IProute2 fwmark does not send incoming GRE traffic out the same tunnel it arrived in

Solution Verified - Updated -

Issue

System has multiple GRE tunnels:

  • Outer IPs GRE1: remote 192.168.0.135 / local 192.168.0.136
  • Inner IPs GRE1: remote 10.11.11.135 / local 10.11.11.136
  • Outer IPs GRE2: remote 192.168.0.50 / local 192.168.0.136
  • Inner IPs GRE2: remote 10.11.11.50 / local 10.11.11.136

External packets with various source IPs and dst IP 10.11.11.136 are routed to 192.168.0.135, coming in either tunnel.

Trying to get the return traffic routed back down the tunnel it came from.

Using iproute fwmark and policy routing rules is not working.

Environment

  • Red Hat Enterprise Linux 7
  • GRE tunnels to multiple external hosts
  • iptables firewall

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