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Networking issue on local network

Linux Kernel, Network, and Services configuration.
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Networking issue on local network

#1 Post by cakedoggo »

Hi, I seem to have a weird networking issue on my local network where I am not able to ping/ssh between two computers.

I have several computers but it only ever happens between two computers intermittently (lets call them A and B). I am able to ssh from A to another computer C and then able to ping/ssh into B.

I am not sure what is happening and I wanted help to troubleshoot the issue?

Also, A is on wifi while B,C are on wired. When i connect A to wire, connectivity is normal.

In the next segments,
A = 10.0.0.13
B = 10.0.0.5

My ipconfig/ip/route/neigh for A is below:

Code: Select all

root@turtle:~# ping 10.0.0.5
PING 10.0.0.5 (10.0.0.5) 56(84) bytes of data.
^C
--- 10.0.0.5 ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2046ms


root@turtle:~# ip neigh
10.0.0.6 dev wlan0 lladdr 00:1e:06:30:be:82 STALE
10.0.0.1 dev wlan0 lladdr 04:a1:51:d3:19:5e REACHABLE
10.0.0.5 dev wlan0 lladdr 6c:62:6d:0a:bd:19 REACHABLE
169.254.0.2 dev wlan0  FAILED
10.0.0.8 dev wlan0 lladdr 44:80:eb:6b:4f:2e STALE
169.254.0.1 dev wlan0  FAILED
10.0.0.20 dev wlan0 lladdr b8:27:eb:1d:a8:e1 STALE
169.254.0.0 dev wlan0  FAILED
fe80::69ab:e2ec:5732:7766 dev wlan0 lladdr 00:21:00:d0:be:40 STALE
fe80::21e:6ff:fe30:be82 dev wlan0 lladdr 00:1e:06:30:be:82 STALE
fe80::4680:ebff:fe6b:4f2e dev wlan0 lladdr 44:80:eb:6b:4f:2e STALE



root@turtle:~# ifconfig -a
eth0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 80:fa:5b:1d:99:c4  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        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
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 4591989  bytes 521533402 (497.3 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 4591989  bytes 521533402 (497.3 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.0.13  netmask 255.255.255.0  broadcast 10.0.0.255
        inet6 fe80::a16d:a4e:4251:d1d9  prefixlen 64  scopeid 0x20<link>
        ether 00:26:b6:f5:f3:26  txqueuelen 1000  (Ethernet)
        RX packets 24631732  bytes 29570946632 (27.5 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 13731301  bytes 2190771668 (2.0 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


root@turtle:~# ip route
default via 10.0.0.1 dev wlan0 proto dhcp metric 600 
10.0.0.0/24 dev wlan0 proto kernel scope link src 10.0.0.13 metric 600 
169.254.0.0/16 dev wlan0 scope link metric 1000 


root@turtle:~# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.0.0.1        0.0.0.0         UG    600    0        0 wlan0
10.0.0.0        0.0.0.0         255.255.255.0   U     600    0        0 wlan0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 wlan0
My ipconfig/ip/route/neigh for B is below:

Code: Select all

root@kraft:~# ping 10.0.0.13
PING 10.0.0.13 (10.0.0.13) 56(84) bytes of data.
^C
--- 10.0.0.13 ping statistics ---
6 packets transmitted, 0 received, 100% packet loss, time 5112ms


root@kraft:~# ip neigh
10.0.0.6 dev enp6s0 lladdr 00:1e:06:30:be:82 REACHABLE
10.0.0.13 dev enp6s0 lladdr 00:26:b6:f5:f3:26 REACHABLE
10.0.0.2 dev enp6s0 lladdr 00:26:b6:f5:f3:26 STALE
10.0.0.8 dev enp6s0 lladdr 44:80:eb:6b:4f:2e STALE
10.0.0.1 dev enp6s0 lladdr 04:a1:51:d3:19:5e STALE



root@kraft:~# ifconfig -a
enp6s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.0.5  netmask 255.255.255.0  broadcast 10.0.0.255
        inet6 fe80::6e62:6dff:fe0a:bd19  prefixlen 64  scopeid 0x20<link>
        ether 6c:62:6d:0a:bd:19  txqueuelen 1000  (Ethernet)
        RX packets 1858518718  bytes 2810368402880 (2.5 TiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 502279682  bytes 34361766023 (32.0 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

enp7s0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 6c:62:6d:0a:bd:1a  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        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 176  bytes 13944 (13.6 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 176  bytes 13944 (13.6 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlp4s0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 2a:60:a2:a8:d4:d5  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


root@kraft:~# ip route
default via 10.0.0.1 dev enp6s0 proto static metric 100 
10.0.0.0/24 dev enp6s0 proto kernel scope link src 10.0.0.5 metric 100 


root@kraft:~# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.0.0.1        0.0.0.0         UG    100    0        0 enp6s0
10.0.0.0        0.0.0.0         255.255.255.0   U     100    0        0 enp6s0
My ipconfig/ip/route/neigh for C is below:

