Appendix K - DECnet
DECnet
Originally created to allow 2 PDP-11s to communicate over Ethernet, DECnet was introduced in 1975 by the Digital Equipment Corporation. DECnet is now used to enable DEC equipment to communicate in an intranet environment. DECnet encompasses 2 architectures, VAX and MIPS.
DECnet VAX Architecture
VAX, Virtual Address Extension, is a CISC architecture that comprises of Micro-VAX and VAX wide systems. VAX equipment can run either VMS or Ultrix. Most VAX servers can be clustered, thereby creating high availability systems that are scalable, can load balance, and can share data and peripherals. VAX servers and peripherals communicate over an external bus called LAVC or Local Area VAX Cluster. LAVC are characterized with 2 to 96 VAX devices interconnected by an external bus. LAVC also incorporate the use of Terminal Servers.
SCA, or System Communication Architecture, provides for LAVC over standard Ethernet. Since Ethernet is an extendable technology, hosts and peripherals can be located in dispersed geographical locations. LAVC over Ethernet can be used to transport various network protocols at the same time. In some cases LAVC devices use a CI bus, or Computer Interconnect bus. This is a high speed bus, usually 70Mbps over 4 coaxial cables, which connects all devices at a star coupler. This bus is limited to 50ft, restricting it to close quartered equipment. On the bus is a HSC, or Hierarchal Storage Controller, that allows for data storage shadowing. Data storage shadowing is a process by which data is written to two dispersed storage devices at the same time.
DECnet LAVC Network
VT100 VT220 VT52 Computer
Terminal server Ethernet
VAX Micro VAX
Star Coupler CI BUS
Micro VAX Disk array Disk array
DECnet MIPS architecture
DECnet MIPS devices run ULTRIX. ULTRIX is DECs version of UNIX. These devices are LAN attached and run communications protocols like TCP/IP.
Page K - 1 Terminal Servers
Terminal Servers are used by dumb terminals, (vt220, vt100, vt52), to communicate with a DEC host, such as a VAX, over Ethernet. Terminal Servers offload virtual terminal key processing from the VAX CPUs. The Terminal servers collect key data from the terminals and pack them into an Ethernet frame. At any given time, a frame may be carrying the key strokes from more than one dumb terminal, therefore, Terminal Servers and VAX hosts keep track of sessions. The LAT, or Local Area Transport, is used between the Terminal Server and the DEC VAX host. LAT advertises its services every 60 seconds. This advertisement is sent, via broadcast, to all hosts on an Ethernet.
DNA – Digital Network Architecture
DECnet is a propriety protocol that has been developed in different stages called phases. The most common DECnet Phase is DECnet Phase IV. Currently DECnet is in Phase V or DECnet/OSI. DECnet Phase IV uses its own 8 layer model, similar in function and structure to the OSI model, to describe its networking features. It is called the DNA, or Digital Network Architecture. The DNA layers are shown below.
Page K - 2 The User Layer supports user services and programs. The Network Management Layer is the only layer that has control and direct access to all layers below it. This layer controls and directs access to all layers. The Network Application Layer is responsible for device I/O and file access control. The Session Control Layer controls flow and conversation. The End Communications Layer is responsible for establishing and destroying end to end communications channel. The Routing Layer is responsible with routing of messages to destination. The Data Link Layer is responsible for communication over physical layer. And the Physical Link Layer is the actual hardware transmissions.
DECnet Phase V – DECnet/OSI
DECnet Phase V, or commonly DECnet/OSI, is a backward compatible protocol that provides for DECnet to run over the OSI Transport, Network and Datalink layers. (See Appendix G – OSI Protocols for more information.) This allows for DECnet systems to operate in a multi-protocol environment. Much of the upper layer protocols are the same in Phase V as in Phase IV. Phase V supports many OSI standard protocols. At the Transport layer Phase V supports ISO TP0 through TP4.
