RFC 4577, "OSPF as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)", June 2006Source of RFC: l3vpn (int)
Errata ID: 4659
Status: Held for Document Update
Reported By: Chao Fu
Date Reported: 2016-04-08
Held for Document Update by: Martin Vigoureux
Date Held: 2018-05-22
Section 4.1.4 says:
If a PE attaches to a CE via a link that is in a non-zero area, then the PE serves as an ABR for that area.
It should say:
PE always serves as an ABR if it attaches to a CE.
Even the PE attaches to a CE via a link that is in backbone area, it should also be thought as an ABR. Otherwise the CE cannot calculate the type 3 LSAs from PE because there is no ABR.
Section 4.2.3 has the similar description and should also be updated:
"If a PE has a link that belongs to a non-zero area, the PE functions
as an Area Border Router (ABR) for that area."
After discussing with authors, a more preferred revision of the text could be:
Since OSPF VPN-IPv4 routes are advertised as inter-area summary (type 3) LSAs, a PE will act as an ABR for attached CEs.