Mac and Mac's automatically hide or delete it. If you attempt to. Unlike normal Assignments, SafeAssign restricts your submissions to specific file formats such. Apply permissions to all items in a folder or a disk. On your Mac, select a folder or a disk, then choose File Get Info. Click the lock icon to unlock it, then enter an administrator name and password (or, if your Mac has Touch ID, use Touch ID).

Introduction to the Media Access Control (MAC) Layer 2 Sublayer

This topic provides an introduction to the MAC sublayerof the data link layer (Layer 2).

In Layer 2 of a network, the Media Access Control (MAC) sublayerprovides addressing and channel access control mechanisms that enableseveral terminals or network nodes to communicate in a network.

The MAC sublayer acts as an interface between the logical linkcontrol (LLC) Ethernet sublayer and Layer 1 (the physical layer).The MAC sublayer emulates a full-duplex logical communication channelin a multipoint network. This channel may provide unicast, multicast,or broadcast communication service. The MAC sublayer uses MAC protocolsto prevent collisions.

In Layer 2, multiple devices on the same physical link can uniquelyidentify one another at the data link layer, by using the MAC addressesthat are assigned to all ports on a switch. A MAC algorithm acceptsas input a secret key and an arbitrary-length message to be authenticated,and outputs a MAC address.

A MAC address is a 12-digit hexadecimal number (48 bits in long).MAC addresses are usually written in one of these formats:

• MM:MM:MM:SS:SS:SS

  

• MM-MM-MM-SS-SS-SS

The first half of a MAC address contains the ID number of theadapter manufacturer. These IDs are regulated by an Internet standardsbody. The second half of a MAC address represents the serial numberassigned to the adapter by the manufacturer.

Contrast MAC addressing, which works at Layer 2, with IP addressing,which runs at Layer 3 (networking and routing). One way to rememberthe difference is that the MAC addresses apply to a physical or virtualnode, whereas IP addresses apply to the software implementation ofthat node. MAC addresses are typically fixed on a per-node basis,whereas IP addresses change when the node moves from one part of thenetwork to another.

IP networks maintain a mapping between the IP and MAC addressesof a node using the Address Resolution Protocol (ARP) table. DHCPalso typically uses MAC addresses when assigning IP addresses to nodes.

Understanding MAC Address Assignment on an EX Series Switch

This topic describes MAC address assignment for interfaces onstandalone Juniper Networks EX Series Ethernet Switches. For informationregarding MAC address assignments in a Virtual Chassis, see Understanding MAC Address Assignment on a Virtual Chassis.

MAC addresses are used to identify network devices at Layer2. Because all Layer 2 traffic decisions are based on an interface’sMAC address, understanding MAC address assignment is important tounderstanding how network traffic is forwarded and received by theswitch. For additional information on how a network uses MAC addressesto forward and receive traffic, see Understanding Bridging and VLANs on Switches.

A MAC address comprises six groups of two hexadecimal digits,with each group separated from the next group by a colon—forinstance, aa:bb:cc:dd:ee:00. The first five groups of hexadecimaldigits are derived from the switch and are the same for all interfaceson the switch.

The assignment of a unique MAC address to each network interfacehelps ensure that functions that require MAC address differentiation—suchas redundant trunk groups (RTGs), Link Aggregation Control Protocol(LACP), and general monitoring functions—can properly function.

On switches that use line cards, this MAC addressing schemedifferentiates the Layer 2 interfaces on different line cards in theswitch.

For EX Series switches, the first five groups of hexadecimaldigits are determined when the switch is manufactured. The switchthen assigns a unique MAC address to each interface by assigning aunique identifier as the last group of hexadecimal digits. The assignmentdepends on how the interface is configured. The switch uses a differentpattern to distinguish between an interface that is configured asany of a routed VLAN interface (RVI), a virtual management Ethernet (VME) interface,or an aggregated Ethernet interface or is not configured as any ofan RVI, a VME, or as an aggregated Ethernet interface.

For aggregated Ethernet interfaces, the MAC address assignmentremains constant regardless of whether the configuration of the interfaceis Layer 2 or Layer 3.

In Junos OS Release 11.3 and later releases through Release12.1, the MAC address assignment for aggregated Ethernet interfaceschanges if the interface is changed from Layer 2 to Layer 3 or thereverse. Starting with Junos Release 12.2, the MAC address assignmentfor aggregated Ethernet interfaces remains constant regardless ofwhether the interface is Layer 2 or Layer 3.

Prior to Junos OS Release 11.3, MAC addresses for Layer2 interfaces could be shared between interfaces and RVIs on differentline cards in the same switch. However, if you upgrade from JunosOS Release 11.2 or earlier to Junos OS Release 11.3 or later on aswitch that supports line cards, the MAC addresses of these interfaceswill change.

MAC addresses are assigned to interfaces automatically—nouser configuration is possible or required. You can view MAC addressesassigned to interfaces using the global-mac-move statement at the global hierarchy level.

To globally disable the MAC move action feature, include the [edit protocols l2-learningglobal-mac-move]. This disables the MAC move action feature,while MAC move detection exists.

To configure the time duration after which the port will beunblocked, include the [edit protocols l2-learning global-mac-move]. The default reopentimer is 180 second.

To configure MAC address move reporting if the MAC address movesat least a specified number of times in one second, include the [edit protocols l2-learningglobal-mac-move] hierarchy level. The default threshold timeis 1 second.

