在IOS-XR上的一個BGP鄰居上同時標籤和未標籤

本檔案將說明在Cisco IOS^® XR中透過一個BGP作業階段接收和播發未標籤和已標籤^路徑的行為。

必要條件

需求

本文件沒有特定需求。

採用元件

本檔案特定於Cisco IOS^® XR，但並不限於特定軟體版本或硬體。

本文中的資訊是根據特定實驗室環境內的裝置所建立。文中使用到的所有裝置皆從已清除（預設）的組態來啟動。如果您的網路正在作用，請確保您已瞭解任何指令可能造成的影響。

簡介

地址系列識別符號(AFI)表示BGP路由的型別。例如，1表示IPv4,2表示IPv6。

後續地址系列識別符號(SAFI)是路由型別的進一步指示。例如，未標籤路由為1，標籤路由為4。

IPv4的未標籤單播為AFI 1和SAFI 1。

標籤為IPv4的單播為AFI 1和SAFI 4。

IPv6的未標籤單播為AFI 2和SAFI 1。

標籤為IPv6的單播為AFI 2和SAFI 4。

標籤單播(LU)通常稱為RFC 3107「在BGP-4中傳送標籤資訊」。

以後，U是指未標籤的單播，因此SAFI 1和LU是指標籤的單播，因此SAFI 4。

請注意，Cisco IOS^® XR需要「allocate-label all| route-policy ...」，否則該路由不會作為SAFI 4發起或傳播到下一個BGP揚聲器。

Cisco IOS^® XR不支援一個BGP會話上的IPv4/v6單播和標籤單^播。

在Cisco IOS^® XR上，一個BGP作業階段上同時啟用未標籤和標籤的支援已在6.2.1中完成。

如果不支援在一個會話上同時運行兩者，則會出現問題，因為上次收到的更新/撤消會覆蓋上一個更新/撤消更新，即使它們是在另一個SAFI上接收到的。

在運行IOS-XR 6.2.1之前的IOS-XR代碼的路由器上，在同一BGP會話上配置SAFI 1和4時，路由器發出以下警告：

bgp[1051]: %ROUTING-BGP-4-INCOMPATIBLE_AFI : IPv4 Unicast and IPv4 Labeled-unicast Address families together are not supported under the same neighbor.

此警告消息是在IOS-XR 5.3.0和IOS-XR 5.2.2中引入的。

功能交換

BGP對等體之間交換的能力必須匹配。否則，BGP作業階段不會啟動。

以下是BGP Open訊息中為AFI 1/SAFI 1和AFI 1/SAFI 4交換功能的Wireshark擷取：

圖1

以下是使用LU配置的IOS-XR的示例，該示例在與使用U配置的IOS的會話中僅配置LU。

IOS-XR:

RP/0/0/CPU0:R4#show bgp neighbor 10.100.1.8
 
BGP neighbor is 10.100.1.8
 Remote AS 65003, local AS 65003, internal link
 Remote router ID 0.0.0.0
  BGP state = Idle
…

  Connections established 0; dropped 0
  Local host: 10.100.1.4, Local port: 179, IF Handle: 0x00000000
  Foreign host: 10.100.1.8, Foreign port: 33396
  Last reset 00:00:14, due to BGP Notification sent: unsupported/disjoint capability
  Time since last notification sent to neighbor: 00:00:14
  Error Code: unsupported/disjoint capability
  Notification data sent:
    None

IOS路由器會為此配置錯誤列印系統日誌消息：

*Aug  8 12:40:44.719: %BGP-3-NOTIFICATION: received from neighbor 10.100.1.4 active 2/7 (unsupported/disjoint capability) 0 by

IOS-XR實施細節

配置U或LU

您可以在BGP neighbor命令下配置「address-family ipv4 unicast」，為BGP會話啟用ipv4單播。

您可以在BGP neighbor命令下配置「address-family ipv6 unicast」，為BGP會話啟用ipv6單播。

您可以在BGP neighbor命令下配置「address-family ipv4 labeled-unicast」，為BGP會話啟用標籤為unicast的ipv4。

您可以在BGP neighbor命令下配置「address-family ipv6 labeled-unicast」，為BGP會話啟用標籤為unicast的ipv6。

在IOS-XR中，AFI/SAFI組合是按每BGP對等體配置的。

以下是具有SAFI 1和4的BGP作業階段的範例：

router bgp 65003
 address-family ipv4 unicast
  redistribute connected
  allocate-label all unlabeled-path
   …
  neighbor 10.100.1.7
   remote-as 65003
   update-source Loopback0
   address-family ipv4 unicast
    route-reflector-client
   !
   address-family ipv4 labeled-unicast
    route-reflector-client

請注意，路由器BGP下仍然只有「address family unicast」而不是「address-family labeled-unicast」。SAFI 1和4路徑都儲存在這個BGP表中。

