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From "dsclose (JIRA)" <>
Subject [jira] [Commented] (CLOUDSTACK-9339) Virtual Routers don't handle Multiple Public Interfaces
Date Tue, 05 Apr 2016 13:54:25 GMT


dsclose commented on CLOUDSTACK-9339:

The iptables rules that allow forwarding between eth0 and eth2 are as follows:

-A FORWARD -i eth2 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i eth0 -o eth2 -j FW_OUTBOUND

When equivalent rules are added for some other interface, such as eth3 or eth4, inbound connections
to IP addresses assigned to those interfaces begin to work.

> Virtual Routers don't handle Multiple Public Interfaces
> -------------------------------------------------------
>                 Key: CLOUDSTACK-9339
>                 URL:
>             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
>              Labels: firewall, nat, router
> 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 router.
> * 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 IP.
> * 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:
> *mangle
> -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:
> *filter
> -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:
> *nat
> -A POSTROUTING -o eth2 -j SNAT --to-source

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