As part of a reconnaissance attack, an attack that in itself may not be damaging, but is used to gather information for future, more destructive attacks.
RFC 3704 (an updated version of RFC 2827) recommends that packets from the following network ranges be prohibited from entering your network:
0.0.0.0 /8
10.0.0.0 /8 (RFC 1918 Class A private range)
127.0.0.0 /8 (loopback address range)
172.16.0.0 /12 (RFC 1918 Class B private range)
192.168.0.0 /16 (RFC 1918 Class C private range)
224.0.0.0 /4 (reserved for IP multicasts)
240.0.0.0 /4 (RFC 1918 Class E private range)
Blocking these address ranges for incoming traffic on your network's perimeter routers is sometimes called "2827 filtering" or "3704 filtering", referring to the original and updated RFCs that discuss this topic in a great deal of detail.
CCNP / BSCI Exam:
In the following configuration, what happens if you leave the subnets option out of the redistribution command?
R3(config)#router ospf 1
R3(config-router)#redistribute rip subnets
R3(config-router)#redistribute connected subnets
Answer: Subnets will not successfully be redistributed into OSPF.
CCNP / BCMSN Exam:
What's the difference between Root Guard, BDPU Guard, and Loop Guard?
Answer: When a port is running Root Guard, no switch found off that port can become the root switch. When a superior BPDU is received on such a port, here's what you'll see:
00:26:46: %SPANTREE-2-ROOTGUARD_BLOCK: Root guard blocking port FastEthernet0/24 on VLAN0023.
If any BPDU comes in on a port that's running BPDU Guard, the port will be shut down and placed into error disabled state, shown on the switch as err-disabled.
CCNP / ONT Exam:
Marking and classification often work hand-in-hand, but they're not quite the same thing. Define each term.
Answer: Classification identifies a certain type of traffic, while Marking is assigning a value to that class of traffic.
Look for free tutorials and more Cisco certification exam question sets on my website as well as this one!
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