ANDing: (Boolean and)
Computers use digital logic to interpret IP addresses
This logic is called a Boolean AND. It is the comparison of two bits to yield:
1 & 1 = 1
1 & 0 = 0
0 & 1 = 0
0 & 0 = 0
Any # ANDed with 0 is always 0
Any # ANDed with 1 is always the original #
The ANDing of an IP address & mask = network address
A subnet mask “masks” the host bits of an IP address
Routers and hosts use ANDing to determine networks
It is frequently necessary to be able to use ANDing
You will need to know how routers make routing decisions
Start with the IP address & mask above/below each other
10101100.00010000.00010100.00100011 172.16.24.35 (Host)
11111111.11111111.11111111.111 00000 255.255.255.224
——————————————————
10101100.00010000.00010100.00100000 172.16.23.32 (network address for
host /27)
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Tags: vlan, ip, wan, cisco, study, switch
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IP addressing
By admin 16 July 2008 at 11:53 pm and have Comments Off
IP Addressing Structure:
IPv4 Address = 32 bit # written as dotted decimals
Always paired with a 32 bit mask
Computers evaluate &
E.G. 10101000 <- high-order that side, -> low order this side.
Network = group of hosts with identical network addresses.
Some portion of the low-order bits = host address.
From our 32 bits, the # of bits used in the host portion determines how many hosts we can have in our network.
E.G. if 200 hosts in our network. We need enough bits in the host portion to make 200+ numbers
2^7 = 128, 2^8 = 256, therefore 8 bits minimum are required to get 200+ hosts.
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Tags: vlan, cisco, switch, ip, router, wan
Bitmindframes cisco networking study guides
EIGRP Commands
Enabling EIGRP Routing
Router(config)# router eigrp AS number (Must be the same on all routers)
Router(config-router)# network network-address [wildcard mask]
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Security on a switch
eMac address flooding or overflow attacks
Switches learn a source MAC address from the MAC address table
If a frame enters a switch and it does not find the destination MAC address in the table, the switch acts like a hub and floods it out all ports. Mac address tables have a limited size.
MAC address flooding uses this limitation to bombard the switch with fake addresses until the table is full. The switch then enters fail-open mode and will act like a hub.
As a result, an attacker can see all of the frames passing through the switch.
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