Posts Tagged ‘ address

ANDing IP Address Subnets 22 July 2008 at 10:35 am by admin

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

+ 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

+ EIGRP routing basic commands By admin 20 June 2008 at 11:12 pm and have Comments Off

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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+ Switch security & common attacks By admin 18 June 2008 at 5:13 pm and have Comments Off

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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