CCNA Module 5

Common scenarios for static routes

- default route forwarding packets to a service provider -For routes outside the routing domain and not learned by the dynamic routing protocol -When the network administrator wants to explicitly define the path for a specific network -For routing between stub networks

Enhanced Interior Gateway Routing Protocol (EIGRP)

-A Cisco proprietary hybrid protocol that uses "hello" packets broadcasted every 60 seconds to form neighbor relationships, has metrics of bandwidth, delay, load, reliability and MTU, is classless (uses VLSM), can support different protocols with PDMs and implements DUAL as it's algorithm to choose best paths to networks -metric is based onslowest bandwidth and delay values -can include load and reliability in metric calculation

Routing Information Protocol (RIP)

-A dynamic protocol that uses distance-vector routing algorithms to decipher which route to send data packets. -metric is hop count -maximum of 15 hops

Open Shortest Path First (OSPF)

-An interior gateway routing protocol developed for IP networks based on the shortest path first or link-state algorithm. -metric is cost which is based on cumulative bandwith -faster links have lower costs than slower links

What are 3 ways a host address can be added to the routing table?

-Automatically installed when an IP address is configured on the router -Configured as a static host route -Host route automatically obtained through other methods

Common scenarios for dynamic routes

-In networks consisting of more than just a few routers -When a change in the network topology requires the network to automatically determine another path -For scalability. As the network grows, the dynamic routing protocol automatically learns about any new networks.

What 3 packet forwarding mechanisms must a router support?

-Process switching -Fast switching -Cisco Express Forwarding (CEF)

How do routers learn about remote networks?

-Static routes - Added to the routing table when a route is manually configured. -Dynamic routing protocols - Added to the routing table when routing protocols dynamically learn about the remote network. Dynamic routing protocols include Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF), as well as several others.

Advantages of dynamic routing protocols

-ability to select a best path -ability to automatically discover a new best path when there is a change in the topology.

2 primary functions of a router

-determine the best path to forward packets based on its routing table - forward packets to their destination

Which of the following routes may be found in a routing table? (Choose all that apply.)

-directly connected routes -static routes -dynamic routing protocol routes -default route

What are the 3 primary uses of static routing?

-it provides ease of routing table maintenance in smaller networks that are not expected to grow significantly. -It uses a single default route to represent a path to any network that does not have a more specific match with another route in the routing table. Default routes are used to send traffic to any destination beyond the next upstream router. -It routes to and from stub networks. A stub network is a network accessed by a single route, and the router has only one neighbor.

Describe the Router Boot Sequence

1. Router performs Power On Self Test (POST) 2. Bootstrap program looks for IOS, usually located in flash memory 3. IOS software looks for the startup-config in NVRAM 4. If found in NVRAM, Router copies the startup-config into RAM and it becomes the running-config. 5. If not found in NVRAM, Router broadcasts for TFTP host (usually will fail) and boots into setup mode.

Describe the router packet forwarding process.

1. the data link frame with an encapsulated IP packet arrives on the ingress interface. 2. The router examines the destination IP address in the packet header and consults its IP routing table. 3. The router finds the longest matching prefix in the routing table. 4. The router encapsulates the packet in a data link frame and forwards it out the egress interface. 5. If there is no matching route entry, the packet is dropped.

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

::/0

Cisco Express Forwarding (CEF)

A Layer 3 switching method. This technique speeds up packet forwarding by decoupling the usual strict interdependence between Layer 2 and Layer 3 decision making. The forwarding decision information is stored in several data structures for CEF switching. This forwarding information can be rapidly referenced to expedite packet forwarding decisions.

default route

A backup route, usually to another router, used when a router cannot determine a path to a message's destination.

Point-to-Point Protocol (PPP)

A common Layer 2 protocol offering features such as multilink interface, looped link detection, error detection, and authentication.

default static route

A default static route is an administratively configured entry in a router's routing table that specifies where traffic for all unknown networks should be sent. creates a gateway of last resort

Which feature on a Cisco router permits the forwarding of traffic for which there is no specific route?

