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IPv6 over MPLS 6PE/6VPE

6PE and 6VPE allow us to run IPv6 over an IPv4-only MPLS core where we use dual stack PE routers.

On the PE routers, we use MP-BGP to exchange IPv6 prefixes and the LSP (Label Switched Path) is based on IPv4. This allows service providers to offer IPv6 to their customers without making major changes to the core of their MPLS network.

To achieve this, a small modification to MP-BGP was needed.  The LSP between the PE routers is based on IPv4 so the next hop addresses are IPv4 addresses. When a PE router advertises an IPv6 prefix through MP-BGP to another PE router, it embeds the IPv4 address in the IPv6 next hop address so that a PE router knows which IPv4 address (and thus which label) to use to get to the other PE router.

  • 6PE uses the global IPv6 routing table on the PE routers.
  • 6VPE uses VRFs on the PE routers (MPLS VPN).

In this lesson, I’ll show you how to configure 6PE and 6VPE.

Configuration

Here is the topology we will use:

Ipv6 Mpls 6pe 6vpe Topology

Above, we have a service provider in AS234 with two PE routers and one P router, the MPLS core is based on IPv4. The SP has a customer that is ready to use IPv6. On each CE router, there is a loopback with an IPv6 address. Between the PE-CE routers, we are going to use MP-BGP to advertise those IPv6 prefixes so that we have connectivity between CE1 and CE2.

Configurations

Want to take a look for yourself? Here you will find the startup configuration of each device.

CE1

hostname CE1
!
ip cef
!
interface Loopback0
 ipv6 address 2001:DB8:1:1::1/128
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:12::1/64
!
end

CE2

hostname CE2
!
ip cef
!
interface Loopback0
 ipv6 address 2001:DB8:5:5::5/128
!
interface GigabitEthernet0/0
 ip address 10.255.1.147 255.255.0.0
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:45::5/64
!
end

P

hostname P
!
ip cef
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.255
!
interface GigabitEthernet0/1
 ip address 192.168.23.3 255.255.255.0
!
interface GigabitEthernet0/2
 ip address 192.168.34.3 255.255.255.0
!
router ospf 1
 mpls ldp autoconfig
 network 3.3.3.3 0.0.0.0 area 0
 network 192.168.23.0 0.0.0.255 area 0
 network 192.168.34.0 0.0.0.255 area 0
!
end

PE1

hostname PE1
!
ip cef
!
interface Loopback0
 ip address 2.2.2.2 255.255.255.255
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:12::2/64
!
interface GigabitEthernet0/2
 ip address 192.168.23.2 255.255.255.0
!
router ospf 1
 mpls ldp autoconfig
 network 2.2.2.2 0.0.0.0 area 0
 network 192.168.23.0 0.0.0.255 area 0
!
router bgp 234
 bgp log-neighbor-changes
 neighbor 4.4.4.4 remote-as 234
 neighbor 4.4.4.4 update-source Loopback0
!
end

PE2

hostname PE2
!
ip cef
!
interface Loopback0
 ip address 4.4.4.4 255.255.255.255
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:45::4/64
!
interface GigabitEthernet0/2
 ip address 192.168.34.4 255.255.255.0
!
router ospf 1
 mpls ldp autoconfig
 network 4.4.4.4 0.0.0.0 area 0
 network 192.168.34.0 0.0.0.255 area 0
!
router bgp 234
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 234
 neighbor 2.2.2.2 update-source Loopback0
!
end


With the configuration above, I have an LSP between PE1 and PE2. These two PE routers are MP-BGP neighbors:

PE1#show ip bgp summary 
BGP router identifier 2.2.2.2, local AS number 234
BGP table version is 1, main routing table version 1

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
4.4.4.4         4          234      65      65        1    0    0 00:55:23        0
PE2#show ip bgp summary 
BGP router identifier 4.4.4.4, local AS number 234
BGP table version is 1, main routing table version 1

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
2.2.2.2         4          234      66      66        1    0    0 00:55:59        0

We can see the transport labels that are used between PE1 (2.2.2.2) and PE2 (4.4.4.4):

PE1#show mpls forwarding-table
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
16         Pop Label  3.3.3.3/32       0             Gi0/2      192.168.23.3
17         Pop Label  192.168.34.0/24  0             Gi0/2      192.168.23.3
18         17         4.4.4.4/32       0             Gi0/2      192.168.23.3
P#show mpls forwarding-table
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
16         Pop Label  2.2.2.2/32       8361          Gi0/1      192.168.23.2
17         Pop Label  4.4.4.4/32       8415          Gi0/2      192.168.34.4
PE2#show mpls forwarding-table
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
16         Pop Label  3.3.3.3/32       0             Gi0/2      192.168.34.3
17         16         2.2.2.2/32       0             Gi0/2      192.168.34.3
18         Pop Label  192.168.23.0/24  0             Gi0/2      192.168.34.3

Now let’s see if we can get IPv6 traffic over this network.

