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Manual Chapter: Working with Trunks
Manual Chapter
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A trunk is a logical grouping of interfaces on the BIG-IP® system. When you create a trunk, this logical group of interfaces functions as a single interface. The BIG-IP system uses a trunk to distribute traffic across multiple links, in a process known as link aggregation. With link aggregation, a trunk increases the bandwidth of a link by adding the bandwidth of multiple links together. For example, four fast Ethernet (100 Mbps) links, if aggregated, create a single 400 Mbps link.
With one trunk, you can aggregate a maximum of eight links. For optimal performance, you should aggregate links in powers of two. Thus, you ideally aggregate two, four, or eight links.
The purpose of a trunk is two-fold: To increase bandwidth without upgrading hardware, and to provide link failover if a member link becomes unavailable.
You can use trunks to transmit traffic from a BIG-IP system to another vendor switch. Two systems that use trunks to exchange frames are known as peer systems.
In a typical configuration where trunks are configured, the member links of the trunk are connected through Ethernet cables to corresponding links on a peer system. Figure 9.1 shows an example of a typical trunk configuration with two peers and three member links on each peer.
A primary goal of the trunks feature is to ensure that frames exchanged between peer systems are never sent out of order or duplicated on the receiving end. The BIG-IP system is able to maintain frame order by using the source and destination addresses in each frame to calculate a hash value, and then transmitting all frames with that hash value on the same member link.
The BIG-IP system automatically assigns a unique MAC address to a trunk. However, by default, the MAC address that the system uses as the source and destination address for frames that the system transmits and receives (respectively), is the MAC address of the lowest-numbered interface of the trunk.
The BIG-IP system also uses the lowest-numbered interface of a trunk as a reference link. The BIG-IP system uses the reference link to take certain aggregation actions, such as implementing the automatic link selection policy. For frames coming into the reference link, the BIG-IP system load balances the frames across all member links that the BIG-IP system knows to be available. For frames going from any link in the trunk to a destination host, the BIG-IP system treats those frames as if they came from the reference link.
Finally, the BIG-IP system uses the MAC address of an individual member link as the source address for any LACP control frames. For more information on LACP, see Overview of LACP, following.
A key aspect of trunks is Link Aggregation Control Protocol, or LACP. Defined by IEEE standard 802.3ad, LACP is a protocol that detects error conditions on member links and redistributes traffic to other member links, thus preventing any loss of traffic on the failed link. On a BIG-IP system, LACP is an optional feature that you can configure.
You can also customize LACP behavior. For example, you can specify the way that LACP communicates its control messages from the BIG-IP system to a peer system. You can also specify the rate at which the peer system sends LACP packets to the BIG-IP system. If you want to affect the way that the BIG-IP system chooses links for link aggregation, you can specify a link control policy. For more information, see Creating a trunk.
You create a trunk using the Configuration utility. The BIG-IP system offers several settings that you can configure for a trunk. These settings are summarized in Table 9.1.
Note: An alternate way to configure trunks is to use the bigpipe utility or tmsh. For more information, see the Bigpipe Utility Reference Guide or the Traffic Management Shell (tmsh) Reference Guide.
Note: Only users with either the Administrator or Resource Administrator user role can create a trunk.
Enables or disables the Link Aggregation Control Protocol (LACP). For more information, see Enabling LACP.
Specifies the way that member links communicate over LACP. Possible values are Active and Passive. For more information, see Specifying the LACP mode.
Specifies the interval in seconds in which the BIG-IP system wants its peer system to send control packets. Possible values are Short and Long. For more information, see Specifying the LACP timeout.
Specifies the policy that the BIG-IP system uses to select a link for processing traffic. Possible values are Auto and Maximum Bandwidth. For more information, see Specifying a link selection policy.
Specifies the basis for the hash that the system uses as the frame distribution algorithm. Possible values are Source/Destination MAC address, Destination MAC address, and Source/Destination IP address.
Use the following procedure to create a trunk. For detailed information about each setting, see the sections following the procedure.
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens.
2.
In the upper-right corner of the screen, click the Create button.
Another Trunks screen opens.
Note: If the Create button is unavailable, you do not have permission to create a trunk. You must have the Administrator or Resource Administrator role assigned to your user account.
