String Binding

The string binding is an unsigned character string composed of strings that represent the binding object UUID, the RPC protocol sequence, the network address, and the endpoint and endpoint options.




UUID of the object operated on by the remote procedure call. At the server, the RPC run-time library maps the object type to a manager entry-point vector (an array of function pointers) to invoke the correct manager routine. For a discussion of how to map object UUIDs to manager entry-point vectors, see Registering Interfaces.


Character string that represents a valid combination of an RPC protocol (such as ncacn), a transport protocol (such as TCP), and a network protocol (such as IP). Microsoft RPC supports the following protocols specified in Protocol Sequence Constants.


Network address of the system to receive remote procedure calls.


The following protocol sequences are not supported as of Windows XP:

The format and content of the network address depend on the specified protocol sequence as follows.

Protocol sequence Network address Examples
ncacn_nb_tcp Computer name myserver
ncacn_nb_ipx Computer name myserver
ncacn_nb_nb Computer name myserver
ncacn_ip_tcp Four-octet Internet address, or host name. If the IPv6 network stack is installed, IPv6 is fully supported and an IPv6 address is also accepted.
ncacn_np Server name (leading double backslashes are optional) myserver \\myotherserver
ncacn_spx IPX Internet address, or server name ~0000000108002B30612C myserver
ncacn_dnet_nsp Area and node syntax 4.120
ncacn_at_dsp Computer name, optionally followed by @ and the AppleTalk zone name. Defaults to @*, the client's zone, if no zone provided servername@zonename servername
ncacn_vns_spp StreetTalk server name of the form item@group@organization printserver@sdkdocs@microsoft
ncadg_mq Server name myserver
ncacn_http Internet address (either four-octet or friendly name, or local server name mylocalsvr
ncadg_ip_udp Four-octet Internet address, or host name
ncadg_ipx IPX Internet address, or server name ~0000000108002B30612C myserver
ncalrpc Machine name thismachine

The network-address field is optional. When you do not specify a network address, the string binding refers to your local host. It is possible to specify the name of the local computer when you use the ncalrpc protocol sequence, however doing so is completely unnecessary.


Endpoint, or address, of the process to receive remote procedure calls. An endpoint can be preceded by the keyword endpoint=. Specifying the endpoint is optional if the server has registered its bindings with the endpoint mapper. See RpcEpRegister.

The format and content of an endpoint depend on the specified protocol sequence as shown in the following Endpoint/Option Table.


Protocol-specific options. The option field is not required. Each option is specified by a {name, value} pair that uses the syntax option name=option value. Options are defined for each protocol sequence as shown in the following Endpoint/Option table.

Protocol sequence Endpoint Examples Option name
ncacn_nb_tcp Integer between 1 and 254. Many values between 0 and 32 are reserved by Microsoft. 100 None
ncacn_nb_ipx (as above) (as above) None
ncacn_nb_nb (as above) (as above) None
ncacn_ip_tcp Internet port number. 1025 None
ncacn_np Named pipe. Name must start with "\\pipe". \\pipe\\pipename Security
ncacn_spx Integer between 1 and 65535. 5000 None
ncacn_dnet_nsp DECnet phase IV object number (must be preceded by the # character), or object name. mailserver #17 None
ncacn_at_dsp A character string, up to 22 bytes long. myservicesendpoint None
ncacn_vns_spp Vines SPP port number between 250 and 511. 500 None
ncadg_mq Integer between 1 and 65535. 5000 None
ncacn_http Internet port number. 2215 HTTP and RPC proxy server names, HttpConnection option
ncadg_ip_udp Internet port number. 1025 None
ncadg_ipx Integer between 1 and 65535. 5000 None
ncalrpc String specifying application or service name. The string cannot include any backslash characters. my_printer Security

The HttpConnectionOption option name, supported for the ncacn_http protocol sequence, takes the following value.

Option name Value
HttpConnectOption UseHttpProxy

The HttpConnectionOption allows you to direct RPC s behavior when making HTTP connections. The UseHttpProxy value instructs RPC to route its traffic through the Http proxy at all times, including when the client has the Internet Options set in Internet Explorer to Bypass proxy server for local addresses. This option directs the client to forcefully connect to the RPC proxy through the Http proxy. This speeds up the time to establish a connection since it bypasses any delay searching for the RPC server directly prior to using the HTTP proxy.

If this HttpConnectionOption option is used and Internet Explorer on the client is not configured to use that Http proxy, connections may fail with RPC_S_INVALID_NETWORK_OPTIONS.


For more information about the HttpConnectionOption, see Using HTTP as an RPC Transport.

The Security option name, supported for the ncalrpc, ncacn_np, ncadg_ip_udp, and ncadg_ipx protocol sequences, takes the following option values.

Option name Option value
Security {identification | anonymous | impersonation} {dynamic | static} {true | false}

If the security option name is specified, one entry from each of the sets of security option values must also be supplied. The option values must be separated by a single-space character. For example, the following Option fields are valid:

Security=identification dynamic true
Security=impersonation static true

The security option values have the following meanings.

Security option value Description
Anonymous The client is anonymous to the server.
Dynamic Changes in the client security identity are seen by the server when the server uses transport security. This is the default mode for LRPC (ncalrpc) transport level security, and for local named pipe (ncacn_np) transport level security.
False Effective = FALSE; all token privileges settings, including those set to OFF, are included in the token on the server and can be enabled by the server. Privileges are relevant for same-machine RPC calls only.
Identification The server has information about the client but cannot impersonate.
Impersonation The server can act on behalf of the client within the local system (transport-level security does not support delegation).
Static Changes in the client security identity are not seen by the server when the server uses transport security. This is the only mode available to remote named pipe (ncacn_np) transport level security. The identity of the caller is saved during the first remote procedure call on that binding handle, not at the time the binding handle is created.
True Effective = TRUE; only token privileges settings set to ON are included in the token on the server. Privileges set to OFF cannot be turned on by the server if this option is used. Privileges are relevant for same-machine RPC calls only.

For more information about security options, Security.


White space is not allowed in string bindings except where required by the Option syntax. Default settings for the NetworkAddress, Endpoint, and Option fields vary according to the value of the ProtocolSequence member.

For all string-binding fields, a single backslash character (\) is interpreted as an escape character. To specify a single literal backslash character, you must supply two backslash characters (\\).

A string binding contains the character representation of a binding handle and occasionally portions of a binding handle. String bindings are convenient for representing portions of a binding handle, but they can't be used for making remote procedure calls. They must first be converted to a binding handle by calling RpcBindingFromStringBinding.

Additionally, a string binding does not contain all of the information from a binding handle. For example, the authentication information, if any, associated with a binding handle is not translated into the string binding returned by calling the RpcBindingToStringBinding.

During the development of a distributed application, servers can communicate their binding information to clients using string bindings to establish a client-server relationship without using the endpoint-map database or name-service database. To establish such a relationship, use the function RpcBindingToStringBinding to convert one or more binding handles from a binding-handle vector to a string binding, and provide the string binding to the client.


The following are examples of valid string bindings. In these examples, obj-uuid is used for convenience to represent a valid UUID in string form. Instead of showing the UUID 308FB580-1EB2-11CA-923B-08002B1075A7, the examples show obj-uuid.

obj-uuid@ncacn_np:[\\pipe\\p3,Security=impersonation static true]
obj-uuid@ncacn_np:\\\\sales[\\pipe\\p1,Security=identification dynamic true]
obj-uuid@ncalrpc:[object2_name,Security=anonymous static true]
obj-uuid@ncadg_ipx: ~0000000108002B30612C[5000]




Using HTTP as an RPC Transport