BGP

[Ciscomania]

Hi Folks,

Can you tell me WHEN exactly I should use BGP instead of OSPF or EIGRP?
Some Real Life Scenarios

[Philip D'Ath · Accepted solution]

It is typically used between different companies, usually when there is more than one path (so failover or load balancing can be managed).  For example, between an ISP and their customer, assuming their customer has at least two circuits to the ISP.

OSPF and EIGRP are typically used within a company.

[Ciscomania]

Thank you for reply.

So why ISP is not using OSPF or EIGRP for load balancing?
technically it is possible right?
The other question is what BGP CAN do,and OSPF or EIGRP cannot?

[Philip D'Ath]

BGP (B=Border) is purpose built as a routing protocol for the borders between organisations.  it has lots of controls that make doing this kind of routing more controllable.

[Ciscomania]

So ISP uses it,because it is like more scalable and flexible right? but ISP also can use OSPF for like load balancing,right?

[Philip D'Ath]

OSPF is a horrible protocol, and I avoid it at all costs. You wouldn't use OSPF between organisation unless you liked a lot of pain. It just wasn't designed for inter-organisation use.

[Ciscomania]

Thank you for prompt replies. What kind of pain can I get with OSPF even within organisation? I introduced this protocol as really good,practical , scalable,with a lot of mechanism of loop prevention between and withing area-s. Can you tell me REAL LIFE scenario when u got pain with OSPF?

[Philip D'Ath]

Well, it is designed to have an "area 0" which is meant to be some centralised backbone.

What happens when you don't have a centralised backbone?  What happens if your company is decentralised?

What happens when there are two organisations and they already have their own area 0's?

All resolvable - in a horribly painful way.

[Ciscomania]

Actually I know how OSPF works.
I dont know how just in REAL LIFE SCENARIO it is.

Thank you for your replies