对IOS-XR上路由策略不佳导致的BGP收敛缓慢问题进行故障排除
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已更新: 2022 年 1 月 31 日
文档 ID:217634
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简介
本文档介绍如何诊断Cisco IOS® XR路由器上由于非最佳路由策略而发生的缓慢BGP收敛问题。
背景
BGP收敛时间包括许多因素。其中之一是通过配置的路由策略处理入口或出口BGP更新的时间。可通过多种方式编写路由策略来执行特定任务。最佳方法有助于改进BGP融合、最小化潜在流量丢弃并避免临时路由环路。Cisco IOS® XR包含一个分析工具，该工具可测量特定路由策略花费的时间，从而估计其处理时间。
问题
BGP收敛缓慢有时是路由策略以非最佳方式写入的结果。
解决方案
有一个用于路由策略的策略分析工具，它可以在不影响性能的情况下使用，以测量路由策略在某个特定连接点上的每条语句所花费的时间。您可以检查路由策略在此特定连接点的运行时间。默认情况下，仅对汇聚路由策略统计启用分析。
router bgp 65000
neighbor 10.0.54.6
remote-as 65000
update-source Loopback0
address-family ipv4 unicast
route-policy INGRESS-ROUTE-POLICY in
!
neighbor 10.0.54.11
remote-as 65001
ebgp-multihop 255
update-source Loopback0
address-family ipv4 unicast
route-policy EGRESS-ROUTE-POLICY out
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-in-dflt default-IPv4-Uni-10.0.54.6 policy profile
Policy profiling data
Policy : INGRESS-ROUTE-POLICY
Pass : 1440233
Drop : 0
# of executions : 1440233
Total execution time : 57095msec <===========
RP/0/RSP1/CPU0:XR1#show bgp ipv4 unicast neighbors 10.0.54.11 | i Update group
Update group: 0.3 Filter-group: 0.5 No Refresh request being processed
RP/0/RSP1/CPU0:XR1#
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-out-dflt default-IPv4-Uni-UpdGrp-0.3-Out policy profile
Policy profiling data
Policy : EGRESS-ROUTE-POLICY
Pass : 726751
Drop : 0
# of executions : 726751
Total execution time : 108099msec <===========
RP/0/RSP1/CPU0:XR1#
您可以看到处理INGRESS-ROUTE-POLICY和EGRESS-ROUTE-POLICY所花费的累计时间。
分析可以应用于任何连接点的入口或出口路由策略。
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 ?
debug-policy Attachpoint name
permnet Attachpoint name
import Attachpoint name
export Attachpoint name
interafi-import Attachpoint name
source-rt Attachpoint name
interafi-export Attachpoint name
retain-rt Attachpoint name
addpath Attachpoint name
neighbor-in-dflt Attachpoint name
neighbor-in-vrf Attachpoint name
neighbor-out-dflt Attachpoint name
neighbor-out-vrf Attachpoint name
orf-dflt Attachpoint name
orf-vrf Attachpoint name
dampening-dflt Attachpoint name
dampening-vrf Attachpoint name
default-originate-dflt Attachpoint name
default-originate-vrf Attachpoint name
clear-policy Attachpoint name
show-policy-node0_RSP1_CPU0 Attachpoint name
aggregation-dflt Attachpoint name
aggregation-vrf Attachpoint name
nexthop Attachpoint name
allocate-label Attachpoint name
label-mode Attachpoint name
l2vpn-import Attachpoint name
l2vpn-export Attachpoint name
redistribution-dflt Attachpoint name
redistribution-vrf Attachpoint name
rib-install-dflt Attachpoint name
rib-install-vrf Attachpoint name
network-dflt Attachpoint name
network-vrf Attachpoint name
redistribution-dflt Attachpoint name
redistribution-vrf Attachpoint name
rib-install-dflt Attachpoint name
rib-install-vrf Attachpoint name
network-dflt Attachpoint name
network-vrf Attachpoint name
l2vpn-export-mp2mp Attachpoint name
l2vpn-export-vfi Attachpoint name
l2vpn-export-evi Attachpoint name
