Secure IPTables rules for Corosync

I have two HA load balancers (hollywood and wolfman) running Corosync and Pacemaker. The eth1 interfaces are connected to the WAN, and the eth0 interfaces to the LAN, using a virtual IP as the gateway for the back end servers. The eth1 IP of hollywood is xxx.xxx.195.45, and the eth1 IP of wolfman is xxx.xxx.195.46. The bindnetaddr in Corosync is xxx.xxx.195.32, the same as the WAN's network address, and the Corosync port is the default 5405.

The relevant IP tables rules on both servers are:

*filter

--flush

:INPUT DROP

--append INPUT --protocol udp --destination-port 5404 --jump ACCEPT
--append INPUT --protocol udp --destination-port 5405 --jump ACCEPT

This setup seems to work fine, but initially I added --in-interface eth1 and --source xxx.xxx.195.46 to wolfman, and --source xxx.xxx.195.45 to hollywood. Most of the time this seemed to work, but rebooting the passive balancer sometimes killed communication between the load balancers, writing these errors to syslog:

[TOTEM ] Totem is unable to form a cluster because of an operating system or network fault. The most common cause of this message is that the local firewall is configured improperly.

So it seems that either my simplistic belief that all the Corosync traffic is directly between the two load balancers over eth1 is wrong, or that something else is causing a problem.

I'd like to lock port 5404/5405 down in IPTables to just the cluster. What do I need to do to make this happen?

Edit: corosync.conf as requested. This is all default Ubuntu other than the bindnetaddr.

# Please read the openais.conf.5 manual page

totem {
        version: 2

        # How long before declaring a token lost (ms)
        token: 3000

        # How many token retransmits before forming a new configuration
        token_retransmits_before_loss_const: 10

        # How long to wait for join messages in the membership protocol (ms)
        join: 60

        # How long to wait for consensus to be achieved before starting a new round of membership configuration (ms)
        consensus: 3600

        # Turn off the virtual synchrony filter
        vsftype: none

        # Number of messages that may be sent by one processor on receipt of the token
        max_messages: 20

        # Limit generated nodeids to 31-bits (positive signed integers)
        clear_node_high_bit: yes

        # Disable encryption
        secauth: off

        # How many threads to use for encryption/decryption
        threads: 0

        # Optionally assign a fixed node id (integer)
        # nodeid: 1234

        # This specifies the mode of redundant ring, which may be none, active, or passive.
        rrp_mode: none

        interface {
                # The following values need to be set based on your environment
                ringnumber: 0
                bindnetaddr: xxx.xxx.195.32
                mcastaddr: 226.94.1.1
                mcastport: 5405
        }
}

amf {
        mode: disabled
}

service {
        # Load the Pacemaker Cluster Resource Manager
        ver:       0
        name:      pacemaker
}

aisexec {
        user:   root
        group:  root
}

logging {
        fileline: off
        to_stderr: yes
        to_logfile: no
        to_syslog: yes
        syslog_facility: daemon
        debug: off
        timestamp: on
        logger_subsys {
                subsys: AMF
                debug: off
                tags: enter|leave|trace1|trace2|trace3|trace4|trace6
        }
}

By default, Corosync uses IP multicast to communicate between nodes:

mcastaddr: 226.94.1.1
mcastport: 5405

Either configure your firewall to allow multicast traffic:

# iptables -A INPUT -p igmp -j ACCEPT
# iptables -A INPUT -m addrtype --dst-type MULTICAST -j ACCEPT

# iptables -A INPUT -p udp -m state --state NEW -m multiport --dports 5404,5405 -j ACCEPT

or switch to unicast.

When using multicast communication (the default for Corosync), IGMP traffic should be allowed and the Corosync packets can be allowed with rules that are much more specific than in the other answer. The following rules are sufficient (assuming that the OUTPUT chain does not block any traffic):

iptables -A INPUT -p igmp -i $corosync_interface -j ACCEPT
for src_addr in $ip_addr_self $ip_addr_partner1 $ip_addr_partner2; do
  iptables -A INPUT -i $corosync_interface -s $src_addr -d $ip_addr_self \
    -p udp --source-port $(($corosync_port - 1)) \
    --destination-port $corosync_port -j ACCEPT
  iptables -A INPUT -i $corosync_interface -s $src_addr -d $ip_addr_mcast \
    -p udp --source-port $(($corosync_port - 1)) \
    --destination-port $corosync_port -j ACCEPT
done

In this example, the following variables are assumed to be defined:

$corosync_interface: the network interface which is used by Corosync
$ip_addr_self: the IP address to which Corosync binds locally (specified as bindnetaddr in corosync.conf)
$ip_addr_partner1, $ip_addr_partner2: the IP addresses of the other Corosync nodes - more can be added if the cluster has more than three nodes.
$ip_addr_mcast: the multicast address used for Corosync (specified as mcastaddr in corosync.conf)
$corosync_port: the (destination) port used by Corosync (specified as mcastport in corosync.conf)

On one node, where the interface used by Corosync is a port that is a member of an Open vSwitch bridge, some of the multicast packets where received on the interface of the bridge instead of the one which had the IP address. Therefore, I had to add an additional rule that allowed multicast packets on this interface:

for src_addr in $ip_addr_self $ip_addr_partner1 $ip_addr_partner2; do
  iptables -A INPUT -i $bridge_interface -s $src_addr -d $ip_addr_mcast -p udp --source-port $(($corosync_port - 1)) --destination-port $corosync_port -j ACCEPT
done

If the OUTPUT chain does not accept the packets by default, rules need to be added that allow IGMP traffic and that allow sending Corosync packets:

iptables -A OUTPUT -p igmp -o $corosync_interface -j ACCEPT
for dst_addr in $ip_addr_self $ip_addr_mcast $ip_addr_partner1 $ip_addr_partner2; do
  iptables -A OUTPUT o $corosync_interface -s $ip_addr_self -d $dst_addr \
    -p udp --source-port $(($corosync_port - 1)) \
    --destination-port $corosync_port -j ACCEPT
done

Secure IPTables rules for Corosync

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