dhcp ipv6 unexpected subnetmask /128

Oskar Berggren oskar.berggren at gmail.com
Wed May 2 13:24:29 UTC 2012

2012/5/2 MAYER Hans <mayer at iiasa.ac.at>:

> In both cases a /128 subnet mask.
> Why /128 ?
> I can ping the link-local address of the other site in each case but I cannot ping the official 2001:... address. I can ping the own IPv6 address but not the other as it is /128 and therefore not accessible within the network. I would expect that the dhcp daemon gives a /64 address as defined in the 'subnet6' declaration.

You expect wrong. DHCPv6 provides no information on the prefix length
or its on-link status - only the host adress. Prefix length and
on-link status, as well as suitable gateway adresses are published
using router advertisements. When the clients receive RAs they should
generate suitable routes, regardless of the adress assigned via

To put it another way: assigning adresses via DHCPv6 does not mean
that you can avoid sending RAs from the router, to the best of my


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