NFD

# NDN hub discovery procedure

When an end host starts up, or detects a change in its network environment, it MAY use this procedure to discover a local or home NDN router, in order to gain connectivity to [the NDN research testbed](http://named-data.net/ndn-testbed/).

## Overview

This procedure contains three methods to discover a NDN router:

1.  Look for a local NDN router by multicast.  

    This is useful in a home or small office network.

2.  Look for a local NDN router by DNS query with default suffix.  

    This allows network administrator to configure a NDN router for a large enterprise network.

3.  Connect to the home NDN router according to user certificate.  

    This ensures connectivity from anywhere.

## Stage 1: multicast discovery

### Request

The end host sends an Interest over a multicast face.

Interest Name is `/localhop/ndn-autoconf/hub`.

### Response

A producer app on the HUB answer this Interest with a Data packet that contains TLV-encoded `Uri` block.

The value of this block is the URI for the HUB, preferrably a UDP tunnel.

## Stage 2: DNS query with default suffix

### Request

The end host sends a DNS query that is equivalent to this command:

    dig +search +short +cmd +tries=2 +ndots=10 _ndn._udp srv

### Response

The DNS server should answer with an SRV record that contains the hostname and UDP port number of the NDN router.

## Stage 3: find home router

This stage assumes that user has configured default certificate using http://ndncert.named-data.net/ as described in http://redmine.named-data.net/attachments/download/23/CertificationArchitecture.pptx

### Request

The end host loads the default user identity (e.g., ``/ndn/edu/ucla/cs/afanasev``) and converts it to DNS format (see https://github.com/named-data/ndnx/blob/master/csrc/util/ndn-name-dnsifier.py as a reference implemenation).

(To get default identity: ``KeyChain::getDefaultIdentity()`` method in ndn-cpp-dev library.)

If either loading default user identity or converting to DNS format, the phase finishes with error code.

The end host sends a DNS query for an SRV record of name `_ndn._udp.` + user identity in DNS format + `_homehub._autoconf.named-data.net`.

### Response

The DNS server should answer with an SRV record that contains the hostname and UDP port number of the home NDN router of this user's site.

## Client procedure

1.  Send a multicast discovery Interest.

    If this Interest got answered, connect to the HUB and abort these steps.

2.  Send a DNS query with default suffix.

    If this query got answered, connect to the HUB and abort these steps.

3.  Extract the site-specific part from the default certificate of the user; fail if this cannot complete.

    Send a DNS query to find home HUB.

    If this query got answered, connect to the home HUB. Otherwise, fail.