MAC Pinning was intially used for VPLS. Its the same feature implemetned in EVPN scenario.
If you configure MAC pinning on a CE interface, that MAC address cannot be moved to any other CE interface. Similarly, if you configure MAC pinning on an MPLS core interface on a PE device, that MAC address cannot be moved to a different interface on the MPLS core.
A MAC move occurs when a MAC address frequently appears on a different physical interface than the one it was learned on. Frequent MAC moves indicate the presence of loops. To avoid loops across interfaces you can configure MAC pinning.
MAC route sequence number is used to determine which MAC route is latest one. Is it similar to OSPF sequence number. Refer following document for MAC mobility sequence number:
https://www.juniper.net/documentation/en_US/junos/topics/concept/mac-mobility.html
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:
#Advertisement routes with a local pinned MAC address (static MAC address).
#Advertisement routes with a remote pinned MAC address (static MAC address).
#Advertisement routes with a higher sequence number.
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Thanks
Vishal