Page K - 3 DECnet Applications
Much like the OSI model and the DOD model, DECnet uses applications at each layer of its model. DECnet applications resemble those of TCP/IP. They include: MOP, NICE, DAP, CTERM, MAIL, DNS, DFS, DQS, SCP, NSP, and DRP. The diagram below illustrates the layer at which each operates.
Page K - 4 NICE
NICE is the DEC Network Information and Control Exchange. It is widely used to manage hosts and the processes that run on them. It can be used for the upload and download of system configurations as well as tracking and trapping network/system events, and can be used to perform tests on hosts.
MOP
Most Terminal Servers are diskless and therefore uses MOP to get their configuration form a VAX host known as the Boot node. The Boot node contains an image of the OS and its configuration for each diskless host on the network. MOP, or Maintenance Operation Procedures, is used to download operating environments to VAX diskless servers much like BOOTP. It is also used to perform diagnostics on VAX hosts.
DAP Similar to TCP/IP FTP, DAP, or Data Access Protocol, allows users and systems to access local file systems remotely. It is currently being replaced by DFS, (Distributed File System), in the DECnet Phase IV model and with FTAM, (File Transfer, Access, and Management), in DECnet/OSI.
MAIL MAIL simply is an e-mail transport system for DECnet.
CTERM CTERM, (Communications Terminal Protocol), is much like TCP/IP TELNET. It is an alternative to LAT.
DNS DNS, (Distributed Naming Services), provides the naming service for DECnet devices. Its purpose is to map names and network addresses.
DFS DFS, (Distributed File System), is much like TCP/IP NFS. It allows hosts to mount file systems that are located on other hosts.
DQS DQS, (Distributed Queuing Services), provide for job control on print queues throughout the DECnet network.
SCP SCP, (Session Control Protocol), is DECnet session layer protocol. It is responsible for the building and teardown of logical links between hosts on an as needed basis.
NSP NSP, (Network Services Protocol), is the transport layer protocol for DECnet Phase IV. It is connection oriented. It is responsible for Data segmentation and reassembly, error correction, flow control, windowing and congestion control. DECnet OSI uses TP4 at this layer.
DRP DRP, (DECnet Routing Protocol), is the network layer protocol for DECnet Phase IV. It is responsible for determining the best route between hosts. It does this based on cost.
Page K - 5 DECnet at the Datalink Layer
At the Datalink layer, DECnet Phase IV uses a frame called the DDCMP or Digital Data Communications Message Protocol. DDCMP is implemented on both Multipoint and Point-To-Point connections. DDCMP provides flow control and error correction over both synchronous and asynchronous communications. Much like the 802.3 frame, DDCMP includes a byte count with in its frame to denote how many bytes are in the frame. Unlike any other frame, DDCMP includes 2 CRC fields, one for the header and 1 for the data. The DDCMP header is 42 bits in length. 2 Bytes are used for frame synchronization. The total maximum frame size is 16402 bytes, or 16.4KB.
Over Ethernet DECnet is carried by Ethernet II and 802.2 LLC frames. No other Ethernet frame is defined for use with DECnet. Ethernet II frames use the following type codes:
Hex Type Code Function 60-01 MOP dump/load
60-02 MOP Remote Diagnostics 60-03 DRP
60-04 LAT 60-07 LAVC
DECnet Phase IV addressing
DECnet Phase IV hosts addresses are 16 bits in length. The address is broken down into a 6 bit area number and a 10bit node number. The address is written is dotted decimal notation. Therefore, Area 6, Host 17 would be written 6.17
The 16 bit address space allows for a total of 63 areas and for 1023 hosts. There can be no host with the address 0 or with the address of 1024. Host address 1024 is reserved for directed broadcasts. Similarly, there can be no network with the address 0 or with the address of 64. The network address of 64 is reserved for limited broadcast. There is only 1 DECnet address per host. That is to say, the address is given to the host not the interface on the host. Each DECnet host imbeds its address in to a DECnet MAC that is used by every interface on the host.
