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Introduction
DLSw stands for Data Link Switching. DLSw is a switch-to-switch protocol that is used to transport IBM SNA and IBM NetBIOS traffic over an IP network. This protocol doesn't provide full routing, but instead provides switching at the SNA Data Link layer and encapsulation in TCP/IP for transport over the Internet.
DLSw+ is Cisco's implementation of DLSw. In addition to the DLSw standard, DLSw+ includes the following features:
- Choice of transport option, including TCP, FST(fast-sequenced transport), and direct encapsulation.
- Scalability enhancements through: peer groups, on-demand peers, explorer firewalls, and location learning.
- Media conversion between local and remote LANs and SDLC or Ethernet.
For more details on DLSw and DLSw+, refer to the white paper (doc id#039WP).
What is the DLSw standard?
For greater detail on the DLSw standard, refer to RFC 1795. (RFC 1434 was made obsolete by RFC 1795). In summary, RFC 1795 describes the switch-to-switch protocol (SSP) used between routers to establish DLSw connections, locate resources, forward data, handle flow control, and error recovery. It also describes how to terminate DLC connections locally and map the DLC connections to a DLSw circuit. By terminating DLC connections locally, DLSw addresses the following problems:
- DLC time-outs
- DLC acknowledgments over the WAN
- Flow and congestion control
- Broadcast control of search packets
- Source-Route Bridging hop counts limits
Sample Configurations
The configurations depicted here are partial configurations; they portray only the part of the configuration required for DLSw+ support, and none of the IP or other protocol support. Since DLSw+ relies on TCP/IP (except when you are using FST or direct), the assumption is that the IP network is already up and running.
1 Ring to Ring over WAN:
RouterA:
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.1.1 dlsw remote-peer 0 tcp 150.150.2.1 ! interface Loopback0 ip address 150.150.1.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.1 255.255.255.0 ! interface TokenRing0 ip address 150.150.10.1 255.255.255.0 ring-speed 16 source-bridge 1 1 2000 source-bridge spanning
RouterB: ! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.2.1 dlsw remote-peer 0 tcp 150.150.1.1 ! interface Loopback0 ip address 150.150.2.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.2 255.255.255.0 ! interface TokenRing0 ip address 150.150.20.2 255.255.255.0 ring-speed 16 source-bridge 2 1 2000 source-bridge spanning
In this example, we pick up one virtual ring, ring number 2000, to easily establish a relationship between the two groups. However since RIF (routing information field) is terminated at the DLSw+ router, you can choose a different virtual ring number for each router. Be careful when choosing the ring number; you should follow the same rules that apply to source-route bridging. Currently Cisco only supports one virtual ring per router.
The dlsw local-peer command is used to define your own DLSw+ IP address for the local router. In the above example, the IP address of the loopback interface is used so that DLSw+ doesn't have to rely on the real physical interface being up to work.
The dlsw remote-peer command defines the IP address of the remote router. The number 0 that follows the remote-peer keyword is the ring-list number. Generally, if you want a fully meshed network, use the number 0. The ring-list number is used to control the flooding of explorer frames by allowing the network to be segmented (see example two for a ring-list demonstration). In this example, all NetBIOS and SNA stations on Ring 1 can talk to all NetBIOS and SNA stations on Ring 2. If there are more rings that are connected to these two routers, they can also talk as long as the configuration for the interface is correctly configured.
2 Ring to Ring with Ring-list
Router A
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.1.1 dlsw remote-peer 0 tcp 150.150.2.1 ! interface Loopback0 ip address 150.150.1.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.1 255.255.255.0 ! interface TokenRing0 ip address 150.150.10.1 255.255.255.0 ring-speed 16 source-bridge 3 1 2000 source-bridge spanning
Router B
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.2.1 dlsw remote-peer 1 tcp 150.150.1.1 dlsw ringlist 1 ring 1 ! interface Loopback0 ip address 150.150.2.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.2 255.255.255.0 ! interface TokenRing0 ip address 150.150.20.2 255.255.255.0 ring-speed 16 source-bridge 1 1 2000 source-bridge spanning interface TokenRing0 ip address 150.150.30.1 255.255.255.0 ring-speed 16 source-bridge 2 1 2000 source bridge spanning
In this example, all the work stations on Ring 3 can only establish sessions with stations on Ring 1 but not Ring 2 and vice versa. Stations on Ring 1 can still talk to stations on Ring 2 since they are locally attached to Router B.
