The Source-Route Bridge (SRB) is an auxiliary interface of a router that is designed to provide a single path between two or more LANs. The bridge is connection-oriented, meaning it uses the MAC destination address of the frame to find the shortest route to the destination.
In the Token Ring environment, the SRB is an essential component that allows users to establish a route through multiple ring networks. The SRB has three main components. The first one, spanning tree logic, sets the state of the bridge. The second, explorer, is used by end stations to discover a routing path. The third, remote source-route bridging, is used by routers to communicate with other devices.
The spanning tree function consists of a number of blocks that interact with other bridges to determine the best route between the end stations. Among them, the SR-type determination block is the most important. This block examines the RT section of the routing information field to determine the corresponding SR type. Specifically routed frame forwarding logic 52 then forwards the frame to the destination station.
The RII bit is a logical “1” when the SR type is determined and is sent to the source routing logic means. This is a stepping stone to examining the rest of the routing information field. If the RII is set to a logical “0”, the frame is dropped. However, if the RII is set to a “1”, the BPDU frame is sent to the spanning tree logic means and is processed. This frame is defined by the ISO 10038 standard. The BPDU frame is not an SRF or STE frame.
The explorer frame is a packet that is copied by all bridges in the network. It contains the information that the end station needs to decide on the best route to send the explorer to the originator. The destination station then reroutes the explorer through a specific route. The explorer frame is then forwarded to the respective end stations. This is done to ensure that the explorer has the correct path to reach the destination. The source routing architecture adds this information to the routing information field and forwards it to the bridges.
The SRT bridge is compatible with any LAN and interconnects two or more LANs. In addition, the SRT bridge can be configured to work with multiple-ring networks. Consequently, the number of nodes in a Token Ring LAN can be limited by the number of available bridges. The bridging hardware can support up to 260 nodes.
The SRT bridge modifies the RIF and the largest frame to form a new, specialized frame. In this way, it creates a virtual ring group of 200 nodes. This is useful to extend the length of a LAN by physically adding more nodes. It can also be used to provide concurrent access to NetWare file services or to provide concurrent access to redundant links. The SRT bridge is also compatible with Novell Internet Access Server 4.1. It can be migrated from an existing bridge.
Transparent bridging is one of the most common bridging methods used in conventional networks. It has several advantages, including efficiency and mobility of the end system. Nevertheless, it also places a lot of requirements on the architecture of a bridge. For example, a transparent bridging system must be able to support end system mobility, network reconfiguration, and a number of other functions.
This type of bridging is implemented primarily in Ethernet networks. When an Ethernet packet is received on a particular port, the bridge examines the header to learn about the MAC address and performs the appropriate filtering. The resulting bridging table helps the bridge transmit data packets to the correct destination. The spanning tree is a logical and practical implication of this process.
The spanning tree is a tree-like model that maintains connectivity between all nodes in the domain. It is customizable to achieve the desired level of scalability. Moreover, it does not create loops that would otherwise cause broadcast radiation. The standard implementation of the spanning tree has multiple domains.
The most common and basic function of a bridge is to accept frames of data passing through a network. This is accomplished by performing a number of operations per frame. For example, it might forward a packet to a specific device or drop it for a certain period of time. Alternatively, it might use a number of different paths to reach the same destination. Despite the simplicity of this process, it is important to remember that the shortest path is not always the most efficient. A transparent bridging system might also combine a number of different bridges.
The filtering database is the key component of a transparent bridging system. It contains all of the MAC addresses of various devices and serves as a central repository for the information required for the routing of data packets. In addition, it manages a number of timers related to the database entries.
The most important of these is the aging timer. The bridge must be able to quickly handle these tasks, otherwise, it might cause performance degradation. For instance, if the aging timer is not managed properly, it might fail to perform a certain operation in a timely manner. A transparent bridging system is also susceptible to problems with services running on a firewall. For example, it might not be possible to use NAT (network address translation) with the system. The MAC address of an Internet-connected host is a good indicator of the source of the traffic that it receives. Therefore, the firewall’s MAC address should never be used as the source of incoming traffic.
A transparent bridging system is also equipped to monitor the source address of a given frame, and determine the best route to send the frame to the expected destination. It then adds the MAC address of the destination to its forwarding table. This is the process of the transparent bridging system’s most important feat.
The bridging process, in essence, is a series of operations that place unknown addresses on the correct routes. The process does not require the presence of a dedicated agent. However, the process is a good indication of how a transparent bridging system works.