在vEdge上实施出口路径时的OMP路径选择问题

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已更新: 2019 年 3 月 28 日

文档 ID:214258

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简介

本文档介绍在vEdge设备上实施重叠管理协议(OMP)路径选择而不是在vSmart控制器上实施冗余设计时出现的问题，该设计会导致不需要的结果，并在链路出现故障时导致远程站点的可达性丢失，即使备用路径可用。此问题也称为“vSmart不考虑远程vEdge上的TLOC状态”。

拓扑

为了更好地了解问题，以下是描述设置的简单拓扑图：

配置

在这里，您可以找到配置的简要说明。

站点DC1具有TLOC颜色“private1”和“biz-internet”
站点DC2具有TLOC颜色“private1”和“biz-internet”
站点HQ仅具有TLOC颜色“private1”
在DC1和DC2中，两种颜色都用于控制与vSmart的连接

两个DC站点（DC1和DC2）通告同一网络198.51.100.0/24。
在每个站点中，vEdge通过某种动态路由协议(例如边界网关协议(BGP))从DC获取路由器。

每个DC站点使用不同的度量标记前缀：

站点DC1 vEdge设置原始度量32
站点DC2 vEdge设置原点 — 度量52

主机名	站点ID	system-ip
DC1	21	10.100.0.21
DC2	41	10.100.0.41
总部	100	10.100.0.100
vSmart	100	10.100.0.20

问题

正常运行时：

1.vSmart从DC1和DC2接收198.51.100.0/24。

vsmart1# show omp routes 198.51.100.0/24
Code:
C   -> chosen
I   -> installed
Red -> redistributed
Rej -> rejected
L   -> looped
R   -> resolved
S   -> stale
Ext -> extranet
Inv -> invalid
Stg -> staged
U   -> TLOC unresolved

                                            PATH                      ATTRIBUTE                                                       
VPN    PREFIX              FROM PEER        ID     LABEL    STATUS    TYPE       TLOC IP          COLOR            ENCAP  PREFERENCE  
--------------------------------------------------------------------------------------------------------------------------------------
3      198.51.100.0/24     10.100.0.21      36     1003     C,R       installed  10.100.0.21      biz-internet     ipsec  -           <===== METRIC 32 (PREFERRED)
                           10.100.0.21      49     1003     C,R       installed  10.100.0.21      private1         ipsec  -           <===== METRIC 32 (PREFERRED)
                           10.100.0.41      36     1003     R         installed  10.100.0.41      biz-internet     ipsec  -           <===== METRIC 52           
                           10.100.0.41      49     1003     R         installed  10.100.0.41      private1         ipsec  -           <===== METRIC 52