l2vpn-export-mspw Attachpoint name
l2vpn-export-instance Attachpoint name
WORD Attachpoint name
RP/0/RSP1/CPU0:XR1#
您可以根据需要清除统计信息。
RP/0/RSP1/CPU0:XR1#clear pcl protocol bgp speaker-0 neighbor-in-dflt default-IPv4-Uni-10.0.54.6 policy profile
RP/0/RSP1/CPU0:XR1#clear pcl protocol bgp speaker-0 neighbor-out-dflt default-IPv4-Uni-UpdGrp-0.3-Out policy profile
如果启用debug pcl profile detail，则会获取每个路由策略条目的详细统计信息。
RP/0/RSP1/CPU0:XR1#debug pcl profile detail
这些输出是在收到完整的Internet BGP表扩展后收集并进一步传播的。
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-in-dflt default-IPv4-Uni-10.0.54.6 policy profile
Policy profiling data
Policy : INGRESS-ROUTE-POLICY
Pass : 720100
Drop : 0
# of executions : 720100
Total execution time : 222788msec <============== about 3.7 minutes to process ingress updates
Node Id Num visited Exec time Policy engine operation
--------------------------------------------------------------------------------
PXL_0_1 720100 221796msec if as-path aspath-match ... then <==============
PXL_0_3 3525 3msec set local-preference 150
3525 0msec
PXL_0_2 716575 225msec set local-preference 50
716575 82msec
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-out-dflt default-IPv4-Uni-UpdGrp-0.3-Out policy profile
Policy profiling data
Policy : EGRESS-ROUTE-POLICY
Pass : 720105
Drop : 0
# of executions : 720105
Total execution time : 221975msec <============== about 3.7 minutes to process egress updates
Node Id Num visited Exec time Policy engine operation
--------------------------------------------------------------------------------
PXL_0_1 720105 3005msec if as-path aspath-match ... then
PXL_0_5 0 0msec set med 70
0 0msec
PXL_0_2 720105 218008msec if as-path aspath-match ... then <==============
PXL_0_3 25 0msec set med 80
25 0msec
PXL_0_4 720080 145msec set med 90
720080 76msec
RP/0/RSP1/CPU0:XR1#如您所见，INGRESS-ROUTE-POLICY的行PXL_0_1和EGRESS-ROUTE-POLICY的行PXL_0_2尤其耗时，而且会降低收敛速度。
如果将它们与路由策略相关联，您会发现INGRESS-ROUTE-POLICY中的AS-PATH-SET-11和EGRESS-ROUTE-POLICY中的AS-PATH-SET-22会导致问题。每个AS路径集由100个正则表达式行组成，这是编写策略的一种非常低效的方法，因为它不会利用任何可能的优化或正则表达式的强大功能。
route-policy INGRESS-ROUTE-POLICY
if as-path in AS-PATH-SET-11 then
set local-preference 150
else
set local-preference 50
endif
end-policy
route-policy EGRESS-ROUTE-POLICY
if as-path in AS-PATH-SET-21 then
set med 70
elseif as-path in AS-PATH-SET-22 then
set med 80
else
set med 90
endif
end-policy
as-path-set AS-PATH-SET-11
ios-regex '^65101 65201_',
ios-regex '^65102 65202_',
ios-regex '^65103 65203_',
ios-regex '^65104 65204_',
ios-regex '^65105 65205_',
--- removed 90 similar lines ---
ios-regex '^65195 65295_',
ios-regex '^65196 65296_',
ios-regex '^65197 65297_',
ios-regex '^65198 65298_',
ios-regex '^65199 65299_'
end-set
as-path-set AS-PATH-SET-21
ios-regex '^$'
end-set
as-path-set AS-PATH-SET-22
ios-regex '^65169(_65169)*$',
ios-regex '^65392(_65392)*$',
ios-regex '^65133(_65133)*$',
ios-regex '^65231(_65231)*$',
ios-regex '^65161(_65161)*$',
--- removed 90 similar lines ---
ios-regex '^65281(_65281)*$',
ios-regex '^65336(_65336)*$',
