© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Chapter 6: Network Layer Introduction to Networks.

Presentation_ID 2 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Chapter 6: Objectives Students will be able to:  Explain how network layer protocols and services support communications across data networks.  Explain how routers enable end-to-end connectivity in a small to medium-sized business network.  Determine the appropriate device to route traffic in a small to medium-sized business network.  Configure a router with basic configurations.  Configure the Default Gateway on network devices.

Presentation_ID 6 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer in Communication The Network Layer End to End Transport processes  Addressing end devices: An end device configured with an IP address is referred to as a host.  Encapsulation: The network layer encapsulates by adding IP header information, such as source (sending) and destination (receiving) IP address. It’s now called a packet. packets to a destination process is known as  Routing: The network layer provides services to direct packets to a destination host on another network. Packet is processed by a routers. Router selects paths for and direct packets toward the destination host; the process is known as routing. A packet may cross many intermediary devices before reaching the destination host. Each route the packet takes to reach the destination host is called a hop.  De-encapsulating: When the packet arrives at the network layer of the destination host. If the destination IP address matches its own IP address, the IP header is removed from the packet, the resulting Layer 4 segment is passed up to the appropriate service at the transport layer.

Presentation_ID 7 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer in Communication Network Layer Protocols Common Network Layer Protocols  Internet Protocol version 4 (IPv4) – 32 binary bits  Internet Protocol version 6 (IPv6) – 128 binary bits Legacy Network Layer Protocols  Novell Internetwork Packet Exchange (IPX)  AppleTalk  Connectionless Network Service (CLNS/DECNet)

Presentation_ID 10 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Characteristics of the IP protocol IP - Connectionless The role of the network layer is to transport packets between hosts while placing as little burden on the network as possible.

Presentation_ID 11 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Characteristics of the IP protocol IP – Best Effort Delivery If out-of-order or missing packets create problems for the application using the data, then upper layer services, such as TCP, must resolve these issues. This allows IP to function very efficiently.

Presentation_ID 12 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Characteristics of the IP protocol IP – Media Independent It is the responsibility of the OSI layer 2 to take an IP packet and prepare it for transmission over the communications medium. This means that the transport of IP packets is not limited to any particular medium ***Exception: The network layer considers: the maximum size of the Packet that each medium can transport (Maximum Transmission Unit; MTU) A router, must split up a packet when forwarding it from one medium to a another medium with a smaller MTU. This process is called fragmenting the packet or fragmentation.

Presentation_ID 13 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential IPv4 Packet Encapsulating IP IP encapsulates, or packages, the transport layer segment by adding an IP header. This header is used to deliver the packet to the destination host.

Presentation_ID 14 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential IPv4 Packet IPv4 Packet Header VersionDifferentiated Services (Priority), Time-to-Live (TTL Source IP Address and Destination IP Address Version, Differentiated Services (Priority), Time-to-Live (TTL), Protocol [ICMP (0x01), TCP (0x06), and UDP (0x11)], Source IP Address and Destination IP Address (each address is 4 Bytes, 32 bits) Version IP Header Length Differentiated Services Total Length DSCPECN IdentificationFlagFragment Offset Time To LiveProtocolHeader Checksum Source IP Address Destination IP Address Options (optional) Padding Byte 1Byte 2Byte 3Byte 4 Usually Header size is 20 Bytes (12 fields)

Presentation_ID 15 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential IPv4 Packet IPv4 Header Fields Internet Header Length (IHL, 4 bits long), Total Length (2 Bytes), Header Checksum, Identification, Flags, Fragment Offset (deals with fragments) Version IP Header Length Differentiated Services Total Length DSCPECN IdentificationFlagFragment Offset Time To LiveProtocolHeader Checksum Source IP Address Destination IP Address Options (optional) Padding Byte 1Byte 2Byte 3Byte 4

Presentation_ID 16 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential IPv4 Packet Sample IPv4 Headers Figure displays the contents of a captured packet. Note that the Source is listed as 192.168.1.109 and the Destination is listed as 192.168.1.1. The middle window contains information about the IPv4 header, such as the header length, total length, and any flags that are set.

