配置基于SRv6的BGP全局IPv6

简介

本文档介绍将IPv6封装段路由(SRv6)应用于BGP IPv6单播会话时的控制平面流。

背景信息

有关详细信息，请参阅Cisco ASR 9000系列路由器IOS XR版本24.1.x、24.2.x、24.3.x、24.4.x的网段路由配置指南。

拓扑

本文档中使用的拓扑如图1所示。SRv6域由三台路由器组成，所有这些路由器都在Cisco IOS-XR上运行。SRv6底层基础设施使用带uSID SRv6的IS-IS实施。BGP IPv6单播对等在路由器R1和R3之间建立，而路由器R2不参与BGP，在此配置中作为P路由器运行。R1和R3上的Loopback 6接口代表必须在两个BGP IPv6单播对等体之间交换的IPv6前缀。

图1.通过SRv6的BGP ipv6单播的拓扑图

SRv6配置

本部分显示所有三台SRv6路由器的配置。路由器R2仅包括SRv6配置，因为它不参与BGP。

路由器 R1 配置

路由器R1是SRv6域的一部分，其定位符为fc00:bb00:1::/48。它还充当BGP IPv6单播路由器，生成本地前缀fc00:aa00:1::1/128。此外，它还通过SRv6基础设施与路由器R3建立BGP IPv6单播对等。以粗体突出显示的配置用作调试本文档中所述控制流的起点，并且是整个过程中使用的唯一触发器。

interface Loopback0
 ipv4 address 10.0.0.1 255.255.255.255
 ipv6 address fc00:bb00:1::1/128
!
interface Loopback6
 ipv6 address fc00:aa00:1::1/128
!
interface TenGigE0/0/0/8
 ipv6 enable
!
router isis 1
 is-type level-1
 net 49.0000.0000.0001.00
 address-family ipv6 unicast
  metric-style wide
  segment-routing srv6
   locator MAIN
   !
  !
 !
 interface TenGigE0/0/0/8
  point-to-point
  address-family ipv6 unicast
  !
 !
!
router bgp 1
 bgp router-id 10.0.0.1
 segment-routing srv6
  locator MAIN
 !
 address-family ipv6 unicast
  segment-routing srv6
   locator MAIN
   alloc mode per-vrf
  !
  network fc00:aa00:1::1/128
 !
 neighbor fc00:bb00:3::1
  remote-as 1
  update-source Loopback0
  address-family ipv6 unicast
   encapsulation-type srv6
  !
 !
segment-routing
 srv6
  encapsulation
   source-address fc00:bb00:1::1
  !
  locators
   locator MAIN
    micro-segment behavior unode psp-usd
    prefix fc00:bb00:1::/48
   !

路由器 R2 配置

路由器R2是SRv6域的一部分，其定位符为fc00:bb00:2::/48。它不参与BGP并在此拓扑中充当P路由器。

interface Loopback0
 ipv4 address 10.0.0.2 255.255.255.255
 ipv6 address fc00:bb00:2::1/128
!
interface TenGigE0/0/0/0
 description TO R1
 ipv6 enable
!
interface TenGigE0/0/0/1
 description TO R2
 ipv6 enable
!
router isis 1
 is-type level-1
 net 49.0000.0000.0002.00
 address-family ipv6 unicast
  metric-style wide
  segment-routing srv6
   locator MAIN
   !
  !
 !
 interface TenGigE0/0/0/0
  point-to-point
  address-family ipv6 unicast
  !
 !
 interface TenGigE0/0/0/1
  point-to-point
  address-family ipv6 unicast
  !
 !
!
segment-routing
 srv6
  encapsulation
   source-address fc00:bb00:2::1
  !
  locators
   locator MAIN
    micro-segment behavior unode psp-usd
    prefix fc00:bb00:2::/48
   !

路由器 R3 配置

路由器R3是SRv6域的一部分，其定位符为fc00:bb00:3::/48。它与路由器R1具有BGP IPv6单播对等，并且两者都交换其Loopback 6接口的IPv6前缀。

interface Loopback0
 ipv4 address 10.0.0.3 255.255.255.255
 ipv6 address fc00:bb00:3::1/128
!
interface Loopback6
 ipv6 address fc00:aa00:3::3/128
!
interface TenGigE0/0/0/1
 description TO R2
 ipv6 enable
!
router isis 1
 is-type level-1
 net 49.0000.0000.0003.00
 address-family ipv6 unicast
  metric-style wide
  segment-routing srv6
   locator MAIN
   !
  !
 !
 interface TenGigE0/0/0/1
  point-to-point
  address-family ipv6 unicast
  !
 !
!
router bgp 1
 bgp router-id 10.0.0.3
 segment-routing srv6
  locator MAIN
 !        
 address-family ipv6 unicast
  segment-routing srv6
   locator MAIN
   alloc mode per-vrf
  !
  network fc00:aa00:3::3/128
 !
 neighbor fc00:bb00:1::1
  remote-as 1
  update-source Loopback0
  address-family ipv6 unicast
   encapsulation-type srv6
  !
 !
segment-routing
 srv6
  encapsulation
   source-address fc00:bb00:3::1
  !
  locators
   locator MAIN
    micro-segment behavior unode psp-usd
    prefix fc00:bb00:3::/48
   !
  !
 !        
!

SRv6 SID的信令流

在底层SRv6基础设施中，每台路由器在整个拓扑中都包含链路状态信息，每台路由器都通过链路状态ISIS协议通告其SRv6定位器。R1上的ISIS数据库显示参与SRv6域的所有路由器的定位器。

RP/0/RSP0/CPU0:R1#show isis database verbose R1 | include SRv6 Locator
  SRv6 Locator:   MT (IPv6 Unicast) fc00:bb00:1::/48 D:0 Metric: 1 Algorithm: 0

RP/0/RSP0/CPU0:R1#show isis database verbose R2 | include SRv6 Locator
  SRv6 Locator:   MT (IPv6 Unicast) fc00:bb00:2::/48 D:0 Metric: 0 Algorithm: 0

RP/0/RSP0/CPU0:R1#show isis database verbose R3 | include SRv6 Locator
  SRv6 Locator:   MT (IPv6 Unicast) fc00:bb00:3::/48 D:0 Metric: 1 Algorithm: 0

此SRv6实施支持全局路由表(GRT)流量重叠。当R1和R3上都启用了全局BGP IPv6单播重叠服务时，每台路由器都会生成新的服务SID。此服务SID与默认VRF关联，并在此场景中使用Endpoint behavior uDT6。必须在BGP IPv6单播对等体之间交换此服务SID，才能在两个BGP对等体之间启用SRv6转发。下一部分将概述BGP信令流的步骤，从触发执行(启用encapsulation-type srv6)开始，直至在路由器R3上对SRv6转发进行编程。

1.启用SRv6封装前的状态

在BGP对等体的IPv6单播SAFI上启用SRv6封装之前，路由器R1必须具有具有已分配服务SID的BGP IPv6前缀。当R1上的IPv6单播全局SAFI下启用“segment-routing srv6”时，会出现这种情况。输出显示本地SID fc00:bb00:1:e002::分配给BGP ipv6单播下的所有前缀。

