# Load the tcp_bbr kernel module
modprobe tcp_bbr

# Confirm that the module is loaded
lsmod | grep tcp_bbr
# Expected output: tcp_bbr 20480 0 (or other non-empty output, indicating that the module is loaded)

# Confirm that BBR is in the list of available algorithms
sysctl net.ipv4.tcp_available_congestion_control
# Expected output: net.ipv4.tcp_available_congestion_control = reno cubic bbr

# View the current algorithm
sysctl net.ipv4.tcp_congestion_control
# Expected output: net.ipv4.tcp_congestion_control = cubic

# Switch to BBR (recommended for high-bandwidth public network scenarios, not recommended for private network scenarios)
sysctl -w net.ipv4.tcp_congestion_control=bbr
# Expected output: net.ipv4.tcp_congestion_control = bbr

# Verify that the switch is successful
sysctl net.ipv4.tcp_congestion_control
# Expected output: net.ipv4.tcp_congestion_control = bbr

# Confirm that the nf_conntrack module is loaded (if it is not loaded, the conntrack parameter path does not exist)
modprobe nf_conntrack

# View current connection tracking statistics
sysctl net.netfilter.nf_conntrack_count
# Expected output: net.netfilter.nf_conntrack_count = 12345 (sample value, the number of currently tracked connections)

sysctl net.netfilter.nf_conntrack_max
# Expected output: net.netfilter.nf_conntrack_max = 65536 (current maximum value)

# Temporarily increase the maximum value of the conntrack table (takes effect at runtime)
sysctl -w net.netfilter.nf_conntrack_max=1048576
# Expected output: net.netfilter.nf_conntrack_max = 1048576

# Confirm that max has been updated (the nf_conntrack module must be loaded, otherwise the parameter path does not exist)
sysctl net.netfilter.nf_conntrack_max
# Expected output: net.netfilter.nf_conntrack_max = 1048576

# Confirm that the current connection count is not close to max to avoid saturation.
sysctl net.netfilter.nf_conntrack_count
# Expected output: a value far below max, with utilization below 70%

# View conntrack statistics (check insert_failed and drop, which should be 0)
cat /proc/net/stat/nf_conntrack
# Or use ctstat to view the summary (ctstat is provided by the iproute-tc package. If it is not installed, run dnf install iproute-tc)
ctstat -s 1
# Expected output: insert_failed=0, drop=0 (if insert_failed keeps increasing, the table is still full)

# View the actual NIC name by using ip link
ip link show

# RSS (Receive Side Scaling): View the NIC multi-queue configuration
ethtool -l <NIC name>
# Expected output: Channel parameters are displayed, where Combined under Pre-set maximums indicates the maximum supported queue count, and Combined under Current hardware settings indicates the current queue count (for example, Combined: 2)

# Set the queue count (requires NIC support. The <queue count> is determined by the number of CPU cores, typically equal to the core count, and must not exceed the maximum Combined value in Pre-set maximums)
ethtool -L <NIC name> combined <queue count>
# Expected output: no errors. Run ethtool -l <NIC name> again to see that Combined queues have been updated

# View the actual NIC name by using ip link
ip link show
# View the NIC interrupt distribution (Note: In virtualized environments, NIC interrupts are identified by the underlying device name, such as virtio0-input.0,
# Using the NIC name with grep may produce no output. Run ethtool -i <NIC name> first to view the driver/bus-info, and then search by the device name.
grep virtio /proc/interrupts
# Expected output: multiple lines, each corresponding to an interrupt of a transmit/receive queue (such as virtio0-input.0 and virtio0-output.0),
# Interrupt counts across queues should be roughly evenly distributed

# Set interrupt affinity (replace <IRQ number> with the actual interrupt number and bind it to a specific CPU mask;
# The mask must not exceed the number of CPUs. For example, on a 2-CPU machine, the maximum valid mask is 3, and writing f will report "write error: Value too large for defined data type".
echo f > /proc/irq/<IRQ_number>/smp_affinity
# Expected output: no errors (f means binding to CPU 0-3, and ff means binding to CPU 0-7. Use f on a 4-CPU machine and ff on an 8-CPU machine)

# Verify affinity
cat /proc/irq/<IRQ_number>/smp_affinity_list
# Expected output: 0-3 (or the corresponding CPU list)

# Set the RPS CPU mask (replace <NIC name> with the actual NIC. rx-0 is the first receive queue)
# ffff is a 16-bit CPU mask, indicating binding to CPU 0-15. If the number of CPUs exceeds 16, use a longer mask.
echo ffff > /sys/class/net/<NIC_name>/queues/rx-0/rps_cpus
# Expected output: No errors.

