1 / 11

Internet Networking recitation #1

Internet Networking recitation #1. Subnet + CIDR. Administrative Information. Course site: webcourse.cs.technion.ac.il/236341 Grading policy: 15% homeworks + 85% final exam 6 home assignments.  Submission is in pairs. Assistants: Anna Levin Phone:   (829)4306

miracle
Download Presentation

Internet Networking recitation #1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Internet Networkingrecitation #1 Subnet + CIDR Spring Semester 2009, Dept. of Computer Science, Technion

  2. Administrative Information • Course site: webcourse.cs.technion.ac.il/236341 • Grading policy: • 15% homeworks + 85% final exam • 6 home assignments.  • Submission is in pairs. • Assistants: • Anna Levin • Phone:   (829)4306 • Office location:   Taub 323 • Roman Sandler • Phone:   (829)4166 • Office location:   Taub 736 Internet Networking

  3. IP Addressing: Original Classful Scheme • IP Address – 32-bit integer globally unique address • Dotted Notation: 132.68.37.54 • IP Classes – dividing an address to net id and host id • The prefix (net id) identifies a network. • The suffix (host id) identifies a host on this network. Internet Networking

  4. IP Addressing: Original Classful Scheme • Class A – 7 bits to net id, 24 bits to host id 1.0.0.0 – 126.0.0.0 • Class B – 14 bits to net id, 16 bits to host id 128.0.0.0 – 191.255.0.0 • Class C – 21 bits to net id, 8 bits to host id 192.0.0.0 – 223.255.255.0 • Class D – for multicasting • Class E – reserved for future use (used for private addresses) Weakness • Growth of routing tables in routers • Tens of thousands small (class C) networks. • Each network must be advertised. • Inflexible • Lack of a network classes for mid-sized organization (between class B and C). • Address space will be eventually exhausted Internet Networking

  5. Subnet Addressing • A site has a single IP network address assigned to it, but has two or more physical networks. • Different technologies. • Limits of technologies. • Network congestion. • Security consideration. • VLAN – separate one physical network into a few logical networks. • Administration (e.g. different departments in academic institute). • From outside it looks like a single network • Only local routers know about multiple physical networks inside and how to route traffic among them • Host ID is divided into a subnet ID and host ID • Accepted as a standard at 1985 (RFC 950). Internet Networking

  6. Subnet Routing • When a router gets a packet, it isolates by Net mask the packet net id address. • Each routing entry contains a net mask. • Routing is done on a longest-match basis. • If the packet is destined to other network then the router sends it to another router. • Otherwise the router sends the packet to the appropriate host on its attached networks. Internet Networking

  7. Subnetting - Example • A site with two physical networks. • Using subnetting, R advertise these networks as a single network (thus, R accepts all traffic for net 128.10.0.0) • Internal routing is done according to subnet id (i.e. the third octet of the address). Network 128.10.1.0/24 128.10.1.1 128.10.1.2 H1 H2 Rest of the Internet R . Network 128.10.2.0/24 All traffic to 128.10.0.0/16 128.10.2.1 128.10.2.2 H3 H4 Internet Networking

  8. Variable-Length Subnetting • Motivation: Consider the case when an organization has a few networks of different sizes. • When we choose the subnet partitioning, we actually define constant number of possible physical subnetworks with maximum number of hosts on them. • Difficult to keep small (waist of subnet numbers) and big (the host id needs more bits) sub networks and there could be unnecessary spending of address space. • Solution: Variable-Length Subnetting. A subnet partition is selected on a per-network basis. Internet Networking

  9. Example – Configuring a Network withVariable-Length Subnetting • We have a network with IP 202.128.236.0/24 • We need to support next sub networks: • 6 networks with 26 hosts • 3 networks with 10 hosts • 4 networks with 2 hosts • If we take subnet mask of /27 bits then we can get 8 sub networks of 30 hosts (all 0’s and all 1’s of host addresses are reserved). • 11111111.11111111.11111111.11100000 • We need only 6 such sub networks. • The rest 2 sub networks we will partition by subnet mask of /28 bits. • 11111111.11111111.11111111.11110000 • We will get 4 sub networks of 14 hosts in each • We need only 3 such sub networks. Internet Networking

  10. Example – Configuring a Network withVariable-Length Subnetting • The rest we will partition by subnet mask of /30 bits. • 11111111.11111111.11111111.11111100 • We will get 4 sub networks of 2 hosts in each. • Subnet mask #1 = /27 • 11111111.11111111.11111111.11100000 • Subnet mask #2 = /28 • 11111111.11111111.11111111.11110000 • Subnet mask #3 = /30 • 11111111.11111111.11111111.11111100 Internet Networking

  11. Classless Inter-Domain Routing (CIDR) - RFC 1519 • Routing destinations are represented by network and mask pairs. • Enabling network aggregation; thereby reducing the size of routing table. Examples: • Class A networks are followed by a /8 • Class C networks are followed by a /24 • 8 Class C hosts network is followed by /21 • Such a network has 21 bits of Net-ID, 11 Bits of Host-ID • Contains 2^21 Net IDs, and 2^11-2 = Hosts in Each network. Internet Networking

More Related