ITS Master Plan - Development Services - City of Oxnard

F INAL S TRATEGIC D E P L O Y M E N T P LAN6.3.2 IP Address ClassesAs the Internet has evolved so have IP schemes. Two schemes worth noting for this discussionare Classful (as discussed above) and Classless (CIDR) schemes. For the purpose of thisdiscussion it is suffice to say that Classful schemes are less in use today and CIDR notation isused now. Since Classful schemes are basically “address hogs”, CIDR -- Classless InterDomain Routing, was essentially invented years ago to keep the Internet from running out of IPaddresses. Network Engineers realized that addresses could be conserved if the class systemwas eliminated. By accurately allocating only the amount of address space that was actuallyneeded for a network, the address space crisis could be avoided, at least until all the4,294,967,296 IPv4 Internet addresses are used up.Under CIDR notation, the subnet mask notation is reduced to “simplified shorthand” and is notconstrained by specific class values. Instead of spelling out the bits of the subnet mask, it issimply listed as the number of 1s bits that start the subnet mask. For example, instead ofwriting an address and subnet mask as “Address 192.60.128.0 with a Subnet Mask255.255.252.0”; the network address would be written simply as: 192.60.128.0/22(11111111.11111111.11111100.00000000 = 22 1’s) which indicates starting address of thenetwork, and number of 1s bits (22) in the network portion of the address. The use of a CIDRnotated address is actually the same as for a Classful address. Classful addresses can easilybe written in CIDR notation (Class A = /8, Class B = /16, and Class C = /24), if you so chose.6.3.3 Private SubnetsThere are three IP network addresses reserved for private networks. The addresses are10.0.0.0, Subnet Mask 255.0.0.0, 172.16.0.0, Subnet Mask 255.240.0.0, and 192.168.0.0,Subnet Mask 255.255.0.0. These addresses are also notated as 10.0.0.0/8, 172.16.0.0/12, and192.168.0.0/16 in CIDR notation. When connecting to the Internet, these private subnets canbe used by anyone setting up internal IP networks, such as a City traffic network, lab or homeLAN behind a NAT or proxy server or a router. It is always safe to use these addresses becauserouters on the Internet by default will never forward packets coming from these addresses. Forthis reason it is always best to use these address ranges for any private network setup.6.3.4 VLANs – Virtual LANsLike Subnets, VLANs are created to provide the segmentation in LAN configurations. VLANsserve to address issues such as scalability, security, and network management. Routers inVLAN networks provide broadcast filtering, security, address summarization, and traffic flowmanagement to control the network VLAN traffic. Switches do not bridge IP traffic betweenVLANs, for this reason whenever VLANs are employed; routers or switches with routingcapabilities are required. Virtual LANs are essentially Layer 2 implementations, whereas IPsubnets are Layer 3. In a campus LAN employing VLANs, a one-to-one relationship is oftenimplied between VLANs and IP subnets. Although it is possible to have multiple subnets on oneVLAN or have one subnet spread across multiple VLANs. Virtual LANs and IP subnets providean independent Layer 2 and Layer 3 method that maps to one another and this correspondenceis useful during the network design process. For the City of Oxnard, it is recommended that thenetwork design VLANs be configured per network traffic function and a switch with routingcapabilities shall be employed for routing requirements. This effort should be coordinated withthe Oxnard IT department.Page 49 of 51 May 2008