Bgp (Art 1) Cheat Sheet

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BGP · P
1
ART
packetlife.net
Attributes
About BGP
Name
Description
Type
Path Vector
Well-known Mandatory · Must be supported and propagated
eBGP AD
20
1 Origin
Origin type (IGP, EGP, or unknown)
iBGP AD
200
List of autonomous systems which the
Standard
RFC 4271
2
AS Path
advertisement has traversed
Protocols
IP
3 Next Hop
External peer in neighboring AS
Transport
TCP/179
Well-known Discretionary · Must be supported; propagation optional
Authentication
MD5
Metric for internal neighbors to reach
5
Local Preference
external destinations (default 100)
Terminology
Includes ASes which have been dropped
Autonomous System (AS)
6
Atomic Aggregate
due to route aggregation
A logical domain under the control of a
single entity
Optional Transitive · Marked as partial if unsupported by neighbor
External BGP (eBGP)
7
Aggregator
ID and AS of summarizing router
BGP adjacencies which span autonomous
8 Community
Route tag
system boundaries
Optional Nontransitive · Deleted if unsupported by neighbor
Internal BGP (iBGP)
BGP adjacencies formed within a single AS
Multiple Exit
Metric for external neighbors to reach the
4
Discriminator (MED)
local AS (default 0)
Synchronization Requirement
A route must be known by an IGP before
9 Originator ID
The originator of a reflected route
it may be advertised to BGP peers
10 Cluster List
List of cluster IDs
Packet Types
13 Cluster ID
Originating cluster
Open
Update
Cisco proprietary, not communicated to
--
Weight
Keepalive
Notification
peers (default 0)
Path Selection
Neighbor States
Attribute
Description
Preference
Idle · Neighbor is not responding
1
Weight
Administrative preference
Highest
Active · Attempting to connect
Communicated between peers
Connect · TCP session established
2
Local Preference
Highest
within an AS
Open Sent · Open message sent
3
Self-originated
Prefer paths originated locally
True
Open Confirm · Response received
4
AS Path
Minimize AS hops
Shortest
Established · Adjacency established
Prefer IGP-learned routes over
5
Origin
IGP
EGP, and EGP over unknown
Troubleshooting
6
MED
Used externally to enter an AS
Lowest
show ip bgp [summary]
7
External
Prefer eBGP routes over iBGP
eBGP
show ip bgp neighbors
8
IGP Cost
Consider IGP metric
Lowest
show ip route [bgp]
9
eBGP Peering
Favor more stable routes
Oldest
clear ip bgp * [soft]
10
Router ID
Tie breaker
Lowest
debug ip bgp […]
Influencing Path Selection
Weight neighbor 172.16.0.1 weight 200
Local Preference bgp default local-preference 100
MED default-metric 400
Route Map neighbor 172.16.0.1 route-map Foo
Ignore
Ignore Cost
bgp bestpath as-path ignore
bgp bestpath cost-community ignore
AS Path
Communities
by Jeremy Stretch
v2.1-r1

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