Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Network tap wikipedia , lookup
Dynamic Host Configuration Protocol wikipedia , lookup
Computer network wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Airborne Networking wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
From Subnetting to VLSM Classful vs. Classless Routing VLSM Explained Why VLSM Suggestions for Teaching VLSM Credits • Virginia Phillips, CCNA, CCAI – Instructor CCNP classes, Youngstown State University • Edmund Ickert, CCNA, CCAI – Instructor CCNA classes, Youngstown State University, completed all CCNP courses • Sandeep Kolwalkar, CCNA – Graduate Student, taking CCNP classes, Youngstown State University Classful vs Classless Routing • Classful routing assigns address space based on the value in the first octet of the 32-bit IP address – RFC Number 791 (760) – Class based on value in first octet value – Receiving router ands subnet mask to determine subnet • Class A • Class B • Class C 0-126 128-191 192-223 • Classless routing ignores classes and uses a CIDR value (number of 1s in network mask) to identify the network – CIDR transmitted as part of IP address – RFC 1517-1520 – Network portion not restricted to entire octet Classless Routing Address Space Issues • Class A and Class B = 75% address space – < 17000 organizations can be assigned address • Class C = 12.5% available address space – Each network limited to 254 maximum hosts – Potential routing problems • Too many network addresses in routing table • Extra work for CPU; more memory required Private Addressing RFC 1918 • Class A 10.0.0.0 to 10.255.255.255 • Class B 172.16.0.0 to 172.31.255.255 • Class C 192.168.0.0 to 192.168.255.255 – Used to extend life of IPv4 addressing – Note: Do not mix private and public IP address in same network – it will create discontiguous subnets which causes problems Classless Routing • Another method used to extend the life of IPv4 • Temporary solution to deal with lack of network numbers • Uses bit mask (NOT 1st octet value) to determine network portion of address • Uses CIDR to summarize routing information; CIDR transmitted with IP address • Enables the use of supernets and/or route aggregation and summarization – Smaller routing tables – Reduced router memory requirements – Reduced number of CPU cycles for routing processes Routing Protocols • Classful – can’t send subnet information in updates – RipV1, IGRP, EGP, BGP3 – also can’t support discontiguous subnets • Classless – Sends CIDR in updates sent via multicasting – Can authenticate • RipV2 (RFC 1058), EIGRP, OSPF, IS-IS, BGP4 – RIPV2 and EIGRP automatically summarize at classful boundary unless you configure differently » RouterA (config-router) no auto-summary VLSM Variable Length Subnet Masking • Subnets a subnet • Can support multiple contiguous routes • Can use more than one subnet mask for address space allocated to a firm • Makes more efficient use of available address space – Creates two-host subnets for serial links Why Not IPv6? 128-bit address space • Slow to arrive • IPv4 revitalized with new features – VLSM, NAT/PAT, IP unnumbered, private addresses • Not supported by legacy systems • Requires new software (and hardware) • Requires retraining Zero Subnet (Ones too?) • Zero subnet – IOS 12.X and higher supports by default – Configure pre-12.x IOS routers • RouterA(config) IP subnet-zero – DO Use it to increase address space available • Ones subnet – Defined in RFC 1878 – Can use it; however can cause problems – Avoid using unless you absolutely need it Route Aggregation Example 1 • Assume you are using three Class B private addresses – 172.16.0.0 – 172.17.0.0 – 172.18.0.0 10101100.000100 00.0.0 10101100.000100 01.0.0 10101100.000100 10.0.0 • Common bits are 10111000.0001 – 8 bits in first octet + 6 bits in second octet = 14 – CIDR is 14 • Insulates upstream routers from route flapping problems (serial link problem) Route Aggregation Example 2 • Assume you are using three Class A private addresses – 