Xconnect over VRF Aware L2TPv3 in ASR1K
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Introduction
This document describes how the Virtual Routing and Forwarding (VRF) can be used when you configure Layer 2 Tunneling Protocol (L2TP)v3 Xconnect over IP and Multiprotocol Label Switching (MPLS) network.
Background Information
L2TP is the tunneling protocol used by Internet Service Providers (ISPs) in order to provide Virtual Private Network (VPN) in the dial access space over the internet.
It combines the best of Cisco's Layer 2 Forwarding (L2F) protocol and Microsoft's Point-to-Point Tunneling Protocol (PPTP). The main components of L2TP are L2TP Access Controller (LAC) and L2TP Network Server (LNS).
L2TP Access Controller: LAC is an access server connected to Public Switched Telephone Network (PSTN). The LAC is the initiator of incoming calls and the receiver of outgoing calls. It is connected to LNS over LAN or WAN.
L2TP Network Server: LNS is the network server for L2TP protcol where PPP sessions terminate and are authenticated. The LNS is the initiator of outgoing calls and the receiver of incoming calls.
L2TPv2 was designed to carry PPP traffic over IP networks. Network access equipment (DSL, cable modem or dial-up access interfaces) accepted PPP connections from subscribers and tunnelled the PPP sessions to the ISP over L2TP. The new version L2TPv3 is designed to carry any Layer 2 payload in addition to PPP which was the only payload that was supported by version 2. Specifically, L2TPv3 defines the L2TP protocol for tunneling Layer 2 payloads over an IP core network with the use Layer 2 VPNs. Benefits of this feature include this:
- L2TPv3 simplifies deployment of VPNs
- L2TPv3 does not require MPLS
- L2TPv3 supports Layer 2 tunneling over IP for any payload
Here is the sample configuration of L2TPv3 pseudowire:
1.
enable
2.configureterminal
3.interface type slot/port
4.xconnectpeer-ip-address vcidencapsulation l2tpv3pw-classpw-class-name
Now take a look at how L2TPv3 Xconnect behaves when VRF is used. Here is the topology that is used for demonstration in which we Xconnect is configured between CPE and ASR1002 (IP) and ASR1004 (MPLS) with endpoints at ASR1000 in VRF (VRF Aware L2TPv3 is not supported on ASR1000 platform).
Test Case I: L2TPv3 Xconnect over IP network with Endpoints in VRF
PE-1 and PE-2 make the MPLS network for ISP. CPE is connected to PE-1 over VRF and ASR1002 is connected to PE-2 over VRF. ASR1002 also has VRF on the interface connected to PE-2. The reachability of CPE loopback from ASR1002 is via VRF over IP interface.
Configuration on CPE for Xconnect towards ASR1002:
interface FastEthernet4.2381
encapsulation dot1Q 2381
xconnect 3.3.3.3 2381 encapsulation l2tpv3 pw-class PSEUDO_CLASS >>>>>>>>>>> Xconnect with ASR1002
pseudowire-class PSEUDO_CLASS
encapsulation l2tpv3
interworking vlan
protocol l2tpv3 L2TP_CLASS
ip local interface Loopback0
ip tos reflect
l2tp-class L2TP_CLASS
authentication
password cisco
interface Gigabit0/1
ip address 192.168.8.190 255.255.255.0
end
Interface Loopback0
ip address 1.1.1.1 255.255.255.255
end
ip route 0.0.0.0 0.0.0.0 192.168.8.1 >>>>>>>>>>>>>> Default route towards PE-1
Working Configuration on ASR1002:
interface GigabitEthernet0/0/0.906 —————————————————> Interface connected to PE-2 is in VRF
encapsulation dot1Q 906
ip vrf forwarding L2TP_VRF
ip address 10.1.1.1 255.255.255.252
interface GigabitEthernet0/0/1.2381
encapsulation dot1Q 2381
xconnect 1.1.1.1 2381 encapsulation l2tpv3 pw-class PSEUDO_CLASS
pseudowire-class PSEUDO_CLASS
encapsulation l2tpv3
interworking vlan
protocol l2tpv3 L2TP_CLASS
ip local interface Loopback11
l2tp-class L2TP_CLASS
authentication
password cisco
interface Loopback11