RP/0/RSP0/CPU0:R1#show bgp ipv6 unicast local-sids 

BGP router identifier 10.0.0.1, local AS number 1
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0800000   RD version: 7
BGP table nexthop route policy: 
BGP main routing table version 7
BGP NSR Initial initsync version 7 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Local Sid                                   Alloc mode   Locator
*> fc00:aa00:1::1/128 fc00:bb00:1:e002::                          per-vrf       MAIN
*>ifc00:aa00:3::3/128 NO SRv6 Sid                                 -            -

Processed 2 prefixes, 2 paths

此服务SID由R1上的sid_mgr进程本地编程，该进程将终端行为作为uDT6，该行为与默认vrf关联并由bgp拥有。这仅仅意味着，只要R1收到目的地址与服务SID fc00:bb00:1:e002::它是最后一个数据段，R1必须解封报头并将解封的数据包提交到IPv6默认vrf表的FIB查找。这是根据列出所有SRv6终端行为的RFC8986进行的。注意以下输出，其中显示sid_mgr创建服务SID fc00:bb00:1:e002::并将此信息传递给RIB，最终传递给FIB。

RP/0/RSP0/CPU0:R1#show segment-routing srv6 sid all

*** Locator: 'MAIN' *** 

SID                         Behavior          Context                           Owner               State  RW
--------------------------  ----------------  --------------------------------  ------------------  -----  --
fc00:bb00:1::               uN (PSP/USD)      'default':1                       sidmgr              InUse  Y 
fc00:bb00:1:e001::          uA (PSP/USD)      [Te0/0/0/8, Link-Local]:0         isis-1              InUse  Y 
fc00:bb00:1:e002::          uDT6              'default'                         bgp-1               InUse  Y 

RP/0/RSP0/CPU0:R1#show segment-routing srv6 sid fc00:bb00:1:e002:: internal 

*** Locator: 'MAIN' *** 

SID                         Behavior          Context                           Owner               State  RW
--------------------------  ----------------  --------------------------------  ------------------  -----  --
fc00:bb00:1:e002::          uDT6              'default'                         bgp-1               InUse  Y 
  SID Function: 0xe002
  SID context: { table-id=0xe0800000 ('default':IPv6/Unicast) }
    App data: [0000000000000000]
  Locator: 'MAIN'
  Allocation type: Dynamic
  Owner List:
     1) Name: bgp-1, Client-ID: 32, Proto-ID: 8, Node-ID: 0, Locator-ID: 5 ()
  Refcount: 1
  Flags: 0x0 ()
  Chkpt Obj ID: 0x2f60
  TI Object:
    Type: Entry
    Ptr: 0x140160285526000, Producer ID: 0
    Flags: 
      Generic:  0x0 ()
      Specific: 0x0 ()
    Modified: Fri Jun 27 16:27:05 EST 2025 (2d01h ago)
  Created: Jun 27 16:17:40.796 (2d01h ago)
  Event history:
    SIDMGR-OPCODE-EVENT-CLASS
    Total entries : 4
    +---------------------------------+----------------------+------+
    | Event                           |     Time Stamp       | S, M |
    +---------------------------------+----------------------+------+
    | object create                   | Jun 27 16:17:40.864  | 1, 0 |
    | object delete                   | Jun 27 16:27:04.320  | 1, 1 |
    | object modify                   | Jun 27 16:27:04.320  | 0, 1 |
    | object refcount decrement       | Jun 27 16:27:04.320  | 0, 1 |
    +---------------------------------+----------------------+------+
RP/0/RSP0/CPU0:R1#show route ipv6 fc00:bb00:1:e002:: detail  

Routing entry for fc00:bb00:1:e002::/64
  Known via "local-srv6 bgp-1", distance 0, metric 0, SRv6 Endpoint uDT6, SRv6 Format f3216
  Installed Jun 27 16:27:06.040 for 2d01h
  Routing Descriptor Blocks
    directly connected
      Route metric is 0
      Label: None
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      NHID: 0x0 (Ref: 0)
  Route version is 0x15 (21)
  No local label
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Flow-tag: Not Set
  Fwd-class: Not Set
  Route Priority: RIB_PRIORITY_LOCAL (3) SVD Type RIB_SVD_TYPE_LOCAL
  Download Priority 0, Download Version 3140327
  No advertising protos. 

RP/0/RSP0/CPU0:R1#show cef ipv6 fc00:bb00:1:e002::
fc00:bb00:1:e002::/64, version 3140327, SRv6 Endpoint uDT6, internal 0x1000001 0x0 (ptr 0x7bb98f54) [1], 0x400 (0x7ba7cfa0), 0x0 (0x7a90d290)
 Updated Jun 27 16:27:06.043
 Prefix Len 64, traffic index 0, precedence n/a, priority 0
  gateway array (0x78e92608) reference count 3, flags 0x0, source rib (7), 0 backups
                [4 type 3 flags 0x8401 (0x78f35598) ext 0x0 (0x0)]
  LW-LDI[type=3, refc=1, ptr=0x7ba7cfa0, sh-ldi=0x78f35598]
  gateway array update type-time 1 Jun 26 15:54:48.345
 LDI Update time Jun 26 15:54:48.349
 LW-LDI-TS Jun 27 16:17:42.533
 Accounting: Disabled
   via ::/128, 0 dependencies, weight 0, class 0 [flags 0x0]
    path-idx 0 NHID 0x0 [0x781b61e8 0x0]
    next hop ::/128

    Load distribution: 0 (refcount 4)

    Hash  OK  Interface                 Address
    0     Y   recursive                 Lookup in table

由于R1未在其BGP ipv6单播对等体下启用SRv6封装，因此R1会在BGP更新中向R3通告这些前缀，而没有SRv6 TLV，即使R1已在本地分配本地SID。

RP/0/RSP0/CPU0:R1#show bgp ipv6 unicast 

BGP router identifier 10.0.0.1, local AS number 1
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0800000   RD version: 7
BGP table nexthop route policy: 
BGP main routing table version 7
BGP NSR Initial initsync version 7 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Next Hop            Metric LocPrf Weight Path
*> fc00:aa00:1::1/128 ::                       0         32768 i
*>ifc00:aa00:3::3/128 fc00:bb00:3::1           0    100      0 i

Processed 2 prefixes, 2 paths

RP/0/RSP0/CPU0:R1#show bgp ipv6 unicast advertised neighbor fc00:bb00:3::1   

fc00:aa00:1::1/128 is advertised to fc00:bb00:3::1
  Path info:
    neighbor: Local           neighbor router id: 10.0.0.1
    valid  local  best  
Received Path ID 0, Local Path ID 1, version 4
  Attributes after inbound policy was applied:
    next hop: ::
    MET ORG AS 
    origin: IGP  metric: 0  
    aspath: 
  Attributes after outbound policy was applied:
    next hop: fc00:bb00:1::1
    MET ORG AS 
    origin: IGP  metric: 0  
    aspath: 

路由器R3从没有SID的路由器R1接收更新。R3将从R1接收的前缀安装到其RIB和FIB表中，但不带SRv6报头。

RP/0/RSP0/CPU0:R3#show bgp ipv6 unicast received-sids 

BGP router identifier 10.0.0.3, local AS number 1
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0800000   RD version: 44
BGP table nexthop route policy: 
BGP main routing table version 44
BGP NSR Initial initsync version 6 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Next Hop                            Received Sid
*>ifc00:aa00:1::1/128 fc00:bb00:1::1                      NO SRv6 Sid
*> fc00:aa00:3::3/128 ::                                  NO SRv6 Sid

Processed 2 prefixes, 2 paths

RP/0/RSP0/CPU0:R3#show route ipv6 unicast fc00:aa00:1::1/128 detail 

Routing entry for fc00:aa00:1::1/128
  Known via "bgp 1", distance 200, metric 0, type internal
  Installed Jun  8 17:34:24.126 for 00:12:38
  Routing Descriptor Blocks
    fc00:bb00:1::1, from fc00:bb00:1::1
      Route metric is 0
      Label: None
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      NHID: 0x0 (Ref: 0)
      Path Grouping ID: 1
  Route version is 0x1d (29)
  No local label
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Flow-tag: Not Set
  Fwd-class: Not Set
  Route Priority: RIB_PRIORITY_RECURSIVE (12) SVD Type RIB_SVD_TYPE_LOCAL
  Download Priority 4, Download Version 162
  No advertising protos. 