6PE

Let’s start with 6PE, this is where we use the global IPV6 routing table on the PE routers.



PE Routers

Let’s start with PE1. There are a couple of things I need to do:

  • Configure the CE1 router as a neighbor.
  • Activate the CE1 router under the IPv6 address-family.
  • Activate the PE2 router under the IPv6 address-family.
  • Send labels for IPv6 prefixes to the PE2 router.

Let’s configure all of this:

PE1(config)#ipv6 unicast-routing 

PE1(config)#router bgp 234
PE1(config-router)#neighbor 2001:DB8:0:12::1 remote-as 1
PE1(config-router)#address-family ipv6
PE1(config-router-af)#neighbor 2001:DB8:0:12::1 activate
PE1(config-router-af)#neighbor 4.4.4.4 activate 
PE1(config-router-af)#neighbor 4.4.4.4 send-label

On the PE2 router, we do the exact same thing:

PE2(config)#ipv6 unicast-routing

PE2(config)#router bgp 234
PE2(config-router)#neighbor 2001:DB8:0:45::5 remote-as 5
PE2(config-router)#address-family ipv6
PE2(config-router-af)#neighbor 2001:DB8:0:45::5 activate
PE2(config-router-af)#neighbor 2.2.2.2 activate
PE2(config-router-af)#neighbor 2.2.2.2 send-label

This completes the configuration of the PE routers.

CE Routers

The configuration of the CE routers is pretty straightforward. We configure MP-BGP for IPv6 and advertise the IPv6 prefix on the loopback interface. Let’s start with CE1:

CE1(config)#ipv6 unicast-routing

CE1(config)#router bgp 1
CE1(config-router)#bgp router-id 1.1.1.1
CE1(config-router)#neighbor 2001:DB8:0:12::2 remote-as 234

CE1(config-router)#address-family ipv6
CE1(config-router-af)#neighbor 2001:DB8:0:12::2 activate 
CE1(config-router-af)#network 2001:DB8:1:1::1/128

The configuration of CE2 is the same as CE1:

CE2(config)#ipv6 unicast-routing 

CE2(config)#router bgp 5
CE2(config-router)#bgp router-id 5.5.5.5
CE2(config-router)#neighbor 2001:DB8:0:45::4 remote-as 234
CE2(config-router)#address-family ipv6     
CE2(config-router-af)#neighbor 2001:DB8:0:45::4 activate 
CE2(config-router-af)#network 2001:DB8:5:5::5/128

That completes our configuration.

Verification

Let’s verify our work. Let’s start with the PE routers to see if MP-BGP has exchanged any prefixes:

PE1#show bgp ipv6 unicast 
BGP table version is 6, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  2001:DB8:1:1::1/128
                       2001:DB8:0:12::1
                                                0             0 1 i
 *>i 2001:DB8:5:5::5/128
                       ::FFFF:4.4.4.4           0    100      0 5 i

We see two entries on the PE router. The 2001:DB8:1:1::1/128 prefix we learned from CE1 and the 2001:DB8:5:5::5/128 prefix we learned from PE2. Take a good look at the next hop address for that second prefix, it has IPv4 address 4.4.4.4 embedded in it.

4.4.4.4 is the IPv4 address on the loopback of the PE2 router which is used for our LSP. This is how the PE1 router is able to figure out what LSP to use if it wants to reach 2001:DB8:5:5::5/128.

Let’s take a closer look at this prefix:

PE1#show bgp ipv6 unicast 2001:DB8:5:5::5/128
BGP routing table entry for 2001:DB8:5:5::5/128, version 6
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     3         
  Refresh Epoch 1
  5
    ::FFFF:4.4.4.4 (metric 3) from 4.4.4.4 (4.4.4.4)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      mpls labels in/out nolabel/19
      rx pathid: 0, tx pathid: 0x0

Above, we see the next hop again but also the VPN label (19) that is used to reach this prefix. You can also use the show bgp ipv6 unicast labels command to see the labels that are used:

PE1#show bgp ipv6 unicast labels 
   Network          Next Hop      In label/Out label
   2001:DB8:1:1::1/128
                    2001:DB8:0:12::1
                                    19/nolabel
   2001:DB8:5:5::5/128
                    ::FFFF:4.4.4.4  nolabel/19

With 6PE, prefixes are installed in the global IPv6 routing table. Let’s take a look:

PE1#show ipv6 route bgp
IPv6 Routing Table - default - 5 entries

B   2001:DB8:1:1::1/128 [20/0]
     via FE80::F816:3EFF:FEEA:B8E3, GigabitEthernet0/1
B   2001:DB8:5:5::5/128 [200/0]
     via 4.4.4.4%default, indirectly connected

Above, we see the two prefixes in the global IPv6 routing table. Let’s take a look at the PE2 router:

PE2#show bgp ipv6 unicast
BGP table version is 5, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 2001:DB8:1:1::1/128
                       ::FFFF:2.2.2.2           0    100      0 1 i
 *>  2001:DB8:5:5::5/128
                       2001:DB8:0:45::5
                                                0             0 5 i

PE2 uses ::FFFF:2:2:2:2 as the next hop address for 2001:DB8:1:1::1/128. That’s the IPv4 address on the loopback interface of the PE1 router, that is used for the LSP.

Let’s take a closer look at the 2001:DB8:1:1::1/128 prefix:

PE2#show bgp ipv6 unicast 2001:DB8:1:1::1/128
BGP routing table entry for 2001:DB8:1:1::1/128, version 3
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     3         
  Refresh Epoch 1
  1
    ::FFFF:2.2.2.2 (metric 3) from 2.2.2.2 (2.2.2.2)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      mpls labels in/out nolabel/19
      rx pathid: 0, tx pathid: 0x0

Above, we see the VPN label (19) that is used.

PE2#show bgp ipv6 unicast labels
   Network          Next Hop      In label/Out label
   2001:DB8:1:1::1/128
                    ::FFFF:2.2.2.2  nolabel/19
   2001:DB8:5:5::5/128
                    2001:DB8:0:45::5
                                    19/nolabel

Let’s check the global routing table:

PE2#show ipv6 route bgp
IPv6 Routing Table - default - 5 entries

B   2001:DB8:1:1::1/128 [200/0]
     via 2.2.2.2%default, indirectly connected
B   2001:DB8:5:5::5/128 [20/0]
     via FE80::F816:3EFF:FEC3:25CB, GigabitEthernet0/1

The PE routers look good, everything we need is there. Let’s take a look at the CE routers:

CE1#show ipv6 route bgp

B   2001:DB8:5:5::5/128 [20/0]
     via FE80::F816:3EFF:FE44:53EA, GigabitEthernet0/1
CE2#show ipv6 route bgp

B   2001:DB8:1:1::1/128 [20/0]
     via FE80::F816:3EFF:FE4C:A56C, GigabitEthernet0/1

Each CE router has a BGP route. Let’s see if we can ping from one loopback interface to another:

CE1#ping 2001:DB8:5:5::5 source 2001:DB8:1:1::1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:5:5::5, timeout is 2 seconds:
Packet sent with a source address of 2001:DB8:1:1::1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/7/10 ms

Our ping is successful, if we want to see the labels then we can use a traceroute:

CE1#traceroute                  
Protocol [ip]: ipv6
Target IPv6 address: 2001:DB8:5:5::5
Source address: 2001:DB8:1:1::1
Insert source routing header? [no]: 
Numeric display? [no]: 
Timeout in seconds [3]: 
Probe count [3]: 1
Minimum Time to Live [1]: 
Maximum Time to Live [30]: 
Priority [0]: 
Port Number [0]: 
Type escape sequence to abort.
Tracing the route to 2001:DB8:5:5::5

  1 2001:DB8:0:12::2 7 msec
  2 ::FFFF:192.168.23.3 [MPLS: Labels 17/19 Exp 0] 12 msec
  3 2001:DB8:0:45::4 [MPLS: Label 19 Exp 0] 9 msec
  4 2001:DB8:0:45::5 8 msec

This is looking good. We see the VPN label (19) and the transport label (17) in this output.

Configurations

Want to take a look for yourself? Here you will find the startup configuration of each device.

CE1

hostname CE1
!
ip cef
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
 ipv6 address 2001:DB8:1:1::1/128
!
interface GigabitEthernet0/0
 ip address 10.255.1.146 255.255.0.0
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:12::1/64
 ipv6 enable
!
router bgp 1
 bgp router-id 1.1.1.1
 bgp log-neighbor-changes
 neighbor 2001:DB8:0:12::2 remote-as 234
 !
 address-family ipv4
  no neighbor 2001:DB8:0:12::2 activate
 exit-address-family
 !
 address-family ipv6
  network 2001:DB8:1:1::1/128
  neighbor 2001:DB8:0:12::2 activate
 exit-address-family
!
end

