Chapter 6: Network Layer

Transcription

1 Chapter 6: Network Layer Introduction to Networks Intro to Networks v5

2 Network Layer Intro to Networks v5 2

3 The Network Layer End to End Transport processes Addressing end devices Encapsulation of Packets Routing De-encapsulating Intro to Networks v5 3

4 Network Layer Protocols Common Network Layer Routed Protocols Internet Protocol version 4 (IPv4) Internet Protocol version 6 (IPv6) Legacy Network Layer Protocols Novell Internetwork Packet Exchange (IPX) AppleTalk Connectionless Network Service (CLNS/DECNet) Intro to Networks v5 4

5 Characteristics of IP Intro to Networks v5 5

6 IP - Connectionless When connectionless protocols are implemented at the lower layers of the OSI model, upper-layer connection-oriented protocols are usually used to acknowledge the data receipt and request the retransmission of missing data. Intro to Networks v5 6

7 IP Best Effort Delivery Intro to Networks v5 7

8 IP Media Independent Intro to Networks v5 8

9 Encapsulating IP Intro to Networks v5 9

10 IPv4 Packet Header Version, Differentiated Services (DS), Time-to-Live (TTL),Protocol, Source IP Address, Destination IP Address, Internet Header Length (IHL), Total Length, Header Checksum, Identification, Flags, Fragment Offset Differentiated services is responsible for defining the priority of the packet Byte 1 Byte 2 Byte 3 Byte 4 Version IP Header Length Differentiated Services DSCP ECN Total Length Identification Flag Fragment Offset Time To Live Protocol Header Checksum Source IP Address Destination IP Address Options (optional) Padding Intro to Networks v5 10

11 Sample IPv4 Headers Intro to Networks v5 11

12 Introducing IPv6 Increased address space Improved packet handling Integrated security Eliminates the need for NAT because any host or user can get a public IPv6 network address because the number of available IPv6 addresses is extremely large: 4 billion IPv4 addresses 4,000,000, undecillion IPv6 addresses 340,000,000,000,000,000,000,000,000,000,000,000,000 Intro to Networks v5 12

13 Encapsulating IPv6 Intro to Networks v5 13

14 IPv6 Packet Header The Flow Label field informs network devices to maintain the same path for real-time application packets Byte 1 Byte 2 Byte 3 Byte 4 Version Traffic Class Flow Label Payload Length Next Header Hop Limit Source IP Address Destination IP Address Intro to Networks v5 14

15 Sample IPv6 Header Intro to Networks v5 15

16 Host Packet Forwarding Decision Hosts have to keep their own local routing table that contains a route to the loopback interface, a local network route, and a remote default route to ensure that their packets are directed to the correct network destination Intro to Networks v5 16

17 Host Tables Hosts must maintain their own, local, routing table to ensure that network layer packets are directed to the correct destination network. The local table of the host typically contains: Direct connection Local network route Local default route R Intro to Networks v5 17

18 Sample IPv4 Host Routing Table Two commands can be used on a Windows host to display the routing table: route print netstat -r Intro to Networks v5 18

19 Sample IPv6 Host Routing Table Intro to Networks v5 19

20 Router Packet Forwarding Decision The router will switch the packet to the directly connected interface immediately after matching the destination IP address to a network on a directly connected routing table entry Intro to Networks v5 20

21 Directly Connected Routing Table Entries PC1 PC /24 G0/0 G0/1 R / S0/0/ R2 10.0/ / /24 A B C C /24 is directly connected, GigabitEthernet0/0 L 19268/32 is directly connected, GigabitEthernet0/0 A B C Identifies how the network was learned by the router. Identifies the destination network and how it is connected. Identifies the interface on the router connected to the destination network. Intro to Networks v5 21

22 Remote Network Routing Table Entries PC1 PC /24 G0/0 G0/1 R / S0/0/ R2 10.0/ / /24 D 10.0/24 [90/ ] via , 00:00:05, Serial0/0/0 A B C D E F G Identifies how the network was learned by the router. Identifies the destination network. Identifies the administrative distance (trustworthiness) of the route source. Identifies the metric to reach the remote network. Identifies the next hop IP address to reach the remote network. Identifies the amount of elapsed time since the network was discovered. Identifies the outgoing interface on the router to reach the destination network. Intro to Networks v5 22

23 IPv4 Router Routing Table Next Hop PC1 PC /24 G0/0 G0/1 R / S0/0/0.226 R2 10.0/ / /24 R1#show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set D D C L C L C L R1# /8 is variably subnetted, 2 subnets, 2 masks 10.0/24 [90/ ] via , 00:00:05, Serial0/0/ /24 [90/ ] via , 00:00:05, Serial0/0/ /24 is variably subnetted, 2 subnets, 3 masks /24 is directly connected, GigabitEthernet0/ /32 is directly connected, GigabitEthernet0/ /24 is variably subnetted, 2 subnets, 3 masks /24 is directly connected, GigabitEthernet0/ /32 is directly connected, GigabitEthernet0/ /24 is variably subnetted, 2 subnets, 3 masks /30 is directly connected, Serial0/0/ /32 is directly connected, Serial0/0/0 Intro to Networks v5 23

24 Hops A hop is an intermediary Layer 3 device (router) that a packet has to traverse to reach its destination A packet from PC-1 to PC-4 has to traverse how many hops? 3 Intro to Networks v5 24

