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Redundant Trunk Groups

 

In a typical enterprise network composed of distribution and access layers, a redundant trunk link provides a simple solution for network recovery when a trunk port on a switch goes down. In that case, traffic is routed to another trunk port, keeping network convergence time to a minimum.

Note

For information on redundant trunk link configurations that include Q-in-Q support and use LAGs with link protection, see Q-in-Q Support on Redundant Trunk Links Using LAGs with Link Protection.

To configure a redundant trunk link, create a redundant trunk group. The redundant trunk group is configured on the access switch and contains two links: a primary or active link, and a secondary link. If the active link fails, the secondary link automatically starts forwarding data traffic without waiting for normal spanning-tree protocol convergence.

Data traffic is forwarded only on the active link. Data traffic on the secondary link is dropped and shown as dropped packets when you issue the operational mode command show interfaces interface-name extensive.

While data traffic is blocked on the secondary link, Layer 2 control traffic is still permitted. For example, an LLDP session can be run between two switches on the secondary link.

Rapid Spanning Tree Protocol (RSTP) is enabled by default on the switches to create a loop-free topology, but an interface is not allowed to be in both a redundant trunk group and in a spanning-tree protocol topology at the same time. You must disable RSTP on an interface if a redundant trunk group is configured on that interface. For example, in Figure 1, in addition to disabling RSTP on the Switch 3 interfaces, you must also disable RSTP on the Switch 1 and Switch 2 interfaces connected to Switch 3. Spanning-tree protocols can, however, continue operating on other interfaces on those switches—for example on the link between Switch 1 and Switch 2.

Figure 1 shows three switches in a basic topology for redundant trunk links. Switch 1 and Switch 2 make up the distribution layer, and Switch 3 makes up the access layer. Switch 3 is connected to the distribution layer through trunk ports ge-0/0/9.0 (Link 1) and ge-0/0/10.0 (Link 2). Link 1 and Link 2 are in a redundant trunk group called group1. Link 1 is designated as the primary link. Traffic flows between Switch 3 in the access layer and Switch 1 in the distribution layer through Link 1. While Link 1 is active, Link 2 blocks traffic.

Figure 1: Redundant Trunk Group, Link 1 Active
Redundant Trunk
Group, Link 1 Active

Figure 2 illustrates how the redundant trunk link topology works when the primary link goes down.

When Link 1 between Switch 1 and Switch 3 goes down, Link 2 takes over as the active link. Traffic between the access layer and the distribution layer is then automatically switched to Link 2 between Switch 3 and Switch 2.

You can manage network convergence by configuring both a primary link and a secondary link on an EX Series switch; this is called a redundant trunk group (RTG). If the primary link in a redundant trunk group fails, it passes its known MAC address locations to the secondary link, which automatically takes over. You can configure a maximum of 16 redundant trunk groups on most standalone switches or on Virtual Chassis. The EX8200 switch and EX8200 Virtual Chassis, however, support up to 254 redundant trunk groups.

Generally, you configure a redundant trunk group by configuring one primary link (and its interface) and one unspecified link (and its interface) to serve as the secondary link. A second type of redundant trunk group, not shown in the procedure in this topic, consists of two unspecified links (and their interfaces); in this case, neither of the links is primary. In this second case, the software selects an active link by comparing the port numbers of the two links and activating the link with the higher port number. The procedure given here describes configuring a primary/unspecified configuration for a redundant trunk group because that configuration gives you more control and is more commonly used.

Rapid Spanning Tree Protocol (RSTP) is enabled by default on EX Series switches to create a loop-free topology, but an interface is not allowed to be in both a redundant trunk group and in a spanning-tree protocol topology at the same time.

A primary link takes over whenever it is able. You can, however, alter the number of seconds that the primary link waits before reestablishing control by configuring the primary link’s preempt cutover timer.

Before you configure the redundant trunk group on the switch, be sure you have:

  • Disabled RSTP on all switches that will be linked to your redundant trunk group.