Page K - 6 DECnet and MAC addresses
DECnet addressing affects the MAC addresses of hosts. Essentially, DECnet overwrites the MAC with its own version of a MAC address. Only 1 MAC address per host is allowed, no matter the number of interfaces the host may have. This may impact any other protocol one may have configured for the host to use. To create the new MAC address DECnet devices go through the following steps:
1. Takes the assigned area number and multiplies it by 1024. 2. Add the host node number to the product of step 1. 3. Swap the two high order bytes of the sum from step 2. 4. Prepend the DEC prefix of AA00.0400 to the number from step 3.
Below is an example of the DECnet MAC conversion process.
Given a host id of 4.3,
Step #1, 4 x 1024 = 4096 Step #2, 3 + 4096 = 4099
All MAC are in Hex so convert the number to hex.
4099 in base 10 is converted to 1003 in base 16.
Step #3, 0x1003 swapped is 0x0310 Step #4, AA00.0400.0310
Another method one may use to convert the MAC is the bitwise split, as shown here.
1. Take the assigned id and transform it to binary. 2. Split the 16 bit binary string in to 2 – 8 bit sections. 3. Convert each 8 bit segment to Hexadecimal. 4. Swap the Hex digits and append to AA00.0400
Below is another example of the DECnet MAC conversion process.
Given a host id of 4.3,
Set #1, 4 is 000100 in 6 bit Binary, and 3 is 0000000011 in 10 bit Binary.
Step #2, take the 16 bit string, 0001000000000011 and split it in to 2 – 8 bit strings 00010000 and 00000011 respectively.
Step #3, 00010000 in Binary is 10 in Hex, and 00000011 in Binary is 03 in Hex.
Step #4, 0x0310 is appended to AA00.0400 to create the address AA00.0400.0310
Page K - 7 DECnet Reserved MAC addresses
The following DECnet MAC are reserved for specific purposes
MAC Address FUNCTION FF:FF:FF:FF:FF:FF Broadcast, not used with DRP
09:00:2B:00:00:0F LAT 09:00:2B:02:00:00 Hello Update between Level 2 Routers
AB:00:00:01:00:00 MOP dump/load AB:00:00:02:00:00 MOP Remote Diagnostics/Console
AB:00:00:03:00:00 Hello/Updates from routes/end nodes to all AB:00:00:04:00:00 Hello/Updates from routers to all hosts
09:00:2B:01:00:01 Hello/Update between Level 2 Routers
Configuring Cisco Routers for DECnet
Configuring Cisco routers for DECnet requires the global command decnet routing
Once the main configuration has been done, each interface that will be used to route DECnet must be configured with a cost, a priority, and split-horizon (if being used). In the above caption is a sample configuration.
Page K - 8 Configuring DECnet on the DOS, OS/2 and Windows Family of OS
Configuring DECnet on the DOS, OS/2, and Windows family of OS requires software developed by Digital called Pathworks. Pathworks comes in versions for DOS, Windows 3.x, and Windows for Workgroups 3.x, Windows 9.x, and Windows NT.
The installation for Pathworks for DOS, Windows 3.x, and Windows for Workgroups 3.x starts off as a DOS based exe called pwsetup.exe. The exe will prompt you for the client configuration type. Pathworks works with most major networking clients such as NetWare client, Lan Manager, Windows For Workgroups, and FTP PCTCP. Once the user has chosen the appropriate client type of the native DECnet client the setup continues and requests the DECnet client configuration parameters. The caption below shows the setup requesting the DECnet node name and address of the client, as well as, the server.
Page K - 9 Once the user configures the DECnet parameters the configuration utility continues the install and completes with a “completion” message as shown below.
A reboot of the workstation is necessary for the options to take affect. Once rebooted the AUTOEXEC file, or another named batch file chosen by the user, is executed to load the DECnet client.
Page K - 10 The Windows version is similar, however, it installs the Pathworks DECnet protocol driver in to the protocol options of the NIC installed in Widows, as shown below.
Once completed the user has a group ICON called PATHWORKS which contains all the necessary utilities to connect to a DECnet network.
Page K - 11 Upon completing the configuration and rebooting, or changing the configuration and rebooting, Pathworks will reload the DECnet client. Pathworks uses an event logger to allow a user to see the status of the Pathworks DECnet client.
