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If Layer 2 communication between guests on different Charon hosts is required, a bridged tunnel solution must be set up between the two Charon host systems.

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External Communication Considerations

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This not a recommended standard solution for security reasons. However, should it be required, two interfaces with public IP addresses can be assigned to the Charon host.
One of these interfaces is then dedicated to the guest system which uses the private interface address and the MAC address assigned to the Charon host by AWS (similar to point 2 in section Host to Guest Communication Considerations above).

Using a Charon host system as a Router

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Should L2 protocols be required between two guest systems on different host systems, a bridge/tunnel solution similar to the one described in SSH VPN - Connecting Charon Host and Guest to Customer Network must be set up between the two host systems to allow the L2 traffic to pass.

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Asymmetric Routing Considerations

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1. Create a configuration file (/etc/sysconfig/network-scripts/ifcfg-<interface-name>) for the second interface (if there is no configuration file for the primary interface, create it as well).
2. Set the correct interface for default route in /etc/sysconfig/network (example: GATEWAYDEV=eth0).
3. To prevent the cloud-init from resetting your custom network configurations, add the following lines to the /etc/cloud/cloud.cfg file:
   network:
  ; config: disabled
4. Restart the network.
5. Create an additional routing table (use the command: ip route add <path> dev <interface-name> table <table-id>). There must be an entry for every IP address assigned to the second interface and any other route to be used.
6. Set rules in the Routing Policy Database (use the command: ip rule add from <ip-address-of-second-interface> lookup <table-id>)
7. Create a static route file (/etc/sysconfig/network-scripts/route-<interface-name>)
8. Create a static rule file (/etc/sysconfig/network-scripts/rule-<interface-name>)

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