RP/0/RSP0/CPU0:R3#show cef ipv6 fc00:aa00:1::1/128

fc00:aa00:1::1/128, version 162, internal 0x5000001 0x40 (ptr 0x7941f0f4) [1], 0x0 (0x0), 0x0 (0x0)
 Updated Jun  8 17:34:24.128
 Prefix Len 128, traffic index 0, precedence n/a, priority 4
  gateway array (0x78eac518) reference count 1, flags 0x2010, source rib (7), 0 backups
                [1 type 3 flags 0x48441 (0x78f4f538) ext 0x0 (0x0)]
  LW-LDI[type=0, refc=0, ptr=0x0, sh-ldi=0x0]
  gateway array update type-time 1 Jun  8 17:34:24.129
 LDI Update time Jun  8 17:34:24.129

  Level 1 - Load distribution: 0
  [0] via fc00:bb00:1::1/128, recursive

 Accounting: Disabled
   via fc00:bb00:1::1/128, 5 dependencies, recursive [flags 0x6000]
    path-idx 0 NHID 0x0 [0x7941edb4 0x0]
    next hop fc00:bb00:1::1/128 via fc00:bb00:1::/48

    Load distribution: 0 (refcount 1)

    Hash  OK  Interface                 Address
    0     Y   TenGigE0/0/0/1            remote

2.启用封装SRv6

启用SRv6封装会导致R1向其属性类型为40的对等设备发送BGP更新消息，该消息用于分段路由以通告具有特定分段路由标识符(SID)的BGP前缀。 路由器R1向R3发送带有相关SID fc00:bb00:1:e002:：的IPv6前缀fc00:bb00:3::1（步骤1）的UPDATE。收到更新后，路由器R3更新其BGP IPv6单播表（步骤2），然后更新其RIB和FIB表（步骤3）。 图2说明了BGP信令流以及相应的步骤。

图2.启用封装srv6后的BGP信令流

在R3对等体上启用SRv6封装后，输出立即显示BGP调试日志，显示R1向R3发送BGP更新消息：

router bgp 1
 neighbor fc00:bb00:3::1
  address-family ipv6 unicast
   encapsulation-type srv6
  !
 !
!
end