  • Configured at least two interfaces with their port mode set to trunk; be sure that these two interfaces are not part of any existing RTG. See Configuring Gigabit Ethernet Interfaces (CLI Procedure) .

To configure a redundant trunk group on a switch:

  1. Turn off RSTP:
    [edit]

    user@switch# set protocols rstp disable

  2. Name the redundant trunk group while configuring one primary and one unspecified trunk interface:
    [edit ethernet-switching-options]

    user@switch# set redundant-trunk-group group name interface interface-name primary

    user@switch# set redundant-trunk-group group name interface interface-name

  3. (Optional) Change the length of time (from the default of 1 second) that a re-enabled primary link waits to take over from an active secondary link:
    [edit ethernet-switching-options]
    set redundant-trunk-group group name preempt-cutover-timer seconds
Note

This example uses Junos OS for EX Series switches or QFX Series with support for the Enhanced Layer 2 Software (ELS) configuration style.. For ELS details, see Using the Enhanced Layer 2 Software CLI.

You can manage network convergence by configuring both a primary link and a secondary link on a switch; this is called a redundant trunk group (RTG). If the primary link in a redundant trunk group fails, it passes its known MAC address locations to the secondary link, which automatically takes over after one minute.

This example describes how to create a redundant trunk group with a primary and a secondary link:

Requirements

This example uses the following hardware and software components:

  • Two EX Series or QFX Series distribution switches

  • One EX Series or QFX Series access switch

  • The appropriate software release for your platform:

    • For EX Series switches: Junos OS Release 13.2X50-D10 or later

    • For the QFX Series: Junos OS Release 13.2X50-D15 or later

Before you configure the redundant trunk links network on the access and distribution switches, be sure you have:

  • Configured interfaces ge-0/0/9 and ge-0/0/10 on the access switch, Switch 3, as trunk interfaces.

  • Configured one trunk interface on each distribution switch, Switch 1 and Switch 2.

  • Connected the three switches as shown in the topology for this example (see Figure 3).

Overview and Topology

In a typical enterprise network composed of distribution and access layers, a redundant trunk link provides a simple solution for trunk interface network recovery. When a trunk interface fails, data traffic is routed to another trunk interface after one minute, thereby keeping network convergence time to a minimum.

This example shows the configuration of a redundant trunk group that includes one primary link (and its interface) and one unspecified link (and its interface) that serves as the secondary link.

A second type of redundant trunk group, not illustrated in the example, consists of two unspecified links (and their interfaces); in this case, neither of the links is primary. The software selects an active link by comparing the port numbers of the two links and activating the link with the higher port number. For example, if the two link interfaces use interfaces ge-0/1/0 and ge-0/1/1, the software activates ge-0/1/1. (In the interface names, the final number is the port number.)

The two links in a redundant trunk group generally operate the same way, whether they are configured as primary/unspecified or unspecified/unspecified. Data traffic initially passes through the active link but is blocked on the inactive link. While data traffic is blocked on the secondary link, note that Layer 2 control traffic is still permitted if the link is active. For example, an LLDP session can be run between two switches on the secondary link. If the active link either goes down or is disabled administratively, it broadcasts a list of its known MAC addresses for data traffic; the other link immediately picks up and adds the MAC addresses to its address table, becomes active, and begins forwarding traffic.

The one difference in operation between the two types of redundant trunk groups occurs when a primary link is active, goes down, is replaced by the secondary link, and then reactivates. When a primary link is re-enabled while the secondary link is active, the primary link waits 1 second (you can change the time interval by using the preempt cutover timer to accommodate your network) and then takes over as the active link. In other words, the primary link has priority and is always activated if it is available. This differs from the behavior of two unspecified links, both of which act as equals. Because the unspecified links are equal, the active link remains active until it either goes down or is disabled administratively; this is the only time that the other unspecified link learns the MAC addresses and immediately becomes active.

The example given here illustrates a primary/unspecified configuration for a redundant trunk group because that configuration gives you more control and is more commonly used.