Presentation_ID 17 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer in Communication Limitations of IPv4  IP Address depletion IPv4 has a limited number of unique public IP addresses available  Internet routing table expansion As the number of servers (nodes) connected to the Internet increases, so too does the number of network routes. IPv4 routes consume a great deal of memory and processor resources on Internet routers  Lack of end-to-end connectivity NAT can be problematic for technologies that require end-to-end connectivity.

Presentation_ID 18 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer in Communication Introducing IPv6  Increased address space (128 instead of 32 binary bits)  Improved packet handling (simplified with fewer fields. This improves packet handling  Eliminates the need for NAT (Private IP addresses no longer needed)  Integrated security (IPv6 natively supports authentication and privacy capabilities)  4 billion IPv4 addresses 4,000,000,000  340 Undecillion IPv6 addresses 340,000,000,000,000,000,000,000,000,000,000,000,000

Presentation_ID 19 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential IPv6 Packet Encapsulating IPv6 The IPv6 simplified header offers several advantages over IPv4: Better routing efficiency for performance and forwarding-rate scalability No requirement for processing checksums Simplified and more efficient extension header mechanisms (as opposed to the IPv4 Options field) A Flow Label field for per-flow processing with no need to open the transport inner packet to identify the various traffic flows

Presentation_ID 20 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential IPv6 Packet IPv6 Packet Header VersionTraffic ClassFlow Label Payload Length Next Header Hop Limit Source IP Address 128 bits Destination IP Address 128 bits Byte 1Byte 2Byte 3Byte 4 The IPv6 header consists of 40 octets (largely due to the length of the source and destination IPv6 addresses) and 8 header fields (3 IPv4 basic header fields and 5 additional header fields). The IPv4 header consists of 20 octets and 12 basic header fields Next Header Indicates the data payload type that the packet is carrying Enables the network layer to pass the data to the appropriate upper-layer protocol. Also used if there are optional extension headers added to the IPv6 packet.

Presentation_ID 22 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Routing Host Routing Tables Another role of the network layer is to direct packets between hosts. A host can send a packet to: I tself - This is a special IP address of 127.0.0.1 which is referred to as the loopback interface. This loopback address is automatically assigned to a host when TCP/IP is running, is useful for testing purposes. Any IP within the network 127.0.0.0/8 refers to the local host. Local host - This is a host on the same network as the sending host. The hosts share the same network address. Remote host - This is a host on a remote network. The hosts do not share the same network address

Presentation_ID 23 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Host Routing Tables Host Packet Forwarding Decision is determined by the IP address and subnet mask combination Whether a packet is destined for a local host or a remote host is determined by the IP address and subnet mask combination of the source (or sending) device compared to the IP address and subnet mask of the destination device.

Presentation_ID 24 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Host Routing Tables Default Gateway Hosts must maintain their own, local, routing table 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 - This is a route to the loopback interface (127.0.0.1).  Local network route - The network which the host is connected to is automatically populated in the host routing table.  Local default route – The default route represents the route that packets must take to reach all remote network addresses. The default gateway address is the IP address of the router that is connected to the local network. The default gateway address can be configured on the host manually or learned dynamically. R

Presentation_ID 25 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Host Routing Tables IPv4 Host Routing Table Host’s Default Gateway Host’s default route to remote networks Broadcast address Host’s default route to local network

Presentation_ID 26 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Host Routing Tables Sample IPv4 Host Routing Table used to store route information A routing table is a data file in RAM that is used to store route information about directly connected network, as well as entries of remote networks the device has learned about.

Presentation_ID 27 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Host Routing Tables Sample IPv6 Host Routing Table Lists all known IPv6 routes IPv6 Route Table - Lists all known IPv6 routes, including direct connections, local network, and local default routes Note: Interfaces in IPv6 commonly have two IPv6 addresses: a link local address and a global uncast address. Also, notice that there are no broadcast addresses in IPv6. IPv6 addresses will be discussed further in the next chapter.

