BGP · PART 1

packetlife.net

Attributes
Name

About BGP

Description

Type Path Vector

Well-known Mandatory · Must be supported and propagated
1 Origin

Origin type (IGP, EGP, or unknown)

2 AS Path

List of autonomous systems which the advertisement has traversed

3 Next Hop

External peer in neighboring AS

Well-known Discretionary · Must be supported; propagation optional
5 Local Preference

Metric for internal neighbors to reach external destinations (default 100)

6 Atomic Aggregate

Includes ASes which have been dropped due to route aggregation

Optional Transitive · Marked as partial if unsupported by neighbor
7 Aggregator

ID and AS of summarizing router

8 Community

Route tag

Optional Nontransitive · Deleted if unsupported by neighbor
4

Multiple Exit
Metric for external neighbors to reach the
Discriminator (MED) local AS (default 0)

9 Originator ID

The originator of a reflected route

10 Cluster List

List of cluster IDs

13 Cluster ID

Originating cluster

-- Weight

iBGP AD 200
Standard RFC 4271
Protocols IP
Transport TCP/179
Authentication MD5
Terminology
Autonomous System (AS)
A logical domain under the control of a single entity

External BGP (eBGP)
BGP adjacencies which span autonomous system boundaries

Internal BGP (iBGP)
BGP adjacencies formed within a single AS

Synchronization Requirement
A route must be known by an IGP before it may be advertised to BGP peers

Packet Types

Cisco proprietary, not communicated to peers (default 0)
Path Selection

Attribute

eBGP AD 20

Open

Update

Keepalive

Notification

Neighbor States

Description

Preference

1 Weight

Administrative preference

Highest

Active · Attempting to connect

2 Local Preference

Communicated between peers within an AS

Highest

Connect · TCP session