BGP表

無論IOS-XR是舊版還是新版6.2.1，只有一個BGP表可以儲存U和LU路由。這一點在路由器bgp下只能配置（啟用）「地址系列ipv4單播」或「地址系列ipv6單播」的事實中顯而易見。不能在路由器bgp下配置「address-family ipv4 labeled-unicast」或「address-family ipv6 labeled-unicast」。

U和LU路徑可以相同。在IOS-XR 6.2.1之前，再次接收相同路徑（這次包含或不包含標籤）會覆蓋先前接收的路徑。在IOS-XR 6.2.1之後，如果兩條相同的路徑僅因標籤的不同而不同，則會視為不同的路徑。路徑新增、刪除或修改由不同的SAFI執行。

以下是具有AFI 1/SAFI 4的BGP表中的路由範例。由於對所有字首啟用了標籤分配，因此此路徑將使用本地標籤儲存。由於只有一個BGP表可儲存U和LU路由，因此字首會顯示為命令「show bgp ipv4 unicast」和「show bgp ipv4 labeled-unicast」！

RP/0/0/CPU0:R4#show bgp ipv4 unicast 10.100.1.1/32
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  5           5
    Local Label: 24000
Last Modified: Aug  6 15:03:59.574 for 16:06:13
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.3 0.4
  Advertised to peers (in unique update groups):
    10.1.45.5
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.3 0.4
  Advertised to peers (in unique update groups):
    10.1.45.5
  65002 65001
    10.1.24.2 from 10.1.24.2 (10.100.1.2)
      Received Label 24003
      Origin IGP, localpref 100, valid, external, best, group-best, labeled-unicast
      Received Path ID 0, Local Path ID 0, version 5
      Origin-AS validity: not-found

請注意，路徑標有「labeled-unicast」。

RP/0/0/CPU0:R4#show bgp ipv4 labeled-unicast 10.100.1.1/32
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  5           5
    Local Label: 24000
Last Modified: Aug  6 15:03:59.574 for 16:08:41
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.3 0.4
  Advertised to peers (in unique update groups):
    10.1.45.5
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.3 0.4
  Advertised to peers (in unique update groups):
    10.1.45.5
  65002 65001
    10.1.24.2 from 10.1.24.2 (10.100.1.2)
      Received Label 24003
      Origin IGP, localpref 100, valid, external, best, group-best, labeled-unicast
      Received Path ID 0, Local Path ID 0, version 5
      Origin-AS validity: not-found

請注意，路徑標有「labeled-unicast」。

如果路徑同時以U和LU的形式存在，則本地路徑ID會有所不同。

RP/0/0/CPU0:R4#show bgp ipv4 labeled-unicast 10.100.1.1/32 detail
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 30          30
    Local Label: 24003 (no rewrite);
    Flags: 0x00003028+0x00010000;
Last Modified: Aug 30 10:45:50.502 for 00:01:59
Paths: (2 available, best #1)
  Advertised IPv4 Unicast paths to peers (in unique update groups):
    10.100.1.8      10.100.1.9
  Advertised IPv4 Labeled-unicast paths to update-groups (with more than one peer):
    0.8
  Path #1: Received by speaker 0
  Flags: 0x4000000009060205, import: 0x20
  Advertised IPv4 Unicast paths to peers (in unique update groups):
    10.100.1.8      10.100.1.9
  Advertised IPv4 Labeled-unicast paths to update-groups (with more than one peer):
    0.8
  65001, (Received from a RR-client)
    10.100.1.9 (metric 2) from 10.100.1.9 (10.100.1.9)
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best
      Received Path ID 0, Local Path ID 1, version 29
  Path #2: Received by speaker 0
  Flags: 0x4080000008020205, import: 0x20
  Not advertised to any peer
  65001, (Received from a RR-client)
    10.100.1.9 (metric 2) from 10.100.1.9 (10.100.1.9)
      Received Label 24001
      Origin IGP, metric 0, localpref 100, valid, internal, labeled-unicast
      Received Path ID 0, Local Path ID 0, version 0

啟用本地標籤分配

您必須配置命令「allocate-label」，以便在BGP中接收的或源路徑具有本地MPLS標籤。如果沒有此命令，路由將沒有本地標籤。

RP/0/0/CPU0:R4#conf t
RP/0/0/CPU0:R4(config)#router bgp 65003
RP/0/0/CPU0:R4(config-bgp)# address-family ipv4 unicast
RP/0/0/CPU0:R4(config-bgp-af)#allocate-label ?
  all           Allocate labels for all prefixes
  route-policy  Use a route policy to select prefixes for label allocation

標籤分配針對所有路由或根據配置的路由策略。

IOS-XR上的新實現

在IOS-XR上的舊實現中，當在同一BGP會話上配置U和LU時會出現警告。IOS-XR 5.3.0和5.2.2版引入了警告。IOS-XR 6.2.1版刪除了警告，因為同一BGP會話支援標籤和未標籤。

