All what you need know to tackle IPv6 over IPv4/MPLS: 6PE and 6VPE on CISCO Routers.

1. IPv6 Over MPLS on CISCO Routers
1. Introduction
When MPLS convinced most Service Providers to switch to MPLS because of services like
MPLS-VPN, IPv6 was just a little baby protocol. No sane Service Providers would have build its
backbone with IPv6.
But beginning of Y2K, IPv6 was requested mostly in Asia and it would have been impossible to
say to a SP who just build and debug its IPv4/MPLS Backbone to switch or build a new IPv6
Backbone. So CISCO decided to develop 6PE. To provide an IPv6 Service to MPLS/IPv4
Backbone customer.
At CISCO it was quite funny because MPLS people did not want to allocate resource on 6PE as
IPv6 was considered a very LOW priority project and IPv6 people did not want neither because
MPLS was evil for them and solution was to build an IPv6 Backbone period. So a small team
was hired around a former IBMer designer who leaved IBM with a colleague. Problem, they
had absolutely NO experience in MPLS and also they were needing a guy to do the dev-test of
this new feature for them. A few bugs on MPLS had generated multiple huge crysis and this
time CISCO wanted to over-test any IPv6 over MPLS solution before releasing any feature and
this is when I joined the team. I was writing the test plan, the test scripts automation and was
troubleshooting problems when I was finding something. I wrote about a dozen of scripts to
test features, performances and other things and each time I was doing it for IPv6, I was also
doing it for IPv4 to show that behavior was consistent.
I worked mostly dedicated on 6PE and 6VPE for about 4 years until the CISCO USA MPLS team
realized that there was good business and a lot of interest for these two features. Then it was
decided that US MPLS Team should overtake it and I traveled to Boston area and transfer my
knowledge of the scripts I designed. I cannot help thinking that the USA guy I worked with did
the same with Bangalore one day!
2. 6PE
There was already 2 scripts to do the functional testing of 6PE when I took it over.
6PE was designed by people in France. François le Faucheur designed the Architecture.
François is one of the best Architect of CISCO and is the author of many RFCs about QoS on

2. MPLS-TE and a lot more. 6PE was very similar to MPLS-VPN but the VPN routes were IPv6
routes and there was no VRF concepts. IPv6 routes were going into the Global Routing Table.
In the first 6PE IOS version the egress 6PE was advertising an Aggregate label in a 16
labels pool for any IPv6 destination. When a packet arrives in a router with this label, it
tells the router to remove the MPLS label and to call CEF, the IPv4 or IPv6 Forwarding
plane to take the routing decision.
This was a double look-up which was no good for performances but had accelerated the
time to market. And 16 labels were advertise instead of only one to enable load-balancing
on the P routers. Problem is that some CISCO distributed hardware platforms did not
support this behavior and CISCO had to review its code to allocate a label per destination.
The featurette was called Fast 6PE!
Then 6PE assigned a label for each IPv6 route which must be reached by remote nodes. This
label is assigned by MP-BGP and get into the CEFv6, the CISCO forwarding data plane,
forwarding entry. With CISCO MPLS, MPLS-VPN, 6PE or 6VPE, label imposition is done by CEF.
CEF will not be involved any further as the LFIB will be responsible for switching the packet
until the egress 6PE which switch the packet using the label that it has allocated from MP-BGP
and announced to remote 6PEs, most of the time via a Route Reflector.
So when the ingress 6PE imposes the labels to the IPv6 packet, the interior label is allocated
from the MP-BGP Label information.

