Conntrack tools

To have something similar to what it provides, you would have to:. This would tell you what firewall rules would have to exist in your firewall to allow the flows or block them. But this is just half of the problem. If you want to understand why a specific flow is being blocked, you would have to trace that flow and check through which firewall rules that flow is flowing.

Correct thing to do would be to trace each flow for a specific amount of time, once its first seen, and then stop it. Skip to content. Star Branches Tags. Could not load branches. Could not load tags. Latest commit. Git stats commits. Failed to load latest commit information. View code. Best way to do this is to rely on debian packaging build.

Note, using directory '. Done Building dependency tree Reading state information The daemon conntrackd covers the specific aspects of stateful Linux firewalls to enable high availability solutions and it can be used as statistics collector of the firewall use as well. In short, yes. The daemon conntrackd synchronizes the states among several replica firewalls, so you can deploy failover setups with stateful Linux firewalls. However, conntrackd follows different principle designs with regards to OpenBSD's pfsync so they are not strictly equivalent.

In the case of UDP this happens automatically. By default conntrack allows mid-stream pickups to not cause problems for flows that existed prior to conntrack becoming active.

As explained in the previous section, the reply tuple listed contains the NAT information. Its possible to filter the output to only show entries with source or destination nat applied. This allows to see which kind of NAT transformation is active on a given flow.

This entry shows a connection from But unlike the previous example, the reply direction is not just the inverted original direction: the source address is changed. The destination host Whenever When This source NAT is due to a nft masquerade rule:.

Two useful extensions are conntrack accounting and timestamping. This is used by conntrackd for state replication. Entries of an active firewall are replicated to a standby system.

The standby system can then take over without breaking connectivity even on established flows. Conntrack can also store metadata not related to the packet data sent on the wire, for example the conntrack mark and connection tracking labels. In some cases, you want to delete enries from the state table. For example, changes to NAT rules have no effect on packets belonging to flows that are already in the table.

The following example removes the given entry from the table:. Most counters will be 0. Other errors accounted for are:. These error conditions are harmless unless they occur frequently.