Chapter 1, Introducing the Traffic Management Operating System
, introduces the concept of virtual local area networks (VLANs). A VLAN
is a logical subset of hosts on a local area network (LAN) that operate in the same IP address space. Grouping hosts together in a VLAN has distinct advantages. For example, with VLANs, you can:
The way that you group hosts into VLANs is by using the Configuration
utility to create a VLAN and associate physical interfaces with that VLAN. In this way, any host that sends traffic to a BIG-IP®
system interface is logically a member of the VLAN or VLANs to which that interface belongs.
The BIG-IP system is a port-based switch that includes multilayer
processing capabilities. These capabilities enhance standard VLAN behavior, in these ways:
By default, the BIG-IP system includes two VLANs, named internal
. When you initially ran the Setup utility, you assigned the following to each of these VLANs:
A typical VLAN configuration is one in which you create the two VLANs external
, and one or more BIG-IP system interfaces assigned to each VLAN. You then create a virtual server, and associate a default load balancing pool with that virtual server. Figure 7.1
shows a typical configuration using the default VLANs external
Every VLAN must have a static self IP address associated with it. The self IP address
of a VLAN represents an address space, that is, the range of IP addresses pertaining to the hosts in that VLAN. When you ran the Setup utility earlier, you assigned one static self IP address to the VLAN external
, and one static self IP address to the VLAN internal
. When sending a request to a destination server, the BIG-IP system can use these self IP addresses to determine the specific VLAN that contains the destination server.
For example, suppose the self IP address of VLAN external
and the self IP address of the VLAN internal
and both self IP addresses have a netmask of 255.255.0.0
. If the IP address of the destination server is 188.8.131.52
, then the BIG-IP system can compare the self IP addresses to the hosts IP address to determine that the destination server is in the VLAN internal
. This process, combined with checking the ARP cache and a VLANs L2 forwarding table, ensures that the BIG-IP system successfully sends the request to the destination server.
When you create a VLAN, you assign a name and an identifying tag to the
VLAN. Then you associate one or more BIG-IP system interfaces with the VLAN. Also, if the BIG-IP system is a unit of a redundant system, you can specify a special MAC address that the two units share, as a way to ensure that connections are successfully processed when failover occurs. Finally, you can specify that you want the BIG-IP system to use VLAN-related events to trigger failover in a redundant-system configuration.
If the Create
button is unavailable, you do not have permission to create a VLAN. You must have the Administrator
or Resource Administrator
role assigned to your user account.
| |In the Tag
box, type a tag for the VLAN, or leave the box blank.
If you do not specify a tag, the BIG-IP system assigns one automatically.
| |In the Resources area, for the Interfaces
setting, click an interface number or trunk name in the Available
box, and using a Move button (<<
), move the interface number to the Untagged
box. Repeat this step as necessary.
For more information on tagged and untagged interfaces, see Assigning interfaces to a VLAN
| |For the MTU
setting, use the default value or type a new value.
When creating a VLAN, you must assign it a unique name. Once you have
finished creating the VLAN, the VLAN name appears in the list of existing VLANs.
A VLAN tag
is a unique ID number that you assign to a VLAN. If you do not explicitly assign a tag to a VLAN, the BIG-IP system assigns a tag automatically. The value of a VLAN tag can be between 1
. Once you or the BIG-IP assigns a tag to a VLAN, any message sent from a host in that VLAN includes this VLAN tag as a header in the message.
A VLAN tag is useful when an interface has multiple VLANs associated
with it; that is, when the interfaces you assigned to the VLAN are assigned as tagged interfaces. In this case, the BIG-IP system can read the VLAN tag in the header of a message to determine the specific VLAN in which the source or destination host resides. For more information on tagged interfaces, see Tag-based access to VLANs
For each VLAN that you create, you must assign one or more BIG-IP
system interfaces to that VLAN, using the Interfaces
setting. When you assign an interface to a VLAN, you indirectly control the hosts from which the BIG-IP system interface sends or receives messages.
Tip: You can use the Interfaces
setting to assign not only individual interfaces to the VLAN, but also trunks. Any trunks that you create are automatically included for selection in the list of available interfaces. For more information on trunks, see Chapter 13, Working with Trunks
For example, if you assign interface 1.11 to VLAN A
, and you then associate VLAN A with a virtual server, then the virtual server sends its outgoing traffic through interface 1.11, to a destination host in VLAN A
. Similarly, when a destination host sends a message to the BIG-IP system, the hosts VLAN membership determines the BIG-IP system interface that should receive the incoming traffic.
Each VLAN has a MAC address. The MAC address of a VLAN is the same
MAC address of the lowest-numbered interface assigned to that VLAN.
