我对使用lwIP IP Stack进行编程感兴趣。为了进行实验，我一直在尝试运行示例应用程序中包含的echo server。但是，我在设置内部网络配置以与服务器通信时遇到困难，我想找到我做错的事情。这是我到目前为止所做的。
首先，我使用sudo成功启动了echo服务器并将其设置为以172.16.0.1作为网关侦听172.16.0.2：
>>sudo ./echop -i 172.16.0.2 -m 255.255.0.0 -g 172.16.0.1
[sudo] password for user:
Host at 172.16.0.2 mask 255.255.0.0 gateway 172.16.0.1
TCP/IP initialized.
SNMP private MIB start, detecting sensors.
Applications started.
程序成功启用tap0界面并启动网关：
>>ifconfig
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.2.15 netmask 255.255.255.0 broadcast 10.0.2.255
inet6 fe80::a00:27ff:fe4c:f329 prefixlen 64 scopeid 0x20<link>
ether 08:00:27:4c:f3:29 txqueuelen 1000 (Ethernet)
RX packets 10860 bytes 10827195 (10.8 MB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 8571 bytes 904790 (904.7 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1 (Local Loopback)
RX packets 811 bytes 93113 (93.1 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 811 bytes 93113 (93.1 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
tap0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.16.0.1 netmask 255.255.0.0 broadcast 172.16.255.255
inet6 fe80::49f:4fff:fe82:d8fb prefixlen 64 scopeid 0x20<link>
ether 06:9f:4f:82:d8:fb txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 129 bytes 14904 (14.9 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
我可以成功ping网关：
>>ping -c 5 172.16.0.1
PING 172.16.0.1 (172.16.0.1) 56(84) bytes of data.
64 bytes from 172.16.0.1: icmp_seq=1 ttl=64 time=0.028 ms
64 bytes from 172.16.0.1: icmp_seq=2 ttl=64 time=0.076 ms
64 bytes from 172.16.0.1: icmp_seq=3 ttl=64 time=0.097 ms
64 bytes from 172.16.0.1: icmp_seq=4 ttl=64 time=0.037 ms
64 bytes from 172.16.0.1: icmp_seq=5 ttl=64 time=0.039 ms
--- 172.16.0.1 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4086ms
rtt min/avg/max/mdev = 0.028/0.055/0.097/0.027 ms
但是，如果我尝试访问实际的echo服务器，则找不到路由：
>>ping -c 5 172.16.0.2
PING 172.16.0.2 (172.16.0.2) 56(84) bytes of data.
From 172.16.0.1 icmp_seq=1 Destination Host Unreachable
From 172.16.0.1 icmp_seq=2 Destination Host Unreachable
From 172.16.0.1 icmp_seq=3 Destination Host Unreachable
From 172.16.0.1 icmp_seq=4 Destination Host Unreachable
From 172.16.0.1 icmp_seq=5 Destination Host Unreachable
如果列出当前路线，似乎已经添加了路线：
>>route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default gateway 0.0.0.0 UG 100 0 0 enp0s3
10.0.2.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s3
link-local 0.0.0.0 255.255.0.0 U 1000 0 0 tap0
172.16.0.0 0.0.0.0 255.255.0.0 U 0 0 0 tap0
为了确保，我尝试向echo服务器添加显式路由，但仍然找不到该路由：
>>sudo route add 172.16.0.2 dev tap0 gw 172.16.0.1
>>route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default gateway 0.0.0.0 UG 100 0 0 enp0s3
10.0.2.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s3
link-local 0.0.0.0 255.255.0.0 U 1000 0 0 tap0
172.16.0.0 0.0.0.0 255.255.0.0 U 0 0 0 tap0
172.16.0.2 172.16.0.1 255.255.255.255 UGH 0 0 0 tap0
>>ping -c 5 172.16.0.2
PING 172.16.0.2 (172.16.0.2) 56(84) bytes of data.
From 172.16.0.1 icmp_seq=1 Destination Host Unreachable
From 172.16.0.1 icmp_seq=2 Destination Host Unreachable
From 172.16.0.1 icmp_seq=3 Destination Host Unreachable
From 172.16.0.1 icmp_seq=4 Destination Host Unreachable
From 172.16.0.1 icmp_seq=5 Destination Host Unreachable
--- 172.16.0.2 ping statistics ---
5 packets transmitted, 0 received, +5 errors, 100% packet loss, time 4094ms
pipe 4
我想帮助配置我的接口/路由，以便我可以尝试在端口7上配置的lwIP（1.30）echo服务器。使用版本1.30，因为我在较旧的设备上使用它。
操作系统信息：
>>uname -a
Linux ReSyst 4.8.0-59-generic #64-Ubuntu SMP Thu Jun 29 19:38:34 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
由于