party routers; I get to choose when it reboots Smiley Wink

 

BT seem to have a done a good job with IPv6, at least in my 'neck of the woods'. I first got it running back October '16 on my router and it's been running solid ever since.

 

To your point "will not be saying nice things if open TCP sessions are broken because the prefix of their source address has unilaterally been changed", surely that's exactly what's going to happen.

 

If I open an SSH session to my web server in France, and then reset the CPE, the prefix delegated to the CPE upon reboot will be different. The hosts on my LAN will know that as they'll receive an IPv6 Router Advertisement adverting the new prefix, but my web server will have a TCP session to the client on the old prefix. TCP broken Smiley Mad

 

 

Regards

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Message 36 of 57

Re: How do I re-enable IPv6 on my HH6?

I've been looking back through various print-outs I made which show the prefix I was allocated at various dates. Not very comprehensive but they show:

 

- the prefix I had (on my HH6) on 22 October 2016 seems to have remained unchanged until I installed my VR600 on 9 December, when the last 2 hex digits changed. (I've no idea how long I'd had it before 22 October.)

 

- that prefix seems to have remained unchanged until I lost IPv6 and temporarily reinstalled my HH6 on 16 January to see if that still had IPv6 (interestingly, it did), getting a new prefix with differences in the latter 32 bits.

 

- my VR600 was connecting with IPv6 again within 3 days but I didn't note the prefix until 24 January, when the last 2 hex digits had changed from 16 January.

 

- my current prefix (26 February) is unchanged from what it was on 24 January.

 

I'm now checking the prefix each day so I'll see how long this one lasts; but my experience to date seems to suggest that prefixes are reasonably sticky (apart from when rebooting or switching routers)..

 

p

 

 

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Message 37 of 57

Re: How do I re-enable IPv6 on my HH6?

See if this throws any light on the issue, between  25 June and 23 September there were 14 reports of IP renewal from the router all returning the same prefix of  2a00:23c0:c780:200:

 

During that time frame no changes were made to the router so only one was mentioned in that list seeing as the prefix wasn't changed.  Over the same period the IPv4 address changed 5 times.  Presumably down to lease renewal of IPv4 by BT servers.

I agree that it's silly having IPv6 dynamic, static would make things much simpler for both customers and ISPs.

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Message 38 of 57

Re: How do I re-enable IPv6 on my HH6?

@smf22writes:

 

> "If I open an SSH session to my web server in France, and then reset the CPE, the prefix delegated to the CPE upon reboot will be different. The hosts on my LAN will know that as they'll receive an IPv6 Router Advertisement adverting the new prefix, but my web server will have a TCP session to the client on the old prefix. TCP broken Smiley Mad"

 

Yeah, but in that scenario it's you who reset the CPE and broke TCP.  Please extend hand while I go fetch the ruler. 😛

 

When we break TCP ourselves we can't really complain, although it may cost us a round of drinks and sniggers from our friends.  When the ISP does it, that's loss of service for customers and rising support costs for the ISP.

 

Happily, the evidence I'm hearing in this short thread is quite the opposite, ie. BT is being sensible on IPv6.

 

This is an excellent parameter for which to be gathering stats automatically.

 

/me waves at the HH5 in encouragement.

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Message 39 of 57

Re: How do I re-enable IPv6 on my HH6?


@MorgaineD wrote:

@smf22writes:

 

> "If I open an SSH session to my web server in France, and then reset the CPE, the prefix delegated to the CPE upon reboot will be different. The hosts on my LAN will know that as they'll receive an IPv6 Router Advertisement adverting the new prefix, but my web server will have a TCP session to the client on the old prefix. TCP broken Smiley Mad"

 

Yeah, but in that scenario it's you who reset the CPE and broke TCP.  Please extend hand while I go fetch the ruler. 😛 

 


Hand extended... though not sure that's allowed in this day and age Smiley Sad

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Message 40 of 57

Re: How do I re-enable IPv6 on my HH6?

It's a core concept in engineering, negative feedback.
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