範例：

RP/0/0/CPU0:ios#conf t
RP/0/0/CPU0:ios(config)#router bgp 65001
RP/0/0/CPU0:ios(config-bgp)#add ipv4 unicast
RP/0/0/CPU0:ios(config-bgp-af)#exit
RP/0/0/CPU0:ios(config-bgp)#neighbor 10.0.0.1
RP/0/0/CPU0:ios(config-bgp-nbr)#remote-as 65001
RP/0/0/CPU0:ios(config-bgp-nbr)#exit
RP/0/0/CPU0:ios(config-bgp)#neighbor 10.0.0.1
RP/0/0/CPU0:ios(config-bgp-nbr)#address-family ipv4 unicast
RP/0/0/CPU0:ios(config-bgp-nbr-af)#exit
RP/0/0/CPU0:ios(config-bgp-nbr)#address-family ipv4 labeled-unicast
RP/0/0/CPU0:ios(config-bgp-nbr-af)#commit

RP/0/0/CPU0:Aug 21 14:14:22.222 : bgp[1052]: %ROUTING-BGP-4-INCOMPATIBLE_AFI : IPv4 Unicast and IPv4 Labeled-unicast Address families together are not supported under the same neighbor. 

此錯誤消息的解釋：

此訊息表示使用者已將IPv4單點傳播和IPv4標籤的單點傳播或IPv6單點傳播和IPv6標籤的單點傳播位址系列設定在同一鄰居之下。不支援此特定配置。 

建議的操作：配置到路由器的兩個鄰居會話。在第一個鄰居會話下配置單播地址系列，並在第二個鄰居會話下配置標籤單播地址系列。

一對IOS-XR路由器之間的兩個BGP會話的配置示例。為每個BGP會話使用不同的（環回）地址。

hostname R1

interface Loopback0
 ipv4 address 10.100.1.1 255.255.255.255
!
interface Loopback1
 ipv4 address 10.100.1.101 255.255.255.255
!
router bgp 65001
 address-family ipv4 unicast
 !
 neighbor 10.100.1.2
  remote-as 65001
 update-source Loopback0
  address-family ipv4 unicast
  !
 !
 neighbor 10.100.1.102
  remote-as 65001
  update-source Loopback1
  address-family ipv4 labeled-unicast
  !
 ! 
   
hostname R2

interface Loopback0
 ipv4 address 10.100.1.2 255.255.255.255
!
interface Loopback1
 ipv4 address 10.100.1.102 255.255.255.255
!
router bgp 65001
 address-family ipv4 unicast
 !
neighbor 10.100.1.1
  remote-as 65001
 update-source Loopback0
  address-family ipv4 unicast
  !
 !
 neighbor 10.100.1.101
  remote-as 65001
  update-source Loopback1
  address-family ipv4 labeled-unicast
  !
 !

在IOS-XR 6.2.1中，在預設VRF上的同一BGP作業階段上支援U和LU!

BGP作業階段是內部還是外部BGP都無關緊要。

任何非預設VRF中的BGP揚聲器都不支援同一會話上的U和LU。

Update-groups

在IOS-XR 6.2.1之前，所有U、LU和U + LU BGP揚聲器都儲存在不同的更新組中。在IOS-XR 6.2.1版之後，情況不再如此。一個更新組中的某些BGP揚聲器只能是U或LU，或者同時是U和LU。

路由傳播

下表顯示了不同方案的通告和撤銷行為。有16種情況。

除非註釋列中另有說明，否則所有選項均適用於IOS-XR 6.2.1版及更高版本。

案例	Bestpath/Addpath型別	本地標籤存在？	NHS或NHU	Update-group SAFI	廣告還是撤退？	意見
1	未標籤的路徑，即無rx標籤	是	NHS	SAFI-1	預設通告 退出方式 advertise local-labeled-route(safi-unicast)disable命令	只能在6.5.1之後進行。
2				SAFI-4	廣告	只能在6.5.1之後進行。 IPv4/v6重新分發路由和6PE:implicit NHS always
3			NHU	SAFI-1	廣告	只能在6.5.1之後進行。
4				SAFI-4	撤消	只能在6.5.1之後進行。 IPv4/v6重新分發路由和6PE:NHU被忽略；implicit NHS always
5		否	NHS	SAFI-1	廣告
6				SAFI-4	撤消
7			NHU	SAFI-1	廣告
8				SAFI-4	撤消
9	標籤路徑，即帶rx標籤	是	NHS	SAFI-1	預設通告 使用advertise local-labeled-route(safi-unicast)disable命令撤消	6.2.1之前：預設行為是Advertise。
10				SAFI-4	廣告
11			NHU	SAFI-1	撤消	6.2.1之前： 行為就是廣告。
12				SAFI-4	廣告
13		否	NHS	SAFI-1	廣告
14				SAFI-4	撤消
15			NHU	SAFI-1	撤消	6.2.1之前： 行為就是廣告。
16				SAFI-4	廣告

