Standard for the transmission of IP datagrams over NetBIOS networks
also
- std-48
Extracted elements (19)
A router that can encapsulate IP in both ordinary data-link protocols (e.g., 802.3) and NetBIOS datagrams allows NetBIOS hosts to communicate with the broader internet, bridging the two encapsulation domains.
ASCII hexadecimal encoding in the name IP.XX.XX.XX.XX was chosen to enable multiplexing of standard datagram protocols over NetBIOS and to allow easy visual confirmation of the correctness of a packet's destination address.
Because each host's NetBIOS name is derived directly and deterministically from its IP address, no ARP-like dynamic address resolution protocol is needed on NetBIOS networks.
Previous versions of this specification used NetBIOS broadcast datagram services to implement IP broadcasting. The current specification replaces this with NetBIOS group name services (IP.FF.FF.FF.FF); the broadcast datagram approach is declared obsolete.
Due to the 512-byte NetBIOS datagram MTU, any host anywhere on the internet communicating with a host on a NetBIOS network may be required to accept and reassemble fragmented IP datagrams.
IP multicast addresses are not mapped to NetBIOS group names; no support for IP multicast is provided in this specification.
After receiving and processing a NetBIOS datagram, the host must immediately resubmit a receive datagram request to remain ready for the next incoming datagram.
Initialization code must add IP.FF.FF.FF.FF to the host's NetBIOS group name table to enable reception of broadcast IP datagrams.
Initialization code must add IP.XX.XX.XX.XX to the host's NetBIOS name table for each supported IP address.
Initialization must submit receive datagram requests for both IP.XX.XX.XX.XX (unicast) and IP.FF.FF.FF.FF (broadcast) to begin accepting incoming IP traffic.
Optionally, the IP software may issue NetBIOS adapter status queries; the document notes that as SNMP support becomes required for IP hosts, these queries may become mandatory.
Outgoing IP datagrams are sent via a NetBIOS send datagram request to either IP.XX.XX.XX.XX for unicast or IP.FF.FF.FF.FF for broadcast destinations.
When IP support for a NetBIOS host is discontinued, a cancel command should be submitted for every pending receive datagram request, and delete name requests should be submitted for both IP.XX.XX.XX.XX and IP.FF.FF.FF.FF.
Broadcast IP addresses are represented by the NetBIOS group name IP.FF.FF.FF.FF. Every IP-over-NetBIOS host must join this group name to receive broadcast datagrams.
Each IP-over-NetBIOS host registers the NetBIOS name IP.XX.XX.XX.XX, where each XX is the two-character ASCII hexadecimal representation of the corresponding octet of the host's IP address. This deterministic mapping eliminates the need for an address resolution protocol such as ARP.
Only the NetBIOS datagram services are used for IP encapsulation; virtual circuit (session) services are not employed. Both point-to-point and group datagram services are used.
The Maximum Transmission Unit (MTU) for IP over NetBIOS is 512 bytes, which equals the maximum data size of a NetBIOS datagram. IP fragmentation and reassembly are therefore required for larger datagrams.
This specification defines no authentication mechanism for NetBIOS name registration. Any host on the NetBIOS network can register the name IP.XX.XX.XX.XX for an arbitrary IP address, making IP address spoofing and traffic interception trivially possible within the NetBIOS scope.
IP datagrams are carried as the data payload of NetBIOS datagram requests with no additional encapsulation header. The NetBIOS destination name field encodes the target IP address in IP.XX.XX.XX.XX form.