3.
In the Name box, type a unique name for the trunk.
4.
For the Interfaces setting, in the Available box, select an interface that you want to include in the trunk, and using the Move button (<<), move the interface to the Members box.
6.
a)
From the LACP Mode list, select Passive mode, or retain the default mode (Active).
b)
From the LACP Timeout list, select Short, or retain the default timeout value (Long).
7.
From the Link Selection Policy list, select or retain a link selection policy.
8.
Click Finished.
You can use the Name setting to specify a unique name for the trunk. This setting is required.
Using the Interfaces setting, you specify the interfaces that you want the BIG-IP system to use as member links for the trunk. Once you have created the trunk, the BIG-IP system uses these interfaces to perform link aggregation.
Tip: To optimize bandwidth utilization, F5 Networks® recommends that, if possible, the number of links in the trunk be a power of 2 (for example, 2, 4, or 8). This is due to the frame balancing algorithms that the system uses to map data streams to links. Regardless of the hashing algorithm, a trunk that has 2, 4, or 8 links prevents the possibility of skewing, which can adversely affect data throughput.
As stated earlier, the BIG-IP system uses the lowest-numbered interface as the reference link. The system uses the reference link to negotiate links for aggregation. For more information on link negotiation, see Specifying a link selection policy.
The interfaces that you specify for the trunk must operate at the same media speed, and must be set at full-duplex mode. Otherwise, the BIG-IP system cannot aggregate the links. Because these media properties are dynamic rather than static (due to auto-negotiation), the lacpd service routinely monitors the current status of these properties and negotiates the links for aggregation accordingly. Thus, when the status of these properties qualifies a link to become a working member link, the system adds the link to the aggregation, and the link can begin accepting traffic. For information on setting media properties for an interface, see Platform Guide: 1500, 3400, 6400, and 6800 or Platform Guide: 8400 and 8800.
Any interface that you assign to a trunk must be an untagged interface. Furthermore, you can assign an interface to one trunk only; that is, you cannot assign the same interface to multiple trunks. Because of these restrictions, the only interfaces that appear in the Interfaces list in the Configuration utility are untagged interfaces that are not assigned to another trunk. Therefore, before creating a trunk and assigning any interfaces to it, you should verify that each interface for the trunk is an untagged interface.
After creating the trunk, you assign the trunk to one or more VLANs, using the same VLAN screen that you normally use to assign an individual interface to a VLAN. For information on assigning a trunk to a VLAN, see Chapter 8, Configuring VLANs and VLAN Groups.
If you are using one of the spanning tree protocols (STP, RSTP, or MSTP), the BIG-IP system sends and receives spanning tree protocol packets on a trunk, rather than on individual member links. Likewise, use of a spanning tree protocol to enable or disable learning or forwarding on a trunk operates on all member links together, as a single unit.
As an option, you can enable LACP on a trunk. Containing a service called lacpd, LACP is an IEEE-defined protocol that exchanges control packets over member links. The purpose of LACP is to detect link error conditions such as faulty MAC devices and link loopbacks. If LCAP detects an error on a member link, the BIG-IP system removes the member link from the link aggregation and redistributes the traffic for that link to the remaining links of the trunk. In this way, no traffic destined for the removed link is lost. LACP then continues to monitor the member links to ensure that aggregation of those links remains valid.
By default, the LACP feature is disabled, to ensure backward compatibility with previous versions of the BIG-IP system. If you create a trunk and do not enable the LACP feature, the BIG-IP system does not detect link error conditions, and therefore cannot remove the member link from link aggregation. The result is that the system cannot redistribute the traffic destined for that link to the remaining links in the trunk, thereby causing traffic on the failed member link to be lost.
The LACP Mode setting appears on the Trunks screen only when you check the LACP setting. You use the LACP mode setting to specify the method that LACP uses to send control packets to the peer system. The two possible modes are:
Active mode
You specify Active mode if you want the system to periodically send control packets, regardless of whether the peer system has issued a request. This is the default setting.
Passive mode
You specify Passive mode if you want the system to send control packets only when the peer system issues a request, that is, when the LACP mode of the peer system is set to Active.
