Hardware Tuning and Troubleshooting

The underlying operating system beneath pfSense® software can be fine-tuned in several ways. A few of these tunables are available under Advanced Options (See System Tunables Tab). Others are outlined in the FreeBSD main page tuning(7).

The default installation includes a well-rounded set of values tuned for good performance without being overly aggressive. There are cases where hardware or drivers necessitate changing values or a specific network workload requires changes to perform optimally.

The hardware sold in the Netgate Store is tuned further since Netgate has detailed knowledge of the hardware, removing the need to rely on more general assumptions.


Changes in /boot/loader.conf.local require a firewall reboot to take effect.

General Issues

Mbuf Exhaustion

A common problem encountered by users of commodity hardware is mbuf exhaustion. To oversimplify, “mbufs” are network memory buffers; portions of RAM set aside for use by networking for moving data around.

The count of active mbufs is shown on the dashboard and is tracked by a graph under Status > Monitoring.

See also

For details on mbufs and monitoring mbuf usage, see Mbuf Clusters.

If the firewall runs out of mbufs, it can lead to a kernel panic and reboot under certain network loads that exhaust all available network memory buffers. In certain cases this condition can also result in expected interfaces not being initialized and made available by the operating system. This is more common with NICs that use multiple queues or are otherwise optimized for performance over resource usage.

Additionally, mbuf usage increases when the firewall is using certain features such as Limiters.

To increase the amount of mbufs available, add the following to /boot/loader.conf.local:


On 64 bit systems with multiple GB of RAM, 1 million (1000000) mbuf clusters is a safe starting point. Should mbuf clusters become fully allocated, that would consume about 2.3 GB of physical memory:

1000000 memory buffer clusters available × (2048 KB per cluster + 256 bytes per
memory buffer)

The amount of available clusters can be reduced for systems with low amounts of physical RAM, or increased further as needed, as long as the value does not exceed available kernel memory.

Some network interfaces may need other similar values raised such as kern.ipc.nmbjumbop. In addition to the graphs mentioned above, check the output of the command netstat -m to verify if any areas are near exhaustion.

Disable MSIX

Message Signaled Interrupts are an alternative to classic style Interrupts for retrieving data from hardware. Some cards behave better with MSI, MSIX, or classic style Interrupts, but the card will try the best available choice (MSIX, then MSI, then Interrupts).

MSIX and MSI can be disabled via loader tunables. Add the following to /boot/loader.conf.local:


To nudge the card to use MSI, disable only MSIX. To nudge the card to use regular Interrupts, disable both MSI and MSIX.

PPPoE with Multi-Queue NICs

Network cards which support multiple queues rely on hashing to assign traffic to a particular queue. This works well with IPv4/IPv6 TCP and UDP traffic, for example, but fails with other protocols such as those used for PPPoE.

This can lead to a network card under performing with the default network settings, as noted on #4821 and FreeBSD PR 203856. This problem primarily affects systems with multiple CPUs and/or CPU cores, as those are the systems which benefit most from multiple NIC queues.

Adding a System Tunable or loader.conf.local entry for net.isr.dispatch=deferred can lead to performance gains on affected hardware.

Tuning the values of net.isr.maxthreads and net.isr.numthreads may yield additional performance gains. Generally these are best left at default values matching the number of CPU cores, but depending on the workload may work better at lower values.


In the past, deferred mode has led to issues on 32-bit platforms, such as crashes/panics, especially with ALTQ. There have been no recent reports, however, so it should be safe on current releases.


The settings for Hardware TCP Segmentation Offload (TSO) and Hardware Large Receive Offload (LRO) under System > Advanced on the Networking tab default to checked (disabled) for good reason. Nearly all hardware/drivers have issues with these settings, and they can lead to throughput issues. Ensure the options are checked. Sometimes disabling via sysctl is also necessary.

Add the following to /boot/loader.conf.local:


IP Input Queue (intr_queue)

This will show the current setting:

sysctl net.inet.ip.intr_queue_maxlen

However, in largely loaded installations this may not be enough. Here is how to check:

sysctl net.inet.ip.intr_queue_drops

If the above shows values above 0, try doubling the current value of net.inet.ip.intr_queue_maxlen.

For example:

sysctl net.inet.ip.intr_queue_maxlen="3000"

Keep performing the above until the point is found where drops are eliminated without any adverse effects.

Afterwards, add an entry under System > Advanced, System Tunables tab to set net.inet.ip.intr_queue_maxlen to 3000

Card-Specific Issues

Broadcom bce(4) Cards

Several users have noted issues with certain Broadcom network cards, especially those built into Dell hardware. If bce interfaces are behaving erratically, dropping packets, or causing crashes, then the following tweaks may help.

Add the following to /boot/loader.conf.local:


That will increase the amount of network memory buffers, disable TSO directly, and disable msix.

Packet loss with many (small) UDP packets

If a lot of packet loss is observed with UDP on bce cards, try changing the netisr settings. These can be set as system tunables under System > Advanced, on the System Tunables tab. On that page, add two new tunables:


Broadcom bge(4) Cards

See above, but change “bce” to “bge” in the setting names.

Chelsio cxgbe(4) Cards

It is possible to disable the allocation of resources that are not related to the router so that the network adapter can use its entire set of resources for the corresponding functions:

Add the following to /boot/loader.conf.local:


Intel igb(4) and em(4) Cards

Certain intel igb cards, especially multi-port cards, can easily exhaust mbufs and cause kernel panics. The following tweak will prevent this from being an issue. Add the following to /boot/loader.conf.local:


That will increase the amount of network memory buffers, allowing the driver enough headroom for its optimal operation.

Intel ix(4) Cards

In /boot/loader.conf.local:


As a sysctl (system tunable):


VMware vmx(4) Interfaces

VMware VMXNET interfaces support multiple queues when using MSI-X. Multiple queues enable network performance to scale with the number of vCPUs and allows for parallel packet processing. Transmit and Receive descriptors may also be increased to help with throughput.

Edit or create /boot/loader.conf.local and add the following content:


Some options have a separate set of tunables for each individual network interface. In these cases, replace <id> replace with the device ID such as 0, 1, etc. where the ID number matches the interface number. For example, tunables for vmx3 are under dev.vmx.3.


Save the file, then reboot and check the change with dmesg | grep -Eiw 'descriptors|queues' at a command prompt.

Flow Control

In some circumstances, flow control may need to be disabled. The exact method depends on the hardware involved, as in the following examples:

These example entries go in /boot/loader.conf.local:

ixgbe(4) (aka ix)

These example entries go in System > Advanced, on the System Tunables tab (System Tunables Tab):


Some options have a separate set of tunables for each individual network interface. In these cases, replace <id> replace with the device ID such as 0, 1, etc. where the ID number matches the interface number. For example, tunables for igc3 are under dev.igc.3.


For ix and others, the flow control value can be further tuned:


No Flow Control


Receive Pause


Transmit Pause


Full Flow Control, Default