Review of Networking Technologies Vahid Tabatabaee Fall 2007

1. Review of Networking Technologies Vahid Tabatabaee Fall 2007

2. References • Title: Internetworking with TCP/IP vol. I Principles, Protocols, and Architecture Author: Douglas E. Comer Publisher: Prentice-Hall • Title: Network Processors Architectures, Protocols, and PlatformsAuthor: Panos C. LekkasPublisher: McGraw-Hill • Title Computer Networking: A Top-Down Approach Author: J.F. Kurose, K.W. Ross Publisher: Addison Wesley

3. Connection Oriented Communication • Connection oriented communication forms a dedicated connection (circuit, path) between two points. • E.g. Telephone systems, ATM, Frame Relay • Potential Advantages: • Easier to make it reliable (note it is not necessarily more reliable). • Guaranteed/reserved bandwidth. • Identify flows by connection identifier rather than source/destination address (tag switching)

4. Connection-less Communication • Data is segmented into packets. • Every packet has identification information that enables network hardware to send it to the specified destination. • E.g. Ethernet, Internet Protocol • Potential Advantages: • More efficient use of resources

5. Network Hierarchy (3 layer) • Enterprise Network • Typical networks in companies, universities. • Based on Ethernet, Fast-Ethernet, WiFi. • Contains one or more LAN connecting PC, printers, servers • They can also have faster connections based on Gigabit Ethernet to connect to server and storage subsystems. • Gateway and customer access routers provide connection to the rest of the world • Access Network (provider network) • Aggregate customer traffic. • Send the aggregated traffic through a larger pipe into the WAN. • We have three kind of routers here: • Provider Edge Router (infamous last mile connection) • Provider core router • The typical speed range OC-3 and OC-48 • WAN • Interconnect provide or career networks • The typical speed ranges between OC-12 and OC-192

6. Conceptual Hierarchy of Networks

7. LAN/MAN/WAN Source: http://www.crema.unimi.it/didattica/Labsistemi/matagg/Tutorial%20Networking.htm

8. MAN • MAN are large network spanning a campus or city. • MAN (WAN) is generally less than (over) 30-50 Km. • WAN spans central office facilities, while a MAN starts and ends in a central office Source: http://www.dbguide.net/know/know103001.jsp?mode=view&pg=1&idx=1038

9. 4 layer Network Hierarchy • Core Router Requirements: • OC-192 wire-speed IP routing and MPLS • VPN • Traffic Engineering • Edge Router Requirements: • Aggregate multiple access network interfaces • Access network uplinks can be GigE OC-12 • Reliability • Redundant component • Hot pluggable line cards • Multiservice Providing Platform (MSSP) • TDM OC-3 to OC-192 • GigE, 10GigE LAN, 10GigE WAN • SAN (Fibre Channel, …) • IP services

10. Sprint Logical Topology • 18 IP routers with 36 bidirectional logical links Source: A. Nucci, A. Sridharan, N. Taft, “The Problem of Synthetically Generating IP Traffic Matrices: Initial Recommendations”, ACM Computer Communication Review, vol. 35, no. 3, pp. 19-32 ,July 2005.

11. Sprint WDM Technology • 36 OXC with 55 WDM fibers.. • Wa = 40 OC-192 channels, Wb = 40 OC-48 channels, Wc = 40 OC-12 channels Source: A. Nucci, A. Sridharan, N. Taft, “The Problem of Synthetically Generating IP Traffic Matrices: Initial Recommendations”, ACM Computer Communication Review, vol. 35, no. 3, pp. 19-32 ,July 2005.

12. Ethernet Technology • Ethernet is the most popular LAN technology: • Shared media • Carrier Sense Multiple Access/ Collision Detection (CSMA/CD) • There are different variants of the Ethernet technology: • Coaxial • Thin wire • Twisted Pair (10Base-T)

13. 10Base-T • Data rate : 10Mbps • Broadcast, bus technology • Best effort delivery: Hardware provide no information to the sender that the packet is delivered Source: http://www.webclasses.net/Courses/Intro/6.1/demo/units/unit02/sec04b.html • Max. Segment length: 100m • Repeaters relay electrical from one cable to another. At most two bridges between any two machines. • Bridges learn addresses and replicate the signal if needed. They isolate Ethernet segments from each other.