Note

Rapid Spanning Tree Protocol (RSTP) is enabled by default on the switches to create a loop-free topology, but an interface is not allowed to be in both a redundant trunk group and in a spanning-tree protocol topology at the same time. You will need to disable RSTP on the two distribution switches in the example, Switch 1 and Switch 2. Spanning-tree protocols can, however, continue operating in other parts of the network—for example, between the distribution switches and also in links between distribution switches and the enterprise core.

Figure 3 displays an example topology containing three switches. Switch 1 and Switch  2 make up the distribution layer, and Switch 3 makes up the access layer. Switch  3 is connected to the distribution layer through trunk interfaces ge-0/0/9.0 (Link 1) and ge-0/0/10.0 (Link 2).

Table 1 lists the components used in this redundant trunk group.

Because RSTP and RTGs cannot operate simultaneously on a switch, you disable RSTP on Switch 1 and Switch 2 in the first configuration task, and you disable RSTP on Switch 3 in the second task.

The second configuration task creates a redundant trunk group called example 1 on Switch 3. The trunk interfaces ge-0/0/9.0 and ge-0/0/10.0 are the two links configured in the second configuration task. You configure the trunk interface ge-0/0/9.0 as the primary link. You configure the trunk interface ge-0/0/10.0 as an unspecified link, which becomes the secondary link by default.

Figure 3: Topology for Configuring the Redundant Trunk Links
Topology for Configuring
the Redundant Trunk Links

Table 1: Components of the Redundant Trunk Link Topology

PropertySettings

Switch hardware

  • Switch 1–1 EX Series or QFX Series distribution switch

  • Switch 2–1 EX Series or QFX Series distribution switch

  • Switch 3–1 EX Series or QFX Series access switch

Trunk interfaces

On Switch 3 (access switch): ge-0/0/9.0 and ge-0/0/10.0

Redundant trunk group

rtg0

Disabling RSTP on Switches 1 and 2

To disable RSTP on Switch 1 and Switch 2, perform this task on each switch:

CLI Quick Configuration

To quickly disable RSTP on Switch 1 and Switch 2, copy the following command and paste it into each switch terminal window:

[edit]


set protocols rstp disable


Step-by-Step Procedure

To disable RSTP on Switch 1 and Switch 2:

  1. Disable RSTP on Switch 1 and Switch 2:
    [edit]

    user@switch# set protocols rstp disable

Results

Check the results of the configuration:

Results

Configuring Redundant Trunk Links on Switch 3

To configure redundant trunk links on Switch 3, perform this task:

CLI Quick Configuration

To quickly configure the redundant trunk group rtg0 on Switch 3, copy the following commands and paste them into the switch terminal window:

[edit]
set protocols rstp disable
set switch-options redundant-trunk-group group rtg0 interface ge-0/0/9.0 primary
set switch-options redundant-trunk-group group rtg0 interface ge-0/0/10.0
set redundant-trunk-group group rtg0 preempt-cutover-timer 60

Step-by-Step Procedure

Configure the redundant trunk group rtg0 on Switch 3.

  1. Turn off RSTP:
    [edit]

    user@switch# set protocols rstp disable

  2. Name the redundant trunk group rtg0 while configuring trunk interface ge-0/0/9.0 as the primary link and ge-0/0/10 as an unspecified link to serve as the secondary link:
    [edit switch-options]

    user@switch# set redundant-trunk-group group rtg0 interface ge-0/0/9.0 primary

    user@switch# set redundant-trunk-group group rtg0 interface ge-0/0/10.0

  3. (Optional) Change the time interval (from the default of 1 second) that a re-enabled primary link waits to take over for an active secondary link:
    [edit switch-options]

    user@switch# set switch-options redundant-trunk-group group rtg0 preempt-cutover-timer 60

Results

Check the results of the configuration:

Verification

To confirm that the configuration is set up correctly, perform this task:

Verifying That a Redundant Trunk Group Was Created

Purpose

Verify that the redundant trunk group rtg0 has been created on Switch 1 and that trunk interfaces are members of the redundant trunk group.