A default static route is used as a gateway of last resort to forward unknown destination traffic to a next hop/exit interface

host route entry

A route table entry that matches all 4 bytes of the desired destination. Network route table entries only match the network bits of the desired address.

host route

A route with a /32 mask, which by virtue of this mask represents a route to a single host IP address. or an IPv6 address with a 128-bit mask

What are two functions of a router?

A router connects multiple IP networks. It determines the best path to send packets.

summary static route

A single static route that can represent multiple contiguous networks to reduce the number of entries in a routing table.

ping

A utility that sends an ICMP echo request message to a host.

When does the router begin to send RA messages?

After the ipv6 unicast-routing command is configured.

Which two route source codes are automatically created within a routing table whenever a router interface is configured with an IP address and activated?

C and L

Which packet forwarding method is used by default on Cisco routers?

Cisco Express Forwarding

Which packet-forwarding method does a router use to make switching decisions when it is using a forwarding information base and an adjacency table?

Cisco Express Forwarding (CEF)

Which type of static route creates a gateway of last resort?

Default static route

show ip interface brief

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

show interfaces

Displays statistics for all interfaces on the device

show ip interface

Displays the IPv4 statistics for all interfaces on a router

show running-config interface

Displays the commands configured on the specified interface.

show ip route

Displays the contents of the IPv4 routing table stored in RAM.

High-Level Data Link Control (HDLC)

Encapsulation method for data on serial links that will not encapsulate multiple network protocols on the same link, it's proprietary

True or False? A default route can only be a static route.

False

quad zero route

IPv4 default static route 0.0.0.0 0.0.0.0

Why must a fully specified static route be used when the next-hop router has a link-local address?

IPv6 link-local addresses are not stored in the IPb6 routing table.

How is the destination network in an IPv6 static route identified?

IPv6 prefix and prefix length

When must a fully specified IPv6 static route be used?

If the IPv6 static route uses an IPv6 link-local address as the next-hop address

administrative distance

In Cisco routers, a means for one router to choose between multiple routes to reach the same subnet when those routes were learned by different routing protocols. The lower the administrative distance, the better the source of the routing information.

Which route entry would be used for a packet with a destination IP address that matches an IP address of one of the router interfaces?

L

show ip protocols

Lists information about the RIP configuration, plus the IP addresses of neighboring RIP routers from which the local router has learned routes.

show interfaces trunk

Lists information about the currently operational trunks (or just for the trunk listed in the command) and the VLANs supported on those trunks.

show interfaces status

Lists one output line per interface, noting the description, operating state, and settings for duplex and speed on each interface

Which two route sources have the ability to automatically discover a new best path when there is a change in the topology?

OSPF EIGRP

Next-hop route

Only the next-hop IP address is specified

Directly connected static route

Only the router exit interface is specified

Remote network

Remote networks are networks that are not directly connected to the router

Describe Router Hardening

Router Hardening: Eliminate potential abuse of unused ports and services o Secure admin control o Disable unused ports o Disable unnecessary services

A network administrator configures a static route for the same destination network that was learned automatically by the router using OSPF. Which route will be installed and why?

Static route

What type of network is accessed by a single route and the router has only one neighbor?

Stub network

Fully specified static route

The next-hop IP address and exit interface are specified.

Fast Switching

This is a common packet forwarding mechanism which uses a fast-switching cache to store next-hop information. When a packet arrives on an interface, it is forwarded to the control plane where the CPU searches for a match in the fast-switching cache. If it is not there, it is process-switched and forwarded to the exit interface. The flow information for the packet is also stored in the fast-switching cache. If another packet going to the same destination arrives on an interface, the next-hop information in the cache is re-used without CPU intervention.

Process Switching

When a packet arrives on an interface, it is forwarded to the control plane where the CPU matches the destination address with an entry in its routing table, and then determines the exit interface and forwards the packet.

Equal Cost Load Balancing

When a router utilizes multiple paths with the same administrative distance and cost to a destination.

stub network

a network accessed by a single route, and the router has only one neighbor

directly connected network

a network that is connected to a device's interface. For example networks that interface with the router are known to be directly connected. Devices learn their initial IP routes based on being connected to these subnets.

