Questions 4

Introducing IPv6

In the early 1990s, the Internet Engineering Task Force (IETF) grew concerned about the issues with IPv4 and began to look for a replacement. This activity led to the development of IP version 6 (IPv6). IPv6 overcomes the limitations of IPv4 and is a powerful enhancement with features that better suit current and foreseeable network demands. Improvements that IPv6 provides include: Increased address space - IPv6 addresses are based on 128-bit hierarchical addressing as opposed to IPv4 with 32 bits. Improved packet handling - The IPv6 header has been simplified with fewer fields. Eliminates the need for NAT - With such a large number of public IPv6 addresses, NAT between a private IPv4 address and a public IPv4 is not needed. This avoids some of the NAT-induced application problems experienced by applications requiring end-to-end connectivity. The 32-bit IPv4 address space provides approximately 4,294,967,296 unique addresses. IPv6 address space provides 340,282,366,920,938,463,463,374,607,431,768,211,456, or 340 undecillion addresses, which is roughly equivalent to every grain of sand on Earth.

What IPv4 means?

Internet Protocol Version 4 (IPv4) is the fourth revision of the Internet Protocol and a widely used protocol in data communication over different kinds of networks. IPv4 is a connectionless protocol used in packet-switched layer networks, such as Ethernet.

What does L identify?

L - Identifies that this is a local interface. This is the IPv4 address of the interface on the router.

In-band router interfaces

LAN and WAN Interfaces

What does O identify?

O: Identifies that the route was learned dynamically from another router using the OSPF routing protocol.

Host Routing Tables

On a Windows host, the route print or netstat -r command can be used to display the host routing table. Both commands generate the same output. The output may seem overwhelming at first, but is fairly simple to understand. Entering the netstat -r command or the equivalent route print command, displays three sections related to the current TCP/IP network connections: Interface List - Lists the Media Access Control (MAC) address and assigned interface number of every network-capable interface on the host, including Ethernet, Wi-Fi, and Bluetooth adapters. IPv4 Route Table - Lists all known IPv4 routes, including direct connections, local network, and local default routes. IPv6 Route Table - Lists all known IPv6 routes, including direct connections, local network, and local default routes.

Router Bootup Process

POST (Step 1)Power On Self Test(stored in room and checks it's interface like land cards etc Bootstrap (Step 2) stored in rom for manufacturing, testing and trouble shooting Find IOS (Internetwork Operating System) (step 3) finds .bin file in flash memory Load IOS (Internetwork Operating System) (step 4) load IOS (loads .bin file into running configuration Find configuration (step 5) finds startup configuration Load configuration (step 6) loads startup configuration into running configuration Run IOS commands (step 7) run IOS commands (Runs IOS on CLI (Cisco line interface)

Inside a router

Power supply Fan Shield for WAN interface card (WIC) or high speed WIC (HWIC) Synchronous dynamic RAM (SDRAM) Used for holding the running configuration and routing tables, and for supporting packet buffering Non-volatile RAM (NVRAM) and boot flash memory this is used for storing the ROMMON boot code as well as NVRAM data CPU - this is the central processing unit Advantaced Integration Module (AIM) This option offloads pocessor-intensive functions such as encryption from the main CPU

What does R identify?

R: Identifies that the route was learned dynamically from another router using the RIP routing protocol.

Basic Router Configuration Steps

Router> enable Router# config t Router(config)# hostname R1 Secure privileged EXEC mode R1(config)# enable secret class Secure user EXEC mode R1(config)# line console 0 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# line vty 0 4 R1(config-line)# password cisco Secure remote Telnet/ SSH access R1(config-line)# login R1(config-line)# exit password-encryption Secure all passwords in the config file R1(config)# service password-encryption banner text R1(config)# banner motd #Authorized access only!# save to Nivam and exit R1# copy running-config startup-config Save config

What does S identify?

S: Identifies that the route was manually created by an administrator to reach a specific network. This is known as a static route.

What is the maximum header size of an IP packet?

So the longest Internet Header (IP header) size can be 15*32 Bits = 480 Bits = 60 Bytes. This is why the header has a maximum size of 60 Bytes. The shortest header size is 20 bytes, where the IHL field has the value 5 (0101).

What is the maximum size of an IPv4 header?

