Can we implement BGP without IGP Protocol ? If yes, then how can we do it ? If no, why ?

Hi,

Yes, for sure it is possible to configure BGP without any IGP. Check at these links where you can information and some examples:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a008009456d.shtml

http://www.cisco.com/en/US/docs/ios/12_4t/ip_route/configuration/guide/t_brbbas.html#wp1077659

Regarding your question, about IGP - If required or not depend in your design.

For example, if you have 2 facing routers to the Internet, both running BGP and with no direct connection between them:

R1   -   R2 -  R4  -   R3

Let suppose internet facing routers running BGP are R1 and R3. Then probably you need to synchronize BGP with a running IGP inside your core. That is to avoid the black hole created in R2 and R4.

but the major number one issue I would have is network convergence; which is very slow with BGP. timers are 60 and 180 ; of course u could change those.

other issues: BGP valid routes are based on path selection which is more complex than simple metric of OSPF or EIGRP. Configuration-wise, setting up BGP as IGP is complex and  challenging in contrast to IGP.

BGP is concern is stability and works perfect in routing Internet routes where changes do not happen to often; IGP are design for speed, fast recovery, re-convergence, multipath or load balancing traffic per default.