Allied Telesis AT-S62 - Manual (Page 338)

Chapter 18: Denial of Service Defenses
338 Section II: Advanced Operations
Note
This defense mechanism requires some involvement by the switch’s
CPU, though not as much as the Teardrop defense. This will not
impact the forwarding of traffic between the switch ports, but it can
affect the handling of CPU events, such as the processing of IGMP
packets and spanning tree BPDUs. For this reason, Allied Telesyn
recommends limiting the use of this defense, activating it only on
those ports where an attack is most likely to originate.
Also note that an attacker can circumvent the defense by sending a
stream of ICMP Echo (Ping) requests with a size of 63,488 to 65,534 bits.
A large number of requests could overwhelm the switch’s CPU.
IP Options
Attack
In the basic scenario of an IP attack, an attacker sends packets containing
bad IP options. There are several different types of IP option attacks and
the AT-S62 management software does not distinguish between them.
The defense mechanism counts the number of ingress IP packets
containing IP options received on a port. If the number exceeds 20
packets per second, the switch considers this a possible IP options attack
and does the following occurs:
ˆ It sends a SNMP trap to the management workstations.
ˆ The switch port discards all ingress packets containing IP options for
one minute.
This defense mechanism does not involve the switch’s CPU. You can
activate it on as many ports as you want without it impacting switch
performance.
Note
This defense does not actually check IP packets for bad IP options.
Consequently, it can only alert you to a possible attack.
Mirroring Traffic
The Land, Teardrop, Ping of Death, and IP Options defense mechanisms
can copy the examined traffic to a mirror port for further analysis with a
data sniffer or analyzer. This feature differs slightly from port mirroring in
that prior to an actual violation of a defense mechanism, only the packets
examined by a defense mechanism, rather than all packets, are mirrored
to the destination port. Should a violation occur, then all ingress packets
on the port where the violation occurred are mirrored.
As an example, activating the mirroring feature in conjunction with the
Teardrop defense on a port sends all examined ingress fragmented IP
traffic to the destination mirror port. If the switch detects a violation, all
ingress packets on the port are copied to the mirror port during the 60
seconds that the port is blocked.