BGP Multiple Sites - Why share the same ASN?

[louisbohls]

We have a scenario where we have two sites, A and B.  We need to deploy our own AS.

Both sites connect to two ISPs.  Both sites are connected to each other via 10gb/s DWDM link.  They use EIGRP as an IGP.

Every scenario I see like this uses the same eBGP AS for both locations?  If AS's are so easy to get, why not use different ASN's for each location?

What am I gaining by using the same ASN in my scenario? I must be missing something obvious.  

[dictat851]

Even though there may be multiple autonomous systems supported by the ISP, the Internet only sees the routing policy of the ISP. That ISP must have an officially registered autonomous system number (ASN).

A unique ASN is allocated to each AS for use in BGP routing. AS numbers are important because the ASN uniquely identifies each network on the Internet.

That is why the commonly used practice in BGP configuration is Multihoming.