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IPv6 prefix advertisement - prefix length error

regexaurus

I'm slowly becoming proficient uncomfortably familiar with IPv6, so the problem I'm reporting could well be due to a mistake on my part. I have Comcast Xfinity Internet at home with a basic cable modem; I can get the model # later if helpful. My Sophos UTM Home edition has its WAN interface configured for DHCP (Dynamic IP) and successfully acquires both IPv4 and IPv6 addressing information (address information in screenshots altered to protect the "innocent" [;)]).

Note the /128 IPv6 address that is assigned to the WAN interface. I think this is identical to the IPv4 parlance 192.168.1.1/32 to specify a single address. But I'm guessing the /128 notation may be related to my problem. Note the Delegated Prefix on the IPv6 > Global screen--I think this prefix is supplied by Comcast (WAN interface)...?

But when I try to add a Prefix Advertisement (IPv6 > Prefix Advertisement) using the WAN interface, when I click Save, I see an error indicating the prefix length of the interface must be /64. I'm guessing the problem is the /128 "prefix" for the IPv6 address assigned to the WAN interface. But I want to set up a prefix advertisement for the /64 delegated prefix.

Any tips / suggestions / help is welcome.

Thank you in advance!



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    OK, I think I figured it out. Using the MAC address for my Sophos UTM internal/LAN interface, I manually generated an EUI-64 address and prepended the 64-bit delegated prefix. I statically assigned the resulting 128-bit IPv6 address to my internal/LAN interface, with a netmask of 64. I then successfully created a Prefix Advertisement using the Internal/LAN interface and confirmed that an IPv6-ready client on my LAN used stateless address autoconfiguration to self-assign a global unicast address with the advertised prefix. A few basic tests succeeded:

    • Pinging the static global unicast IPv6 address assigned to the LAN interface of my Sophos UTM appliance, from an IPv6 test client on the LAN.
    • Pinging 2001:4860:4860::8888 (IPv6 address for a Google DNS server) from the test client.
    • Browsing to http://ipv6test.google.com

    Woot! [:D]

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