Topic A Explain Characteristics of Routing

•Metric—

A preference value assigned to the route, with low values being preferred over high ones.

Any routing over that boundary (that is, a /21 network or higher) takes place solely within the ISP's network, rather than over the general Internet. The ISP's network is referred to as an _____.

Autonomous System

The______ is designed to be used between routing domains, or Autonomous Systems (A Ses), and as such is used as the routing protocol on the Internet, primarily between ISPs.

Border Gateway Protocol (BGP)

Classless IPv4 routing uses a mix of flat and hierarchical structures to make more efficient use of the limited address space compared to the old method of classful address allocation. The system is based on the _________specification.

Classless Inter-Domain Routing(CIDR)

___ is the process whereby routers running dynamic routing algorithms agree on routes through the internetwork.

Convergence

On a router, information about the location of other IP networks and hosts is stored in a routing table. Each entry in the routing table represents an available route to a destination network or host, and contains (at least) the following parameters:

Destination IP address and netmask Gateway/next hop Interface Metric

___ algorithms require that routers periodically propagate their entire routing table to their immediate neighbors. Distance vector algorithms provide for slower convergence than link-state algorithms.

Distance vector

An ____ is one that performs routing within a network under the administrative control of a single owner, also referred to as an Autonomous System (AS). An Exterior Gateway Protocol (EGP) is one that can perform routing between autonomous systems.

Interior Gateway Protocol (IGP)

The____ was developed by Cisco to provide a routing protocol for routing within a domain or autonomous system.

Interior Gateway Routing Protocol (IGRP)

BGP works with CIDR IP network prefixes called _______. Route selection is based on multiple metrics, including hop count, weight, local preference, origin, and community. BGP is not a pure distance-vector algorithm but uses a hybrid approach.

Network Layer Reachability Information (NLRI)

The hierarchical link-state routing protocol ____ is suited to large organizations with multiple redundant paths between networks. It has high convergence performance compared to RIP. It was designed from the outset to support classless addressing.

Open Shortest Path First (OSPF)

____is a long-established distance vector-based routing protocol. It uses a hop count metric to determine the distance to the destination network. Generally speaking, each router is assigned a hop count value of1.

Routing Information Protocol (RIP)

_______means that you manually add routes to a routing table, and they change only if you edit them. Configuring static routing entries can be useful in some circumstances, but it can be problematic if the routing topology changes often, as each route on each affected router needs to be updated manually.

Static routing

•Path length—

The end-to-end cost of using a route (hop count). You might assign a value to a path between router A and B and between B and C. The end-to-end pathlength is the sum of A-to-B and B-to-C.

If the packet has been routed, the ____ is decreased by at least 1. This could be greater if the router is congested. When the TTL is 0, the packet is discarded. This prevents badly addressed packets from permanently circulating the network.

Time to Live (TTL)

Different routing ____, as implemented in the various protocols, may use different metrics and make comparisons of available paths in different ways. However, the desired result is always the same—to choose the optimal path for a specific packet at a given moment.

algorithms

In _____ routing systems, certain routers form a routing backbone. Other routers are grouped into logical collections, sometimes called areas or domains.

hierarchical

In the case of a directly connected route, the router uses ARP (IPv4) or Neighbor Discovery (ND in IPv6)to determine the interface address of the destination host and encapsulates the packet in the appropriate frame format for delivery over the interface. If there is no directly connected route, the router consults its routing table to determine the next ____.

hop router

Routers that can connect to multiple areas are known as ____. A backbone (always called Area 0) is created by the collection of border routers. This backbone is only visible to the border routers and invisible to the routers within a specific area.

area border routers

A ___ means that a packet is discarded without notification back to the source; a loop causes a packet to be forwarded around the network until its TTL expires.

black hole

If no route exists, the packet is either forwarded to the___ of the router(also referred to as the default route or gateway of last resort) or dropped (and the source host is notified that it was undeliverable).

default gateway

A ____ is a special type of static route that identifies the next hop router for an unknown destination. The destination address 0.0.0.0/0 (IPv4) or ::/0 (IPv6) is used to represent the default route.

default route

When a router receives a packet, it goes through the same process that the source host did to calculate if the packet needs to be routed to another router or it can be delivered locally to another interface (a ____ route).

directly connected

Early routers were manually configured with this routing information. These days, almost all routers use some sort of ____ to learn about remote networks and the most efficient route to those networks.

dynamic routing protocol

Hosts with no capacity to forward packets to other IP networks are referred to as ____.Routers that interconnect IP networks and can perform this packet forwarding process are known as intermediate systems (ISs).

end systems (ESs)

Non-hierarchical systems are referred to as ____—a situation where all routers can inter-communicate with one another. Each network ID requires a separate entry in the routing table, which can be problematic in very large internetworks.

flat

A _____ is one that was communicated to the router by another router by using a dynamic routing protocol. Routers use these protocols to exchange information about connected networks periodically and select the best available route to a destination.

learned route

Routers implementing a ____ algorithm propagate information about only their own links to other routers on the internetwork. Routers update each other only when one of their links changes state.

link-state

Instead, an Internet core router will consolidate the route to a group of networks, as identified by their shared network routing prefix, to a single routing table entry. This is referred to as _____ or route summarization.

route aggregation

All IP hosts are capable of functioning as ___, but most workstation and server computers are configured with a single network adapter connected to only one network. Although potentially capable of routing, they are not equipped with the necessary interfaces and knowledge of the location of other networks.

routers

The process of _____ takes place when a host needs to communicate with a host on a different IP network or a different subnet.

routing

A network where all the routers share the same topology is described as ____. The time taken to reach steady state is a measure of a routing protocol's convergence performance.

steady state

Maximum Transmission Unit (MTU)

—How large a packet can be sent without the need for fragmentation.

•Latency

—It takes time for a packet to traverse an internetwork. Delay-based metrics measure transit time. This metric is most important if the route is used to carry time-sensitive data, such as voice or video.

•Bandwidth

—Metrics based on bandwidth look at the maximum achievable bandwidth on a link and do not consider the available bandwidth. This is a less efficient metric than delay-based metrics.

•Reliability

—Over time, it might become obvious that some links between routers are more reliable than others. You can assign a value for this reliability that routers can assess when determining an effective path.

•Destination IP address and netmask

—Routes can be defined to specific hosts butare more generally directed to network IDs

.•Gateway/next hop

—The IP address of the next router along the path.

•Interface

—The local port to use to forward a packet along the chosen route.

Price/costs

—You can assign a monetary cost to various links, and the router using a cost metric will try to select the cheapest link available. This is useful for organizations routing on a budget.

Each routing algorithm uses different metrics to help determine the appropriate path to use. These metrics might include:

•Path length— •Reliability •Latency •Bandwidth Maximum Transmission Unit (MTU) Price/costs