ios-regex '^65238(_65238)*$',
ios-regex '^65381(_65381)*$',
ios-regex '^65103(_65103)*$'
end-set
为了提高策略性能，可以使用本地as-path匹配操作而不是正则表达式来评估AS路径集的配置。或者，可以在路由策略内以折叠方式使用正则表达式，从而减少使用的正则表达式行数。
此表列出了路由策略语言(RPL)提供的AS路径匹配条件。 本机匹配函数使用二进制匹配算法，与正则表达式匹配引擎相比具有更好的性能。大多数常见的ios-regex匹配场景都可以与其一起编写（或其组合）。
|
命令 |
描述 |
|
is-local |
确定路由器（或此自治系统或联盟中的另一台路由器）是否发起路由 |
|
长度 |
根据AS路径的长度执行条件检查 |
|
neighbor-is |
根据一个或多个整数值或参数的序列，测试AS路径头部的一个或多个自主系统编号。 |
|
源自 |
从开始根据AS序列测试AS路径使用发起路由的AS编号。 |
|
直通 |
测试，以了解指定的整数或参数是否出现在AS路径中的任何位置，或是否出现整数和参数的序列。 |
|
unique-length |
根据AS路径的长度执行特定检查，忽略重复项 |
确认
这些策略是借助本地匹配条件重新编排的路由策略。这显着地减少了处理时间。
route-policy INGRESS-ROUTE-POLICY
if as-path in AS-PATH-SET-11 then
set local-preference 150
else
set local-preference 50
endif
end-policy
route-policy EGRESS-ROUTE-POLICY
if as-path is-local then
set med 70
elseif as-path in AS-PATH-SET-22 and as-path unique-length is 1 then
set med 80
else
set med 90
endif
end-policy
as-path-set AS-PATH-SET-11
neighbor-is '65101 65201',
neighbor-is '65102 65202',
neighbor-is '65103 65203',
neighbor-is '65104 65204',
neighbor-is '65105 65205',
--- removed 90 similar lines ---
neighbor-is '65195 65295',
neighbor-is '65196 65296',
neighbor-is '65197 65297',
neighbor-is '65198 65298',
neighbor-is '65199 65299'
end-set
as-path-set AS-PATH-SET-22
originates-from '65169',
originates-from '65392',
originates-from '65133',
originates-from '65231',
originates-from '65161',
--- removed 90 similar lines ---
originates-from '65281',
originates-from '65336',
originates-from '65238',
originates-from '65381',
originates-from '65103'
end-set
这些输出是在收到完整的Internet BGP表扩展后收集并进一步传播的。
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-in-dflt default-IPv4-Uni-10.0.54.6 policy profile
Policy profiling data
Policy : INGRESS-ROUTE-POLICY
Pass : 720100
Drop : 0
# of executions : 720100
Total execution time : 9612msec <============== about 10 seconds to process ingress updates
Node Id Num visited Exec time Policy engine operation
--------------------------------------------------------------------------------
PXL_0_1 720100 8540msec if as-path aspath-match ... then
PXL_0_3 7128 2msec set local-preference 150
7128 1msec
PXL_0_2 712972 276msec set local-preference 50
712972 80msec
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-out-dflt default-IPv4-Uni-UpdGrp-0.3-Out policy profile
Policy profiling data
Policy : EGRESS-ROUTE-POLICY
Pass : 720126
Drop : 0
# of executions : 720126
Total execution time : 12399msec <============== about 12 seconds to process egress updates
Node Id Num visited Exec time Policy engine operation
--------------------------------------------------------------------------------
PXL_0_1 720126 190msec if as-path is-local then
PXL_0_7 0 0msec set med 70
0 0msec
PXL_0_2 720126 11190msec if as-path aspath-match ... then
PXL_0_4 262734 65msec if as-path unique-length is 1 then
PXL_0_5 25 0msec set med 80
25 0msec
PXL_0_6 720101 164msec set med 90
720101 57msec
GOTO : PXL_0_6
RP/0/RSP1/CPU0:XR1#或者，可以折叠ios-regex行。这还有助于提高性能。
route-policy INGRESS-ROUTE-POLICY
