Tag Archives: IPv6 Prefix

DHCPv6 Prefix Delegation

DHCP/DHCPv6, IPv6, , , , , , ,

What is DHCPv6 Prefix Delegation? Coming from IPv4, you’re already familiar with DHCP (for IPv4) which hands out IPv4 addresses to clients. The same applies to (stateful) DHCPv6: it hands out IPv6 addresses to clients.

However, with IPv6 we’re heavily dealing with subnets rather than just single addresses. Again, you’re familiar with IPv4: For an IPv4-based ISP connection, you’re getting either a single public IPv4 address or a small subnet such as a /29, /28, or the like for your WAN interface. For an IPv6-based ISP connection, you’re getting a subnet which includes multiple unique subnets to be used for other layer 3 segments rather than a single address (with NAT on the CPE). This is where DHCPv6 prefix delegation (commonly abbreviated as DHCPv6-PD) kicks in: It hands out IPv6 subnets to routers.

Let’s have a closer look:

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#heiseshow: IPv6 setzt sich langsam durch – die wichtigsten Fragen

Conference Talks, Internet Access, IPv6, , , , , ,

Ich durfte zu Gast bei der #heiseshow zum Thema IPv6 sein. In Anlehnung an die Artikelserie über IPv6 in der c’t 7/2022, in der auch mein Artikel über die Vorteile von IPv6-Adressen erschienen ist, ging es bei diesem Video-Podcast um gängige Fragen zu IPv6 sowohl im Heimanwender- als auch im Enterprise-Segment. Ne knappe Stunde lief die Schose und ich empfand es als ziemlich kurzweilig. ;)

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SharkFest’18 Europe: Crash Course: IPv6 and Network Protocols

Conference Talks, IPv6, Routing, Switching, , , , , , ,

I did a session at SharkFest’18 Europe in Vienna with the title of “Crash Course: IPv6 and Network Protocols“. Since the presentation slides + audio were recorded you can listen to the talk, too. Here are some notes about the motivation for this session as well as feedback from the attendees.

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2001:db8::/32 in the Wild

Internet Access, IPv6, , , ,

If you have ever read some docs or RFCs about IPv6 you should be quite familiar with the 2001:db8::/32 “IPv6 Address Prefix Reserved for Documentation”, RFC 3849. This RFC clearly states how you should handle addresses within this range: “This assignment implies that IPv6 network operators should add this address prefix to the list of non-routeable IPv6 address space, and if packet filters are deployed, then this address prefix should be added to packet filters.”

I was interested whether those addresses are actually used in the Internet. For this purpose I analyzed my firewall logs for 6 months to get an idea. Though it was not that much, I actually got a couple of connections inbound and outbound (!) sourced or destined to those reserved IPv6 addresses.

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IPv6 Interface ID Structure

IPv6, Memorandum, , ,

While there are many approaches on how to structure your IPv6 prefix into /64 subnets (blogposts, books, talks) there are only a few hints what you can do with the other 64 bits of the addresses, namely the IPv6 interface identifier or IID. To my mind you can put some (but not too much) logic into those IIDs to a) have some structure for your addresses that b) helps you identifying those addresses when seeing them in logs or anywhere else. Hence it is easier for you to remember the IPv6 address behind a name (forward DNS) as well as the host when seeing the address (reverse DNS).

This post just shows the approach I am using in my lab. You might find it useful or you might disagree completely. Anyhow, feel free to comment your experiences or solutions for that. :D I am wondering why there isn’t much discussion about these IIDs at all. Maybe for some good reasons I am not seeing yet?

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