表1 iBGP和eBGP會話的通告行為

NHS =下一跳自己

NHU =下一跳不變。

如果NHU有效，則表示沒有為iBGP會話配置下一跳自身。

請注意，當BGP發言人傳送到eBGP對等體時，NHS總是如此。

對於iBGP揚聲器，可以有NHS或NHU，具體取決於下一跳自身的配置。iBGP對等點的預設行為是NHU。

對於第二列：請注意，僅當最佳路徑或標籤有add-path的路徑之一未標籤或標籤時，才會認為路徑未標籤或標籤。

對於路由傳播，最佳路徑具有哪些特徵非常重要。根據特徵（列2到4），它確定路徑通告為U還是LU，還是同時通告為U。

如果啟用了附加路徑(ADD-PATH)功能，並且路徑標籤為「add-path」，則該路徑的特徵也會對如何通告該路徑產生影響。

"本地標籤存在？:否」表示以下內容：可能收到帶有所接收更新的標籤，但是未安裝該標籤。如果命令「allocate-label」不存在，則不安裝本地標籤。

您可以通過詳細檢視字首來驗證本地標籤是否存在。使用「show bgp <prefix> detail」或「show route <prefix> detail」。

在以下示例中，接收字首時沒有標籤（因此通過SAFI 1對等），並且未分配本地標籤：

RP/0/0/CPU0:R2#show bgp ipv4 labeled-unicast 10.100.1.5/32 detail
BGP routing table entry for 10.100.1.5/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  3           3
    Flags: 0x04001001+0x00000000;
Last Modified: Sep  5 03:44:45.647 for 01:01:27
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.3
  Path #1: Received by speaker 0
  Flags: 0x4000000001040207, import: 0x00
  Advertised to update-groups (with more than one peer):
    0.3
  Local, (Received from a RR-client)
    10.100.1.1 (metric 2) from 10.100.1.1 (10.100.1.1)
      Origin incomplete, metric 0, localpref 100, valid, internal, best, group-best
      Received Path ID 0, Local Path ID 1, version 3

RP/0/0/CPU0:R2#show route 10.100.1.5/32 detail

Routing entry for 10.100.1.5/32
  Known via "bgp 65001", distance 200, metric 0, type internal
  Installed Sep  5 03:44:45.480 for 01:01:37
  Routing Descriptor Blocks
    10.100.1.1, from 10.100.1.1
      Route metric is 0
      Label: None
      Tunnel ID: None
      Extended communities count: 0
      NHID:0x0(Ref:0)
  Route version is 0x23 (35)
  No local label
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Flow-tag: Not Set
  Route Priority: RIB_PRIORITY_RECURSIVE (12) SVD Type RIB_SVD_TYPE_LOCAL
  Download Priority 4, Download Version 52
  No advertising protos.

分配本地標籤

為未標籤的路徑分配標籤

預設情況下，即使設定了「allocate-label」指令，也不會對未標籤的路徑(SAFI 1)進行標籤。

自IOS-XR 6.5.1版起，"allocate-label"命令的關鍵字"unlabeled-path"便可為未標籤的路徑分配標籤。

RP/0/0/CPU0:R4#conf t
RP/0/0/CPU0:R4(config)#router bgp 65003
RP/0/0/CPU0:R4(config-bgp)# address-family ipv4 unicast
RP/0/0/CPU0:R4(config-bgp-af)#allocate-label all ?
  unlabeled-path  Allocate label for unlabeled paths too
  <cr>
RP/0/0/CPU0:R4(config-bgp-af)#allocate-label all unlabeled-path ?
  <cr>
RP/0/0/CPU0:R4(config-bgp-af)#allocate-label all unlabeled-path
RP/0/0/CPU0:R4(config-bgp-af)#commit

該路徑是SAFI 1路徑，因此沒有收到任何標籤。

由於「unlabeled-path」命令，現在有一個本地標籤。

RP/0/0/CPU0:R4#show bgp ipv4 labeled-unicast 10.100.1.1/32 detail
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 16          16
    Local Label: 24003 (no rewrite);
    Flags: 0x01303028+0x00000000;
Last Modified: Aug 27 19:08:47.502 for 00:00:59
Paths: (1 available, best #1)
  Advertised IPv4 Unicast paths to update-groups (with more than one peer):
    0.3
  Advertised IPv4 Labeled-unicast paths to update-groups (with more than one peer):
    0.7
  Advertised IPv4 Labeled-unicast paths to peers (in unique update groups):
    10.1.45.5
  Path #1: Received by speaker 0
  Flags: 0x4000000009040207, import: 0x20
  Advertised IPv4 Unicast paths to update-groups (with more than one peer):
    0.3
  Advertised IPv4 Labeled-unicast paths to update-groups (with more than one peer):
    0.7
  Advertised IPv4 Labeled-unicast paths to peers (in unique update groups):
    10.1.45.5
  65001, (Received from a RR-client)
    10.100.1.10 (metric 2) from 10.100.1.10 (10.100.1.10)
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best
      Received Path ID 0, Local Path ID 1, version 16