The BIG-IP system supports two methods for sending and receiving
messages through an interface that is a member of one or more VLANs. These two methods are port-based access to VLANs and tag-based access to VLANs. The method used by a VLAN is determined by the way that you add a member interface to a VLAN.
With port-based access to VLANs, the BIG-IP system accepts frames for a
VLAN simply because they are received on an interface that is a member of that VLAN. With this method, an interface is an untagged member of the VLAN. Frames sent out through untagged
interfaces contain no tag in their header.
to VLANs occurs when you add an interface to a VLAN as an untagged
interface. In this case, the VLAN is the only VLAN that you can associate with that interface. This limits the interface to accepting traffic only from that VLAN, instead of from multiple VLANs. If you want to give an interface the ability to accept and receive traffic for multiple VLANs, you add the same interface to each VLAN as a tagged interface. The following section describes tagged interfaces.
With tag-based access to VLANs, the BIG-IP system accepts frames for a
VLAN because the frames have tags in their headers and the tag matches the VLAN identification number for the VLAN. An interface that accepts frames containing VLAN tags is a tagged member
of the VLAN. Frames sent out through tagged interfaces contain a tag in their header.
to VLANs occurs when you add an interface to a VLAN as a tagged
interface. You can add the same tagged interface to multiple VLANs, thereby allowing the interface to accept traffic from each VLAN with which the interface is associated.
When you add an interface to a VLAN as a tagged interface, the BIG-IP
system associates the interface with the VLAN identification number, or tag
, which becomes embedded in a header of a frame.
Each time you add an interface to a VLAN, either when creating a VLAN or
modifying its properties, you can designate that interface as a tagged
interface. A single interface can therefore have multiple tags associated with it.
The result is that whenever a frame comes into that interface, the interface
reads the tag that is embedded in a header of the frame. If the tag in the frame matches any of the tags associated with the interface, the interface accepts the frame. If the tag in the frame does not
match any of the tags associated with the interface, the interface rejects the frame.
, shows the difference between using three untagged interfaces (where each interface must belong to a separate VLAN) versus one tagged interface (which belongs to multiple VLANs).
The configuration on the left shows a BIG-IP unit with three internal
interfaces, each a separate, untagged interface. This is a typical solution for supporting three separate customer sites. In this scenario, each interface can accept traffic only from its own VLAN.
Conversely, the configuration on the right shows a BIG-IP system with one
internal interface and an external switch. The switch places the internal interface on three separate VLANs. The interface is configured on each VLAN as a tagged interface. In this way, the single interface becomes a tagged member of all three VLANs, and accepts traffic from all three. The configuration on the right is the functional equivalent of the configuration on the left.
When you enable the Source Check
setting, the BIG-IP system verifies that the return path for an initial packet is through the same VLAN from which the packet originated. The system performs this verification only if you check the Source Check
box for the VLAN, and if the global setting Auto Last Hop
is not enabled. For information on the Auto Last Hop
setting, see Chapter 2, Configuring the BIG-IP Platform and General Properties
The value of the maximum transmission unit, or MTU
, is the largest size that the BIG-IP system allows for an IP datagram passing through a BIG-IP system interface. The default value is 1500
Every VLAN has a media access control (MAC) address that corresponds to
the VLANs self IP address. The MAC address of a VLAN is the MAC address of the lowest-numbered interface assigned to that VLAN. For example, if the lowest-numbered interface assigned to VLAN internal
is 3.1, and the MAC address of that interface is 0:0:0:ac:4c:a2
, then the MAC address of VLAN internal
is also 0:0:0:ac:4c:a2
A MAC masquerade address
is a variation of the VLANs MAC address, and this address is shared between two units of a redundant system. When you specify a MAC masquerade address, a destination server sending a response to the BIG-IP system sends its response to the VLANs MAC masquerade address, instead of to the VLANs regular MAC address. The server accomplishes this by using the VLANs floating self IP address as the default route when sending responses to the BIG-IP system. (For more information on configuring a server to use a floating IP address as the default route, see Chapter 16, Configuring High Availability
When you assign a MAC masquerade address to a VLAN, the BIG-IP
system automatically sends a gratuitous ARP message to the default router and other devices on the network. This gratuitous ARP message notifies these devices that the MAC address of the BIG-IP system interface assigned to the VLAN has changed to the MAC masquerade address.
The MAC masquerade address must be a unique address, in order to avoid
frame collisions. The safest way to create a MAC masquerade address is to first determine the MAC address of the VLAN (that is, the MAC address of the lowest-numbered interface assigned to that VLAN), and then logically OR
the first byte with 0x02
. This makes the MAC address a locally-administered MAC address.
Continuing with the example above where the VLANs MAC address is 0:0:0:ac:4c:a2
, a MAC masquerade address of 02:0:0:ac:4c:a2
is suitable to use on both BIG-IP units in the redundant system. For help in finding the MAC address of a VLAN, see To find the MAC address of a VLAN
| |In the Interfaces
setting, note the lowest-numbered interface assigned to the VLAN.
