The above network has RIPv2, OSPF, and EIGRP protocols in Intranet and is connec

Question

The above network has RIPv2, OSPF, and EIGRP protocols in Intranet and is connected to two ISPs thru BGP protocol. As a consultant write a technical proposal to implement the following solutions.

1. Implement a redistribution solution

2. Implement BGP connection to ISPs

3. Implement a solution which avoids your network becoming a transit hub for BGP external routes

Multiprotocol Network RIP Network Redistribution RIPv2 to OSPF OSPF to RIPv2 EIGRP Network. SPF real OSPF Area 0 Redistribution OSPF to EIGRP EIGRP to OSPF OSPF Area 2 BGP BGP ISP 1 ISP 2

Explanation / Answer

A)The use of a routing protocol to advertise routes that are learned by some other means, such as by another routing protocol, static routes,
or directly connected routes is called redistribution.While running a single routing protocol throughout your entire IP internetwork is desirable, multi-protocol routing is common for a number of reasons, such as company mergers, multiple departments managed by multiple network administrators, path length and multi-vendor environments. Running different routing protocols is often part of a network design. In any case, having a multiple protocol environment makes redistribution a necessity.Differences in routing protocol characteristics, such as metrics, administrative distance, classful and classless capabilities can effect redistribution. Consideration must be given to these differences for redistribution to succeed.

RIPv2:
The RIP metric is composed of hop count, and the maximum valid metric is 15. Anything above 15 is considered infinite; you can use 16 to describe an infinite metric in RIP. When redistributing a protocol into RIP, Cisco recommends that you use a low metric, such as 1. A high metric, such as 10, limits RIP even further. If you define a metric of 10 for redistributed routes, these routes can only be advertised to routers up to 5 hops away, at which point the metric (hop count) exceeds 15. By defining a metric of 1, you enable a route to travel the maximum number of hops in a RIP domain. But, doing this increases the possibility of routing loops if there are multiple redistribution points and a router learns about the network with a better metric from the redistribution point than from the original source, as explained in the Administrative Distance section of this document. Therefore, you have
when there to make sure that the metric is neither too high, preventing it from being advertised to all the routers, or too low, leading to out when there are multiple redistribution points.

OSPF:
The OSPF metric is a cost value based on 108/ bandwidth of the link in bits/sec. For example, the OSPF cost of Ethernet is 10: 108/107 = 10
When there is a major net that is subnetted, you need to use the keyword subnet to redistribute protocols into OSPF. Without this keyword, OSPF only redistributes major nets that are not subnetted.It is possible to run more than one OSPF process on the same router. However, running more than one process of the same protocol is rarely needed, and consumes the router's memory and CPU.You do not need to define metric or use the default-metric command when redistributing one OSPF process into another.

EIGRP:
IGRP and EIGRP need five metrics when redistributing other protocols: bandwidth, delay, reliability, load, and MTU, respectively.Multiple EIGRP processes can run on the same router, with redistribution between them. For example, IGRP1 and IGRP2 can run on the same router. However, running two processes of the same protocol on the same router is rarely necessary, and can consume the router's memory and CPU.
The redistribution of IGRP/EIGRP into another IGRP/EIGRP process does not require any metric conversion, so there is no need to define metrics or use the default-metric command during redistribution.A redistributed static route takes precedence over the summary route because the static route has an administrative distance of 1 whereas Eigrp summary route has an administrative distance of 5. This happens when a static route is redistributed with the use of redistributing static under the Eigrp process and the Eigrp process has a default route.

B)BGP is a relatively simple protocol with a few salient features. First, BGP is an incremental protocol, where after a complete
routing table is exchanged between neighbors, only changes to that information are exchanged. These changes may be new
route advertisements, route withdrawals, or changes to route attributes. Second, BGP is a path-vector protocol where advertisements
contain a list of Ases used to reach the destination. Third, routes are advertised at the prefix level, so an AS
would send a separate update for each of its reachable prefixes. Fourth, BGP update messages may contain several fields, including
a list of prefixes being advertised, a list of prefixes being withdrawn, and a list of route attributes that describe various
characteristics of each advertised route. An ISP implements its policies by modifying route attributes and changing the way
routers react to advertisements with certain route attributes.

C)A BGP router in an ISP may have several alternate routes to
reach a particular destination. In the absence of policy, the
router would choose the route with the path length,
with some arbitrary way to break ties between routes with the
same path length. However, in order to give operators greater
Table 1: Steps in the BGP decision process.
Step Attribute Controlled by local
or neighbor AS?
1. Highest LocalPref local
2. Lowest AS path length neighbor
3. Lowest origin type neither
4. Lowest MED neighbor
5. eBGP-learned over iBGP-learned neither
6. Lowest IGP cost to border router local
7. Lowest router ID (to break ties) neither
control over route selection, several additional attributes were
added to advertisements, allowing a router to alter its decisions
based on the values of these attributes. The end result is the
BGP decision process, consisting of an ordered list of attributes
across which routes are compared, as shown in Table 1. The
router goes down the list, comparing each attribute in the list
across the two routes. If the routes have different values for the
attribute, the router chooses the one that has the more desirable
attribute, otherwise it moves on to compare the next attribute
in the list. The route that is chosen is used by the router to forward
packets. The ordering of attributes allows the operator to
influence various stages of the decision process. For example,
the Local Preference (LocalPref) is the first step in the decision
process. By changing LocalPref, an operator can force a
route with a longer AS path to be chosen over a shorter one. As
another example, the Multi-Exit Discriminator (MED) is typically
used by two ASes connected by multiple links to indicate
which peering link should be used to reach the AS advertising
the attribute. MED was placed lower in the decision process
as this allows an ISP to override these suggestions, e.g. by setting
LocalPref. Using a strict ordering of attributes in the decision
process simplifies policy expression and makes it easier
to predict the outcome of making configuration changes. While
some vendors allow operators to disable certain steps in the decision
process, they typically do not permit the operators to put
the steps in a different order. Hence some policies that violate
this ordering (e.g. ignore AS path length, or first choose lowest
MED then highest LocalPref) may require various hacks which
can complicate router configuration and lead to unforeseen side
effects.
There are different locations where a route attribute can be set
by policy: (a) Locally, for example LocalPref is an integer value
set at and propagated throughout the local AS and filtered before
sending to neighboring ISPs. (b) Neighbor, for example
the MED attribute is typically used by two ASes connected by
multiple links to indicate which peering link should be used to
reach the AS advertising the MED attribute, and is not used
to compare routes through two different next-hop ASes. (c)
Neither: some attributes, for example whether the route was
learned through an external BGP (eBGP) neighbor or from an
internal router speaking BGP (iBGP), are set by the protocol
and cannot be changed.
The collective results of the decision process across routers is
to produce a set of equally good border routers for each pre-
fix, where each router in the set is equivalent according to the
first four steps of the decision process that compare BGP attributes.
Each internal router then chooses the router in that
set that is closest according to the Interior Gateway Protocol
(IGP) path cost to reach that border router

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