RP/0/0/CPU0:R4#show route 10.100.1.1/32 detail

Routing entry for 10.100.1.1/32
  Known via "bgp 65003", distance 200, metric 0
  …
  Route version is 0x4 (4)
  Local Label: 0x5dc3 (24003)
  IP Precedence: Not Set
  …

這將允許表1中的案例1至4。

要瞭解刪除「allocate-label」命令時為什麼仍分配本地標籤，請運行debug "debug bgp label"。

以下是範例：

RP/0/0/CPU0:R4#debug bgp label

RP/0/0/CPU0:R4#show debug

####  debug flags set from tty 'con0_0_CPU0'  ####
ip-bgp default label flag is ON with value '##########'

最好為特定字首或字首組啟用此調試。以下是範例：

RP/0/0/CPU0:R4#sh running-config route-policy match-prefix
route-policy match-prefix
  if destination in (10.100.1.1/32) then
    pass
  else
    drop
  endif
end-policy
!

RP/0/0/CPU0:R4#debug bgp label route-policy match-prefix 

RP/0/0/CPU0:R4#show debug

####  debug flags set from tty 'con0_0_CPU0'  ####

ip-bgp default label flag is ON with value '######match-prefix####'

RP/0/0/CPU0:R4#con t
RP/0/0/CPU0:R4(config)#router bgp 65003
RP/0/0/CPU0:R4(config-bgp)# address-family ipv4 unicast
RP/0/0/CPU0:R4(config-bgp-af)#no   allocate-label all
RP/0/0/CPU0:R4(config-bgp-af)#commit

RP/0/0/CPU0:Aug 23 12:43:02.786 : bgp[1048]: [default-lbl] (ip4u): Label computation done: table=TBL:default (1/1), net=10.100.1.1/32: netfl=0x05043001, path=0x1073ed5c(10.1.24.2/32,10.1.24.2,0,0x400000000d060001), pathrcvdlabel=24002: asbr=1, rr=0/1, nhselfcount=1: result="label required"

您可以看到此路由器已收到字首10.100.1.1/32的標籤，是ASBR，不是RR，並且具有至少一個BGP會話的下一跳自身。這會導致該字首需要本地標籤。

本地標籤保持不變：

RP/0/0/CPU0:R4#show bgp ipv4 unicast 10.100.1.1/32 detail
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 13          13
    Local Label: 16002 (no rewrite);
    Flags: 0x05043001+0x00000200;
Last Modified: Aug 23 12:37:11.133 for 00:05:53
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.6
  Advertised to peers (in unique update groups):
    10.1.46.6       10.100.1.8      10.100.1.7
  Path #1: Received by speaker 0
  Flags: 0x400000000d060001, import: 0x1f
  Advertised to update-groups (with more than one peer):
    0.6
  Advertised to peers (in unique update groups):
    10.1.46.6       10.100.1.8      10.100.1.7
  65002 65001
    10.1.24.2 from 10.1.24.2 (10.100.1.2)
      Received Label 24002
      Origin IGP, localpref 100, valid, external, best, group-best, import-candidate
      Received Path ID 0, Local Path ID 1, version 13
      Origin-AS validity: not-found


RP/0/0/CPU0:R4#show route 10.100.1.1/32 detail 
Routing entry for 10.100.1.1/32
  Known via "bgp 65003", distance 20, metric 0, [ei]-bgp, labeled unicast (3107)
  Tag 65002, type external
  Installed Aug 23 12:37:11.440 for 00:06:02
  Routing Descriptor Blocks
    10.1.24.2, from 10.1.24.2, BGP external
      Route metric is 0
      Label: 0x5dc2 (24002)
      Tunnel ID: None
      Extended communities count: 0
      NHID:0x0(Ref:0)
  Route version is 0x4 (4)
  Local Label: 0x3e82 (16002)
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Route Priority: RIB_PRIORITY_NON_RECURSIVE_LOW (11) SVD Type RIB_SVD_TYPE_LOCAL
 Download Priority 4, Download Version 28
  No advertising protos.

當不需要本地標籤時，調試將顯示以下消息：

RP/0/0/CPU0:Aug 23 13:01:15.801 : bgp[1048]: [default-lbl]: Prefix 10.100.1.1/32:()doesn't require label, releasing

RP/0/0/CPU0:Aug 23 13:01:15.801 : bgp[1048]: [default-lbl]: bgp_label_release_label: perform label release onnet 10.100.1.1/32net retain 0 label_retain 0

如果字首位於LFIB中，則取決於是否收到帶有標籤的字首，以及allocate-label是否應用於該字首。

接收的標籤用24002以下字首進行標籤。  它未安裝在LFIB中，因為BGP沒有allocate-label命令。

RP/0/0/CPU0:R4#show bgp ipv4 unicast  10.100.1.1/32
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  4           4
    Local Label: 24002
Last Modified: Aug  8 13:52:57.276 for 00:00:36
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.6
  Advertised to peers (in unique update groups):
    10.100.1.7
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.6
  Advertised to peers (in unique update groups):
    10.100.1.7
  65002 65001
    10.1.24.2 from 10.1.24.2 (10.100.1.2)
      Received Label 24002
      Origin IGP, localpref 100, valid, external, best, group-best, labeled-unicast
      Received Path ID 0, Local Path ID 0, version 4
      Origin-AS validity: not-found

router bgp 65003
 bgp unsafe-ebgp-policy
 address-family ipv4 unicast
 !