CE2

hostname CE2
!
ip cef
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
 ipv6 address 2001:DB8:5:5::5/128
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:45::5/64
!
router bgp 5
 bgp router-id 5.5.5.5
 bgp log-neighbor-changes
 neighbor 2001:DB8:0:45::4 remote-as 234
 !
 address-family ipv4
  no neighbor 2001:DB8:0:45::4 activate
 exit-address-family
 !
 address-family ipv6
  network 2001:DB8:5:5::5/128
  neighbor 2001:DB8:0:45::4 activate
 exit-address-family
!
end

P

hostname P
!
ip cef
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.255
!
interface GigabitEthernet0/1
 ip address 192.168.23.3 255.255.255.0
!
interface GigabitEthernet0/2
 ip address 192.168.34.3 255.255.255.0
!
router ospf 1
 mpls ldp autoconfig
 network 3.3.3.3 0.0.0.0 area 0
 network 192.168.23.0 0.0.0.255 area 0
 network 192.168.34.0 0.0.0.255 area 0
!
end

PE1

hostname PE1
!
ip cef
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
 ip address 2.2.2.2 255.255.255.255
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:12::2/64
!
interface GigabitEthernet0/2
 ip address 192.168.23.2 255.255.255.0
!
router ospf 1
 mpls ldp autoconfig
 network 2.2.2.2 0.0.0.0 area 0
 network 192.168.23.0 0.0.0.255 area 0
!
router bgp 234
 bgp log-neighbor-changes
 neighbor 4.4.4.4 remote-as 234
 neighbor 4.4.4.4 update-source Loopback0
 neighbor 2001:DB8:0:12::1 remote-as 1
 !
 address-family ipv4
  neighbor 4.4.4.4 activate
  no neighbor 2001:DB8:0:12::1 activate
 exit-address-family
 !
 address-family ipv6
  neighbor 4.4.4.4 activate
  neighbor 4.4.4.4 send-label
  neighbor 2001:DB8:0:12::1 activate
 exit-address-family
!
end

PE2

hostname PE2
!
ip cef
ipv6 unicast-routing
ipv6 cef
!
interface Loopback0
 ip address 4.4.4.4 255.255.255.255
!
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:45::4/64
!
interface GigabitEthernet0/2
 ip address 192.168.34.4 255.255.255.0
!
router ospf 1
 mpls ldp autoconfig
 network 4.4.4.4 0.0.0.0 area 0
 network 192.168.34.0 0.0.0.255 area 0
!
router bgp 234
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 234
 neighbor 2.2.2.2 update-source Loopback0
 neighbor 2001:DB8:0:45::5 remote-as 5
 !
 address-family ipv4
  neighbor 2.2.2.2 activate
  no neighbor 2001:DB8:0:45::5 activate
 exit-address-family
 !
 address-family ipv6
  neighbor 2.2.2.2 activate
  neighbor 2.2.2.2 send-label
  neighbor 2001:DB8:0:45::5 activate
 exit-address-family
!
end

6VPE

Now let’s try the 6VPE configuration. I’ll use the same startup configuration I showed in the beginning of this lesson.

PE Routers

6VPE uses VRFs so that’s the first thing I am going to configure. We’ll create a VRF called “CUSTOMER” and use RD 1:1:

PE1(config)#vrf definition CUSTOMER
PE1(config-vrf)#rd 1:1
PE1(config-vrf)#address-family ipv6
PE1(config-vrf-af)#route-target both 1:1

PE1(config)#interface GigabitEthernet 0/1
PE1(config-if)#vrf forwarding CUSTOMER
PE1(config-if)#ipv6 address 2001:DB8:0:12::2/64

Make sure IPv6 unicast routing is enabled before you configure MP-BGP:

PE1(config)#ipv6 unicast-routing

Now we can configure MP-BGP. I need to enable the VPNv6 address family and activate the PE2 router. We also need to configure the CE router as a neighbor under the VRF:

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Forum Replies

  1. Hi,

    what is the send label command do? is it allowing the PE routers to add the transport label and the VPN label to IPv6 prefixes and then forward to other PE routers?

  3. Hi Guys - quick question - is dual stack in terms of IPv6 simply running v4 and v6 addresses on the same interfaces? Cheers - Gareth.

  4. Hello Gareth

    The term “dual stack” can mean several things depending on the context. In general, the term means that a single device is running both IPv4 and IPv6 simultaneously. On a host with one NIC, this means that the NIC has both an IPv4 and IPv6 address. On a router, this could mean that a single port has both an IPv4 and IPv6 address, or, as is the case in this specific lesson, it simply means that the same device is running both IPv4 and IPv6 simultaneously, but not necessarily on the same interface.

    I hope this has been helpful!

    Laz

  5. Thanks Laz - good to know that it’s just a generic term.

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