Internet Protocol Addressing and Routing. Redes TCP/IP

Transcription

1 Internet Protocol Addressing and Routing Redes TCP/IP

2 Internet Topology Internet - WAN Gateway or router Physical Network (LAN) internet LAN LAN LAN

3 Dotted Decimal Notation Binary notation 2 7 = = = = Dotted decimal notation

4 IP Addresses IP Address: Network ID (Prefix) + Host ID 32-bit Address Net ID Host ID host LAN Rede física internet hosts com identificadores de rede distintos. Rede física Rede Física hosts com o mesmo identificador de rede.

5 Classful IP Addressing Class Octets Prefixes Addresses per Prefix Address Range A (0) R H H H B (10) R R H H C (110) R R R H to D (1110) to Res. (1111) reserved reserved to

6 Prefix Size Interpretation 10.x.x.x 16M A x.x 65K 255 B C x...

7 Address Assignment NET ID HOST ID sub-net router sub-net Router has one address assigned to each interface

8 Limitations of the Classful Address Model Organization A Organization B hosts hosts

9 Number of Prefixes and Network Topology Universidade A Universidade A 253 computadores computadores 2000 computadores 8 Class-C Prefixes 2024 addresses 1 Class-B Prefix addresses

10 Classless IP Addressing Classless Inter-Domain Routing (CIDR) Introduced in 1993, CIDR has modified how the size of the network prefix is determined. CIDR introduces the subnet masks, which permits to define prefixes of any size. VLSM (Variable Length Subnet Masking) IP (32 bits) Subnet Mask(32 bits)

11 Subnet Mask IP Address: Subnet Mask: Prefix: 10. or /8 1 bit in the mask indicates that the corresponding IP bit is a prefix Default Masks: class A: or /8 or class B: or /16 or class C: or /24 or

12 Subnetting / / / / (32 IPs) (64 IPs) (256 IPs) (128 IPs) / / (32 IPs) /25 (64 IPs) (128 IPs) /24 = /25 = /26 = /27 =

13 Supernetting / (256 IPs) / (256 IPs) / (512 IPs) / /24 = /23 = /22 = (1024 IPs) / (256 IPs) / / (512 IPs) (256 IPs)

14 Masks in Decimal Dotted Notation A class C mask defines a block of 256 addresses: To divide into 2 blocks of 128 addresses, the mask is: To divide into 4 blocks of 64 addresses, the mask is: To divide into 8 blocks of 32 addresses, the mask is: To divide into 16 blocks of 16 addresses, the mask is:

15 Exercise of Subnet Assignment Subnet 3 How to divide the block /24? Subnet 2 r 3 r computadores computadores r computadores Subnet 1

16 Solution Subnet / Subnet /26 r3 r / r Subnet /25

17 Special IP Addresses Can t be used as unicast addresses: First address in a subnet (all host bits = 0) Identifies the network Last address in the subnet (all host bits = 1) Broadcast to the subnet /8: Loopback addresses : Indicates that the host has no address yet (DHCP) : Universal broadcast

18 Loopback = Local Communication IP packets with destination loopback address are not sent to lower layers of the TCP / IP stack, but handled locally by the station itself. Recommendation of the IETF: /8 is reserved for loopback process A process B Port A Port B Transport Network Data Link Physical

19 Address Resolution A network device with a single NIC is called single-homed NIC = Network Interface Card. A network device with multiple NICs is called multi-homed A router is always multi-homed. Every NIC is assigned to two addresses: A physical address (MAC) and an IP address. 48-bit address (6 bytes) NIC MAC ( B3) IP ( )

20 MAC Address The IEEE 802 standard defines two types of MAC addresses: locally administered addresses Defined locally by the administrator. universal addresses (globally unique) Defined by the manufacturer OUI (Organization Unique Identifier) Serial Number

21 NIC Address Filtering IP Network MAC Data Link interruption MAC D = NIC MAC MAC D = BROADCAST (FF.FF.FF.FF.FF.FF) MAC D MAC O IP O IP D PAYLOAD CRC

22 IP and MAC Addresses Host A Host B IP A O.S. O.S. IP B MAC A NIC NIC MAC B packet MAC B MAC A IP A IP B Payload Frame

23 Address Resolution Protocol - ARP The ARP is a protocol that permits to find the MAC address corresponding to an IP address. Messages are transmitted by the network layer with only the destination IP address specified. The ARP protocol must determine the MAC address of the destination IP address for the data link layer. Netwok Layer Source IP Destination IP Payload Data Link Layer Type Destination MAC Source MAC Payload CRC

24 ARP Messages Which is the MAC of IP ? The MAC of the IP is C ARP REQUEST ARP REPLY A B C Host B ignores the question...