Code: Select all

sync0:~$ ping 10.0.0.5
PING 10.0.0.5 (10.0.0.5) 56(84) bytes of data.
64 bytes from 10.0.0.5: icmp_seq=1 ttl=64 time=0.484 ms
64 bytes from 10.0.0.5: icmp_seq=2 ttl=64 time=0.479 ms
^C
--- 10.0.0.5 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1004ms
rtt min/avg/max/mdev = 0.479/0.481/0.484/0.022 ms


sync0:~$ sudo ifconfig -a
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.0.6  netmask 255.255.255.0  broadcast 10.0.0.255
        inet6 fe80::21e:6ff:fe30:be82  prefixlen 64  scopeid 0x20<link>
        ether 00:1e:06:30:be:82  txqueuelen 1000  (Ethernet)
        RX packets 30539203  bytes 1550850481 (1.4 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 14420119  bytes 3237965135 (3.0 GiB)
        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 15304574  bytes 3006465356 (2.7 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 15304574  bytes 3006465356 (2.7 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


sync0:~$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    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: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:1e:06:30:be:82 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.6/24 brd 10.0.0.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::21e:6ff:fe30:be82/64 scope link 
       valid_lft forever preferred_lft forever


sync0:~$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.0.0.1        0.0.0.0         UG    0      0        0 eth0
10.0.0.0        0.0.0.0         255.255.255.0   U     0      0        0 eth0

sync0:~$ ip neigh
10.0.0.13 dev eth0 lladdr 00:26:b6:f5:f3:26 DELAY
10.0.0.8 dev eth0 lladdr 44:80:eb:6b:4f:2e STALE
10.0.0.5 dev eth0 lladdr 6c:62:6d:0a:bd:19 STALE
10.0.0.1 dev eth0 lladdr 04:a1:51:d3:19:5e REACHABLE
fe80::69ab:e2ec:5732:7766 dev eth0 lladdr 00:21:00:d0:be:40 STALE
fe80::a16d:a4e:4251:d1d9 dev eth0 lladdr 00:26:b6:f5:f3:26 STALE
fe80::4680:ebff:fe6b:4f2e dev eth0 lladdr 44:80:eb:6b:4f:2e STALE
No firewalls are active at the moment. I checked the arp entries and they both have the correct MAC addr of each other and I am able to arping each other.
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arzgi
Posts: 1194
Joined: 2008-02-21 17:03
Location: Finland
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Re: Networking issue on local network

#2 Post by arzgi »

Cehck your router settings, if it enables wifi to access wired network and vice versa.
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Re: Networking issue on local network

#3 Post by cakedoggo »

Hi arzgi, yes, I have access from wifi to all other wired computers. I also have access to B but it is the only computer which has intermittent issues.
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arzgi
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Re: Networking issue on local network

#4 Post by arzgi »

cakedoggo wrote:Hi arzgi, yes, I have access from wifi to all other wired computers. I also have access to B but it is the only computer which has intermittent issues.
Ok, good to check easy solutions first.

I've never used ip neigh befoure, but now just tested, did not read anything, and does not seem reliable as such:

Code: Select all

arto@samsung:~$ ip neigh
192.168.1.1 dev wlan0 lladdr 84:16:f9:db:9a:18 STALE
arto@samsung:~$ ping 192.168.1.1
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=2.26 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=1.72 ms
64 bytes from 192.168.1.1: icmp_seq=3 ttl=64 time=1.42 ms
^C
--- 192.168.1.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 1.428/1.803/2.260/0.346 ms
arto@samsung:~$
196.168.1.1 is my router, to which I'm currently connected through wifi.

What else, do you have firewalls, or ssh servers running and exported keys?

Post also error message, what you get when ssh can't connect.
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Re: Networking issue on local network

#5 Post by cakedoggo »

arzgi wrote: What else, do you have firewalls, or ssh servers running and exported keys?

Post also error message, what you get when ssh can't connect.
Hi arzgi,
Yes, I have ssh keys configured to allow passwordless access from A to everything. I have disabled ufw on both computers (A and B). iptables -L shows nothing either.

