0-0 llse~~~ntlr
2.2.3 Data Link Switching
The 6611 Network Processor provides a new function called Data Link Switching or more simply DLS. The DLS function provides the capability to integrate the transport of the NetBIOS and SNA protocol suites with the other protocol suites that can be routed by the 6611 Network Processor.
Devices which make use of the DLS function are configured as if they were directly attached to each other via a single data link or data link network. This is illustrated in Figure 18.
Data
Device Device
Link
Figure 1 B. Device View of a DLS Connection
In reality these devices only have a direct data link or data link network connection to a 6611 Network Processor. The 6611 Network Processor then transports information received on the data link or data link network connection to another 6611 Network Processor. This second 6611 Network Processor has a direct data link or data link network connection with the ultimate destination device. This is illustrated in Figure 19.
Data Transport Data
Device
6611 6611Device
Link Network Link
Figure 19. Real View of DLS Connection
The two data links or data link networks that are connected via the DLS function need not be the same type of data link or data link network. For example an SNA device attached via an SDLC data link to a 6611 Network Processor can use the DLS function to connect to an SNA device attached via a Token-Ring Network data link network.
The DLS function uses the TCP transport layer protocol (part of the TCP/IP protocol suite) to implement a transport network between 6611 Network Processors. This transport network can comprise many intermediate nodes, data links and data link networks, if required, through the use of the IP network layer protocol (also part of the TCP/I P protocol suite).
Note: Intermediate nodes in the transport network used to connect 6611 Network Processors that are providing the DLS function do not have to be 6611 Network Processors, provided that they can support the IP network layer protocol.
40 IBM 6611 Network Processor
A TCP connection is automatically established between each pair of 6611 Network Proc.essors that are participating in the DLS function across the TCP/IP transport network. To support the establishment of these TCP connections, each 6611 Network Processor is config u red with the TCP/I P network addresses of the other 6611 Network Processors participating in the DLS function.
It is possible to configure a 6611 Network Processor to accept incoming DLS TCP connections from other 6611 Network Processors without explicitly configuring the other 6611 Network Processors. This may reduce the amount of
configuration effort required to set up complex DLS environments. However, at
• Those which support indirect data links to Token-Ring Network devices (both SNA and NetBIOS) via a remote source route bridge configuration.
• Those which support connection to the TCP/IP transport network used to interconnect 6611 Network Processors that provide the DLS function.
The communication adapter features that can be used with the DLS function in each of these roles are summarized in Table 6.
Table 6. Communication Adapter Features Supported for Data Link Switching
Adapter Direct Direct Remote TCP/IP
SNA NetBIOS Bridge Transport
6611 2-Port Serial Adapter No No Yes Yes
Note: Support for NetBIOS devices attached via the 6611 Ethernet Adapter will not be included in the initial general availability of the 6611 Network Processor.
Refer to the 6611 Network Processor and Multiprotocol Network Program announcement letters for the date when support for NetBIOS devices attached via the 6611 Ethernet Adapter will become available.
The DLS function incorporates several features to reduce the need to send data across the TCP/I P network that interconnects the 6611 Network Processors participating in the DLS function.
The key feature is the cache in which each 6611 Network Processor maintains a table of remote SNA and NetBIOS devices along with the 6611 Network
Processor that is able to reach that remote device by the fastest path. Each 6611 Network Processor constructs its cache dynamically by sending queries to other
Chapter 2. Overview of 6611 Hardware and Functions 41
6611 Network Processors only when needed. The cache can be preloaded with default entries when the 6611 Network Processor is configured to further reduce the need for queries to be sent to other 6611 Network Processors.
An age out timer is used to. remove old cache entries after a a period of time.
The timeout used by the age out timer can be set when the 6611 Network Processor is configured.
Note: At the time of writing, the cache used by the DLS function could only be used to locate the MAC addresses of remote SNA and NetBIOS devices. As a consequence, NetBIOS requests to locate particular NetBIOS names were copied to all interfaces enabled for DLS on all 6611 Network Processors that participate in the DLS function. However, it is intended that the cache will also be able to be used to locate NetBIOS names of remote NetBIOS devices. This would dramatically reduce the number of NetBIOS broadcasts that flow across the TCP/IP network that interconnects all 6611 Network Processors participating in the DLS function.
