In MPLS L3VPN environments sometimes you need to advertise default for internet access to some of the VPN customers/networks. I posted this technical article few years ago at the Cisco Support Community CSC. In this post (refer to the link below) you will see there are multiple ways to inject default route into certain MPLS VPNs, however, each one has different considerations and implications from design point of view. There no single recommended option, as it depends on many factors such as the size of the network ( e.g. number of VPN customers need internet access, number of PEs), whether you need to advertise full Internet routes or only default route to the customer etc.
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