Cisco 2 - Ch 1 - Routing Concepts

IPv6 Routing Protocols

1. RIPng (RIP next generation) 2. OSPFv3 3. EIGRP for IPv6

DHCP servers provide what?

1. valid IP address 2. Subnet mask 3. Default gateway

MTBF

Mean time between failure A measurement of reliability, or probability of failure.

"show history" command

privileged EXEC command to display the contents of the history buffer.

To be available, an interface must be this:

1. Configured with an IP address and a subnet mask (using ip address ip-address subnet-mask interface configuration command) 2. Activated (using the no shutdown command) (The interface must also be connected to another device like a hub, a switch, or another router, for the physical layer to be active.)

Console Connection Requirements

1. Console Cable - RJ45 to DB9 serial connection - USB serial cable 2. Terminal Emulation Software - Teraterm - Putty

Steps to Router Switching

1. De-encapsulates the Layer 2 frame header and trailer to expose the Layer 3 packet. 2. Examines the destination IP address of the IP packet to find the best path in the routing table. 3. If the router finds a path to the destination, it encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface. Note: It is common for packets to require encapsulation into a different type of Layer 2 frame than the one which was received. i.e. fast ethernet to serial link.

Network addressing Adequate Components

1. Device Names 2. Interfaces 3. IP addresses and Subnet masks 4. Default gateway address

Possible routing table search results

1. Directly connected network - the destination IP address of the packet belongs to a device on a network that is directly connected to one of the interfaces of the router. This means that the destination IP address of the packet is a host address on the same network as the router's interface. This packet is forwarded directly to the destination device. 2. Remote network - the destination IP address of the packet belongs to a remote network. The packet is forwarded to another router. 3. No route determined - the destination IP address of the packet does not belong to either a connected or remote network. The router determines if there is a Gateway of Last Resort available. A Gateway of Last Resort is set when a default route is configured or learned on a router. If there is a default route, the packet is forwarded to the Gateway of Last Resort. If the router does not have a default route, the packet is discarded.

Types of Routes

1. 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. 2. Remote routes - These are remote networks connected to other routers. Routes to these networks can either be statically configured or dynamically learned through dynamic routing protocols.

IPv4 Routing Protocols

1. EIGRP - Enhanced Interior Gateway Routing Protocol 2. OSPF - Open Shortest Path First 3. IS-IS - Intermediate System-to-Intermediate System 4. RIP - Routing Information Protocol A router running a dynamic routing protocol does not only make a best path determination to a network, it also determines a new best path if the initial path becomes unusable

Primary Functions of a Router

1. Forward the packet to the destination 2. Choose the best path for the packet to take. (using the routing table)

Configuration tasks which should always be performed

1. Name the device 2. Secure with passwords 3. Banner message

Packet Forwarding Mechanisms

1. Process Switching 2. Fast Switching 3. Cisco Express Forwarding

what happens when a packet arrives at a first hop router

1. R1 examines the destination MAC address, which matches the MAC address of the receiving interface, FastEthernet 0/0. R1, therefore, copies the frame into its buffer. 2. R1 identifies the Ethernet Type field as 0x800, which means that the Ethernet frame contains an IPv4 packet in the data portion of the frame. 3. R1 de-encapsulates the Ethernet frame. 4. R1 searches the routing table for a network address that would include the destination IPv4 address of the packet. 5. R1 re-encapsulates the IPv4 packet into a new Ethernet frame with the destination MAC address of the IPv4 address of the next-hop router. -If the nest hop address is not known, R1 sends out an ARP request.

Remote Network Routing Entry Information

1. Route source - Identifies how the route was learned. 2. Destination network - Identifies the address of the remote network. 3. Administrative distance - Identifies the trustworthiness of the route source. Lower values indicate preferred route source. 4. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. 5. Next-hop - Identifies the IPv4 address of the next router to forward the packet to. 6. Route timestamp - Identifies how much time has passed since the route was learned. 7. Outgoing interface - Identifies the exit interface to use to forward a packet toward the final destination.

