openssl req error with DN having a / in it

[Robert Moskowitz <rgm@xxxxxxxxxxxxxxx>]

Developing saga on creating an intermediate CA cert with only CN and 
said CN should be:

CN=IPv6::2001:24:28:24/64

Note that / in CN that seems to be a challenge.

   commonName="/CN=IPv6::2001:24:28:24/64"
   DN=$commonName
   echo $DN

   openssl req -config $cadir/openssl-root.cnf\
       -key $dir/private/intermediate.key.pem \
       -keyform pem -outform $format -subj "$DN" -new\
       -out $dir/csr/intermediate.csr.pem

req: Hit end of string before finding the equals.
problems making Certificate Request

Then I tried:

   commonName="/CN=IPv6::2001:24:28:24//64"
   DN=$commonName
   echo $DN

guessing that / was acting as an escape designator, tried the command 
again and got the same

req: Hit end of string before finding the equals.
problems making Certificate Request

So how do I get that / into the CN?

thanks