14. Collision Detection and Recovery • It is possible that two transmitters send data simultaneously and collision happens. • Each transceiver monitors the cable to see if there is a coliision. • When it detects collision it aborts transmission and remain idle before trying again. • They use a binary exponential back-off policy.

15. Ethernet Hardware Address • Ethernet defines a 48-bit addressing scheme. • Each hardware card has a unique address assigned to it. • Ethernet addresses are sometimes called hardware or physical addresses. • Interface card receives all packets, but only send to the host that are addressed to it. • Three types of address: • Physical address of one network interface. • The network broadcast address (all 1s) • Multicast address: some interfaces can be programmed to recognize multicast addresses.

16. 10101011 Alternating 0 and 1 Ethernet Frame Format • Ethernet frame size are between 64 and 1518 bytes (including header, data, and CRC). • There is also 12 byte gap between Ethernet frames.

17. 1 GigE and 10 GigE • It preserves compatibility with legacy software applications developed for running on 10BaseT. • The technology has been proposed both for LAN and MAN/WAN. • The jumbo frames can be up to 9000 bytes data. • 10 GigE is not based on the CSMA/CD technology anymore.

18. Internet Architecture • Networks are connected by routers • Routers need to know about the topology of the internet beyond the networks to which they connect. • Routers use the destination network, not the destination host, when routing a packet.

19. Questions • What is the exact form of Internet Addresses? • How Internet addresses are mapped to the Hardware addresses such as Ethernet addresses?

20. Host Universal Identifiers • Host Identifiers are: • Names: specify what an object is. • Addresses: Where it is. • Routes: How to get there.

21. Classes of IP Addresses • Each host has a unique 32 bit internet address. • Each address is a pair of (netid, hostid). 0.0.0.0 --127.255.255.255 128.0.0.0 --191.255.255.255 192.0.0.0 --223.255.255.255 224.0.0.0 --239.255.255.255 240.0.0.0 --255.255.255.255 • 127.0.0.1 is the loopback address in IP. (127.0.0.0 to 127.255.255.255) • 0.0.0.0 – 0.255.255.255 (zero addresses should not be used). • 255.255.255.255 broadcast to all other nodes on the LAN • In general zeros mean this and ones mean all.

22. Classless Inter-Domain Routing • It replaces the older system based on classes • Most sites were too big for class C and received class B number. • Depletion of class B addresses (~16,000 total) • It looks like a normal IP address but it ends with a slash and a number following it. • It facilitates routing by allowing blocks of addresses to be grouped together into single routing table entries. Source: http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing

23. An example for CIDR • Different CIDR prefixes are used in different locations for routing Outside MCI network Inside MCI network Inside ARS network

24. Weaknesses in Internet Addressing • If a computer moves from one network to another, its IP address must change. • This is the main source of challenge for mobile IP. • The path used for hosts with multiple IP addresses (multi-homed hosts) depends on the address used. • If host B connection to network 1 fails, packets from host A that uses I3 address can not reach host B.

25. Address Aggregation Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

26. More specific routes Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

27. Mapping Internet Address to Physical Address • Consider two machines A and B on the same network. • IA, IB are internet addresses and PA, PB are physical addresses of A and B respectively. • A wants to send a packet to B, but it only has IB address of B. • Address Resolution Protocol (ARP) resolves this problem for networks with static address and broadcast capability.

