Configure MAC Address for Layer 2 Learning and Forwarding

You can manually add static MAC entries for the logical interfaces in a bridge domain. You can specify one or more static MAC addresses for each logical interface.

To add a static MAC address for a logical interface in a bridge domain, include the static-mac mac-address statement at the [edit bridge-domains bridge-domain-name bridge-options interface interface-name] hierarchy level.

[edit]
bridge-domains {
    bridge-domain-name {
        domain-type bridge;
        bridge-options {
            interface interface-name {
                static-mac mac-address {
                    <vlan-id number>;
                }
            }
        }
    }
}

You can optionally specify a VLAN identifier for the static MAC address by using the vlan-id statement. To specify a VLAN identifier for a static MAC address, you must use the all option when configuring a VLAN identifier for the bridge domain.

You can modify the size of the MAC address table for each bridge domain. The default table size is 5120 addresses. The minimum you can configure is 16 addresses, and the maximum is 1,048,575 addresses.

If the MAC table limit is reached, new addresses can no longer be added to the table. Unused MAC addresses are removed from the MAC address table automatically. This frees space in the table, allowing new entries to be added.

To modify the size of the MAC table, include the mac-table-size limit statement at the [edit bridge-domains bridge-domain-name bridge-options] hierarchy level:

[edit]
bridge-domains {
    bridge-domain-name {
        domain-type bridge;
        bridge-options {
            mac-table-size limit {
                packet-action drop;
            }
        }
    }
}

You can configure a limit on the number of MAC addresses learned from a specific bridge domain or from a specific logical interface that belongs to a bridge domain.

To configure a limit for the number of MAC addresses learned from each logical interface in a bridge domain, include the interface-mac-limit limit statement at the [edit bridge-domains bridge-domain-name bridge-options] hierarchy level:

[edit]
bridge-domains {
    bridge-domain-name {
        domain-type bridge;
        interface interface-name;
        bridge-options {
            interface-mac-limit limit;
        }
    }
}

To limit the number of MAC addresses learned from a specific logical interface in a bridge domain or an entire bridge domain, include the interface-mac-limit limit statement at the [edit bridge-domains bridge-domain-name bridge-options interface interface-name] or [edit bridge-domains bridge-domain-name bridge-options] hierarchy level:

[edit]
bridge-domains {
    bridge-domain-name {
        domain-type bridge;
        interface interface-name;
        bridge-options {
            interface-mac-limit limit{
                packet-action drop;
            }
            interface interface-name {
                interface-mac-limit limit{
                    packet-action drop;
                }
            }
        }
    }
}

For an access port, the default limit on the maximum number of MAC addresses that can be learned on an access port is 1024. Because an access port can be configured in only one bridge domain in a network topology, the default limit is 1024 addresses, which is same as the limit for MAC addresses learned on a logical interface in a bridge domain (configured by including the interface-mac-limit limit statement at the [edit bridge-domains bridge-domain-name bridge-options interface interface-name] or [edit bridge-domains bridge-domain-name bridge-options] hierarchy level.

For a trunk port, the default limit on the maximum number of MAC addresses that can be learned on a trunk port is 8192. Because a trunk port can be associated with multiple bride domains, the default limit is the same as the limit for MAC addresses learned on a logical interface in a virtual switch instance (configured by including the interface-mac-limit limit statement at the [edit routing-instances routing-instance-name switch- options interface interface-name] for a virtual switch instance).

The value you configure for a specific logical interface overrides any value you specify for the entire bridge domain at the [edit bridge-domains bridge-domain-name bridge-options] hierarchy level.

The default limit to the number of MAC addresses that can be learned on a logical interface is 1024. The range that you can configure for a specific logical interface is 1 through 131,071.

After the MAC address limit is reached, the default is for any incoming packets with a new source MAC address to be forwarded. You can specify that the packets be dropped by including the packet-action drop statement. To specify that packets be dropped for the entire bridge domain, include the packet-action drop statement at the [edit bridge-domains bridge-domain-name bridge-options interface-mac-limit limit] hierarchy level:

[edit bridge-domains bridge-domain-name bridge-options interface-mac-limit limit]
packet-action drop;

To specify that the packets be dropped for a specific logical interface in a bridge domain, include the packet-action drop statement at the [edit bridge-domains bridge-domain-name bridge-options interface interface-name interface-mac-limit limit] hierarchy level:

[edit bridge-domains bridge-domain-name bridge-options interface interface-name interface-mac-limit limit]
packet-action drop;

You can also configure a limit to the number of MAC addresses learned for an MX Series router.

By default, MAC accounting is disabled. On MX Series routers, you can enable packet accounting either for the router as a whole or for a specific bridge domain. After you enable packet accounting, the Junos OS maintains packet counters for each MAC address learned.

To enable MAC accounting for an MX Series router, include the global-mac-statistics statement at the [edit protocols l2-learning] hierarchy level:

[edit protocols l2-learning]
global-mac-statistics;

To enable MAC accounting for a bridge domain, include the mac-statistics statement at the [edit bridge-domains bridge-domain-name bridge-options] hierarchy level:

[edit bridge-domains bridge-domain-name bridge-options]
mac-statistics;

You can disable MAC learning for all logical interfaces in a specified bridge domain, or for a specific logical interface in a bridge domain. Disabling dynamic MAC learning prevents the specified interfaces from learning source MAC addresses.

To disable MAC learning for all logical interfaces in a bridge domain in a virtual switch, include the no-mac-learning statement at the [edit bridge-domains bridge-domain-name bridge-options] hierarchy level:

[edit]
bridge-domains {
    bridge-domain-name {
        domain-type bridge;
        interface interface-name;
        bridge-options {
            no-mac-learning;
        }
    }
}

To disable MAC learning for a specific logical interface in a bridge domain, include the no-mac-learning statement at the [edit bridge-domains bridge-domain-name bridge-options interface interface-name] hierarchy level.

[edit]
bridge-domains {
    bridge-domain-name {
        domain-type bridge;
        interface interface-name;
        bridge-options {
            interface interface-name {
                no-mac-learning;
            }
        }
    }
}

The MAC table aging process ensures that a router tracks only active MAC addresses on the network and is able to flush out address that are no longer used.

You can configure the MAC table aging time, the maximum time that an entry can remain in the MAC table before it “ages out,” on all bridge domains, one or all VPLS instances, or one or all Ethernet virtual private network (EVPNs) instances on the router. This configuration 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 routing table, the router floods the traffic to all interfaces.

Depending on how long you want to keep a MAC address in a MAC table before it expires, you can either increase or decrease the aging timer. By default, the timeout interval for all entries in the MAC table is 300 seconds. You can modify the timeout interval for MAC table entries on an MX Series router. You cannot modify the timeout interval for a virtual switch.

The range for seconds is from 10 through 1,000,000.

You can modify the timeout interval for a router(at the global level) or on a per-domain basis (bridge domain).