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[RFC] peer discovery with mDNS #80

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merged 14 commits into from
May 6, 2019
Merged

[RFC] peer discovery with mDNS #80

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a4626ef
feat: initial description of peer discovery with MDNS
richardschneider Jul 23, 2018
9e0e1f5
fix: grammar
richardschneider Jul 23, 2018
154424f
fix: typos
richardschneider Jul 23, 2018
b2c450e
docs: multiaddress
richardschneider Jul 25, 2018
105fd2b
fix: '_ipfs' => '_p2p'
richardschneider Jul 27, 2018
a9c587c
fix: use TXT dnsaddr for multi address
richardschneider Jul 27, 2018
2e0219a
feat: open issues
richardschneider Jul 27, 2018
8cc1297
fix: names are case insensitive
richardschneider Sep 13, 2018
53d9faf
doc: long peer names
richardschneider Oct 11, 2018
409c019
docs: link to discovery/mdns.md
richardschneider Oct 11, 2018
59e0793
docs: worked example
richardschneider Oct 11, 2018
2f3e55d
docs: few edits to the structure
daviddias Oct 12, 2018
479f07c
editorial refinements.
raulk Apr 24, 2019
4c5a459
feat: private networks
richardschneider May 5, 2019
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27 changes: 11 additions & 16 deletions discovery/mdns.md
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Expand Up @@ -14,12 +14,11 @@ As responses come in, the peer adds the other peers information into is local da

`service-name` is the DNS-SD service name for all peers. It is defined as `_p2p._udp.local`.

`host-name` is the name of the peer. It is derived from the peer's ID and `p2p.local`, for example
`Qmid.p2p.local`.
`host-name` is the fully qualified name of the peer. It is derived from the peer's name and `p2p.local`.

`peer-id` is the ID of the peer. It normally is the base-58 enconding of the hash of the peer's public key.
`peer-name` is the case-insenstive ID of the peer and less than 64 characters. It is normally is the base-32 encoding of peer's ID.
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@lidel lidel Sep 17, 2018 •
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I guess until ipfs/kubo#5287 is solved this would require apps to do a manual step of converting back to Base58, yes?

peer-name is just a unique name, we should not assume it's the peer id. The dnsaddr ends with the peer ID.

What if PeerID is longer than 64 characters? Should we split after 63 characters like noted in ipfs/in-web-browsers#89 ?

I think Workaround A: Split at 63rd character makes sense.

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`port` is a port that the peer listens on. Normally 4001.
Note that all names are case insensitive.

## Peer Discovery

Expand All @@ -28,22 +27,22 @@ As responses come in, the peer adds the other peers information into is local da
To find all peers, a DNS message is sent with the question `_p2p._udp.local PTR`.
Peers will then start responding with their details.

Note that a peer must respond to it's own query. Thus allows other peers to passively discover it.
Note that a peer must respond to it's own query. This allows other peers to passively discover it.

### Response

On receipt of a `find all peers` query, a peer sends a DNS response message (QR = 1) that contains
the **answer**

<service-name> PTR <peer-id>.<service-name>
<service-name> PTR <peer-name>.<service-name>

The **additional records** of the response contain the peer's discovery details

<peer-id>.<service-name> TXT "dnsaddr=..."
<peer-name>.<service-name> TXT "dnsaddr=..."

The TXT record contains the multiaddresses that the peer is listening on. Each multiaddress
is a TXT attribute with the form `dnsaddr=/ip4/.../tcp/.../p2p/QmId`. Multiple `dnsaddr` attributes
are expected.
is a TXT attribute with the form `dnsaddr=.../p2p/QmId`. Multiple `dnsaddr` attributes
and/or TXT records are allowed.

## DNS Service Discovery

Expand All @@ -63,26 +62,22 @@ A peer responds with the answer

On receipt of a `find all peers` query, the following **additional records** should be included

<peer-id>.<service-name> SRV ... <port> <host-name>
<peer-name>.<service-name> SRV ... <host-name>
<host-name> A <ipv4 address>
<host-name> AAAA <ipv6 address>

If a peer is listening on multiple ports, it should respond with multiple `SRV` records for each
port it is listening on.

### Gotchas

Many existing tools ignore the Additional Records and always send individual queries for the
peer's discovery details. To accomodate this, a peer should respond to the following queries:

- `<peer-id>.<service-name> SRV`
- `<peer-id>.<service-name> TXT`
- `<peer-name>.<service-name> SRV`
- `<peer-name>.<service-name> TXT`
- `<host-name> A`
- `<host-name> AAAA`

## Issues

- like urls, dns names are case insensitive. A `peer-id` is base58btc encoded and is case sensitive.
- MDNS requires link local addresses. Loopback and "nat busting" addresses should not sent and must
be ignored on receipt?

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