This object is the maximum transmission size used by this specific association, derived from the smallest MTU among all the IP addresses involved in it. This determines the largest signaling message the association can send without fragmentation; because it is automatically pinned to the worst-case path in a multihomed setup, adding a secondary path with a smaller MTU, for example through a VPN, silently shrinks this value and starts fragmenting messages that previously fit in one packet. An association with an MTU of 1460, typical for a path through a PPPoE or VPN hop, will fragment any signaling message just a few dozen bytes larger than that, where a plain 1500-byte Ethernet path would not.