Some Sniffer decodes of Lat packets, for your amusement
A Service announcment, listing all the group codes available
SUMMARY Delta T Destination Source Summary
223 4.7321 DEC_LAT_Units BRUVAX LAT Change Node=BRUVAX Desc=Welcome to OpenVMS VAX V6.0
LAT: ----- Local Area Transport -----
LAT:
LAT: Message type / flags = 28
LAT: 0010 10.. = Service
LAT: .... ..0. = From host
LAT: .... ...0 = No response requested
LAT: Server circuit timer = 8 x 10msec
LAT: Highest supported protocol version = 5
LAT: Lowest supported protocol version = 5
LAT: Current protocol version = 5
LAT: Current protocol ECO = 2
LAT: Message ID = 60
LAT: Change flags = F7
LAT: .... ...1 = Node groups have changed
LAT: .... ..1. = Node descriptor has changed
LAT: .... .1.. = Service names have changed
LAT: .... 0... = Service ratings have not changed
LAT: ...1 .... = Service descriptors have changed
LAT: ..1. .... = Service classes have changed
LAT: 1... .... = Other parameters have changed
LAT: Receive frame size = 1500 bytes
LAT: Multicast timer = 60 seconds
LAT: Host status = 02
LAT: .... ...0 = Host is accepting new sessions
LAT: Node groups:
LAT: Node group length = 32 bytes
LAT: Group byte 0, Groups enabled: 0, 1, 2, 3, 4, 5, 6, 7
LAT: Group byte 1, Groups enabled: 8, 9, 10, 11, 12, 13, 14, 15
LAT: Group byte 2, Groups enabled: 16, 17, 18, 19, 20, 21, 22, 23
LAT: Group byte 3, Groups enabled: 24, 25, 26, 27, 28, 29, 30, 31
LAT: Group byte 4, Groups enabled: 32, 33, 34, 35, 36, 37, 38, 39
LAT: Group byte 5, Groups enabled: 40, 41, 42, 43, 44, 45, 46, 47
LAT: Group byte 6, Groups enabled: 48, 49, 50, 51, 52, 53, 54, 55
LAT: Group byte 7, Groups enabled: 56, 57, 58, 59, 60, 61, 62, 63
LAT: Group byte 8, Groups enabled: 64, 65, 66, 67, 68, 69, 70, 71
LAT: Group byte 9, Groups enabled: 72, 73, 74, 75, 76, 77, 78, 79
LAT: Group byte 10, Groups enabled: 80, 81, 82, 83, 84, 85, 86, 87
LAT: Group byte 11, Groups enabled: 88, 89, 90, 91, 92, 93, 94, 95
LAT: Group byte 12, Groups enabled: 96, 97, 98, 99, 100, 101, 102, 103
LAT: Group byte 13, Groups enabled: 104, 105, 106, 107, 108, 109, 110, 111
LAT: Group byte 14, Groups enabled: 112, 113, 114, 115, 116, 117, 118, 119
LAT: Group byte 15, Groups enabled: 120, 121, 122, 123, 124, 125, 126, 127
LAT: Group byte 16, Groups enabled: 128, 129, 130, 131, 132, 133, 134, 135
LAT: Group byte 17, Groups enabled: 136, 137, 138, 139, 140, 141, 142, 143
LAT: Group byte 18, Groups enabled: 144, 145, 146, 147, 148, 149, 150, 151
LAT: Group byte 19, Groups enabled: 152, 153, 154, 155, 156, 157, 158, 159
LAT: Group byte 20, Groups enabled: 160, 161, 162, 163, 164, 165, 166, 167
LAT: Group byte 21, Groups enabled: 168, 169, 170, 171, 172, 173, 174, 175
LAT: Group byte 22, Groups enabled: 176, 177, 178, 179, 180, 181, 182, 183
LAT: Group byte 23, Groups enabled: 184, 185, 186, 187, 188, 189, 190, 191
LAT: Group byte 24, Groups enabled: 192, 193, 194, 195, 196, 197, 198, 199
LAT: Group byte 25, Groups enabled: 200, 201, 202, 203, 204, 205, 206, 207
LAT: Group byte 26, Groups enabled: 208, 209, 210, 211, 212, 213, 214, 215
LAT: Group byte 27, Groups enabled: 216, 217, 218, 219, 220, 221, 222, 223
LAT: Group byte 28, Groups enabled: 224, 225, 226, 227, 228, 229, 230, 231
LAT: Group byte 29, Groups enabled: 232, 233, 234, 235, 236, 237, 238, 239
LAT: Group byte 30, Groups enabled: 240, 241, 242, 243, 244, 245, 246, 247
LAT: Group byte 31, Groups enabled: 248, 249, 250, 251, 252, 253, 254, 255
LAT: Node name = "BRUVAX"
LAT: Node description = "Welcome to OpenVMS VAX V6.0"
LAT: Number of service descriptors = 1
LAT: Service descriptor 0:
LAT: Rating = 64
LAT: Service name = "BRUVAX"
LAT: Service description = "Welcome to OpenVMS VAX V6.0"
LAT: Service classes:
LAT: Number of service classes = 1
LAT: Service 0 = 1 (Remote terminal service)
LAT:
Plain average run message, just a couple of machines in mid flow, there's
only one data slot in the virtual circuit so not a very exciting packet. The
user on the async terminal has just pressed '[B' as part of a cursor control
sequence.
Notice the 32 padding bytes at the end. The run message did not contain enough information to fill up the minimum 64 bytes of data for an ethernet packet. So the Lat protocol pads the packet with '0's. Tinygram compression, as used when bridgeing Lat over WAN links, strips out these extra padding '0's and then re-inserts them at the opposite end. Very usefull when bridging Lat over narrw pipes. But do be carefull of the re-stuffing. Some early IOSs used to re-pad with old user data, and some interesting stuff could be found in the packet.
SUMMARY Delta T Destination Source Summary
82 0.0952 DECnet000228 00605CF38A67 LAT C Data D=EC01 S=0601 NR=3E NS=00 Len=2
LAT: ----- Local Area Transport -----
LAT:
LAT: Message type / flags = 02
LAT: 0000 00.. = Run
LAT: .... ..1. = To host
LAT: .... ...0 = No response requested
LAT: Number of slots = 1
LAT: Destination circuit ID = EC01
LAT: Source circuit ID = 0601
LAT: Sequence number = 00
LAT: Acknowlegement number = 3E
LAT:
LAT: ----- Local Area Transport Data To Host (Slot 0) -----
LAT:
LAT: Destination slot ID = 01
LAT: Source slot ID = 01
LAT: Data length = 2
LAT: Slot type / Credits = 00
LAT: 0000 .... = Data
LAT: .... 0000 = 0 Credits
LAT: Data = "[B"
LAT:
LAT: [32 padding byte(s)]
LAT:
ADDR HEX ASCII
0000 AA 00 04 00 02 28 00 60 5C F3 8A 67 60 04 02 01 .....(.`\..g`...
0010 01 EC 01 06 00 3E 01 01 02 00 5B 42 00 00 00 00 .....>....[B....
0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0030 00 00 00 00 00 00 00 00 00 00 00 00 ............