10.20.0.0 – 10.21.0.0 – 10.22.0.0 00001010.000101 00.0.0 00001010.000101 01.0.0 00001010.000101 10.0.0 • Common bits are 00001010.000101 – 8 bits in first octet + 6 bits in second octet = 14 – CIDR is 14 Supernet Example 1 • Company assigned 4 contiguous Class C networks – – – – 200.10.10.0 200.10.11.0 200.10.12.0 200.10.13.0 11001000.00001010.00001010.0 11001000.00001010.00001011.0 11001000.00001010.00001100.0 11001000.00001010.00001101.0 • Summarize on common bits = 21 • Appears in routing table as 200.10.10.0/21 Supernet Example 2 • Company assigned 4 contiguous Class C networks – – – – 200.10.101.0 200.10.102.0 200.10.103.0 200.10.104.0 11001000.00001010.11001001.0 11001000.00001010.11001010.0 11001000.00001010.11001011.0 11001000.00001010.11001100.0 • Summarize on common bits = 21 • Appears in routing table as 200.10.101.0/21 Network Subnet Example • 128.1.0.0/16 is assigned IP address – 130 subnets needed – Requires use of third octet for subnet values • 1,2,3,4, …., 254 – Each subnet can support 254 hosts – Each serial connection will use a subnet and waste 252 address spaces Network Subnet Example • Assigned IP address is 128.1.0.0 – Scenario - 130 subnets needed and 20 serial connections used now – Requires use of third octet for subnets • 128.1.0.0 to 128.1.254.0, subnet mask 255.255.255.0 or CIDR 24 • Each subnet can support 254 hosts • To use an entire subnet for a serial connection would waste 252 address spaces and we have 20 now – SO….. Network Subnet Example Subnet the Subnet • Use subnets 128.1.0.0 to 128.1.129.0 for needed subnets with a CIDR of 24 • Subnet subnet 128.1.130.0 using CIDR 30 – – – – – 128.1.130.0/30 128.1.130.4/30 128.1.130.8/30 ……………….. 128.1.130.252/30 Network 2 Subnet Example • A Network address of 200.10.20.0 is assigned – Subnet with a CIDR of 26 • 200.10.20.0, 200.10.20.64 (62 hosts) – Subnet subnet 128 with a CIDR of 28 • 200.10.20.128, 200.10.20.144, 200.10.20.160 (14 hosts) – Subnet subnet 200.10.20.176 with a CIDR of 30 • 200.10.20.176, 200.10.20.180, 200.10.20.184 (2 hosts) • Can summarize (aggregate) on – 200.10.20.0/26 Using VLSM • Variable Length Subnet Masking – allows division of address space based on the size of networks – Start with network requiring the most addresses – Create a subnet mask (use CIDR – Classless InterDomain Routing – number) – Subnet the subnet as needed to provide address space required for other subnets • Be logical – start at beginning or end or address space • Addresses must be contiguous to enable route summarization Teaching Tips 1 • Make certain students understand subnetting – Provide students with a mix of subnetting problems using Class A, B, and C addresses and different numbers of bits borrowed to ensure they do understand • Show relationship of CIDR number of subnet mask Teaching Tips 2 • Explain reasons for using VLSM • Explain route aggregation (summarization) • Explain supernetting • Show how to summarize using common bits • Show how to supernet using common bits Teaching Tips 3 • Show a simple VLSM example using the third octet – First subnet for 255 subnets with 254 hosts; CIDR = 24 – Then subnet one of the subnets for subnets with CIDR of 28 • Subnet 200.16, 200.32, 200.48, etc. – Then subnet one of the subnets for subnets to use for serial lines and a CIDR of 30 • Subnet 201.4, 201.8, 201.12, 201.16, etc. Teaching Tips 4 • Show a second example using the fourth octet – Subnet for 8 subnets with a CIDR of 27 • Subnets 0, 32, 64, 96, 128, 160, 192, 224 – Subnet subnet 96, 128, and 160 with a CIDR of 28 • Subnets 96, 112, 128, 144, 160, 176 – Subnet subnets 192 and 224 with a CIDR of 30 • Subnets 192, 196, 200, 204, 208, 212, 216, 220, 224, 228, 232, 236, 240, 244, 248, 252 Teaching Tips 5 • Show examples of divided address spaces – Do not use slides – use hard copy and give students a copy • Give several problems moving from a very simple problem to a very complex problem – Provide answers for each problem for students to check as problem is completed