If you set only one of the peer systems to Active mode, the BIG-IP system uses Active mode for both systems. Also, whenever you change the LACP mode on a trunk, LACP renegotiates the links that it uses for aggregation on that trunk.
Tip: We recommend that you set the LACP mode to Passive on one peer system only. If you set both systems to Passive mode, LACP does not send control packets.
The LACP Timeout setting appears on the Trunks screen only when you check the LACP setting. You use the LACP Timeout setting to indicate to the BIG-IP system the interval in seconds at which the peer system should send control packets. The timeout value applies only when the LACP mode is set to Active on at least one of the switch systems. If both systems are set to Passive mode, LACP does not send control packets.
If LACP sends three consecutive control packets without receiving a response from the peer system, LACP removes that member link from link aggregation.
Short
When you set the timeout value to Short, the peer system sends LACP control packets once every second. If this value is set to Short and LACP receives no peer response after sending three consecutive packets, LACP removes the link from aggregation in three seconds.
Long
When you set the timeout value to Long, the peer system sends LACP control packets once every 30 seconds. A timeout value of Long is the default setting. If set to Long and LACP receives no peer response after sending three consecutive packets, LACP removes the link from aggregation in ninety seconds.
Whenever you change the LACP timeout value on a trunk, LACP renegotiates the links that it uses for aggregation on that trunk.
In order for the BIG-IP system to aggregate links, the media speed and duplex mode of each link must be the same on both peer systems. Because media properties can change dynamically, the BIG-IP system monitors these properties regularly, and if it finds that the media properties of a link are mismatched on the peer systems, the BIG-IP system must determine which links are eligible for aggregation.
The way the system determines eligible links depends on a link selection policy that you choose for the trunk. When you create a trunk, you can choose one of two possible policy settings: Auto and Maximum Bandwidth.
Note: The link selection policy feature represents an F5 Networks enhancement to the standard IEEE 802.3ad specification for LACP.
When you set the link selection policy to Auto (the default setting), the BIG-IP system uses the lowest-numbered interface of the trunk as a reference link. (A reference link is a link that the BIG-IP system uses to make a link aggregation decision.) The system then aggregates any links that have the same media properties and are connected to the same peer as the reference link.
For example, using Figure 9.1, suppose that you created a trunk to include interfaces 1.2 and 1.3, each with a media speeds of 100 Mbps, and interface 1.4, with a different media speed of 1 Gbps. If you set the link selection policy to Auto, the BIG-IP system uses the lowest-numbered interface, 1.2, as a reference link. The reference link operates at a media speed of 100 Mbps, which means that the system aggregates all links with that media speed (interfaces 1.2 and 1.3). The media speed of interface 1.4 is different (1 Gbps), and therefore is not considered for link aggregation. Only interfaces 1.2 and 1.3 become working member links and start carrying traffic.
If the media speed of interface 1.4 changes to 100 Mbps, the system adds that interface to the aggregation. Conversely, if the media speed of interface 1.4 remains at 1 Gbps, and the speed of the reference link changes to 1 Gbps, then interfaces 1.2 and 1.4 become working members, and 1.3 is now excluded from the aggregation and no longer carries traffic.
When you set the link selection policy to Maximum Bandwidth, the BIG-IP system aggregates the subset of member links that provide the maximum amount of bandwidth to the trunk.
Continuing with our previous example, if interfaces 1.2 and 1.3 each operate at a media speed of 100 Mbps, and interface 1.4 operates at speed of 1 Gbps, then the system selects only interface 1.4 as a working member link, providing 1 Gbps of bandwidth to the trunk. If the speed of interface 1.4 drops to 10 Mbps, the system then aggregates links 1.2 and 1.3, to provide a total bandwidth to the trunk of 200 Mbps. The peer system detects any non-working member links and configures its aggregation accordingly.
Tip: To ensure that link aggregation operates properly, make sure that both peer systems agree on the link membership of their trunks.
When frames are transmitted on a trunk, they are distributed across the working member links. The distribution function ensures that the frames belonging to a particular conversation are neither mis-ordered nor duplicated at the receiving end.
The BIG-IP system distributes frames by calculating a hash value based on the source and destination addresses (or the destination address only) carried in the frame, and associating the hash value with a link. All frames with a particular hash value are transmitted on the same link, thereby maintaining frame order. Thus, the system uses the resulting hash to determine which interface to use for forwarding traffic.
