В данной статье рассмотрим особенности применения local AS в BGP на оборудовании серии ME.
Рассмотрим изменения атрибута AS-PATH в различных режимах работы функционала local-as.
Проверим работу функционала на предложенной схеме. В данной статье приведен пример конфигурации только узла R2.
1) Режим работы local-as без дополнительной команды 'mode':
router bgp 65100
neighbor 172.27.72.229
address-family ipv4 unicast
local-as 65432
mode no-prepend
remote-as 45679
update-source 172.27.72.227
exit
neighbor 2.1.3.1
address-family ipv4 unicast
exit
remote-as 65106
update-source 2.1.3.2
exit
exit |
0/ME5200S:KONDA-PE21# show bgp neighbors 2.1.3.1 advertised-routes
Thu Mar 12 05:40:03 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 2.1.3.1
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
2.1.1.0/24 2.1.3.2 0 0 advertised no-aggregation 65100 65432 45679 i
Total entries: 1
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229 advertised-routes
Thu Mar 12 05:40:05 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 172.27.72.229
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
192.0.1.0/24 172.27.72.227 0 0 advertised no-aggregation 65432 65100 65106 123 i
Total entries: 1
|
Cессия с соседом устанавливается с использованием номера сконфигурированного командой local-as <number AS>. Как мы можем наблюдать, как к полученным маршрутам от R1, так и к переданным маршрутам R3, мы добавили как local-as, так и global-as в атрибут AS-PATH.
2) mode no-prepend
router bgp 65100
neighbor 172.27.72.229
address-family ipv4 unicast
local-as 65432
mode no-prepend
remote-as 45679
update-source 172.27.72.227
exit
neighbor 2.1.3.1
address-family ipv4 unicast
exit
remote-as 65106
update-source 2.1.3.2
exit
exit |
0/ME5200S:KONDA-PE21# show bgp neighbors 2.1.3.1 advertised-routes
Thu Mar 12 05:40:03 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 2.1.3.1
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
2.1.1.0/24 2.1.3.2 0 0 advertised no-aggregation 65100 45679 i
Total entries: 1
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229 advertised-routes
Thu Mar 12 05:40:05 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 172.27.72.229
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
192.0.1.0/24 172.27.72.227 0 0 advertised no-aggregation 65432 65100 65106 123 i
Total entries: 1
|
В данном режиме к маршруту полученному от R3, добавили local as и global as в атрибут AS-PATH при отправке соседу R1, а к маршруту полученному от R1, добавили global as в атрибуте AS-PATH при отправке соседу R3.
3) mode no-prepend-replace
router bgp 65100
neighbor 172.27.72.229
address-family ipv4 unicast
local-as 65432
mode no-prepend-replace
remote-as 45679
update-source 172.27.72.227
exit
neighbor 2.1.3.1
address-family ipv4 unicast
exit
remote-as 65106
update-source 2.1.3.2
exit
exit |
0/ME5200S:KONDA-PE21# show bgp neighbors 2.1.3.1 advertised-routes
Thu Mar 12 05:40:03 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 2.1.3.1
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
2.1.1.0/24 2.1.3.2 0 0 advertised no-aggregation 65100 45679 i
Total entries: 1
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229 advertised-routes
Thu Mar 12 05:40:05 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 172.27.72.229
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
192.0.1.0/24 172.27.72.227 0 0 advertised no-aggregation 65432 65106 123 i
Total entries: 1
|
К маршруту полученному от R3, добавили local-as в атрибут AS-PATH при отправке соседу R1, а к маршруту полученному от R1 добавили global-as в атрибуте AS-PATH при отправке соседу в R3.
3) mode no-prepend-replace-dual
Происходит тот же самый процесс добавления AS-PATH к маршрутам, что и в mode no-prepend-replace, но отличием является то, что есть возможность установить bgp соседство как по local-as так и по global-as и в зависимости от того с каким номером as установилось соседство такой as и будет добавляться к маршрутам.
router bgp 65100
neighbor 172.27.72.229
address-family ipv4 unicast
local-as 65432
mode no-prepend-replace-dual
remote-as 45679
update-source 172.27.72.227
exit
neighbor 2.1.3.1
address-family ipv4 unicast
exit
remote-as 65106
update-source 2.1.3.2
exit
exit
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229
Thu Mar 12 07:48:53 2026
BGP router identifier 172.27.72.227, local AS number 65100
BGP neighbor is 172.27.72.229
Description:
Remote AS 45679, local AS 65432, external link << соседство поднято от AS 65432
|
0/ME5200S:KONDA-PE21# show bgp neighbors 2.1.3.1 advertised-routes
Thu Mar 12 05:40:03 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 2.1.3.1
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
2.1.1.0/24 2.1.3.2 0 0 advertised no-aggregation 65100 45679 i << к маршруту от R1 добавили global AS-PATH
Total entries: 1
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229 advertised-routes
Thu Mar 12 05:40:05 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 172.27.72.229
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
192.0.1.0/24 172.27.72.227 0 0 advertised no-aggregation 65432 65106 123 i << к маршруту от R3 добавили local AS-PATH
Total entries: 1
|
Со стороны R1 поменяем конфигурацию remote-as на 65100
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229
Thu Mar 12 08:37:09 2026
BGP router identifier 172.27.72.227, local AS number 65100
BGP neighbor is 172.27.72.229
Description:
Remote AS 45679, local AS 65100, external link << соседство поднято от AS 65100 |
0/ME5200S:KONDA-PE21# show bgp neighbors 2.1.3.1 advertised-routes
Thu Mar 12 05:40:03 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 2.1.3.1
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
2.1.1.0/24 2.1.3.2 0 0 advertised no-aggregation 65100 45679 i << к маршруту от R1 добавился global AS-PATH
Total entries: 1
0/ME5200S:KONDA-PE21# show bgp neighbors 172.27.72.229 advertised-routes
Thu Mar 12 05:40:05 2026
BGP router identifier 172.27.72.227, local AS number 65100
Graceful Restart is disabled
BGP table state: active
Status codes: a additional-path
Origin codes: i igp, e egp, ? incomplete
Advertised routes for peer: 172.27.72.229
Network Next hop Metric LocPrf Advertisement status Local agr type Path
--------------------- ---------------- ------- ------- --------------------- ------------------------------- -----
192.0.1.0/24 172.27.72.227 0 0 advertised no-aggregation 65100 65106 123 i << к маршруту от R3 добавился global AS-PATH
Total entries: 1
|