Troubleshooting The daemon conntrackd supports two working modes: State table synchronization: the daemon can be used to synchronize the connection tracking state table between several firewall replicas. This can be used to deploy fault-tolerant stateful firewalls. This is the main feature of the daemon. Flow-based statistics collection: the daemon can be used to collect flow-based statistics.

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Troubleshooting The daemon conntrackd supports two working modes: State table synchronization: the daemon can be used to synchronize the connection tracking state table between several firewall replicas. This can be used to deploy fault-tolerant stateful firewalls. This is the main feature of the daemon. Flow-based statistics collection: the daemon can be used to collect flow-based statistics.

This feature is similar to what ulogd State table synchronization Requirements In order to get conntrackd working in synchronization mode, you have to fulfill the following requirements: A high availability manager like keepalived that manages the virtual IPs of the firewall cluster, detects errors, and decide when to migrate the virtual IPs from one firewall replica to another. Without it, conntrackd will not work appropriately.

The state synchronization setup requires a working installation of keepalived , preferibly a recent version. Check if your distribution comes with a recent packaged version. Otherwise, you may compile it from the sources.

There is a very simple example file in the conntrackd sources to setup a simple HA cluster with keepalived see the file keepalived. If you use a different high availability manager, make sure it works correctly before going ahead. A dedicated link.

The dedicated link between the firewalls is used to transmit and receive the state information. The use of a dedicated link is mandatory for security reasons as someone may pick the state information that is transfered between the firewalls.

A well-formed stateful rule-set. Otherwise you are likely to experience problems during the fail-over. An example of a well-formed stateful iptables rule-set is available in the conntrack-tools website.

This protocol sends and receives the state information without performing any specific checking. Thus, the protocol can recover from message loss, re-ordering and corruption. It is based on a alarm-based protocol that periodically re-sends the flow state to the backup firewall replicas. This protocol consumes a lot of bandwidth but it resolves synchronization problems fast. The three existing approaches are soft real-time asynchronous replication protocols that are aimed to have negligible impact in terms of latency and bandwidth throughput in the stateful firewall filtering.

There are several parameters that you have to tune to adapt the example configuration file to your setup. Active-Backup setup Stateful firewall architectures A good reading to extend the information about firewall architectures is Demystifying cluster-based fault-tolerant firewalls published in IEEE Internet Computing magazine.

In the Active-Backup setup, one of the stateful firewall replicas filters traffic and the other acts as backup. If you use this approach, you have to copy the script primary-backup.

If a stateful firewall replica: becomes active to recover the filtering. The script is simple, and it contains the different actions that conntrackd performs to recover the filtering or purge obsolete entries from the state table, among others. The script is commented, you can have a look at it if you need further information.

Active-Active setup The Active-Active setup consists of having more than one stateful firewall replicas actively filtering traffic. Thus, we reduce the resource waste that implies to have a backup firewall which does nothing.

We can classify the type of Active-Active setups in several families: Symmetric path routing: The stateful firewall replicas share the workload in terms of flows, ie. Asymmetric multi-path routing: The packets that are part of a flow can be filtered by whatever stateful firewall in the cluster.

Thus, every flow-states have to be propagated to all the firewalls in the cluster as we do not know which one would be the next to filter a packet. This setup goes against the design of stateful firewalls as we define the filtering policy based on flows, not in packets anymore. As for 0. Unfortunately, you will have to wait for the support for the Active-Active setup based on dynamic approach, ie.

On the other hand, the asymmetric scenario may work if your setup fulfills several strong assumptions. However, in the opinion of the author of this work, the asymmetric setup goes against the design of stateful firewalls and conntrackd. Therefore, you have two choices here: you can deploy an Active-Backup setup or go back to your old stateless rule-set in that case, the conntrack-tools will not be of any help anymore, of course.

Moreover, if conntrackd is running fine, you can dump the current status of the daemon: conntrackd -s cache internal: current active connections: 4 connections created: 4 failed: 0 connections updated: 0 failed: 0 connections destroyed: 0 failed: 0 cache external: current active connections: 0 connections created: 0 failed: 0 connections updated: 0 failed: 0 connections destroyed: 0 failed: 0 traffic processed: 0 Bytes 0 Pckts multicast traffic: Bytes sent 0 Bytes recv 22 Pckts sent 0 Pckts recv 0 Error send 0 Error recv multicast sequence tracking: 0 Pckts mfrm 0 Pckts lost This command displays the number of entries in the internal and external cache: The internal cache contains the states that this firewall replica is filtering, ie.