2.vSmart向HQ通告目标DC1（通过专用1和商业互联网）的路由，因为它根据OMP路由选择标准具有最低的源度量。

vsmart1# show omp routes 198.51.100.0/24 vpn 3 detail                        

---------------------------------------------------
omp route entries for vpn 3 route 198.51.100.0/24
---------------------------------------------------
            RECEIVED FROM:                      <================= RECEIVED FROM vEdge in DC1 in "biz-internet" color
peer            10.100.0.21
path-id         36
label           1003
status          C,R
loss-reason     not set
lost-to-peer    not set
lost-to-path-id not set
    Attributes:
     originator       10.100.0.21
     type             installed
     tloc             10.100.0.21, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          21
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set
            RECEIVED FROM:                      <================= RECEIVED FROM vEdge in DC1 in "private1" color                   
peer            10.100.0.21
path-id         49
label           1003
status          C,R
loss-reason     not set
lost-to-peer    not set
lost-to-path-id not set
    Attributes:
     originator       10.100.0.21
     type             installed
     tloc             10.100.0.21, private1, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          21
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set
            RECEIVED FROM:                      <================= RECEIVED FROM vEdge in DC2 in "biz-internet" color                       
peer            10.100.0.41
path-id         36
label           1003
status          R
loss-reason     origin-metric
lost-to-peer    10.100.0.21
lost-to-path-id 49
    Attributes:
     originator       10.100.0.41
     type             installed
     tloc             10.100.0.41, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          41
     preference       not set
     tag              1000030041
     origin-proto     eBGP
     origin-metric    52
     as-path          "65001 65001 65001 65001 65001"
     unknown-attr-len not set
            RECEIVED FROM:                      <================= RECEIVED FROM vEdge in DC2 in "private1" color                     
peer            10.100.0.41
path-id         49
label           1003
status          R
loss-reason     tloc-id
lost-to-peer    10.100.0.41
lost-to-path-id 36
    Attributes:
     originator       10.100.0.41
     type             installed
     tloc             10.100.0.41, private1, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          41
     preference       not set
     tag              1000030041
     origin-proto     eBGP
     origin-metric    52
     as-path          "65001 65001 65001 65001 65001"
     unknown-attr-len not set
            ADVERTISED TO:                        <================= WE ADVERTISE TO HQ vEdge ONLY BEST ROUTES WITH METRIC 32                 
peer    10.100.0.100
    Attributes:
     originator       10.100.0.21
     label            1003
     path-id          4410
     tloc             10.100.0.21, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     site-id          21
     overlay-id        1
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set
    Attributes:
     originator       10.100.0.21
     label            1003
     path-id          4439
     tloc             10.100.0.21, private1, ipsec
     ultimate-tloc    not set
     domain-id        not set
     site-id          21
     overlay-id        1
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set

3. HQ vEdge将TLOC为“biz-internet”的路由标记为“Inv，U”，因为此vEdge没有TLOC biz-internet。

4. HQ vEdge将TLOC为“private1”的路由标记为“C、I、R”并安装该路由。

DC1故障场景：

1.在故障场景中，颜色为“private1”的DC1 vEdge上行链路发生故障（接口进入关闭状态），而“biz-internet”保持打开。

2.vSmart从DC1（仅可通过Biz-Internet访问）和DC2(Biz-Internet和Private1)接收198.51.100.0/24。

3.vSmart向HQ vEdge通告到DC1的路由(通过biz-internet)，因为DC1具有最低度量。

vsmart1# show omp routes 198.51.100.0/24 detail

---------------------------------------------------
omp route entries for vpn 3 route 198.51.100.0/24
---------------------------------------------------
            RECEIVED FROM:                   
peer            10.100.0.21
path-id         36
label           1003
status          C,R
loss-reason     not set
lost-to-peer    not set
lost-to-path-id not set
    Attributes:
     originator       10.100.0.21
     type             installed
     tloc             10.100.0.21, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          21
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set
            RECEIVED FROM:                   
peer            10.100.0.41
path-id         36
label           1003
status          R
loss-reason     origin-metric
lost-to-peer    10.100.0.21
lost-to-path-id 36
    Attributes:
     originator       10.100.0.41
     type             installed
     tloc             10.100.0.41, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          41
     preference       not set
     tag              1000030041
     origin-proto     eBGP
     origin-metric    52
     as-path          "65001 65001 65001 65001 65001"
     unknown-attr-len not set
            RECEIVED FROM:                   
peer            10.100.0.41
path-id         49
label           1003
status          R
loss-reason     tloc-id
lost-to-peer    10.100.0.41
lost-to-path-id 36
    Attributes:
     originator       10.100.0.41
     type             installed
     tloc             10.100.0.41, private1, ipsec
     ultimate-tloc    not set
     domain-id        not set
     overlay-id        1
     site-id          41
     preference       not set
     tag              1000030041
     origin-proto     eBGP
     origin-metric    52
     as-path          "65001 65001 65001 65001 65001"
     unknown-attr-len not set
            ADVERTISED TO:                   
peer    10.100.0.31
    Attributes:
     originator       10.100.0.21
     label            1003
     path-id          5906
     tloc             10.100.0.21, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     site-id          21
     overlay-id        1
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set
            ADVERTISED TO:                   
peer    10.100.0.41
    Attributes:
     originator       10.100.0.21
     label            1003
     path-id          7689
     tloc             10.100.0.21, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     site-id          21
     overlay-id        1
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set
            ADVERTISED TO:        <===== THIS IS WHAT WE ADVERTISE TO HQ SITE                
peer    10.100.0.100
    Attributes:
     originator       10.100.0.21
     label            1003
     path-id          4410
     tloc             10.100.0.21, biz-internet, ipsec
     ultimate-tloc    not set
     domain-id        not set
     site-id          21
     overlay-id        1
     preference       not set
     tag              1000030021
     origin-proto     eBGP
     origin-metric    32
     as-path          "65001 65001 65001"
     unknown-attr-len not set

