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reactors/pex: specify hash function (#94)

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https://github.com/tendermint/tendermint/pull/4810/files
This commit is contained in:
Anton Kaliaev
2020-05-08 22:15:08 +04:00
committed by GitHub
parent c3cd54a8e0
commit 3c27335db3
1 changed files with 29 additions and 5 deletions
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34
spec/reactors/pex/pex.md
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@@ -33,8 +33,8 @@ connections die, or we fail to dial, we will redial every 5s for a few minutes,
then switch to an exponential backoff schedule, and after about a day of
trying, stop dialing the peer. This behavior is when `persistent_peers_max_dial_period` is configured to zero.
But If `persistent_peers_max_dial_period` is set greater than zero, terms between each dial to each persistent peer
will not exceed `persistent_peers_max_dial_period` during exponential backoff.
But If `persistent_peers_max_dial_period` is set greater than zero, terms between each dial to each persistent peer
will not exceed `persistent_peers_max_dial_period` during exponential backoff.
Therefore, `dial_period` = min(`persistent_peers_max_dial_period`, `exponential_backoff_dial_period`)
and we keep trying again regardless of `maxAttemptsToDial`
@@ -54,9 +54,33 @@ Peers are added to the address book from the PEX when they first connect to us o
when we hear about them from other peers.
The address book is arranged in sets of buckets, and distinguishes between
vetted (old) and unvetted (new) peers. It keeps different sets of buckets for vetted and
unvetted peers. Buckets provide randomization over peer selection. Peers are put
in buckets according to their IP groups.
vetted (old) and unvetted (new) peers. It keeps different sets of buckets for
vetted and unvetted peers. Buckets provide randomization over peer selection.
Peers are put in buckets according to their IP groups.
IP group can be an IP block (e.g. `/16` for IPv4, `/32` for IPv6) or `local`
for local addresses or `unroutable` for unroutable addresses. Each group has a
limited number of buckets to prevent DoS attacks coming from that group (e.g.
an attacker buying a `/16` block of IPs and launching a DoS attack).
[highwayhash](https://arxiv.org/abs/1612.06257) is used as a hashing function
when calculating a bucket.
When placing a peer into a new bucket:
```
hash(key + sourcegroup + int64(hash(key + group + sourcegroup)) % bucket_per_group) % num_new_buckets
```
When placing a peer into an old bucket:
```
hash(key + group + int64(hash(key + addr)) % buckets_per_group) % num_old_buckets
```
where `key` - random 24 HEX string, `group` - IP group of the peer (e.g. `/16`),
`sourcegroup` - IP group of the sender (peer who sent us this address) (e.g. `/16`),
`addr` - string representation of the peer's address (e.g. `174.11.10.2:26656`).
A vetted peer can only be in one bucket. An unvetted peer can be in multiple buckets, and
each instance of the peer can have a different IP:PORT.