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Manual Chapter: Detecting and Preventing Network DoS Attacks on a Virtual Server
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About detecting and preventing Network DoS attacks on a virtual server

Network DoS protection is a type of security that collects several DoS checks in a DoS profile. Attack detection and prevention serves several functions:

  • To detect and report on packets based on behavior characteristics of the sender or characteristics of the packets, without enforcing any rate limits.
  • To detect, report on, and rate limit packets based on behavior characteristics that signify specific known attack vectors.
  • To identify Bad Actor IP addresses from which attacks appear to originate, by detecting packets per second from a source, and to apply rate limits to such IP addresses.
  • To blacklist Bad Actor IP addresses, with configurable detection times, blacklist durations, and blacklist categories, and allow such IP addresses to be advertised to edge routers to offload blacklisting.

You can configure the Network DoS Protection profile to detect possible attack vectors by packet-per-second or percentage-increase-over-time thresholds, which can indicate that a possible attack is in process. Such attacks can be logged and reported through system logging facilities. You can also rate limit packets of known vectors. You can configure settings manually, and for many vectors you can allow AFM to manage thresholds automatically.

You can specify an address list as a whitelist that the DoS checks allow. Whitelisted addresses are passed by the DoS profile, without being subject to the checks in the DoS profile.

Per-virtual server DoS protection requires that your virtual server includes a DoS profile that includes network security.

Task list

Detecting and protecting a virtual server against network DoS attacks with a DoS profile

The BIG-IP® system handles network attacks that use malformed packets and malicious attack vectors. Possible malicious packets and attacks are detected by logging when packets exceed a threshold of packets per second, and by detecting the rate increase percentage in packets of a certain type over time. You can configure settings to identify and rate limit possible network attacks with a DoS profile. For many vectors, you can also automatically blacklist IP addresses.
  1. On the Main tab, click Security > DoS Protection > DoS Profiles .
    The DoS Profiles list screen opens.
  2. Click Create.
    The New DoS Profile screen opens.
  3. In the Name field, type the name for the profile.
  4. Click Finished.
    The DoS Protection: DoS Profiles screen opens.
  5. Click the profile name you configured to open the DoS Profile settings screen.
  6. Select the Threshold Sensitivity.
    Select Low, Medium, or High. A lower setting means the automatic threshold algorithm is less sensitive to changes in traffic and CPU usage, but will also trigger fewer false positives.
  7. In the Whitelist Address List field, begin typing the name of the address list to use as the whitelist, and select the address list when the name appears.
  8. To configure network security settings, click Network Security.
  9. To change the threshold or rate increase for a particular network attack, in the Attack Type column, click the name of the attack.
    The DoS attack properties appear in the right pane on the screen.
  10. Next to the DoS vector name, choose the enforcement option.
    • Select Enforce to enforce the DoS vector with the settings you configure or with automatic settings.
    • Select Don't Enforce to configure the vector and log the results of the vector you configure or the automatic settings, without applying rate limits or other actions.
    • Select Disable to disable logging and enforcement of the DoS vector.
  11. To allow the DoS vector thresholds to be automatically adjusted, select Auto-Threshold Configuration.
  12. To configure DoS vector thresholds manually, select Manual Configuration.
  13. From the Detection Threshold PPS list, select Specify or Infinite.
    • Use Specify to set a value (in packets per second) for the attack detection threshold. If packets of the specified types cross the threshold, an attack is logged and reported. The system continues to check every second, and registers an attack for the duration that the threshold is exceeded.
    • Use Infinite to set no value for the threshold. This specifies that this type of attack is not logged or reported based on this threshold.
  14. From the Detection Threshold Percent list, select Specify or Infinite.
    • Use Specify to set a value (in percentage of traffic) for the attack detection threshold. If packets of the specified types cross the percentage threshold, an attack is logged and reported. The system continues to check every second, and registers an attack for the duration that the threshold is exceeded.
    • Use Infinite to set no value for the threshold. This specifies that this type of attack is not logged or reported based on this threshold.
  15. From the Rate Limit Threshold PPS list, select Specify or Infinite.
    • Use Specify to set a value (in packets per second), which cannot be exceeded by packets of this type. All packets of this type over the threshold are dropped. Rate limiting continues until the rate no longer exceeds.
    • Use Infinite to set no value for the threshold. This specifies that this type of attack is not rate-limited.
  16. Select Simulate Auto Threshold to log the results of the current automatic thresholds, when enforcing manual thresholds.
  17. To detect IP address sources from which possible attacks originate, enable Bad Actor Detection.
    Note: Bad Actor Detection is not available for every vector.
  18. In the Per Source IP Detection (PPS) field, specify the number of packets of this type per second from one IP address that identifies the IP source as a bad actor, for purposes of attack detection and logging.
  19. In the Per Source IP Rate Limit (PPS) field, specify the number of packets of this type per second from one IP address, above which rate limiting or leak limiting occurs.
  20. Select the Blacklist Address check box to enable automatic blacklisting.
  21. From the Blacklist Category list, select a black list category to apply to automatically blacklisted addresses.
  22. In the Detection Time field, specify the duration in seconds after which the attacking endpoint is blacklisted. By default, the configuration adds an IP address to the blacklist after one minute (60 seconds). Enabled.
  23. In the Duration field, specify the amount of time in seconds that the address will remain on the blacklist. The default is 14400 (4 hours).
  24. To allow IP source blacklist entries to be advertised to edge routers so they will null route their traffic, select Allow Advertisement.
    Note: To advertise to edge routers, you must configure a Blacklist Publisher at Security > Options > External Redirection > Blacklisting for the blacklist category.
  25. Click Update to save your changes. The DoS vector is updated on the Network Security screen.
You have now configured a DoS Protection profile to analyze network packet behavior for DoS attacks, to allow specific configured attacks to be identified in system logs and reports, and to allow rate limiting of such attacks. DNS queries on particular record types you have configured in the DNS Query Attack Detection area are detected as attacks at your specified thresholds and rate increases, and rate limited as specified.
Associate the DoS profile with a virtual server to enable network DoS protection.