After you have created a VLAN, you can use the Configuration utility to
modify its properties, delete the VLAN, or to maintain its Layer 2 forwarding table.
Using the Configuration utility, you can modify all of the properties of a
VLAN, except the VLAN name and the MAC address with which the VLAN is associated (that is, the MAC address of the lowest-numbered interface that is assigned to the VLAN).
| |Click Delete
A confirmation query appears.
Layer 2 forwarding
is the means by which frames are exchanged directly between hosts, with no IP routing required. This is accomplished using a simple forwarding table for each VLAN. The L2 forwarding table
is a list that shows, for each host in the VLAN, the MAC address of the host, along with the interface that the BIG-IP system needs for sending frames to that host. The intent of the L2 forwarding table is to help the BIG-IP system determine the correct interface for sending frames, when the system determines that no routing is required.
The BIG-IP system learns the interfaces that correspond to various MAC
entries as frames pass through the system, and automatically adds entries to the table accordingly. These entries are known as dynamic entries
. You can also add entries to the table manually, and these are known as static entries
. Entering static entries is useful if you have network devices that do not advertise their MAC addresses. The system does not automatically update static entries.
The BIG-IP system does not always need to use the L2 forwarding table to
find an interface for frame transmission. For instance, if a VLAN has only one interface assigned to it, then the BIG-IP system automatically uses that interface.
Occasionally, the L2 forwarding table does not include an entry for the
destination MAC address and its corresponding BIG-IP system interface. In this case, the BIG-IP system floods the frame through all interfaces associated with the VLAN, until a reply creates an entry in the L2 forwarding table.
You can use the Configuration utility to view the static entries in the L2
forwarding table. Note that the Configuration utility does not display any dynamic L2 forwarding table entries.
| |On the menu bar, click Layer 2 Static Forwarding Table
This displays any static entries currently in the L2 forwarding table.
You can add static entries to the L2 forwarding table when you want to give
the BIG-IP system the ability to send messages to a specific host in the VLAN.
| |On the menu bar, click Layer 2 Static Forwarding Table
This displays any entries currently in the L2 forwarding table.
| |Click Create
This displays the screen for adding entries to the table.
| |For the Interfaces
setting, select an interface number.
| |In the MAC Address
box, type the MAC address of the host to which the entry applies.
| |Click Repeat
if you want to add another entry, or click Finished
Setting the L2 forwarding aging time
Entries in the L2 forwarding table have a specified life span, after which
they are removed if the MAC address is no longer present on the network. This life span is called the Layer 2 cache aging time
. The default value is 300 seconds. Using the Configuration utility, you can change this value.
| |In the Layer 2 Cache Aging Time
box, change the value.
A VLAN group
is a logical container that includes two or more distinct VLANs. VLAN groups are intended for load balancing traffic in a Layer 2 network, when you want to minimize the reconfiguration of hosts on that network. Figure 7.3
shows an example of a VLAN group.
A VLAN group also ensures that the BIG-IP system can process traffic
successfully between a client and server when the two hosts reside in the same address space. Without a VLAN group, when the client and server both reside in the same address space, the client request goes through the virtual server, but instead of sending its response back through the virtual server, the server attempts to send its response directly to the client, bypassing the virtual server altogether. As a result, the client cannot receive the response, because the client expects the address of the response to be the virtual server IP address, not the server IP address.
Although one way to solve this problem is to enable source network address
translation (SNAT), a simpler approach is to create a VLAN group. With a VLAN group, you do not need to translate the client IP address to a different source address. You can preserve the original client IP address, and the server can still send its response to the client successfully.
When you create a VLAN group, the two existing VLANs become child
VLANs of the VLAN group. To create a VLAN group, you use the Configuration utility. For information on managing a VLAN group, see Managing a VLAN group
When you create a VLAN group, you assign a name and a VLAN group ID.
Then you specify the existing VLANs that you want the VLAN group to contain. Finally, you specify a transparency mode, and some settings related to redundant-system configuration.
Use the following procedure to create a VLAN group. For detailed
information about each setting, see the sections following the procedure.
If the Create
button is unavailable, you do not have permission to create a VLAN group. You must have the Administrator
role assigned to your user account.
| |In the VLAN Group ID
box, type a unique VLAN ID.
If you do not specify a VLAN ID, the BIG-IP system automatically assigns one.
| |In the Configuration area, for the VLANs
setting, click a VLAN name in the Available
box, and using the Move button (<<
), move the VLAN name to the Members
Repeat this step as necessary.
| |From the Transparency Mode
list, select a transparency mode, or use the default setting.
| |Check the Bridge All Traffic
setting if you want the VLAN group to forward all frames, including non-IP traffic.
| |For the Bridge in Standby
setting, leave the box checked if you want the VLAN group to forward frames even when the system is the standby unit of a redundant system.
