Data-Link Switching (DLSw) 487
Figure 13-12
LLC2 Frames
NOTE
Processor utilization thresholds can vary. For example, a 7206 with an NPM 400 processor
module can easily withstand a steady 80% utilization rate. However, a less-powerful CPU on
the 3600 series router might be susceptible to dropping packets at a steady 80% utilization rate.
Data-Link Switching (DLSw)
DLSw is a method of transporting SNA and NetBIOS traffic over a campus network or WAN
with TCP/IP. Think of DLSw as Token Ring over non-Token Ring media. The end systems can
attach to the network over Token Ring, Ethernet, SDLC, QLLC, or FDDI.
NOTE
QLLC is LLC2 frames over X.25 media. This is not discussed in this book.
Supported by IBM, Cisco, 3Com, Nortel, and others, DLSw uses TCP for reliable transport.
It also supports direct encapsulation over Frame Relay or serial links. If there is a + after the
letters DLSw, the + represents Cisco's own proprietary version of DLSw. DLSw supports
STUN and SDLLC capabilities. This first version of DLSw, as specified in RFC 1434, has the
following features:
·
Provides for load balancing
·
Allows for backup of peer routers
Token
Ring
IBM S/370
Router A
LLC2
IBM 3x74
IBM 3x74
IBM 3x74
Router B
Router C
Router D
sdlc
sdlc
sdlc
Cluster Controllers
Frame Relay
cloud
DLSW+
LLC2 frames are
converted to SDLC
frames
LLC2 frames are
converted to SDLC
frames
87200333.book Page 487 Wednesday, August 22, 2001 1:41 PM