Cisco Certifications Tutorials

22 http:\\ciscocertifications.info automatically becomes part of our Subnetwork ID (172.16.3). We know by the table that an 11-bit subnet mask will have 30 hosts and 32 addresses in each range. Since we are subnetting more than 8- bits, the four octet of our subnet will always begin with 0. So the first 32 Ip address available to us in 172.16.3 are 172.16.3.0 - 172.16.3.31. Our given IP address (172.16.3.57) is not in this range. The next range of 32 IP addresses is 172.16.2.32 - 172.16.3.63. Bingo...This is the subnet we are looking for. We know that the first address in the subnet range is always the Network ID (172.16.3.32). The next 30 are all valid hosts (172.16.3.33 - 172.16.3.62). The remaining address (172.16.3.63) is our broadcast address. QUESTION: You have a class C network address of 192.158.17.0. You need the largest possible number of subnets with up to 12 hosts on each. Which subnet mask would you use? ANSWER: 255.255.255.240 (look at the table) QUESTION: You have a Network ID of 172.191.0.0. with 8 subnets. You need to allow for the larg- est possible number of hosts per subnet. Which subnet mask would you use? ANSWER: 255.255.240.0 (look at the table) Private IP Addresses You can use certain IP addresses privately within you own Intranet as long as they are not seen by the global community. These addresses are listed below: · 10.0.0.0 · 172.16.0.0 · 192.168.0.0 *Keypoints: We highly recommend you quickly draw the above IP tables when you first enter the testing room. You are going to have to know this information. For the Class B table, the key is to memorize the first two columns (# of bits and subnet mask). For the 3 rd column (Subnets), you just have to memo- rize the "2" in the first row. After that you can just use the formula (previous number x 2 + 2 = next entry). For example, the next row would be 2 x 2 + 2 = 6. The fourth column is easy, it is just the inverse or opposite of the 3 rd column. Turn the 3 rd column upside down and you have the forth col- umn. The fifth column (Range) is pretty easy also. Just remember that the first row is "64". Then as you go down the column use the formula (previous number divided by 2) until you get to the "1". Then start over again with "128" and divide by 2 again as you go down the column. Know that 6 bits of subnetting is the most you can have with a class C address. Know the three ranges of Private IP Addresses above. Know that it is the subnet mask that actually determines what part of the IP address that is the Net- work Number and what part is the Host Node. Enabling IP Routing IP routing is enabled by default on Cisco routers. To enable IP on an interface, you have to be in the interface configuration mode: Router(config-if)# ip address <IP address><Subnet Mask> Add static IP routes with: ip route <network> <mask> <address | interface > <admin distance> ip default-network <network>