Back Panel Connection Cisco Router 1941

Cisco router has several types of ports and interfaces that are used to interconnect many other devices and other routers. For this reason, these devices have numerous types of ports and interfaces are used. Figure 1 illustrates the back panel of Cisco router 1941.  Here is the short explanation of back panel of the Cisco router 1941.

Back Pannel Explanation of Cisco Router 1941

1. These are 2 USB ports providing additional storage space similar to flash. These ports are labeled as USB 0 and USB 1.


2. These are Gigabit Ethernet interfaces. These ports generally provide LAN access by connecting to switches, other routers, and users. The ports are labeled as GE0/0 and GE0/1.


3. These ports are Auxiliary (AUX) RJ-45 ports. Auxiliary ports are being used for remote management access similar to the Console port. Now considered a legacy port because of providing support for dial-up modems.


4. These are console ports of the router which is important for initial configuration of the router. Two ports are available; the commonly used regular RJ-45 port at the left and a new USB Type-B (mini-B USB) connector at the right side at number 4. However, the console can only be accessed by one port at a time.


5. Enhanced High-speed WAN Interface Card (eHWIC)- This slot is labeled as eHWIC 0 and eHWIC 1. These ports provide modularity and flexibility by enabling the router to support different types of interface modules, including serial, digital subscriber line (DSL), switch port, and wireless.


6. Compact Flash slots labeled as CF0 and CF1 to provide increased storage flash space upgradable to 4 GB compact flash card per slot. By default, CF0 is populated with a 256 MB compact flash card and is the default boot location.

Routers CPU, OS and Memory

In chapter 1 we have already studied the general introduction of the router here we will briefly discuss routers. It is similar to a computer. Regardless of their function, size or complexity, all router models are basically computers. Just like computers, tablets, and smart devices, It also requires:

• Central processing units (CPU)


• Operating systems (OS)


• Memory consisting of random-access memory (RAM), read-only memory (ROM), nonvolatile random-access memory (NVRAM), and flash.

Here in this section, we will discuss Cisco routers. Like all computers, tablets, gaming consoles, and smart devices, Cisco devices require a CPU to execute OS instructions, such as system initialization, routing functions, and switching functions.

Central Processing Unit (CPU)

The central processing unit (CPU) of a router is a hardware that carries out the instructions of the OS to perform routing and switching.  The CPU is sometimes also referred to as the central processor unit or processor for short. The CPU generates interrupts (IRQ) in order to communicate with the other electronic components in the router.

Routers Operating System

The Cisco Internetwork Operating System (IOS) is the operating system used for most Cisco devices. Cisco IOS is a family of software used on most Cisco routers, Cisco network switches, Cisco access points and many other devices. Earlier switches run CatOS.  IOS is a package of routing, switching, internetworking and telecommunications functions integrated into a multitasking operating system. Routers Memory-Cisco router uses four types of memory which are following:

Random Access Memory(RAM)

RAM is a hardware device that allows information to be stored and retrieved on a router. This is volatile memory used in Cisco routers. This memory store application, 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).  As we know that it is a volatile memory and requires power to keep the data accessible. If the router is turned off, all data contained in RAM is lost.RAM has following the main function:

• Store routing table.


• Running IOS.


• Store ARP Table


• Packet buffer


• Store running configuration file.

ROM

The ROM is used to start and maintain the router. This is a volatile memory of the router. It contains some code, like the Bootstrap and POST, which helps the router do some basic tests and boot up when it's powered on or reloaded. ROM is firmware embedded on an integrated circuit inside the router which can only be altered by Cisco You cannot alter any of the code in this memory as it has been set from the factory and is Read Only. ROM stores the following:

• Bootup information that provides the startup information.


• Power-on self-test (POST)


• Limited IOS to provide a backup version of the IOS. When full feature IOS has been deleted or corrupted, this limited IOS is used to restore full featured IOS.

NVRAM

This is non-volatile RAM. The NVRAM is a place where the router holds its configuration. This is the permanent memory storage of the router. When you configure a router and then save the configuration, it is stored in the NVRAM. This memory is not big at all when compared to the system's RAM. When a router starts up after it loads the IOS image it will look into the NVRAM and load the configuration file in order to configure the router. The NVRAM is not erased when the router is reloaded or even switched off.