4. HQ vEdge将TLOC为“Inv，U”的路由标记为“Inv，U”，因为此vEdge没有TLOC biz-internet。

结果是HQ vEdge无法到达198.51.100.0/24。

解决方案

vSmart可能已向DC2发送路由（具有较低优先级的较高度量），在这种情况下，HQ vEdge仍将通过DC2使用“private1” TLOC到达目的地，DC2仍处于工作状态：

VEDGE-HQ-1# show bfd sessions site-id 41
                                      SOURCE TLOC      REMOTE TLOC                                      DST PUBLIC                      DST PUBLIC         DETECT      TX                              
SYSTEM IP        SITE ID  STATE       COLOR            COLOR            SOURCE IP                       IP                              PORT        ENCAP  MULTIPLIER  INTERVAL(msec) UPTIME          TRANSITIONS 
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
10.100.0.41      41       up          private1         private1         192.168.11.1                    192.168.41.1                    12406       ipsec  7           1000           12:04:02:25     0

但是，由于vSmart已选择度量较低的业务互联网路由作为最佳路径，因此，vSmart不会默认通告具有不同度量的OMP路由，因此，不允许接收vEdge设备决定采用哪条路径（并考虑可用的TLOC），因此，在HQ vEdge上没有通过“private1” TLOC的路由和其状态)。 vSmart不考虑远程设备（在本例中为HQ vEdge）上可用的TLOC颜色，也不考虑路由的状态，因为没有这种机制来控制此情况。

这是在具有iBGP路由反射器的类似拓扑中可以看到的OMP拐角情况，以及物理接口地址上的对等。

第一个解决方案选项是使用OMP中提供的类似路径的功能(RFC7911)，在vSmart上称为“发送备份路径”：

omp
  send-backup-paths

它通告所有可用路径，因此远程HQ vEdge会根据TLOC可用性选择路径。

此处的第二个解决方案选项是删除DC1和DC2 vEdge上对应前缀的路由策略操作“set metric”，然后通过vSmart控制策略执行集中式路由选择实施，如下所示：

policy
 lists
 site-list site_11
 site-id 11
 !
 prefix-list PREFIX
 ip-prefix 198.51.100.0/24
 !
 control-policy SET_PREF
 sequence 10
 match route
 prefix-list PREFIX
 site-id 21
 !
 action accept
 set
 preference 200
 !
 !
 !
 sequence 20
 match route
 prefix-list PREFIX
 site-id 41
 !
 action accept
 set
 preference 100
 !
 !
 !
 default-action accept
 !
apply-policy
 site-list site_11
 control-policy SET_PREF out
 !

此处，site-id 11是HQ vEdge，前缀列表前缀包含您希望优先于一种或另一种TLOC颜色的前缀。由于两个OMP路由都在HQ vEdge上，因此一旦vEdge无法再到达biz-internet，它将从其OMP路由表在路由信息库(RIB)中安装通过private1的路由。

由思科工程师提供

Eugene Khabarov
Cisco TAC Engineer

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