Presentation_ID 29 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Routing Tables IPv4 Router Routing Table 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 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.11.0/24 is directly connected, GigabitEthernet0/1 L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks C 209.165.200.224/30 is directly connected, Serial0/0/0 L 209.165.200.225/32 is directly connected, Serial0/0/0 R1# 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2 Directly-connected routes – These routes come from the active router interfaces. Remote routes - These routes come from remote networks connected to other routers

Presentation_ID 30 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Routing Tables Directly Connected Routing Table Entries C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 A B C A Identifies how the network was learned by the router. B Identifies the destination network and how it is connected. C Identifies the interface on the router connected to the destination network. 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 64.100.0.1.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2

Presentation_ID 31 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Routing Tables Remote Network Routing Table Entries D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 A Identifies how the network was learned by the router. B Identifies the destination network. C Identifies the administrative distance (trustworthiness) of the route source. D Identifies the metric (cost) to reach the remote network. E Identifies the next hop IP address to reach the remote network. F Identifies the amount of elapsed time since the network was discovered. G Identifies the outgoing interface on the router to reach the destination network. 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 64.100.0.1.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2

Presentation_ID 32 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Routing Tables Next-Hop Address 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 64.100.0.1.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2 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 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.11.0/24 is directly connected, GigabitEthernet0/1 L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks C 209.165.200.224/30 is directly connected, Serial0/0/0 L 209.165.200.225/32 is directly connected, Serial0/0/0 R1#

Presentation_ID 34 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Anatomy of a Router A Router is a Computer There are many types of infrastructure routers available. In fact, Cisco routers are designed to address the needs of: Branch - Teleworkers, small business, and medium-size branch sites. Includes Cisco 800, 1900, 2900, and 3900 Integrated Series Routers (ISR) G2 (2nd generation). WAN - Large businesses, organizations, and enterprises. Includes the Cisco Catalyst 6500 Series Switches and the Cisco Aggregation Service Router (ASR) 1000. Service Provider - Large service providers. Includes Cisco ASR 1000, Cisco ASR 9000, Cisco XR 12000, Cisco CRS-3 Carrier Routing System, and 7600 Series routers. all router models are essentially computers Regardless of their function, size or complexity, all router models are essentially computers. Routers also require: an IOS, a CPU, RAM, Flash, and NVRAM

Presentation_ID 36 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Anatomy of a Router Router Memory Memory Volatile / Non-Volatile Stores RAMVolatile Running IOS Running configuration file IP routing and ARP tables Packet buffer ROMNon-Volatile Bootup instructions Basic diagnostic software Limited IOS NVRAMNon-VolatileStartup configuration file FlashNon-Volatile IOS Other system files Most Cisco routers come with external Compact Flash slots. Slot can support high-speed storage upgradeable to 4GB in density.

Presentation_ID 38 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Anatomy of a Router Router Backplane Two 4 GB flash card slots Double-wide eHWIC slots eHWIC 0AUX port LAN interfaces USB Ports Console USB Type B Console RJ45 Management Interface (EHWIC) Enhanced high-speed WAN interface card Compact flash can store the Cisco IOS software image, log files, voice configuration files, HTML files, backup configurations, or any other file needed for the system.

Presentation_ID 40 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Anatomy of a Router LAN and WAN Interfaces Serial interfaces LAN interfaces light emitting diode (LED) indicators to provide status information

Presentation_ID 41 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Boot-up Cisco IOS Cisco IOS for routers provides the following: Addressing Interfaces Routing Security QoS Resources Management The IOS file itself is several megabytes in size and similar to Cisco IOS switches, is stored in flash memory. Using flash allows the IOS to be upgraded to newer versions or to have new features added. During bootup, the IOS is copied from flash memory into RAM.

Presentation_ID 42 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Boot-up Bootset Files The IOS image file is stored in flash memory The startup configuration file is stored in NVRAM. When changes are made to the running-config file, it should be saved to NVRAM as the startup configuration file, in case the router is restarted or loses power.

Presentation_ID 43 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Boot-up Router Bootup Process System Bootstrap, Version 15.0(1r)M15, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport 1.Perform the POST and load the bootstrap program 2.Locate and load the Cisco IOS software 3.Locate and load the startup configuration file or enter setup mode When the router is powered on, software on the ROM chip conducts the POST After the POST, the bootstrap program is copied from ROM into RAM. 6.3.2.5 Video Demonstration - The Router Boot Process

