Probably one of the most confusing topics for people studying BGP/MPLS VPNs are EIGRP SoO and Cost communities. Not the concepts themselves, but rather their purpose. Lack of clear documentation makes it hard to understand why and how the specific features are implemented. In this blog post we discuss the BGP Cost community and EIGRP SoO attribute. First, a brief overview of MP-BGP is given along with general concepts of route redistribution in MPLS/BGP VPNs. Next, the problems that arise when using EIGRP in multihomed VPN environment are demonstrated. Lastly, the two specific EIGRP features are described and their use demonstrated. As usual, a reader is assumed to have basic understanding of fundamental L3 VPNs and PE-CE routing concepts. You may download the post in PDF format at the following link: Understanding EIGRP SoO and BGP Cost Community