RP/0/0/CPU0:R4# show mpls forwarding
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes
Label  Label       or ID              Interface                    Switched
------ ----------- ------------------ ------------ --------------- ------------
24000  Aggregate   10.1.24.0/24       default                      0
24001  Aggregate   10.1.45.0/24       default                      0

如果存在allocate-label命令，則本地標籤存在於LFIB中：

router bgp 65003
 bgp unsafe-ebgp-policy
 address-family ipv4 unicast
  allocate-label all
 !

RP/0/0/CPU0:R4#show mpls forwarding
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes
Label  Label       or ID              Interface                    Switched
------ ----------- ------------------ ------------ --------------- ------------
24000  Aggregate   10.1.24.0/24       default                      0
24001  Aggregate   10.1.45.0/24       default                      0
24002  24002       10.100.1.1/32                   10.1.24.2       0

即使BGP字首是通過LU會話接收的，但未分配本地標籤，如果完成NHS，則不會通過其他LU會話通告路由。這是表1中的案例14。如果傳出BGP會話是eBGP，則會發生這種情況。

範例：

RP/0/0/CPU0:R2#show bgp ipv4 unicast 10.100.1.1/32 detail
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  3           3
    Flags: 0x00001001+0x00000000;
Last Modified: Aug 22 09:00:20.646 for 00:10:56
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0x4080000001060001, import: 0x20
  Not advertised to any peer
  65001
    10.1.12.1 from 10.1.12.1 (10.100.1.1)
      Received Label 3
      Origin IGP, metric 0, localpref 100, valid, external, best, group-best, labeled-unicast
      Received Path ID 0, Local Path ID 0, version 3
      Origin-AS validity: not-found

RP/0/0/CPU0:R2#show route 10.100.1.1/32 detail

Routing entry for 10.100.1.1/32
  Known via "bgp 65002", distance 20, metric 0, labeled unicast (3107)
  Tag 65001, type external
  Installed Aug 22 09:00:20.416 for 00:10:59
  Routing Descriptor Blocks
    10.1.12.1, from 10.1.12.1, BGP external
      Route metric is 0
      Label: 0x100004 (1048580)
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      NHID:0x0(Ref:0)
  Route version is 0x1 (1)
  No local label
  IP Precedence: Not Set
  …

這可能是因為路由器BGP下沒有地址系列單播的命令「allocate-label」。

刪除「allocate-label」命令時，您需要重新啟動進程BGP，以便路由器刪除BGP路由的本地標籤。

表1中的新advertise local-labeled-route命令是一個新命令，它指示帶有本地標籤的路由不應通過SAFI-1通告為未標籤的路由。

此命令如下：

   通告local-labeled-route [disable]

此命令在neighbor address-family下配置。此命令的作用是指示是否應該通過IPv4/v6單播(SAFI 1)將具有本地標籤的IPv4/v6路由通告給BGP鄰居。

預設行為是使用本地標籤通告路由。

新命令還可配置為：

   通告local-labeled-route safi-unicast [disable]

此命令在BGP部分的af-group下配置。其功能與上述功能相同，適用於所有BGP鄰居。

預設行為是使用本地標籤通告路由。

地址系列IPv4 Unicast下的命令「show bgp neighbor」上存在行「Advertise routes with local-label via Unicast SAFI」或「Do not advertise routes with local-label via Unicast SAFI」，指示BGP揚聲器允許通告帶有或不帶有本地標籤的路由。

預設行為示例：

RP/0/0/CPU0:R4#show bgp neighbor 10.1.45.5
…
For Address Family: IPv4 Unicast
  BGP neighbor version 5
  Update group: 0.1 Filter-group: 0.5  No Refresh request being processed
    Extended Nexthop Encoding: advertised and received
  Route refresh request: received 0, sent 0
  0 accepted prefixes, 0 are bestpaths
  Exact no. of prefixes denied : 0.
  Cumulative no. of prefixes denied: 0.
  Prefix advertised 2, suppressed 0, withdrawn 0
  Maximum prefixes allowed 1048576
  Threshold for warning message 75%, restart interval 0 min
  An EoR was not received during read-only mode
  Last ack version 5, Last synced ack version 0
  Outstanding version objects: current 0, max 1, refresh 0
  Additional-paths operation: None
  Advertise routes with local-label via Unicast SAFI
…

