为具有故障情形的多个站点之间的相同VPN配置重叠IP
简介
本文档介绍在SD-WAN重叠中的多个站点上同一VPN中存在重叠地址空间的场景。它描述了示例网络、正常/故障切换场景中的流量行为、配置和验证。
先决条件
要求
Cisco建议您具备SD-WAN知识。
使用的组件
本文档中的信息基于以下软件和硬件版本：
- SD-WAN控制器版本20.6.3
-
Cisco IOS® XE（在控制器模式下运行）17.6.3a
- 主机设备(CSR1000V)17.3.3
本文档中的信息都是基于特定实验室环境中的设备编写的。本文档中使用的所有设备最初均采用原始（默认）配置。如果您的网络处于活动状态，请确保您了解所有命令的潜在影响。
背景信息
您可以在此处找到本文中使用的缩写词列表。
- 安全互联网网关 — SIG
- 虚拟路由和转发 — VRF
- 虚拟专用网络 — VPN
- 直接互联网接入 — DIA
- 网络地址转换 — NAT
- 多协议标签交换 — MPLS
- 服务端网络地址转换 — SS-NAT
- 数据中心 — DC
- 重叠管理协议 — OMP
- Internet协议 — IP
有关服务端NAT：服务端NAT的详细信息，请参阅思科文档
网络图
在此特定拓扑中，有1个DC（DC只有MPLS传输，但在实际场景中可能有多个传输）和2个通过MPLS和互联网传输与SD-WAN重叠连接的分支机构位置。所有位置都配置了服务VPN 10。分支将SIG隧道（主隧道和备用隧道）配置到Zscaler。DIA针对特定目标IP进行配置，以绕过Zscaler。如果分支机构出现互联网链路故障，预计所有流量必须通过MPLS传输发送到DC。
eBGP在服务VPN 10上配置，在DC端使用Zscaler路由器。DC路由器从Zscaler路由器接收默认路由并重新分配到OMP。
规格
- 利用服务端VPN 10上Branch 1和Branch 2的重叠IP地址。
- 在典型场景中，当MPLS和互联网传输启动时，来自VPN 10的流量必须通过SIG隧道退出。
- 对于特定IP目标前缀，流量必须绕过SIG隧道并通过DIA退出。
- 如果Internet链路发生故障，来自VPN 10的所有/Internet绑定流量必须通过DC退出。
解决方案
为实现此要求，使用了SD-WAN功能服务端NAT和带数据策略的DIA。
- 服务端NAT在每个分支路由器上使用不同的NAT池IP地址配置。
- 如果向SD-WAN重叠发送流量时发生Internet链路故障，则会将源IP从配置的NAT池通过NAT转换到IP地址。
- DC路由器会看到重叠子网的NAT后地址。
配置
Branch-1配置
Branch-1路由器的配置如下。
vrf definition 10
rd 1:10
!
address-family ipv4
route-target export 1:10
route-target import 1:10
exit-address-family
!
interface GigabitEthernet2
description "Internet TLOC"
ip address 198.51.100.1 255.255.255.0
ip nat outside
!
interface GigabitEthernet3
description "MPLS TLOC"
ip address 172.20.1.10 255.255.255.0
!
interface GigabitEthernet4
description "Service Side VPN 10"
vrf forwarding 10
ip address 192.168.10.1 255.255.255.0
!
interface Tunnel2
ip unnumbered GigabitEthernet2
tunnel source GigabitEthernet2
tunnel mode sdwan
!
interface Tunnel3
ip unnumbered GigabitEthernet3
tunnel source GigabitEthernet3
tunnel mode sdwan
!
interface Tunnel100512
ip address 10.10.1.1 255.255.255.252
tunnel source GigabitEthernet2
tunnel destination 203.0.113.1
tunnel vrf multiplexing
!
interface Tunnel100513
ip address 10.10.1.5 255.255.255.252
tunnel source GigabitEthernet2
tunnel destination 203.0.113.2
tunnel vrf multiplexing
!
ip sdwan route vrf 10 0.0.0.0/0 tunnel active Tunnel100512 backup Tunnel100513
ip nat pool natpool1 172.16.2.1 172.16.2.2 prefix-length 30
ip nat inside source list nat-dia-vpn-hop-access-list interface GigabitEthernet2 overload
ip nat inside source list global-list pool natpool1 vrf 10 match-in-vrf overload
ip nat route vrf 10 192.0.2.1 255.255.255.255 global
!
ip route 0.0.0.0 0.0.0.0 198.51.100.100
ip route 0.0.0.0 0.0.0.0 172.20.1.100
!
