Technical Documentation

Example: Configuring Reflective Relay for Use with VEPA Technology

Reflective relay returns packets to a device using the same downstream port that delivered the packets to the switch. You need to use reflective relay, for example, when a switch receives aggregated virtual machine packets from a technology such as virtual Ethernet packet aggregation (VEPA).

This example shows how to configure a switch port interface to return packets sent by VEPA on the downstream interface back to the server using the same downstream interface:

Requirements

This example uses the following hardware and software components:

One EX Series switch
Junos OS Release 11.1 or later for EX Series switches

Before you configure reflective relay on a switch port, be sure you have:

Configured a server with six virtual machines, VM 1 through VM 6. See your server documentation.
Configured the server with three VLANS named VLAN_Purple, VLAN_Orange, and VLAN_Blue and added two virtual machines to each VLAN. See your server documentation.
Configured the same three VLANS named VLAN_Purple, VLAN_Orange, and VLAN_Blue on one interface. See Configuring VLANs for EX Series Switches (CLI Procedure).
Installed and configured a VEPA to aggregate the virtual machine packets.

Overview and Topology

In this example, illustrated in Figure 1, a switch is connected to one server that is hosting six virtual machines and is configured with a VEPA for aggregating packets. The server’s six virtual machines are VM 1 through VM 6 and each virtual machine belongs to one of the three server VLANs, VLAN_Purple, VLAN_Orange, or VLAN_Blue. Instead of the server directly passing packets between virtual machines, packets from any of the three VLANS that are destined for another one of the three VLANs are aggregated with VEPA technology and passed to the switch for processing. You must configure the switch port to accept these aggregated packets on the downstream interface and to return appropriate packets to the server on the same downstream interface after they are processed. Figure 1 shows the topology for this example.

Figure 1: Reflective Relay Topology

In this example, you configure the physical Ethernet switch port interface for tagged-access port mode and reflective relay. Configuring tagged-access port mode allows the interface to accept VLAN tagged packets. Configuring reflective relay allows the downstream port to return those packets on the same interface. Table 1 shows the components used in this example.

Table 1: Components of the Topology for Configuring Reflective Relay

Component	Description
EX Series switch	For a list of switches that support this feature, see EX Series Switch Software Features Overview.
ge-7/0/2	Switch interface to the server.
Server	Server with virtual machines and VEPA technology.
Virtual machines	The six virtual machines located on the server are named V1, V2, V3, V4, V5, and V6.
VLANs	The three VLANs are named VLAN_Purple, VLAN_Orange, and VLAN_Blue. Each VLAN has two virtual machine members.
VEPA	Virtual Ethernet port aggregator that aggregates virtual machine packets on the server before the resulting single stream is transmitted to the switch.

Configuration

To configure reflective relay, perform these tasks:

Configuring Reflective Relay on the Port

Configuring Reflective Relay on the Port

CLI Quick Configuration

To quickly configure reflective relay, copy the following commands and paste them into the switch window:

[edit]

set interfaces ge-7/0/2 unit 0 family ethernet-switching
port-mode tagged-access

set interfaces ge-7/0/2 unit 0 family ethernet-switching
reflective-relay

set interfaces ge-7/0/2 unit 0 family ethernet-switching
vlan members [VLAN_Blue VLAN_Orange VLAN_Purple]

Step-by-Step Procedure

To configure reflective relay:

Configure the tagged-access port mode on the interface:
[edit] user@switch# set interfaces ge-7/0/2 unit 0 family ethernet-switching port-mode tagged-access
Configure reflective relay on the interface to allow it to both accept and send packets:
[edit] user@switch# set interfaces ge-7/0/2 unit 0 family ethernet-switching reflective-relay
Configure the interface for the three VLANs on the server:
[edit] user@switch# set interfaces ge-7/0/2 unit 0 family ethernet-switching vlan members [VLAN_Purple VLAN_Orange VLAN_Blue]

Results

Check the results of the configuration:

[edit interfaces ge-7/0/2]
user@switch# show 
unit 0 {
        family ethernet-switching {
        port-mode tagged-access;
        reflective-relay;
        vlan {
        	members [ VLAN_Purple VLAN_Orange VLAN_Blue ];
        }
    }
}

Verification

To confirm that reflective relay is enabled and working correctly, perform these tasks:

Verifying That Reflective Relay Is Enabled and Working Correctly

Verifying That Reflective Relay Is Enabled and Working Correctly

Purpose

Verify that reflective relay is enabled and working correctly.

Action

Use the show ethernet-switching interfaces detail command to display the reflective relay status:

user@switch> show ethernet-switching interfaces
ge-7/0/2 detail

Interface: ge-7/0/2, Index: 66, State: down, Port mode: Tagged-access
Reflective Relay Status: Enabled
Ether type for the interface: 0x8100
VLAN membership:
    VLAN_Purple, 802.1Q Tag: 450, tagged, unblocked
    VLAN_Orange, 802.1Q Tag: 460, tagged, unblocked
    VLAN_Blue, 802.1Q Tag: 470, tagged, unblocked
Number of MACs learned on IFL: 0

Next, confirm that reflective relay is working by sending a Layer 2 broadcast message from a virtual machine located in one VLAN to a virtual machine located in a different VLAN. Check the switch to verify that the switch sends the packets back on the same interface on which they were received. One way to check this is to set up port mirroring on the switch interface, connect a traffic generator to the mirrored interface, and use the traffic generator to examine packets. See Configuring Port Mirroring to Analyze Traffic (CLI Procedure) for details on setting up port mirroring.

Alternatively, if you don’t have a traffic generator available, you can send traffic between two virtual machines with FTP, Telnet, or SSH, while running tcpdump on the receiver virtual machine port to capture reflected packets.

Meaning

The reflective relay status is Enabled, meaning that interface ge-7/0/2 is configured for the tagged-access port mode, which accepts VLAN-tagged packets, and for reflective relay, which accepts and returns packets on the same interface.

When the traffic generator shows packets arriving at the switch and returning to the server on the same interface, reflective relay is working.

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