Application of Router Bridge Function in VLAN Technology Division

Compatibility with proprietary protocols of router bridging technology. However, some problems were encountered when preparing to implement the VLAN plan. We know that a virtual local area network VLAN is an independent physical network that can be logically divided, and can generally be considered equivalent to a layer 2 broadcast domain. Data frames cannot be forwarded between two VLANs in the switch. To achieve communication between VLANs, the switch needs to be connected to a layer 3 device (such as a router or layer 3 switch) for routing. Generally speaking, a physical port belongs to only one VLAN, so the number of VLANs must be consistent with the number of Ethernet physical ports of the router and the number of ports used by the switch for cascading, which will cause a lot of port waste and greatly limit the VLAN The flexibility of expansion and division. In order to solve this problem, to realize the transmission of multiple VLAN data streams on a physical port, you can use the "Tagging" (Tagging) technology, that is, tag each data frame on this port to mark the frame to which the frame belongs For VLANs, the system uses its VLAN identification number, or VLAN ID, to determine the forwarding of data frames. This requires network devices to support the Tagging encapsulation protocol.

The technical difficulty encountered in this example is that Catalyst 1924 switches and SuperStack 1100 switches support different VLAN tagging encapsulation protocols: Catalyst 1924 can encapsulate Cisco proprietary ISL protocol, while SuperStack 1100 can only encapsulate IEEE 802.1Q, These two protocols are incompatible with each other. In this way, the two types of switches cannot simultaneously transmit multiple VLAN data streams through a cascade port, which will inevitably cause port waste and limit the flexibility of VLAN division.

Fortunately, the unit also has a Cisco 3640 router, and the router contains two Ethernet ports. At the same time, the IOS version of the Cisco 3640 supports the above two VLAN tagging encapsulation protocols. At this time, you can use the router's transparent bridging function. . Before introducing the solution, first briefly explain the transparent bridging feature of the Cisco router.

Transparent bridging of Cisco routers with router bridging technology

In Cisco routers, its IOS software supports transparent bridging based on Ethernet, FDDI fiber networks, and serial links.

Cisco routers provide integrated routing and bridging (Integrated RouTIng and Bridging, IRB) functions. When IRB is configured, non-routable protocol data streams can be bridged and exchanged on ports configured as the same bridge group, while routable protocol data streams can be routed between other routing ports or different bridge groups .

There is a concept mentioned here, namely the Bridge-Group. To realize the bridge exchange between different ports, these ports must be grouped into the same bridge group. Conceptually, all ports configured in the same bridge group belong to the same Layer 2 broadcast domain, regardless of whether the port type is a WAN port or an Ethernet port, and whether the port is a physical port or a logical port (such as X.25 sub-port or Ethernet VLAN sub-port). The Cisco router automatically generates a virtual interface for each bridge group that has been configured. This is called the Beidge-Group Virtual Interface (BVI). It can implement routing capabilities between different BVIs or between BVIs and other ports. The following describes the main concepts of BVI and IRB configuration tasks.

Among them, ports E0, E1, E2 are bridge ports, which are grouped into the same bridge group Bridge-Group 1. For this purpose, the router automatically generates a logical virtual interface BVI 1, and port E3 is a routing port. In terms of working principle, the router configured in this figure is equivalent to such a network connection, that is, a 4-port switch composed of E0, E1, E2 and an uplink port and a 2-port router composed of BVI 1, E3 pass The BVI 1 interface is connected. Obviously the three ports E0, E1 and E2 are in the same broadcast domain.

Router Bridge Technology Solution

With the relevant concepts of IRB, you can solve the aforementioned problems. In the actual solution, first, assign VLANs to Catalyst 1924 and SuperStack 1100 switches, and enable ISL and IEEE 802.1Q tagging protocols on their uplink ports, and then connect them to the two Ethernets of the Cisco 3640 router, respectively. On the network port, the Bx port of the Catalyst 1924 and the port 26 of the SuperStack 1100 are used as the uplink ports. After completing the physical cable connection, the main job is to configure the Cisco 3640 router. As an example, consider the case of two VLANs, VLAN 1 and VLAN 2, respectively, assuming that they correspond to the sales department and the financial department, respectively. The network structure is shown in the figure.

In the router, to make the Ethernet port transmit different VLAN data streams at the same time, the Tagging protocol should be encapsulated into the sub-port. For example, on the port connecting Cisco 3640 and Catalyst 1924, the corresponding configuration command for VLAN 1 should be as follows:

interface fastethernet 0 / 0.1

encapsulaTIon isl 1

Similarly, the port connected to the SuperStack 1100 also needs to be configured with a sub-port, but the encapsulation protocol must be changed to IEEE 802.1Q. The command is as follows:

interface fastethernet 0 / 1.1

encapsulaTIon dot1q 1

With the VLAN sub-ports, as long as the sub-ports of the same VLAN are grouped into the same bridge group, the VLAN interconnection of the Catalyst 1924 and SuperStack 1100 can be achieved. Here, if both fastethernet 0 / 0.1 and fastethernet 0 / 1.1 are grouped into bridge-group 1, then VLAN 1 of Catalyst 1924 and VLAN 1 of SuperStack 1100 will be logically merged into one VLAN.

Finally, by configuring an IP address for the BVI interface of the bridge group and supplemented by certain ACL list settings, you can implement secure routing between VLAN 1 and VLAN 2.

When configuring servers and workstations on the network, the default gateway of the computer in the VLAN 1 finance department should be set to the address of interface BVI 1 in the router configuration, which is Similarly, the default gateway of the computer in the VLAN 2 sales department should be set to the address of interface BVI 2, which is

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