Action

List all redundant trunk groups configured on the switch:

Meaning

The show redundant-trunk-group command lists all redundant trunk groups configured on the switch as well as the interface names and their current states (up or down for an unspecified link, and up or down and primary for a primary link). For this configuration example, the output shows that the redundant trunk group rtg0 is configured on the switch. The Up beside the interfaces indicates that both link cables are physically connected. The Pri beside trunk interface ge-0/0/9.0 indicates that it is configured as the primary link.

Note

This example uses Junos OS for EX Series switches that does not support the Enhanced Layer 2 Software (ELS) configuration style. If your switch runs software that supports ELS, see Example: Configuring Redundant Trunk Links for Faster Recovery on Devices with ELS Support. For ELS details, see Using the Enhanced Layer 2 Software CLI.

You can manage network convergence by configuring both a primary link and a secondary link on a switch; this is called a redundant trunk group (RTG). If the primary link in a redundant trunk group fails, it passes its known MAC address locations to the secondary link, which automatically takes over after one minute.

This example describes how to create a redundant trunk group with a primary and a secondary link:

Requirements

This example uses the following hardware and software components:

  • Two EX Series distribution switches

  • One EX Series access switch

  • Junos OS Release 10.4 or later for EX Series switches

Before you configure the redundant trunk links network on the access and distribution switches, be sure you have:

  • Configured interfaces ge-0/0/9 and ge-0/0/10 on the access switch, Switch 3, as trunk interfaces. See Configuring Gigabit Ethernet Interfaces (CLI Procedure).

  • Configured one trunk interface on each distribution switch, Switch 1 and Switch 2.

  • Connected the three switches as shown in the topology for this example (see Figure 4).

Overview and Topology

In a typical enterprise network composed of distribution and access layers, a redundant trunk link provides a simple solution for trunk interface network recovery. When a trunk interface fails, data traffic is routed to another trunk interface after one minute, thereby keeping network convergence time to a minimum.

This example shows the configuration of a redundant trunk group that includes one primary link (and its interface) and one unspecified link (and its interface) that serves as the secondary link.

A second type of redundant trunk group, not illustrated in the example, consists of two unspecified links (and their interfaces); in this case, neither of the links is primary. In this second case, the software selects an active link by comparing the port numbers of the two links and activating the link with the higher port number. For example, if the two link interfaces use interfaces ge-0/1/0 and ge-0/1/1, the software activates ge-0/1/1. (In the interface names, the final number is the port number.)

The two links in a redundant trunk group generally operate the same way, whether they are configured as primary/unspecified or unspecified/unspecified. Data traffic initially passes through the active link but is blocked on the inactive link. While data traffic is blocked on the secondary link, note that Layer 2 control traffic is still permitted if the link is active. For example, an LLDP session can be run between two switches on the secondary link. If the active link either goes down or is disabled administratively, it broadcasts a list of its known MAC addresses for data traffic; the other link immediately picks up and adds the MAC addresses to its address table, becomes active, and begins forwarding traffic.

The one difference in operation between the two types of redundant trunk groups occurs when a primary link is active, goes down, is replaced by the secondary link, and then reactivates. When a primary link is re-enabled while the secondary link is active, the primary link waits 1 second (you can change the length of time using the preempt cutover timer to accommodate your network) and then takes over as the active link. In other words, the primary link has priority and is always activated if it is available. This differs from the behavior of two unspecified links, which act as equals. Because the unspecified links are equal, the active link remains active until it either goes down or is disabled administratively; this is the only time that the other unspecified link learns the MAC addresses and immediately becomes active.

The example given here illustrates a primary/unspecified configuration for a redundant trunk group because that configuration gives you more control and is more commonly used.

Note

Rapid Spanning Tree Protocol (RSTP) is enabled by default on EX Series switches to create a loop-free topology, but an interface is not allowed to be in both a redundant trunk group and in a spanning-tree protocol topology at the same time. You will need to disable RSTP on the two distribution switches in the example, Switch 1 and Switch 2. Spanning-tree protocols can, however, continue operating in other parts of the network—for example, between the distribution switches and also in links between distribution switches and the enterprise core.