Flash

Flash memory is non-volatile memory used as permanent storage for the IOS and other systems related files such as log files, voice configuration files, HTML files, backup configurations, and much more. When a router is rebooted, the IOS is copied from flash into RAM. The RAM is an EEPROM (Electrical Erasable Programmable Read Only Memory) card. It fits into a special slot normally located at the back of the router and contains nothing more than the IOS image. Usually, it comes in sizes of 4MB for the smaller routers and goes up from there depending on the router model.

IPv4 Router Routing Table

On a Cisco IOS router, the "show ip route" command can be used to display the router’s routing table, as shown in the figure. The show command is working in User Privilege Mode. If we want to use show commands in global configuration mode then (do) will be used before show command. The router routing table provides the following information:

• The routing information for directly-connected networks


• The routing information for remote networks.


• Information how the route was learned.


• The reliability of the route.


• Rating of the route.


• When was the route last updated?


• Which interface to use to reach the requested destination?

When a packet received at the router interface, the router read the packet header to decide the destination network for the packet. If the destination network matches a route in the routing table, then the router forwards the packet using the information in the routing table. If there are two or more possible routes to the same destination, the metric is used to make a decision which route is best.

Figure 1 shows the topology diagram which is consists of two router Rawalpindi and Peshawar. Topology in Packet Tracer can be download from here. Figure 2 shows the routing table on Rawalpindi router.

Directly Connected Routing Table Entries

When a router interface is configured with an IPv4 address and is activated with no shutdown command, the following two routing table entries are automatically created:

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


• L- Identifies that this is a local interface and also show the IPv4 address of the interface on the router.

Figure 2 describes the routing table entries on Rawalpindi for the directly-connected networks 192.168.3.0, 192.168.4.0 and 192.168.10.0 These entries were automatically added to the routing table when these interfaces were configured and activated with no shutdown command. Local interface entries did not appear in routing tables previous to IOS Release 15. The IOS version of the router Rawalpindi is 12.4. so Its does not display local interface entries.

The routing table entries show that how the network was learned (C, L), the destination network for example (192.168.3.0) and outgoing interface (FastEthernet 0/0)

Remote Network Routing Table Entries

As we know that router typically has multiple interfaces configured. The routing table stores information about both directly-connected networks and remote networks. Figure 2 also shows the result of Remote Network Routing Table Entries.

The figure shows the Rawalpindi route to remote network 192.168.0.0 and 192.168.1.0. Following are the explanation of the route.

Source

Identifies how the route was learned by the router. Common routing sources include S (static route), D (Enhanced Interior Gateway Routing Protocol or EIGRP), and O (Open Shortest Path First or OSPF). Other route sources are also shown in the figure.

Destination Network

Identifies the destination network for the local router.

Administrative Distance

[90/2172416] 90 is the administrative distance of the route. It shows the trustworthiness of the router source. Lower values indicate increased the trustworthiness of the route source.

Metric

[90/2172416] The value in red show the metric of the route. Metric Identifies the value assigned to reach the remote network. Lower values indicate preferred routes.

Next-Hop

Via 192.168.10.1 is the IP address of the next router. This IP is next-hop for this route.

Route Timestamp

This is the last time when the route was updated (hours: minutes: seconds).

Outgoing interface

Last entry is the outgoing interface to use to forward a packet toward the final destination.

Router Packet Forwarding Decision

When a host going to sends a packet to another host; it will use host routing table where to send the packet. If the destination host is not on the same network, as a result the packet will be forwarded to the default gateway. When a packet arrives at the default gateway, which is generally a router. So the routers consult its routing table to decide where to forward this packet. The routing table of a router contains information about:

Directly connected routes

These routes come from the router active 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 or dynamically configured on the local router by the network administrator.

Default route 

Routers also use a default route as a last option if there is no other route to the desired network in the routing table.

The figure identifies the directly connected networks and remote networks of router-1. Networks in the red rectangles are directly connected networks for router-1 and network in the blue rectangles are a remote network for router-1 and vice versa.