25 Router Memory Memory RAM ROM Volatile / Non-Volatile Volatile Non-Volatile Stores Running IOS Running configuration file IP routing and ARP tables Packet buffer Basic diagnostic software Bootup instructions Limited IOS NVRAM Non-Volatile Startup configuration file Flash Non-Volatile IOS Other system files Intro to Networks v5 25

26 Router Bootup Process A. B. C. ROM Basic IOS Rom Monitor Mode A. B. C. Intro to Networks v5 26

27 Router Bootup Process Routing table and ARP cache will be lost when the router loses power, is turned off, or restarted The IOS image file and startup configuration are copied into RAM as a router, with the default configuration register setting, boots up If the full IOS cannot be found, the IOS image held in ROM would be used to boot the router A packet to a destination host in the same LAN will be sent directly to the destination host Intro to Networks v5 27

28 Show Version Router# show version Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Version 15.2(4)M1, RELEASE SOFTWARE (fc1) Technical Support: Copyright (c) by Cisco Systems, Inc. Compiled Thu 26-Jul-12 19:34 by prod_rel_team IOS Information ROM: System Bootstrap, Version 15.0(1r)M15, RELEASE SOFTWARE (fc1) Router uptime is 10 hours, 9 minutes System returned to ROM by power-on System image file is "flash0:c1900-universalk9-mz.spa52-4.m1.bin" Last reload type: Normal Reload Last reload reason: power-on <Output omitted> Cisco CISCO1941/K9 (revision 1.0) with K/77824K bytes of memory. Processor board ID FTX Z 2 Gigabit Ethernet interfaces 2 Serial(sync/async) interfaces 1 terminal line DRAM configuration is 64 bits wide with parity disabled. 255K bytes of non-volatile configuration memory K bytes of ATA System CompactFlash 0 (Read/Write) <Output omitted> Technology Package License Information for Module:'c1900' ROM Information IOS Image file RAM Interfaces NVRAM for Configuration file Flash for IOS files Technology Technology-package Technology-package Current Type Next reboot ipbase ipbasek9 Permanent ipbasek9 security None None None data None None None Configuration Register setting Configuration register is 0x2142 (will be 0x2102 at next reload) Router# Intro to Networks v5 28

29 Router Configuration Steps PC1 PC /24 G0/0 G0/1 R / S0/0/0.226 R2 10.0/ / /24 Router> enable Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# hostname R1 R1(config)# OR Router> en Router# conf t Enter configuration commands, one per line. End with CNTL/Z. Router(config)# ho R1 R2(config)# R1(config)# enable secret class R1(config)# R1(config)# line console 0 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# exit R1(config)# R1(config)# line vty 0 4 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# exit R1(config)# R1(config)# service password-encryption R1(config)# R1(config)# banner motd # Enter TEXT message. End with the character '#'. *********************************************** WARNING: Unauthorized access is prohibited! *********************************************** # R1(config)# R1# copy running-config startup-config Destination filename [startup-config]? Building configuration... [OK] R1# Intro to Networks v5 29

30 Configure LAN Interfaces LAN and WAN interfaces will allow access via the VTY lines to configure the router PC1 PC /24 G0/0 G0/1 R / S0/0/0.226 R2 10.0/ / /24 R1# conf t Enter configuration commands, one per line. End with CNTL/Z. R1(config)# R1(config)# interface gigabitethernet 0/0 R1(config-if)# ip address R1(config-if)# description Link to LAN-10 R1(config-if)# no shutdown %LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to up %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up R1(config-if)# exit R1(config)# R1(config)# int g0/1 R1(config-if)# ip add R1(config-if)# des Link to LAN-11 R1(config-if)# no shut %LINK-5-CHANGED: Interface GigabitEthernet0/1, changed state to up %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up R1(config-if)# exit R1(config)# Intro to Networks v5 30

31 Verify Interface Configuration A configured and activated router interface must be connected to another device in order to operate PC1 PC /24 G0/0 G0/1 R / S0/0/0.226 R2 10.0/ / /24 R1# show ip interface brief (Summary of interfaces) Interface IP-Address OK? Method Status Protocol GigabitEthernet0/ YES manual up up GigabitEthernet0/ YES manual up up Serial0/0/ YES manual up up Serial0/0/1 unassigned YES NVRAM administratively down down Vlan1 unassigned YES NVRAM administratively down down R1# R1# ping Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to , timeout is 2 seconds:!!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/9 ms R1# Intro to Networks v5 31

32 Configuring the Default Gateway A computer MUST have an IP address, a subnet mask, and a default gateway address to communicate on the network DNS server (optional) is usually configured PC1 PC /24 G0/0 R1 G0/1 PC1 PC /24 G0/0 R1 G0/1 PC3 PC3 PC /24 PC /24 Intro to Networks v5 32

33 Default Gateway on a Switch Switch Virtual Interface (SVI) Management VLAN S1#show running-config Building configuration...! <output omitted> service password-encryption! hostname S1! Interface Vlan1 ip address ! ip default-gateway <output omitted> PC / /24 PC2 1 S1.50 G0/0 R1 G0/1 S2 If the default gateway were not configured on S1, response packets from S1 would not be able to reach the administrator at The administrator would not be able to mange the device remotely. Intro to Networks v5 33

34 Intro to Networks v5 34