So the longest Internet Header (IP header) size can be 15*32 Bits = 480 Bits = 60 Bytes. This is why the header has a maximum size of 60 Bytes. The shortest header size is 20 bytes, where the IHL field has the value 5 (0101).1

What is outgoing interface?

Static routes with outgoing interfaces This is on the assumption that, on broadcast medium such as Ethernet, routers only pick up packets who's destination MAC addresses match either their own interface addresses or are multicasts/broadcasts.

routing table

Table kept by the router to help determine which route entry is the best fit for the network A route entry with the longest prefix is the most specific network -Example: 10.1.1.0/24 more specific than 10.0.0.0/8 Example: Routing Table Dstn Ntwk Next Rtr Port Route Cost 125.0.0.0 137.3.14 1 12 161.5.0.0 197.3.6.6 1 4 134.7.0.0 164.17.3.12 2 10 Which Dstn address is most specific? 2 and 3

What are network layer protocols?

The IP (Internet Protocol) is a protocol that uses datagrams to communicate over a packet-switched network, such as the Internet. The IP protocol operates at the network layer protocol of the OSI reference model and is a part of a suite of protocols known as TCP/IP. ... Other protocol information is also carried.

next hop address

The IP address of the next networking device that can be used to forward the data packet to its destination

IP - Best Effort Delivery

The IP protocol does not guarantee that all packets that are delivered are, in fact, received. Unreliable means that IP does not have the capability to manage and recover from undelivered or corrupt packets. This is because while IP packets are sent with information about the location of delivery, they contain no information that can be processed to inform the sender whether delivery was successful. Packets may arrive at the destination corrupted, out of sequence, or not at all. IP provides no capability for packet retransmissions if errors occur. If out-of-order packets are delivered, or packets are missing, then applications using the data, or upper layer services, must resolve these issues. This allows IP to function very efficiently. In the TCP/IP protocol suite, reliability is the role of the transport layer.

What is header in protocol?

The Internet Protocol (IP) Header. ... On the other hand, if the computer is generating a packet to send to the network then, as the packet travels down the OSI model and reaches the Network layer, the destination and source IP Address of this packet are added in the IP Header.

Why is IP connectionless?

The Internet Protocol (IP) and User Datagram Protocol (UDP) are connectionless protocols. ... The alternative to the connectionless approach uses connection-oriented protocols, which are sometimes described as stateful because they can keep track of a conversation.

What does the IPv6 packet header consist of?

The upper layer protocol data unit (PDU) usually consists of an upper layer protocol header and its payload (for example, an ICMPv6 message, a UDP message, or a TCP segment). The IPv6 packet payload is the combination of the IPv6 extension headers and the upper layer PDU. Normally, it can be up to 65,535 bytes long.

Network Layer Protocols

There are several network layer protocols in existence. However, there are only two network layer protocols that are commonly implemented: · Internet Protocol version 4 (IPv4) · Internet Protocol version 6 (IPv6)

Encapsulating IP

To encapsulate an IP datagram using IP in IP encapsulation, an outer IP header is inserted before the datagram's existing IP header. The outer IP header Source Address and Destination Address identify the "endpoints" of the tunnel. Protocol suite: TCP/IP Protocol type: Transport layer protocol IP Protocol: 4

Default Gateway for a Switch

Typically, a workgroup switch that interconnects client computers is a Layer 2 device. As such, a Layer 2 switch does not require an IP address to function properly. However, if you wish to connect to the switch and administratively manage it over multiple networks, you will need to configure the SVI with an IPv4 address, subnet mask, and default gateway address. The default gateway address is typically configured on all devices that wish to communicate beyond just their local network. In other words, to remotely access the switch from another network using SSH or Telnet, the switch must have an SVI with an IPv4 address, subnet mask, and default gateway address configured. If the switch is accessed from a host within the local network, then the default gateway IPv4 address is not required. To configure a default gateway on a switch, use the ip default-gateway global configuration command. The IP address configured is that of the router interface of the connected switch. Enter global configuration and configure '192.168.10.1' as the default gateway for S1. S1# configure terminal Enter configuration commands, one per line. End with CNTL/Z. S1(config)# ip default-gateway 192.168.10.1 S1(config)# A common misconception is that the switch uses its configured default gateway address to determine where to forward packets originating from hosts connected to the switch and destined for hosts on remote networks. Actually, the IP address and default gateway information is only used for packets that originate from the switch. Packets originating from host computers connected to the switch must already have the default gateway address configured on their host computer operating systems.

