{"id":17,"date":"2018-09-20T21:25:14","date_gmt":"2018-09-21T04:25:14","guid":{"rendered":"http:\/\/chucko.com\/blog\/?p=17"},"modified":"2020-10-29T23:39:10","modified_gmt":"2020-10-30T06:39:10","slug":"an-ipv6-cheat-sheet-for-folks-familiar-with-ipv4","status":"publish","type":"post","link":"http:\/\/chucko.com\/blog\/2018\/09\/20\/an-ipv6-cheat-sheet-for-folks-familiar-with-ipv4\/","title":{"rendered":"An IPv6 cheat sheet for folks familiar with IPv4"},"content":{"rendered":"

In the course of setting up a new home router based on pfSense<\/a>, I decided to wade into the IPv6 waters. I couldn’t find the kind of short, pithy information I was looking for. So here’s what I think is important to know. It assumes the reader knows what an RFC is and where to find them<\/a>, and has a passing familiarity with IPv4.<\/p>\n

I plan to update this as I learn more. Links to the relevant RFCs and standards will be added, eventually. Comments and corrections are welcomed.<\/p>\n

Addressing<\/h2>\n

128 bits total, a huge expansion from IPv4’s 32. We’ll never need to expand addressing again. (Never say never – address allocation grows to fill the available space, a corollary of Parkinson’s Law.)<\/p>\n

Fully specified format is 32 hex digits, separated by colons every 4 digits. Leading zeroes in a group can be omitted. E.g.<\/p>\n

1234:5678:9ABC:DEF0:0FED:CBA9:8765:4321<\/pre>\n
Groups of all zeroes can be elided, but only once per address. Anywhere you see double colons, imagine a bunch of zeroes between them. This convention makes it a little easier to deal with the 128 bit format. Examples below.<\/p>\n
Networks or address ranges are specified with a slash and the number of prefix bits,\u00a0e.g. the above address is routed to the network<\/p>\n
1234:5678:9ABC:DEF0::\/64<\/pre>\n
Interpretation varies by purpose. More below.<\/p>\n
Wait a minute… HOW MANY addresses per interface?<\/h3>\n
Typically two or more. And they serve different purposes.<\/p>\n
All interfaces must have a link-local address (see below). This is used between neighbors on the network segment, and by the router(s). This cannot be routed to from another network segment, so will never be seen outside the local network segment. Link-local addresses always start with\u00a0FE80:<\/strong>.<\/p>\n
Interfaces may also have a\u00a0secured routable address, and a temporary one as\u00a0well. These can be visible to the world.<\/p>\n
A network can have more than one prefix\/subnet pair. (One example being a network served by multiple ISPs for redundancy.) In this case an interface can have multiple global addresses, one or more per prefix\/subnet.<\/p>\n
On my Mac, ‘ifconfig en0’ shows 3 addresses:<\/p>\n