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.

Packets are sent to IP addresses

lookup AAAA

Ask a resolver which IPv6 address this name stands for.

Your computer cannot send a packet to a name. Every time you use a domain name, it is resolved into an IP address.

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.

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.

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.

A prefix is a range of addresses

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.

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.

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.

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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