Figure 4 displays an example topology containing three switches. Switch 1 and Switch  2 make up the distribution layer, and Switch 3 makes up the access layer. Switch  3 is connected to the distribution layer through trunk interfaces ge-0/0/9.0 (Link 1) and ge-0/0/10.0 (Link 2).

Table 2 lists the components used in this redundant trunk group.

Because RSTP and RTGs cannot operate simultaneously on a switch, you disable RSTP on Switch 1 and Switch 2 in the first configuration task, and you disable RSTP on Switch 3 in the second task.

The second configuration task creates a redundant trunk group called example 1 on Switch 3. The trunk interfaces ge-0/0/9.0 and ge-0/0/10.0 are the two links configured in the second configuration task. You configure the trunk interface ge-0/0/9.0 as the primary link. You configure the trunk interface ge-0/0/10.0 as an unspecified link, which becomes the secondary link by default.

Figure 4: Topology for Configuring the Redundant Trunk Links
Topology for Configuring
the Redundant Trunk Links

Table 2: Components of the Redundant Trunk Link Topology

PropertySettings

Switch hardware

  • Switch 1–1 EX Series distribution switch

  • Switch 2–1 EX Series distribution switch

  • Switch 3–1 EX Series access switch

Trunk interfaces

On Switch 3 (access switch): ge-0/0/9.0 and ge-0/0/10.0

Redundant trunk group

example1

Disabling RSTP on Switches 1 and 2

To disable RSTP on Switch 1 and Switch 2, perform this task on each switch:

CLI Quick Configuration

To quickly disable RSTP on Switch 1 and Switch 2, copy the following command and paste it into each switch terminal window:

[edit]


set protocols rstp disable


Step-by-Step Procedure

To disable RSTP on Switch 1 and Switch 2:

  1. Disable RSTP on Switch 1 and Switch 2:
    [edit]

    user@switch# set protocols rstp disable

Results

Check the results of the configuration:

Results

Configuring Redundant Trunk Links on Switch 3

To configure redundant trunk links on Switch 3, perform this task:

CLI Quick Configuration

To quickly configure the redundant trunk group example1 on Switch 3, copy the following commands and paste them into the switch terminal window:

[edit]
set protocols rstp disable
set ethernet-switching-options redundant-trunk-group group example1 interface ge-0/0/9.0 primary
set ethernet-switching-options redundant-trunk-group group example1 interface ge-0/0/10.0
set ethernet-switching-options redundant-trunk-group group example1 preempt-cutover-timer 60

Step-by-Step Procedure

Configure the redundant trunk group example1 on Switch 3.

  1. Turn off RSTP:
    [edit]

    user@switch# set protocols rstp disable

  2. Name the redundant trunk group example1 while configuring trunk interface ge-0/0/9.0 as the primary link and ge-0/0/10 as an unspecified link to serve as the secondary link:
    [edit ethernet-switching-options]

    user@switch# set redundant-trunk-group group example1 interface ge-0/0/9.0 primary

    user@switch# set redundant-trunk-group group example1 interface ge-0/0/10.0

  3. (Optional) Change the length of time (from the default of 1 second) that a re-enabled primary link waits to take over for an active secondary link:
    [edit ethernet-switching-options]

    user@switch# set redundant-trunk-group group example1 preempt-cutover-timer 60

Results

Check the results of the configuration:

Verification

To confirm that the configuration is set up correctly, perform this task:

Verifying That a Redundant Trunk Group Was Created

Purpose

Verify that the redundant trunk group example1 has been created on Switch 1 and that trunk interfaces are members of the redundant trunk group.

Action

List all redundant trunk groups configured on the switch:

Meaning

The show redundant-trunk-group command lists all redundant trunk groups configured on the switch, both links’ interface addresses, and the links’ current states (up or down for an unspecified link, and up or down and primary for a primary link). For this configuration example, the output shows that the redundant trunk group example1 is configured on the switch. The (Up) beside the interfaces indicates that both link cables are physically connected. The (Pri) beside trunk interface ge-0/0/9.0 indicates that it is configured as the primary link.