There are several differences in the operation of the DLS function for SNA and NetBIOS devices. For this reason each will be described separately in the following sections.
2.2.3.1 SNA Data Link Switching
The DLS function supports the interconnection of SNA devices attached to either a Token-Ring Network or an SDLC multipoint non-switched line. A typical example of the use of the DLS function for SNA devices is illustrated in Figure 20.
~I
LANIl N~~!~rk
]1 LANIlI;l
L:·J·l!~1
Processor~
6611
Network Processor
6611
Network Processor
Figure 20. SNA Data Link Switching - Example Configuration
As a prerequisite for the DLS function, each participating 6611 Network Processor that supports TOken-Ring Network attached SNA devices, must be configured to support source route local bridging on all Token-Ring Network interfaces used with the DLS function.
Note: Local bridging will be used in preference to the DLS function to provide connections between Token-Ring Network attached SNA devices that are
42 IBM 6611 Network Processor
connected to the same 6611 Network Processor via different Token-Ring Network segments.
Each 6611 Network Processor participating in the DLS function must also be configured with a virtual segment number. This virtual segment must be the same for all 6611 Network Processors participating in the DLS function.
Additionally, SNA devices attached to a 6611 Network Processor via a SDLC multipoint non-switched line are assigned a Token-Ring Network LAA (Locally Administered Address), SAP (Service Access Point) and SNA XID (Exchange 10) which will be used by the 6611 Network Processor to represent such devices to other SNA devices that are using the DLS function.
SNA devices attached to a 6611 Network Processor via Token-Ring Network segments establish connections with SNA devices attached to other 6611 Network Processors as if they are on the virtual segment. This is illustrated in Figure 21 for the SNA devices on Token-Ring Network segments X '001' and X '002' in Figure 20 on page 42.
r;l g
Br; dgeQr;l
~~ BN=l ~~
~~ G00~
Figure 21. Logical View for SNA Devices on Segments 001 and 002
Note: A single hop is used in the RI (Routing Information) field to reach an SNA device accessible via the DLS function from a Token-Ring Network segment directly attached to a 6611 Network Processor. Therefore SNA devices can be at most six hops (seven less one) from a 6611 Network Processor to reach SNA devices accessible via the DLS function.
SNA devices attached to a 6611 Network Processor via Token-Ring Network segments establish connections with SNA devices attached to the same 6611 Network Processor via SDLC as if they were on the virtual segment. This is illustrated in Figure 22 on page 44 for the SNA devices on Token-Ring Network segment X '003' in Figure 20 on page 42.
Chapter 2. Overview of 6611 Hardware and Functions 43
Figure 22. Logical View for Devices on Segment 003
The DLS function only supports the attachment of SNA devices via SDLC multipoint lines that are of PU (Physical Unit) type 2.0. The attachment of PU type 2.1 devices is not supported unless they provide a PU type 2.0 compatibility mode. The attachment of PU type 4 devices (such as the IBM 3745
Communications Controller) is not supported either.
There are two consequences of this:
1. SDLC attached devices cannot establish connections with other SDLC attached devices. This is because SNA PU type 2.0 devices cannot directly communicate with each other as peers.
2. SDLC attached devices can only support a single connection to another SNA device attached to a Token-Ring Network. The other SNA device will usually be a PU type 4 such as the IBM 3745 Communications Controller or a PU type 5.
For example, Figure 23 shows the logical view of the SNA devices attached to the SDLC line in Figure 20 on page 42. Each SDLC attached device can be logically connected to only one other Token-Ring Network attached SNA device at any time.
I [Q--{J ~~ ? = Anyone of A,B,E,F,G or H
Figure 23. Logical View for Devices on SOLe Multipoint Line
2.2.3.2 NetBIOS Data Link Switching
The DLS function supports the interconnection of NetBIOS devices attached to either a Token-Ring Network or a CSMA/CD (Carrier Sense Multiple
Access/Collision Detection) LAN using either DIX Ethernet V2 or IEEE 802:3 frame formats. A typical example of the DLS function for NetBIOS devices is illustrated in Figure 24 on page 45.
44 IBM 6611 Network Processor
6611