cisco ccna 200-301 exam questions

cisco ccna 200-301 exam questions.First, a wildcard mask is not a subnet mask. Like IP addresses and subnet masks, the length of a wildcard mask is 32 bits. Table 21.3 compares the meanings of the bit values in wildcard masks and subnet masks. In the wildcard mask, 0 indicates that the ground in the ACL statementChapter 21 Access Control Lists 555address and the corresponding bit of the IP address in the packet must be the same; a 1 means that the address in the ACL statement and the corresponding bit of the IP address in the packet do not have to be the same. The wildcard mask tells the router which bits of the address in the ACL statement and the IP address in the packet must be the same. In effect, a wildcard mask is like an inverted subnet mask; for example, to match all addresses in a subnet or network, you can invert the bits of its subnet mask (turning 1 into 0 and 0 into 1) to get the desired wildcard mask.Let's see an example of converting a subnet mask to a wildcard mask. Suppose you have a subnet mask 255.255.0.0, which is represented in binary as 11111111.11111111.0000000000.00000000. To convert it to a wildcard mask, invert the digits and the result is T: 00000000.00000000.111111111.11111111; then, convert it to Decimal representation: 0.0.255.255o This is the subnet mask255.255.0.0 corresponds to the wildcard mask. This wildcard mask tells the router to continue processing the ACL statement if the IP address in the statement is the same as the first 16 bits of the IP address in the packet, and to process the next ACL statement otherwise. As you can see, this example is very simple.Let's look at a more difficult example, assuming that you want to match all addresses in a subnet with a subnet mask of 255.255.240.0. The binary representation of this subnet mask is as follows: 11111111.11111111.111110000.00000000, where bytes 1, 2, and 4 are easy to convert, but it is byte 3 that is more difficult. To convert this subnet mask to a wildcard mask, invert all the bits and the result is as follows: 00000000.00000000.0000001111.111111110 Next, convert it to decimal and the final wildcard mask is 0.0.15.255.However, in the second example, the third byte is more difficult to convert. The following method simplifies the conversion from subnet mask to wildcard mask: when performing the conversion, the value of each byte in the subnet mask is subtracted from 255, and the result is the value of the corresponding byte of the wildcard mask. For the example of a subnet mask of 255.255.240.0, this quick method is used. But this. First byte: . Second byte: 255-255 (value of the first byte of the subnet mask) = 0 (value of the first byte of the wildcard mask) o255-255 . Third byte: (value of the second byte of the subnet mask) = 0 (value of the second byte of the wildcard mask) 255-240 (value of the sub . Fourth byte: value of the third byte of the netmask) = 15 (value of the third byte of the wildcard mask) 255-0 (subnet mask(value of the fourth byte) = 255 (value of the fourth byte of the wildcard mask). This gives you the wildcard mask 0.0.15.240. using this simple technique, converting between a subnet mask and a wildcard mask is a snap.The wildcard mask is used to specify which bits of the IP address in the ACL statement and the IP address in the packet must be the same. A 0 indicates that the corresponding bits must be the same, and a 1 indicates that the corresponding bits are irrelevant. If you want to match an entire subnet, you can invert its subnet mask. A quicker method is to subtract 255 from the value of each byte of the subnet mask to get the value of the corresponding byte of the wildcard mask. This trick is used in many ACL-related exam questions.