Oracle Linux: Ethernet packets appear to be routed incorrectly when multiple IP addresses/interfaces exist on the same subnet (Doc ID 1276507.1)

Last updated on DECEMBER 02, 2015

Applies to:

Linux OS - Version Enterprise Linux 3.0 to Oracle Linux 7.2 [Release RHEL3 to OL7U2]
Linux x86
Linux x86-64

Symptoms

Ethernet packets are not routed correctly when multiple interfaces/IP addresses exist in the same subnet, for example.

Host A has two network interface cards (NICs) each with a static IP address in the same subnet

Host B has two NICs each with static IP addresses in the same subnet:

The following behavior is observed when one server pings the other.

Scenario: host A pings host B with specifiying the NIC ...

1. When unplugging port 2 on host B for the first time, ping to port 2 continues, but those to port 1 stop, then both ping responses continue
2. When unplugging port 1 on host B, all ping responses stop
3. When unplugging port 2 on host B again, ping responses continue

Scenario: host A pings host B specifying the NIC ...

1. When unplugging port 2 on host B for the first time, both ping responses stop and restart - some ICMP packets go missing during this time
2. When unplugging port 1 on host B, both ping responses stop
3. When unplugging port 2 on host B again, ping responses continue

Note that the above behaviour differs to other operating systems e.g. Microsoft Windows where given the same scenario, unplugging one port would result in complete packet loss to the corresponding port.

Changes

The system with two NICs is configured with two IP addresses on the same subnet.

Cause

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