[CentOS] Network conections problems

[Rommel Rodriguez Toirac]

El 21 de febrero de 2017 7:00:03 GMT-05:00, centos-request at centos.org escribió:
>Send CentOS mailing list submissions to
>	centos at centos.org
>
>
>From: Kahlil Hodgson <kahlil.hodgson at dp.exchange>
>To: CentOS mailing list <centos at centos.org>
>Subject: Re: [CentOS] Network conections problems

>
>First guess is that you may have two devices on the network with the
>same ip address.
>
>Next time this happens, try doing
>
>1. 'arp -n' from a machine other than the db server
>2. ping the other machine from the db server, then
>3. 'arp -n' from the other machine
>
>Compare the outputs of the two invocations of arp. If the outputs show
>different MAC addresses for 192.168.41.4 then you have two different
>devices with the same IP address.
>
>
 I resolve the problem of network conection loose, but still a dude of how it happend and how it can be fixe. 
When I check with arping the MAC of sever change, for example

rommel at p6:~$ arping 192.168.41.4
ARPING 192.168.41.4 from 192.168.41.6 enp3s0
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.653ms
Unicast reply from 192.168.41.4 [6C:92:BF:26:C7:03]  0.683ms
Unicast reply from 192.168.41.4 [6C:92:BF:26:C7:03]  0.622ms
Unicast reply from 192.168.41.4 [6C:92:BF:26:C7:03]  0.631ms
^CSent 3 probes (1 broadcast(s))
Received 4 response(s)

The first answer is with a MAC diferent to the others one. 
But when I arping from the server inseft look the MAC associate to de IP address: 

[root at pgtm ] arping 192.168.41.4 -I eth1
ARPING 192.168.41.4 from 192.168.41.4 eth1
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.658ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.654ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.654ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.662ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.655ms
Sent 5 probes (1 broadcast(s))
Received 5 response(s)

Looking in the config of network device I can not find the MAC 00:1D:09:FF:44:4B

[root at pgtm ] ifconfig
eth0      Link encap:Ethernet  HWaddr 6C:92:BF:26:C7:02  
          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)
          Memory:c7220000-c723ffff 

eth1      Link encap:Ethernet  HWaddr 6C:92:BF:26:C7:03  
          inet addr:192.168.41.4  Bcast:192.168.41.255  Mask:255.255.255.0
          inet6 addr: fe80::6e92:bfff:fe26:c703/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:95819 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1924 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:11728605 (11.1 MiB)  TX bytes:263674 (257.4 KiB)
          Memory:c7200000-c721ffff 

eth2      Link encap:Ethernet  HWaddr 00:E0:ED:33:4E:9C  
          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)
          Memory:c7120000-c713ffff 

eth3      Link encap:Ethernet  HWaddr 00:E0:ED:33:4E:9D  
          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)
          Memory:c7100000-c711ffff 

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:249609 errors:0 dropped:0 overruns:0 frame:0
          TX packets:249609 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:52090343 (49.6 MiB)  TX bytes:52090343 (49.6 MiB)

 The solution was another IP address to this network device and then everything work fine. 
 Why this happend? How I can erase the link beteewn MAC 00:1D:09:FF:44:4B and IP 192.168.41.4? Where can be stored this link?
 Right now in the network is not assignet the IP address 192.168.41.4 to no one device (printserver, switch, router, workstation or server) and still whe I make arping have the answer:

rommel at p6:~$ arping 192.168.41.4
ARPING 192.168.41.4 from 192.168.41.6 enp3s0
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.631ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.623ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.623ms
Unicast reply from 192.168.41.4 [00:1D:09:FF:44:4B]  0.691ms
^CSent 4 probes (1 broadcast(s))
Received 4 response(s)

arping to the new server IP address look like this (this is the MAC of eth0, where a plug the network cable):

rommel at p6:~$ arping 192.168.41.7
ARPING 192.168.41.7 from 192.168.41.6 enp3s0
Unicast reply from 192.168.41.7 [6C:92:BF:26:C7:02]  0.580ms
Unicast reply from 192.168.41.7 [6C:92:BF:26:C7:02]  0.607ms
Unicast reply from 192.168.41.7 [6C:92:BF:26:C7:02]  0.613ms
Unicast reply from 192.168.41.7 [6C:92:BF:26:C7:02]  0.594ms
^CSent 4 probes (1 broadcast(s))
Received 4 response(s)



Rommel Rodriguez Toirac
rommelrt at nauta.cu