This means that there will be no broadcast from Ring 2 that will be delivered to Router A. Using ring-list, port-list, and b-group list statements is very useful when you want to control the broadcast traffic over the wide area network.
3 Ring to Ethernet over WAN:
Router A
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.1.1 dlsw remote-peer 0 tcp 150.150.2.1 ! interface Loopback0 ip address 150.150.1.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.1 255.255.255.0 ! interface TokenRing0 ip address 150.150.10.1 255.255.255.0 ring-speed 16 source-bridge 1 1 2000 source-bridge spanning
Router B
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.2.1 dlsw remote-peer 0 tcp 150.150.1.1 dlsw bridge-group 1 ! interface Loopback0 ip address 150.150.2.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.2 255.255.255.0 ! interface Ethernet0 ip address 150.150.30.1 255.255.255.0 bridge-group 1 ! bridge 1 protocol ieee !
In this example, the station on the Ethernet segment is allowed to talk to the stations on the Token Ring segment. The DLSw+ router will take care of the conversion from Ethernet format into Token Ring format. The bridge-group number is used to tie the Ethernet segment to the DLSw+ process just like the source bridge statement ties the Token Ring segment to the DLSw+ through the virtual ring-group.
4 Ethernet to Ethernet over WAN:
Router A
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.1.1 dlsw remote-peer 0 tcp 150.150.2.1 dlsw bridge-group 1 ! interface Loopback0 ip address 150.150.1.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.1 255.255.255.0 ! interface Ethernet0 ip address 150.150.30.1 255.255.255.0 bridge-group 1 ! bridge 1 protocol ieee !
Router B:
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.2.1 dlsw remote-peer 0 tcp 150.150.1.1 dlsw bridge-group 1 ! interface Loopback0 ip address 150.150.2.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.2 255.255.255.0 ! interface Ethernet0 ip address 150.150.40.1 255.255.255.0 bridge-group 1 ! bridge 1 protocol ieee
5 Token Ring to Ethernet in the same router.
If you need to connect stations between Ethernet and Token Ring which are local to the router, you must use SR/TLB (translational bridging).
Router A:
source-bridge ring-group 2000 source-bridge transparent 2000 1000 1 1 ! interface Ethernet0 ip address 150.150.40.1 255.255.255.0 bridge-group 1 ! interface TokenRing0 ip address 150.150.10.1 255.255.255.0 ring-speed 16 source-bridge 1 1 2000 source-bridge spanning
The above is the sample config of SR/TLB in one router. SR/TLB and DLSw+ can also be run at the same router (Example 6).
6 SR/TLB and DLSw+ together.
Router A:
source-bridge ring-group 2000 source-bridge transparent 2000 1000 1 1 dlsw local-peer peer-id 150.150.1.1 dlsw remote-peer 0 tcp 150.150.2.1 dlsw bridge-group 1
interface Ethernet0 ip address 150.150.40.1 255.255.255.0 bridge-group 1 ! interface TokenRing0 ip address 150.150.10.1 255.255.255.0 ring-speed 16 source-bridge 1 1 2000 source-bridge spanning ! bridge 1 protocol ieee
Router B:
source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.2.1 dlsw remote-peer 0 tcp 150.150.1.1 ! interface TokenRing0 ip address 150.150.11.1 255.255.255.0 ring-speed 16 source-bridge 2 1 2000 source-bridge spanning
7 Token Ring to SDLC over WAN:
Router A
! source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.1.1 dlsw remote-peer 0 tcp 150.150.2.1 ! interface Loopback0 ip address 150.150.1.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.1 255.255.255.0 ! interface TokenRing0 ip address 150.150.10.1 255.255.255.0 ring-speed 16 source-bridge 1 1 1000 source-bridge spanning
Router B
source-bridge ring-group 2000 dlsw local-peer peer-id 150.150.2.1 dlsw remote-peer 0 tcp 150.150.1.1 ! interface Loopback0 ip address 150.150.2.1 255.255.255.0 ! interface Serial0 ip address 150.150.100.2 255.255.255.0 ! interface Serial 1 no ip address encapsulation sdlc no keepalive clockrate 9600 sdlc role primary sdlc vmac 4000.9999.0100 sdlc address 01 sdlc xid 01 05D20001 sdlc partner 4000.1020.1000 01 sdlc dlsw 1 !
The above configuration examples are some common network scenarios. You can do a lot more with DLSw+ but these configurations provide you with some of the basics. Keep in mind that DLSw+ is enhanced RSRB with the additional capability of interoperability with other routers that are in compliance with RFC 1745.
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