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I read on a website: " link local addresses use the address block of Fe80::/10 (from FE80:: to FE80:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF). However, the standard states that the 54 bits after FE80/10 should all be 0. so we won't see link local addresses begining with FE9, FEA or FEB. only FE8 " I don't get it. if all the 54bits after /10 were set to 0s then We cannot have LLA address like this FE80:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF because the first 54 bits after the /10 should be set to 0 as they stated, so the correct form of the address should be FE80:0000:0000:0000:FFFF:FFFF:FFFF:FFFF . I'm I missing something simple?

2 Answers 2

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As per RFC4291 [2.5.6]:

|   10     |
|  bits    |         54 bits         |          64 bits           |
+----------+-------------------------+----------------------------+
|1111111010|           0             |       interface ID         |
+----------+-------------------------+----------------------------+

The first 10 bits are the global routing prefix. The next 54 bits are the subnet ID, which is all zero.

3

fe80::/10 is the prefix reserved for link-local addresses but only the single subnet fe80::/64 is actually allocated for proper use.

We cannot have LLA address like this FE80:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF because the first 54 bits after the /10 should be set to 0 as they stated, so the correct form of the address should be FE80:0000:0000:0000:FFFF:FFFF:FFFF:FFFF.

That is correct.

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