Users Guide

1400 BGP
Autonomous Systems
Dell EMC Networking BGP supports both exterior routing (eBGP) between
autonomous systems (inter-AS) and interior routing within an AS (iBGP).
Dell EMC Networking BGP is suitable for use in enterprise and data center
deployments. Dell EMC Networking switches do not have sufficient capacity
to hold a full Internet routing table.
Dell EMC Networking supports BGP version 4 with 2-byte Autonomous
System Numbers (ASN). An autonomous system number is a globally unique
identifier for a group of IP networks that has a single, clearly defined external
routing policy.
BGP Operations
Decision Process Overview
The BGP decision process is logic that applies inbound policy to routing
information from peers, computes routes, and advertises routes to peers.
Figure 39-1 shows an overview of the decision process. BGP parses incoming
UPDATE messages, storing routing information in Adj RIB-In. Phase 1 of the
decision process applies inbound policy to routes in Adj RIB In. Routes that
pass inbound policy are copied to Accept-RIB-In and LOCAL_PREF is set.
BGP uses the routing table to resolve a BGP next hop to a local next hop.
Locally originated routes (those configured with the network command or
redistributed from another protocol) go directly to Accept-RIB-In. Phase 2 of
the decision process selects the best route to each destination in Accept-RIB-
In. Each best route is stored in the local RIB and given to RTO. Phase 3 of the
decision process applies outbound policy to routes in the local RIB and
determines the status of aggregate routes. Active aggregates and individual
routes that pass outbound policy are placed in an Adj-RIB-Out specific to
each update group, and UPDATE messages are sent to communicate the
routes to neighbors.