RP/0/RSP0/CPU0:R1(config)#commit
bgp[1100]: [default-upd] (ip6u): Added reference to table TBL:default (2/1) refcount 9
bgp[1100]: [default-upd] (ip6u): Created update group for table TBL:default (2/1), index 0.3 neighbor fc00:bb00:3::1
bgp[1100]: [default-upd] (ip6u): Removed neighbor fc00:bb00:3::1 from update group 0.2 for IPv6 Unicast
bgp[1100]: [default-upd] (ip6u): Removing neighbor fc00:bb00:3::1 from update filter-group 0.2 in IPv6 Unicast sub-group 0.2 in updgrp 0.2
bgp[1100]: [default-upd]: Enqueue Wdw: Nbr:fc00:bb00:3::1(5) Wdw:0 Del:0 Pending:0 RefreshPending:0
bgp[1100]: [default-upd]: Deleting filter-group 0.2 in TBL:default (2/1) refcount 2
bgp[1100]: [default-upd] (ip6u): Deleted update group 0.2
bgp[1100]: [default-upd] (ip6u): Added reference to table TBL:default (2/1) refcount 10
bgp[1100]: [default-upd]: Compute RT set for vrf default neighbor fc00:bb00:3::1 from old filter-group 0.2 rtset 0in subgrp 0.2
bgp[1100]: [default-upd]: Allocating filter-group 0.3in TBL:default (2/1)
bgp[1100]: [default-upd] (ip6u): Added reference to table TBL:default (2/1) refcount 11
bgp[1100]: [default-upd] (ip6u): Adding vrf default neighbor fc00:bb00:3::1 to new filter-group 0.3 in IPv6 Unicast sub-group 0.1 rtset size 0 in updgrp 0.3
bgp[1100]: [default-upd] (ip6u): Added vrf default neighbor fc00:bb00:3::1 to update filter-group 0.3 in IPv6 Unicast sub-group 0.1
bgp[1100]: [default-upd] (ip6u): Added neighbor fc00:bb00:3::1 to update sub-group 0.1 in IPv6 Unicast update-group 0.3 bgp[1100]: [default-upd] (ip6u): Added vrf default neighbor fc00:bb00:3::1 to update group 0.3 for IPv6 Unicast bgp[1100]: [default-upd] (ip6u): Removed reference to Table TBL:default (2/1) refcount 10
bgp[1100]: [default-upd] (ip6u): Started updgrp timer for updgrp 0.3:: delay=0.010, delaytype=0
bgp[1100]: [default-upd] (ip6u): Removed reference to Table TBL:default (2/1) refcount 9
bgp[1100]: [default-upd] (ip6u): Starting updgen walk for updgrp 0.3:: targetver=27:  tblver=27, labelver=27, minfwdver=27, ackdfwdver=27, standbyver=0
bgp[1100]: [default-upd] (ip6u): Computing updates for update sub-group 0.1 (Regular)
bgp[1100]: [default-upd] (ip6u): bgp_srv6_execute_sid_alloc_mode_policy: Use default SRv6 alloc mode per-vrf as policy NOT in use/configured for net  and table TBL:default (2/1)
bgp[1100]: [default-upd]: table-attr walk for table TBL:default (2/1), resume version 0, subgrp version 0, target version 27
bgp[1100]: [default-upd] (ip6u): process UPDATE for: tbl=TBL:default (2/1), afi=5: ug=0.3, (Regular), pelem (Regular), sg=0.1, ugfl=0x00104183: bgpctxfl=0x00, tblctxfl=0x10000021, ltblctxfl=0x10000021, sendlab=0: net=fc00:aa00:1::1/128, nver=24: PELEM=0x7f4566d78f60 (lpathid=1, ver=24, fl=0x00000001): PATH=0x7f4566ee3eb8 (::/128,::,0, 0x20000000010401a3)::: allowbe=0, isbe=0, allowspurwdr=0, pelem-send=1, pelem-wdr=0, netExtflag=21000000
bgp[1100]: [default-upd] (ip6u): Ran 'internal' policy '(null)', result 'TRUE', ptr 0x7f4584005f30, use (nil)
bgp[1100]: [default-upd] (ip6u):     : tbl=TBL:default (2/1), afi=5: ug=0.3, sg=0.1, ugfl=0x00104183: net=fc00:aa00:1::1/128, PELEM=0x7f4566d78f60(lpathid=1, fl=0x00000001), PATH=0x7f4566ee3eb8(::/128,::,0, 0x20000000010401a3), reflected=0, bmsgfl=0x00000000, wdr=0::: netlab=0/0, pathlab=1048577, updlab=
bgp[1100]: [default-upd] (ip6u):     <NH&LABEL-SEL>: tbl=TBL:default (2/1), afi=5: ug=0.3, sg=0.1, ugfl=0x00104183+0x00001022: net=fc00:aa00:1::1/128, netlab=0/0, PELEM=0x7f4566d78f60(lpathid=1, fl=0x00000001), PATH=0x7f4566ee3eb8(::/128,::,0, 0x20000000010401a3), pathlab=1048577, reflected=0, bmsgfl=0x00000000::: pelemwdr=0, isnhself=1, enforcenhself=0, nhselectdone=0, nhcfgeval=1, updnh=0x00000000, nhlen=16, nhif=0x00000000, nh3rdp=0
bgp[1100]: [default-upd] (ip6u):     <nh&label-sel>::: labselectdo=1, labselectdone=0, updlab=1048577(0x00100001)
bgp[1100]: [default-upd]: Comm-lib: Assigned ID (0x1d000008) for elem-type PREFIX_SID SRV6_L3SVC 
bgp[1100]: [default-upd]: Comm-lib: Assigned ID (0x900000c) for elem-type Attribute 
bgp[1100]: [default-upd] (ip6u): Permit UPDATE to filter-group 0.3 (Regular, pelem Regular) for fc00:aa00:1::1/128 (changedfl=0x0/0x0), path 
bgp[1100]: [default-upd] (ip6u): Sending UPDATE message(0x0x7f4589fd4ba4) to sub-group 0.1 (Regular, pelem Regular) for fc00:aa00:1::1/128 (changedfl=0x0/0x0) -  creating new message with bmsgflags=0x00000000, attributes: nexthop ::, originator 0.0.0.0
bgp[1100]: [default-upd] (ip6u): origin i, path , metric 0, localpref 100, Prefix-SID attribute 0x05002200 0x01001e00 0xfc00bb00 0x0001e002 0x00000000 0x00000000 0x00003e00 0x01000620 0x10100000 0x0000
bgp[1100]: [default-upd] (ip6u): Created msg elem 0x0x7f4589e3afc8 (pointing to message 0x0x7f4589fd4ba4), for filtergroup 0.3
bgp[1100]: [default-upd] (ip6u): process UPDATE for: tbl=TBL:default (2/1), afi=5: ug=0.3, (Regular), pelem (Regular), sg=0.1, ugfl=0x00104183: bgpctxfl=0x00, tblctxfl=0x10000021, ltblctxfl=0x10000021, sendlab=0: net=fc00:aa00:3::3/128, nver=27: PELEM=0x7f4566d78d30 (lpathid=1, ver=27, fl=0x00000001): PATH=0x7f4566ee3d98 (fc00:bb00:3::1/128,fc00:bb00:3::1,0, 0x2000000001060005)::: allowbe=0, isbe=0, allowspurwdr=0, pelem-send=1, pelem-wdr=0, netExtflag=20000000
bgp[1100]: [default-upd] (ip6u): No unreachable (not advertising to sender: fc00:bb00:3::1) sent to sub-group 0.1 (Regular) with fc00:aa00:3::3/128 - already withdrawn
bgp[1100]: [default-upd] (ip6u): Generated 1 updates for update sub-group 0.1 (average size = 126 bytes, maximum size = 126 bytes)
bgp[1100]: [default-upd] (ip6u): Updates replicated to neighbor fc00:bb00:3::1
bgp[1100]: [default-iowt]: fc00:bb00:3::1 send UPDATE length (incl. header) 126
bgp[1100]: [default-iowt]: Send message dump for fc00:bb00:3::1:
bgp[1100]: [default-iowt]: ffff ffff ffff ffff ffff ffff ffff ffff 
bgp[1100]: [default-iowt]: 007e 0200 0000 6790 0e00 2600 0201 10fc 
bgp[1100]: [default-iowt]: 00bb 0000 0100 0000 0000 0000 0000 0100 
bgp[1100]: [default-iowt]: 80fc 00aa 0000 0100 0000 0000 0000 0000 
bgp[1100]: [default-iowt]: 0140 0101 0040 0200 8004 0400 0000 0040 
bgp[1100]: [default-iowt]: 0504 0000 0064 c028 2505 0022 0001 001e 
bgp[1100]: [default-iowt]: 00fc 00bb 0000 01e0 0200 0000 0000 0000 
bgp[1100]: [default-iowt]: 0000 003e 0001 0006 2010 1000 0000  
bgp[1100]: [default-iowt]: bgp_io_nbr_add_version: New ver: nbr=fc00:bb00:3::1, io_wr_txsn=58992, acksn=58866: ver=27 <58992>, osver=2
bgp[1100]: [default-iowt]: bgp_io_nbr_derive_acked_version: nbr=fc00:bb00:3::1, io_wr_txsn=58992, acksn=58866, osver=2
bgp[1100]: [default-iowt]: fc00:bb00:3::1 (afi:4) advancedpeer_acked_version to 10refresh peer acked version to 0
bgp[1100]: [default-iowt]: fc00:bb00:3::1 (afi:5) received ack for version 27
bgp[1100]: [default-iowt]: bgp_write_list_tonet: IO_SENDMSG: nbr=fc00:bb00:3::1, fd=530: total=1, send-attempt=1 (size 126), sent-successful=1: res=0  allmsg_adv_count = 1 msg 0x7f4589fd4ba4 bmsg_nbr_count  0 
bgp[1100]: [default-iowt] (ip6u): Deleting msg elem 0x0x7f4589e3afc8 (message 0x0x7f4589fd4ba4), for filtergroup 0.3
bgp[1100]: [default-iowt] (ip6u): Deleting message 0x0x7f4589fd4ba4, from subgroup 0.1
bgp[1100]: [default-iowt]: Keepalive timer started for fc00:bb00:3::1(loc 10): last 529293 this 529308
bgp[1100]: [default-iowt]: bgp write for afi 4 for neighbor fc00:bb00:3::1 (fd 530)
bgp[1100]: [default-iowt]: bgp write for afi 5 for neighbor fc00:bb00:3::1 (fd 530)
bgp[1100]: [default-iowt]: bgp_io_nbr_derive_acked_version: nbr=fc00:bb00:3::1, io_wr_txsn=58992, acksn=58866, osver=1
bgp[1100]: [default-iowt]: fc00:bb00:3::1 (afi:4) advancedpeer_acked_version to 10refresh peer acked version to 0
bgp[1100]: [default-iowt]: fc00:bb00:3::1 (afi:5) advancedpeer_acked_version to 27refresh peer acked version to 0
bgp[1100]: [default-iowt]: bgp_io_write_nbr_ver_timer_process: nbr_ver_timer handler: Walk complete: nbrcount=1, synctrigger=1