DoS profile attack types

You can specify specific threshold, rate increase, rate limit, and other parameters for supported network DoS attack types, to more accurately detect, track, and rate limit attacks.

Attention: All hardware-supported vectors are performed in hardware on vCMP® guests, provided that the vCMP guests have the same software version as the vCMP host.
DoS Category Attack Name Dos Vector Name Information Hardware accelerated
+ TTL <= <tunable> ttl-leq-one An IP packet with a destination that is not multicast and that has a TTL greater than 0 and less than or equal to a tunable value, which is 1 by default. To tune this value, in tmsh: modify sys db dos.iplowttl value , where value is 1-4. Yes
+ IP Option Frames ip-opt-frames IPv4 address packet with option.db variable tm.acceptipsourceroute must be enabled to receive IP options Yes
+ IPv6 extension header too large ext-hdr-too-large An extension header is too large. To tune this value, in tmsh: modify sys db dos.maxipv6extsize value , where value is 0-1024. Yes
+ IPv6 hop count <= <tunable> hop-cnt-leq-one The IPv6 extended header hop count is less than or equal to <tunable>. To tune this value, in tmsh: modify sys db dos.ipv6lowhopcnt value , where value is 1-4. Yes
+ IPv6 Extended Header Frames ipv6-ext-hdr-frames IPv6 address contains extended header frames Yes
+ Too Many Extended Headers too-many-ext-hdrs For an IPv6 address, there are more than <tunable> extended headers (the default is 4). To tune this value, in tmsh: modify sys db dos.maxipv6exthdrs value , where value is 0-15. Yes
+ Option Present With Illegal Length opt-present-with-illegal-len Option present with illegal length Yes
+ TCP Bad URG tcp-bad-urg Packet contains a bad URG flag, this is likely malicious Yes
+ TCP Option Overruns TCP Header tcp-opt-overruns-tcp-hdr The TCP option bits overrun the TCP header. Yes
+ Unknown TCP Option Type unk-tcp-opt-type Unknown TCP option type Yes
+ ICMPv4 Flood icmpv4-flood Flood with ICMP v4 packets Yes
+ ICMPv6 Flood icmpv6-flood Flood with ICMP v6 packets Yes
+ IP Fragment Flood ip-frag-flood Fragmented packet flood with IPv4 Yes
+ IPv6 Fragment Flood ipv6-frag-flood Fragmented packet flood with IPv6 No
+ TCP RST Flood tcp-rst-flood TCP RST flood Yes
+ TCP SYN ACK Flood tcp-synack-flood TCP SYN/ACK flood Yes
+ TCP SYN Flood tcp-syn-flood TCP SYN flood Yes
+ TCP Window Size tcp-window-size The TCP window size in packets exceeds the maximum. To tune this value, in tmsh: modify sys db dos.tcplowwindowsize value , where value is <=128. Yes
+ TCP SYN Oversize tcp-syn-oversize Detects TCP data SYN packets larger than the maximum specified by the dos.maxsynsize parameter. To tune this value, in tmsh: modify sys db dos.maxsynsize value . The default size is 64 and the maximum allowable value is 9216. Yes
+ UDP Flood udp-flood UDP flood attack Yes
+ ICMP Fragment icmp-frag ICMP fragment flood Yes
+ Sweep sweep Sweep on a single endpoint. You can configure packet types to check for, and packets per second for both detection and rate limiting. You can also configure automatic blacklisting for IPs that initiate sweep attacks, using the IP intelligence mechanism. No
+ Host Unreachable host-unreachable Host unreachable error Yes
+ TIDCMP tidcmp ICMP source quench attack Yes

