feat: content routing overview (#292)

content/concepts/content-routing/overview.md

@@ -4,4 +4,58 @@ description: "Learn about Noise in libp2p."
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-Coming soon!
+## Overview
+
+The most widely used method for accessing data today is via location addressing,
+where the desired content can be located by its name on a specific server.
+This makes routing simple, as the server information is readily available.
+For example, the URL `example.com/cat.jpg` informs us that the server with
+the domain name `example.com` has a file named `cat.jpg`.
+
+However, with content-addressed data the content itself serves as the address.
+Routing becomes a challenge since we only know what the data looks like, not who
+has it.  This is where content routing comes into play, giving us a way to
+figure out who has the content and how we can communicate with them.
+
+Content routing is the abstract process of identifying a specific peer that
+holds certain data and the means to connect to them within a P2P network.
+
+One of the main challenges of content routing in P2P networks is scalability.
+As the number of peers increases, it becomes more difficult to efficiently find
+and retrieve the desired content due to the larger number of potential sources.
+
+In general, specific characteristics of P2P networks complicate this process, including:
+
+- The lack of universal orchestration that a central server can provide when
+  querying and retrieving content.
+- Not having a central directory that contains information about how to reach
+  every peer in the network.
+- The presence of high node churn.
+- Creating a resilient, scalable, and optimal routing protocol resistant to
+  Sybil attacks.
+- Forward compatibility.
+
+Content routing protocols have to deal with these problems while still providing
+a way to find out who has the requested data.
+
+## Content Routing in libp2p
+
+```go
+interface ContentRouting {
+ Provide(CID, bool) error
+ FindProviders(CID) [Multiaddr]
+}
+```
+
+In libp2p, content routing is based on a [Distributed Hash Table (DHT) called
+Kademlia](../introduction/protocols/kaddht.md). At a high level, the DHT stores
+the content ID (CID) as a key and the value is the list of peers who can provide
+it. The DHT handle spreading the load across the network and building in resiliency.
+
+More information on Kademlia can be found in the [Kad-DHT content routing document](kaddht.md).
+
+{{< alert icon="" context="note">}}
+While there are different design approaches for a content routing protocol, such as
+Kademlia DHT, DNS, and BitTorrent trackers, libp2p provides a Kademlia
+implementation that applications can use to find and provide content.
+{{< /alert >}}