A host shows ARP entries from subnets where it's not directly connected to

Solution Verified - Updated -

Issue

  • A RHEL host shows ARP entries from subnets where it's not directly connected to:

    $  ip -o a
1: lo    inet 127.0.0.1/8 scope host lo\       valid_lft forever preferred_lft forever
3: eth0  inet 192.168.1.11/24 brd 192.168.1.255 scope global dynamic noprefixroute eth0\       valid_lft 68982sec preferred_lft 68982sec

$ ip neigh show
192.168.1.1 dev eth0 lladdr aa:aa:aa:aa:aa:aa REACHABLE
10.0.0.100 dev eth0 lladdr cc:cc:cc:cc:cc:cc REACHABLE

Environment

  • Red Hat Enterprise Linux.
  • Hosts from two different subnets are connected to the same L2 segment.
  • The same router acts as gateway device for both subnets.
  • The router is configured to access both subnets over the same physical interface.
  • The router is configured to send ICMP redirect messages on this physical interface.
  • At least one of the hosts is configured to accept ICMP Redirect messages.

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