BGP



Overview

BGP is a protocol that is used to connect an AS to another AS.

It can be used to connect multicast domains and share link state databases.



BGP is a layer 4 protocol and uses TCP as a transport protocol. It is not a routed protocol itself.

It is a path vector EGP protocol and is currently in v4.

Uses MD5 and TCP option 19 to secure peering sessions.

OLD BGP Speakers use an AS number that ranges from 1-65535(64512-65525 is private) as a 2 Byte "asplain" number.

NEW BGP Speakers use an AS number that ranges from 65536-4294967295.

TYPES

BGP networks can be either transit or stub networks.

Stub: Stub networks are networks where packets entering can only originate or have a destination within the AS.

Transit: Packets entering the AS can be for another AS and will use the AS to transit from one to another. By definition a transit network is connected to at least two separate ASs.


Peering

When peering if the routers are using the same AS it will be a IBGP if using different ASs it will be EBGP.

Basic configuration

We will start BGP and assign a AS number. A router id can be set but it will use one from an int/loopback.


(conf)#router bgp "AS"

(conf-router)#bgp router-id "id"

(conf-router)#network "network address" mask "netmask not wild card"

(conf-router)#neighbor "address" remote-as "Remote-AS"

We will then associate BGP with an address family. For the basic config it is ipv4 unicast.


(conf-router)#address-family ipv4 unicast

(conf-router)#neighbor 192.168.1.1 activate


Show Commands

show ip bgp rib-failure

Attributes

Communities

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