Dynamic protocols and their metrics

1. Routing Information Protocol (RIP) - Hop count 2. Open Shortest Path First (OSPF) - Cisco's cost based on cumulative bandwidth from source to destination 3. Enhanced Interior Gateway Routing Protocol (EIGRP) - Bandwidth, delay, load, reliability

types of static routes in the routing table

1. Static route to a specific network: must be configured 2. Default static route: similar to a default gateway, specifies the exit point to use when the routing table does not contain a path for the destination network, useful when a router has only one exit point to another router, A static route is identified in the routing table with the code 'S'.

Ways to remotely connect to a device

1. Telnet 2. SSH 3. HTTP 4. HTTPS

Best Path Rules

1. Whenever multiple paths to the same network exist, each path uses a different exit interface on the router to reach that network. 2. The best path is selected by a routing protocol based on the value or metric it uses to determine the distance to reach a network 3. The routing algorithm generates a value, or a metric, for each path through the network, and the best path to a network is the path with the lowest metric.

The Routing Table

1. a data file in RAM that is used to store route information about directly connected and remote networks 2. contains network or next hop associations, which tell a router that a particular destination can be optimally reached by sending the packet to a specific router that represents the next hop on the way to the final destination

benefits of using static routes

1. improved security and resource efficiency. 2. use less bandwidth than dynamic routing protocols 3. No CPU cycles are used to calculate and communicate routes. The main disadvantage to using static routes is the lack of automatic reconfiguration if the network topology changes.

Filtering show commands

1. section - Shows entire section that starts with the filtering expression 2. include - Includes all output lines that match the filtering expression 3. exclude - Excludes all output lines that match the filtering expression 4. begin - Shows all the output lines from a certain point, starting with the line that matches the filtering expression.

What happens when a packet reaches the final router connected to the destination device

1. the router searches for the destination IPv4 address of the packet in its Address Resolution Protocol (ARP) cache. If the entry is not in the ARP cache, the router sends an ARP request out of its FastEthernet 0/0 interface (the end device will send ARP reply) 2. The IPv4 packet is encapsulated into a new Ethernet data link frame and sent out the FastEthernet 0/0 interface of R3. 3. The end device receives/examines the frames destination MAC address, which matches the MAC address of the receiving interface, its Ethernet network interface card (NIC). The end device copies the rest of the frame into its buffer. 4. PC2 identifies the Ethernet Type field as 0x800, indicating the Ethernet frame contains an IPv4 packet 5. the end device de-encapsulates the Ethernet frame and passes the IPv4 packet to the IPv4 process of its operating system.

What address and prefix length is used when configuring an IPv6 default static route?

::/0 The IPv6 address and prefix for a default static route is ::/0. This represents all zeros in the address and a prefix length of zero.

How the router determines the best path for a packet

A Router examines the DESTINATION address of a PACKET against its own ROUTING TABLE to determine the NETWORK address. The routing table includes the INTERFACE of all known networks that the router can forward to, and instructs the router to ENCAPSULATE the packet into the DATA-LINK LAYER FRAME of the outgoing/exit interface, which is sent out the correct interface/towards the correct network.

Fast Switching

A form of router packet forwarding in which a cache of next-hop information is stored. When packets arrive at the router interface which happen to contain next hop info already stored in the cache, those packets bypass the CPU control plane and do NOT need to be compared to the routing table. They are sent immediately to the exit interface. If packets next hop info is not recognized, it is sent to the CPU and processed normally.

Routers and Interfaces

A router connects multiple networks, which means that it has multiple interfaces that each belong to a different IP network. When a router receives an IP packet on one interface, it determines which interface to use to forward the packet to the destination. Each network that a router connects to typically requires a separate interface. These interfaces are used to connect a combination of both local-area networks (LANs) and wide-area networks (WANs). LANs are commonly Ethernet networks that contain devices, such as PCs, printers, and servers. WANs are used to connect networks over a large geographical area.