Pathworks uses an “explorer” style interface to connect network drives and printers. The interface, shown below, is quite simple.
Page K - 12 Configuring DECnet on UNIX Family of OS
Configuring DECnet on a UNIX machine requires the download and installation of a DECnet client such as dnprogs and the patching of the UNIX kernel to support DECnet. DNPROGS is available from Patrick Caulfield and the Linux DECnet project team. The current version is available is called dnsprogs.rpm. Once the package is installed, the installation walks the administrator through the DECnet configuration.
Page K - 13 DRP - DECnet Routing Protocol
DRP, DECnet Routing Protocol, is much like OSPF, using a DR and Areas, and is a link state protocol. Routers in DRP are given 1 network address for all interfaces. Much like EIGRP, DRP is a hybrid Link-State/Distance-Vector protocol that uses Split-Horizon to eliminate routing loops. DRP routers send out Hello packets every 15 seconds. DRP routers send out updates as the happen or at specified intervals. DRP hosts are categorized as one of three types: End nodes, Level 1 Routers, and Level 2 Routers.
End Nodes
End nodes have only 1 NIC. End nodes rely on Level 1 Routers to communicate with other hosts. End nodes find Level 1 Routers via a multicast Hello message sent to the address AB:00:00:03:00:00.
Level 1 Routers
Level 1 Routers communicate only with other Level 1 Routers and all Level 2 Routers within an area. Level 1 Routers do not share routing tables with Level 2 Routers. Level 1 Routers update their neighbors every 3 minutes. Level 1 Routers keep track of all nodes within an area. Level 1 Routers learn of nodes and other Level 1 Routers from the End node periodic broadcasts. Router update packets from a Level 1 Router includes: number of nodes, start node number on segment, and cost for each node. Level 1 Routers send their routing updates to the multicast address AB:00:00:03:00:00. One Level 1 Router is elected a DR, or designated router. The DR is the router all other Level 1 Routers contact when information the Level 1 Router does not have a route to the destination. The DR is determined by router priority and highest MAC address.
Level 2 Routers
Level 2 Routers communicate with other Level 2 Routers and with the Level 1 Routers within an area. Level Two routers build intra-area routing tables. Level 2 Routers only share their tables with other Level 2 Routers. Level 2 Routers learn of other routers and End nodes from periodic updates of Level 1 Routers and End node periodic broadcasts. Level 2 Routers send their updates to other Level 2 Routers on multicast address 09:00:2B:01:00:01.
Page K - 14
DECnet Hello Packet
DECnet hello packets have the same format for all levels of routers. The packet format is as follows:
Below is a Sniffer trace of a DECnet Hello Packet… DLC: ----- DLC Header ----- DLC: Destination = Multicast AB0000030000, DEC_lv1_Router DLC: Source = Station DECnet000204 DLC: Ethertype = 6003 (DECNET) DRP: ----- DECNET Routing Protocol ----- DRP: Data Length = 34 DRP: Control Packet Format = 0B DRP: 0...... = no padding DRP: .000 .... = reserved DRP: .... 101. = Ethernet Router Hello Message DRP: ...... 1 = Control Packet Format DRP: Control Packet Type = 05 DRP: Version Number = 02 DRP: ECO Number = 00 DRP: User ECO Number = 00 DRP: ID of Transmitting Node = 1.2 DRP: Information = 01 DRP: 0...... = reserved DRP: .0...... = not blocking request DRP: ..0. .... = multicast traffic accepted DRP: ...0 .... = verification ok DRP: .... 0... = do not reject DRP: .... .0.. = no verification required DRP: ...... 01 = level 2 router DRP: Receive Block Size = 1498 DRP: Router's priority = 10 DRP: Area (reserved) = 0 DRP: Hello timer (seconds) = 15 DRP: MPD (reserved) = 15 DRP: E-List length = 15 DRP: Ethernet Name, reserved = 00000000000000 DRP: Router/State length = 7 DRP: Router ID = 8.1 DRP: Priority and State = 81 DRP: 1...... = State known 2-way DRP: .000 0001 = Router's priority ADDR HEX ASCII 0000: ab 00 00 03 00 00 aa 00 04 00 02 04 60 03 22 00 | «.....ª.....`.". 0010: 0b 02 00 00 aa 00 04 00 02 04 01 da 05 0a 00 0f | ....ª...... Ú.... 0020: 00 0f 0f 00 00 00 00 00 00 00 07 aa 00 04 00 01 | ...... ª.... 0030: 20 81 00 00 00 00 00 00 00 00 00 00 | ......
