Border Gateway Protocol (BGP) policy accounting measures and classifies IP traffic that is sent to, or received from, different peers. Policy accounting is enabled on an input interface, and counters based on parameters such as community list, autonomous system number, or autonomous system path are assigned to identify the IP traffic.

Using the BGP table-map command, prefixes added to the routing table are classified by BGP attribute, autonomous system number, or autonomous system path. Packet and byte counters are incremented per input interface. A Cisco IOS policy-based classifier maps the traffic into one of eight possible buckets, representing different traffic classes.

Using BGP policy accounting, you can account for traffic according to the route it traverses. Service providers (SPs) can identify and account for all traffic by customer and bill accordingly. In the figure below, BGP policy accounting can be implemented in Router A to measure packet and byte volumes in autonomous system buckets. Customers are billed appropriately for traffic that is routed from a domestic, international, or satellite source.

Figure 1

Sample Topology for BGP Policy Accounting

BGP policy accounting using autonomous system numbers can be used to improve the design of network circuit peering and transit agreements between Internet service providers (ISPs).

1.    Router(config)# ip community-list community-list-number{permit| deny} community-number

2.    Router(config)# route-map map-name[permit| deny] [sequence-number]

3.    Router(config-route-map)# match community-list community-list-number[exact]

4.    Router(config-route-map)# set traffic-index bucket-number

1.    Router(config)# router bgp as-number

2.    Router(config-router)# table-map route-map-name

3.    Router(config-router)# network network-number[mask network-mask]

4.    Router(config-router)# neighbor ip-address remote-as as-number

5.    Router(config-router)# exit

6.    Router(config)# interface interface-type interface-number

7.    Router(config-if)# no ip directed-broadcast

8.    Router(config-if)# ip address ip-address mask

9.    Router(config-if)# bgp-policy accounting

1.    Enter the show ip cef EXEC command with the detail keyword to learn which accounting bucket is assigned to a specified prefix.

2.    Enter the show ip bgp EXEC command for the same prefix used in Step 1--192.168.5.0-- to learn which community is assigned to this prefix.

3.    Enter the show cef interface policy-statistics EXEC command to display the per-interface traffic statistics.

To monitor and maintain the BGP Policy Accounting feature, use the following commands in EXEC mode, as needed:

Router# show cef interface [type number] policy-statistics

Router# show ip bgp [network] [network mask] [longer-prefixes]

Router# show ip cef [network [mask]] [detail]

In the following example, BGP communities are specified in community lists, and a route map named set_bucket is configured to match each of the community lists to a specific accounting bucket using the set traffic-index command:

ip community-list 30 permit 100:190
ip community-list 40 permit 100:198
ip community-list 50 permit 100:197
ip community-list 60 permit 100:296
!
route-map set_bucket permit 10
match community 30
set traffic-index 2
!
route-map set_bucket permit 20
match community 40
set traffic-index 3
!
route-map set_bucket permit 30
match community 50
set traffic-index 4
!
route-map set_bucket permit 40
match community 60
set traffic-index 5

In the following example, BGP policy accounting is enabled on POS interface 7/0 and the table-map command is used to modify the bucket number when the IP routing table is updated with routes learned from BGP:

router bgp 65000
 table-map set_bucket
 network 10.15.1.0 mask 255.255.255.0
 neighbor 10.14.1.1 remote-as 65100
!
ip classless
ip bgp-community new-format 
!
interface POS7/0
 ip address 10.15.1.2 255.255.255.0
 no ip directed-broadcast
 bgp-policy accounting
 no keepalive
 crc 32
 clock source internal