Hey all, i am fighting with a strange behavior here - i have two systems connected via a direct crosslink wire. After booting, the connection is up and both systems can reach the other one. After a small time window the interface is down. $ dmesg |grep eth4 igb 0000:41:00.2: added PHC on eth4 igb 0000:41:00.2: eth4: (PCIe:5.0Gb/s:Width x4) igb 0000:41:00.2: eth4: PBA No: G13158-000 8021q: adding VLAN 0 to HW filter on device eth4 igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX igb: eth4 NIC Link is Down igb: eth4 NIC Link is Up 10 Mbps Full Duplex, Flow Control: RX/TX igb: eth4 NIC Link is Down igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX igb: eth4 NIC Link is Down igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX igb: eth4 NIC Link is Down igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX igb: eth4 NIC Link is Down igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX igb: eth4 NIC Link is Down if i bring the connection manually up (ethtool -r eth4), i just have to wait and the status shows "down" again. $ grep eth4 /var/log/messages Jun 5 18:35:17 node2 kernel: igb 0000:41:00.2: added PHC on eth4 Jun 5 18:35:17 node2 kernel: igb 0000:41:00.2: eth4: (PCIe:5.0Gb/s:Width x4) Jun 5 18:35:17 node2 kernel: igb 0000:41:00.2: eth4: PBA No: G13158-000 Jun 5 18:35:17 node2 kernel: 8021q: adding VLAN 0 to HW filter on device eth4 Jun 5 18:35:17 node2 kernel: igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX Jun 5 18:38:10 node2 kernel: igb: eth4 NIC Link is Down Jun 5 19:23:21 node2 kernel: igb: eth4 NIC Link is Up 10 Mbps Full Duplex, Flow Control: RX/TX Jun 5 19:23:47 node2 kernel: igb: eth4 NIC Link is Down Jun 5 19:23:50 node2 kernel: igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX Jun 5 19:24:57 node2 kernel: igb: eth4 NIC Link is Down Jun 5 19:24:60 node2 kernel: igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX Jun 5 19:25:45 node2 kernel: igb: eth4 NIC Link is Down Jun 5 19:25:60 node2 kernel: igb: eth4 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX Jun 5 19:48:57 node2 kernel: igb: eth4 NIC Link is Down its a quad nic $ cat /etc/udev/rules.d/70-persistent-net.rules ... # PCI device 0x8086:0x1521 (igb) SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="...", ATTR{type}=="1", KERNEL=="eth*", NAME="eth4" the eth4 link is not in use right now. the other ports on the nic are currently in use (bonded). Had anyone ever seen such a behavior (on el6)? -- Thanks LF PS: cable already substituted / el6 system is up to date