Evaluate the range of issues that may occur in the routed environment, including a detailed exploration of the issues affecting router performance when EIGRP, OSPF and BGP are used.

At X EIGRP, OSPF are used for countries or regional offices. BGP is used between Countries and high bandwidth WAN links.

Bellow is a Summery of the differences between the routing protocols (Cisco,2010):

	OSPF	EIGRP	BGP
Protocol type	Link State	Advanced Distance Vector	Path Distance Vector
Classless	Yes	Yes	Yes
VLSM	Yes	Yes	Yes
Automatic Summarization	No	Yes (Possible to disable)	Yes
Size	Large	Large	Very Large
Convergent time	Fast	Very Fast	Slow
Metric	Cost	Composite Metric	Path Attribute
Proprietary	No	Yes	No
Complexity to configure	Medium	Low	High
Boundary separation	Areas	Summarization	Autonomous Systems
Administrative distance Internal	110	90	200
Administrative distance External	Na	170	20
Table - Summary EIGRP, OSPF, BGP

Why so many routing protocols in one network?

EIGRP and OSPF are primary used as internal gateway protocols within and an autonomous system i.e. (Where one group of administrators have control). X primarily uses OSPF but there are sum sections of the network that use EIGRP because of old infrastructure from mergers and acquisitions.
Santander prefers OSPF because it is non-proprietary i.e. (cheaper) and can be used in large networks serving the same purpose i.e. (To provide routing in large network) as EIGRP. Also not all network related equipment within X is CISCO. Santander could be loosing in convergence speed, but OSPF can be custom configured to converge as fast, or even faster, than the default EIGRP configurations.
BGP is slow in convergence and has large routing tables i.e. (which are made smaller through summarization) but is a robust protocol that is used by the internet. BGP does not automatically discover neighbours through advertisements such as OSPF or EIGRP. Neighbours need to be manually configures for BGP, then information is automatically exchanged between these neighbours.
A major danger with BGP is the “clear ip bgp *” which can cause routing tables that are 100MB's big to be downloaded not to mention that BGP is used to connect high bandwidth WAN links resulting in loss of connectivity to whole countries.
Main and backup ISP's are used to connect regions via WAN connection types such as Frame relay or P2P. BGP is well supported by ISP's where EIGRP or OSPF are not. ISP's use BGP because of the size of there networks and large routing tables that would demand more processing power and bandwidth if they had to converge or send as many neighbour advertisements as EIGRP and OSPF. Also ISP's are often measured by there SLA agreements and can't afford to lower connectivity/service levels for constant topology changes.
To summarize the reason we have different routing protocols like OSPF, EIGRP and BGP is to serve very different business needs. OSPF and EIGRP are used for small to large sized networks which require fast and frequent convergence and topology changes. BGP is used for huge networks which require robustness and have few topology changes.

How the performance of a router is effected by its protocol?

There are 3 factors that effect the router performance of a protocol. (1)The size of routing table and topology tables i.e. (effecting memory) (2) Amount of communication between nodes i.e. (effecting bandwidth) (3) Algorithm handling of Topology changes i.e. (effecting CPU utilization).(Cisco,2010)
To summarize the Memory, Bandwidth and CPU utilization of OSPF, EIGRP and BGP:

	OSPF	EIGRP	BGP
Memory	Medium – Store all link states	Low – nodes learned by neighbours.	High – Big Routing tables
CPU	Medium– Dead Timer 40 sec but more CPU cycles to maintain link states, SPF (Shortest path first)	Medium – Hold Time 15 sec, DUAL( Diffusing Update Algorithm)	Low – Hold timer 180 sec.
Bandwidth	Medium - Hello (10 sec), DBD, LSR, LSU, LSAck.	High - Hello (5 sec), Update, Query, Reply, , ACK	Low - Keep-alive (60 sec)
Comment	Optimize summarization at border routers and stubby areas.	Optimize router with summarization.	Optimize router with summarization.
Table – Router Performance EIGRP, OSPF, BGP

Looking at the above table one can see OSPF and EIGRP come out the same with an average of medium while BGP coming first with the lowest utilization. So why doesn't everybody just use BGP?

The main reason been the slow convergence and those huge routing tables. With convergence of services over one link this would mean a large business would have to go a full 3 min or more with no VOIP(Voice over Internet Protocol) telephones or applications and internet. In Santander, BGP routers are the gateways into networks that are connected to large bandwidth connections on heavy duty routers such as the CISCO Catalyst 6500,which are not cheap, including a cost factor.

OSPF seems like an obvious selection over EIGRP because it has a medium performance like EIGRP but is not proprietary making it cheaper. However EIGRP is easier to configure if you in a CISCO environment and therefore requires less labour input bringing down costs. However Santander is not in a CISCO only network environment making OSPF the preferred protocol.

Conclusion

OSPF, EIGRP are overall performance wise very close but a business needs to ask its self “Am I working in a CISCO environment?” and “Do I have the manpower and skills to use this protocol?”. Making the deciding factor between EIGRP and OSPF the business environment.
BGP which is really the only established path distance vector protocol out there is a specialized protocol that specializes in long distance travel across Autonomous Systems and big networks. Its Robustness is its biggest weakness when it comes to small to medium sized networks making it unsuitable for a internal gateway protocol, however its biggest strength is also its robustness when it comes to large networks like the internet.
So one should choose a routing protocol based on the situation.”Proprietary or non proprietary”, “Manpower or no manpower” and “Robustness vs speed and convergence” to get the best value out of routers.