When the reference count is reduced to zero, VFR is automatically disabled.Īn interface (such as GigabitEthernet 0/0/0), VFR (input/output) is enabled onĭevice(config-if)# do show ip virtual-reassembly features Reference count to keep track of the number of features that have enabled VFR. IPSec, NAT64, and onePK enable and disable VFR internally that is, when theseįeatures are enabled on an interface, VFR is automatically enabled on thatįeature attempts to automatically enable VFR on an interface, VFR maintains a By default, NAT, Cisco IOS XE Firewall, Crypto-based Work with any feature that requires fragment reassembly (such as Cisco IOS XEįirewall, NAT, and IPSec). Within the specified time, the timer expires and the IP datagram and all of its If the IP datagram does not receive all of the fragments Maximum threshold values being configured, each IP datagram is associated withĪ managed timer. Number of fragments per datagram is reached, subsequent fragments are dropped,Īnd the global statistics item “ReassTooManyFrags” is incremented by one. Subsequent fragments are dropped, and the global statistics item “ReassDrop” is Number of datagrams that can be reassembled at any given time is reached, all Ip virtual-reassembly-out command to specify these Of IP datagrams that are being reassembled and the number of fragments per Overflow and control memory use, configure a maximum threshold for the number VFR drops all fragments within a fragment chain if an overlapĪttack-In this type of denial-of-service (DoS) attack, the attacker canĬontinuously send a large number of incomplete IP fragments, causing theįirewall to consume time and memory while trying to reassemble the fake IP fragments, it might create wrong IP packets, causing the memory to overflow Offset in the noninitial IP fragment packets. “VFR-3-TINY_FRAGMENTS” is logged to the syslog server.įragment attack-In this type of attack, the attacker can overwrite the fragment VFR drops all tiny fragments, and an alert message such as Thus, the ACL rules that have been configured for those fields do not match. Information About Virtual Fragmentation Reassemblyįor detecting and preventing the following types of fragment attacks:Īttack-In this type of attack, the attacker makes the fragment size smallĮnough to force Layer 4 (TCP and UDP) header fields into the second fragment. Nexus devices), VFR may fail and fragments may be dropped.
#IP VIRTUAL REASSEMBLY SERIES#
If fragments within an IPĭatagram are sent to different devices due to load balancing (per packet loadīalancing or include ports on Cisco Catalyst 6500 Series Switches or Cisco Process requires all fragments within an IP datagram. This performance impact varies depending on the number of concurrent IP datagrams that are being reassembled. VFR causes a performance impact on the basis of functions such as packet copying, fragment validation, and fragment reorder. Restrictions for Virtual Fragmentation Reassembly To access Cisco Feature Navigator, go to An account on is not required.
#IP VIRTUAL REASSEMBLY SOFTWARE#
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. Your software release may not support all the features documented in this module.
#IP VIRTUAL REASSEMBLY HOW TO#
Reassembly (VFR) is automatically enabled by some features (such as NAT, Cisco
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