Default Route vs BGP??

Hi there,

I failed miserably my CCNA last Friday with a 834..damn buggy Flash (don't know if anyone has had problems with this but one of my sims kept crashing all the time

) The question anyway I still don't know the right answer is:
You have some company X with a router and to it two networks attached to it. Now this router is connected to an ISP router which on it's turn is connected to the Internet. Now the question was what routing protocols to use on both routers. The only 2 answers that made sense were default route from X to ISP router and BGP on ISP router or BGP on both routers (actually not 100% sure about this one). The thing is I've actually taken the Cisco course and there on the topic of BGP they gave this specific example where a company would use BGP to connect to the ISP and ISP would use BGP to connect to other ISPs. Yet in all of their examples for default routes they use similar scenarios. Any thoughts because this annoys the hell out of me and retake is in 3 days....
Thanks in advance

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Comments

steve-o87

There is no BGP on the CCNA test!

It is an advanced CCNP/IP subject, check the CCNA blueprint!

http://www.cisco.com/web/learning/le3/current_exams/640-801.html

Sorry to hear you failed - it's A sh!t feeling but having said that, dont give up. Just remember CCNA isn't easy. At least now you know what to expect in the test and you can brush up on your weaker areas!

Good luck!! and let us know as soon as you pass

limpet_drone

Thanks for the reply, however this question was ON the test I failed. It's a pity I can't show you the picture, but it was not concerning anything in particular with BGP, you only had to say which protocol to use where. That's it.

EdTheLad

Your explanation is not clear, one router, 2 networks, one isp?? i dont know what you means.The main question you are asking is how to know when to use bgp or when to use static routes.

If you are connected to an isp via one physical link, you will use a static route.The isp will also create a static route to your network and redistribute this in bgp.

If you have 2 two different routers connected to the isp and you want backup or load sharing you can choose either static or bgp.To use static routes you would need to create a default static route to the physical int conected to the isp like so. ip route 0.0.0.0 0.0.0.0 s0, then you would need to redistribute it in your local igp.If you wanted a backup link you would also have to set the admin distance on the backup higher than the igp so that it will be floating and ready to use if the primary drops.
Now the big consideration to take into account is the physical link to the isp.Imagine your router was connected to the isp via a switch,if the physical interface on the isp router fails your primary interface s0 is still up, no switchover will occur and you lose traffic.So the main concern when choosing static routes or bgp comes down to layer1/layer2 connectivity.If your router is directly connected to the isp router your interface will detect the physical fail and the backup path would be active.
Bgp used in this environment will detect link failures so it can work no matter what physical topology you have.

When multihomed to two different isp's you absolutely need bgp.The reason is because with static routes you wouldnt be able to detect an internal error in an isp and thus wouldnt switch to the backup isp.Bgp will
will learn about any lost routes so dynamically it will choose the second isp.

limpet_drone

Ok I'll try to describe as accurate as posibble: You have company X which has ONLY ONE router, there are apparently 2 subnets (from what I could distinguish on 2 different interfaces of the router) now this router is connected through the serial interface to a SINGLE ISP router, ISP has ONLY one router as well. And finally the ISP router is connected to the internet - no other connections.

mp3spy

I would thinkg BGP is used in this scenario when going out from the ISP to the internet....

EdTheLad

limpet_drone wrote:

Ok I'll try to describe as accurate as posibble: You have company X which has ONLY ONE router, there are apparently 2 subnets (from what I could distinguish on 2 different interfaces of the router) now this router is connected through the serial interface to a SINGLE ISP router, ISP has ONLY one router as well. And finally the ISP router is connected to the internet - no other connections.

Only static routes are needed.Since there is only one physical line to the internet, bgp isnt needed as it wouldnt provide any benefit.

hectorjhrdz

from x to ISP you need static only, it's enough.

and the routing prot at the ISP should be BGP to share route information with its peer.

hectorjhrdz

and a static route form ISP to X

listo!!!