if as-path in (ios-regex '^(65101_65201|65102_65202|65103_65203|65104_65204|65105_65205|65106_65206|65107_65207|65108_65208|65109_65209|65110_65210)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65111_65211|65112_65212|65113_65213|65114_65214|65115_65215|65116_65216|65117_65217|65118_65218|65119_65219|65120_65220)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65121_65221|65122_65222|65123_65223|65124_65224|65125_65225|65126_65226|65127_65227|65128_65228|65129_65229|65130_65230)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65131_65231|65132_65232|65133_65233|65134_65234|65135_65235|65136_65236|65137_65237|65138_65238|65139_65239|65140_65240)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65141_65241|65142_65242|65143_65243|65144_65244|65145_65245|65146_65246|65147_65247|65148_65248|65149_65249|65150_65250)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65151_65251|65152_65252|65153_65253|65154_65254|65155_65255|65156_65256|65157_65257|65158_65258|65159_65259|65160_65260)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65161_65261|65162_65262|65163_65263|65164_65264|65165_65265|65166_65266|65167_65267|65168_65268|65169_65269|65170_65270)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65171_65271|65172_65272|65173_65273|65174_65274|65175_65275|65176_65276|65177_65277|65178_65278|65179_65279|65180_65280)') then
set local-preference 150
endif
if as-path in (ios-regex '^(65181_65281|65182_65282|65183_65283|65184_65284|65185_65285|65186_65286|65187_65287|65188_65288|65189_65289|65190_65290)') then
set local-preference 150
else
set local-preference 50
endif
end-policy
route-policy EGRESS-ROUTE-POLICY
if as-path in (ios-regex '^$') then
set med 70
endif
if as-path in (ios-regex '^65169(_65169)*$|^65392(_65392)*$|^65133(_65133)*$|^65231(_65231)*$|^65161(_65161)*$') then
set med 80
endif
if as-path in (ios-regex '^65354(_65354)*$|^65331(_65331)*$|^65342(_65342)*$|^65295(_65295)*$|^65208(_65208)*$') then
set med 80
endif
if as-path in (ios-regex '^65149(_65149)*$|^65350(_65350)*$|^65115(_65115)*$|^65300(_65300)*$|^65322(_65322)*$') then
set med 80
endif
if as-path in (ios-regex '^65102(_65102)*$|^65329(_65329)*$|^65237(_65237)*$|^65218(_65218)*$|^65153(_65153)*$') then
set med 80
endif
if as-path in (ios-regex '^65263(_65263)*$|^65116(_65116)*$|^65112(_65112)*$|^65114(_65114)*$|^65378(_65378)*$') then
set med 80
endif
if as-path in (ios-regex '^65105(_65105)*$|^65296(_65296)*$|^65211(_65211)*$|^65317(_65317)*$|^65115(_65115)*$') then
set med 80
endif
if as-path in (ios-regex '^65371(_65371)*$|^65214(_65214)*$|^65325(_65325)*$|^65354(_65354)*$|^65384(_65384)*$') then
set med 80
endif
if as-path in (ios-regex '^65220(_65220)*$|^65277(_65277)*$|^65219(_65219)*$|^65213(_65213)*$|^65336(_65336)*$') then
set med 80
endif
if as-path in (ios-regex '^65249(_65249)*$|^65112(_65112)*$|^65314(_65314)*$|^65385(_65385)*$|^65152(_65152)*$') then
set med 80
endif
if as-path in (ios-regex '^65196(_65196)*$|^65252(_65252)*$|^65162(_65162)*$|^65271(_65271)*$|^65357(_65357)*$') then
