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I cannot ping 192.168.10.1, the default gateway, from the Ubuntu Linux 15.10 computer, 192.168.10.22. But I can ping 192.168.10.1, the default gateway, from the Windows 7 computer, 192.168.10.15. The netmask is 255.255.255.0 . As a result, the two computers are on the same network segment.

Does it have anything to do with what an expert told me that my Ubuntu Linux network configuration file, /etc/network/interfaces, was messed up?

Here it is:

#interfaces(5) file used by ifup(8) and ifdown(8)

auto lo

iface lo inet loopback

What should the corrected /etc/network/interfaces look like?

vendat@vendat-ThinkStation-S10:~$ ip address show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp13s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 00:1e:37:f4:59:b2 brd ff:ff:ff:ff:ff:ff
3: enp15s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:1e:37:f4:59:b3 brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.22/24 brd 192.168.10.255 scope global enp15s0
       valid_lft forever preferred_lft forever
    inet6 2606:a000:8301:2d00:21e:37ff:fef4:59b3/64 scope global noprefixroute dynamic 
       valid_lft 3603sec preferred_lft 3603sec
    inet6 fe80::21e:37ff:fef4:59b3/64 scope link
       valid_lft forever preferred_lft forever
vendat@vendat-ThinkStation-S10:~$ ip route show
default via 192.168.10.1 dev enp15s0  proto static  metric 100
169.254.0.0/16 dev enp15s0  scope link  metric 1000
192.168.10.0/24 dev enp15s0  proto kernel  scope link  src 192.168.10.22  metric 100

Where should I look on the Windows 7 computer for the information necessary to add to the Ubuntu Linux, /etc/network/interfaces?

Here is the ip link show result:

ThinkStation-S10:/etc$ ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp13s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
    link/ether 00:1e:37:f4:59:b2 brd ff:ff:ff:ff:ff:ff
3: enp15s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 00:1e:37:f4:59:b3 brd ff:ff:ff:ff:ff:ff

where enp15s0 is the Ethernet link of interest.

Here is thhe sudo tcmpdump -i enp15s0 output. Why are we using it?

vendat@vendat-ThinkStation-S10:~$ sudo tcpdump -n -i enp15s0
[sudo] password for vendat: 
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on enp15s0, link-type EN10MB (Ethernet), capture size 262144 bytes
08:55:15.891889 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:17.552598 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:17.639375 IP6 fe80::921a:caff:fe80:3337 > 2606:a000:8301:2d00:21e:37ff:fef4:59b3: ICMP6, neighbor solicitation, who has 2606:a000:8301:2d00:21e:37ff:fef4:59b3, length 32
08:55:17.639675 IP6 2606:a000:8301:2d00:21e:37ff:fef4:59b3 > fe80::921a:caff:fe80:3337: ICMP6, neighbor advertisement, tgt is 2606:a000:8301:2d00:21e:37ff:fef4:59b3, length 24
08:55:17.840114 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:17.891996 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:18.549060 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:19.549061 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:19.892102 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:20.840177 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:21.892211 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:22.557655 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:22.759777 IP6 fe80::921a:caff:fe80:3337 > fe80::21e:37ff:fef4:59b3: ICMP6, neighbor solicitation, who has fe80::21e:37ff:fef4:59b3, length 32
08:55:22.760077 IP6 fe80::21e:37ff:fef4:59b3 > fe80::921a:caff:fe80:3337: ICMP6, neighbor advertisement, tgt is fe80::21e:37ff:fef4:59b3, length 24
08:55:23.557059 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:23.840340 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:23.892318 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:24.557060 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:25.892426 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:26.840686 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:27.892534 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 query
08:55:28.565074 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:29.565102 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:29.840687 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:29.892641 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 query
08:55:30.565069 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:31.892750 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 query
08:55:32.734690 LLDP, length 197: Cisco IP Phone SPA504G
08:55:32.840776 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:33.570134 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:33.892857 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 query
08:55:34.569061 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:35.294281 IP6 fe80::921a:caff:fe80:3337.59002 > ff02::1:3.5355: UDP, length 90
08:55:35.295283 IP6 fe80::921a:caff:fe80:3337.59002 > ff02::1:3.5355: UDP, length 90
08:55:35.483794 IP6 fe80::921a:caff:fe80:3337.41980 > ff02::1:3.5355: UDP, length 90
08:55:35.484593 IP6 fe80::921a:caff:fe80:3337.41980 > ff02::1:3.5355: UDP, length 90
08:55:35.569065 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:35.841139 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
08:55:35.892964 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:37.893073 90:1a:ca:80:33:3f > ff:ff:ff:ff:ff:ff, RRCP-0x23 reply
08:55:38.575236 ARP, Request who-has 192.168.10.1 tell 192.168.10.22, length 28
08:55:38.841177 IP6 fe80::921a:caff:fe80:3337 > ff02::1: ICMP6, router advertisement, length 56
^C
42 packets captured
42 packets received by filter
0 packets dropped by kernel
  • Can the Ubuntu host ping the Windows host and vice versa? How did you put the network settings for your Ubuntu host? Obviously not using /etc/network/interfaces. Can you show us these settings? Also, open a terminal on the Ubuntu machine and show us the result of ip links show. Maybe we can help you with this additional information – Bananguin Feb 22 '16 at 7:34
  • Do you have network on that ubuntu box? Did you set manually the IP/gateway/netmask settings? IF that is true add can you try with dhcp? Simply add: iface eth0 inet dhcp in your /etc/network/interfaces and restart the networking service. Can you give us the output from netstat -r -n? Long story short, give us more information. – Svetlin Tonchev Feb 22 '16 at 8:21
  • @Bananguin,Windows 7 can ping Ubuntu Linux 15.10. Ubuntu Linux 15.10 cannot ping WIndows 7. Here is a network setting I put in /etc/hosts, 192.168.10.15 Frankc. The ip link show result is shown in the original question. Thank you. – Frank Feb 22 '16 at 9:25
  • @SvetlinTonchev, /etc/network/interfaces is read only. How do I add to it? Thanks. – Frank Feb 22 '16 at 9:35
  • You need to enable DHCP. You need sudo rights or access to root user to edit /etc/interfaces. You can do something like sudo echo "iface eth0 inet dhcp" >> /etc/interfaces; sudo /etc/init.d/networking restart. Or use some GUI tool to edit the file/ network settings – Svetlin Tonchev Feb 22 '16 at 11:25
1