Page K - 15
Below, a diagram showing the location of routers and hosts within a DECnet network.
DECnet Routing Process
When an End node has information to be delivered to another End node, DECnet follows the following process:
· End node finds nearest Level 1 Router via multicast · Level 1 Router receives information bound for destination · Level 1 Router checks routing table to see if it knows the path to the destination. · If the Level 1 Router knows the destination, it sends data to destination End node. · If Level 1 Router does not know where destination is, it Checks the DR, Designated Router for router determination · If the DR does not have the route, the Level 1 Router formats the packet and sends it to the nearest Level 2 Router.
Page K - 16 DECnet Level 1 Routing Update
DECnet Level 1 Routers broadcast updates every 3 minutes. In a Level 1 update, the only entries are host ids. The packet format is shown below.
With in the Level 1 Update there is a RIC, Routing Information Count, which determines the number of routing entries, and the number of host ids per entry. Therefore, if the RIC is 32 then there would be 32 routing entries with 32 host entries per routing entry. If the packet is too big for a single frame to carry it will be broken up in to as many frames as required to send all the host entries. Note that all the entries in the packet are byte swapped.
Below is a Sniffer trace of a Level 1 Router Update DLC: ----- DLC Header ----- DLC: Destination = Multicast AB0000030000, DEC_lv1_Router DLC: Source = Station DECnet000204 DLC: Ethertype = 6003 (DECNET) DRP: ----- DECNET Routing Protocol ----- DRP: Data Length = 1434 DRP: Control Packet Format = 07 DRP: 0...... = no padding DRP: .000 .... = reserved DRP: .... 011. = Level 1 Routing Message DRP: ...... 1 = Control Packet Format DRP: Source Node = 1.2 DRP: Reserved field = 0 DRP: RTGINFO count = 32 DRP: Start ID = 0 DRP: ID = 0 to 1: Hops = 31 Cost = 1023 DRP: ID = 2: Hops = 0 Cost = 0 DRP: ID = 3 to 31: Hops = 31 Cost = 1023
<***** More Routing Entries *****>
DRP: Checksum = 9B91 (Correct Phase IV value) ADDR HEX ASCII 0000: ab 00 00 03 00 00 aa 00 04 00 02 04 60 03 9a 05 | «.....ª.....`.š. 0010: 07 02 04 00 20 00 00 00 ff 7f ff 7f 00 00 ff 7f | ...... 0020: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0030: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0040: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0050: ff 7f ff 7f ff 7f ff 7f 20 00 20 00 ff 7f ff 7f | ...... <***** More Routing Entries *****> 0590: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 05a0: ff 7f ff 7f ff 7f ff 7f 91 9b | ...... ‘›
Page K - 17 DECnet Level 2 Routing Update
DECnet Level 2 Routers share routing information only with other Level 2 Routers. Each packet contains summary of the areas the router can reach. The packet format is shown below.
As with in the Level 1 Update there is a RIC, Routing Information Count, which determines the number of routing entries, and the number of area ids per entry. The RIC in this packet is 32. Since, the maximum network id is 64 only 1 frame is required to carry 2 routing entries. The fields in the RIC are also byte swapped.