或

RP/0/0/CPU0:R4# conf t
RP/0/0/CPU0:R4(config)#router bgp 65003
RP/0/0/CPU0:R4(config-bgp)# neighbor 10.1.45.5
RP/0/0/CPU0:R4(config-bgp-nbr)#  address-family ipv4 unicast
RP/0/0/CPU0:R4(config-bgp-nbr-af)#advertise local-labeled-route disable
RP/0/0/CPU0:R4(config-bgp-nbr-af)#commit


RP/0/0/CPU0:R4#show bgp neighbor 10.1.45.5

BGP neighbor is 10.1.45.5
…
For Address Family: IPv4 Unicast
  BGP neighbor version 5
  Update group: 0.1 Filter-group: 0.5 (Update-group Change
pending)
  No Refresh request being processed
    Extended Nexthop Encoding: advertised and received
  Route refresh request: received 0, sent 0
  0 accepted prefixes, 0 are bestpaths
  Exact no. of prefixes denied : 0.
  Cumulative no. of prefixes denied: 0.
  Prefix advertised 2, suppressed 0, withdrawn 0
  Maximum prefixes allowed 1048576
  Threshold for warning message 75%, restart interval 0 min
  An EoR was not received during read-only mode
  Last ack version 5, Last synced ack version 0
  Outstanding version objects: current 0, max 1, refresh 0
  Additional-paths operation: None
  Do not advertise routes with local-label via Unicast SAFI

最佳路徑計算

最佳路徑計算流程沒有變化。如果路徑是SAFI 1或SAFI 4，或者路徑是否有標籤，則最佳路徑計算流程不會有任何不同。因此，SAFI 1或SAFI 4路徑之間沒有優先順序。無論同一BGP作業階段或不同作業階段上是否存在SAFI 1/SAFI 4，都會發生這種情況。因此，如果一個BGP作業階段是SAFI 1和4，且兩個位址系列上都收到首碼，則最佳路徑計算會選取一個作為最佳路徑，因為所有屬性都相同。如果U路徑和LU路徑之間的所有BGP屬性相同，則最後接收的路徑將成為最佳路徑。

如果從不同的BGP對等點收到SAFI 1和SAFI 4路徑，則通向BGP的路徑總是會有所不同，從兩個路徑中選取相同的最佳路徑。即使在這種情況下，所有屬性都相同，鄰居地址也會不同。檢視BGP最佳路徑選取演演算法，會選取來自具有最低鄰居位址的鄰居的路徑（最後步驟13）作為最佳路徑。

使用命令「show bgp <AFI> <SAFI> <prefix> bestpath-compare」驗證最佳路徑最佳的原因。

此首選項可由使用者使用RPL建立。

下面是這樣的RPL示例。

RP/0/0/CPU0:R7#show bgp ipv4 un 10.100.1.1/32 detail
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                682         682
    Flags: 0x00003001+0x00010000;
Last Modified: Aug 28 13:16:26.826 for 00:00:10
Paths: (2 available, best #2)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0x4000000000020005, import: 0x20
  Not advertised to any peer
  65001
    10.100.1.4 (metric 2) from 10.100.1.4 (10.100.1.10)
      Origin IGP, metric 0, localpref 100, valid, internal
      Received Path ID 1, Local Path ID 0, version 0
      Originator: 10.100.1.10, Cluster list: 10.100.1.4
  Path #2: Received by speaker 0
  Flags: 0x4080000001060005, import: 0x20
  Not advertised to any peer
  65001
    10.100.1.4 (metric 2) from 10.100.1.4 (10.100.1.10)
      Received Label 24003
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, labeled-unicast
      Received Path ID 1, Local Path ID 0, version 682
      Originator: 10.100.1.10, Cluster list: 10.100.1.4

LU路徑是最佳路徑。

帶權重的RPL用於優先使用U路徑。

route-policy weight
  if destination in (10.100.1.1/32) then
    set weight 60000
  endif
end-policy

router bgp 65003
 address-family ipv4 unicast
  additional-paths receive
  additional-paths send
 !
 neighbor 10.100.1.4
  remote-as 65003
  update-source Loopback0
  address-family ipv4 unicast
   route-policy weight in
  !
  address-family ipv4 labeled-unicast
  !
 !

RP/0/0/CPU0:R7#show bgp ipv4 un 10.100.1.1/32 bestpath-compare
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                726         726
Last Modified: Aug 28 13:39:27.826 for 00:04:54
Paths: (2 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65001
    10.100.1.4 (metric 2) from 10.100.1.4 (10.100.1.10)
      Origin IGP, metric 0, localpref 100, weight 60000, valid, internal, best, group-best
      Received Path ID 1, Local Path ID 0, version 726
      Originator: 10.100.1.10, Cluster list: 10.100.1.4
      best of AS 65001, Overall best
  Path #2: Received by speaker 0
  Not advertised to any peer
  65001
    10.100.1.4 (metric 2) from 10.100.1.4 (10.100.1.10)
      Received Label 24003
      Origin IGP, metric 0, localpref 100, valid, internal, labeled-unicast
      Received Path ID 1, Local Path ID 0, version 0
      Originator: 10.100.1.10, Cluster list: 10.100.1.4
      Lower weight than best path (path #1)