Branch-2配置
Branch-2路由器的配置如下。
vrf definition 10
rd 1:10
!
address-family ipv4
route-target export 1:10
route-target import 1:10
exit-address-family
!
address-family ipv6
exit-address-family
!
interface GigabitEthernet2
description "Internet TLOC"
ip address 198.51.100.2 255.255.255.0
ip nat outside
!
!
interface GigabitEthernet3
description "MPLS TLOC"
ip address 172.20.1.20 255.255.255.0
!
interface GigabitEthernet4
description "Service Side VPN 10"
vrf forwarding 10
ip address 192.168.10.1 255.255.255.0
!
interface Tunnel2
ip unnumbered GigabitEthernet2
tunnel source GigabitEthernet2
tunnel mode sdwan
!
interface Tunnel3
ip unnumbered GigabitEthernet3
tunnel source GigabitEthernet3
tunnel mode sdwan
!
interface Tunnel100512
ip address 10.10.2.1 255.255.255.252
tunnel source GigabitEthernet2
tunnel destination 203.0.113.1
tunnel vrf multiplexing
!
interface Tunnel100513
ip address 10.10.2.5 255.255.255.252
tunnel source GigabitEthernet2
tunnel destination 203.0.113.2
tunnel vrf multiplexing
!
!
ip sdwan route vrf 10 0.0.0.0/0 tunnel active Tunnel100512 backup Tunnel100513
ip nat route vrf 10 192.0.2.1 255.255.255.255 global
ip nat pool natpool1 172.16.2.9 172.16.2.10 prefix-length 30
ip nat inside source list nat-dia-vpn-hop-access-list interface GigabitEthernet2 overload
ip nat inside source list global-list pool natpool1 vrf 10 match-in-vrf overload
!
ip route 0.0.0.0 0.0.0.0 198.51.100.100
ip route 0.0.0.0 0.0.0.0 172.20.1.100
!
DC-Router配置
DC路由器配置如下。
vrf definition 10
rd 1:10
!
address-family ipv4
route-target export 10:10
route-target import 10:10
exit-address-family
!
interface Tunnel2
ip unnumbered GigabitEthernet2
tunnel source GigabitEthernet2
tunnel mode sdwan
!
interface GigabitEthernet2
ip address 172.20.1.30 255.255.255.0
description "MPLS TLOC"
!
interface GigabitEthernet4
description "Service Side VPN 10"
vrf forwarding 10
ip address 172.31.19.19 255.255.255.252
!
router bgp 10
bgp log-neighbor-changes
distance bgp 20 200 20
!
address-family ipv4 vrf 10
redistribute omp
neighbor 172.31.19.20 remote-as 100
neighbor 172.31.19.20 activate
neighbor 172.31.19.20 send-community both
exit-address-family
!
!
ip route 0.0.0.0 0.0.0.0 172.20.1.100
!
vSmart策略
vSmart策略配置如下。
data-policy _VPN10-VPN20_1-Branch-A-B-Central-NAT-DIA
vpn-list VPN10
sequence 1
match
source-ip 192.168.10.0/24
!
action accept
nat pool 1
!
default-action accept
!
site-list BranchA-B
site-id 11
site-id 22
!
site-list DC
site-id 33
!
vpn-list VPN10
vpn 10
!
prefix-list _AnyIpv4PrefixList
ip-prefix 0.0.0.0/0 le 32
!
apply-policy
site-list BranchA-B
data-policy _VPN10_1-Branch-A-B-Central-NAT-DIA from-service
!
故障切换场景
Branch-1流量正常场景
当两个传输均如输出所示处于启用状态时，默认情况下，流量通过主SIG隧道退出 Tunnel100512. 当主隧道关闭时，流量会切换到备用隧道 Tunnel100513.