Below is a Sniffer trace of a Level 2 Router Update DLC: ----- DLC Header ----- DLC: Destination = Multicast 09002B020000, DEC_lv2_Router DLC: Source = Station DECnet000204 DLC: Ethertype = 6003 (DECNET) DRP: ----- DECNET Routing Protocol ----- DRP: Data Length = 140 DRP: Control Packet Format = 09 DRP: 0...... = no padding DRP: .000 .... = reserved DRP: .... 100. = Level 2 Routing Message DRP: ...... 1 = Control Packet Format DRP: Source Node = 1.2 DRP: Reserved field = 0 DRP: RTGINFO count = 32 DRP: Start Area = 1 DRP: Area = 1: Hops = 0 Cost = 0 DRP: Area = 2 to 32: Hops = 31 Cost = 1023 DRP: RTGINFO count = 31 DRP: Start Area = 33 DRP: Area = 33 to 63: Hops = 31 Cost = 1023 DRP: Checksum = 0043 (Correct Phase IV value) ADDR HEX ASCII 0000: 09 00 2b 02 00 00 aa 00 04 00 02 04 60 03 8c 00 | .+...ª.....`.Œ. 0010: 09 02 04 00 20 00 01 00 00 00 ff 7f ff 7f ff 7f | ...... 0020: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0030: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0040: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0050: ff 7f ff 7f ff 7f ff 7f 1f 00 21 00 ff 7f ff 7f | ...... !..... 0060: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0070: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0080: ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f ff 7f | ...... 0090: ff 7f ff 7f ff 7f ff 7f ff 7f 43 00 | ...... C.
Page K - 18 DECnet at the Transport Layer
At the Transport layer, DECnet Phase IV uses NSP, Network Services Protocol. NSP uses DRP to get to its destination. The DRP packet format is 6. The DRP Type 6 packet allows network routing information to be sent along with data. The NSP packet itself has many formats. All formats begin with the basics: 1 Byte Message Identifier, 2 Bytes to represent the Logical Link Destination and Source. The general packet format is shown below:
Sniffer Trace of a NSP packet…
DLC: ----- DLC Header ----- DLC: Destination = Station DECnet001504 DLC: Source = Station DECnet001D04 DLC: Ethertype = 6003 (DECNET) DRP: ----- DECNET Routing Protocol ----- DRP: Data Length = 29 DRP: Optional Padding Length = 1 DRP: Data Packet Format = 26 DRP: 0...... = no padding DRP: .0...... = version DRP: ..1. .... = Intra-Ethernet packet DRP: ...0 .... = not return packet DRP: .... 0... = do not return to sender DRP: .... .110 = Long Data Packet Format DRP: Data Packet Type = 6 DRP: Destination Area = 00 DRP: Destination Sub-area = 00 DRP: Destination ID = 1.21 DRP: Source Area = 00 DRP: Source Sub-area = 00 DRP: Source ID = 1.29 DRP: Next Level 2 Router = 00 DRP: Visit Count = 0 DRP: Service Class = 00 DRP: Protocol Type = 00 NSP: ----- Network Services Protocol ----- NSP: Message Identifier = 14 NSP: 0...... = Non-extensible field NSP: .0...... = always zero NSP: ..01 .... = Other-Data Acknowledgment Message NSP: .... 01.. = Acknowledgment Message NSP: ...... 00 = always zero NSP: Type = 1 (Acknowledgment Message) NSP: Sub-type = 1 (Other-Data Acknowledgment Message) NSP: Logical Link Destination = 52 NSP: Logical Link Source = 65442 NSP: Link Acknowledgment Number NSP: Acknowledge Qualifier = ACK NSP: Message Number Acknowledged = 3311 ADDR HEX ASCII 0000: aa 00 04 00 15 04 aa 00 04 00 1d 04 60 03 1d 00 | ...... `... 0010: 81 26 00 00 aa 00 04 00 15 04 00 00 aa 00 04 00 | .&...... 0020: 1d 04 00 00 00 00 14 34 00 a2 ff ef 8c 00 00 08 | ...... 4.¢.ï.... 0030: aa aa aa aa a0 05 00 10 50 00 00 00 | ...... P...