The external cache contains the states that the other firewall replica is filtering. Other configuration options The daemon allows several configuration options that you may want to enable. This section contains some information about them. Disabling external cache It is possible to disable the external cache.

Thus, conntrackd directly injects the flow-states into the in-kernel Connection Tracking System of the backup firewall. You can do it by enabling the DisableExternalCache option in the conntrackd. This increases CPU consumption in the backup firewall but now you do not need to commit the flow-states during the master failures since they are already in the in-kernel Connection Tracking table. Moreover, you save memory in the backup firewall since you do not need to store the foreign flow-states anymore.

Disabling internal cache You can also disable the internal cache by means of the DisableInternalCache option in the conntrackd. This mode provides unreliable flow-state synchronization between firewalls.

Thus, if flow-states are lost during the synchronization, the protocol provides no way to recover them. UDP and multicast are unreliable but together with the FT-FW mode provide partial reliable flow-state synchronization. TCP introduces latency in the flow-state synchronization due to the congestion control. Under flow-state message are lost, the FIFO delivery becomes also a problem since the backup firewall quickly gets out of sync. For that reason, its use is discouraged.

Redundant dedicated links You can set redundant dedicated links without using bonding, you have to configure as many redundant links as you want in the configuration file.

In case of failure of the master dedicated link, conntrackd failovers to one of the backups. Reducing the amount of events generated helps to reduce CPU consumption in the active firewall. The connection tracking system provides helpers that allows you to filter multi-flow application protocols like FTP, H.

These protocols usually split the control and data traffic in different flows. Moreover, the control flow usually announces layer 3 and 4 information to let the other peer know where the data flows will be open. This sort of protocols require that the firewall inspects the content of the packet, otherwise filtering by layer 3 and 4 selectors like addresses and ports become a real nightmare.

Netfilter already provides the so-called helpers that track this protocol aspects to allow deploying appropriate filtering. These helpers create expectation entries that represent expected traffic that will arrive to the firewall according to the inspected packets. In case that you have enabled tracking of these protocols, you may want to enable the state-synchronization of expectation as well. Thus, established flows for this specific protocols will not suffer any disruption.

In my testbed, there are two firewalls in a primary-backup configuration running keepalived. They use a couple of floating cluster IP address These firewalls protect one FTP server The following steps detail how to check that the expectation support works fine with FTP traffic: Switch to the client. PASS nothing Login successful. Switch to fw-1 primary to check that the expectation is in the internal cache.

Now fw-2 becomes primary. Switch to fw-2 primary to commit the external cache into the kernel. LIST Switch to term-2, it should display the listing. That means everything has worked fine. You may want to try disabling the expectation support and repeating the steps to check that it does not work without the state-synchronization. Connection tracking helpers allows you to filter multi-flow protocols that usually separate control and data traffic into different flows. This is problematic for gateways since they operate at packet-level, ie.

Helpers inspect packet content at layer 7 and create the so-called expectations. These expectations are added to one internal table that resides in the gateway. For each new packet arriving to the gateway, the gateway first looks up for matching expectations. Note this lookup only occurs for the first packet that is part of one newly established flow, not for all packets.

Since 1. The main features of the user-space infrastructure for helpers are: Rapid connection tracking helper development, as developing code in user-space is usually faster. Reliability: A buggy helper does not crash the kernel. If the helper fails, ie. Security: Avoid complex string matching and mangling in kernel-space running in privileged mode. Going further, we can even think about running user-space helper as a non-root process. It allows the development of very specific helpers for proprietary protocols that are not standard.

Implementing this in kernel-space may be problematic, since this may not be accepted for ainline inclusion in the Linux kernel. As an alternative, we can still distribute this support as separate patches. This highly increase the overhead in the maintainance.

NFSv3, mind that version 4 does not require this helper. FTP this helper is also available in kernel-space. If there is no instance of conntrackd configured to support user-space helpers, no inspection happens and packets are not sent to user-space.

Add configuration to conntrackd.


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Men Direccin de Internet Podemos utilizar de momento 4 lneas WAN a las que iremos colocando los datos correspondientes a cada una de ellas. Su configuracin es sencilla, siempre teniendo en cuenta el colocar el nombre correcto en Dispositivo de Red. Tambin podemos ver al final un apartado para las DNS. Guardamos y en el caso de que nos lo pida BrazilFW, reiniciamos.


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