Example: Prevention of Loops in Bridge Domains by Enabling the MAC Pinnning Feature on Access Interfaces

Topology

In this example, you configure the interfaces ge-4/0/6 and xe-4/2/0 on the MX Series router as access interfaces. Access interfaces accept both untagged and tagged packets and forward the packets within a specified bridge domain, bd1. Specify 1 as the VLAN ID for the interfaces and the bridge domain. When an untagged or a tagged packet is received on any of the access interfaces, the packet is accepted, the VLAN ID is added to the packet, and the packet is forwarded within the bridge domain that is configured with the matching ID.

In the bridge domain, after specifying the VLAN ID, specify 131071 as the maximum number of MAC addresses that can be learned on the access interfaces and specify 1048575 as the size of the MAC address table for the bridge domain or VLAN.

In this topology, frequent MAC moves can occur, which can result in loops. To prevent these loops, you can configure MAC pinning. When you configure MAC pinning on an interface, the MAC address learned on the interface cannot be learned on another interface in the same bridge domain. For example, configure MAC pinning on the access interface ge-4/0/6. When a packet is received on this interface, the packet is accepted, the VLAN ID is added and the packet is forwarded within the bridge domain with the matching ID. However, if a packet with the same MAC address is received on any other access interface, say xe-4/2/0, the packet is discarded or dropped as that MAC address is pinned to the access interface ge-4/0/6 . This behavior is common to all access interfaces configured on the router, regardless of whether access pinning is enabled on the access interface or not.

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

set interfaces ge-4/0/6 encapsulation ethernet-bridge
set interfaces ge-4/0/6 unit 0 family bridge interface-mode access
set interfaces ge-4/0/6 unit 0 family bridge vlan-id 1
set interfaces xe-4/2/0 encapsulation ethernet-bridge
set interfaces xe-4/2/0 unit 0 family bridge interface-mode access
set interfaces xe-4/2/0 unit 0 family bridge vlan-id 1
set bridge-domains bd1 vlan-id 1
set bridge-domains bd1 bridge-options mac-table-size 1048575
set bridge-domains bd1 bridge-options interface ge-4/0/6.0 interface-mac-limit 131071
set bridge-domains bd1 bridge-options interface ge-4/0/6.0 mac-pinning
set bridge-domains bd1 bridge-options interface xe-4/2/0.0 interface-mac-limit 131071
set bridge-domains bd1 bridge-options interface xe-4/2/0.0 mac-pinning

Procedure

Results

From configuration mode, confirm your configuration by entering show interfaces and show bridge-domains commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

user@host# show interfaces
ge-4/0/6 {
encapsulation ethernet-bridge;
    unit 0 {
        family bridge {
            interface-mode access;
        vlan-id 1;
        }
    }
}
xe-4/2/0 {
encapsulation ethernet-bridge;
    unit 0 {
        family bridge {
            interface-mode access;
        vlan-id 1;
        }
    }
}

user@host# show bridge-domains
bridge-domains {
    bd1 {
        vlan-id 1;
        bridge-options {
            mac-table-size {
                1048575;
                }
                interface ge-4/0/6.0 {
                interface-mac-limit {
                131071;
                }
                mac-pinning;
            }
            interface xe-4/2/0.0 {
                interface-mac-limit {
                131071;
                }
                mac-pinning;
            }
        }
    }
}

If you have completed configuring the device, enter commit from the configuration mode.

Verifying That MAC Pinning Is Configured Correctly

• Purpose
• Action
• Meaning

user@host> show l2-learning interface 
Routing Instance Name : default-switch
Logical Interface flags (DL -disable learning, AD -packet action drop,
                         LH - MAC limit hit, DN - Interface Down, MP - MAC Pinning)
Logical             BD         MAC        STP          Logical
Interface           Name       Limit      State        Interface flags  
xe-4/0/6.0                     131000                               MP
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
Routing Instance Name : default-switch
Logical Interface flags (DL -disable learning, AD -packet action drop,
                         LH - MAC limit hit, DN - Interface Down, MP - MAC Pinning)
Logical             BD         MAC        STP          Logical
Interface           Name       Limit      State        Interface flags  
xe-4/2/0.0                     131000                               MP
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding  
                    BD_Tru..   131000     Forwarding