Cisco Systems BC-281 Manual De Usuario

The DLSw standard, documented in RFC 1795, defines the switch-to-switch protocol between DLSw 
routers. The standard also defines a mechanism to terminate data-link control connections locally and 
multiplex the traffic from the data-link control connections to a TCP connection. The standard always 
calls for the transport protocol to be TCP and always requires that data-link control connections be 
locally terminated (the equivalent of Cisco’s local acknowledgment option). The standard also requires 
that the SRB RIF be terminated at the DLSw router. The standard describes a means for prioritization 
and flow control and defines error recovery procedures that ensure data-link control connections are 
appropriately disabled if any part of their associated circuits breaks.

The DLSw standard does not specify when to establish TCP connections. The capabilities exchange 
allows compliance to the standard, but at different levels of support. The standard does not specify how 
to cache learned information about MAC addresses, RIFs, or NetBIOS names. It also does not describe 
how to track either capable or preferred DLSw partners for either backup or load-balancing purposes. 
The standard does not provide the specifics of media conversion, but leaves the details up to the 
implementation. It does not define how to map switch congestion to the flow control for data-link 
control. Finally, the MIB is documented under a separate RFC.

In the Version 1 standard, a network design requires fully meshed connectivity so that all peers were 
connect to every other peer. This design creates unnecessary broadcast traffic because an explorer 
propagates to every peer for every broadcast.

The Version 2 standard is documented in RFC 2166. It includes RFC 1795 and adds the following 
enhancements:

Users implement DLSw Version 2 for scalability if they are using multivendor DLSw devices with an IP 
multicast network. DLSw Version 2 requires complex planning because it involves configuration 
changes across an IP network. 

Multicast service avoids duplication and excessive bandwidth of broadcast traffic because it replicates 
and propagates messages to its multicast members only as necessary. It reduces the amount of network 
overhead in the following ways: 

Avoids the need to maintain TCP Switch-to-Switch Protocol (SSP) connections between two DLSw 
peers when no circuits are available 

Ensures that each broadcast results in only a single explorer over every link

DLSw Version 2 is for customers who run a multicast IP network and do not need the advantages of 
border peering.