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Old 10-05-2017, 01:42 PM   #1
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Issue with packets being dropped (presumably) on CentOS server with two LANS

Hello all,

Long time lurker, first time poster. Yada, yada.

I'm have a weird collection of linux skills so bear with me here. It's very possible I missed something obvious in my setup and troubleshooting.

The site in question has two physical networks, and These are not VLANS but two physical networks. is the server network while all client machines are on the other segment.

I have a CentOS 6.9 server setup running arpwatch that has a NIC on each network. I've come to find that when I'm on a machine on the, I cannot SSH or connect to any other services on the arpwatch box unless I connect to it using its IP address. The IP in the .15 network ( is what the server's A record is pointing to and it would be nice to be able to use this to connect.

I've done packet captures and from what I can see, the syn from a .20 client is received by the CentOS server, however, it never acknowledges it. The .20 client just keeps retransmitting the syn.

iptables is not running on the server so I'm not sure what else could be causing this.

Old 10-06-2017, 03:38 PM   #2
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Hello and welcome to LQ.

Unless I'm wrong /24 should force it to watch for the .20.x network only so you'd need to use a gateway to get outside of that.

Guess you could set a static arp in your 15's on that server to make it in subnet or configure gateway or fix subnet.

Again I may misunderstand the question. I don't know if your arpwatch program could fix it other than monitor.

Last edited by jefro; 10-06-2017 at 03:39 PM.


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