BGP Overview
369
BGP Path Attributes
Classification of path attributes
Path attributes fall into four categories:
■
Well-known mandatory: Must be recognized by all BGP routers and must be
included in every update message. Routing information error occurs without
this attribute.
■
Well-known discretionary: Can be recognized by all BGP routers and optional
to be included in every update message as needed.
■
Optional transitive: Transitive attribute between ASs. A BGP router not
supporting this attribute can still receive routes with this attribute and advertise
them to other peers.
■
Optional non-transitive: If a BGP router does not support this attribute, it will
not advertise routes with this attribute.
The usage of each BGP path attribute is described in the following table.
Usage of BGP path attributes
1
ORIGIN
ORIGIN is a well-known mandatory attribute and defines the origin of routing
information and how a route becomes a BGP route. It involves three types:
■
IGP: Has the highest priority. Routes added to the BGP routing table using the
network
command have the IGP attribute.
■
EGP: Has the second highest priority. Routes obtained via EGP have the EGP
attribute.
■
incomplete: Has the lowest priority. The source of routes with this attribute is
unknown, which does not mean such routes are unreachable. The routes
redistributed from other routing protocols have the incomplete attribute.
2
AS_PATH
AS_PATH is a well-known mandatory attribute. This attribute identifies the
autonomous systems through which routing information carried in this Update
message has passed. When a route is advertised from the local AS to another AS,
each passed AS number is added into the AS_PATH attribute, thus the receiver can
Table 46
Usage of BGP path attributes
Name Category
ORIGIN Well-known
mandatory
AS_PATH Well-known
mandatory
NEXT_HOP Well-known
mandatory
LOCAL_PREF Well-known
discretionary
ATOMIC_AGGREGATE Well-known
discretionary
AGGREGATOR Optional
transitive
COMMUNITY Optional
transitive
MULTI_EXIT_DISC (MED)
Optional non-transitive
ORIGINATOR_ID Optional
non-transitive
CLUSTER_LIST Optional
non-transitive
Содержание 4800G Series
Страница 26: ...26 CHAPTER NETWORKING APPLICATIONS ...
Страница 30: ...30 CHAPTER 1 LOGGING IN TO AN ETHERNET SWITCH ...
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Страница 70: ...70 CHAPTER 5 LOGGING IN THROUGH WEB BASED NETWORK MANAGEMENT SYSTEM ...
Страница 72: ...72 CHAPTER 6 LOGGING IN THROUGH NMS ...
Страница 82: ...82 CHAPTER 8 CONTROLLING LOGIN USERS ...
Страница 98: ...98 CHAPTER 9 VLAN CONFIGURATION ...
Страница 108: ...108 CHAPTER 10 VOICE VLAN CONFIGURATION ...
Страница 119: ...GVRP Configuration Examples 119 DeviceB display vlan dynamic No dynamic vlans exist ...
Страница 120: ...120 CHAPTER 11 GVRP CONFIGURATION ...
Страница 160: ...160 CHAPTER 17 PORT ISOLATION CONFIGURATION ...
Страница 172: ...172 CHAPTER 19 LINK AGGREGATION CONFIGURATION ...
Страница 196: ...196 CHAPTER 22 DLDP CONFIGURATION ...
Страница 240: ...240 CHAPTER 23 MSTP CONFIGURATION ...
Страница 272: ...272 CHAPTER 27 RIP CONFIGURATION ...
Страница 364: ...364 CHAPTER 29 IS IS CONFIGURATION ...
Страница 426: ...426 CHAPTER 31 ROUTING POLICY CONFIGURATION ...
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Страница 488: ...488 CHAPTER 36 IPV6 BGP CONFIGURATION ...
Страница 498: ...498 CHAPTER 37 ROUTING POLICY CONFIGURATION ...
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Страница 552: ...552 CHAPTER 41 MULTICAST OVERVIEW ...
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