Presentation_ID 44 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Router Boot-up Show Versions Output Router# show version Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Version 15.2(4)M1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2012 by Cisco Systems, Inc. Compiled Thu 26-Jul-12 19:34 by prod_rel_team 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.SPA.152-4.M1.bin" Last reload type: Normal Reload Last reload reason: power-on Cisco CISCO1941/K9 (revision 1.0) with 446464K/77824K bytes of memory. Processor board ID FTX1636848Z 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. 250880K bytes of ATA System CompactFlash 0 (Read/Write) Technology Package License Information for Module:'c1900' ----------------------------------------------------------------- Technology Technology-package Technology-package Current Type Next reboot ------------------------------------------------------------------ ipbase ipbasek9 Permanent ipbasek9 security None None None data None None None Configuration register is 0x2142 (will be 0x2102 at next reload) Router#

Presentation_ID 46 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Configure Initial Settings Router Configuration Steps Router> enable Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# hostname R1 R1(config)# 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2 Router> en Router# conf t Enter configuration commands, one per line. End with CNTL/Z. Router(config)# ho R1 R2(config)# OR 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#

Presentation_ID 47 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Configure Interfaces Configure LAN Interfaces 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2 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 192.168.10.1 255.255.255.0 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 192.168.11.1 255.255.255.0 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)#

Presentation_ID 48 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Configure Interfaces Verify Interface Configuration 192.168.10.0/24 R2 192.168.11.0/24 10.1.1.0/24 10.1.2.0/24 209.165.200.224 /30.226.10.1 G0/1.225 S0/0/0 G0/0.1 R1 PC1 PC2 R1# show ip interface brief Interface IP-Address OK? Method Status Protocol GigabitEthernet0/0 192.168.10.1 YES manual up up GigabitEthernet0/1 192.168.11.1 YES manual up up Serial0/0/0 209.165.200.225 YES manual up up Serial0/0/1 unassigned YES NVRAM administratively down down Vlan1 unassigned YES NVRAM administratively down down R1# R1# ping 209.165.200.226 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 209.165.200.226, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/9 ms R1#

Presentation_ID 50 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Configuring the Default Gateway Default Gateway on a Host 192.168.10.0/24 192.168.11.0/24 G0/1.1 G0/0 R1.10 PC1.10 PC2.10 PC4.10 PC3 192.168.10.0/24 192.168.11.0/24 G0/1.1 G0/0 R1.10 PC1.11 PC2.11 PC4.10 PC3

Presentation_ID 51 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Configuring the Default Gateway Default Gateway on a Switch 192.168.11.0/24.1 G0/1.1 G0/0 R1 192.168.10.0/24.10 PC1.11 PC2 S1#show running-config Building configuration... ! service password-encryption ! hostname S1 ! Interface Vlan1 ip address 192.168.10.50 ! ip default-gateway 192.168.10.1 S1 S2.50 If the default gateway were not configured on S1, response packets from S1 would not be able to reach the administrator at 192.168.11.10. The administrator would not be able to mange the device remotely.

Presentation_ID 52 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer Summary In this chapter, you learned:  The network layer, or OSI Layer 3, provides services to allow end devices to exchange data across the network.  The network layer uses four basic processes: IP addressing for end devices, encapsulation, routing, and de- encapsulation.  The Internet is largely based on IPv4, which is still the most widely-used network layer protocol.  An IPv4 packet contains the IP header and the payload.  The IPv6 simplified header offers several advantages over IPv4, including better routing efficiency, simplified extension headers, and capability for per-flow processing.

Presentation_ID 53 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer Summary In this chapter, you learned:  In addition to hierarchical addressing, the network layer is also responsible for routing.  Hosts require a local routing table to ensure that packets are directed to the correct destination network.  The local default route is the route to the default gateway.  The default gateway is the IP address of a router interface connected to the local network.  When a router, such as the default gateway, receives a packet, it examines the destination IP address to determine the destination network.

Presentation_ID 54 © 2008 Cisco Systems, Inc. All rights reserved.Cisco Confidential Network Layer Summary In this chapter, you learned:  The routing table of a router stores information about directly- connected routes and remote routes to IP networks. If the router has an entry in its routing table for the destination network, the router forwards the packet. If no routing entry exists, the router may forward the packet to its own default route, if one is configured, or it will drop the packet.  Routing table entries can be configured manually on each router to provide static routing or the routers may communicate route information dynamically between each other using a routing protocol.  In order for routers to be reachable, the router interface must be configured.

© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Chapter 6: Network Layer Introduction to Networks.

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© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 Chapter 6: Network Layer Introduction to Networks.

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