# Set the RPS flow table size
echo 32768 > /proc/sys/net/core/rps_sock_flow_entries
# Expected output: No errors.

# Verify the RPS configuration
cat /sys/class/net/<NIC_name>/queues/rx-0/rps_cpus
# Expected output: ffff

# View the actual NIC name by using ip link
ip link show

# Check whether the interrupt distribution is balanced across queues (in virtualized environments, search by the underlying device name, such as virtio)
grep virtio /proc/interrupts
# Expected output: The interrupt counts are roughly even across queues, with no single core saturated.

# View softirq network processing statistics (each line corresponds to one CPU, and values are in hexadecimal format without a prefix)
cat /proc/net/softnet_stat
# Expected output: multiple lines, where the second column (drop, in hexadecimal) should be 00000000,
# The third column (time_squeeze, in hexadecimal) should be small and not grow continuously.

# Write to /etc/sysctl.d/ for persistence
cat > /etc/sysctl.d/99-tos-net-tune.conf << 'EOF'
net.core.somaxconn = 65535
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_congestion_control = bbr
net.ipv4.tcp_max_syn_backlog = 8192
net.ipv4.tcp_max_tw_buckets = 1048576
net.netfilter.nf_conntrack_max = 1048576
EOF

# Configure the BBR module to load automatically at boot
echo "tcp_bbr" > /etc/modules-load.d/tcp_bbr.conf

# Apply the configuration
sysctl --system
# Expected output: * Applying /etc/sysctl.d/99-tos-net-tune.conf ... and listing each parameter value

# Verify that each key parameter has been persisted and taken effect
sysctl net.ipv4.tcp_congestion_control
# Expected output: net.ipv4.tcp_congestion_control = bbr

sysctl net.core.somaxconn
# Expected output: net.core.somaxconn = 65535

sysctl net.netfilter.nf_conntrack_max
# Expected output: net.netfilter.nf_conntrack_max = 1048576

# Load the corresponding module
modprobe nf_conntrack
# Confirm that the parameter path appears
ls /proc/sys/net/netfilter/nf_conntrack_max

# Manually load the module
modprobe tcp_bbr
# Confirm that bbr is in the available list
sysctl net.ipv4.tcp_available_congestion_control
# If bbr is not available, check the kernel version (TencentOS Server 4 with kernel 6.6 LTS has built-in BBR support)
uname -r

# Check whether the NIC supports queue adjustment
ethtool -l <NIC name>
# If "Maximum" is not supported after Combined queues is output, adjustment is not possible
# Use RPS (software distribution) instead of hardware RSS (ffff is a 16-bit CPU mask representing CPUs 0-15; use a longer mask when there are more than 16 CPUs)
echo ffff > /sys/class/net/<NIC_name>/queues/rx-0/rps_cpus

# View the current buckets (read-only)
cat /sys/module/nf_conntrack/parameters/hashsize
# Adjust buckets through kernel boot parameters (a restart is required; the recommended value does not exceed nf_conntrack_max / 4, and the maximum value is limited by system memory)
grubby --update-kernel=ALL --args="nf_conntrack.hashsize=262144"
# Restart (a restart will cause service interruption, so perform it within a maintenance window)
reboot
# Confirm that buckets have been updated after the restart.
cat /sys/module/nf_conntrack/parameters/hashsize

# Check for duplicate definitions.
grep -r "tcp_congestion_control" /etc/sysctl.conf /etc/sysctl.d/
# Consolidate them into /etc/sysctl.d/99-tos-net-tune.conf and delete the conflicting entries in other files.
# Confirm the loading order (the 99- prefix ensures that it is loaded last)
sysctl --system