AFAIK, the default network management mode of ubuntu boxes nowadays is "NetworkManager". The configuration file resides in

/etc/NetworkManager/NetworkManager.conf

and subsequent directories, but need a lot of reading to be understood. When the network-Manager runs, there will be a corresponding Widget in the Desktop Managers's Taskbar, where you can re-configure your configuration.

Try to find this, and re-configure the default Network Connection, maybe it is simply not enabled.

There should be no need to manually configure /etc/network/interfaces , then.

  • I tried reconfiguring default Network Connection and nothing improved. Thank you. – Frank Feb 22 '16 at 9:29
  • What does "ip route show" tell you? – gerhard d. Feb 22 '16 at 12:20
  • Here is the ip route show: vendat@vendat-ThinkStation-S10:~$ ip route show default via 192.168.10.1 dev enp15s0 proto static metric 100 169.254.0.0/16 dev enp15s0 scope link metric 1000 192.168.10.0/24 dev enp15s0 proto kernel scope link src 192.168.10.22 metric 100 – Frank Feb 22 '16 at 13:21
  • Thank you for your answer. What does an Unmanaged Network Interface Controller(N.I.C) mean for enp15s0 on the Ubuntu 15.10 Linux machine? – Frank Feb 22 '16 at 21:25
  • Obviously, you only see broadcast packets, but get no answer from arp though. Ask the switch admin, if there is some vlan or mac security applied to the switchport. Cisco IP phones by default reside in a "voice vlan", when you get traffic from them, this means you're at least in the trunk getting the voice vlan. Make sure with the admin, that you also are in the "computers" vlan. – gerhard d. Feb 23 '16 at 8:11
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One can change the unmanaged and ping behaviour of enp15s0 by:

To do this - in a terminal: sudo nano /etc/NetworkManager/NetworkManager.conf

change the line managed=false to managed=true

Save, stop and start network manager: sudo service network-manager restart


Alternatively, you can remove the interface from /etc/network/interfaces.

backup the current interfaces file: sudo cp /etc/network/interfaces /etc/network_interfaces_backup

Then open the file: sudo nano /etc/network/interfaces

Delete everything in that file and copy and paste the following: auto lo iface lo inet loopback

Save, stop and start network manager: sudo service network-manager restart

  • Did that really solve the routing problem? Your routing table was correct. Can you append the network configuration and routing table AFTER your modifications, also? Thanks. – gerhard d. Feb 27 '16 at 10:18
  • @gerhard d, You are a genius and absolutely correct that my answer is wrong. Please read my next answer and comment on it or test it. Thanks – Frank Jan 25 '17 at 8:15
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I discovered at 3 A.M last summer that Ubuntu 16.04 ping is a SUID command which can only be invoked by the root superuser

SUID (Set owner User ID up on execution) is a special type of file permissions given to a file. Normally in Linux/Unix when a program runs, it inherit’s access permissions from the logged in user. SUID is defined as giving temporary permissions to a user to run a program/file with the permissions of the file owner rather that the user who runs it. In simple words users will get file owner’s permissions as well as owner UID and GID when executing a file/program/command.

Normal users don’t have permissions to open socket files and open ports. So SUID bit is set on this file/command so that whoever executes this will get owner (Root user’s) permissions to them when executing this command. So when this command start executing it will inherit root user permissions to this normal user and opens require socket files and ports.

Here is the way I solved the above problem in early June 2016.

C# applications must be started on Linux using mono, so you should use

Process.Start("mono", "full_path_of_your_exe");

edited Sep 15 '13 at 23:46 answered Sep 15 '13 at 3:29

Lex Li 30.9k44666

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