ip vrf forwarding L2TP_VRF ————————————————————————————> Source is in VRF
ip address 3.3.3.3 255.255.255.255
router bgp 1
address-family ipv4 vrf L2TP_VRF
redistribute connected
neighbor 10.1.1.2 remote-as 2 ———————————————> eBGP with PE-2 in VRF
neighbor 10.1.1.2 activate
neighbor 10.1.1.2 soft-reconfiguration inbound
exit-address-family
VRF L2TP_VRF:
B 1.1.1.1/32 [20/0] via 10.1.1.2, 1d ——————————> Xconnect end point learned via eBGP in VRF
Let us now check the status of Xconnect on CPE:
CPE #sh xconnect all de
Legend: XC ST=Xconnect State S1=Segment1 State S2=Segment2 State
UP=Up DN=Down AD=Admin Down IA=Inactive
SB=Standby HS=Hot Standby RV=Recovering NH=No Hardware
XC ST Segment 1 S1 Segment 2 S2
------+---------------------------------+--+---------------------------------+--
UP pri ac Fa4.2381:2381(Eth VLAN) UP l2tp 3.3.3.3:2381 DOWN
Interworking: vlan Session ID: 1906980494
Tunnel ID: 2886222725
Protocol State: DOWN
Remote Circuit State: DOWN
pw-class: PSEUDO_CLASS_VLAN
It says Segment 2 is down, which means the path from CPE to ASR1002 is having an issue. However, we are able to ping the Endpoint. The debugs on CPE shows that tunnel to Endpoint is failed or there is no route to endpoint.
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]: I CDN, flg TLS, ver 3, len 80
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]:IETF v2:
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]:Result Code
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]: Call disconnected for administrative reasons(3)
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]: Error code
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]: No error(0)
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]: Optional msg
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]: "Tunnel failed to 3.3.3.3" >>>>>>>>>>>>>>>>>
*Feb 15 08:12:47.225: L2TP _____:18136:8DF92CB9/uid:0[1.1.1.1/2381]:Cisco v3:
The main issue here is that Endpoint is reachable via VRF on ASR1002. The Xconnect endpoint needs to be in Global Routing Table for it to come up. Let us now configure a route for CPE Loopback 1.1.1.1/32 in global pointing to interface GigabitEthernet0/0/0.906 which is itself in VRF.
ip route 1.1.1.1 255.255.255.255 GigabitEthernet0/0/0.906 10.1.1.2
S 1.1.1.1/32 [1/0] via 10.1.1.2, GigabitEthernet0/0/0.906
Once the dummy static route is configured, Xconnect comes up. You can also point it to Null0. This is a workaround to let the router believe that Endpoint is reachable via Global not VRF and is just used for Control Plane. The actual data plane traffic will be via VRF only.
Here are the ping results with and without VRF:
ASR1002 #ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Ping vrf L2TP_VRF 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 33/50/72 ms
Status of Xconnect on CPE:
CPE #sh xconnect all de
Legend: XC ST=Xconnect State S1=Segment1 State S2=Segment2 State
UP=Up DN=Down AD=Admin Down IA=Inactive
SB=Standby HS=Hot Standby RV=Recovering NH=No Hardware
XC ST Segment 1 S1 Segment 2 S2
------+---------------------------------+--+---------------------------------+--
UP pri ac Fa4.2381:2381(Eth VLAN) UP l2tp3.3.3.3:2381 UP
Interworking: vlan Session ID: 1906980494
Tunnel ID: 2886222725
Protocol State: UP
Remote Circuit State: UP
pw-class: PSEUDO_CLASS_VLAN
Test Case II: L2TPv3 Xconnect over MPLS network with Endpoints in VRF
PE-1, PE-2 and PE-3 make the MPLS network for ISP with PE-2 acting as Route Reflector (RR). CPE is connected to PE-1 over VRF and ASR1004 is connected to PE-2 with MPLS enabled on the interface. ASR1004 also has VRF in which it is supposed to receive the VPNv4 routes from PE-1 via RR. The reachability of CPE looback from ASR1004 is via VRF over MPLS interface.