Page K - 19 DECnet at the Session Layer
At the session layer DECnet uses SCP, Session Control Protocol. As with NSP, SCP is encapsulated within the protocols below it. SCP gets encapsulated in to NSP and then DRP. Below is the basic packet format.
Sniffer trace of a SCP packet…
DRP: ----- DECNET Routing Protocol ----- DRP: Data Length = 47 DRP: Optional Padding Length = 1 DRP: Data Packet Format = 2E DRP: Data Packet Type = 6 DRP: Destination Area = 00 DRP: Destination Sub-area = 00 DRP: Destination ID = 1.11 DRP: Source Area = 00 DRP: Source Sub-area = 00 DRP: Source ID = 1.1 DRP: Next Level 2 Router = 00 DRP: Visit Count = 1 DRP: Service Class = 00 DRP: Protocol Type = 00 NSP: ----- Network Services Protocol ----- NSP: Message Identifier = 68 NSP: Logical Link Destination = 0 NSP: Logical Link Source = 76 NSP: Requested Services = 05 NSP: 0000 ..0. = always zero NSP: .... 01.. = segment request count NSP: ...... 1 = always one NSP: Version Information = 07 NSP: 0000 01.. = should be zero NSP: ...... 11 = reserved NSP: Segment Size (bytes) = 1418 SCP: ----- Session Control Protocol ----- SCP: Destination Name: SCP: Name Format Type = 1 SCP: Object Type = 0 (General Task, User Process) SCP: Name Length = 3 SCP: Name = "VAL" SCP: Source Name: SCP: Name Format Type = 1 SCP: Object Type = 0 (General Task, User Process) SCP: Name Length = 6 SCP: Name = "SYSTEM" SCP: Menu Version = 20 SCP: 0...... = non-extensible field SCP: .01. .... = reserved SCP: ...0 00.. = reserved SCP: ...... 0. = USRDATA field not included SCP: ...... 0 = RQSTRID, PASSWRD and ACCOUNT fields not included ADDR HEX ASCII 0000: aa 00 04 00 a7 04 aa 00 04 00 01 04 60 03 2f 00 | ....§...... `./. 0010: 81 2e 00 00 aa 00 04 00 0b 04 00 00 aa 00 04 00 | ...... 0020: 01 04 00 01 00 00 68 00 00 4c 00 05 07 8a 05 01 | ...... h..L...... 0030: 00 03 56 41 4c 01 00 06 53 59 53 54 45 4d 20 | ..VAL...SYSTEM
Page K - 20 Configuring the DECnet Routing Protocol on Cisco Routers
To configure DECnet on Cisco routers, one must execute the task set forth in order:
· Task #1, Enable DECnet routing on the router. To enable DECnet routing on a Cisco router, one needs the Area and Host ID of the router. At the global command prompt type the command “decnet routing” followed by the Area/Host ID of the router.
· Task #2, Configure node type on the router. To designate a router as a DRP Level 1 router requires the designator “routing-iv” node-type. Designating a Level Two router requires the designator “area” node-type.
· Task #3, Configure DECnet cost on the interfaces to be used. Enabling DECnet routing only starts the routing process within the router. To activate an interface for DECnet routing one must assign a “decnet cost” to that interface.
· Task #4, Configure DECnet priority on the interfaces to be used. Assigning a router priority lets the router participate in the DR election. The router with the highest priority is elected the DR.
· Task #5, Configure Split-Horizon on the interfaces to be used. Enabling split-horizon allows the router to compute loop free routes.
*** NOTE *** When configuring DECnet with other routing protocols, you MUST configure DECnet first due to the change of MAC addresses to DECnet MAC addresses.
Example Router configuration: ! hostname router3 ! decnet routing 1.2 decnet node-type routing-iv ! interface Ethernet0 decnet cost 10 decnet router-priority 10 decnet split-horizon ! interface Ethernet1 decnet cost 10 decnet router-priority 10 decnet split-horizon !
