Bgp

Front 1

path attribute

Back 1

A term generally describing characteristics about BGP paths that are advertised in BGP Updates.

Front 2

BGP table

Back 2

A table inside a router that holds the path attributes and NLRI known by the BGP implementation on that router.

Front 3

BGP Update

Back 3

A BGP message that includes withdrawn routes, path attributes, and NLRI.

Front 4

established

Back 4

A BGP neighbor state in which the BGP neighbors have stabilized and can exchange routing information using BGP Update messages.

Front 5

iBGP

Back 5

internal BGP Refers to how a router views a BGP peer relationship, in which the peer is in the same AS.

Front 6

eBGP

Back 6

External BGP. A term referring to how a router views a BGP peer relationship, in which the peer is in another AS.

Front 7

EGP

Back 7

Exterior Gateway Protocol An exterior routing protocol that predates BGP. It is no longer used today.

Front 8

BGP

Back 8

Border Gateway Protocol. An exterior routing protocol designed to exchange prefix information between different autonomous systems. The information includes a rich set of characteristics called path attributes, which in turn allows for great flexibility regarding routing choices.

Front 9

peer group

Back 9

In BGP, a configuration construct in which multiple neighbors' parameters can be configured as a group, thereby reducing the length of the configuration. Additionally, BGP performs routing policy logic against only one set of Updates for the entire peer group, improving convergence time.

Front 10

eBGP multihop

Back 10

A BGP feature that defines the IP TTL field value in packets sent between two eBGP peers. This feature is required when using IP addresses other than the interface IP address on the link between peers.

Front 11

autonomous system

Back 11

In BGP, a set of routers inside a single administrative authority, grouped together for the purpose of controlling routing policies for the routes advertised by that group to the Internet.

Front 12

AS number

Back 12

A number between 1 and 64,511 (public) and 64,512 and 65,535 (private) assigned to an AS for the purpose of identifying a specific BGP domain.

Front 13

AS_PATH

Back 13

A BGP path attribute that lists ASNs through which the route has been advertised. The AS_PATH includes four types of segments: AS_SEQ, AS_SET, AS_CONFED_SEQ, and AS_CONFED_SET. Often, this term is used synonymously with AS_SEQ.

Front 14

ORIGIN

Back 14

A BGP path attribute that implies how the route was originally injected into some router's BGP table.

Front 15

NLRI

Back 15

network layer reachability information. A BGP term referring to an IP prefix and prefix length.

Network Layer Reachability Information (NLRI) is included in BGP routing update messages which describe a route and how to get there. In this context, an NLRI is a prefix. A BGP-update message carries one or more NLRI prefixes and the attributes of a route for the NLRI prefixes; the route attributes include a BGP next hop gateway address, community values, and other information.

Front 16

NEXT_HOP

Back 16

A BGP path attribute that lists the next-hop IP address used to reach an NLRI.

Front 17

MULTI_EXIT_DISC

Back 17

(MED) A BGP path attribute that allows routers in one AS to set a value and advertise it into a neighboring AS, impacting the decision process in that neighboring AS. A smaller value is considered better. Also called the BGP metric.

Front 18

LOCAL_PREF

Back 18

A BGP path attribute that is communicated throughout a single AS to signify which route of multiple possible routes is the best route to be taken when leaving that AS. A larger value is considered to be better.

Front 19

routing black hole

Back 19

A problem that occurs when an AS does not run BGP on all routers, with synchronization disabled. The routers running BGP may believe they have working routes to reach a prefix, and forward packets to internal routers that do not run BGP and do not have a route to reach the prefix.

Front 20

synchronization

Back 20

In BGP, a feature in which BGP routes cannot be considered to be a best route to reach an NLRI unless that same prefix exists in the router's IP routing table as learned via some IGP.

Front 21

confederation

Back 21

A BGP feature that overcomes the requirement of a full mesh of iBGP peers inside a single AS by separating the AS into multiple sub-autonomous systems.

Front 22

route reflector

Back 22

A BGP feature by which a router learns iBGP routes, and then forwards them to other iBGP peers, reducing the required number of iBGP peers while also avoiding routing loops.

Front 23

confederation identifier

Back 23

In an IOS confederation configuration, the actual ASN as seen by eBGP peers.

Front 24

sub-AS

Back 24

The term referring to a group of iBGP routers in a confederation, with the group members being assigned a hidden ASN for the purposes of loop avoidance.

Front 25

route reflector server

Back 25

A BGP router that forwards iBGP-learned routes to other iBGP routers

Front 26

route reflector client

Back 26

A BGP router that, unknown to it, is aided by a route reflector server to cause all iBGP routers in an AS to learn all eBGP learned prefixes.

Front 27

route reflector non-client

Back 27

A BGP router in an AS that uses route reflectors, but that is not aided by any RR server.

Front 28

confederation ASN

Back 28

The ASN assigned to a confederation sub-AS.

Front 29

confederation eBGP peer

Back 29

A BGP peer connection between two routers inside the same ASN, but in different confederation sub-autonomous systems.

Front 30

weight

Back 30

A local Cisco-proprietary BGP setting that is not advertised to any peers. A larger value is considered to be better.