Subject: Scattered Name Service Disgregation
This text describes the Scattered Name Service Disgregation, an extension of the ANDNA protocol. It will be included in the final documentation, so feel free to correct it. But if you want to change the system here described, please contact us first.
The Scattered Name Service Disgregation is the ANDNA equivalent of the SRV Record of the Internet Domain Name System, which is defined here: http://www.ietf.org/rfc/rfc2782.txt For a brief explanation you can read: http://en.wikipedia.org/wiki/SRV_record
SNSD isn't the same of the "SRV Record", in fact, it has its own unique features.
With the SNSD it is possible to associate IPs and hostnames to another hostname. Each assigned record has a service number, in this way the IPs and hostnames which have the same service number are grouped in an array. In the resolution request the client will specify the service number too, therefore it will get the record of the specified service number which is associated to the hostname. Example:
The node X has registered the hostname "angelica". The default IP of "angelica" is 184.108.40.206. X associates the "depausceve" hostname to the `http' service number (80) of "angelica". X associates the "220.127.116.11" IP to the `ftp' service number (21) of "angelica".
When the node Y resolves normally "angelica", it gets 18.104.22.168, but when its web browser tries to resolve it, it asks for the record associated to the `http' service, therefore the resolution will return "depausceve". The browser will resolve "depausceve" and will finally contact the server. When the ftp client of Y will try to resolve "angelica", it will get the "22.214.171.124" IP. If Y tries to resolve a service which hasn't been associated to anything, it will get the mainip 126.96.36.199
The node associated to a SNSD record is called "SNSD node". In this example "depausceve" and 188.8.131.52 are SNSD nodes.
The node which registers the records and keeps the registration of the main hostname is always called "register node", but it can also be named "Zero SNSD node", in fact, it corresponds to the most general SNSD record: the service number 0.
Note that with the SNSD, the NTK_RFC 0004 will be completely deprecated.
Service, priority and weight number
The service number specifies the scope of a SNSD record. The IP associated to the service number `x' will be returned only to a resolution request which has the same service number.
A service number is the port number of a specific service. The port of the service can be retrieved from /etc/services.
The service number 0 corresponds to a normal ANDNA record. The relative IP will be returned to a general resolution request.
The SNSD record has also a priority number. This number specifies the priority of the record inside its service array. The client will contact first the SNSD nodes which have the higher priority, and only if they are unreachable, it will try to contact the other nodes which have a lower priority.
==== Weight ===
The weight number, associated to each SNSD record, is used when there are more than one records which have the same priority number. In this case, this is how the client chooses which record using to contact the servers:
The client asks ANDNA the resolution request and it gets, for example, 8 different records. The first record which will be used by the client is chosen in a pseudo-random manner: each record has a probability to be picked, which is proportional to its weight number, therefore the records with the heavier weight are more likely to be picked. Note that if the records have the same priority, then the choice is completely random.
It is also possible to use a weight equal to zero to disable a record.
The weight number has to be less than 128.
The registration method of a SNSD record is similar to that described in the NTK_RFC 0004.
It is possible to associate up to 16 records to a single hostname. The maximum number of total records which can be registered is 256.
The registration of the SNSD records is performed by the same register_node. The hash_node which receives the registration won't contact the counter_node, because the hostname is already registered and it doesn't need to verify anything about it. It has only to check the validity of the signature.
The register node can also choose to use an optional SNSD feature to be sure that a SNSD hostname is always associated to its trusted machine. In this case, the register_node needs the ANDNA pubkey of the SNSD node to send a periodical challenge to the node. If the node fails to reply, the register_node will send to ANDNA a delete request for the relative SNSD record.
The registration of SNSD records of hostnames which are only queued in the andna_queue is discarded.
Practically, the steps necessary to register a SNSD record are:
- Modify the /etc/netsukuku/snsd_nodes file.
register_node# cd /etc/netsukuku/ register_node# cat snsd_nodes # # SNSD nodes file # # The format is: # hostname:snsd_hostname:service:priority:weight[:pub_key_file] # or # hostname:snsd_ip:service:priority:weight[:pub_key_file] # # The `pub_key_file' parameter is optional. If you specify it, NetsukukuD will # check periodically `snsd_hostname' and it will verify if it is always the # same machine. If it isn't, the relative snsd will be deleted. # depausceve:pippo:http:1 depausceve:184.108.40.206:21:0 angelica:frenzu:ssh:1:/etc/netsukuku/snsd/frenzu.pubk register_node# register_node# scp frenzu:/usr/share/andna_lcl_keyring snsd/frenzu.pubk
- Send a SIGHUP to the NetsukukuD of the register node:
register_node# killall -SIGHUP ntkd # or, alternatively register_node# rc.ntk reload
Zero SNSD IP
The main IP associated to a normal hostname has these default values:
IP = register_node IP # This value can't be changed service = 0 priority = 16 weight = 1
It is possible to associate other SNSD records in the service 0, but it isn't allowed to change the main IP. The main IP can only be the IP of the register_node. Although it isn't possible to set a different association for the main IP, it can be disabled by setting its weight number to 0.
The string used to change the priority and weight value of the main IP is:
hostname:hostname:0:priority:weight # For example: register_node# echo depausceve:depausceve:0:23:12 >> /etc/netsukuku/snsd_nodes
Since it is possible to assign different aliases and backup IPs to the zero record, there is the possibility to create a SNSD chain. For example:
depausceve registers: depausceve:80 --> pippo pippo registers: pippo:0 --> frenzu frenzu registers: frenzu:0 --> angelica
However the SNSD chains are ignored, only the first resolution is considered valid. Since in the zero service there's always the main IP, the resolution is always performed. In this case ("depausceve:80 --> pippo:0") the resolution will return the main IP of "pippo:0".
The reply to a resolution request of service zero, returns always IPs and not hostnames.