HubDiscovery » History » Revision 7
Revision 6 (Alex Afanasyev, 03/05/2014 08:54 AM) → Revision 7/8 (Alex Afanasyev, 03/05/2014 08:55 AM)
# 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`. For example
_ndn._udp.afanasev.cs.ucla.edu.ndn._homehub._autoconf.named-data.net _ndn._udp.afanasev.cs.ucla.edu._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.