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    Understanding Integrated Routing and Bridging Interfaces and Routed VLAN Interfaces on EX Series Switches

    Virtual LANs (VLANs), by definition, divide a LAN’s broadcast environment into isolated virtual broadcast domains, thereby limiting the amount of traffic flowing across the entire LAN and reducing the possible number of collisions and packet retransmissions within the LAN. For example, you might want to create a VLAN that includes the employees in a department and the resources that they use often, such as printers, servers, and so on.

    Of course, you also want to allow these employees to communicate with people and resources in other VLANs. To forward packets between VLANs, you traditionally needed a router that connected the VLANs. However, you can also accomplish this forwarding with a switch by configuring one of the following features:

    • On Juniper Networks EX Series Ethernet Switches that run Juniper Networks Junos operating system (Junos OS) that supports the Enhanced Layer 2 Software (ELS) configuration style, configure an integrated routing and bridging (IRB) interface.
    • On EX Series switches that run Junos OS that does not support ELS, configure a routed VLAN interface (RVI).

    Note: IRB interfaces and RVIs provide the same functionality. Where the functionality for both features is the same, this topic uses the term these interfaces to refer collectively to both IRB interfaces and RVIs. Where differences exist between the two features, this topic calls out the IRB interfaces and RVIs separately.

    Configuring a switch to route traffic between VLANs reduces complexity and eliminates the costs associated with purchasing, installing, managing, powering, and cooling a router.

    These interfaces route only VLAN traffic and work by logically dividing a switch into multiple virtual routing instances, thereby isolating VLAN traffic traveling across the network into virtual segments. These interfaces allow switches to recognize which packets are being sent to another VLAN’s MAC addresses—then, packets are bridged (switched) whenever the destination is within the same VLAN and are routed through these interfaces only when necessary. Whenever packets can be switched instead of routed, several layers of processing are eliminated. The switches rely on their Layer 3 capabilities to provide this basic routing between VLANs:

    • Two VLANs on the same switch
    • Two VLANs on different switches (routing is provided by an intermediary third switch.)

    Figure 1 illustrates a switch routing VLAN traffic between two access layer switches using one of these interfaces.

    Figure 1: An IRB Interface or RVI on a Switch Providing Routing Between Two Access Switches

    An IRB Interface or RVI on a
Switch Providing Routing Between Two Access Switches

    This topic describes:

    When Should I Use an IRB Interface or RVI?

    Configure an IRB interface or an RVI for a VLAN if you need to:

    • Allow traffic to be routed between VLANs.
    • Provide Layer 3 IP connectivity to the switch.
    • Monitor individual VLANs for billing purposes. Service providers often need to monitor traffic for this purpose, but this capability can be useful for enterprises where various groups share the cost of the network.

    How Does an IRB Interface or RVI Work?

    For an IRB interface, the switch provides the name irb, and for an RVI, the switch provides the name vlan. Like all Layer 3 interfaces, these interfaces require a logical unit number with an IP address assigned to it. In fact, to be useful, the implementation of these interfaces in an enterprise with multiple VLANs requires at least two logical units and two IP addresses—you must create units with addresses in each of the subnets associated with the VLANs between which you want traffic to be routed. That is, if you have two VLANs (for example, VLAN red and VLAN blue) with corresponding subnets, your interfaces must have a logical unit with an address in the subnet for red and a logical unit with an address in the subnet for blue. The switch automatically creates direct routes to these subnets and uses these routes to forward traffic between VLANs.

    The interface on the switch detects both MAC addresses and IP addresses, then routes data to other Layer 3 interfaces on routers or other switches. These interfaces detect both IPv4 and IPv6 unicast and multicast virtual routing and forwarding (VRF) traffic. Each logical interface can belong to only one routing instance and is further subdivided into logical interfaces, each with a logical interface number appended as a suffix to the names irb and vlan—for example, irb.10 and vlan.10.

    Creating an IRB Interface or RVI

    There are four basic steps in creating an IRB interface or RVI as shown in Figure 2.

    Figure 2: Creating an IRB Interface or RVI

    Creating an IRB Interface or
RVI

    The following explanations correspond to the four steps for creating a VLAN, as depicted in Figure 2.

    • Configure VLANs—Virtual LANs are groups of hosts that communicate as if they were attached to the same broadcast stream. VLANs are created with software and do not require a physical router to forward traffic. VLANs are Layer 2 constructs.
    • Create IRB interfaces or RVIs for the VLANs—The switch’s IRB interfaces and RVIs use Layer 3 logical interfaces (unlike routers, which can use either physical or logical interfaces).
    • Assign an IP address to each VLAN—An IRB interface or RVI cannot be activated unless it is associated with a physical interface.
    • Bind the VLANs to the logical interfaces—There is a one-to-one mapping between a VLAN and an IRB interface or RVI, which means that only one of these interfaces can be mapped to a VLAN.

    For specific instructions for creating an IRB interface, see Configuring Integrated Routing and Bridging Interfaces (CLI Procedure), and for an RVI, see Configuring Routed VLAN Interfaces (CLI Procedure).

    Viewing IRB Interface and RVI Statistics

    Some switches automatically track IRB interface and RVI traffic statistics. Other switches allow you to configure tracking. Table 1 illustrates the IRB interface- and RVI-tracking capability on various switches.

    Table 1: Tracking IRB Interface and RVI Usage

    Switch

    Input (ingress)

    Output (Egress)

    EX4300

    Automatic

    Automatic

    EX3200, EX4200

    Automatic

    EX8200

    Configurable

    Automatic

    EX2200, EX3300, EX4500, EX6200

    You can view input (ingress) and output (egress) totals with the following commands:

    • For IRB interfaces, use the show interfaces irb extensive command. Look at the input and output values in the Transit Statistics field for IRB interface activity values.
    • For RVI, use the show interfaces vlan extensive command. Look at the input and output values in the Logical Interface Transit Statistics field for RVI activity values.

    IRB Interfaces and RVI Functions and Other Technologies

    IRB interfaces and RVIs are similar to switch virtual interfaces (SVIs) and bridge-group virtual interfaces (BVIs), which are supported on other vendors’ devices. They can also be combined with other functions:

    • VRF is often used in conjunction with Layer 3 subinterfaces, allowing traffic on a single physical interface to be differentiated and associated with multiple virtual routers. For more information about VRF, see Understanding Virtual Routing Instances on EX Series Switches .
    • For redundancy, you can combine an IRB interface or RVI with implementations of the Virtual Router Redundancy Protocol (VRRP) in both bridging and virtual private LAN service (VPLS) environments. For more information about VRRP, see Understanding VRRP on EX Series Switches.

    Modified: 2016-12-06