Overview of MAC Mobility

MAC mobility describes the scenario where a host moves from one Ethernet segment to another segment in the EVPN network. Provider Edge (PE) devices discover the host MAC address from its local interfaces or from remote PE devices. When a PE device learns of a new local MAC address, it sends a MAC advertisement route message to other devices in the network. During this time, there are two advertised routes and the PE devices in the EVPN network must decide which of the MAC advertisement messages to use.

To determine the correct MAC address location, PE devices use the MAC mobility extended community field, as defined in RFC 7432, in the MAC advertisement route message. The MAC mobility extended community includes a static flag and a sequence number. The static flag identifies pinned MAC addresses that should not be relocated. The sequence number identifies newer MAC advertisement messages. Starting at 0, the sequence number is incremented for every MAC address mobility event. PE devices running Junos OS apply the following precedence order in determining the MAC advertisement route to use:

1. Advertisement routes with a local pinned MAC address (static MAC address).

2. Advertisement routes with a remote pinned MAC address (static MAC address).

3. Advertisement routes with a higher sequence number.

Figure 1 illustrates a network where a MAC address is relocated from PE1 to PE2. Before the move, a MAC advertisement route message sent by PE1 has the active route for all PE devices in the network. After the relocation, PE2 learns of the new local MAC address and sends an updated MAC advertisement route message. Table 1 lists the action taken by each PE device based on the two MAC advertisements. The PE device generates a syslog message when it encounters conflicts with a pinned MAC address.

Figure 1: MAC Mobility in an EVPN Network

Junos supports MAC mobility automatically by default. To disable MAC mobility, use the set protocols evpn mac-mobility no-sequence-numbers statement.