Information Technology Reference
In-Depth Information
Example 4-36
Interface CAR Status (Continued)
exceeded 0 packets, 0 bytes; action: drop
last packet: 1300ms ago, current burst: 0 bytes
last cleared 00:13:15 ago, conformed 1694 bps, exceeded 0 bps
BGP Policy Accounting
BGP policy accounting (BPA) is another BGP feature that takes advantage of the FIB
policy parameters. In this case, the parameter is traffic index. Traffic index is a router
internal counter within a FIB leaf with values between 1 and 8. Think of the traffic index as
a table of eight independent buckets. Each can account for one type of traffic matching
certain criteria. The number of packets and bytes in each bucket of an interface is recorded.
You can use this feature to account for IP traffic differentially on an edge router by
assigning counters based on BGP prefixes and attributes on a per-input interface basis.
Configuration of BPA generally involves the following steps:
Identify BGP prefixes that require preferential treatment and tag them
with appropriate BGP attributes.
Step 1
Set a FIB traffic index for each type of traffic.
Step 2
Enable BPA on an incoming interface.
Step 3
Figure 4-10 shows how BGP policy accounting works. As prefix 172.16.0.0/16 is
propagated from AS 200 to AS 300, certain BGP attributes are modified. On R4, a traffic
index number can be set when a match is made for the attributes using the
table-map
command. A total of eight traffic classes can be accounted.
Figure 4-10
How BGP Policy Accounting Works
Using BGP
Attributes to Set
FIB Traffic Index
172.16.0.0/16
AS 100
AS 200
AS 300
R1
R3
R4
R2
R5
BGP Propagates Attributes
Set BGP
Attributes
Enable Policy Accounting
Bucket # Packets Bytes
1
2
…
8