Here is what ssh -vvv gives:

Code: Select all

OpenSSH_7.7p1 Debian-2, OpenSSL 1.0.2n  7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolve_canonicalize: hostname 10.0.0.5 is address
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to 10.0.0.5 [10.0.0.5] port 22.
debug1: connect to address 10.0.0.5 port 22: Connection timed out
ssh: connect to host 10.0.0.5 port 22: Connection timed out
Same with ping:

Code: Select all

root@turtle:~# ping 10.0.0.5
PING 10.0.0.5 (10.0.0.5) 56(84) bytes of data.
^C
--- 10.0.0.5 ping statistics ---
24 packets transmitted, 0 received, 100% packet loss, time 23547ms
But arp is fine:

Code: Select all

root@turtle:~# arping 10.0.0.5 -I wlan0
ARPING 10.0.0.5 from 10.0.0.13 wlan0
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.715ms
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.524ms
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.537ms
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.604ms
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.454ms
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.696ms
Unicast reply from 10.0.0.5 [6C:62:6D:0A:BD:19]  1.601ms
^CSent 7 probes (1 broadcast(s))
Received 7 response(s)
And I get the same issues when going from B to A.
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arzgi
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Re: Networking issue on local network

#6 Post by arzgi »

Check next your router, that client list shows each connected pc. Then check each connected pc's NIC, that you see there yellow and green leds on.

If these are ok, I'm beginning to suspect hw failure. But check those first, thanks for reporting!
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Re: Networking issue on local network

#7 Post by cakedoggo »

arzgi wrote:Check next your router, that client list shows each connected pc. Then check each connected pc's NIC, that you see there yellow and green leds on.

If these are ok, I'm beginning to suspect hw failure. But check those first, thanks for reporting!
Hi arzgi,

I do not have access to the router credentials as it is a student housing.

I checked each NIC. There are green and red/yellow LEDs on/blinking. All of them are connecting to the internet and to each other on LAN.

Do you think it is hardware failure on B? It seems to connect fine though just not to A :(
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arzgi
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Re: Networking issue on local network

#8 Post by arzgi »

cakedoggo wrote:
arzgi wrote:Check next your router, that client list shows each connected pc. Then check each connected pc's NIC, that you see there yellow and green leds on.

If these are ok, I'm beginning to suspect hw failure. But check those first, thanks for reporting!
Hi arzgi,

I do not have access to the router credentials as it is a student housing.

I checked each NIC. There are green and red/yellow LEDs on/blinking. All of them are connecting to the internet and to each other on LAN.

Do you think it is hardware failure on B? It seems to connect fine though just not to A :(
Makes a little bit harder, but you can only use tools available. .

Green means it's online, yellow would blink if activity.

Do you find any irregulaties of this?

If you have or can lend a rj45 cable tester, I would try that too.
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Re: Networking issue on local network

#9 Post by cakedoggo »

arzgi wrote: Makes a little bit harder, but you can only use tools available. .
Can you tell me the name of a tool?
arzgi wrote:Green means it's online, yellow would blink if activity.

Do you find any irregulaties of this?

If you have or can lend a rj45 cable tester, I would try that too.
And not really - they seem to blink just like the other computers' NIC.
I will look into a rj45 cable tester!
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arzgi
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Re: Networking issue on local network

#10 Post by arzgi »

cakedoggo wrote:
arzgi wrote: Makes a little bit harder, but you can only use tools available. .
Can you tell me the name of a tool?
arzgi wrote:Green means it's online, yellow would blink if activity.

Do you find any irregulaties of this?

If you have or can lend a rj45 cable tester, I would try that too.
And not really - they seem to blink just like the other computers' NIC.
I will look into a rj45 cable tester!
You could possible get results also by changing cables, without cable tester, but that can be tedious task..

So you would change, was it C, which worked wired, it's cable to B, which was achievable onfly by wifi.
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Re: Networking issue on local network

#11 Post by cakedoggo »

arzgi wrote: You could possible get results also by changing cables, without cable tester, but that can be tedious task..
So you would change, was it C, which worked wired, it's cable to B, which was achievable onfly by wifi.
I checked them both a few days ago and they seemed fine. (B still couldn't connect while C connected fine when swapped).
I used nmap to see if both are registered to the router and they were.

So, i left my laptop shutdown for the night after a long time (as compared to just a quick reboot) and it seems to be able to connect to B again. So I am unsure if the router is handling this routing incorrectly or something..
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arzgi
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Re: Networking issue on local network

#12 Post by arzgi »

Can you change NICs: C <> B ?
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cakedoggo
Posts: 7
Joined: 2018-07-21 19:23

Re: Networking issue on local network

#13 Post by cakedoggo »

arzgi wrote:Can you change NICs: C <> B ?
Hi, sorry for the super late reply - no this is not possible as they are all SBCs except for my laptop and the problematic server.
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