The Frame Distribution Hash setting specifies the basis for the hash that the system uses as the frame distribution algorithm.
The default value is Source/Destination IP address.
Source/Destination MAC address
This value specifies that the system bases the hash on the combined MAC addresses of the source and the destination.
Destination MAC address
This value specifies that the system bases the hash on the MAC address of the destination.
Source/Destination IP address
This value specifies that the system bases the hash on the combined IP addresses of the source and the destination.
Note: Only users with either the Administrator or Resource Administrator user role can manage trunks.
Before you create a new trunk, you might want to view a list of existing trunks. When you use the Configuration utility to view a list of trunks, you not only see the trunk names, but also some data about each trunk:
Trunk status (UP or DOWN)
LACP mode (Active or Passive)
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens.
For any existing trunk, you can use the Configuration utility to view or modify the properties of that trunk. These properties consist of not only the settings that you configured for the trunk, but also other read-only LACP-specific properties that conform to the IEEE 802.3ad standard.
Note that the term actor refers to the local endpoint of the trunk, and peer refers to the remote endpoint of the trunk.
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens, showing the list of existing trunks.
2.
Click a trunk name.
The properties screen for that trunk opens.
4.
In the Configuration area of the screen, view or modify the setting values.
For information on selecting values for these settings, see Creating a trunk.
5.
If you modified any values, click Update. Otherwise, click Cancel.
After creating a trunk, you can add the trunk to a VLAN. You add a trunk to a VLAN by using the VLAN screens of the Configuration utility. For more information, see Chapter 8, Configuring VLANs and VLAN Groups.
You can use the Configuration utility to delete an existing trunk. When you delete a trunk, individual interfaces are no longer considered to be member links of a trunk and are no longer aggregated.
Remember that when you added the interfaces to the trunk, the BIG-IP system first required you to remove the individual interfaces from VLAN membership. Therefore, after deleting the trunk, if you want the individual interfaces of the trunk to become VLAN members again, you must explicitly assign them to one or more VLANs, using the VLANs screens of the Configuration utility.
You cannot delete any trunk that is a member of VLAN or that participates in Spanning Tree Protocol. For this reason, you must remove the trunk from any VLAN to which it is assigned, and from STP configuration, before you delete the trunk.
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens, showing the list of existing trunks.
4.
Click the Delete button.
A confirmation message appears.
5.
Click Delete to delete the trunk.
Note: After deleting the trunk, if you recreate the trunk using the same name and the same interfaces as its members, any interface statistics that you display using the bigpipe utility trunk show command display the same statistics as those shown prior to deleting the trunk.
You can manage the interfaces of a trunk by adding them to or deleting them from a trunk. You can also view trunk-related properties of an interface in the trunk.
Note: The following procedure for adding an interface to a trunk is equivalent to modifying the Interfaces property of the trunk, as described in step 4 of the section To view or modify properties of a trunk.
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens, showing the list of existing trunks.
2.
Click a trunk name.
The properties screen for that trunk opens.
3.
On the menu bar, click Resources.
This displays the list of interfaces assigned to the trunk, along with some interface properties.
5.
For the Interfaces setting, in the Available box, select an interface that you want to include in the trunk, and using the Move button (<<), move the interface to the Members box.
7.
Click Update.
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens, showing the list of existing trunks.
2.
Click a trunk name.
The properties screen for that trunk opens.
3.
On the menu bar, click Resources.
This displays the list of interfaces assigned to the trunk, along with some interface properties.
4.
In the Name column, locate the interface that you want to remove, and check the Select box to the left of the Status column.
5.
Click Delete.
A confirmation message appears.
6.
Click Delete to remove the interface from the trunk.
1.
On the Main tab of the navigation pane, expand Network, and click Trunks.
The Trunks screen opens, showing the list of existing trunks.
2.
Click a trunk name.
The properties screen for that trunk opens.
3.
On the menu bar, click Resources.
This displays the list of interfaces assigned to the trunk, along with some interface properties.
4.
In the Name column, click the interface for which you want to view trunk-related properties.
This displays trunk-related properties for the interface.
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