Branch-1#show ip route vrf 10
Routing Table: 10
<SNIP>
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S* 0.0.0.0/0 [2/0], Tunnel100512
192.0.2.0/32 is subnetted, 1 subnets
n Nd 192.0.2.1 [6/0], 3d02h, Null0
n Ni 172.16.2.0 [7/0], 3d04h, Null0
m 172.16.2.8 [251/0] via 172.31.31.2, 3d01h, Sdwan-system-intf
Branch-1#
Traceroute显示流量采用SIG隧道。
Host-BR-1#ping 192.0.2.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/49/101 ms
Host-BR-1#
Host-BR-1#traceroute 192.0.2.100 numeric
Type escape sequence to abort.
Tracing the route to 192.0.2.100
VRF info: (vrf in name/id, vrf out name/id)
1 192.168.10.1 38 msec 7 msec 4 msec
2 203.0.113.1 79 msec * 62 msec
Host-BR-1#
发往特定目的地的流量 192.0.2.1 通过DIA（NAT转换到WAN IP地址）退出。
Host-BR-1#ping 192.0.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/49/101 ms
Host-BR-1#
Branch-1#sh ip nat translation
Pro Inside global Inside local Outside local Outside global
icmp 198.51.100.1:1 192.168.10.10:1 192.0.2.1:1 192.0.2.1:1
Total number of translations: 1
Branch-1#
Branch-2流量正常场景
在Branch-2路由器上也观察到类似行为。
Branch-2#show ip route vrf 10
Routing Table: 10
<SNIP>
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S* 0.0.0.0/0 [2/0], Tunnel100512
192.0.2.0/32 is subnetted, 1 subnets
n Nd 192.0.2.1 [6/0], 00:00:08, Null0
m 172.16.2.0 [251/0] via 172.31.31.1, 3d01h, Sdwan-system-intf
n Ni 172.16.2.8 [7/0], 3d04h, Null0
Branch-2#
Host-BR-2#ping 192.0.2.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/49/101 ms
Host-BR-2#
Host-BR-2#traceroute 192.0.2.100 numeric
Type escape sequence to abort.
Tracing the route to 192.0.2.100
VRF info: (vrf in name/id, vrf out name/id)
1 192.168.10.1 38 msec 7 msec 4 msec
2 203.0.113.1 79 msec * 62 msec
Host-BR-2#
Host-BR-2#ping 192.0.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/49/101 ms
Host-BR-2#
Branch-2#show ip nat translation
Pro Inside global Inside local Outside local Outside global
icmp 198.51.100.2:1 192.168.10.10:1 192.0.2.1:1 192.0.2.1:1
Total number of translations: 1
Branch-2#
故障场景
Branch-1故障场景
本节介绍Internet故障期间的行为。
Internet链路被管理性关闭以模拟Internet故障链路。
Branch-1#show sdwan control local-properties
<SNIP>
PUBLIC PUBLIC PRIVATE PRIVATE PRIVATE MAX
INTERFACE IPv4 PORT IPv4 IPv6 PORT VS/VM COLOR STATE CNTRL
---------------------------------------------------------------------------------------------------------------------
GigabitEthernet2 198.51.100.1 12346 198.51.100.1 :: 12346 1/0 biz-internet down
GigabitEthernet3 172.20.1.10 12346 172.20.1.10 :: 12346 1/1 mpls up
Branch-1#
输出显示，在Internet链路故障场景中，Branch-1路由器通过OMP从DC路由器接收默认路由。172.31.31.3是DC路由器的系统IP。
Branch-1#show ip route vrf 10
<SNIP>
Gateway of last resort is 172.31.31.3 to network 0.0.0.0
m* 0.0.0.0/0 [251/0] via 172.31.31.3, 00:01:17, Sdwan-system-intf
<SNIP>
目的地为 192.0.2.100 将NAT转换为服务端NAT池并通过DC退出。
Host-BR-1#ping 192.0.2.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 10/37/103 ms
Host-BR-1#
Branch-1#show ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 172.16.2.1:3 192.168.10.1:3 192.0.2.100:3 192.0.2.100:3
Total number of translations: 1
Branch-1#
Traceroute结果显示流量采用DC路径。172.20.1.30是DC路由器的MPLS传输广域网IP。
Host-BR-1#traceroute 192.0.2.100 numeric
Type escape sequence to abort.
