I am interested in programming with the lwIP IP Stack. In order to experiment, I've been trying to run the echo server which is included in the example applications. However, I am having difficulty setting up the internal networking configuration to communicate with the server, and I'd like to find what I'm doing wrong. Here's what I've done so far.
So first, I'm successfully starting the echo server using sudo and setting it to listen on 172.16.0.2 with 172.16.0.1 as gateway:
>>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.
The program successfully enables the tap0 interface and starts the gateway:
>>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
I can successfully ping the gateway:
>>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
However if I try to reach the actual echo server, the route is not found:
>>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
It does seems as if the route has been added if I list the current routes:
>>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
To make sure, I've tried to add an explicit route to the echo server, but the route still cannot be found:
>>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
I would like help on configuring my interfaces/routes so that I can experiment with the lwIP (1.30) echo server, which is configured on port 7. Using version 1.30 as I'm using it with older devices.
OS info:
>>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
Thanks