IPv4 header functions

Version - Always set to 0100 for IPv4 Differentiatied Services - Identifies the priority of each packet Time-to-Live - Commonly referred to as hop count Protocol - Identifies the upper-layer protocol to be used next Source IP Address - The IP address of the sending host Destination IP Address - The IP address of the destination host

Basic Switch Configuration Steps

- The Router Boot Process POST (Step 1)Power On Self Test(stored in room and checks it's interface like land cards etc Bootstrap (Step 2) stored in rom for manufacturing, testing and trouble shooting Find IOS (Internetwork Operating System) (step 3) finds .bin file in flash memory Load IOS (Internetwork Operating System) (step 4) load IOS (loads .bin file into running configuration Find configuration (step 5) finds startup configuration Load configuration (step 6) loads startup configuration into running configuration Run IOS commands (step 7) run IOS commands (Runs IOS on CLI (Cisco line interface) Basic Switch Configuration Steps Click card to see the definition 👆 configure terminal Enter global configuration mode hostname name Configure a name for the device ip address x.x.x.x x.x.x.x Configure interface IP address no shutdown Enable the interface exit Return to global configuration mode interface fastethernet 0/1 Enter the interface to assign VLAN switchport mode access Define the VLAN membership mode for the port switchport access vlan X Assign the port to a VLAN duplex auto Configure the interface duplex mode to enable AUTO duplex configuration speed auto Configure the interface speed and enable AUTO speed configuration mdix auto Enable auto-MDIX on the interface ip default-gateway x.x.x.x Configure the default gateway on the switch ip http authentication enable Configure the HTTP server for authentication using the enable parameter ip http server Enable HTTP server line console 0 Switch from global configuration mode to line configuration mode for console 0 password cisco Set cisco as the password for the console login Set the console line to require the password to be entered before access is granted line vty 0 15 Switch from global configuration mode to line configuration mode for vty terminals 0-15 enable password cisco Configure cisco as the enable password to enter privileged EXEC mode enable secret class Configure class as the enable secret password to enter privileged EXEC mode service password-encryption Encrypt all the system passwords that are stored in clear text banner login #text# Configure a login banner. # delimits the beginning and end of the banner banner motd #text# Configure a message of the day login banner, # delimits the beginning and end of the banner

IPv6 header fields

- Version (4-bit) - Traffic class (8 bits) - Flow label (20 bits) - Payload length (16 bits) - Next header (8 bits) - Hop limit (8 bits) - Source address (128 bits) - Destination address (128 bits)

What is the size of the IPv6 header?

40 octets The IPv4 header's total length comprises a minimum of 20 octets (8 bits per octet), or five 32-bit words. The IPv6 header, as Figure B shows, has only 8 fields with a fixed length of 40 octets. The Ver (version) field remains in IPv6.

What is the minimum size of the IPv6 packet header?

40 octets The IPv6 packet header has a minimum size of 40 octets.

Using the Default Gateway

A host's routing table will typically include a default gateway. The host receives the IPv4 address of the default gateway either dynamically from Dynamic Host Configuration Protocol (DHCP) or configured manually. In the figure, PC1 and PC2 are configured with the default gateway's IPv4 address of 192.168.10.1. Having a default gateway configured creates a default route in the routing table of the PC. A default route is the route or pathway your computer will take when it tries to contact a remote network. The default route is derived from the default gateway configuration and is placed in the host computer's routing table. Both PC1 and PC2 will have a default route to send all traffic destined to remote networks to R1.

What is in the header of a packet?

A packet header is the portion of an IP (Internet protocol) packet that precedes its body and contains addressing and other data that is required for it to reach its intended destination.

Remote Network Routing Table Entries

A router typically has multiple interfaces configured. The routing table stores information about both directly-connected networks and remote networks.

WHAT IS routing table in networking?

A routing table is a set of rules, often viewed in table format, that is used to determine where data packets traveling over an Internet Protocol (IP) network will be directed. All IP-enabled devices, including routers and switches, use routing tables.

What is in a routing table?