Tracing the route to 192.0.2.100
1 192.168.10.1 26 msec 5 msec 3 msec
2 172.20.1.30 10 msec 5 msec 27 msec
<SNIP>
Branch-1#show sdwan bfd sessions
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
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
172.31.31.2 22 up mpls mpls 172.20.1.10 172.20.1.20 12406 ipsec 7 1000 0:14:56:54 0
172.31.31.3 33 up mpls mpls 172.20.1.10 172.20.1.30 12406 ipsec 7 1000 0:14:56:57 0
Branch-1#
发往特定IP 192.0.2.1的流量也通过NAT转换到服务端NAT池，并通过DC退出。
Host-BR-1#ping 192.0.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 10/37/103 ms
Host-BR-1#
Branch-1#show ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 172.16.2.1:4 192.168.10.10:4 192.0.2.1:4 192.0.2.1:4
Total number of translations: 1
Branch-1#
Host-BR-1#traceroute 192.0.2.1 numeric
Type escape sequence to abort.
Tracing the route to 192.0.2.1
1 192.168.10.1 26 msec 5 msec 3 msec
2 172.20.1.30 10 msec 5 msec 27 msec
<SNIP>
从vSmart推送的数据策略配置：
Branch-1#show sdwan policy from-vsmart
from-vsmart data-policy _VPN10-VPN20_1-Branch-A-B-Central-NAT-DIA
direction from-service
vpn-list VPN10
sequence 1
match
source-ip 192.168.10.0/24
action accept
count NAT_VRF10_BRANCH_A_B_-968382210
nat pool 1
!
from-vsmart lists vpn-list VPN10
vpn 10
!
Branch-1#
Branch-1#show run | sec "natpool1"
<SNIP>
ip nat pool natpool1 172.16.2.1 172.16.2.2 prefix-length 30
Branch-2故障场景
发生互联网故障切换时，Branch-2路由器上也会出现类似行为。
Branch-2#show sdwan control local-properties
<SNIP>
PUBLIC PUBLIC PRIVATE PRIVATE PRIVATE MAX
INTERFACE IPv4 PORT IPv4 IPv6 PORT VS/VM COLOR STATE CNTRL
---------------------------------------------------------------------------------------------------------------------
GigabitEthernet2 198.51.100.2 12346 198.51.100.2 :: 12346 1/0 biz-internet down
GigabitEthernet3 172.20.1.20 12346 172.20.1.20 :: 12346 1/1 mpls up
Branch-2#
Branch-2#show ip route vrf 10
<SNIP>
Gateway of last resort is 172.31.31.3 to network 0.0.0.0
m* 0.0.0.0/0 [251/0] via 172.31.31.3, 00:10:17, Sdwan-system-intf
<SNIP>
Host-BR-2#ping 192.0.2.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 10/37/103 ms
Host-BR-2#
Branch-2#show ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 172.16.2.9:3 192.168.10.1:3 192.0.2.100:3 192.0.2.100:3
Total number of translations: 1
Branch-2#
Host-BR-2#traceroute 192.0.2.100 numeric
Type escape sequence to abort.
Tracing the route to 192.0.2.100
1 192.168.10.1 26 msec 5 msec 3 msec
2 172.20.1.30 10 msec 5 msec 27 msec
<SNIP>
Host-BR-2#ping 192.0.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 10/37/103 ms
Host-BR-2#
Branch-2#show ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 172.16.2.9:4 192.168.10.10:4 192.0.2.1:4 192.0.2.1:4
Total number of translations: 1
Branch-2#
Host-BR-2#traceroute 192.0.2.1 numeric
Type escape sequence to abort.
Tracing the route to 192.0.2.1
1 192.168.10.1 26 msec 5 msec 3 msec
2 172.20.1.30 10 msec 5 msec 27 msec
<SNIP>
Branch-2#show sdwan policy from-vsmart
from-vsmart data-policy _VPN10-VPN20_1-Branch-A-B-Central-NAT-DIA
direction from-service
vpn-list VPN10
sequence 1
match
source-ip 192.168.10.0/24
action accept
count NAT_VRF10_BRANCH_A_B_-968382210
nat pool 1
!
from-vsmart lists vpn-list VPN10-VPN20
vpn 10
!
Branch-2#
Branch-2#show run | sec "natpool1"
<SNIP>
ip nat pool natpool1 172.16.2.9 172.16.2.9 prefix-length 30
DC路由器路由状态
路由表捕获来自DC路由器。
如输出所示，DC路由器能够通过 post-NAT IP源自 SS-NAT pool （172.16.2.0和172.16.2.8）而不是实际的LAN IP 192.168.10.0/24172.31.31.1 和 172.31.31.2 是 system-ip 配置为Branch-1/Branch-2。系统IP 172.31.31.10 属于 vSmart.
