Comment 13 for bug 1923592

Reviewed: https://review.opendev.org/c/openstack/neutron/+/791178
Committed: https://opendev.org/openstack/neutron/commit/f450886ff93a201c6520d84088c3a97330814140
Submitter: "Zuul (22348)"
Branch: master

commit f450886ff93a201c6520d84088c3a97330814140
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Thu May 13 06:13:57 2021 +0000

    Allow the use of legacy routers within RPN segments

    This patch adds to legacy routers (no HA nor DVR) to be connected
    to a router provider network segment through the gateway interface.
    The router will be connected to one single segment of the RPN; that
    means the router will have L2 connectivity to one single subnet.
    The gateway router port will have an IP address on the subnet CIDR;
    that will provide connectivity to the broadcast domain of this CIDR
    (as usual, that doesn't change).

    The router, in other scenarios, adds the other subnet CIDRs to the
    router namespace routing table. That allows to SNAT any packet to
    those CIDRs through the gateway port.

    In the RPN case those routes are not added because there is no
    broadcast connectivity with the other subnets. Any packet that needs
    to reach these other subents, should go through the local segment
    gateway IP address. This default route is added always into the
    router namespace.

    Closes-Bug: #1923592

    Change-Id: Ib66b1d7b60eb0ac0a9e3dfd08aae29cb03abde34