Netbios Packet Formats - 3Com PathBuilder S200 Series Owner's Manual

NetBIOS Packet Formats

Introduction
NetBIOS Name Filtering operates only on the Microsoft or IBM-compatible
NetBIOS implementations, which represents the majority of NetBIOS
implementations. It does not recognize at this time Novell's implementation of
NetBIOS over IPX, nor does it recognize the packet format of NetBIOS over TCP
(RFC 1000).
NetBIOS Name Filtering operates on Ethernet LANs.
IBM NetBIOS
IBM NetBIOS formats are documented in the IBM publication LAN Technical
Formats
Report for IEEE 802.2 and NetBIOS Interfaces, SC-303587.
When to Use
Configure NetBIOS Name Filtering when:
NetBIOS Name
All of the following are true:
Filtering
Either one of the following is true:
When Filters Are
NetBIOS name filters are applied to the broadcast packets that are transmitted in
Applied
order to initiate NetBIOS sessions and to broadcast datagrams. Application of
NetBIOS filters does not halt the operation of any NetBIOS sessions already in
progress.
Bridging
T0008-16F
• The bridged packet is a MAC-level multicast or broadcast, that is, the first
transmitted bit of the destination is set.
• The bridged packet contains an 802.2 LLC field (that is, on Ethernet
implementation, the packet does not use an EtherType code to distinguish the
packet format).
• The LLC DSAP/SSAP/CTL fields are:
0xF0 0xF0 x03
The first byte following the above LLC layer is considered offset 0 of the NetBIOS
PDU (protocol data unit).
• The two bytes at NetBIOS offset 2-3 are 0xFF and 0xFE (NetBIOS frame
delimiter).
• The NetBIOS command byte at offset 4 is:
00 (Add_Group_Name) or 01 (Add_Name Query)
The packet field to be compared to the NetBIOS Name Filter list is the SOURCE
name field, occupying the 16 bytes starting an offset 0x1C in the NetBIOS PDU.
• The NetBIOS command byte at offset 4 is:
08 (Datagram) or 0x0A (Name Query)
The packet field to be compared to the NetBIOS Name Filter list is the
DESTINATION name field, occupying the 16 bytes starting at offset 0x0C of the
NetBIOS PDU.
Bridge Filtering
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Release 5.2M