what are single/dual homed/multi-homed network topologies?

在討論廣域網路如何將客戶端(client)連向伺服端(server)，或輻輳(spoke)連向軸心(hub)的連線拓樸時，
常根據源頭(source or home)個數，及線路(link)個數，將連線拓樸依其可靠度/成本分成四類如下:

1.single homed = single-link single-source 單線路單源頭拓樸
2.dual homed = dual-link single-source 雙線路單源頭拓樸
3.single multi-homed = single-link multiple-source 單線路多源頭拓樸
4.dual multi-homed = dual-link multiple-source 雙線路多源頭拓樸

單線路單源頭(single homed)拓樸的成本最低，但是可靠度最差。
雙線路多源頭(dual multi-homed)拓樸的可靠度最佳，但是成本最高。

四類連線拓樸的各種實例可參考如下網頁介紹:
  https://datapacket.com/blog/multihomed-network-vs-single-homed-network