- play_arrow Understanding Layer 2 Networking
- play_arrow Configuring MAC Addresses
- play_arrow Configuring MAC Learning
- play_arrow Configuring MAC Accounting
- play_arrow Configuring MAC Notification
- play_arrow Configuring Learning and Forwarding
- play_arrow Configuring Bridging and VLANs
- play_arrow Configuring 802.1Q VLANs
- 802.1Q VLANs Overview
- 802.1Q VLAN IDs and Ethernet Interface Types
- Configuring Dynamic 802.1Q VLANs
- Enabling VLAN Tagging
- Configuring Tagged Interface with multiple tagged vlans and native vlan
- Sending Untagged Traffic Without VLAN ID to Remote End
- Configuring Tag Protocol IDs (TPIDs) on QFX Series Switches
- Configuring Flexible VLAN Tagging on PTX Series Packet Transport Routers
- Configuring an MPLS-Based VLAN CCC with Pop, Push, and Swap and Control Passthrough
- Binding VLAN IDs to Logical Interfaces
- Associating VLAN IDs to VLAN Demux Interfaces
- Configuring VLAN and Extended VLAN Encapsulation
- Configuring a Layer 2 VPN Routing Instance on a VLAN-Bundled Logical Interface
- Example: Configuring a Layer 2 VPN Routing Instance on a VLAN-Bundled Logical Interface
- Specifying the Interface Over Which VPN Traffic Travels to the CE Router
- Configuring Access Mode on a Logical Interface
- Configuring a Logical Interface for Trunk Mode
- Configuring the VLAN ID List for a Trunk Interface
- Configuring a Trunk Interface on a Bridge Network
- Configuring a VLAN-Bundled Logical Interface to Support a Layer 2 VPN Routing Instance
- Configuring a VLAN-Bundled Logical Interface to Support a Layer 2 VPN Routing Instance
- Configuring a Layer 2 Circuit on a VLAN-Bundled Logical Interface
- Example: Configuring a Layer 2 Circuit on a VLAN-Bundled Logical Interface
- Guidelines for Configuring VLAN ID List-Bundled Logical Interfaces That Connect CCCs
- Specifying the Interface to Handle Traffic for a CCC
- Specifying the Interface to Handle Traffic for a CCC Connected to the Layer 2 Circuit
- play_arrow Configuring Static ARP Table Entries
- play_arrow Configuring Restricted and Unrestricted Proxy ARP
- play_arrow Configuring Gratuitous ARP
- play_arrow Adjusting the ARP Aging Timer
- play_arrow Configuring Tagged VLANs
- play_arrow Stacking and Rewriting Gigabit Ethernet VLAN Tags
- Stacking and Rewriting Gigabit Ethernet VLAN Tags Overview
- Stacking and Rewriting Gigabit Ethernet VLAN Tags
- Configuring Frames with Particular TPIDs to Be Processed as Tagged Frames
- Configuring Tag Protocol IDs (TPIDs) on PTX Series Packet Transport Routers
- Configuring Stacked VLAN Tagging
- Configuring Dual VLAN Tags
- Configuring Inner and Outer TPIDs and VLAN IDs
- Stacking a VLAN Tag
- Stacking Two VLAN Tags
- Removing a VLAN Tag
- Removing the Outer and Inner VLAN Tags
- Removing the Outer VLAN Tag and Rewriting the Inner VLAN Tag
- Rewriting the VLAN Tag on Tagged Frames
- Rewriting a VLAN Tag on Untagged Frames
- Rewriting a VLAN Tag and Adding a New Tag
- Rewriting the Inner and Outer VLAN Tags
- Examples: Stacking and Rewriting Gigabit Ethernet IQ VLAN Tags
- Understanding Transparent Tag Operations and IEEE 802.1p Inheritance
- Understanding swap-by-poppush
- Configuring IEEE 802.1p Inheritance push and swap from the Transparent Tag
- play_arrow Configuring Private VLANs
- Private VLANs
- Understanding Private VLANs
- Bridge Domains Setup in PVLANs on MX Series Routers
- Bridging Functions With PVLANs
- Flow of Frames on PVLAN Ports Overview
- Guidelines for Configuring PVLANs on MX Series Routers
- Configuring PVLANs on MX Series Routers in Enhanced LAN Mode
- Example: Configuring PVLANs with Secondary VLAN Trunk Ports and Promiscuous Access Ports on a QFX Series Switch
- IRB Interfaces in Private VLANs on MX Series Routers
- Guidelines for Configuring IRB Interfaces in PVLANs on MX Series Routers
- Forwarding of Packets Using IRB Interfaces in PVLANs
- Configuring IRB Interfaces in PVLAN Bridge Domains on MX Series Routers in Enhanced LAN Mode
- Example: Configuring an IRB Interface in a Private VLAN on a Single MX Series Router
- play_arrow Configuring Layer 2 Bridging Interfaces
- play_arrow Configuring Layer 2 Virtual Switch Instances
