147 lines
5.9 KiB
C#
147 lines
5.9 KiB
C#
namespace DnsClient.Protocol.Record
|
|
{
|
|
/* RFC 2782 (https://tools.ietf.org/html/rfc2782)
|
|
|
|
The format of the SRV RR
|
|
|
|
Here is the format of the SRV RR, whose DNS type code is 33:
|
|
|
|
_Service._Proto.Name TTL Class SRV Priority Weight Port Target
|
|
|
|
(There is an example near the end of this document.)
|
|
|
|
Service
|
|
The symbolic name of the desired service, as defined in Assigned
|
|
Numbers [STD 2] or locally. An underscore (_) is prepended to
|
|
the service identifier to avoid collisions with DNS labels that
|
|
occur in nature.
|
|
Some widely used services, notably POP, don't have a single
|
|
universal name. If Assigned Numbers names the service
|
|
indicated, that name is the only name which is legal for SRV
|
|
lookups. The Service is case insensitive.
|
|
|
|
Proto
|
|
The symbolic name of the desired protocol, with an underscore
|
|
(_) prepended to prevent collisions with DNS labels that occur
|
|
in nature. _TCP and _UDP are at present the most useful values
|
|
for this field, though any name defined by Assigned Numbers or
|
|
locally may be used (as for Service). The Proto is case
|
|
insensitive.
|
|
|
|
Name
|
|
The domain this RR refers to. The SRV RR is unique in that the
|
|
name one searches for is not this name; the example near the end
|
|
shows this clearly.
|
|
|
|
TTL
|
|
Standard DNS meaning [RFC 1035].
|
|
|
|
Class
|
|
Standard DNS meaning [RFC 1035]. SRV records occur in the IN
|
|
Class.
|
|
|
|
Priority
|
|
The priority of this target host. A client MUST attempt to
|
|
contact the target host with the lowest-numbered priority it can
|
|
reach; target hosts with the same priority SHOULD be tried in an
|
|
order defined by the weight field. The range is 0-65535. This
|
|
is a 16 bit unsigned integer in network byte order.
|
|
|
|
Weight
|
|
A server selection mechanism. The weight field specifies a
|
|
relative weight for entries with the same priority. Larger
|
|
weights SHOULD be given a proportionately higher probability of
|
|
being selected. The range of this number is 0-65535. This is a
|
|
16 bit unsigned integer in network byte order. Domain
|
|
administrators SHOULD use Weight 0 when there isn't any server
|
|
selection to do, to make the RR easier to read for humans (less
|
|
noisy). In the presence of records containing weights greater
|
|
than 0, records with weight 0 should have a very small chance of
|
|
being selected.
|
|
|
|
In the absence of a protocol whose specification calls for the
|
|
use of other weighting information, a client arranges the SRV
|
|
RRs of the same Priority in the order in which target hosts,
|
|
|
|
specified by the SRV RRs, will be contacted. The following
|
|
algorithm SHOULD be used to order the SRV RRs of the same
|
|
priority:
|
|
|
|
To select a target to be contacted next, arrange all SRV RRs
|
|
(that have not been ordered yet) in any order, except that all
|
|
those with weight 0 are placed at the beginning of the list.
|
|
|
|
Compute the sum of the weights of those RRs, and with each RR
|
|
associate the running sum in the selected order. Then choose a
|
|
uniform random number between 0 and the sum computed
|
|
(inclusive), and select the RR whose running sum value is the
|
|
first in the selected order which is greater than or equal to
|
|
the random number selected. The target host specified in the
|
|
selected SRV RR is the next one to be contacted by the client.
|
|
Remove this SRV RR from the set of the unordered SRV RRs and
|
|
apply the described algorithm to the unordered SRV RRs to select
|
|
the next target host. Continue the ordering process until there
|
|
are no unordered SRV RRs. This process is repeated for each
|
|
Priority.
|
|
|
|
Port
|
|
The port on this target host of this service. The range is 0-
|
|
65535. This is a 16 bit unsigned integer in network byte order.
|
|
This is often as specified in Assigned Numbers but need not be.
|
|
|
|
Target
|
|
The domain name of the target host. There MUST be one or more
|
|
address records for this name, the name MUST NOT be an alias (in
|
|
the sense of RFC 1034 or RFC 2181). Implementors are urged, but
|
|
not required, to return the address record(s) in the Additional
|
|
Data section. Unless and until permitted by future standards
|
|
action, name compression is not to be used for this field.
|
|
|
|
A Target of "." means that the service is decidedly not
|
|
available at this domain.
|
|
|
|
*/
|
|
|
|
/// <summary>
|
|
/// The SRV RR allows administrators to use several servers for a single
|
|
/// domain, to move services from host to host with little fuss, and to
|
|
/// designate some hosts as primary servers for a service and others as
|
|
/// backups.
|
|
///
|
|
/// Clients ask for a specific service/protocol for a specific domain
|
|
/// (the word domain is used here in the strict RFC 1034 sense), and get
|
|
/// back the names of any available servers.
|
|
///
|
|
/// Note that where this document refers to "address records", it means A
|
|
/// RR's, AAAA RR's, or their most modern equivalent.
|
|
/// </summary>
|
|
public class SrvRecord : DnsResourceRecord
|
|
{
|
|
public ushort Port { get; }
|
|
|
|
public ushort Priority { get; }
|
|
|
|
public string Target { get; }
|
|
|
|
public ushort Weight { get; }
|
|
|
|
public SrvRecord(ResourceRecordInfo info, ushort priority, ushort weigth, ushort port, string target)
|
|
: base(info)
|
|
{
|
|
Priority = priority;
|
|
Weight = weigth;
|
|
Port = port;
|
|
Target = target;
|
|
}
|
|
|
|
public override string RecordToString()
|
|
{
|
|
return string.Format(
|
|
"{0} {1} {2} {3}",
|
|
Priority,
|
|
Weight,
|
|
Port,
|
|
Target);
|
|
}
|
|
}
|
|
} |