输出显示R1上的BGP跟踪条目：

default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:7799: trying to find update group for nbr fc00:bb00:3::1, afi IPv6 Unicast
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:6752: created update group for table TBL:default (2/1), index 0.3, nbr fc00:bb00:3::1, flags 0x104183
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:2039: Filter-group op (Filter-group Rm Nbr) Tbl/Nbr(Afi:IPv6 Unicast:Nbr:fc00:bb00:3::1) fgrp idx 0.2 subgrp idx 0.2 updgrp 0.2 rtset 0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:1501: Filter-group op (Delete) Tbl/Nbr(TBL:default (2/1)) fgrp idx 0.2 subgrp idx 0.2 updgrp 0.0 rtset 2
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:6798: Delete update group for table TBL:default (2/1), index 0.2
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:2181: Filter-group op (Filter-group Compute Nbr RT) Tbl/Nbr(fc00:bb00:3::1) fgrp idx 0.2 subgrp idx 0.2 updgrp 0.3 rtset 0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:1411: Filter-group op (Alloc) Tbl/Nbr(TBL:default (2/1)) fgrp idx 0.3 subgrp idx 0.1 updgrp 0.0 rtset 3
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:2725: Filter-group op (Filter-group Add Nbr new) Tbl/Nbr(Afi:IPv6 Unicast:Vrf:default:Nbr:fc00:bb00:3::1) fgrp idx 0.3 subgrp idx 0.1 updgrp 0.3 rtset 0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:2751: created filtergrp 3 for vrf default nbr fc00:bb00:3::1, afi 5, subgrp version 0, refresh 0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:4473: Created subgrp:1(0x840070a0) refr:0 for nbr fc00:bb00:3::1 (vrf default), afi 5  version 0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:6935: added vrf default nbr fc00:bb00:3::1 to update group 0.3, afi IPv6 Unicast, flags 0x104183
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:3088: TBL:default (2/1) free subgrp SG:2 subgrp:0x84007440
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:1316: Update gen Start bit operation Filtergrp delete-timer fgrp idx/size 2
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:11342: Updgen - TBL:default (2/1) UG: 0.3 SG: 0.1 msg: 1
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:11344: Updgen - pfx: [tot]  adv/wdn/sup/skp/be[2] 1/0/0/1/0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:11351: Updgen - fpx: wdn/skp[0/0] ver: 0 -> 27 res ver: 0 -> 27
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:4009: Updgen - UG: 3 FG: 3 afi:5 msg: 1 ver -> 27
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t32561 [UPD]:4011: pfx: adv/wdn/sup/skp 1/0/0/1
default-bgp/spkr-tr2-common 0/RSP0/CPU0 t32558 [COMMON]:638: vrf default nbr fc00:bb00:3::1, set peer ack version to 27, afi 5, loc 2
default-bgp/spkr-tr2-gen 0/RSP0/CPU0 t32501 [GEN]:617: vrf default nbr 2000:0:0:1::1, old state 1, new state 3, fd type 2, fd 0

解码的BGP UPDATE消息显示属性类型40和TLV类型5，其中包含服务SID fc00:bb00:1:e002::。

.

完整的解码BGP UPDATE消息如下：

Message #1 - 126 bytes

FF FF FF FF  FF FF FF FF  FF FF FF FF  FF FF FF FF  
00 7E 02 00  00 00 67 90  0E 00 26 00  02 01 10 FC  
00 BB 00 00  01 00 00 00  00 00 00 00  00 00 01 00  
80 FC 00 AA  00 00 01 00  00 00 00 00  00 00 00 00  
01 40 01 01  00 40 02 00  80 04 04 00  00 00 00 40  
05 04 00 00  00 64 C0 28  25 05 00 22  00 01 00 1E  
00 FC 00 BB  00 00 01 E0  02 00 00 00  00 00 00 00  
00 00 00 3E  00 01 00 06  20 10 10 00  00 00 



BGP Marker:	0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
BGP Length:	0x007E	- 126 bytes
BGP Type:	0x02	- UPDATE

UPDATE
UNFEASIBLE ROUTES LENGTH:	0x0000	- 0 bytes
TOTAL PATH ATTRIBUTES LENGTH:	0x0067	- 103 bytes

Attribute

ATTRIBUTE FLAG:		0x90
ATTRIBUTE FLAG binary:	10010000
	Bit 0, the Optional bit, is 1 so this is an optional attribute
	Bit 1, the Transitive bit, is 0 so this is a non-transitive attribute
	Bit 2, the Partial bit, is not set
	Bit 3, the Extended Length Bit, is 1 so the length field is 2 bytes
	The lower-order four bits of the Attribute Flag are unused and are set to 0000

ATTRIBUTE TYPE:		0x0E	- 14 
ATTRIBUTE LENGTH:	0x0026	- 38 bytes
ATTRIBUTE CONTENT:	0x00020110FC00BB000001000000000000000000010080FC00AA00000100000000000000000001

	AFI:		2 (0x0002)
	Sub AFI:	1 (0x01)
	NEXTHOP Length:	16 (0x10) bytes
	NEXTHOP:	FC00:BB00:0001:0000:0000:0000:0000:0001
	Numb of SNPAs:	0 (0x00)


	NLRI Length:	 128 bits	(0x80)
	MP_REACH_NLRI:	 FC00:AA00:0001:0000:0000:0000:0000:0001/128	(0xFC00AA00000100000000000000000001)




Attribute

ATTRIBUTE FLAG:		0x40
ATTRIBUTE FLAG binary:	01000000
	Bit 0, the Optional bit, is 0 so this is a well-known attribute
	Bit 1, the Transitive bit, is 1 so this is a transitive attribute
	Bit 2, the Partial bit, is not set
	Bit 3, the Extended Length Bit, is 0 so the length field is 1 byte
	The lower-order four bits of the Attribute Flag are unused and are set to 0000

ATTRIBUTE TYPE:		0x01	- 1 
ATTRIBUTE LENGTH:	0x01	- 1 bytes
ATTRIBUTE CONTENT:	0x00	- IGP




Attribute

ATTRIBUTE FLAG:		0x40
ATTRIBUTE FLAG binary:	01000000
	Bit 0, the Optional bit, is 0 so this is a well-known attribute
	Bit 1, the Transitive bit, is 1 so this is a transitive attribute
	Bit 2, the Partial bit, is not set
	Bit 3, the Extended Length Bit, is 0 so the length field is 1 byte
	The lower-order four bits of the Attribute Flag are unused and are set to 0000

ATTRIBUTE TYPE:		0x02	- 2 
ATTRIBUTE LENGTH:	0x00	- 0 bytes





Attribute

ATTRIBUTE FLAG:		0x80
ATTRIBUTE FLAG binary:	10000000
	Bit 0, the Optional bit, is 1 so this is an optional attribute
	Bit 1, the Transitive bit, is 0 so this is a non-transitive attribute
	Bit 2, the Partial bit, is not set
	Bit 3, the Extended Length Bit, is 0 so the length field is 1 byte
	The lower-order four bits of the Attribute Flag are unused and are set to 0000

ATTRIBUTE TYPE:		0x04	- 4 
ATTRIBUTE LENGTH:	0x04	- 4 bytes
ATTRIBUTE CONTENT:	0x00000000	- 0




Attribute

ATTRIBUTE FLAG:		0x40
ATTRIBUTE FLAG binary:	01000000
	Bit 0, the Optional bit, is 0 so this is a well-known attribute
	Bit 1, the Transitive bit, is 1 so this is a transitive attribute
	Bit 2, the Partial bit, is not set
	Bit 3, the Extended Length Bit, is 0 so the length field is 1 byte
	The lower-order four bits of the Attribute Flag are unused and are set to 0000