25 ARP Cache Before sending a ARP request message, the ARP protocol searches the requested IP in the ARP Cache. If found, the MAC address is copied from the cache. If not, an ARP Request message is sent in broadcast to the subnet. Because it is based on a broadcast message, It is only possible to find the MAC address of a hosts in the same LAN. ARP Cache IP address MAC address type B3 dynamic ca dynamic

26 ARP works only in the LAN ARP request Routers don t forward broadcast packets

27 Duplicated IP Address Detection Which is the MAC of ? The MAC of is C!!! ARP REQUEST ARP REPLY A B C

28 Intranet and Internet Communication Intra-net communcation internet LAN LAN LAN LAN Inter-net communication

29 Intranet communication Frame Format The physical destination address of the frame matches the physical address of the target computer. Internet Communication The physical destination address of the frame matches the physical address of the target computer. Intranet MAC DST HOST MAC SRC HOST IP SRC HOST IP DST HOST PAYLOAD Internet MAC ROUTER MAC SRC HOST IP SRC HOST IP DST HOST PAYLOAD

30 Internet Communication The source and destination IP addresses remain the same when a packet traverse multiple routers. The MAC addresses, however, are modified to mach the elements participating of each hop /24 Router1 Router /24 Source Destination MAC 1 MAC 2 MAC 3 MAC 4 MAC 5 MAC 6

31 ARP in Internet Communication B A IP A IP D D C IP A IP D B C IP B IP C A D IP A ARP Request Who has IP B? ARP Request Who has IP D? IP D

32 Example First hop: Source: Destination: Source physical address: A Destination physical address: B Second hop: Source: Destination: Source physical address: C Destination physical address: D Third hop: Source: Destination: Source physical address: E Destination physical address: F frame frame frame net net router router net source IP: MAC: A IP: MAC: D destination IP: MAC: E IP: MAC: F IP: MAC: B IP: MAC: C

33 Routing Table Destination Network Gateway or Next Hop Interface Cost or Metric e.g., or /24 e.g., e.g., eth0, Fa0/0 or e.g., 1 or 1/ / Base Address Property Performing an AND operation between any address in the subnet range and the netmask results in the base address.

34 Destination Network Defined as a base address followed by a netmask: Destinatin Network (MASK ) Range of Addresses to (MASK ) to (MASK ) (MASK ): DEFAULT ROUTE OR INTERNET to

35 Routing Table Example Subnet / A INTERNET Router 1 Router / / B Subnet /24

36 Routing Table of Host B Destination Address Gateway Interface Cost /24 none eth0 or / eth0 or / eth0 or router / B eth0

37 How routes tables are tested One destination address may match more than one routing table entry. The routing table entries are testes in a specific order, and the first match decides the destination of the packet: 1) Longest prefix match (Maximum prefix length match) e.g., /24 is tested before /16, and /16 before /8. i.e., prefixes corresponding to smaller block of addresses are tested first 2) Lowest cost match This criteria is used only when two or more routing tables entries with the same prefix size match the destination address

38 Routing Table of Router 1 Destination Network Gateway Interface Cost /24 none /24 none / / / Router 1 Router / / /30

39 Routing Table of Router 2 Destination Network Gateway Interface Cost / / / / / /24 INTERNET router 1 router / / /30

40 Default Gateway and Default Route Destination Address Gateway Interface Cost /24 não tem eth0 or / eth0 or / eth0 or router 1 The router 1 is the default gateway for hosts in the subnet because it is the first hop to all other networks / B eth0

41 Multiple Routes and Cost Destination Network Gateway Interface Cost / (10) / (2) / (11) / (1) /24 Não tem / / /30 R1 10 Mbps R2 INTERNET / Mbps 100 Mbps R / /24

42 Route Aggregation / A / /30 INTERNET router 1 router / / B /25

43 Routing Tables with Route Aggregation Computer A Destination Network Gateway Interface Cost /25 none / Router 1 Destination Network Gateway Interface Cost /25 none /25 none / Router 2 Destination Network Gateway Interface Cost / /

44 Classful Addressing Scheme Conclusion Classless Addressing Scheme (CIDR or VLSM) ARP (Address REsolution Protocol) Routing Tables Routes Aggregation