To configure reporting of a MAC address move if the MAC addressmoves for a specified period of time, include the [edit protocols l2-learning global-mac-move] hierarchy level. The default notification timer is 1 second.

To configure reporting of a MAC address move if the MAC addressmoves a specified number of times, include the [edit protocols l2-learning global-mac-move] hierarchy level. The default threshold count is 50 moves.

Use the show l2-learning mac-move-buffer active commandto view the set of IFLs blocked as a result of MAC move action.

Use the clear l2-learning mac-move-buffer active commandto unblock the IFBDs that were blocked by MAC move action feature.This allows the user to keep the clear ethernet-switching recovery-timeout command.

The different ways of setting a MAC limit aredescribed in the following sections:

Limiting the Number of MAC Addresses Learned by an Interface

To secure a port, you can set the maximum number of MACaddresses that can be learned by an interface:

• Set the MAC limit on an interface, and specify an actionthat the switch takes after the specified limit is exceeded:
  [edit switch-options]
user@switch# set interface limitpacket-action
• Set the maximum number of MAC addresses that can be learnedby a VLAN, and specify an action that the switch takes after the specifiedlimit is exceeded:
  [edit vlans]
  user@switch# set limitpacket-actionNote

  If you specify a MAC limit and packet action for all interfacesin the VLAN and a specific interface in the VLAN,the MAC limit and packet action specified at the specific interfacelevel takes precedence. Also, at the VLAN interface level, only the drop-and-log options are supported.

  [edit vlans]
user@switch# set interface-nameinterface-mac-limitaction

  [edit vlans]
  user@switch# set limitpacket-actionmac-table-size statement or for interfaces associated with a VLAN by using the Note

  On a QFX Series Virtual Chassis, if you include the [edit vlans interface-name interface-mac-limitpacket-action] hierarchy level and issue the shutdown optionat the interface-name interface-mac-limit packet-action] hierarchy level.

Adding a Static MAC Address Entry to the Ethernet SwitchingTable on a Switch with ELS Support

Note

This task uses Junos OS for EX Series switches and JunosOS for QFX3500 and QFX3600 switches with support for the EnhancedLayer 2 Software (ELS) configuration style. If your switch runs softwarethat does not support ELS, see Adding a Static MAC Address Entry to the Ethernet Switching Table. For ELS details, see Using the Enhanced Layer 2 Software CLI.

The Ethernet switching table, also known as the forwarding table,specifies the known locations of VLAN nodes and the addresses of deviceswithin those nodes. There are two ways to populate the Ethernet switchingtable on a switch. The easiest method is to let the switch updatethe table with MAC addresses.

The second way to populate the Ethernet switching table is tomanually insert addresses into the table. You can do this to reduceflooding and speed up the switch’s automatic learning process.

Before configuring a static MAC address, besure that you have:

• Set up the VLAN. See Configuring VLANs for EX Series Switches with ELS Support (CLI Procedure).

To configure an interface to have a static MAC address:

[edit vlans interface-name]
user@switch# mac-address

Adding a Static MAC Address Entry to the Ethernet SwitchingTable

Note

This task uses Junos OS for EX Series switches and JunosOS for QFX3500 and QFX3600 switches that does not support the EnhancedLayer 2 Software (ELS) configuration style. If your switch runs softwarethat supports ELS, see Adding a Static MAC Address Entry to the Ethernet Switching Table on a Switch with ELS Support. For ELSdetails, see Using the Enhanced Layer 2 Software CLI.

The Ethernet switching table, also known as the forwarding table,specifies the known locations of VLAN nodes. There are two ways topopulate the Ethernet switching table on a switch. The easiest methodis to let the switch update the table with MAC addresses.

The second way to populate the Ethernet switching table is tomanually insert a VLAN node location into the table. You can do thisto reduce flooding and speed up the switch’s automatic learningprocess. To further optimize the switching process, indicate the nexthop (next interface) packets will use after leaving the node.

Before configuring a static MAC address, besure that you have:

• Set up the VLAN. See Configuring VLANs for EX Series Switches orConfiguring VLANs on Switches.

To add a MAC address to the Ethernet switching table:

1. Specify the MAC address to add to the table:
   [edit ethernet-switching-options]
vlan-name mac-address
2. Indicate the next hop MAC address for packets sent tothe indicated MAC address:
   [edit ethernet-switching-options]
vlan-name mac-address interface

Example: Configuring the Default Learning for Unknown MAC Addresses

This example shows how to configure the deviceto use only ARP requests to learn the outgoing interfaces for unknowndestination MAC addresses.

Requirements

Before you begin, determine the MAC addressesand associated interfaces of the forwarding table. See Layer 2 Learning and Forwarding for VLANs Overview.

Overview



In this example, you configure the device to use only ARP querieswithout traceroute requests.

Configuration

CLI Quick Configuration

To quickly configure this example, copy thefollowing commands, paste them into a text file, remove any line breaks,change any details necessary to match your network configuration,copy and paste the commands into the CLI at the commit from configuration mode.

Step-by-Step Procedure

To configure the device to use only ARP requests to learnunknown destination MAC addresses:

1. Enable the device.
2. If you are done configuring the device, commit the configuration.

Verification

To verify the configuration is working properly,enter the