On 5/3/20 17:47 , Alan White wrote:
> Folks
>
> I’m struggling to find the right syntax in the ISC dhclient and server for the following scenario, which I thought should be fairly common, but I’m new to ipv6 so maybe I’m about to find out it’s not a good use case.
>
> I have a dual homed host, the wlan interface is being allocated a global ipv6 address fine by the ISP’s router. The host also has a hardwired connection to a gigE switch which has a number of other single-homed hosts hanging off it. I would like the interfaces on all hosts on the private gigE switch to be allocated global IPv6 addresses. I’d like them to be on a dedicated subnet so I can discover them using link local multicasts. The hosts are all workers running an identical ubuntu image that will use SLAAC to generate an address from a DP, these have no embedded identity other than their mac address. I’m trying to treat them as cattle.
>
> ISP provides a /56 DP, leaving me with 8 bits for my own subnets. My understanding is I set up the client to request the DP with an IA that will become the subnet, eg an IA of 1 will result in the 8 bits after the /56 in the DP being set to 1, to extend the /56 to become a /64 with a subnet of 1.
>
> What I’d then like to do is advertise that /64 DP, ie with the locally unique subnet id of 1 on the hardwired link, so the other hosts can receive the prefix and generate ipv6 addresses.
>
> I’m trying to avoid hardcoding the DP, i.e. just take what’s delegated, and use it as the prefix for DHCP server on the other interface.
>
> Does it look like I’ve misunderstood how this should work, which would explain why I can’t find the right options to configure in the DHCP client and server on the dual homed host? Any and all help gratefully received.
It should be fairly simple to do what you want, but (at least a few years
ago when I last researched it, and I don't think it's changed since),
there's no automagic way to do that completely internal to dhclient.
You'll need to supply a hook script to set up the internal side according
to your local policies. Something like this:
https://gist.github.com/jayeye/689cb1de2275798659c58c62ab92cfaa should be a
good starting point. (disclaimer: not my code, but I've been using a mildly
customized variant of that for years with both ATT UVerse and Google Fiber)
HTH,
-e
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