Advanced IP Addressing CS-765 A Aspects Of Systems Administration Spring-2005 Instructure: Jan Schauman Stevens Institute Of Technology, NJ. Prepared By: Modh, Jay A. M.S. NIS SID: 999-14-0352 Date: 05/02/2005 1
Objective Advanced IP Address Management: Subnetting Fixed-length subnet masking(flsm) Variable-length subnet masking (VLSM) Classless interdomain routing (CIDR) Route summarization (Supernatting) IP Unnumbered 2
IP Addresses IP Address consists of 4 binary octets. Total length of IPv4 Address is 32-bits. There are Five classes of IP Addresses: Class A First bit of first octet Starts with 0 0000 0000-0111 1111 0-127 (decimal) Class B First 2 bits of first octet starts with 10 1000 0000-1011 1111 128-191(decimal) Class C First 3 bits of first octet starts with 110 1100 0000-1101 1111 192-223(decimal) Class D First 4 bits of first octet starts with 1110 1110 0000-1110 1111 224-239(decimal) Class E First 4 bits of first octet starts with 1111 1111 0000 1111 1111 239-255(decimal) 3
Network ID/Host ID Class A IP Address: First Octet Network ID : Max. possible networks : 2 8-1 = 127 Exception: 127.0.0.0 is loopback address Three Octets Host ID : Max. possible hosts : 2 24 = 16,777,214 Class B IP Address: First 2 Octet Network ID : Max. possible networks : 2 16 =16384. Two Octets Host ID : Max. possible hosts : 2 16 = 65,334. Class C IP Address: First 3 Octet Net. ID: Max. possible networks :2 24 = 16,777,214. Two Octets Host ID : Max. possible hosts : 2 8 = 128. Class D IP Address: Multicast groups. Class E IP Address: Research purposes. 4
Subnet Mask Breaking one large groups into Smaller Subnetworks. Better Logical organization of IP addresses. A subnet mask is a 32-bit number. Itacts as a counterpart to the IP address. Each bit in the mask corresponds to its counterpart bit in the IP address. Logical ANDing is applied to the address and mask. If a bit in the IP address corresponds to a 1 bit in the subnet mask, the IP address bit represents a network number. If a bit in the IP address corresponds to a 0 bit in the subnet mask, the IP address bit represents a host number. Class A: 255.0.0.0 Class B: 255.255.0.0 Class C: 255.255.255.0 Class D: - - - - - - - - - - Class E: - - - - - - - - - - 5
6 subnets : Subnet bits=2 n 2 =no. of subnets, n=3. Max. possible hosts = 2 5-2 =30 Core ISP 192.168.1.0/24 Note: 192.168.1.0/27 & 192.168.1.224/27 Can not be used n/w ID or host ID with all 0 s & 1 s can t be used on WAN FLSM 192.168.1.32/27 192.168.1.96/27 192.168.1.96/27 192.168.1.64/27 192.168.1.128/27 192.168.1.192/27 SM: 255.255.255.224(111 0 0000) 192.168.1.64/29 192.168.1.72/29 192.168.1.80/29 192.168.1.88/29 VLSM SM: 255.255.255.248(111 1 1000) 192.168.1.72/24 192.168.1.76/24 VLSM SM: 255.255.255.252(1111 1100) 6
Classless/Classful Routing Protocols Routers in a variably subnetted network to properly update each other, they must send masks in their routing updates. Without subnet information in the routing updates, routers would nothing but the address class and their own subnet mask to go on. Only routing protocols that ignore the rules of address class and use have classless prefixes work properly with VLSM. Classful routing protocols : RIPv1, IGRP, EGP, BGP3 They don t send subnet info. in updates, but only the address class. Classless routing protocols: RIPv2, EIGRP, OSPF, BGP4,IS-IS They send subnet information in updates. Supports VLSM CIDR, Supernatting etc.. 7
IP Address crisis IETF re-tooled IPv4 using following techniques: CIDR Route Aggregation Supernatting Summarization Replacement of classful addressing with a more flexible and less wasteful classless scheme. Enhanced route aggregation, also known as supernetting or summarization Supernetting, which is the combination of contiguous network addresses into a new address defined by the subnet mask 8
Route Summarization More efficient routing Reduced number of CPU cycles when recalculating a routing table or when sorting through the routing table entries to find a match Reduced router memory requirements 9
Private Addressing TCP/IP is the dominant routed protocol in the world, most network applications and operating systems offer extensive support for it. Many private networks exist alongwith public networks, so using any random IP address would result in wastage of IP address. RFC 1918 sets aside three blocks of IP addresses for private or internal use: A Class A range 10.0.0.0 to 10.255.255.255 A Class B range 172.16.0.0 to 172.31.255.255 A Class C range 192.168.0.0 to 192.168.255.255 10
NAT Network Address Translation A NAT-enabled device, such as a UNIX computer or a Cisco router, operates at the border of a stub domain. A host inside the stub domain wants to transmit to a host on the outside, it forwards the packet to the NAT-enabled device. The NAT process then looks inside the IP header and, if appropriate, replaces the inside IP address with a globally unique IP address. NAT does the following: Receives IP request. Checks the current table of network address translations. Replaces the destination address with the original inside source. 11
IP Unnumbered (For Classful Routing protocols) If the network runs Classful Routing Protocol than IPunnumbered might be the only solution to maximize the addresses. When a serial interface is configured for IPunnumbered, it does not need its own address. This is because it borrows the IP address of another interface, usually a LAN interface or loopback interface. Configuring IP unnumbered on an interface has two ground rules: The interface is both serial and connected by way of a point-to-point link. The same major network with the same mask is used to address the LAN interfaces that lend their IP address on both sides of the WAN link. 12
IPv6 IPv6 is an alternative and a solution to the IPv4 address crisis. It will not be easy for organizations deeply invested in the IPv4 scheme to migrate to a totally new architecture IPv6 covers issues such as the following (RFC1752): Address depletion Quality of service Address autoconfiguration Authentication Security Growth in Routing tables so as IP addresses 13
References http://www.cisco.com/univercd/home/home.htm http://www.cisco.com/warp/public/701/3.html CCIE Routing & Switching by Jeff Doyle. TCP/IP Networking guide, by Comer. 14