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From "dsclose (JIRA)" <>
Subject [jira] [Created] (CLOUDSTACK-9339) Virtual Routers don't handle Multiple Public Interfaces
Date Tue, 05 Apr 2016 13:52:25 GMT
dsclose created CLOUDSTACK-9339:

             Summary: Virtual Routers don't handle Multiple Public Interfaces
                 Key: CLOUDSTACK-9339
             Project: CloudStack
          Issue Type: Bug
      Security Level: Public (Anyone can view this level - this is the default.)
          Components: Virtual Router
    Affects Versions: 4.8.0
            Reporter: dsclose

There are a series of issues with the way Virtual Routers manage multiple public interfaces.
These are more pronounced on redundant virtual router setups. I have not attempted to examine
these issues in a VPC context. Outside of a VPC context, however, the following is expected

* eth0 connects the router to the guest network.
* In RvR setups, keepalived manages the guests' gateway IP as a virtual IP on eth0.
* eth1 provides a local link to the hypervisor, allowing Cloudstack to issue commands to the
* eth2 is the routers public interface. By default, a single public IP will be setup on eth2
along with the necessary iptables and ip rules to source-NAT guest traffic to that public
* When a public IP address is assigned to the router that is on a separate subnet to the source-NAT
IP, a new interface is configured, such as eth3, and the IP is assigned to that interface.
* This can result in eth3, eth4, eth5, etc. being created depending upon how many public subnets
the router has to work with.

The above all works. The following, however, is currently not working:

* Public interfaces should be set to DOWN on backup redundant routers. The script
is responsible for setting public interfaces to UP during a keepalived transition. Currently
the check_is_up method of the CsIP class brings all interfaces UP on both RvR. A proposed
fix for this has been discussed on the mailing list. That fix will leave public interfaces
DOWN on RvR allowing the keepalived transition to control the state of public interfaces.
Issue #1413 includes a commit that contradicts the proposed fix so it is unclear what the
current state of the code should be.

* Newly created interfaces should be set to UP on master redundant routers. Assuming public
interfaces should be default be DOWN on an RvR we need to accommodate the fact that, as interfaces
are created, no keepalived transition occurs. This means that assigning an IP from a new public
subnet will have no effect (as the interface will be down) until the network is restarted
with a "clean up."

* Public interfaces other than eth2 do not forward traffic. There are two iptables rules in
the FORWARD chain of the filter table created for eth2 that allow forwarding between eth2
and eth0. Equivalent rules are not created for other public interfaces so forwarded traffic
is dropped.

* Outbound traffic from guest VMs does not honour static-NAT rules. Instead, outbound traffic
is source-NAT'd to the networks default source-NAT IP. New connections from guests that are
destined for public networks are processed like so:

1. Traffic is matched against the following rule in the mangle table that marks the connection
with a 0x0:
-A PREROUTING -i eth0 -m state --state NEW -j CONNMARK --set-xmark 0x0/0xffffffff

2. There are no "ip rule" statements that match a connection marked 0x0, so the kernel routes
the connection via the default gateway. That gateway is on source-NAT subnet, so the connection
is routed out of eth2.

3. The following iptables rules are then matched in the filter table:
-A FORWARD -i eth0 -o eth2 -j FW_OUTBOUND

4. Finally, the following rule is matched from the nat table, where the IP address is the
source-NAT IP:

-A POSTROUTING -o eth2 -j SNAT --to-source

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