DECnet over Token Ring
DECnet does not byte swap its MAC header of AA:00:04:00 in Token Ring. Recall that, Token Ring reorders the bits of the MAC address from Canonical to Non-Canonical. This produces a problem. In Token Ring, the header AA:00:04:00 indicates a multicast address. One may use Token Ring for two Cisco devices to communicate via DECnet but, the routers will not communicate with native DECnet devices. To over come this problem, Cisco provides for DECnet encapsulation on Token Ring. To enable this DECnet encapsulation the interface command is “decnet encapsulation dec”.
Page K - 21 Phase IV to Phase V Conversion
Phase IV to Phase V conversion allows for a Cisco router to communicate with both Phase IV hosts and Phase V hosts. Cisco routers with conversion enabled allow for Phase IV and Phase V hosts to communicate. Routers that have conversion enabled must use the ISO CLNS IS-IS routing protocol enabled. To enable this conversion the global command is “decnet conversion” followed by the CLNS IS- IS area number.
*** NOTE *** When configuring DECnet Phase IV to Phase V conversion with IS-IS, one must be sure to enable IS- IS on all the interfaces of the router, to include those not participating in routing IS-IS.
Phase IV over OSI networks
When two Phase IV areas are separated by a Phase V area, the two Phase IV areas will be unable to communicate with each other because Phase V does not propagate Phase IV addresses. To force route propagation across an OSI network one must configure “dummy clns routes” on each side for each area in the Phase IV networks. This configuration must be done at the routers that border the Phase IV/Phase V networks. Each side must be configured to advertise the networks they can reach to the other side. There are three tasks involved in this:
· Task #1, enable Phase IV to Phase V conversion
· Task #2, Configure DECnet to advertise the areas. The global configuration command “decnet advertise” followed by the area, hosts, and cost. For example, to advertise the area 2 with hops set to 2 and cost set to 1, the command would be “decnet advertise 2 2 1”
· Task #3, Advertise the dummy clns routes on each side The global configuration command “clns route” followed by the IS-IS area and the ID of the DECnet area, then followed by the option “discard”. For example, to advertise the Phase IV Area 2 through IS-IS area 1, the command would be: “clns route 1.0002 discard”.
Example Phase IV to Phase V conversion with OSI backbone…
Page K - 22 Cisco Address Translation Gateways
DECnet Address Translation Gateways were created to overcome the problem when two networks with identical area numbers merge. Cisco provides a similar solution called Cisco Address Translation Gateways. Only one router needs to be configured for ATG between the two networks. The following tasks list provides the steps necessary to configure an ATG. Most implementations will have the ATG router configured as a Level 1 in the first area and a Level 2 for the virtual network.
· Task #1, Configure a router with an interface on each network with DECnet. The global command for configuring multiple DECnet routing processes on a Cisco router is “decnet” followed by the routing process number, followed by “routing” followed by the router ID on the first network. Configure the node type for the router. Do the same for the second routing process. One of the processes should be configured as a Level 1 Router, the other as a Level 2 Router.
· Task #2, Configure the interfaces for DECnet in their respective DECnet networks. The interface command for this is “decnet”, followed by the routing process number, followed by “cost” followed by the cost of that interface.
· Task #3, Configure the mappings between AREA IDs. The global command for this is “decnet”, followed by the routing process number, followed by “map”, followed by the mapping
Below is an example configuration and network diagram.
In the diagram above, when the Micro VAX in network B sends a packet to host 50.3, it will be translated by the ATG to 1.2 on network A.
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DECnet Show Commands
Various commands can be used to verify DECnet configurations on Cisco routers. Among them are: show decnet neighbor and show decnet route
The command show decnet neighbor displays a list of DECnet devices that share the same segment as the current router. The output for the command is shown below.
The output of Show Decnet Neighbor in an Ethernet environment….
The output of Show Decnet Neighbor in a Token Ring environment….
Notice the MAC address of device 1.4 starts with 5500.2000 instead of aa00.0400.
Page K - 24 The command show decnet route displays a list of the current routes associated with a particular DECnet router. On a Level 2 router the routing tables will contain the list of hosts with in a given area, as well as, the area of address of other Level 2 routers.
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