ferrix/slides/sections/01-resources.md

Internet Numbering Resources

Notes: Before we look at what's going on in the internet, let's refresh on how the Internet is even addressed.

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Packets are sent to IP addresses

lookup AAAA

Ask a resolver which IPv6 address this name stands for.

IP packets are sent to IP addresses, not domain names. Every time you use a domain name, it is resolved into an IP address via DNS.

Notes: Live: type a few names the students use. ethz.ch has an AAAA record; github.com has none (only A), which shows that the two address families are separate. The answer comes from Google Public DNS over HTTPS (dns.google), so it needs the lecture-hall network.

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Who does the address belong to?

whois

Paste the address from the last slide.

The inet6num says who was assigned the block; the route6 says which AS is allowed to originate it.

Notes: Paste the AAAA answer from the previous slide. ETH's /48 is ASSIGNED PI (provider independent, sponsored by SWITCH) and its route6 names AS559, SWITCH. Try 2a0d:d741:1::1 as well: the lab prefix, origin AS210036. The box takes AS numbers too (AS559). Same source as whois -h whois.ripe.net, over the database's REST API.

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An IPv6 address is 128 bits

2001:0db8:0001:0000:0000:0000:0000:0001     eight groups of 16 bits, in hex
2001:db8:1:0:0:0:0:1                        drop leading zeros in a group
2001:db8:1::1                               one run of zero groups becomes ::

:: may appear once, or the address would be ambiguous. 2001:db8::/32 is reserved for documentation, so it never appears on the real Internet.

Notes: Ask: why only once? Because 2001::1::1 could put the zeros in several places. 2001:db8::/32 is RFC 3849: set aside for examples, never routed.

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A prefix is a range of addresses

In BGP, the control plane for the internet, it's not viable to talk about single addresses, so we use prefix ranges.

Notes: Live. Drag the slider: the fixed part grows and the range shrinks by half per bit. Try /47 or /50 to see a hex digit split in two. The three rows above the bar are three of the shorter prefixes that contain it, with its position and share in each: there is no such thing as "the" parent prefix, only whatever someone chose to allocate from. 2^80 addresses in one /48, about 1.2 million billion billion. The /n is a count of leading bits, nothing more.

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The global IPv6 address space

Notes: Not to scale: a /64 is 2^-64 of the space. Only the first ring matters for routing; the others are how the space is handed down, which is next.

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Who hands out the addresses

Notes:

• The Internet Assigned Numbers Authority comes up with allocations of IP addresses from the global space
• Blocks are assigned to Regional Internet Registries (RIRs), which allocate them to Local Internet Registries (LIRs), who assign to end users
• The RIPE lookup two slides back showed exactly this chain: ETH's /48 is ASSIGNED PI, sponsored by SWITCH (the LIR), registered at RIPE NCC (the RIR). Nobody owns addresses; they are registered to you.

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AS numbers

• Used to identify networks under a single oeprator, and required for exchanging BGP traffic
• Managed by IANA and the RIRs
• 16 bits at first: 1 to 65535
• 32 bits since RFC 6793: up to 4294967295
• In order to have a smooth transition, AS23456 is used as a placeholder when the AS number is > 16 bits
• 32 bit AS numbers are then exchanged using a BGP capability message to be backwards compatible
• Private use: 64512–65534 and 4200000000–4294967294

AS numbers come down the same chain: IANA to the RIRs, an RIR to whoever runs a network. The lab daemon is AS4200000001, a private one, stripped before the Internet sees your route.

Notes: Nobody "owns" numbers or addresses; they are registered to you. RFC 6996 reserves the private ranges. The upstream router removes the private AS from the path, so the origin everybody else sees is AS210036.

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Handout Part 1