BGP Flashcards

Flashcards generated from lecture notes on Border Gateway Protocol (BGP)

Border Gateway Protocol (BGP)

A standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet.

Path-vector routing protocol

BGP is classified as a path-vector routing protocol, and it makes routing decisions based on paths, network policies, or rule-sets configured by a network administrator.

Interior Border Gateway Protocol (IBGP)

BGP used for routing within an autonomous system.

Exterior Border Gateway Protocol (EBGP)

The Internet application of the BGP protocol.

BGP Peers

BGP neighbors, called peers, are established by manual configuration among routers to create a TCP session on port 179.

Internal BGP (iBGP)

BGP runs between two peers in the same autonomous system (AS).

External BGP (eBGP)

BGP runs between different autonomous systems.

Route-maps

Mechanism consisting of a set of rules to control how routes are propagated, allowing actions such as dropping or modifying route attributes based on given criteria.

Autonomous System Number (ASN)

A special number assigned by IANA used primarily with Border Gateway Protocol which uniquely identifies a network under a single technical administration that has a unique routing policy, or is multi-homed to the public internet.

Public ASN

An ASN in the public range is globally unique and may be announced on the global Internet to your ISP or at an internet exchange point (peering point) via BGP.

Private ASN

The private ASN should not be seen on the global Internet (they shouldn't be announced via your exterior gateway routing protocol); they are used by ISPs using BGP confederations or in private networks.

Multi-homed

Having a connection to more than one ISP.

iBGP

A routing protocol used for exchanging routing information between two or more routers within an autonomous system (AS).

eBGP

A routing protocol used to exchange information between two autonomous systems (AS), connecting distinct networks such as those of different internet service providers.

Loopback Interface

A virtual interface that will never go down unless the router crashes or is manually shut down, making it best practice to use for configuring IBGP.

EBGP Multihop

A configuration used when eBGP neighbors are not directly connected, requiring the TTL value of BGP packets to be increased.

BGP Idle State

The first BGP state that listens for an incoming connection request from its peer router. BGP may also get stuck in this state for many reasons, such as TCP port 179 or ports over 1023 being closed.

BGP Connect State

A state where BGP tries to complete the three-way TCP handshake. If successful, it resets the ConnectRetry timer and shifts to the OpenSent state.

BGP Active State

A state where BGP kicks off and attempts a new TCP connection. If it is established successfully, it will send an Open message to its peer and move to the OpenSent state.

BGP OpenSent State

A state where BGP is listening for an Open message from its neighbor. Once received, it checks for matching parameters and potential errors.

BGP OpenConfirm State

A state where BGP listens for Keepalive messages from its peer. If they are sent and received successfully, BGP shifts to the final Established state.

BGP Established State

A state where the BGP neighbor adjacency has been created, and update and Keepalive messages are exchanged.

BGP update-source

A command that tells BGP which interface to source the BGP packets out of.

Split horizon

A method used by distance vector protocols to prevent network routing loops by never sending routing information back in the direction from which it was received.

iBGP split horizon

A BGP router will not advertise prefixes from one iBGP neighbor to another iBGP neighbor.

Route Reflector

A BGP mechanism that overrides the general behavior of not sharing routes by BGP routers and shares routes to its neighbors based on certain rules, in order to avoid loops and stale routes.

Route Reflector Cluster

A route reflector and its clients, or possibly multiple route reflectors sharing the same clients.

Confederation

An AS that has been subdivided into a group of sub-autonomous systems, known as member autonomous systems.

Route Recursion

The process that all routers complete to find out what interface to use when routing to a particular prefix.

Next-hop-self

A command that forces BGP to use a specific next hop instead of protocol’s choice, commonly used to ensure IBGP peers learn how to reach advertised routes.

BGP Weight

A Cisco-specific parameter used in BGP to influence outbound routing, where a higher weight is preferred; it is only locally significant and not passed between neighbors.

BGP Local Preference

A BGP attribute used to influence the outbound routing decision of a router, where a higher local preference is preferred; it is passed between iBGP neighbors but not eBGP neighbors.

AS Path Prepend

A technique to influence BGP best path selection by artificially increasing the AS path length, making a path less desirable for routing.

BGP Origin Codes

BGP Path attribute that defines the origin of routing information, with 'i' (IGP) having the highest priority, followed by 'e' (EGP), and '?' (incomplete).

Deterministic-med

Command that ensures the comparison of the MED variable when choosing routes advertised by different peers in the same autonomous system.

Always-compare-med

Command that ensures the comparison of the MED for paths from neighbors in different autonomous systems.

EIGRP Leak Map

A method to advertise a specific prefix within the range of a summary advertisement in EIGRP.

Prefix list

Mechanism containing one or more ordered entries, processed sequentially, to permit or deny routes based on prefix and length.

Atomic Aggregate

Used in BGP to alert speakers that information has been lost due to route aggregation, and the aggregate path might not be the best.

BGP Communities

A group of destinations that share a common property, used to trigger routing decisions, such as acceptance, rejection, preference, or redistribution.

BGP Conditional Route Injection

This feature allows more specific routes to be generated based on administrative policy or traffic engineering information in order to provide more specific control over the forwarding of packets to these more specific routes, which are injected into the BGP routing table only if the configured conditions are met.

BGP Conditional Advertisement

Feature triggered if a route prefix is not present in output of the non-exist-map command, then the route specified by the advertise-map command is announced.

BGP Maximum-Prefix

Feature that controls how many prefixes can be received from a neighbor, useful for protecting against route overloads.

Regular Expressions

A way to define patterns to match specific AS paths.

Regular Expression: .*

Match anything .

Regular Expression: ^$

Match locally originated routes.

Regular Expression: ^100_

Match learned from AS 100.

Regular Expression: _100$

Match originated in AS 100.

Regular Expression: 100

Match any instance of AS 100.

Regular Expression: ^[0-9]+$

Match directly connected ASes.