Ipv6 is a “new world” that challenges us to break our telecom paradigms at all moments. We are so used to IPv4, I say at times even addicted, that we need to free ourselves from some concepts deeply fixed in our memory to avoid problems with our IPv6 clients.
To recapitulate a little, when a PPPoE client router establishes a v4 session, it receives the IP to use in its WAN interface and the CPE itself oversees performing NAT from an internal range that is not known of the operator, not requiring any changes in the clients on the internal network, making the IP exchange "transparent".
For this reason, we are used to not caring if the client uses dynamic IP on its v4 connection.
Now let's think about IPv6. When the client's router connects to PPPoE in v6, it needs to receive via DHCPv6, or generate in SLAAC, a Unique Global for WAN, and via DHCPv6 a Prefix-Delegation for LAN, because NAT will no longer be performed on the client router and clients from LAN needed to receive or generate their own Unique Global.
Problem:
By default, even in v6, the NAS maintains both WAN IPv6 and Prefix-Delegation in dynamic mode, which causes the two to change whenever a PPPoE session reconnects.
The exchange of IPv6 from the WAN does not cause any adverse effect, as it happens with IPv4. Our problem is in changing the Prefix-Delegation because it causes all internal clients of this client router to perform the RS / RA process again to configure the new Global Exclusive IP belonging to the new range that has been designated.
This process causes a much greater interruption in access than just the PPPoE reconnection process, which is already slow due to the nature of the protocol.
Solution:
The solution is very simple, we keep the IPv6 of the WAN dynamic and we configure the NAS to fix the clients' PD in its table, making the v6 behave with the same reconnection speed observed in v4.
For this, on PD pool needs to configure the command below:
#
ipv6 prefix xpto_lan delegation
prefix 2001:DB8:CA00::/40 delegating-prefix-length 56
reserved prefix mac lease
#
This causes the first connection to be registered, through the MAC of the client router, which the PD was assigned to connect to, and the range is no longer changed in case of reconnection.
You can learn more on https://support.huawei.com/hedex/hdx.do?docid=EDOC1100169782&id=EN-US_CLIREF_0314069513&lang=en
I ask you to comment on your experience with what has been described so that we can build more knowledge for the community.
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