H3C Technologies H3C S5120 Series Switches - Manual (Page 217)

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Follow these steps to enable the SYN Cookie feature:
To do... Use the command... Remarks
Enter system view system-view —
Enable the SYN Cookie feature tcp syn-cookie enable
Required
Disabled by default.
z If MD5 authentication is enabled, the SYN Cookie feature will not function after enabled. Then, if
you disable MD5 authentication, the SYN Cookie feature will be enabled automatically.
z With the SYN Cookie feature enabled, only the MSS, instead of the window’s zoom factor and
timestamp, is negotiated during TCP connection establishment.
Enabling Protection Against Naptha Attacks
Naptha attacks are similar to the SYN Flood attacks. Attackers can perform Naptha attacks by using the
six TCP connection states (CLOSING, ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, LAST_ACK, and
SYN_RECEIVED), and SYN Flood attacks by using only the SYN_RECEIVED state.
Naptha attackers control a huge amount of hosts to establish TCP connections with the server, keep
these connections in the same state (any of the six), and request for no data so as to exhaust the
memory resource of the server. As a result, the server cannot process normal services.
Protection against Naptha attacks reduces the risk of such attacks by accelerating the aging of TCP
connections in a state. After the feature is enabled, the device periodically checks the number of TCP
connections in each state. If it detects that the number of TCP connections in a state exceeds the
maximum number, it will accelerate the aging of TCP connections in this state.
Follow these steps to enable the protection against Naptha attack:
To do... Use the command... Remarks
Enter system view system-view —
Enable the protection
against Naptha attack
tcp anti-naptha enable
Required
Disabled by default.
Configure the maximum of
TCP connections in a
state
tcp state { closing |
established | fin-wait-1 |
fin-wait-2 | last-ack |
syn-received }
connection-number number
Optional
5 by default.
If the maximum number of TCP
connections in a state is 0, the
aging of TCP connections in this
state will not be accelerated.
Configure the TCP state
check interval tcp timer check-state
timer-value
Optional
30 seconds by default.