Child route

a route that is a subnet of a classful network address. Also known as a level 2 route

What are two common types of static routes in routing tables?

a static route to a specific network default static route

Network Discovery

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.

What is an advantage of using dynamic routing protocols instead of static routing?

ability to search and find a new best path if the current path is no longer available.

The output of the show ip route command contains the following entry: S 10.2.0.0 [1/0] via 172.16.2.2. What value is indicated by the 1 in the [1/0] portion of the output?

administrative distance

Which value represents the "trustworthiness" of a route and is used to determine which route to install into the routing table when there are multiple routes toward the same destination?

administrative distance

What three advantages are provided by static routing?

better security use less bandwidth provide a known path to the destination

Which type of route would typically be used on a border router so that devices inside the company could access the Internet?

default route is commonly used on the edge router of a company to connect to an ISP

Which two methods can be used to identify the next hop in a static route?

destination IP address exit interface

Which type of static route that is configured on a router uses only the exit interface?

directly connected static route

What are three functions of dynamic routing protocols?

discover the network maintain routing tables calculate the best path

begin filter command

displays all the output lines from a certain point, starting with the line that matches the filtering expression.

section filter command

displays the entire section that starts with the filtering expression

Primary responsibility of the packet forwarding function

encapsulate packets in the appropriate data link frame type for the outgoing interface.

A. Standard static route

entered manually into the routing table

What does the routing table consist of?

entries consisting of a prefix (network address) and prefix length.

exclude filter command

excludes all output lines that match the filtering expression

show running-config | section ip route

filters the running configuration for only IPv4 static routes.

What action will a router take on a packet with a destination IP address that is on a remote network?

forward the packet to the next hop router

What type of static route is created when the next-hop IP address and exit interface are specified?

fully specified static route

include filter command

includes all output lines that match the filtering expression

What is the correct syntax of a floating static route

ip route {ip address subnet mask} {exit interface} {AD}

How does a router forward a packet to a device on a directly connected network?

it uses the ARP table or the Neighbor cache to find the MAC address associated with the packet destination IP address.

When a router learns that multiple paths are available to a destination network from the same routing protocol, which factor is considered by a router to choose the best path to forward a packet?

lowest metric

What are two reasons why an administrator might choose to use static routing rather than dynamic routing?

more security less processing and bandwidth

What is used to determine the minimum number of far-left bits that must match between the prefix in the route entry and the destination IP address.

prefix length in the routing table entry

How does a router forward a packet to the next-hop router?

router searches its ARP table or neighbor cache for IP address of the next-hop router

What table does a router use to determine how to forward an IP packet?

routing table

show ip route network

show routing table entries for a specific network

show ip route static

show routing table entries for static routes

show ip route ospf

show routing table entries learned through OSPF

floating static route

static routes that are used to provide a backup path to a primary static or dynamic route

A network administrator uses the command ip route 172.18.0.0 255.255.0.0 S0/0/1 to configure a floating static route on a router. That route will function as a backup route to reach the EIGRP learned network 172.18.0.0/16. After this configuration, the EIGRP route is removed from the routing table even though EIGRP is still functioning properly. Why is the static route not functioning as intended?

the administrative distance is not high enough

What is the best path in a routing table?

the longest match; a process the router uses to find a match between the destination IP address and an entry in the routing table

longest match

the route in the routing table that has the greatest number of far-left matching bits with the destination IP address of the packet. The route with the greatest number of equivalent far-left bits, or the longest match, is always the preferred route.

If a router needs to send an ARP Request for the IPv4 address in one of its route entries, this means the packet will be forwarded:

to a next-hop router

A network administrator configures a router by the command ip route 0.0.0.0 0.0.0.0 209.165.200.226. What is the purpose of this command?

to provide a route to forward packets for which there is no route in the routing table.

If a router needs to send an ARP Request for the destination IPv4 address of the packet, this means the packet will be forwarded:

to the device with the destination IPv4 address of the packet

How does a router determine the path a packet should take to reach its destination?

uses its IP routing table

When does a router enter the setup mode?

when the configuration is missing in nvram

When does a router drop a packet?

when there is no match in the routing table and no default route.