SR88X从EBGP邻居RT1、RT2学习两条明细路由1.1.1.1/32和1.1.1.2/32,本地聚合为1.1.1.0/24,并发送给EBGP邻居RT3。
当RT2上的1.1.1.2/32路由发生振荡,理论上SR88X聚合路由仍能存在,但实际上SR88X聚合路由也发生了振荡,导致RT3配置的bgp dampening生效、抑制了聚合路由。
SR88X学到的两条明细路由,分别来自于RT1的network发布和RT2的import引入,origin属性存在差异。在明细路由origin包括igp和incomplete两种时,SR88X会将聚合路由的origin置为incomplete。
<H3C>dis bgp routing-table ipv4 1.1.1.1 32
BGP local router ID: 20.0.0.2
Local AS number: 200
Paths: 1 available, 1 best
BGP routing table information of 1.1.1.1/32:
From : 10.0.0.1 (1.1.1.1)
Rely nexthop : 10.0.0.1
Original nexthop: 10.0.0.1
OutLabel : NULL
RxPathID : 0x0
TxPathID : 0x0
AS-path : 100
Origin : igp
Attribute value : MED 0, pref-val 0
State : suppressed, valid, external, best
IP precedence : N/A
QoS local ID : N/A
Traffic index : N/A
<H3C>dis bgp routing-table ipv4 1.1.1.2 32
BGP local router ID: 20.0.0.2
Local AS number: 200
Paths: 1 available, 1 best
BGP routing table information of 1.1.1.2/32:
From : 20.0.0.1 (20.0.0.1)
Rely nexthop : 20.0.0.1
Original nexthop: 20.0.0.1
OutLabel : NULL
RxPathID : 0x0
TxPathID : 0x0
AS-path : 100
Origin : incomplete
Attribute value : MED 0, pref-val 0
State : suppressed, valid, external, best
IP precedence : N/A
QoS local ID : N/A
Traffic index : N/A
<H3C>dis bgp routing-table ipv4 1.1.1.0
BGP local router ID: 20.0.0.2
Local AS number: 200
Paths: 1 available, 1 best
BGP routing table information of 1.1.1.0/24:
Original nexthop: 127.0.0.1
OutLabel : NULL
RxPathID : 0x0
TxPathID : 0x0
AS-path : (null)
Origin : incomplete
Attribute value : pref-val 32768
State : valid, local, best
This route is an atomic-aggregated route
Aggregator : AS 200, Aggregator ID: 20.0.0.2
IP precedence : N/A
QoS local ID : N/A
Traffic index : N/A
当RT2的明细路由1.1.1.2/32撤销,SR88X的聚合路由对应的明细路由origin仅有igp一种,此时聚合路由的origin会变成igp。对于RT3的bgp dampening来说,属性的变化也属于路由更新,会触发路由抑制。
<H3C>dis bgp routing-table ipv4 1.1.1.0
BGP local router ID: 20.0.0.2
Local AS number: 200
Paths: 1 available, 1 best
BGP routing table information of 1.1.1.0/24:
Original nexthop: 127.0.0.1
OutLabel : NULL
RxPathID : 0x0
TxPathID : 0x0
AS-path : (null)
Origin : igp
Attribute value : pref-val 32768
State : valid, local, best
This route is an atomic-aggregated route
Aggregator : AS 200, Aggregator ID: 20.0.0.2
IP precedence : N/A
QoS local ID : N/A
Traffic index : N/A
针对此类情况,可以在SR88X聚合路由时,增加路由策略的配置,使origin固定为igp。
#
bgp 200
#
address-family ipv4 unicast
aggregate 1.1.1.0 255.255.255.0 detail-suppressed attribute-policy 1
#
route-policy 1 permit node 10
apply origin igp
#
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