ATTRIBUTE TYPE:		0x05	- 5 
ATTRIBUTE LENGTH:	0x04	- 4 bytes
ATTRIBUTE CONTENT:	0x00000064	- 100




Attribute

ATTRIBUTE FLAG:		0xC0
ATTRIBUTE FLAG binary:	11000000
	Bit 0, the Optional bit, is 1 so this is an optional attribute
	Bit 1, the Transitive bit, is 1 so this is a transitive attribute
	Bit 2, the Partial bit, is not set
	Bit 3, the Extended Length Bit, is 0 so the length field is 1 byte
	The lower-order four bits of the Attribute Flag are unused and are set to 0000

ATTRIBUTE TYPE:		0x28	- 40 
ATTRIBUTE LENGTH:	0x25	- 37 bytes
ATTRIBUTE CONTENT:	0x0500220001001E00FC00BB000001E002000000000000000000003E00010006201010000000

	BGP Prefix-SID:
	Type:		 5 (0x05) - SRv6 L3 Service
	Length:		 34 - 0x0022
	Value:		 0x0001001E00FC00BB000001E002000000000000000000003E00010006201010000000
	Reserved:	 0x00
	Sub Type:	 1 (0x01)
	Sub Length:	 30 (0x001E)
	SRv6 SID = FC00:BB00:0001:E002:0000:0000:0000:0000
	SID Flags:	 0 (0x00)
	Endpoint Behavior:	 62 (0x003E)
	Reserved2 :	 0 (0x00)
	SRv6 SID Optional Type:	 1 (0x01)
	SRv6 SID Optional Len:	 6 (0x0006)
	SRv6 SID Optional Value:	 35253360001024 (0x201010000000)



NLRI
NLRI LENGTH:	UPDATE Length - 23 - TOTAL PATH ATTRIBUTES LENGTH - UNFEASIBLE ROUTES LENGTH
NLRI LENGTH:	126 - 23 - 103 - 0
NLRI LENGTH:	0 bytes

