BGP Route Aggregation www huawei com HUAWEI TECHNOLOGIES

Foreword BGP in many cases needs to aggregate specific routes, and announce the aggregated route to neighboring AS’. This section shall explain how the BGP traffic flow can be manipulated by each AS through the changing of various attributes as well as BGP aggregation and the problems caused by aggregation and the implementation of effective solutions. HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 2

Objectives Upon completion of this section, you will be able to: l Master the method of BGP route aggregation l Understand the behavior of AS_PATH attributes l Understand the configuration of BGP route aggregation l Understand the policy of BGP route aggregation HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 3

Contents What is route aggregation AS_SET Change the route aggregation attribute HUAWEI TECHNOLOGIES CO.

Route Aggregation Overview Routing Table 192. 168. 1. 16/28 192. 168. 1. 32/28 192. 168. 1. 48/28 192. 168. 1. 0/26 192. 168. 1. 16/28 192. 168. 1. 32/28 Routing Table 192. 168. 1. 0/26 192. 168. 1. 48/28 l We can use the configuration command in BGP to summarize a range of prefixes into one aggregate. HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 6

Route Aggregation Rule Decimal binary 192. 168. 1. 16 11000000. 10101000. 00000001. 00 010000 192. 168. 1. 32 11000000. 10101000. 00000001. 00 100000 192. 168. 1. 48 11000000. 10101000. 00000001. 00 110000 26 bits l The aggregate route： 192. 168. 1. 0/26 HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 7

BGP Route Aggregation Modes— Automatic Aggregation l Automatic Aggregation [ Aggregate the imported IGP subnet routes to their major network addresses automatically. After the relevant configuration, BGP no longer receives the subnet routes from IGP. BGP receives only the aggregate network addresses. AS-100 192. 168. 1. 1/32 192. 168. 1. 2/32 192. 168. 1. 3/32 10. 1. 1. 1 RTA AS-101 10. 1. 1. 2 RTB [RTB]display bgp routing-table [RTA]bgp 100 [RTA-bgp]import-route direct [RTA-bgp]peer 10. 1. 1. 2 as-num 101 [RTA-bgp]summary automatic Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn *> 10. 0 *> 192. 168. 1. 0 HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved 10. 1. 1. 1 Page 8 100?

BGP Route Aggregation Modes— Manual Aggregation l Manual Aggregation [ Aggregate the local BGP routes. In general, the preference of the manual aggregation is much higher than the automatic aggregation. AS-100 192. 168. 1. 1/32 192. 168. 1. 2/32 192. 168. 1. 3/32 10. 1. 1. 1 AS-101 10. 1. 1. 2 RTA RTB [RTA]bgp 100 [RTA-bgp]network 192. 168. 1. 1 255 [RTA-bgp]network 192. 168. 1. 2 255 [RTA-bgp]network 192. 168. 1. 3 255 [RTA-bgp]peer 10. 1. 1. 2 as-num 101 [RTA-bgp]aggregate 192. 168. 1. 0 24 detail-suppressed [RTB]display bgp routing-table Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn *> 192. 168. 1. 0 HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved 10. 1. 1. 1 Page 9 100 i

BGP Route Aggregation Design Considerations l BGP Route Aggregation Design Considerations [ The advertisement of specific route [ Inherited BGP Path Attribute − AS-Path − Origin − Community −…… HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 10

Route Aggregation without AS_SET 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 AS-300 RTC aggregate 160. 0 255. 0. 0. 0 detail-suppressed RTD AS-400 HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 12

Route Aggregation without AS_SET 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 AS-300 10. 2. 2. 2 11. 1. 1. 2 [RTC] display bgp routing-table RTC Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn RTD AS-400 HUAWEI TECHNOLOGIES CO. , LTD. *> 160. 0/8 s> 160. 10. 0. 0 s> 160. 20. 0. 0 All rights reserved 127. 0. 0. 1 10. 2. 2. 2 11. 1. 1. 2 Page 14 i 200 i 100 i

Route Aggregation without AS_SET AS-300 RTC [RTD] display bgp routing-table 4. 4. 4. 1 4. 4. 4. 2 RTD AS-400 Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn *> 160. 0/8 4. 4. 4. 1 300 i l The aggregate route is generated by AS 300. The as-path information of the specified routes 160. 10. 0. 0/16 and 160. 20. 0. 0/16 are lost. HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 15

Route Aggregation with AS_SET 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 AS-300 RTC aggregate 160. 0 255. 0. 0. 0 detail-suppressed as-set RTD AS-400 HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 16

Route Aggregation with AS_SET 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 AS-300 11. 1. 1. 2 10. 2. 2. 2 RTC [RTC] display bgp routing-table Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn RTD AS-400 HUAWEI TECHNOLOGIES CO. , LTD. *> 160. 0/8 s> 160. 10. 0. 0 s> 160. 20. 0. 0 All rights reserved 127. 0. 0. 1 10. 2. 2. 2 11. 1. 1. 2 Page 17 {200 100} i 200 i 100 i

Route Aggregation with AS_SET AS-300 RTC [RTD] display bgp routing-table RTD AS-400 Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn *> 160. 0/8 4. 4. 4. 1 300 {200 100} i l AS_SET information plays an important role in preventing routing loops. This is because it records the AS` information for the components of the aggregate route that have been traversed. HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 18

Route Aggregation with AS_SET 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 X AS-300 RTC [RTD] display bgp routing-table RTD Network Next. Hop *> 160. 0/8 4. 4. 4. 1 AS-400 HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 20 Path/Ogn 300 {200} i

Contents What’s route aggregation AS_SET Change the route aggregation attribute HUAWEI TECHNOLOGIES CO. ,

Aggregate Route Issue l An aggregate route does not inherit the original BGP route attributes l Can modify the attributes of the BGP aggregate route by using the command below: aggregate ip-address mask [ as-set | attribute-policy route-policy-name 1 | detailsuppressed | origin-policy route-policy-name 2 | suppress-policy route-policy-name 3 ] HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 22

Attribute-Policy 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 AS-300 RTC RTD AS-400 HUAWEI TECHNOLOGIES CO. , LTD. Aggregate 160. 0 255. 0. 0. 0 detail-suppressed attribute-policy att 1 # route-policy att 1 permit node 10 apply origin incomplete All rights reserved Page 23

Attribute-Policy 160. 20. 0. 0/16 RTB RTA 160. 10. 0. 0/16 AS-200 AS-100 AS-300 RTC [RTD] display bgp routing-table Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network Next. Hop Path/Ogn RTD AS-400 HUAWEI TECHNOLOGIES CO. , LTD. *> 160. 0/8 All rights reserved 4. 4. 4. 1 Page 24 300 ?

Route Filtering Policy l origin-policy [ Using the key word origin-policy, will only perform route aggregation on the specific routes that fulfill the route policy l suppress-policy [ Using the key word suppress-policy, an aggregate route can be generated while the detail route can be suppressed. You can use the if-match of route-policy to selectively suppress some of the specific routes. Some of the other routes still can be advertised. HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 25

Summary l Describe the function of the AS_SET used in BGP route aggregation. l Describe the necessary precautions to be taken when performing BGP route aggregation. HUAWEI TECHNOLOGIES CO. , LTD. All rights reserved Page 26

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