28. ARP • Host A has an ARP cache of recently acquired IP-to-physical address bindings. • If IB is not in the cache, then A broadcasts an ARP request containing IB. • Host B responds with an ARP reply to A that contains (IB, PB). It also adds (IA, PA) to its own cache. • Sender A queues all packets destined to B until it receives ARP reply. • Expiring timer for the binding entries in the cache. • Resending the request (at least once) if did not get a reply. • In most technologies a single type value is used for ARP frames. • In Ethernet type field of (0806)16 is for ARP messages.

29. RARP • A machine uses Reverse Address Resolution Protocol (RARP) to get its IP address from the server at the startup. • The server has a list of IP addresses of the machines. • Machine uses its physical address to communicate on the network.

30. IP Packet (Datagram) delivery • The maximum size of an IP datagram is 216 octets. • It is more efficient to carry each IP packet in a network frame (encapsulation). • Each technology has a different maximum frame size • Ethernet 1500 octets • FDDI 4470 octets • IP chooses a appropriate initial datagram size. • Fragmentation is the process of dividing larger packets into smaller ones to adhere to the network Maximum Transfer Unit (MTU). • Destination uses the Identification, Flags, and Fragment offset to reassembly the packet.

31. Time To Live field • Time To Live field specifies how long a packet is allowed to be in the Internet. • The source sets the maximum time that the datagram should survive. • Each router decrement this field by one when it process the packet. • To take into account buffering delay, each router records arrival time and decrement the field by seconds that packet stays in the router. • When TTL reaches zero, the router discards the packet.

32. IP routing • Direct Delivery: Transmission of packets from one machine across a SINGLE physical network to another. • Indirect Delivery: Destination is not connected directly to the network of the sender, hence sender should pass the packet to a router for delivery.

33. Direct Delivery • Does not involve the router. • Sender encapsulates the datagram in a single physical frame. • Binds the destination IP address to a physical hardware address using ARP (if needed). • How does the sender know if the destination is directly connected to the same network?

34. Indirect Delivery • Host (sender): Encapsulates the datagram in a physical network frame and send it to a router attached to the network. • Router: Extracts the encapsulated datagram, Decides the next router to send the datagram to. Encapsulates the Datagram for transmission over the next network. • Question: How a router and host decide next router to send the datagram to?

35. IP Routing Table • Every host and router has a routing table • Routing table has information about destination and how to reach them. • We can not have a separate entry for every possible destination. • First refinement: We can have a single entry for all hosts connected to the same network and only check the netid part of the internet address. • Second refinement: We only need to keep the information for the next hop not the entire path for each destination. • All next hop routers listed in router M routing table must lie on networks to which M connects directly.

36. Routing Table • Longest Prefix Match: • Recall that in CIDR more than one table entry may match the destination address. • The one with largest prefix number is used for routing. • Routing Table Entries: • 192.168.0.0/16 • 192.168.20.16/28 • Default Routes: • A default route is used by a router or a server when no other known route works for a packet destination address. • The default route in CIDR is 0.0.0.0/0 • Hosts and routers in an organization generally point the default route towards the router that has connection to a network service provider Both entries match the destination address 192.168.20.19, but the second one with larger prefix number is used. Source:Wikipedia

37. Example: Route Selection in Cisco Routers • This example is based on the “Route Selection in Cisco Routers, Document ID: 8651 available at: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094823.shtml

38. Routing Table There are three process involved in building and maintaining the routing table: • Various Routing Process, which run a routing protocol such as: • Enhanced Interior Gateway Routing Protocol (EIGRP) • Border Gateway Protocol (BGP) • Intermediate System-to-Intermediate System (IS-IS) • Open Shortest Path First (OSPF) • The routing table, which accepts information from routing process and replies to requests from the forwarding process. • The forwarding process, which requests information from the routing table for packet forwarding.