3. R3接收BGP更新并将其安装到BGP IPv6单播表中

路由器R3收到来自R1的BGP更新，可以通过在R3上启用BGP调试来观察此情况。收到的BGP更新数据包必须与R1发送的数据包匹配，如debug输出所示。

bgp[1100]: [default-rtr]: UPDATE from fc00:bb00:1::1 contains nh fc00:bb00:1::1/128, gw_afi 5, flags 0x0, nlri_afi 5
bgp[1100]: [default-rtr]: NH-Validate-Create: addr=fc00:bb00:1::1/128, len=16, nlriafi=5, nbr=fc00:bb00:1::1, gwafi=5, gwlen=32, gwaddrlen=128::: nhout=0x0x7fc41b5fdcb0, validity=1, attrwdrflags=0x00000000
bgp[1100]: [default-rtr]: --bgp4_rcv_attributes--: END: nbr=fc00:bb00:1::1:: msg=0x0x7fc420108bdc/126, updlen=107, attrbl=0x0x7fc420108bf3/103, ipv4reachlen=0, msginpath=0x0x7fc3e2d54830, asloopcheck=1, attrwdrfl=0x00000000:: samecluster=0, local_as_prepended=0, attr_wdr_flags 0x00000000, myascount=0:: myconfedascount=0::rcvdata=0x0x7fc420108c5a/0, errptr=0x0x7fc420108c32/40
bgp[1100]: [default-rtr]: Comm-lib: Assigned ID (0x1d0000ac) for elem-type PREFIX_SID SRV6_L3SVC 
bgp[1100]: [default-rtr]: Comm-lib: Assigned ID (0x90000de) for elem-type Attribute 
bgp[1100]: [default-rtr] (ip6u): Received UPDATE from fc00:bb00:1::1 with attributes: 
bgp[1100]: [default-rtr] (ip6u): nexthop fc00:bb00:1::1/128, origin i, localpref 100, metric 0
bgp[1100]: [default-rtr] (ip6u): Received prefix fc00:aa00:1::1/128 (path ID: none) from fc00:bb00:1::1
bgp[1100]: [default-rtr] (ip6u): Handling OCRIB attrs while relacing path 0x7fc3e1be61d8. Old oc attr (nil), new oc attr (nil)
bgp[1100]: [default-rtr]: bgp_bmp_table_path_update_cb: Operation: 0x1, Inbound Post-Policy Route Mon is not enabled (0) (or) not primary active - return
bgp[1100]: [default-rtr] (ip6u): Done modify path (old tlv size=0 new tlv size=0) for net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00003001+0x20000000: usedpath=0x0x7fc3e1be61d8(fc00:bb00:1::1/128,fc00:bb00:1::1,0,0x2000000000060005), rcvdpath=0x0x7fc3e2d52b20: needmove=0, pcount=1 IdenticalPath=0, TLVPresent=0
bgp[1100]: [default-rtr]: bgp_set_path_metric:8712 afi 5 net fc00:aa00:1::1/128 path 0x7fc3e1be61d8 nh fc00:bb00:1::1/128 (0x7fc41b5fdcb0) metric 21
bgp[1100]: [default-rtr] (ip6u): bestpath: (full bp 1) start for net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00003001+0x20000200: lastpath=0x0x7fc3e1be61d8(fc00:bb00:1::1/128,fc00:bb00:1::1,0,0x2000000000060005): PELEM=0x0x7fc3e1a82930(lpathid=1, ver=2000371, fl=0x00000801, path=0x0x7fc3e1be61d8)
bgp[1100]: [default-rtr] (ip6u): bestpath: (full 1) calculated for net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00003001+0x20000200, pelemver=2000371, pelemfl=0x00000881: oldbest=0x0x7fc3e1be61d8(fc00:bb00:1::1/128,fc00:bb00:1::1,0,0x2000000001060005), newbest=0x0x7fc3e1be61d8(fc00:bb00:1::1/128,fc00:bb00:1::1,0,0x2000000001060005), lastpath=0x0x7fc3e1be61d8(fc00:bb00:1::1/128,fc00:bb00:1::1,0,0x2000000001060005), bumpv=1
bgp[1100]: [default-rtr] (ip6u): bestpath: change for net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00003001+0x20000200: oldbest=0x0x7fc3e1be61d8: PELEM=0x0x7fc3e1a82930(lpathid=1, ver=2000371, fl=0x00000901, path=0x0x7fc3e1be61d8)
bgp[1100]: [default-rtr] (ip6u): bestpath: update flags for net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00003001+0x20000200: oldtblattr=0x0x7fc41b5eccc0, oldnh=0x0x7fc41b5fdcb0: PELEM=0x0x7fc3e1a82930(lpathid=1, ver=2000371, fl=0x00000901, path=0x0x7fc3e1be61d8)
bgp[1100]: [default-rtr] (ip6u): bestpath: modified path: net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00003001+0x20000200: PELEM=0x0x7fc3e1a82930(lpathid=1, ver=2000371, fl=0x00001901, path=0x0x7fc3e1be61d8)
bgp[1100]: [default-rtr] (ip6u): bgp_srv6_get_alloc_mode_locator_from_policy: Use default SRv6 alloc mode as policy NOT in use/configured for net  and table TBL:default (2/1)
bgp[1100]: [default-rtr] (ip6u): bestpath: complete for net=fc00:aa00:1::1/128, nver=2000371, nfl=0x00007001+0x20000200: pselect=0x0, bumpv=1(1:1,0,0,0)
bgp[1100]: [default-rtr]: Received UPDATE from fc00:bb00:1::1 (length incl. header = 126)
bgp[1100]: [default-rtr]: Receive message dump for fc00:bb00:1::1:
bgp[1100]: [default-rtr]: ffff ffff ffff ffff ffff ffff ffff ffff 
bgp[1100]: [default-rtr]: 007e 0200 0000 6790 0e00 2600 0201 10fc 
bgp[1100]: [default-rtr]: 00bb 0000 0100 0000 0000 0000 0000 0100 
bgp[1100]: [default-rtr]: 80fc 00aa 0000 0100 0000 0000 0000 0000 
bgp[1100]: [default-rtr]: 0140 0101 0040 0200 8004 0400 0000 0040 
bgp[1100]: [default-rtr]: 0504 0000 0064 c028 2505 0022 0001 001e 
bgp[1100]: [default-rtr]: 00fc 00bb 0000 01e0 0200 0000 0000 0000 
bgp[1100]: [default-rtr]: 0000 003e 0001 0006 2010 1000 0000  
bgp[1100]: [default-rtr]: Enabling read from: fc00:bb00:1::1 readset: 1 msgcount: 0
bgp[1100]: [default-iowt]: bgp write for afi 4 for neighbor fc00:bb00:1::1 (fd 516)
bgp[1100]: [default-iowt]: bgp write for afi 5 for neighbor fc00:bb00:1::1 (fd 516)
bgp[1100]: [default-impt] (ip6u): START import walk from 2000371 to 2000372 skip_walk 1
bgp[1100]: [default-rib2] (ip6u): RIB thread triggered for versioned walk: current version 2000371, acked version 2000371, target version 2000371
bgp[1100]: [default-rib2] (ip6u): RNH rib opaque update for (IPv6 Unicast)
bgp[1100]: [default-rib2] (ip6u): RIB thread triggered for RNH walk for nh table(IPv6 Unicast): current version 2000371, target version 2000372
bgp[1100]: [default-lbl] (ip6u): Label update triggered: current version 2000371, target version 2000372, mpls component is up  
bgp[1100]: [default-lbl]: Table: TBL:default (2/1) bgp_label_srv6_sid_config_release: label_sid_need_eval:0 loc trigger:0 srv6 enabled:1 label disabled:1 dual mode:0 label alloc mode:2 sid alloc mode:0 sid release:0
bgp[1100]: [default-lbl]: uSID WLIB allocation is (LIB Default)
bgp[1100]: [default-lbl]: Table: TBL:default (2/1) bgp_label_thread_walk_type: rd:0x7fc3e1efbf30(ALLzero:0:0) rd_flags:0x1 SRv6 eval/en/cnt:1/1/1 locator:MAIN Label up/dis/cnt: 1/1/0 dual mode:0 ibgp_nhself_count:0 policy_set_nhself:0
bgp[1100]: [default-lbl] (ip6u): rd:0x7fc3e1efbf30 sid_walk:1 label_walk:0
bgp[1100]: [default-lbl]: uSID WLIB allocation is (LIB Default)
bgp[1100]: [default-upd] (vpn4u): Started updgrp timer for updgrp 0.1:: delay=0.010, delaytype=0
bgp[1100]: [default-lbl] (ip6u): SRv6 SID process for net: TBL:default (2/1)fc00:aa00:1::1/128(SID N) extflags 20000000 Default locator Y UP/exh/oor/rclm MAIN/N/N/N mode 0 clear handle 0
bgp[1100]: [default-lbl] (ip6u): SRv6 SID process for net: TBL:default (2/1)fc00:aa00:1::1/128 point 1 sid_mode 0 clear_handle 0
bgp[1100]: [default-lbl]: uSID WLIB allocation is (LIB Default)
bgp[1100]: [default-lbl] (ip6u): Label update run from 2000371 target label version 2000372, rib version 2000371, bgp table version 2000372,best-external allocs 0
bgp[1100]: [default-lbl] (ip6u): Wake up rib thread, label version 2000372, rib version 2000371, bgp table version 2000372,
bgp[1100]: [default-rib2] (ip6u): RIB thread triggered for versioned walk: current version 2000371, acked version 2000371, target version 2000372
bgp[1100]: [default-rib2] (ip6u): RNH rib opaque update for (IPv6 Unicast)
bgp[1100]: [default-rib2] (ip6u): RIB thread triggered for RNH walk for nh table(IPv6 Unicast): current version 2000371, target version 2000372
bgp[1100]: [default-rib2] (ip6u): Rib Batch-buf Route ADD: table=TBL:default (2/1), tableid=0xe0800000, net=fc00:aa00:1::1/128, netfl=0x00003001: label=1048577, dist=200, attrkey=0x00000000, pathcount=1: batchres=1, succ=1, send=0 locator prefix No, 0
bgp[1100]: [default-rib2] (ip6u): Revise route batch: installing fc00:aa00:1::1/128 with next hop fc00:bb00:1::1(tbl-id=0xe0800000, ifh=0x0), pathribflags: 0x9800000008, #ext-comms=0, to IP-RIB table[0xe0800000]
bgp[1100]: [default-rib2] (ip6u): [0]: Rib Batch-buf Path ADD: table=TBL:default (2/1), net=fc00:aa00:1::1/128: nh=fc00:bb00:1::1, nhifh=0x00000000, nhtableid=0xe0800000: rlabel=1048577, metric=0, bsid=0, numecomms=0: pelemfl=0x00001001, pathfl=0x2000000001060005,pathribfl=0x9800000008, nhresplenmin=0 (constraint=1):: batchres=1, succ=1, sendbatch=0
bgp[1100]: [default-rib2] (ip6u): Sending convergence info for IPv6 Unicast - not converged, version: 0, last received version 0
bgp[1100]: [default-upd] (ip6u): Started updgrp timer for updgrp 0.1:: delay=0.010, delaytype=0
bgp[1100]: [default-rib2] (ip6u): vrf default: RIB update run to 2000372: installed 0, modified 1, skipped 0, removed 0 IPv6 Unicast prefixes, installed 0 attributes, removed 0 attributes.
bgp[1100]: [default-rib2] (ip6u): RIB thread finished versioned walk: table version 2000372, acked table version 2000372
bgp[1100]: [default-upd] (vpn4u): Starting updgen walk for updgrp 0.1:: targetver=463:  tblver=463, labelver=463, minfwdver=463, ackdfwdver=463, standbyver=0
bgp[1100]: [default-upd] (ip6u): Starting updgen walk for updgrp 0.1:: targetver=2000372:  tblver=2000372, labelver=2000372, minfwdver=2000372, ackdfwdver=2000372, standbyver=0
bgp[1100]: [default-upd] (ip6u): Computing updates for update sub-group 0.1 (Regular)
bgp[1100]: [default-upd] (ip6u): bgp_srv6_execute_sid_alloc_mode_policy: Use default SRv6 alloc mode per-vrf as policy NOT in use/configured for net  and table TBL:default (2/1)
bgp[1100]: [default-upd]: table-attr walk for table TBL:default (2/1), resume version 0, subgrp version 2000371, target version 2000372
bgp[1100]: [default-upd] (ip6u): process UPDATE for: tbl=TBL:default (2/1), afi=5: ug=0.1, (Regular), pelem (Regular), sg=0.1, ugfl=0x00104183: bgpctxfl=0x00, tblctxfl=0x10000021, ltblctxfl=0x10000021, sendlab=0: net=fc00:aa00:1::1/128, nver=2000372: PELEM=0x7fc3e1a82930 (lpathid=1, ver=2000372, fl=0x00001001): PATH=0x7fc3e1be61d8 (fc00:bb00:1::1/128,fc00:bb00:1::1,0, 0x2000000001060005)::: allowbe=0, isbe=0, allowspurwdr=0, pelem-send=1, pelem-wdr=0, netExtflag=20000000
bgp[1100]: [default-upd] (ip6u): No unreachable (not advertising to sender: fc00:bb00:1::1) sent to sub-group 0.1 (Regular) with fc00:aa00:1::1/128 - already withdrawn

