NVR dual LAN ports capability and suggested usage

Symptom:

Incoming network packets cannot be received by correct LAN port causing disconnect issue (camera or server) or recording lost issue.

本文章主在探討由於NVR收進來的網路封包丟失，導致可能的斷線問題(攝影機或是伺服器)或是錄影丟失問題。

Description:
NVR with dual LAN ports provided, the main purpose is to separate the network environment into two parts - one is for Local Area Network (LAN) access with cameras, and another one is for Wide Area Network (WAN) access to the Internet. The dual LAN ports architecture is not for the purposes of increasing network throughput (link aggregation), doing load balance, or for network redundancy. So, if clients setup both LAN ports to the same subnet, it might result in the network packets lost because the network packets might be sent to the incorrect route.

針對有提供雙網路介面的NUUO NVR，該雙網路介面主要提供用來將NVR所連接的網路區分成兩塊 - 一個是用來與攝影機連接的內網(LAN)以及另一個用來連外並可提供存取網際網路的外網(WAN)。這樣的雙網路介面架構並不是提供NVR俱備增加網路吞吐量(鏈路聚合 - link aggregation)、網路負載平衡或者網路備援等等功能用。因此，如果使用者將NVR的雙網路介面都接到同一個網段底下時，將會因為網路封包被不正確的網路介面接收了導致網路封包丟失的情況。

For example, as shown in below routing table, this is a WRONG routing table setup by the users. Both LAN ports (eth0 and eth1) are setup to be as 192.168.0.x/24. So, the NVR routing table would look like the result shown in below figure.

例如，如底下附圖的路由表所顯示的，這是由於錯誤的雙網路介面設定所導致的錯誤情形，雙網路介面(eth0以及eth1)都被設在192.168.0.x/24這個網段底下，因此，便會形成底下的路由表。

For routing table mechanism, it will try to match the IP prefix (in the packet that is about to send out from the NVR.) in bits format as many as possible with the "Destination" IP address shown in the routing table list (started from top to the bottom) to decide on which route the packet would be sent through. Due to the Destination IP addresses for dual LAN ports is the same in the NVR routing table, the LAN2 interface (eth1) would be chosen always to forward all the network packets out from the NVR since it has been listed at the first place.

根據路由表的架構，他運行方式會依據位元的形式，將IP位址字首(這個資訊會存在在那些將被從NVR送出的封包裡)拿來與路由表裡"Destination"欄位裡顯示的IP位址拿來比較，符合越多位元的網路介面所使用的IP位址便會被使用來送出封包。以上圖來說，雙網路介面在路由表裡"Destination"欄位所顯示的IP位址是一樣的，被條列在第一行的第二網路介面(eth1)將會一直被用來送出網路封包。

So, if the network packets from LAN1 (eth0) are about to send out, it will be fill out with LAN2 (eth1) information in the network packets and reached the destination IP address device. And if there is any responding network packets that would be generated by the destination IP address device, those network packets would be received by LAN2 (eth1) even they've been expecting by LAN1 (eth0). For those tasks in NVR waiting for any responding network packets via LAN1 (eth0), they will never receive any related responding. Then the connection would be lost since the tasks are timed out due to that responding network packets cannot be received by LAN1 (eth0) anymore.

因此，假如第一網路介面(eth0)的網路封包要被送出時，在網路封包裡便會被填上第二網路介面(eth1)的相關資訊並送出到達目標裝置。一旦目標裝置有產生任何的網路回應封包時，即便這些網路回應封包原本預期應該要被NVR的第一網路介面(eth0)給接收的，那些網路回應封包將會被NVR的第二網路介面(eth1)給接收走。此時，正在NVR端運行的預計要收到來自任何由第一網路介面(eth0)收到的網路回應封包的程序，將無法收到相應的回應。也因為這個緣故，運行的程序將會因為沒收到回應而運行超時，進而導致斷線的結果。

Solution:

To avoid this situation, please change the both LAN ports to different network subnet then see if this issue is still remains or not. Please see an example shown below.

為避免這樣的情形，請將NVR雙網路介面設成兩個不同的網段使用，並檢查看看問題是否有效被解決，下圖是一個實例供參考。