DC-RTR#show ip route vrf 10
Routing Table: 10
<SNIP>
m 172.16.2.0 [251/0] via 172.31.31.1, 02:44:25, Sdwan-system-intf
m 172.16.2.8 [251/0] via 172.31.31.2, 02:43:33, Sdwan-system-intf
m 192.168.10.0[251/0] via 172.31.31.2, 03:01:35, Sdwan-system-intf
[251/0] via 172.31.31.1, 03:01:35, Sdwan-system-intf
DC-RTR#show sdwan omp routes
<SNIP> PATH ATTRIBUTE
VPN PREFIX FROM PEER ID LABEL STATUS TYPE TLOC IP COLOR ENCAP PREFERENCE
--------------------------------------------------------------------------------------------------------------------------------------
10 172.16.2.0/30 172.31.31.10 6 1002 C,I,R installed 172.31.31.1 mpls ipsec -
172.31.31.10 10 1002 Inv,U installed 172.31.31.1 biz-internet ipsec -
10 172.16.2.8/30 172.31.31.10 8 1002 C,I,R installed 172.31.31.2 mpls ipsec -
10 192.168.10.0/24 172.31.31.10 1 1002 C,I,R installed 172.31.31.1 mpls ipsec -
172.31.31.10 2 1002 C,I,R installed 172.31.31.2 mpls ipsec -
172.31.31.10 12 1002 Inv,U installed 172.31.31.1 biz-internet ipsec -
验证
当前没有可用于此配置的特定验证过程。
故障排除
目前没有针对此配置的故障排除信息。
其他信息
场景1
在控制器处于版本20.3.4且cEdge运行具有相同配置的17.3.3a或更低版本的情况下，可以观察到，在正常/故障切换情况下，流量会通过NAT转换到服务端NAT池，并中断流量。
cEdge捕获：
Host-BR-1#ping 192.0.2.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.0.2.100, timeout is 2 seconds:
U.U.U
Success rate is 0 percent (0/5)
Host-BR-1#
Branch-1#show ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 172.16.2.1:3 192.168.10.1:3 192.0.2.100:3 192.0.2.100:3
Total number of translations: 1
Branch-1#
WOW-Branch-1#show run | sec "natpool1"
<SNIP>
ip nat pool natpool1 172.16.2.1 172.16.2.2 prefix-length 30
从17.3.3a版本上运行的cEdge捕获输出。通过SIG隧道发往的流量通过NAT转换到SS-NAT池并被丢弃。从17.3.6版本开始提供修复程序。
场景2
要求(带UTD检查的服务端NAT(SS-NAT))
假设用户已请求以下要求：
1.当互联网和MPLS传输均正常运行时，VPN 10中的无线客户端可以定向到数据中心中的ISE进行身份验证。此外，通过SD-WAN重叠传输的VPN 10流量可以接受检查。由于此流量是重叠的一部分，VPN 10使用SS-NAT功能。[UTD + SS-NAT]
2.如果互联网传输不可用，则可以使用MPLS传输通过重叠路由来自VPN 10的所有流量，包括无线和有线流量。此流量也可以接受检查。[UTD + SS-NAT]
这些要求旨在确保Branch 1中的VPN 10在不同网络条件下安全且受监控的流量。
在上述两个场景中，您都有使用SS-NAT组合的UTD检测。以下是此场景的UTD配置示例。
policy utd-policy-vrf-10
all-interfaces
vrf 10
threat-inspection profile TEST_IDS_Policy
exit
警告：请注意，目前不支持UTD与SS-NAT的组合。因此，此组合未按预期工作。此问题的修复可能包含在未来的版本中。
解决方法
解决方法是在重叠IP VPN（本例中为VPN 10）上禁用UTD策略并启用全局VPN。
注：此配置已在17.6版本中测试和验证。
policy utd-policy-vrf-global
all-interfaces
vrf global
threat-inspection profile TEST_IDS_Policy
exit
修订历史记录
| 版本 | 发布日期 | 备注 |
|---|---|---|
1.0 |
09-Oct-2023 |
初始版本 |
反馈