How IPv6 differs in sending packets to routers

A similar process is used for IPv6 packets to IPv4. Instead of the ARP process, IPv6 address resolution uses ICMPv6 Neighbor Solicitation and Neighbor Advertisement messages. IPv6-to-MAC address mapping are kept in a table similar to the ARP cache, called the neighbor cache.

Remote manage a Switch

A switch does not have a dedicated interface on which an IP address can be assigned, so it it is configured on a VIRTUAL INTERFACE called an SVI (switch virtual interface)

How a device determines if a destination IPv4 address is on the same network

ANDing 1. First on its OWN IPv4 address and subnet mask 2. Then on the packets destination IPv4 subnet mask and the original devices subnet mask.

Directly Connected Routing Table Entry information

An active, properly configured, directly connected interface creates two routing table entries 1. Route source - Identifies how the route was learned. Directly connected interfaces have two route source codes. 'C' identifies a directly connected network. 'L' identifies the IPv4 address assigned to the router's interface. 2. Destination network - The address of the remote network. 3. Outgoing interface - Identifies the exit interface to use when forwarding packets to the destination network.

self generating ipv6 rule

An interface can generate its own IPv6 link-local address without having a global unicast address by using the "ipv6 enable interface" configuration command.

Cisco Express Forwarding (CEF)

Builds an FIB/Forwarding Information Base, and an Adjacency Table for converged networks. The entries of the FIB and the Adjacency table are CHANGE-TRIGGERED, changing when something changes in the network topology (like converging the network). They hold all the information a router needs to consider when forwarding a packet. The FIB has: pre-computed reverse look-ups Interfaces Layer 2 info (next hop info for routes) most recent, preferred

7 Network Characteristics

CARTSSS Cost Availability Reliability Topology Security Scalability Speed

Components of a network capable device

COM CPU Operating System Memory and storage

Console Cable Connections

Connects between the serial port on the host and the console port on the device. If the host does not have a serial port, then use a USB port to create a console connection. BUT, a special USB to RS232 serial port adapter would be required.

Router

Connects one network to another network. Responsible for the EFFICIENT delivery of Packets between/among networks, as well as finding the best path through the network(s)

show ip interface brief

Displays a summary for all interfaces including the IPv4 address of the interface and current operational status.

show ip route

Displays the contents of the IPv4 routing table stored in RAM. In Cisco IOS 15, active interfaces should appear in the routing table with two related entries identified by the code 'C' (Connected) or 'L' (Local). In previous IOS versions, only a single entry with the code 'C' will appear.

Process Switching

EACH packet is received by the routers interface and sent to the CPU's control plane, where the CPU compares the destination address of the packet to the entries in the routing table. Even if all packets in a stream of packets has the same destination address. older slower less used model of packet forwarding

How a device sends a packet on the same network

If the destination network address is the same network as the originating device, then the original device does not use the default gateway, instead, it refers to its ARP cache for the MAC address of the device with that destination IPv4 address. If the MAC address is not in the cache, then the original device generates an ARP request to acquire the address to complete the packet and send it to the destination.

Enabling and assigning a loopback address

In global config mode 1. "interface loopback" (number) 2. "ip address" (ip address and SM) 3. "exit"

How to configure an IPv4 Router Interface

In global config mode command: 1. "interface" "and the interface you want (gigabitethernet/serial, etc.). 2. enter IP address and subnet Mask 3. "description Link ("") to ("") " 4. "no shutdown"

How to configure an IPv6 Router Interface

In global config mode command: 1. "interface" "and the interface you want (gigabitethernet/serial, etc.). 2. enter IPv6 address with prefix length 3. "description Link ("") to ("") " 4. "no shutdown"

Remote management rule

Network infrastructure devices require IP addresses in order to be able to be managed remotely

The Router Switching Function

The process used by a router to accept a packet on one interface and forward it out of another interface. A key responsibility of this function is to encapsulate packets in the appropriate data link frame type for the outgoing data link

How a device sends a packet on different networks.