Configuration on CPE for Xconnect towards ASR1004:
interface FastEthernet4.2380
encapsulation dot1Q 2380
xconnect 2.2.2.2 2380 encapsulation l2tpv3 pw-class PSEUDO_CLASS >>>>>>>>>>Xconnect with ASR1004
interface FastEthernet4.2381
encapsulation dot1Q 2381
xconnect 3.3.3.3 2381 encapsulation l2tpv3 pw-class PSEUDO_CLASS >>>>>>>>>>> Xconnect with ASR1002
pseudowire-class PSEUDO_CLASS
encapsulation l2tpv3
interworking vlan
protocol l2tpv3 L2TP_CLASS
ip local interface Loopback0
ip tos reflect
l2tp-class L2TP_CLASS
authentication
password cisco
interface Gigabit0/1
ip address 192.168.8.190 255.255.255.0
end
Interface Loopback0
ip address 1.1.1.1 255.255.255.255
end
ip route 0.0.0.0 0.0.0.0 192.168.8.1 >>>>>>>>>>>>>> Default route towards PE-1
Configuration on ASR1004:
interface GigabitEthernet0/0/1
no ip address
negotiation auto
service instance 2 ethernet
encapsulation dot1q 2380
xconnect 1.1.1.1 2380 encapsulation l2tpv3 pw-class PSEUDO_CLASS_VLAN
!
end
interface Loopback11
ip vrf forwarding L2TP_VRF —————————————————> Source Loopback in in VRF
ip address 2.2.2.2 255.255.255.255
end
pseudowire-class PSEUDO_CLASS_VLAN
encapsulation l2tpv3
interworking vlan
protocol l2tpv3 L2TP_CLASS
ip local interface Loopback11
l2tp-class L2TP_CLASS
authentication
password cisco
router bgp 2
address-family ipv4 vrf L2TP_VRF
redistribute connected
redistribute static
default-information originate
exit-address-family
Route entry for Xconnect End Point:
ASR1004#sh ip rou vrf L2TP_VRF 1.1.1.1 . ——————————————————> Xconnect End Point also learned via VRF
Routing Table: L2TP_VRF
Routing entry for 1.1.1.1/32
Known via "bgp 2", distance 200, metric 0, type internal
Last update from 11.11.11.11 6d17h ago
Routing Descriptor Blocks:
* 11.11.11.11 (default), from 22.22.22.22, 6d17h ago
Route metric is 0, traffic share count is 1
AS Hops 0
MPLS label: 18
MPLS Flags: MPLS Required
We observed that Segment 2 was continuously flapping on both ends.
ASR1004#sh xc all de
Legend: XC ST=Xconnect State S1=Segment1 State S2=Segment2 State
UP=Up DN=Down AD=Admin Down IA=Inactive
SB=Standby HS=Hot Standby RV=Recovering NH=No Hardware
XC ST Segment 1 S1 Segment 2 S2
------+---------------------------------+--+---------------------------------+--
DN pri ac Gi0/0/1:2380(Eth VLAN) UP l2tp 1.1.1.1:2380 DN >>>>>>>>>>>>>>
Interworking: vlan Session ID: 2543426569
Tunnel ID: 3352120314
Protocol State: DOWN
Remote Circuit State: DOWN
pw-class: PSEUDO_CLASS_VLAN
ASR1004#sh xc all de
Legend: XC ST=Xconnect State S1=Segment1 State S2=Segment2 State
UP=Up DN=Down AD=Admin Down IA=Inactive
SB=Standby HS=Hot Standby RV=Recovering NH=No Hardware
XC ST Segment 1 S1 Segment 2 S2
------+---------------------------------+--+---------------------------------+--
UP pri ac Gi0/0/1:2380(Eth VLAN) UP l2tp 1.1.1,1:2380 UP >>>>>>>>>>>>>>>>
Interworking: vlan Session ID: 2543426569
Tunnel ID: 3352120314
Protocol State: UP
Remote Circuit State: UP
pw-class: PSEUDO_CLASS_VLAN
Logs from CPE:
CPE#sh xconnect all de
Legend: XC ST=Xconnect State S1=Segment1 State S2=Segment2 State
UP=Up DN=Down AD=Admin Down IA=Inactive
SB=Standby HS=Hot Standby RV=Recovering NH=No Hardware
XC ST Segment 1 S1 Segment 2 S2
------+---------------------------------+--+---------------------------------+--
DN pri ac Fa4.2380:2380(Eth VLAN) UP l2tp 2.2.2.2:2380 DN ---------------à Flapping with ASR1004
Interworking: vlan Session ID: 3434660693
Tunnel ID: 1760690853
Protocol State: DOWN
Remote Circuit State: DOWN
pw-class: PSEUDO_CLASS
UP pri ac Fa4.2381:2381(Eth VLAN) UP l2tp 3.3.3.3:2381 UP ---------------------à Stable with ASR1002
Interworking: vlan Session ID: 1906980494
Tunnel ID: 2886222725
Protocol State: UP
Remote Circuit State: UP
pw-class: PSEUDO_CLASS
CPE#sh l2tp session
L2TP Session Information Total tunnels 2 sessions 2
LocID RemID TunID Username, Intf/ State Last Chg Uniq ID
Vcid, Circuit
2714490989 3697021268 1760690853 2380, Fa4.2380:2380 est 00:00:03 0 ————————> Flapping with ASR1004
1906980494 2361475239 2886222725 2381, Fa4.2381:2381 est 15:37:06 0 ————————> Stable with ASR1002
You cannot configure a static route in this case as exit interface is MPLS enabled interface. As a workaround, there are two interfaces looped back to each other and configured one in VRF with other in global. Then configured a static route in global pointing towards VRF interface, with this Xconnect became stable.
