Frequently Asked Questions

Q— I have an SF hub and an SJ hub. Do you think it is better to separate them into different ASs and run BGP instead of running an IGP in between?

A— This doesn't sound like a candidate for segmentation via BGP. Remember that even though segmentation gives better hierarchy and control, it introduces more routing policies dictated by BGP's behavior. In small networks such as yours, you could achieve the same stability by performing adequate hierarchical routing using an IGP.

Q— I do not have enough BGP peers to justify using route reflectors. What happens if I use them anyway?

A— You will achieve normal routing. You just need to understand that with this model, you need to rely on the centralized routers to forward BGP routes to another part of your network. Not only does the RR have to do more processing, but it also becomes a single point of failure. Therefore, additional provisioning will have to be performed to ensure at least two RRs for redundancy. You also have to deal with the potential for other issues, such as peer groups and attribute modification, as described in this chapter. If you think that the overhead is not an issue, configuring RRs is no problem.

Q— With confederations, an EBGP external route is more preferred than a confederation external route. Does this mean that I can never use another sub-AS as an exit point?

A— No. You could always use attributes such as local preference to prefer whichever exit point you want.

Q— Because local preference is not passed between ASs, it won't be passed between sub-ASs inside a confederation, will it?

A— That is not true. Using additional configuration, the sub-AS will know that it is talking to an external peer inside a confederation and will maintain all attributes that are normally maintained by IBGP.

Q— I need to configure route reflectors, but the current software on my routers does not support it. Do I need to upgrade all my routers at the same time?

A— No. You need to upgrade only the routers that will become RRs. Other routers will behave as a conventional IBGP speaker. This will help you cautiously migrate your network to the new design.