# 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
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.
---
## Who does the address belong to?
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
```text
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
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.
---
## 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.
---
## Handout Part 1