Last protocol I’ll be focusing on for CE-PE connection is EIGRP. As in OSPF redistributing routes from EIGRP to BGP and back to EIGRP makes them external from routing protocol perspective. Using BGP extended communities many characteristics including AS number, tags or metric components are passed between PE routers and allows reconstruction of prefix. If the EIGRP route is internal it’s redistributed back as internal if AS numbers on remote PE router matches the source one (it’s encoded using external community). Otherwise it’s redistributed as EIGRP external.
Read More →