A routing table is a set of rules, often viewed in table format, that is used to determine where data packets traveling over an Internet Protocol (IP) network will be directed. All IP-enabled devices, including routers and switches, use routing tables.

What is the purpose of administrative distance?

Administrative distance is the feature that routers use in order to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol.

What routing table contains?

All IP-enabled devices, including routers and switches, use routing tables. A routing table contains the information necessary to forward a packet along the best path toward its destination. Each packet contains information about its origin and destination.

What is an IPv4 Packet?

An IP packet consists of header information as well as encapsulated data. An IP header consists of 14 fields and contains necessary information required to deliver the packet at another end. IP Packet Structure. Version: Provides the version number of Internet Protocol used (such as IPv4).

IPv4 Packet Header

An IPv4 packet header consists of fields containing important information about the packet. These fields contain binary numbers which are examined by the Layer 3 process. The binary values of each field identify various settings of the IP packet. Protocol header diagrams, which are read left to right, and top down, provide a visual to refer to when discussing protocol fields. The IP protocol header diagram in the figure identifies the fields of an IPv4 packet. Significant fields in the IPv4 header include: · Version · Differentiated Services or DiffServ (DS) · Time-to-Live (TTL) · Protocol Source IPv4 Address · Destination IPv4 Address The Internet Header Length (IHL), Total Length, and Header Checksum fields

What is an IPv4 header?

An Internet Protocol version 4 packet header (IPv4 packet header) contains application information, including usage and source/destination addresses. IPv4 packet headers contain 20 bytes of data and are normally 32 bits long. A packet is a network communication data unit containing fixed or variable lengths.

Why is IP called best effort delivery protocol?

Because IP provided basic packet delivery services without guarantees, it is called a best-effort delivery service. It does its best to deliver packets to the destination, but takes no steps to recover packets that are lost or misdirected.

What is best effort basis?

Best efforts is a contractual term in which an underwriter promises to make their best effort to sell as much of a securities offering (e.g., IPO) as possible. Best-effort agreements are used mainly for securities in a less-than-ideal market condition or with higher risk, such as an unseasoned offering.

Bootset Files

Both Cisco routers and switches load the IOS image and startup configuration file into RAM when they are booted, as shown in the figure. The running configuration is modified when the network administrator performs device configurations. Changes made to the running-config file should be saved to the startup configuration file in NVRAM, in case the router is restarted or loses power.

What does C identify?

C - Identifies a directly-connected network. Directly-connected networks are automatically created when an interface is configured with an IP address and activated.

How many classes are there in IPv4?

Class Theoretical Address Range Binary Start A 0.0.0.0 to 127.255.255.255 0 B 128.0.0.0 to 191.255.255.255 10 C 192.0.0.0 to 223.255.255.255 110 D 224.0.0.0 to 239.255.255.255 1110 E 240.0.0.0 to 247.255.255.255 1111

Characteristics of IP

Connectionless Best Effort Media Independent

IP characteristics

Connectionless - No connection with the destination is established before sending data packets. Will still send if the destination is not available to receive. Best Effort (unreliable) - Packet delivery is not guaranteed. Media Independent - Operation is independent of the medium carrying the data. fiber optics cabling, satellite and wireless can be used to route the same packet.

version

Contains a 4-bit binary value set to 0100 that identifies this as an IP version 4 packet.

What is flow label in IPv6 header?

Flow Label/QoS management (20 bits) The 20-bit flow label field in the IPv6 header can be used by a source to label a set of packets belonging to the same flow. A flow is uniquely identified by the combination of the source address and of a non-zero Flow label.

Default Gateway for a Host

For an end device to communicate over the network, it must be configured with the correct IP address information, including the default gateway address. The default gateway is only used when the host wants to send a packet to a device on another network. The default gateway address is generally the router interface address attached to the local network of the host. The IP address of the host device and the router interface address must be in the same

Configure Router Interfaces

For routers to be reachable, the in-band router interfaces must be configured. There are many different types of interfaces available on Cisco routers. In this example, the Cisco 1941 router is equipped with: Two Gigabit Ethernet interfaces - GigabitEthernet 0/0 (G0/0) and GigabitEthernet 0/1 (G0/1) A serial WAN interface card (WIC) consisting of two interfaces - Serial 0/0/0 (S0/0/0) and Serial 0/0/1 (S0/0/1) R1# configure terminal Enter configuration commands, one per line. End with CNTL/Z. R1(config)# interface gigabitethernet 0/0 R1(config-if)# ip address 192.168.10.1 255.255.255.0 R1(config-if)# description LAN-10 R1(config-if)# no shutdown R1(config)# interface gigabitethernet 0/1 R1(config-if)# ip address 192.168.11.1 255.255.255.0 R1(config-if)# description LAN-11 R1(config-if)# no shutdown

What is host routing?