路由器R3生成与来自R1的更新处理对应的BGP跟踪，最终导致R3更新其BGP IPv6单播表。此更新包含BGP属性类型40，涉及从R1安装收到的SID以及关联的BGP IPv6单播前缀。

RP/0/RSP0/CPU0:R3#show bgp trace
default-bgp/spkr-tr2-imp 0/RSP0/CPU0 t16100 [IMPORT]:6661: Skipping Import walk: import ver 2000371 -> 2000372: afi 5 forced 0
default-bgp/spkr-tr2-rib 0/RSP0/CPU0 t30391 [RIB]:17177: RIB walk for afi IPv6 Unicast: target version 2000371, min_fwdtable_version 2000371, import_version 2000372,  label_version 2000371, table_version 2000372
default-bgp/spkr-tr2-label 0/RSP0/CPU0 t16061 [LABEL]:8505: label walk afi:IPv6 Unicast, lbl ver 2000371 -> 2000372, be 0, skp 0  upd 0
default-bgp/spkr-tr2-label 0/RSP0/CPU0 t16061 [LABEL]:8510: label walk afi:IPv6 Unicast, lbl ver 2000371 -> 2000372, be 0, skp 0  upd 1
default-bgp/spkr-tr2-rib 0/RSP0/CPU0 t30391 [RIB]:17177: RIB walk for afi IPv6 Unicast: target version 2000372, min_fwdtable_version 2000371, import_version 2000372,  label_version 2000372, table_version 2000372
default-bgp/spkr-tr2-rib 0/RSP0/CPU0 t30391 [RIB]:14681: send converge to RIB, afi IPv6 Unicast, tableid 0xe0800000, converged 0, send_version 0, last_recv_version 0
default-bgp/spkr-tr2-rib 0/RSP0/CPU0 t30391 [RIB]:15892: RIB(default:v6u): ver 2000371 -> 2000372 :pfx inst/upd/skip/rem 0/1/0/0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t16101 [UPD]:11342: Updgen - TBL:default (2/1) UG: 0.1 SG: 0.1 msg: 0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t16101 [UPD]:11344: Updgen - pfx: [tot]  adv/wdn/sup/skp/be[1] 0/0/0/1/0
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t16101 [UPD]:11351: Updgen - fpx: wdn/skp[0/0] ver: 2000371 -> 2000372 res ver: 0 -> 2000372
default-bgp/spkr-tr2-common 0/RSP0/CPU0 t16101 [COMMON]:3628: vrf default nbr fc00:bb00:1::1, set peer ack version to 2000372, afi 5, loc 4
default-bgp/spkr-tr2-upd 0/RSP0/CPU0 t16101 [UPD]:11663: Updgen - Skip EoR for Tbl:(TBL:default (2/1)) subgrp:(1) UG:(1) end 2000372

RP/0/RSP0/CPU0:R3#show bgp ipv6 unicast received-sids 

BGP router identifier 10.0.0.3, local AS number 1
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0800000   RD version: 46
BGP table nexthop route policy: 
BGP main routing table version 46
BGP NSR Initial initsync version 6 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Next Hop                            Received Sid
*>ifc00:aa00:1::1/128 fc00:bb00:1::1                      fc00:bb00:1:e002::
*> fc00:aa00:3::3/128 ::                                  NO SRv6 Sid

Processed 2 prefixes, 2 paths

4. R3安装RIB和FIB

最终R3安装RIB和FIB以完成信令过程。然后R3充当SID列表fc00:bb00:1:e002::.的SRv6头端。此入口R1充当SR策略中封装的SRv6头端，缩写为H.Encaps（RFC 8986，第5.1节）。 此行为将数据包封装到IPv6报头中，强制实施数据段列表并在需要时添加SRH。在这种情况下，无需添加SRH，因为只有一个网段。数据包将发送目的地址fc00:bb00:1:e002::，这是R1上具有SRv6终端UDT6行为的服务SID。

RP/0/RSP0/CPU0:R3#show route ipv6 fc00:aa00:1::1/128 detail 

Routing entry for fc00:aa00:1::1/128
  Known via "bgp 1", distance 200, metric 0, type internal
  Installed Jun  8 17:52:31.546 for 00:53:55
  Routing Descriptor Blocks
    fc00:bb00:1::1, from fc00:bb00:1::1
      Route metric is 0
      Label: None
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      NHID: 0x0 (Ref: 0)
      Path Grouping ID: 1
      SRv6 Headend: H.Encaps.Red [f3216], SID-list {fc00:bb00:1:e002::}
  Route version is 0x1f (31)
  No local label
  IP Precedence: Not Set
  QoS Group ID: Not Set
  Flow-tag: Not Set
  Fwd-class: Not Set
  Route Priority: RIB_PRIORITY_RECURSIVE (12) SVD Type RIB_SVD_TYPE_LOCAL
  Download Priority 4, Download Version 166
  No advertising protos. 

RP/0/RSP0/CPU0:R3#show cef ipv6 fc00:aa00:1::1/128
fc00:aa00:1::1/128, version 166, SRv6 Headend, internal 0x5000001 0x40 (ptr 0x7941f0f4) [1], 0x0 (0x0), 0x0 (0x7ad58368)
 Updated Jun  8 17:52:31.551
 Prefix Len 128, traffic index 0, precedence n/a, priority 4
  gateway array (0x78eac428) reference count 1, flags 0x2010, source rib (7), 0 backups
                [1 type 3 flags 0x48441 (0x78f4f4d8) ext 0x0 (0x0)]
  LW-LDI[type=0, refc=0, ptr=0x0, sh-ldi=0x0]
  gateway array update type-time 1 Jun  8 17:52:31.551
 LDI Update time Jun  8 17:52:31.551

  Level 1 - Load distribution: 0
  [0] via fc00:bb00:1::/128, recursive

 Accounting: Disabled
   via fc00:bb00:1::/128, 5 dependencies, recursive [flags 0x6000]
    path-idx 0 NHID 0x0 [0x7941edb4 0x0]
    next hop fc00:bb00:1::/128 via fc00:bb00:1::/48
    SRv6 H.Encaps.Red SID-list {fc00:bb00:1:e002::}

    Load distribution: 0 (refcount 1)

    Hash  OK  Interface                 Address
    0     Y   TenGigE0/0/0/1            remote         

图4显示了路由器R3(fc00:aa00:3::3)ping R1(fc00:aa00:1::1)时的数据包格式。

图4.沿SRv6上BGP IPv6单播路径的数据包处理