39. Building the Routing Table Main considerations in building the routing table: • Administrative Distance: This indicates how much we trust source of the route. • Metric: This is a measure used by the routing protocol to calculate the best path to a given destination. • Prefix length

40. Routing Table Entry Update Assume there are four routing process running: • EIGRP, OSPF, RIP, IGRP • All 4 process learned various routes to 192.168.24.0/24 and each has chosen its best path to that network using its internal metrics and process. • Each routing process attempts to install their route in the routing table. • The one with lowest administrative distance (EIGRP here) can install its route in the routing table • Other routes may be used as backup routes

41. Prefix Lengths • Assume the three routing process have received these routes: • EIGRP (internal): 192.168.32.0 / 26 • RIP: 192.168.32.0 / 24 • OSPF: 192.168.32.0 / 19 • ALL these routes will be installed in the routing table, since they have different prefix length. • Routing Table: .... D 192.168.32.0/26 via 10.1.1.1 R 192.168.32.0/24 via 10.1.1.2 O 192.168.32.0/19 via 10.1.1.3 .... A packet destined for 192.168.32.1 is forwarded to 10.1.1.1, which has the longest prefix match (26 bits verses 24 or 19 bits). A packet destined for 192.168.32.100 is forwarded to 10.1.1.2, because it does NOT fall within 192.168.32.0/26 (192.168.32.0—192.168.32.63). But it falls within the 192.168.32.0/24 destination (192.168.32.0-192.168.32.255)

42. Forwarding Decision Process

43. Dynamic Host Configuration Protocol (DHCP) • The router IP addresses are typically configured manually, often remotely with a network management tool. • Host addresses is typically configured using the DHCP protocol. • DHCP can give a host the same IP address each time it connects to the network or assign a temporary IP address that will be different each time the host connects to the network • DHCP also provides additional information such as subnet mask, address of the first hop router (default gateway) and address of the local DNS server. • DHCP is also used commonly in residential access networks and in wireless LANs.

44. DHCP architecture • DHCP is a client-server protocol • Newly arriving hosts are clients • DHCP server has the information requested by the clients • Subnets may have a DHCP server • If there is no server in a subnet, a DHCP relay agent knows the address of a DHCP server for that network Source:http://www.windowsitpro.com/Files/5181/Figure_02.gif

45. DHCP 4-step process • DHCP server discovery: Newly arriving host sends DHCPDISCOVER message a UDP packet to port 67. This message is broadcasted. • DHCP sservers respond with DHCPOFFER, which is again broadcasted. The message cotains the transaction ID, the proposed IP address, the network mask, lease time. • The client will choose one server offer and respond to that server with a DHCPrequest message. • The server responds with DHCPACK When the renewal timer expires When the rebinding timer expires Source:http://www.windowsitpro.com/Files/5181/Figure_01.gif

46. Mobility Management • Home Network: The permanent home of a mobile node. • Home Agent: The entity within the home network that performs the mobility management functions. • Foreign Network: The network where the mobile node is currently residing. • Foreign Agent: The entity in the foreign network that help the mobile node with the mobility management functions. • Correspondent: The entity that wants to communicate with the mobile node

47. Mobile Network Architecture Source: “Computer Networking: A Top-Down Approach” by J.F. Kurose, K.W. Ross

48. Addressing (Naïve Approach) • Foreign Network advertises to its neighbors that it has a highly specific route to the mobile node permanent IP address. • When mobile node leaves one foreign network and joins another the new foreign network, the new foreign agent would advertise that it has a specific route and the old one eould withdraw its routing information. • Drawback: Scalability; it completely destroys the hierarchical structure of IP addresses.

49. Addressing for mobile • Foreign agent is located at the edge of the foreign network. • Foreign agent creates a care-of address (COA) for the mobile node, with the network portion of the COA matching that of the foreign network. • Note that there are two addresses for the mobile node: • Permanent address • Foreign address • The foreign agent informs the home agent that the mobile node is in its network and has the given COA.

50. Indirect Routing to a Mobile Node • The correspondent addresses the packet to the mobile node’s permanent address. • The packet is first routed to the mobile node home agent. • The home agent forwards the packet to a mobile node in two steps: • The packet is first forwarded to the foreign agent using the COA • From the foreign agent to the mobile node. • Mobile node can address directly its packets to the correpondent.