現在U路徑是最好的。

沒有新命令可優先使用標籤路徑而非未標籤路徑。您只需在BGP鄰居的address-family unicast或labeled-unicast下配置RPL。

檢驗BGP中的行為

要在IOS-XR中調試BGP更新傳播，可以開啟以下debug命令：debug bgp update <BGP neighbor> in |退出。

這將顯示來自或發往該BGP發言者的傳入或傳出BGP更新。對於未標籤的IPv4非廣播(AFI 1/SAFI 1)，位址系列顯示為(ip4u)，對於標籤的IPv4單點傳播(AFI 1/SAFI 4)，顯示為(ipv4lu)。 對於IPv6，會出現相同的情況。

有一個新欄位「labeled-unicast」，表示路徑是透過SAFI 4得知的。

範例：

RP/0/0/CPU0:R1#show bgp ipv4 unicast 10.100.1.7/32
BGP routing table entry for 10.100.1.7/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 26          26
Last Modified: Sep  4 10:45:44.551 for 00:29:11
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  Local
    10.100.1.4 (metric 3) from 10.100.1.102 (10.100.1.4)
      Received Label 24000
      Origin incomplete, metric 0, localpref 100, valid, internal, best, group-best, labeled-unicast
      Received Path ID 0, Local Path ID 1, version 26
      Originator: 10.100.1.4, Cluster list: 10.100.1.2

若要驗證是否已通告字首，可以在結尾使用關鍵字「advertised-routes」的「show bgp ... neighbors」命令。

範例：

R4兩次向鄰居10.100.1.7通告10.100.1.1/32，因為已啟用新增路徑（兩個路徑不同）。

RP/0/0/CPU0:R4#show bgp ipv4 labeled-unicast neighbors 10.100.1.7 advertised-routes
Network            Next Hop        From            AS Path
10.1.24.0/24       10.100.1.4      Local           ?
10.1.34.0/24       10.100.1.4      Local           ?
10.1.45.0/24       10.100.1.4      Local           ?
10.1.46.0/24       10.100.1.4      Local           ?
10.1.47.0/24       10.100.1.4      Local           ?
10.1.48.0/24       10.100.1.4      Local           ?
10.1.49.0/24       10.100.1.4      Local           ?
10.1.104.0/24      10.100.1.4      Local           ?
10.1.114.0/24      10.100.1.4      Local           ?
10.100.1.1/32      10.100.1.4      10.100.1.9      65001i
                                   10.100.1.10     65001i
10.100.1.4/32      10.100.1.4      Local           ?

Processed 11 prefixes, 12 paths

iBGP和下一躍點自我 — 整合MPLS

表1中的規則適用。使用統一MPLS或無縫MPLS，區域邊界路由器(ABR)充當路由反射器，但也是iBGP路由的下一跳。ABR位於標籤流量的轉發路徑中。ABR必須具有下一跳自身的顯式配置。

因應措施

• 如果一個BGP會話不支援U和LU，則解決方法是在一對路由器之間具有兩個BGP會話。每台路由器上必須使用兩個（環回）介面。

IOS-XR的配置示例。

interface Loopback0
 ipv4 address 10.100.1.7 255.255.255.255
!
interface Loopback1
 ipv4 address 10.100.1.107 255.255.255.255
!
router bgp 65003
 address-family ipv4 unicast
!
 neighbor 10.100.1.4   -> towards loopback0 on peer
  remote-as 65003
  update-source Loopback0
  address-family ipv4 unicast
  !
 !
 neighbor 10.100.1.104  -> towards loopback1 on peer
  remote-as 65003
  update-source Loopback1
  address-family ipv4 labeled-unicast
  !

U和LU路徑通過兩個不同的BGP會話傳送/接收。

RP/0/0/CPU0:R7#show bgp ipv4 unicast 10.100.1.1/32 detail
BGP routing table entry for 10.100.1.1/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                753         753
    Flags: 0x00001001+0x00010000;
Last Modified: Aug 28 14:06:40.826 for 00:22:10
Paths: (2 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0x4000000001060005, import: 0x20
  Not advertised to any peer
  65001
    10.100.1.4 (metric 2) from 10.100.1.4 (10.100.1.10)
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best
      Received Path ID 1, Local Path ID 0, version 753
      Originator: 10.100.1.10, Cluster list: 10.100.1.4
  Path #2: Received by speaker 0
  Flags: 0x4080000000020005, import: 0x20
  Not advertised to any peer
  65001
    10.100.1.104 (metric 2) from 10.100.1.104 (10.100.1.10)
      Received Label 24003
      Origin IGP, metric 0, localpref 100, valid, internal, labeled-unicast
      Received Path ID 1, Local Path ID 0, version 0
      Originator: 10.100.1.10, Cluster list: 10.100.1.4