- play_arrow Configuring Link Layer Discovery Protocol
- play_arrow Configuring Layer 2 Protocol Tunneling
- play_arrow Configuring Virtual Routing Instances
- play_arrow Configuring Layer 3 Logical Interfaces
- play_arrow Configuring Routed VLAN Interfaces
- play_arrow Configuring Integrated Routing and Bridging
- play_arrow Configuring VLANS and VPLS Routing Instances
- play_arrow Configuring Multiple VLAN Registration Protocol (MVRP)
- play_arrow Configuring Ethernet Ring Protection Switching
- play_arrow Configuring Q-in-Q Tunneling and VLAN Translation
- play_arrow Configuring Redundant Trunk Groups
- play_arrow Configuring Proxy ARP
- play_arrow Configuring Layer 2 Interfaces on Security Devices
- play_arrow Configuring Security Zones and Security Policies on Security Devices
- play_arrow Configuring Ethernet Port Switching Modes on Security Devices
- play_arrow Configuring Ethernet Port VLANs in Switching Mode on Security Devices
- play_arrow Configuring Secure Wire on Security Devices
- play_arrow Configuring Reflective Relay on Switches
- play_arrow Configuring Edge Virtual Bridging
- play_arrow Troubleshooting Ethernet Switching
- play_arrow Configuration Statements and Operational Commands
MAC Table Aging
Understanding MAC Table Aging
Juniper Networks EX Series Ethernet Switches store MAC addresses in the Ethernet switching table, also called the MAC table. When the aging time for a MAC address in the table expires, the address is removed.
If your switch runs Juniper Networks Junos operating system (Junos OS) for EX Series switches with support for the Enhanced Layer 2 Software (ELS) configuration style, you can configure the MAC table aging time on all VLANs on the switch. If your switch runs Junos OS that does not support ELS, you can configure the MAC table aging time on all VLANs on the switch or on specified VLANs, as well as configure aging time to be unlimited, either on all VLANs or on specified VLANs, so that MAC addresses never age out of the table.
To learn MAC addresses, the switch reads all packets that it detects on the LAN or on the local VLAN, looking for MAC addresses of sending nodes. It places these addresses into its Ethernet switching table, along with two other pieces of information—the interface on which the traffic was received and the time when the address was learned.
When the switch receives traffic on an interface, it searches the Ethernet switching table for the MAC address of the destination. If the MAC address is not found, the traffic is flooded out all of the other interfaces associated with the VLAN. For example, if traffic is received on an interface that is associated with VLAN v-10 and there is no entry in the Ethernet switching table for VLAN v-10 (the Ethernet switching table is organized by VLAN), then the traffic is flooded to all access and trunk interfaces that are members of VLAN v-10.
Flooding allows the switch to learn about destinations that are not yet in its Ethernet switching table. If a particular destination MAC address is not in the Ethernet switching table, the switch floods the traffic to all interfaces except the interface on which it was received. When the destination node receives the flooded traffic, it sends an acknowledgment packet back to the switch, allowing the switch to learn the MAC address of the node and to add the address to its Ethernet switching table.
The switch uses a mechanism called aging to keep the Ethernet switching table current. For each MAC address in the Ethernet switching table, the switch records a timestamp of when the information about the network node was learned. Each time the switch detects traffic from a MAC address that is in its Ethernet switching table, it updates the timestamp of that MAC address. A timer on the switch periodically checks the timestamp, and if the MAC address of a node is older than the value set, the switch removes that MAC address from the Ethernet switching table. This aging process ensures that the switch tracks only active MAC addresses on the network and that it is able to flush out from the Ethernet switching table MAC addresses that are no longer available.