set med 80
endif
if as-path in (ios-regex '^65317(_65317)*$|^65360(_65360)*$|^65198(_65198)*$|^65256(_65256)*$|^65246(_65246)*$') then
set med 80
endif
if as-path in (ios-regex '^65356(_65356)*$|^65359(_65359)*$|^65302(_65302)*$|^65118(_65118)*$|^65346(_65346)*$') then
set med 80
endif
if as-path in (ios-regex '^65225(_65225)*$|^65307(_65307)*$|^65313(_65313)*$|^65189(_65189)*$|^65288(_65288)*$') then
set med 80
endif
if as-path in (ios-regex '^65381(_65381)*$|^65292(_65292)*$|^65145(_65145)*$|^65325(_65325)*$|^65361(_65361)*$') then
set med 80
endif
if as-path in (ios-regex '^65156(_65156)*$|^65184(_65184)*$|^65367(_65367)*$|^65302(_65302)*$|^65290(_65290)*$') then
set med 80
endif
if as-path in (ios-regex '^65351(_65351)*$|^65116(_65116)*$|^65341(_65341)*$|^65123(_65123)*$|^65258(_65258)*$') then
set med 80
endif
if as-path in (ios-regex '^65397(_65397)*$|^65302(_65302)*$|^65188(_65188)*$|^65187(_65187)*$|^65358(_65358)*$') then
set med 80
endif
if as-path in (ios-regex '^65217(_65217)*$|^65107(_65107)*$|^65203(_65203)*$|^65377(_65377)*$|^65381(_65381)*$') then
set med 80
endif
if as-path in (ios-regex '^65219(_65219)*$|^65308(_65308)*$|^65364(_65364)*$|^65277(_65277)*$|^65396(_65396)*$') then
set med 80
endif
if as-path in (ios-regex '^65281(_65281)*$|^65336(_65336)*$|^65238(_65238)*$|^65381(_65381)*$|^65103(_65103)*$') then
set med 80
else
set med 90
endif
end-policy
这些输出是在收到完整的Internet BGP表扩展后收集的，然后进一步传播。
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-in-dflt default-IPv4-Uni-10.0.54.6 policy profile
Policy profiling data
Policy : INGRESS-ROUTE-POLICY
Pass : 720100
Drop : 0
# of executions : 720100
Total execution time : 30119msec <============== about 30 seconds to process ingress updates
Node Id Num visited Exec time Policy engine operation
--------------------------------------------------------------------------------
PXL_0_1 720100 4434msec if as-path aspath-match ... then
PXL_0_2 361 0msec set local-preference 150
PXL_0_3 720100 3039msec if as-path aspath-match ... then
--- removed lines ---
GOTO : PXL_0_3
RP/0/RSP1/CPU0:XR1#show pcl protocol bgp speaker-0 neighbor-out-dflt default-IPv4-Uni-UpdGrp-0.3-Out policy profile
Policy profiling data
Policy : EGRESS-ROUTE-POLICY
Pass : 720110
Drop : 0
# of executions : 720110
Total execution time : 106566msec <============== about 1.8 minutes to process egress updates
Node Id Num visited Exec time Policy engine operation
--------------------------------------------------------------------------------
PXL_0_1 720110 2958msec if as-path aspath-match ... then
PXL_0_2 0 0msec set med 70
PXL_0_3 720110 5222msec if as-path aspath-match ... then
PXL_0_4 3 0msec set med 80
PXL_0_5 720110 4979msec if as-path aspath-match ... then
PXL_0_6 set med 80
--- removed lines ---
GOTO : PXL_0_3
RP/0/RSP1/CPU0:XR1# 结论
使用本地as-path匹配或折叠正则表达式模式可以提高路由策略的性能。
修订历史记录
| 版本 | 发布日期 | 备注 |
|---|---|---|
2.0 |
31-Jan-2022
|
次要编辑 |
1.0 |
14-Jan-2022
|
初始版本 |
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