PowerConnect B-Series FCX Configuration Guide
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Protecting against TCP SYN attacks
38
•
Blind TCP reset attack using the synchronization (SYN) bit
•
Blind TCP packet injection attack
The TCP security enhancement is automatically enabled.
Protecting against a blind TCP reset attack using the RST bit
In a blind TCP reset attack using the RST bit, a perpetrator attempts to guess the RST bits to
prematurely terminate an active TCP session.
To prevent a user from using the RST bit to reset a TCP connection, the RST bit is subject to the
following rules when receiving TCP segments:
•
If the RST bit is set and the sequence number is outside the expected window, the Dell
PowerConnect device silently drops the segment.
•
If the RST bit is exactly the next expected sequence number, the Dell PowerConnect device
resets the connection.
•
If the RST bit is set and the sequence number does not exactly match the next expected
sequence value, but is within the acceptable window, the Dell PowerConnect device sends an
acknowledgement.
Protecting against a blind TCP reset attack using the SYN bit
In a blind TCP reset attack using the SYN bit, a perpetrator attempts to guess the SYN bits to
prematurely terminate an active TCP session.
To prevent a user from using the SYN bit to tear down a TCP connection, in current software
releases, the SYN bit is subject to the following rules when receiving TCP segments:
•
If the SYN bit is set and the sequence number is outside the expected window, the Dell
PowerConnect device sends an acknowledgement (ACK) back to the peer.
•
If the SYN bit is set and the sequence number is an exact match to the next expected
sequence, the Dell PowerConnect device sends an ACK segment to the peer. Before sending
the ACK segment, the software subtracts one from the value being acknowledged.
•
If the SYN bit is set and the sequence number is acceptable, the Dell PowerConnect device
sends an acknowledgement (ACK) segment to the peer.
Protecting against a blind injection attack
In a blind TCP injection attack, a perpetrator tries to inject or manipulate data in a TCP connection.
To reduce the chances of a blind injection attack, an additional check on all incoming TCP
segments is performed.
Displaying statistics about packets dropped
because of DoS attacks
To display information about ICMP and TCP SYN packets dropped because burst thresholds were
exceeded, enter the following command.
Содержание PowerConnect B-FCXs
Страница 1: ...53 1002266 01 18 March 2011 PowerConnect B Series FCX Configuration Guide ...
Страница 136: ...94 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Viewing information about software licenses 4 ...
Страница 228: ...186 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 229: ...PowerConnect B Series FCX Configuration Guide 187 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 230: ...188 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 248: ...206 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IPv6 management commands 7 ...
Страница 346: ...304 PowerConnect B Series FCX Configuration Guide 53 1002266 01 802 1s Multiple Spanning Tree Protocol 8 ...
Страница 374: ...332 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Jumbo frame support 9 ...
Страница 424: ...382 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Virtual Switch Redundancy Protocol VSRP 10 ...
Страница 568: ...526 PowerConnect B Series FCX Configuration Guide 53 1002266 01 CLI examples 14 ...
Страница 588: ...546 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Sample application 15 ...
Страница 674: ...632 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Enabling or disabling layer 2 switching 19 ...
Страница 684: ...642 PowerConnect B Series FCX Configuration Guide 53 1002266 01 VLAN based mirroring 20 ...
Страница 724: ...682 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Reading CDP packets 23 ...
Страница 768: ...726 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing cached LLDP neighbor information 24 ...
Страница 930: ...888 PowerConnect B Series FCX Configuration Guide 53 1002266 01 26 ...
Страница 948: ...906 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Configuring MLD snooping 27 ...
Страница 962: ...920 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying CPU utilization statistics 28 ...
Страница 1022: ...980 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying OSPF information 29 ...
Страница 1142: ...1100 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing diagnostic buffers 30 ...
Страница 1258: ...1216 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Using Secure copy with SSH2 33 ...
Страница 1314: ...1272 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying port security information 35 ...
Страница 1348: ...1306 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Example configurations 36 ...
Страница 1406: ...1364 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IP source guard 39 ...
Страница 1422: ...1380 PowerConnect B Series FCX Configuration Guide 53 1002266 01 SNMP v3 Configuration examples 40 ...