ECP-206 Exam Dumps : Ericsson Certified Associate - IP Networking

The router function that advertises external routes in OSPF is ASBR, which stands for Autonomous System Boundary Router. An ASBR is a router that connects an OSPF domain to another routing domain, such as another OSPF domain or a different routing protocol domain. An ASBR can redistribute routes from other routing domains into OSPF as external routes, which are carried in type 5 or type 7 LSAs. External routes have two types: E1 and E2. E1 routes include the cost from the ASBR to the destination, while E2 routes only include the cost advertised by the ASBR34.

References: OSPF External Routes ⋆ IpCisco, OSPF External Route selection algorithm - Cisco Community

The purpose of the RT attribute is to identify the destination VPN on the egress PE. RT stands for route target, which is a BGP extended community attribute that is used in MPLS VPNs. RT is attached to VPN routes by the ingress PE router and is used to control the import and export of routes between different VPNs. The egress PE router uses the RT value to determine which VPN routes belong to which VPN customers and installs them in the appropriate VRF table56.

References: IP Routing: BGP Configuration Guide - BGP-RT and VPN … - Cisco, : The Ruby Text element - MDN Web Docs

A BGP session is established between two routers by sending a unicast OPEN message. BGP uses TCP as its transport protocol, which means that before exchanging any BGP information, a TCP connection must be established between the routers. The TCP connection uses port 179 as both source and destination port. After establishing a TCP connection, each router sends an OPEN message to its neighbor, containing parameters such as BGP version number, AS number, hold time, BGP identifier, and optional capabilities. The OPEN message also serves as a keepalive message for BGP. If both routers agree on these parameters, they proceed to exchange UPDATE messages containing routing information and establish a BGP session.

A BGP router does not send a NOTIFICATION message to establish a session, but rather to terminate a session due to an error or a manual shutdown. A BGP router does not send a CONNECT message, as this is a TCP state, not a BGP message. A BGP router does not send a multicast HELLO packet, as this is an OSPF message, not a BGP message. References: BGP Neighbor States > BGP Fundamentals | Cisco Press, Demystifying BGP Session Establishments - Packet Pushers, The TCP/IP Guide - BGP Connection Establishment: Open Messages