Downloads

Cisco Packet Tracer 6.2 Instructor version

Cisco Packet Tracer 7.0-32 Bit

Cisco Packet Tracer 7.0 – 64 bits

Putty – 64 bits

Putty – 32 bits

Wireshark - Network Analyzer

Lab - Routing Table Entries

Lab - Configuring and Verifying Router Interfaces

Lab - Identifying MAC and IP Address

Lab- Assigning IPv6 Address to Router Interfaces and Configure Static Route

Host Routing Table

On Windows host, we can check the host routing table by the help of any one of the following commands.

• route print


• netstat -r

The above mention commands can be used to display the host routing table. Both commands generate the same result. Entering the netstat -r command or the route print command displays the result which has three sections related to the current TCP/IP network connections:

Interface List

This lists show the MAC address and assigned interface number of every network-capable interface on the host, including Ethernet, Wi-Fi, and Bluetooth adapters.

IPv4 Routing Table

This show all IPv4 routes, as well as direct connections, local network, and local default routes.

IPv6 Routing Table

This show all IPv6 routes, as well as direct connections, local network, and local default routes.

The Default Gateway

The default gateway is the device that routes traffic from one network to other networks. Usually, router work as the default gateway. Which allows devices on one network to communicate with devices in another network. Therefore default simply means that this gateway is used by default unless an application specifies another gateway.

If you use the similarity that a network is like a home. The rooms in a home are like a computer in the network. The main gate of your home as just like a default gateway. If you want to get into another home then you will use the main gate of your home. Same is for a computer network; when you want to go outside from your network you will use the interface which is connected to outside networks. PC or computer that does not know the IP address of the default gateway is like a person, in a home, that does not know where the main gate is. They can talk to other people in the home or network, but if they do not know the default gateway address, or there is no gateway, then there is no way out.

The default gateway's main purpose in most homes and small offices is to direct Internet traffic from the local network to the cable or DSL modem, which connects to the Internet service provider (ISP), and vice versa. The default IP address for gateway assigned by vendors of consumer routers.

The Host Default Gateway

End device required configuration with correct IP address information, including the default gateway address of the network. The host default gateway is used when the host wants to communicate outside the network. Usually, the host default gateway address is the router interface address attached to the local network of the host. The host IP address and the router interface address should be on the same network.

A host's routing table will usually include a default gateway. The host receives the IPv4 address of the default gateway dynamically from Dynamic Host Configuration Protocol (DHCP) or configured manually. In figure 1, PCs in the local network are configured with the default gateway’s IPv4 address of 192.168.1.1. If a default getaway is configured, it creates a default route in the routing table of the PC. A default route is a route, your computer will take when it tries to contact a remote network. IPv4 address 192.168.1.1 is the address of router interface. The default route is derived from the default gateway configuration and is placed in the host computer’s routing table. In addition, all computer on the local network will have a default route to send all traffic destined to remote networks to ISP Router.

The figures 2 show a topology of a router with two networks connected with its two interfaces. FE 0/0 is connected to network 192.168.10.0/24, while FE 0/1 is connected to network 192.168.20.0/24. Each host device is configured with the right gateway address.PCs are in the same subnet, so they don’t need a gateway to communicate. It's only required destination  IP address and MAC address.

When PC1 sends a packet to PC2 on the same network, the gateway address is not used. PC1 forwards the packet directly to PC2 through the switch using the IP address of the PC-2.

If PC1 sends a packet to PC4 which is not in the same network with PC-1. In this example, PC1 addresses the packet with the IP address of the PC3, but then forwards the packet to the router. The router accepts the packet, and then accesses its routing table to decide the correct exit interface based on the destination address, and then forwards the packet out of the correct interface to reach PC4.

The Switch Default Gateway

Switch that is working in the workgroup is a layer 2 device that does not require an IP address to function properly. But, if you want to connect to the switch remotely for administration purpose over multiple networks; you will require configuring the SVI with an IPv4 address, subnet mask, and default gateway address. 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 switch gateway address is not required. The default gateway address is necessary to configure on each device that wants to communicate beyond the local network.

The gateway address is typically the address of a router interface that is connected to switch. To configure a default gateway on a Cisco switch use the “ip default-gateway” command in global configuration mode.

Packets originating from host computers connected to the switch must already have the gateway address configured on their host computer operating systems. So they host computer do not need a default gateway configured on the switch. Actually, the IP address and default gateway information are only used for packets that originate from the switch.