ECP-206 - Ericsson Certified Associate - IP Networking

Route summarization is a technique that reduces the number of routes that a router advertises to its neighbors by creating a single summary route that covers multiple subnets or networks. Route summarization has several benefits, such as:

• It reduces the size of a routing table, which saves memory and CPU resources on the router. A smaller routing table also improves the lookup efficiency and convergence time of the routing protocol.
• It reduces signaling, which means that less bandwidth is consumed by routing updates and less processing is required by neighboring routers. This also enhances the stability and scalability of the network, as fewer routing changes are propagated.
• It improves route aggregation, which means that more specific routes are replaced by a less specific route that can be advertised to other autonomous systems or routing domains. This simplifies the inter-domain routing and hides the internal topology details.

Route summarization does not necessarily summarize the routing table entries into a default route, although a default route can be considered a special case of route summarization where all destinations are covered by one route. Route summarization also does not improve the best route calculation, as it may introduce suboptimal routing or black holes if not done properly. References: Introduction to Route Summarization - NetworkLessons.com, Route Summarization > Example for Understanding Route Summarization - Cisco Press

Peers recognize each other’s ability to use MP-BGP extensions by advertising the ability using the capabilities field during the session establishment. MP-BGP is an extension to BGP that allows BGP to carry routing information for multiple network layer protocols, such as IPv6, VPNv4, multicast, etc. To support MP-BGP, peers need to exchange their capabilities during the session establishment phase, which consists of three steps: open, keepalive, and update. In the open message, peers can include an optional parameter called capabilities, which indicates what kind of address families and subsequent address families they can support. If both peers agree on a common set of capabilities, they can proceed to exchange routing information for those address families using update messages56.

References: Use of MP-BGP Extensions for IPv6 Interdomain Routing, MP-EBGP Configuration Example - Cisco

There are 8 different priorities available to use in a VLAN header. A VLAN header is a 4-byte field that is inserted into an Ethernet frame to indicate the VLAN membership and priority of the frame. The VLAN header consists of two subfields: the tag protocol identifier (TPID) and the tag control information (TCI). The TCI subfield contains three subfields: the priority code point (PCP), the drop eligible indicator (DEI), and the VLAN identifier (VID). The PCP subfield is a 3-bit field that specifies the priority level of the frame, ranging from 0 (lowest) to 7 (highest). The PCP values can be used to implement quality of service (QoS) mechanisms on bridges and switches12.

References: HTML rt Tag - W3Schools, VLAN 0 Priority Tagging Support - Cisco