【补充方案】
在开发板上明确标识出了 ETH1及 ETH0/GETH标识号
通过ifconfig发现只有eth0及lo两个网络接口，即可确定网线该插入eth0口。
【原来解决方案】
官方使用的文件系统是 Poky 1.5.1
1. 进入文件系统后检查网络配置情况，发现IP地址没有配置
root@sama5d3_xplained:~# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 06:b7:e8:f8:58:a1
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:26 Base address:0x8000
2. 将IP地址配置成一个网段
root@sama5d3_xplained:~# ifconfig eth0 192.168.1.81
root@sama5d3_xplained:~# ifconfig
eth0 Link encap:Ethernet HWaddr 06:b7:e8:f8:58:a1
inet addr:192.168.1.81 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:26 Base address:0x8000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
3. ping一下宿主机，PING不通
root@sama5d3_xplained:~# ping 192.168.1.25
PING 192.168.1.25 (192.168.1.25) 56(84) bytes of data.
From 192.168.1.81 icmp_seq=1 Destination Host Unreachable
From 192.168.1.81 icmp_seq=2 Destination Host Unreachable
From 192.168.1.81 icmp_seq=3 Destination Host Unreachable
From 192.168.1.81 icmp_seq=4 Destination Host Unreachable
From 192.168.1.81 icmp_seq=5 Destination Host Unreachable
From 192.168.1.81 icmp_seq=6 Destination Host Unreachable
4. 诊断当前的eth0是哪一个网口（支持到1000baseT，即千兆网口）
root@sama5d3_xplained:~# ethtool eth0
Settings for eth0:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Speed: 10Mb/s
Duplex: Half
Port: MII
PHYAD: 7
Transceiver: external
Auto-negotiation: on
Link detected: no
5. 将网线插到千兆网口后，重新ping宿主机，Ok.