Associating a DoS profile with a virtual server

You must first create a DoS profile separately, to configure denial-of-service protection for applications, the DNS protocol, or the SIP protocol. For application-level DoS protection, the virtual server requires an HTTP profile (such as the default http).
You add denial-of-service protection to a virtual server to provide enhanced protection from DoS attacks, and track anomalous activity on the BIG-IP® system.
  1. On the Main tab, click Local Traffic > Virtual Servers .
    The Virtual Server List screen opens.
  2. Click the name of the virtual server you want to modify.
  3. In the Destination Address field, type the IP address in CIDR format.
    The supported format is address/prefix, where the prefix length is in bits. For example, an IPv4 address/prefix is 10.0.0.1 or 10.0.0.0/24, and an IPv6 address/prefix is ffe1::0020/64 or 2001:ed8:77b5:2:10:10:100:42/64. When you use an IPv4 address without specifying a prefix, the BIG-IP® system automatically uses a /32 prefix.
  4. On the menu bar, from the Security menu, choose Policies.
  5. To enable denial-of-service protection, from the DoS Protection Profile list, select Enabled, and then, from the Profile list, select the DoS profile to associate with the virtual server.
  6. Click Update to save the changes.
DoS protection is now enabled, and the DoS Protection profile is associated with the virtual server.

Allowing addresses to bypass DoS profile checks

You can specify whitelisted addresses that the DoS Profile does not subject to DoS checks. Whitelist entries are specified on a security address list, and can be configured directly on the DoS Profile screen.
  1. On the Main tab, click Security > DoS Protection > DoS Profiles .
    The DoS Profiles list screen opens.
  2. Click the profile name you configured to open the DoS Profile settings screen.
  3. In the Default Whitelist field, begin typing the name of the address list to use as the whitelist, and select the address list when the name appears.
  4. In the Whitelist Address List field, begin typing the name of the address list to use as the whitelist, and select the address list when the name appears.
  5. To define an address list to use as a whitelist, on the right side of the screen under Shared Objects, click the + under Address Lists.
    The Address List Properties pane opens at the bottom right of the screen.
  6. Type a Name for the address list.
  7. Optionally, type a Description for the address list.
  8. In the Contents field, type an address, and click Add.
    You can type an IP address, a geographic location, or the name of another address list. Begin typing, and select the object when the name appears.
  9. Click Update to update the address list.
    If this is a new address list, type and select the address list name in the Default Whitelist field.
  10. Click Update to update the DoS Profile.
You have now configured a whitelist to bypass DoS checks for a DoS profile.

