DoS Protection Profiles
Protect groups of devices and critical individual devices from flood attacks, and limit the maximum concurrent sessions for resources.
DoS Protection profiles set thresholds that protect against new session IP flood attacks and provide resource protection (maximum concurrent session limits for specified endpoints and resources). DoS Protection profiles protect specific devices (classified profiles) and groups of devices (aggregate profiles) against SYN, UDP, ICMP, ICMPv6, and Other IP flood attacks. Configuring Flood Protection thresholds in a DoS Protection profile is similar to configuring Flood Protection in a Zone Protection profile, but Zone Protection profiles protect entire ingress zones, while DoS protection profiles and policy rules are granular and targeted, and can even be classified to a single device (IP address). The firewall measures the aggregate number of connections-per-second (CPS) to a group of devices (aggregate profile) or measures the CPS to individual devices (classified profile).
Measure and monitor firewall dataplane CPU consumption to ensure that each firewall is properly sized to support DoS and Zone Protection and any other features that consume CPU cycles, such as decryption. If you use Panorama to manage your firewalls, Device Monitoring (
) shows you the CPU and memory consumption of each managed firewall. It can also show you a 90-day trend line of CPU average and peak use to help you understand the typical available capacity of each firewall.
For each flood type, you set three thresholds for new CPS to a group of devices (aggregate) or to individual devices (classified) and a
Block Duration, and you can set a drop
Actionfor SYN floods:
- Alarm Rate—When new CPS exceeds this threshold, the firewall generates a DoS alarm. For classified profiles, set the rate to 15-20% above the device’s average CPS rate so that normal fluctuations don’t cause alerts. For aggregate profiles, set the rate to 15-20% above the group’s average CPS rate.
- Activate Rate—When new CPS exceeds this threshold, the firewall begins to drop new connections to mitigate the flood until the CPS rate drops below the threshold. For classified profiles, theMax Rateshould be an acceptable CPS rate for the device(s) you’re protecting (theMax Ratewon’t flood the critical device(s)). You can set theActivate Rateto the same threshold as theMax Rateso that the firewall doesn’t use RED or SYN Cookies to begin dropping traffic before it reaches theMax Rate. Set theActivate Ratelower than theMax Rateonly if you want to drop traffic before it reaches theMax Rate. For aggregate profiles, set the threshold just above the average peak CPS rate for the group to begin mitigating floods using RED (or SYN Cookies for SYN floods).
- Max Rate—When new CPS exceeds this threshold, the firewall blocks (drops) all new connections from the offending IP address for the specifiedBlock Durationtime period. For classified profiles, base theMax Ratethreshold on the capacity of the device(s) you’re protecting so that the CPS rate can’t flood them. For aggregate profiles, set to 80-90% of the group’s capacity.
- Block Duration—When new CPS exceeds theMax Rate, the firewall blocks new connections from the offending IP address. TheBlock Durationspecifies the amount of time the firewall continues to block the IP address’s new connections. While the firewall blocks new connections, it doesn’t count incoming connections and doesn’t increment the threshold counters. For classified and aggregate profiles, use the default value (300 seconds) to block the attacking session without penalizing legitimate sessions from the source for too long a period of time.
SYN Flood Protection is the only type for which you set the drop
Action. Start by setting the
SYN Cookies. SYN Cookies treats legitimate traffic fairly and only drops traffic that fails the SYN handshake, while using Random Early Drop drops traffic randomly, so RED may affect legitimate traffic. However, SYN Cookies is more resource-intensive because the firewall acts as a proxy for the target server and handles the three-way handshake for the server. The tradeoff is not dropping legitimate traffic (SYN Cookies) versus preserving firewall resources (RED). Monitor the firewall, and if SYN Cookies consumes too many resources, switch to RED. If you don’t have a dedicated DDoS prevention device in front of the firewall, always use RED as the drop mechanism.
The default threshold values are high so that DoS Protection profiles don’t unexpectedly drop legitimate traffic. Monitor connection traffic and adjust the thresholds to values appropriate for your network. Start by taking baseline measurements of average and peak CPS for each flood type to determine the normal traffic conditions for the critical devices you want to protect. Because normal traffic loads experience some fluctuation, it’s best not to drop connections too aggressively. Monitor and adjust the flood thresholds as needed and as your network evolves.
Another method of setting flood thresholds is to use the baseline measurements to set the maximum CPS you want to allow and work back from there to derive reasonable flood mitigation alarm and activation rates.
Firewalls with multiple dataplane processors (DPs) distribute connections across DPs. In general, the firewall divides the CPS threshold settings equally across its DPs. For example, if a firewall has five DPs and you set the
Alarm Rateto 20,000 CPS, each DP has an
Alarm Rateof 4,000 CPS (20,000 / 5 = 4,000), so if the new sessions on a DP exceeds 4,000, it triggers the
Alarm Ratethreshold for that DP.
In addition to setting IP flood thresholds, you can also use DoS Protection profiles to detect and prevent session exhaustion attacks in which a large number of hosts (bots) establish as many sessions as possible to consume a target’s resources. On the profile’s
Resources Protectiontab, you can set the maximum number of concurrent sessions that the device(s) defined in the DoS Protection policy rule to which you apply the profile can receive. When the number of concurrent sessions reaches its maximum limit, new sessions are dropped.
The maximum number of concurrent sessions to set depends on your network context. Understand the number of concurrent sessions that the resources you are protecting (defined in the DoS Protection policy rule to which you attach the profile) can handle. Set the threshold to approximately 80% of the resources’ capacity, then monitor and adjust the threshold as needed.
For aggregate profiles, the
Resources Protectionthreshold applies to all traffic of the devices defined in the policy rule (source and destination). For classified profiles, the
Resources Protectionthreshold applies to the traffic based on whether the classified policy rule applies to the source IP only, to the destination IP only, or to both the source and destination IPs.
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