To determine the MAC address of the default gateway, a device checks its ARP table for the IPv4 address of the default gateway and its associated MAC address. If an ARP entry does not exist in the ARP table for the default gateway, PC1 sends an ARP request. Router R1 sends back an ARP reply. The device can then forward the packet to the MAC address of the default gateway, the Fa0/0 interface of router R1.

Routing table

Used by a router to determine the best path to use for a packet

Switches

Used to forward Ethernet frames between devices. Operates on layer 2

Equal Cost Load Balancing

When a router has two or more paths to a destination with equal cost metrics, then the router forwards the packets using both paths equally. The routing table contains the single destination network, but has multiple exit interfaces, one for each equal cost path. The router forwards packets using the multiple exit interfaces listed in the routing table

What happens when a connection between routers is a serial connection

When the interface is a point-to-point (P2P) serial connection, the router encapsulates the IPv4 packet into the proper data link frame format used by the exit interface (HDLC, PPP, etc.). Because there are no MAC addresses on serial interfaces, the router sets the data link destination address to an equivalent of a broadcast, no source address is required.

loopback interface

a logical interface internal to the router, not assigned to a physical port and can therefore never be connected to any other device. It is considered a software interface that is automatically placed in an "up" state, as long as the router is functioning.

A serial link

a point-to-point connection that uses a Layer 2 frame that does not require the use of a MAC address.

IPv4 Dynamic Routing "D" entries

entries in a routing table beginning with 'D*EX' identifies that the source of this entry was EIGRP ('D'). The route is a candidate to be a default route ('*'), and the route is an external route ('*EX') forwarded by EIGRP.

Routing Table Sources

identified by a code that identifies how the route was learned. 1. L - Local route. Identifies the address assigned to a router's interface. This allows the router to efficiently determine when it receives a packet for the interface instead of being forwarded. 2. C - Identifies a directly connected network. 3. S - Identifies a static route created to reach a specific network. 4. D - Identifies a dynamically learned network from another router using EIGRP. 5. O - Identifies a dynamically learned network from another router using the OSPF routing protocol.

Active console port rule

only one console port can be active at a time. When a cable is plugged into the USB console port, the RJ-45 port becomes inactive. When the USB cable is removed from the USB port, the RJ-45 port becomes active.

To return to more recent commands in the history buffer

press Ctrl+N or the Down Arrow key. (keep pressing the down arrow key to get more successively recent commands)

To recall commands in the history buffer

press Ctrl+P or the Up Arrow key. (pressing the up arrow key more, gives you successively older commands.

Administrative Distance

represents the "trustworthiness" of the route; the lower it is, the more trustworthy the route source. Given two separate routes to the same destination, the router chooses the route with the lower/lowest.

Router

specialized network capable devices which use Cisco IOS as their OS

command history feature`

temporarily stores the list of executed commands to be recalled.

Network discovery

the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol. Instead of depending on manually configured static routes to remote networks on every router, a dynamic routing protocol allows the routers to automatically learn about these networks from other routers. These networks, and the best path to each, are added to the routing table of the router, and identified as a network learned by a specific dynamic routing protocol. During network discovery, routers exchange routes and update their routing tables. Routers have converged after they have finished exchanging and updating their routing tables. Routers then maintain the networks in their routing tables.

S 10.2.0.0 [1/0] via 172.16.2.2.

the numbers inside the bracket indicate the administrative distance and metric respectively.

Metric

the quantitative value used to measure the distance to a given network. The best path to a network is the path with the lowest metric. The routing algorithm generates a value, or a metric, for each path through the network Metrics can be based on either a single characteristic or several characteristics of a path

what the router does to determine a packets best path

the router searches its routing table for a network address that matches the destination IP address of the packet.

default gateway

the router to which a packet is sent when the final destination is a host outside the network from which the packet is being sent

The pale blue background behind console port

the standard color that is used on Cisco devices to indicate a console connection.

Dynamic Routing

used by routers to share information about the reachability and status of remote networks responsible for network discovery and maintaining routing tables.

"terminal history size" command

user EXEC command to increase or decrease the size of the buffer.