When creating a VLAN group, you must assign it a unique name. Once you
have finished creating the VLAN group, the VLAN group name appears in the list of existing VLANs groups.
A VLAN group ID
is a tag for the VLAN group. Every VLAN group needs a unique ID number. If you do not specify an ID for the VLAN group, the BIG-IP system automatically assigns one. The value of a VLAN group ID can be between 1
. For more information on VLAN tags, see Tag-based access to VLANs
The BIG-IP system is capable of processing traffic using a combination of
Layer 2 and Layer 3 forwarding, that is, switching and IP routing. When you set the transparency mode, you specify the type of forwarding that the BIG-IP system performs when forwarding a message to a host in a VLAN. The default setting is translucent
, which means that the BIG-IP system uses a mix of Layer 2 and Layer 3 processing. Table 7.3
lists the allowed values.
| || |
| || |
| || |Layer 2 forwarding with a locally-unique bit, toggled in ARP
response across VLANs. This is the default setting. When you choose this value and you have a virtual server that references a Fast L4 profile, the BIG-IP system automatically changes the PVA Acceleration
setting to None
| || |Layer 2 forwarding with the original MAC address of the
remote system preserved across VLANs. When you choose this value and you have a virtual server that references a Fast L4 profile, the BIG-IP system automatically changes the PVA Acceleration
setting to None
When you enable this option, you are instructing the VLAN group to
forward all non-IP traffic. Note that IP traffic is bridged by default. The default value for this setting is disabled (unchecked).
When enabled, the Bridge in Standby
setting ensures that the VLAN group can forward packets when the system is the standby unit of a redundant system configuration. Note that this setting applies to non-IP and non-ARP frames only, such as Bridge Protocol Data Units (BPDUs).
This setting is designed for deployments in which the VLAN group is
defined on a redundant system. You can use the Bridge in Standby
setting in transparent or translucent modes, or in opaque mode when MAC masquerading is not enabled and when the global variable Failover.Standby.LinkDownTime
is set to 0
When you place VLANs into a VLAN group, devices on the network
automatically send responses to the MAC masquerade address that you assigned to the VLAN group. In this case, the BIG-IP system ignores the MAC masquerade addresses that you assigned to the individual VLANs of the group.
The procedure for assigning a MAC masquerade address to a VLAN group
is similar to the procedure for assigning one to a VLAN. However, because interfaces are not assigned directly to a VLAN group, you can use the MAC address of the lowest-numbered interface of any VLAN in the VLAN group when you decide on a MAC masquerade address for the VLAN group.
Using the Configuration utility, you can change the properties of a VLAN
group, delete the VLAN group, or manage the way that the VLAN group handles proxy ARP forwarding.
| |From the VLAN Groups
menu, choose List.
This shows a list of existing VLAN groups.
As described earlier, a host in a VLAN cannot normally communicate to a
host in another VLAN. This rule applies to ARP requests as well. However, if you put the VLANs into a single VLAN group, the BIG-IP system can perform a proxied ARP request.
A proxied ARP request
is an ARP request that the BIG-IP system can send, on behalf of a host in a VLAN, to hosts in another VLAN. A proxied ARP request requires that both VLANs belong to the same VLAN group.
In some cases, you might not want a host to forward proxied ARP requests
to a specific host, such as an active unit in a redundant system that forwards a proxied ARP request to the standby unit, or to other hosts in the configuration. To exclude specific hosts from receiving forwarded proxied ARP requests, you use the Configuration utility and specify the IP addresses that you want to exclude.
| |On the menu bar, from VLAN Groups
Proxy Exclusion List.
This opens the Global Proxy Exclusion List screen.
| |Click Repeat
if you want to type another IP address, or click Finished
After you create a VLAN or a VLAN group, you must assign it a self IP
address. You assign self IP addresses to VLANs and VLAN groups using the Configuration utility.
| || |Assigning a self IP address to a VLAN
The self IP address that you assign to a VLAN should represent an address space that includes the self IP addresses of the hosts that the VLAN contains. For example, if the address of one host is 184.108.40.206
and the address of the other host is 220.127.116.11
, you could assign an address of 18.104.22.168
, with a netmask of 255.255.255.0
, to the VLAN.
| || |Assigning a self IP address to the VLAN group
The self IP address that you assign to a VLAN group should represent an address space that includes the self IP addresses of the VLANs that you assigned to the group. For example, if the address of one VLAN is 10.0.0.1
and the address of the other VLAN is 10.0.0.2
, you could assign an address of 10.0.0.100
, with a netmask of 255.255.255.0
, to the VLAN group.