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SDLC via STUN

SDLC via serial tunneling (STUN) encapsulates SDLC frames into Internet Protocol (IP) packets and routes the encapsulated packets over IP supported network media. The SDLC frame is transmitted without modification, and the information within the frame is transparent to the network. All SNA physical unit (PU) types are supported. SDLC is the synchronous, bit-oriented protocol used by the SNA data link control lay The SDLC data link allows a reliable exchange of information over a communication facility between SNA devices. The protocol synchronizes receivers and transmitters and detects transmission errors. It accomplishes these functions by acknowledging frame receipt and by performing a cyclic redundancy check (CRC) on the data.
 

Data Link Switching DLSW

Data link switching is a means of transporting SNA and NetBIOS traffic over an IP network. Data link switching is an alternative to source route bridging (SRB) that can be used as a basis to address several problems inherent in the SRB protocol, including:

SRB hop count limits (SRB limit is 7)
Broadcast traffic (from SRB explorer frames or NetBIOS name queries)
Unnecessary traffic (acknowledgments and keepalives)
DLC timeouts
Lack of flow control and prioritization

IBM uses the ALL ROUTE EXPLORES (ARE) to broadcast out MAC addressees.
There can be DUPLICATE macs present on the same network BUT not on the same segment or bridge. RSB allows for multiple physical paths with one logical open route.
 
 

DLSw+ offers enhanced availability by maintaining a list of multiple paths per destination MAC addresses or NetBIOS names. Each Cisco router maintains a preferred route and one or more capable routes to participating DLSw+ Border Peers that can reach the destination. If the circuit over the preferred route through a pair of DLSw+ routers is broken, the next available route is promoted to the new preferred route.
No additional broadcasts are required, and recovery over an alternate path is immediate.
The remote and local routers can also perform a LOCAL ACK which reduces network polling bandwidth.

The exact way that multiple capable peers are handled with DLSw+ can be biased to meet the needs of the network.
 

• Fault Tolerance : In order to rapidly reconnect if a data link connection is lost
• Load Balancing : In order to distribute the network traffic over multiple DLSw+ peers in the network

Whenever a new circuit is established between a pair of end systems and the end to end path for the circuit is already known (that is, it is cached), the originating DLSw+ router sends a route verification message directly to the preferred partner in order to validate the cache. If the preferred partner is no longer available, a route verification is sent to a capable router in the cache.

This route verification exchange between routers can also be configured to perform load balancing by sending the directed verify in round robin fashion through the list of capable routers.

This feature is especially attractive in SNA networks. A very common technique used in the hierarchical SNA environment is assigning the same MAC address to different Token Ring interface couplers (TICs) on the IBM frontend processors (FEPs). DLSw+ assures that duplicate TIC addresses are found, and if multiple DLSw+ peers can be used to reach the FEPs, they are all cached. This technique can be used not
only for fault tolerance but for load balancing. When using this technique for fault tolerance, it facilitates a timely reconnection after session outages. When using this technique for load balancing, it improves overall SNA performance

Configuration Examples

• Set up source bridge ring groups and peers.
• Make unique segments on LAN interfaces.

WPIS01
source-bridge ring-group 555
source-bridge remote-peer 555 tcp 192.203.241.222
source-bridge remote-peer 555 tcp 199.4.137.6
!
interface Loopback0
 no ip address
!
interface Serial0
 ip address 192.168.150.6 255.255.255.252
 bandwidth 1344
 hold-queue 130 in
 hold-queue 100 out
 ipx network C300
!
interface Serial1
 ip address 192.168.150.10 255.255.255.252
 bandwidth 1344
 hold-queue 130 in
 hold-queue 100 out
 ipx network C301
!
interface TokenRing0
 ip address 192.168.1.1 255.255.255.0 secondary
 ip address 192.168.2.1 255.255.255.0 secondary
 ip address 192.203.241.222 255.255.255.0
 ipx network BB0
 ring-speed 16
 multiring all
 source-bridge 2817 1 555
 source-bridge input-type-list 200
!
interface TokenRing1
 no ip address
 shutdown
 ipx network 67
 ipx output-network-filter 876
 ipx output-sap-filter 1001
 ring-speed 16
 multiring all
 source-bridge 2999 2 555
 source-bridge spanning
 source-bridge input-type-list 200
!