phy provides 綁定 ont 互聯 with arr ace 路由

通常情況下NAS存儲網絡布線為雙上聯對稱布線，交換機推薦做堆疊，存儲和交換機分別配置鏈路聚合（推薦LACP），此網絡環境為對稱網絡環境。

但在非對稱網絡環境中，比如華為的mlag技術，交換機可以不堆疊，但可以通過端口互聯實現跨交換機端口綁定功能。這樣跨交換機綁定的端口其中一個端口down掉後，在netapp C-mode默認網絡配置中有可能造成有的請求無法收到回包，有的正常。通常情況下會從網絡層面排除故障，具體原因NetApp廠商給了如下回復及解決辦法：

            該中情況是由於NetApp 缺省開啟了IP fast path，這個功能 是NetApp 的網絡優化的機制之一，默認情況下是開啟的。
 

目的是避免路由表的查詢，回包時會使用incoming traffic 相同的端口。

What is fast path?
Fast path is an alternative routing mechanism to the routing table, in which the responses to incoming network traffic are sent back by using the same interface as the incoming traffic. By avoiding the routing table lookup, fast path provides a shorter route for data access. Fast path is used in all TCP and NFS/UDP protocols.

但是對於某些特殊的網絡環境， 比如非對稱路由，或者開啟了Vpc 環境中是不適合的，可能導致網絡的異常。
原因是開啟了ip fast path 後， 存儲會回復真實的switch or route 的MAC address 而不是虛擬的MAC address.

Fastpath is a feature that is enabled by default in Data ONTAP systems. Essentially, Fastpath eliminates overhead used by the routing logic (that is, route table lookups) by sending frames out of the same interface that we received the traffic on. This is done via interface to MAC address caching. This feature has been in place and used by NetApp for years. Other vendors do this as well.

Due to fastpath caching incoming MAC address information, considerations should be made when HSRP is in use in combination with vPCs as well. From the perspective of the storage system, if a frame arrives on an ethernet interface on the storage system with the physical MAC address of the switch, then the load balancing algorithim of a vif or ifgrp could choose to return the traffic to the originating MAC address through an interface connected to the neighboring switch (that does not use that MAC address), causing the potential for performance degradation or packet loss due to traffic traversing the peer-link.

通過抓包的結果分析，NetApp用源端主機發送過來MAC來做二層的封裝，而沒有查詢本地路由表和ARP表，和上述基本一致，因此可以確定原因就是這個了。
通過如下命令關閉此功能：

options -option-name ip.fastpath.enable -option-value off

下面鏈接詳細介紹了fast path的工作原理和過程，供參考。

https://kb.netapp.com/app/answers/answer_view/a_id/1002602/loc/en_US#__highlight

關閉此功能的影響：

此功能只是做了簡單的網絡優化，即存儲端不用查詢路由表，而是通過緩存MAC直接進行轉發，因此對系統影響可以忽略不計。

NetApp C-mode 非對稱網絡NAS lif網絡故障處理