Host Routing is the routing process that occurs when a host (computer) on a network forwards a packet to a destination host on the network.

RAM applications and processes

IOS image running configuration file The routing table to determine the best path to forward packets. The ARP cache used to map IPv4 addresses to MAC addresses The packet buffer used to temporarily store packets before forwarding to destination

Limitations of IPv4

IP address depletion - IPv4 has a limited number of unique public IPv4 addresses available. Although there are approximately 4 billion IPv4 addresses, the increasing number of new IP-enabled devices, always-on connections, and the potential growth of less-developed regions have increased the need for more addresses. Internet routing table expansion - A routing table is used by routers to make best path determinations. As the number of servers connected to the Internet increases, so too does the number of network routes. These IPv4 routes consume a great deal of memory and processor resources on Internet routers. Lack of end-to-end connectivity - Network Address Translation (NAT) is a technology commonly implemented within IPv4 networks. NAT provides a way for multiple devices to share a single public IPv4 address. However, because the public IPv4 address is shared, the IPv4 address of an internal network host is hidden. This can be problematic for technologies that require end-to-end connectivity.

IP - Connectionless

IP is connectionless, meaning that no dedicated end-to-end connection is created before data is sent. connectionless communication is conceptually similar to sending a letter to someone without notifying the recipient in advance. Connectionless data communications work on the same principle. IP requires no initial exchange of control information to establish an end-to-end connection before packets are forwarded. IP also does not require additional fields in the header to maintain an established connection. This process greatly reduces the overhead of IP. However, with no pre-established end-to-end connection, senders are unaware whether destination devices are present and functional when sending packets, nor are they aware if the destination receives the packet, or if they are able to access and read the packet.

IP - Media Independent

IP operates independently of the media that carry the data at lower layers of the protocol stack. , IP packets can be communicated as electronic signals over copper cable, as optical signals over fiber, or wirelessly as radio signals. It is the responsibility of the OSI data link layer 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. There is, however, one major characteristic of the media that the network layer considers: the maximum size of the PDU that each medium can transport. This characteristic is referred to as the maximum transmission unit (MTU). Part of the control communication between the data link layer and the network layer is the establishment of a maximum size for the packet. The data link layer passes the MTU value up to the network layer. The network layer then determines how large packets can be. In some cases, an intermediate device, usually a router, must split up a packet when forwarding it from one medium to another medium with a smaller MTU. This process is called fragmenting the packet or fragmentation.

What is IP source route?

IP provides a provision that allows the source IP host to specify a route through the IP network. ... Source routing is specified as an option in the IP header. If source routing is specified, the software forwards the packet according to the specified source route.

What is the purpose of extension headers in IPv6?

IPv6 extension headers contain supplementary information used by network devices (such as routers, switches, and endpoint hosts) to decide how to direct or process an IPv6 packet. The length of each extension header is an integer multiple of 8 octets. This allows subsequent extension headers to use 8-octet structures.

What is difference between IPv4 & IPv6?

IPv6 is an upgrade that has vastly larger address space (32 bit vs. 2^128 bit)

What is extension header in IPv6?

IPv6 options are placed in separate extension headers that are located between the IPv6 header and the transport-layer header in a packet. Most IPv6 extension headers are not examined or processed by any router along a packet's delivery path until the packet arrives at its final destination.

Route timestamp

Identifies how much time has passed since the route was learned.

Route source

Identifies how the network was learned by the router. common route sources are (S) static route, (D) Enhanced Interior Gateway Routing Protocol (EIGRP), (O) Open Shortest Path First (OSPF)

outgoing interface

Identifies the exit interface to use to forward a packet toward the final destination.

What is source based routing?

In computer networking, source routing, also called path addressing, allows a sender of a packet to partially or completely specify the route the packet takes through the network. In contrast, in conventional routing, routers in the network determine the path incrementally based on the packet's destination.

