Seeking clarifying information on RFC 4291 and link-local address format ...

[John Spence]

Reading RFC 4291, I am not 100% clear on the format for link-local addresses.  In some places the document specifies “fe80::/10”, which I read as “the first ten bits must be 1111 1110 10, the remaining 54 bits can be anything, up to the /64 bit boundary .  Later in the document I see this:   2.5.6.  Link-Local IPv6 Unicast Addresses      Link-Local addresses are for use on a single link.  Link-Local    addresses have the following format:      |   10     |    |  bits    |         54 bits         |          64 bits           |    +----------+-------------------------+----------------------------+    |1111111010|           0             |       interface ID         |   Which I read as “the first 64 bits are always fe80::”, but then I would think we’d write that as “fe80::/64”.   So, do those middle 54 bits have to be zero, or can they be anything?   Thanks for any insight.     John Spence, Command Information [EMAIL PROTECTED]

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