ASR1004#sh run int gi0/0/2
Building configuration...
Current configuration : 95 bytes
!
interface GigabitEthernet0/0/2 ——————————> Looped to Gi0/0/3
ip address 20.20.20.2 255.255.255.252
negotiation auto
end
#sh run int gi0/0/3
Building configuration...
Current configuration : 126 bytes
!
interface GigabitEthernet0/0/3
ip vrf forwarding L2TP_VRF
ip address 20.20.20.1 255.255.255.252
negotiation auto
end
ip route 10.246.131.62 255.255.255.255 20.20.20.1 ———————> Static route pointing towards an IP interface in Global
CPE#sh xconnect all de
Legend: XC ST=Xconnect State S1=Segment1 State S2=Segment2 State
UP=Up DN=Down AD=Admin Down IA=Inactive
SB=Standby HS=Hot Standby RV=Recovering NH=No Hardware
XC ST Segment 1 S1 Segment 2 S2
------+---------------------------------+--+---------------------------------+--
DN pri ac Fa4.2380:2380(Eth VLAN) UP l2tp 2.2.2.2:2380 UP
Interworking: vlan Session ID: 3434660693
Tunnel ID: 1760690853
Protocol State: DOWN
Remote Circuit State: DOWN
pw-class: PSEUDO_CLASS
UP pri ac Fa4.2381:2381(Eth VLAN) UP l2tp 3.3.3.3:2381 UP
Interworking: vlan Session ID: 1906980494
Tunnel ID: 2886222725
Protocol State: UP
Remote Circuit State: UP
pw-class: PSEUDO_CLASS
CPE#sh l2tp session
L2TP Session Information Total tunnels 2 sessions 2:
LocID RemID TunID Username, Intf/ State Last Chg Uniq ID
Vcid, Circuit
2714490989 3697021268 1760690853 2380, Fa4.2380:2380 est 00:20:03 0
1906980494 2361475239 2886222725 2381, Fa4.2381:2381 est 15:37:06 0
The traffic flow is seen as in case of ASR1004:
- When traffic comes from CPE on ASR1004, it comes in MPLS interface Gi0/0/1 and gets switched directly to Gi0/0/0 Access port.
- When traffic comes from Access Port Gi0/0/0, it takes the looped path of Gi0/0/0 -> Gi0/0/2 -> Gi0/0/3 -> Gi0/0/1.
The main issue with this workaround is for QFP utilization on ASR1000 platform as packet processing is done twice:
ASR1004# show platform packet-trace summary
Pkt Input Output State Reason
0 Gi0/0/3 Gi0/0/1 FWD
1 Gi0/0/3 Gi0/0/1 FWD
2 Gi0/0/3 Gi0/0/1 FWD
3 Gi0/0/0 Gi0/0/2 FWD
4 Gi0/0/0 Gi0/0/2 FWD
5 Gi0/0/0 Gi0/0/2 FWD
6 Gi0/0/0 Gi0/0/2 FWD
7 Gi0/0/0 Gi0/0/2 FWD
This behavior is documented in Doc Bug: CSCvi42964
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