What does ROM store?

bootup information that provides startup instructions Power on self test Post which tests the hardware components limited IOS to provide a backup version of IOS. it is used to load a full version of IOS when is deleted or corrupted.

what does destination network do?

identifies how the destination network and how it is learnt

what does outgoing source do?

identifies the exit interface and how to use it to forward the packet to final destination

Next Hop

identifies the ip address of the next router to forward a packet.

what does route source do?

identifies the network was learnt by the router

Router Memory

router has access to volatile or non-volatile memory storage. Volatile memory requires continual power to maintain its information. When the router is powered down or restarted, the content is erased and lost. Non-volatile memory retains its information even when a device is rebooted. Specifically, a Cisco router uses four types of memory: RAM - This is volatile memory used in Cisco routers to store applications, processes, and data needed to be executed by the CPU. Cisco routers use a fast type of RAM called synchronous dynamic random access memory (SDRAM). Click RAM in the figure to view more information. ROM - This non-volatile memory is used to store crucial operational instructions and a limited IOS. Specifically, ROM is firmware embedded on an integrated circuit inside the router which can only be altered by Cisco. Click ROM in the figure to view more information. NVRAM - This is non-volatile memory is used as the permanent storage for the startup configuration file (startup-config). Flash - This non-volatile computer memory used as permanent storage for the IOS and other system related files such as log files, voice configuration files, HTML files, backup configurations, and more. When a router is rebooted, the IOS is copied from flash into RAM.

IPv4 Routing Table

routing table, there are no column headings identifying the information contained in a router's routing table. It is important to learn the meaning of the different items included in each entry of the routing table.

Verify Interface Configuration

show ip interface brief show ip route - Displays the contents of the IPv4 routing table stored in RAM. show interfaces - Displays statistics for all interfaces on the device. show ip interface - Displays the IPv4 statistics for all interfaces on a router. verify connectivity from the interface using the ping command.

IPv4 Router Routing Table

the show ip route command can be used to display the router's IPv4 routing table, as shown in the figure. In addition to providing routing information for directly-connected networks and remote networks, the routing table also has information on how the route was learned, the trustworthiness and rating of the route, when the route was last updated, and which interface to use to reach the requested destination. When a packet arrives at the router interface, the router examines the packet header to determine the destination network. If the destination network matches a route in the routing table, the router forwards the packet using the information specified in the routing table. If there are two or more possible routes to the same destination, the metric is used to decide which route appears in the routing table.

Show Version Output

the show version command displays information about the version of the Cisco IOS software currently running on the router, the version of the bootstrap program, and information about the hardware configuration, including the amount of system memory.

What does D identify?

D: Identifies that the route was learned understanding routine route entriesally from another router using the EIGRP routing protocol.

What is IP encapsulation?

Data Encapsulation and the TCP/IP Protocol Stack. ... When a protocol on the sending host adds data to the packet header, the process is called data encapsulation. Moreover, each layer has a different term for the altered packet

What is the purpose of a routing protocol?

Each route in a routing table has a code that identifies how the route was learned by the router. The code letter D is used to identify routes that are learned through EIGRP. What is the purpose of a routing protocol? It allows a router to share information about known networks with other routers.

Connect to a Router

The connections on a Cisco router can be grouped into two categories: In-band router interfaces and management ports. Similar to a Cisco switch, there are several ways to access user EXEC mode in the CLI environment on a Cisco router. These are the most common: Console - This is a physical management port that provides out-of-band access to a Cisco device. Out-of-band access refers to access via a dedicated management channel that is used for device maintenance purposes only. Secure Shell (SSH) - SSH is a method for remotely establishing a secure CLI connection through a virtual interface, over a network. Unlike a console connection, SSH connections require active networking services on the device including an active interface configured with an address. Telnet - Telnet is an insecure method of remotely establishing a CLI session through a virtual interface, over a network. Unlike SSH, Telnet does not provide a securely encrypted connection. User authentication, passwords, and commands are sent over the network in plaintext. Note: Some devices, such as routers, may also support a legacy auxiliary port that was used to establish a CLI session remotely using a modem. Similar to a console connection, the AUX port is out-of-band and does not require networking services to be configured or available. Telnet and SSH require an inband network connection which means that an administrator must access the router through one of the WAN or LAN interfaces. Inband interfaces receive and forward IP packets. Every configured and active interface on the router is a member or host on a different IP network. Each interface must be configured with an IPv4 address and subnet mask of a different network. The Cisco IOS does not allow two active interfaces on the same router to belong to the same network.

