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From "ASF GitHub Bot (JIRA)" <>
Subject [jira] [Commented] (CLOUDSTACK-9339) Virtual Routers don't handle Multiple Public Interfaces
Date Thu, 26 May 2016 06:15:13 GMT


ASF GitHub Bot commented on CLOUDSTACK-9339:

GitHub user dsclose reopened a pull request:

    Cloudstack 9339: Virtual Routers do not handle Multiple Public Interfaces

    This PR addresses CLOUDSTACK-9339 and may need a code review from someone familiar with
the System VM scripts. In particular, this PR has not been tested in a VPC RvR context. Only
standalone routers and RvR routers have been demonstrated.
    - **d582358: Leave public interfaces down in backup redundant routers.** Previously backup
routers were bringing all interfaces up and thus arping public IPs away from the master router.
    - **9ee1eb6: Add the default gateway to the main routing table when interfaces are configured.**
The gateway for the first public IP was always being added to the main routing table. Sometimes
a router would consequently add the gateway for an IP other than the default source-NAT IP.
This would prevent outbound connectivity for guest VMs.
    - **ad9d72f: Add default gateway to device-specific routing tables.** Link-level routes
were being put into the device-specific routing tables (accessed via firewall marks) but these
are unnecessary. Instead, the default gateway is needed to allow the kernel to make an appropriate
routing decision.
    - **8db879e: Only mark guest connections when they are part of a static-NAT.** Guest connections
were being marked with a zero. This added no functionality and prevented static-NAT rules
from routing outbound traffic properly as device-specific routing tables would not be used.
Instead, all traffic would be routed out via the default public interface.
    - **788b1be: Allow forwarding and collect network stats on any public interface.** Forwarding
rules and network stats were limited to eth2 on RvR networks. This needed to be decoupled
from eth2 and reapplied to whichever interface was under consideration.
    - **b19e8aa: Ensure that CONNMARK --restore-mark only appears once.** This is a bit of
a hack and can do with being improved. The CONNMARK rule was not being picked up by the de-duplication
logic in CsNetfilter and was being added twice. This caused checksum errors on packets traversing
    - **bf285e1: Transition to master state should add all necessary routes.** Now that backup
routers keep their interfaces down, the route logic executed at configuration-time cannot
be applied. Instead, once the interface is brought up during a transition to master, routers
must re-evaluate what routes are needed and add them. Unfortunately I couldn't see a way to
re-use the existing route logic with the variables that I had in scope so there is some duplication.
In some cases, routers did not successfully arp IPs away from the old master so some arp logic
was added. During a failover most connections with guest VMs will be maintained with only
minor packet loss. SSH sessions implemented via port-forwarding rules on an interface other
than the source-NAT interface consistently get dropped, however, so the failover isn't quite
seamless. It's possible that there's an easy fix for that.
    I expect that a number of tests may need to be modified/written as part of this PR. Any
feedback or pointers would be useful as initially I'll be relying on the CI failures to tell
me where to look.

You can merge this pull request into a Git repository by running:

    $ git pull CLOUDSTACK-9339

Alternatively you can review and apply these changes as the patch at:

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #1519
commit e7a63be161bdd14c985a8b483bffe4bfdaa3f5d4
Author: dean.close <>
Date:   2016-05-09T10:31:26Z

    CLOUDSTACK-9339: Handle multiple public subnets on virtual routers.


> 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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