To enable BGP routing, you establish a BGP routing process and define the local network. Protocols Configuration Guide, Release 12.4. “BGP Nonstop Forwarding (NSF) Awareness” section of the When the neighboring router is NSF-capable,Īnd this feature is enabled, the Layer 3 Device continues to forward packets from the neighboring router during the interval between the primary Route Processor (RP) inĪ router failing and the backup RP taking over, or while the primary RP is manually reloaded for a nondisruptive software To enable this feature with BGP routing, you need to enable Graceful Restart. The BGP NSF Awareness feature is supported for IPv4 in the Within BGP and supports the advertising of IP prefixes. CIDR eliminates the concept of network classes (CIDR) so you can reduce the size of your routing tables by creating aggregate “Configuring BGP Decision Attributes” section for information about BGPīGP Version 4 supports classless interdomain routing When multiple routes areĪvailable, BGP bases its path selection on attribute values. IGP (unless IGP synchronization is disabled). Running Cisco IOS does not select or use an IBGP route unless it has a routeĪvailable to the next-hop router and it has received synchronization from an Routing loops, and to enforce AS-level policy decisions. This information can be used to determine AS connectivity, to prune Information, including information about the list of AS paths, with other BGP Primary function of a BGP system is to exchange network reachability Through (the autonomous system path), and a list of other path attributes. Notification messages (in response to errors or special conditions).Ī network number, a list of autonomous systems that information has passed BGP peersĪlso exchange keepalive messages (to ensure that the connection is up) and Their full BGP routing tables and then send only incremental updates. Reduce the requirement for a logical full mesh: confederations and routeġ00 and AS 300-that is, AS 200 is used to transfer packets between AS 100 and Within an AS must be fully meshed logically. Must establish a peer relationship with each other. Running that allows the two neighbors to reach one another, IBGP peers do not Note that the EBGP peers areĭirectly connected and that the IBGP peers are not. BGP uses this information to construct aĮBGP, and Routers B and C are running IBGP. The routing information is a series of AS numbers that describe the full In the aboveįigure, Routers A and B are BGP peers, as are Routers B and C and Routers C andĭ. Two BGP speakers that have a TCP connection to each other forĮxchanging routing information are known as peers or neighbors. Transmission Control Protocol (TCP) as its transport protocol (specifically Routing process are often referred to as BGP speakers. With an external AS, BGP ensures that networks within the AS can be reached byĭefining internal BGP peering among routers within the AS and by redistributingīGP routing information to IGPs that run within the AS, such as IGRP and OSPF. The figure givenīelow shows a network that is running both EBGP and IBGP. The difference is that the routing updates are exchanged eitherīetween autonomous systems (EBGP) or within an AS (IBGP). Most configuration commands are the same for configuringĮBGP and IBGP. (AS) and that exchange BGP updates run internal BGP (IBGP), and routers thatīelong to different autonomous systems and that exchange BGP updates runĮxternal BGP (EBGP). Routers that belong to the same autonomous system Reference, Volume 2 of 3: Routing Protocols Published by Cisco Press, and in the “Configuring BGP” chapter in theĬommands and keywords, see the “IP Routing Protocols” part of the You can find detailed information about BGP in The protocol is defined in RFCs 1163, 1267, and 1771. BGP Version 4 is the standard EGP for interdomain OSPF, within their boundaries and that interconnect by using an Exterior The loop-free exchange of routing information between autonomous systems.Īutonomous systems are made up of routers that operate under the sameĪdministration and that run Interior Gateway Protocols (IGPs), such as RIP or Gateway protocol used to set up an interdomain routing system that guarantees The Border Gateway Protocol (BGP) is an exterior Graceful Restart is enabled the session will flap. A peer device with an unsupported hold time can establish a session with a device through an open message, but once The BGP hold time must always be configured higher than the Graceful Restart hold time on a device, even with Graceful Restartĭisabled. Configuring Routing Domain Confederations.Configuring Aggregate Addresses in a Routing Table.Configuring BGP Neighbors and Peer Groups.Configuring Prefix Lists for BGP Filtering.Configuring BGP Filtering by Access Lists and Neighbors.Configuring BGP Filtering with Route Maps.
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