You configure how long MAC addresses remain in the Ethernet switching table by:
(On switches that run Junos OS with support for the ELS configuration style) Using the
global-mac-table-aging-time
statement in the[edit protocols l2-learning]
hierarchy.(On switches that run Junos OS that does not support ELS) Using the
mac-table-aging-time
statement in either the [edit ethernet-switching-options] or the [edit vlans] hierarchy, depending on whether you want to configure it for the entire switch or only for specific VLANs.
For example, in a topology with EX switches that run Junos OS that does not support ELS, if you have a printer VLAN, you might choose to configure the aging time for that VLAN to be considerably longer than for other VLANs so that MAC addresses of printers on this VLAN age out less frequently. Because the MAC addresses remain in the table, even if a printer has been idle for some time before traffic arrives for it, the switch still finds the MAC address and does not need to flood the traffic to all other interfaces.
Similarly, in a data center environment where the list of servers connected to the switch is fairly stable, you might choose to increase MAC address aging time, or even set it to unlimited, to increase the efficiency of the utilization of network bandwidth by reducing flooding.
See Also
Configuring MAC Table Aging on Switches
MAC table aging ensures that a switch tracks only active nodes on the network and that it is able to flush out network nodes that are no longer available.
To manage MAC entries more efficiently, you can configure an entry’s aging time, which is the maximum time that an entry can remain in the MAC address table before it is deleted because it has reached its maximum age.
The following example uses Junos OS for Junos OS for
QFX3500 and QFX3600 switches with no support for the Enhanced Layer
2 Software (ELS) configuration style. Use the set-mac-table-aging-time
command to configure how long entries remain in the Ethernet switching
table before expiring. Here the VLAN is employee-vlan:
[edit vlans employee-vlan] user@switch# set mac-table-aging-time 200
This command applies to all VLANs configured for the switch. You cannot configure separate MAC table aging times for specific VLANs.
The following example uses Junos OS for QFX Series switches
with support for the Enhanced Layer 2 Software (ELS) configuration
style. Use the global-mac-table-aging-time
command to configure
how long entries remain in the Ethernet switching table before expiring,
as follows:
[edit protocols l2-learning] user@switch# set global-mac-table-aging-time 200
This command applies to all VLANs configured for the switch. You cannot configure separate MAC table aging times for specific VLANs.
The following example uses Junos OS for EX Series switches with support for the Enhanced Layer 2 Software (ELS) configuration style.
The Ethernet switching table (or MAC table) aging process ensures that the EX Series switch tracks only active MAC addresses on the network and is able to flush out MAC addresses that are no longer used.
You can configure the MAC table aging time, the maximum time that an entry can remain in the Ethernet Switching table before it ages out, on all VLANs on the switch. This setting can influence efficiency of network resource use by affecting the amount of traffic that is flooded to all interfaces because when traffic is received for MAC addresses no longer in the Ethernet switching table, the switch floods the traffic to all interfaces.
[edit] user@switch# set protocols l2-learning global-mac-table-aging-time seconds
The following example uses Junos OS for EX Series switches that do not support the Enhanced Layer 2 Software (ELS) configuration style.
The Ethernet switching table (or MAC table) aging process ensures that the EX Series switch tracks only active MAC addresses on the network and is able to flush out MAC addresses that are no longer used.
You can configure the MAC table aging time, the maximum time that an entry can remain in the Ethernet Switching table before it “ages out,” either on all VLANs on the switch or on particular VLANs. This setting can influence efficiency of network resource use by affecting the amount of traffic that is flooded to all interfaces because when traffic is received for MAC addresses no longer in the Ethernet switching table, the switch floods the traffic to all interfaces.
To configure the MAC table aging time on all VLANs on the switch:
[edit] user@switch# set ethernet-switching-options mac-table-aging-time seconds
To configure the MAC table aging time on a VLAN:
[edit] user@switch# set vlans vlan-name mac-table-aging-time seconds
You can set the MAC table aging time to unlimited. If you specify the value as unlimited, entries are never removed from the table. Generally, use this setting only if the switch or the VLAN has a fairly static number of end devices; otherwise the table will eventually fill up. You can use this setting to minimize traffic loss and flooding that might occur when traffic arrives for MAC addresses that have been removed from the table.