What is the main purpose of a default gateway?

The default gateway device passes traffic from the local subnet to devices on other subnets. The default gateway often connects the local network to the internet, although internal gateways for communication within a local network also serve a useful purpose in corporate networks.

Default Gateway

The default gateway is the network device that can route traffic to other networks. It is the router that can route traffic out of the local network. If you use the analogy that a network is like a room, then the default gateway is like a doorway. If you want to get to another room or network you need to find the doorway. Alternatively, a PC or computer that does not know the IP address of the default gateway is like a person, in a room, that does not know where the doorway is. They can talk to other people in the room or network, but if they do not know the default gateway address, or there is no default gateway, then there is no way out.

What is the difference between IP address and IP packet?

The difference is that TCP is responsible for the data delivery of a packet and IP is responsible for the logical addressing. In other words, IP obtains the address and TCP guarantees delivery of data to that address.

IPv6 Packet Header

The fields in the IPv6 packet header include: Version - This field contains a 4-bit binary value set to 0110 that identifies this as an IP version 6 packet. Traffic Class - This 8-bit field is equivalent to the IPv4 Differentiated Services (DS) field. Flow Label - This 20-bit field suggests that all packets with the same flow label receive the same type of handling by routers. Payload Length - This 16-bit field indicates the length of the data portion or payload of the IPv6 packet. Next Header - This 8-bit field is equivalent to the IPv4 Protocol field. It indicates the data payload type that the packet is carrying, enabling the network layer to pass the data to the appropriate upper-layer protocol. Hop Limit - This 8-bit field replaces the IPv4 TTL field. This value is decremented by a value of 1 by each router that forwards the packet. When the counter reaches 0, the packet is discarded, and an ICMPv6 Time Exceeded message is forwarded to the sending host, indicating that the packet did not reach its destination because the hop limit was exceeded. Source IPv6 Address - This 128-bit field identifies the IPv6 address of the sending host. Destination IPv6 Address - This 128-bit field identifies the IPv6 address of the receiving host. An IPv6 packet may also contain extension headers (EH), which provide optional network layer information. Extension headers are optional and are placed between the IPv6 header and the payload. EHs are used for fragmentation, security, to support mobility and more. Unlike IPv4, routers do not fragment routed IPv6 packets.

What is the purpose of routing?

The main purpose of a router is to connect multiple networks and forward packets destined either for its own networks or other networks. A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address.

Network Layer

The network layer is the third level of the Open Systems Interconnection Model (OSI Model) and the layer that provides data routing paths for network communication. Data is transferred in the form of packets via logical network paths in an ordered format controlled by the network layer.

Destination network

The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet. ... A directly connected network is a network that is directly attached to one of the router interfaces.

Administrative distance

a term used to describe the value assigned for the trustworthiness of the source of the route that is learned by a router

Router Packet Forwarding Decision

When a host sends a packet to another host, it will use its routing table to determine where to send the packet. If the destination host is on a remote network, the packet is forwarded to the default gateway. What happens when a packet arrives at the default gateway, which is usually a router? The router looks at its routing table to determine where to forward packets. The routing table of a router can store information about: Directly-connected routes - These routes come from the active router interfaces. Routers add a directly connected route when an interface is configured with an IP address and is activated. Each of the router's interfaces is connected to a different network segment. Remote routes - These routes come from remote networks connected to other routers. Routes to these networks can be manually configured on the local router by the network administrator or dynamically configured by enabling the local router to exchange routing information with other routers using a dynamic routing protocol. Default route - Like a host, routers also use a default route as a last resort if there is no other route to the desired network in the routing table.

Directly Connected Routing Table Entries

When a router interface is configured with an IPv4 address, a subnet mask, and is activated, the following two routing table entries are automatically created: C - Identifies a directly-connected network. Directly-connected networks are automatically created when an interface is configured with an IP address and activated. L - Identifies that this is a local interface. This is the IPv4 address of the interface on the router.