Creating a custom Network Firewall Logging profile

Create a custom Logging profile to log messages about BIG-IP® system Network Firewall events.
  1. On the Main tab, click Security > Event Logs > Logging Profiles .
    The Logging Profiles list screen opens.
  2. Click Create.
    The New Logging Profile screen opens.
  3. In the Name field, type a unique name for the profile.
  4. Select the Network Firewall check box.
  5. In the Network Firewall area, from the Publisher list, select the publisher the BIG-IP system uses to log Network Firewall events.
  6. Set an Aggregate Rate Limit to define a rate limit for all combined network firewall log messages per second. Beyond this rate limit, log messages are not logged.
  7. For the Log Rule Matches setting, select how the BIG-IP system logs packets that match ACL rules. You can select any or all of the options. When an option is selected, you can configure a rate limit for log messages of that type.
    Option Description
    Option Enables or disables logging of packets that match ACL rules configured with:
    Accept action=Accept
    Drop action=Drop
    Reject action=Reject
  8. Select the Log IP Errors check box, to enable logging of IP error packets. When enabled, you can configure a rate limit for log messages of this type.
  9. Select the Log TCP Errors check box, to enable logging of TCP error packets. When enabled, you can configure a rate limit for log messages of this type.
  10. Select the Log TCP Events check box, to enable logging of open and close of TCP sessions. When enabled, you can configure a rate limit for log messages of this type.
  11. Enable the Log Translation Fields setting to log both the original IP address and the NAT-translated IP address for Network Firewall log events.
  12. Enable the Log Geolocation IP Address setting to specify that when a geolocation event causes a network firewall action, the associated IP address is logged.
  13. From the Storage Format list, select how the BIG-IP system formats the log. Your choices are:
    Option Description
    None Specifies the default format type in which the BIG-IP system logs messages to a remote Syslog server, for example: "management_ip_address","bigip_hostname","context_type","context_name","src_ip","dest_ip","src_port","dest_port","vlan","protocol","route_domain","acl_rule_name","action","drop_reason
    Field-List This option allows you to:
    • Select from a list, the fields to be included in the log.
    • Specify the order the fields display in the log.
    • Specify the delimiter that separates the content in the log. The default delimiter is the comma character.
    User-Defined This option allows you to:
    • Select from a list, the fields to be included in the log.
    • Cut and paste, in a string of text, the order the fields display in the log.
  14. In the IP Intelligence area, from the Publisher list, select the publisher that the BIG-IP system uses to log source IP addresses, which are identified and configured for logging by an IP Intelligence policy.
    Note: The IP Address Intelligence feature must be enabled and licensed.
  15. Set an Aggregate Rate Limit to define a rate limit for all combined IP Intelligence log messages per second. Beyond this rate limit, log messages are not logged.
  16. Enable the Log Translation Fields setting to log both the original IP address and the NAT-translated IP address for IP Intelligence log events.
  17. In the Traffic Statistics area, from the Publisher list, select the publisher that the BIG-IP system uses to log traffic statistics.
  18. Enable the Active Flows setting to log the number of active flows each second.
  19. Enable the Reaped Flows to log the number of reaped flows, or connections that are not established because of system resource usage levels.
  20. Enable the Missed Flows setting to log the number of packets that were dropped because of a flow table miss. A flow table miss occurs when a TCP non-SYN packet does not match an existing flow.
  21. Enable the SYN Cookie (Per Session Challenge) setting to log the number of SYN cookie challenges generated each second.
  22. Enable the SYN Cookie (White-listed Clients) setting to log the number of SYN cookie clients whitelisted each second.
  23. Click Finished.
Assign this custom network firewall Logging profile to a virtual server.

Configuring an LTM virtual server for DoS Protection event logging

Ensure that at least one Log Publisher exists on the BIG-IP® system.
Assign a custom DoS Protection Logging profile to a virtual server when you want the BIG-IP system to log DoS Protection events on the traffic the virtual server processes.
Note: This task applies only to LTM®-provisioned systems.
  1. On the Main tab, click Local Traffic > Virtual Servers .
    The Virtual Server List screen opens.
  2. Click the name of the virtual server you want to modify.
  3. On the menu bar, click Security > Policies .
    The screen displays network firewall security settings.
  4. From the Log Profile list, select Enabled. Then, for the Profile setting, move the profiles that log specific events to specific locations from the Available list to the Selected list.
  5. Click Update to save the changes.
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