3. The external label is imposed by LDP and the Internal Routing Protocol together. The other
option was to modify the Routing Protocol to distribute the label. This option had much better
performances and not the drawbacks of LDP but considering that too much protocols would
have to be changed if MPLS was really Multiprotocol, the M of MPLS they decided to have a
separate protocol for label distribution. This was TDP which became LDP. LDP could have
been used to distribute the interior label too.
Now that it is clear that MPLS will never be Multiprotocol and that the two routing protocols to
change are OSPF and ISIS, the option to distribute labels with Routing Protocol is coming back
as it would give superior performances and better convergence in some scenario where
Routing Protocols converge much faster than LDP and that user traffic is black holed during
this time.
You need to have an IPv4 MPLS backbone with LDP. RSVP can be used instead if you decide to
use PE to PE MPLS-TE which is not really scalable if you have a lot of PEs. There are many
options combining LDP and MPLS-TE with RSVP but I will not get into this here as I want to
keep it simple.
6PE configuration on CISCO routers is very straightforward. You just need to configure an IPv6
IPv6 address-family in the BGP section with the /32 IPv4 loopback address of your Route
Reflector configured as a neighbor or the other 6PE in a lab with only 2 6PEs.
Then you need to add the command “neighbor X.X.X.X send­label” and your 6PE is
configured.
Minimum back to back routers 6PE relevant Configuration:
Router A
ip cef
mpls ip
int lo0
description used for BGP peering. MUST be a /32
ip address 10.100.0.2 255.255.255.255
int Fa0/0
ip address 10.1.0.2 255.255.255.0
mpls ip
int fa0/1
ipv6 address 2001:db8:100:111::1/64
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
router bgp 100

4. neighbor 10.100.0.2 remote­as 100
neighbor 10.100.0.2 update­source lo0
address­family ipv6
neighbor 10.100.0.2 activate
neighbor 10.100.0.2 send­label
Router B
ip cef
mpls ip
int lo0
description used for BGP peering. MUST be a /32
ip address 10.100.0.1 255.255.255.255
int Fa0/0
ip addresss 10.1.0.1 255.255.255.0
mpls ip
int fa0/1
ipv6 address 2001:db8:100:112::1/64
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
router bgp 100
neighbor 10.100.0.1 remote­as 100
neighbor 10.100.0.1 update­source lo0
address­family ipv6
neighbor 10.100.0.1 activate
neighbor 10.100.0.1 send­label
3. 6VPE
The concept of VPN exists in IPv6 with the Scoped Address Architecture that we use for IPv6
Link-Local and Multicast addresses.
The Admin scope used in multicast is very similar to the concept of a VRF as you can define
random scopes where each one will have its own Routing table and Forwarding Information
base.
Also in IPv6 we already have 40 bits to keep private addresses unique with the capability to

5. record them in a central database to make sure your local address unique address. So there
is no risk of overlapping if one day you merge your IPv6 network with somebody else. Adding
another 64 bits in the MP-BGP table for the RD to make a vpnv6 address-family unique does
not help anything for IPv6!
But 6VPE idea was to add IPv6 in the VRF to have consistent dual-stacked VRFs and was
requested by customers.
Scoped Address architecture infrastructure was customized for an IPv6 VRF to be actually a
Scoped zone for IPv6. You can see this with the VRF route next-hop sitting in another zone,
the Global Routing table. It has the % sign which in IPv6 indicates a zone in an address. For
instance fe80::948:f087:2561:def0%Ethernet0 where Ethernet0 is the zone name given to
this link-local address. Microsoft Windows uses numbers to identify zones.
MPLS was supposed to be multiprotocol but even the CISCO CLI to define VRF was really
designed for IPv4, the command was “ip vrf <VRF name>” . There was no room to configure
anything else but IPv4 in the VRF. So a new command was introduced. This was “vrf

6. definition <VRF Name>”.
For instance, this is a dual stacked VRF. All the VRF will have the same RD, 10:11 while each
address-family will have its own RT policy. Here ipv6 address family import a RT, 170:200
which may be imported by all the IPv6 VRF as it may contain shared resources.
vrf definition acme
rd 10:11
address­family ipv4
route­target both 100:1
address­family ipv6
route­target export 100:1
route­target import 100:1
route­target import 170:200
You need to place a command to configure that an interface is in a VRF: “vrf forwarding
<vrf­name>”
Then the other commands still apply to MP-BGP which have to advertise IPv6 VRF Routes with
a Route Descriptor (RD) and Route-Targets (RT) Extended Community Attributes configured
for Export.
Despite the IPv6 very long address, the Route Distinguisher (RD) is still needed as there is
only one BGP table and 6VPE gives each customer the illusion to have its own dedicated
network and can apply any addressing plan even the most stupids!
MPLS-VPN was great for IPv4 as most customers were using the same private RFC1918
Addresses but in IPv6 the private addresses have 40 bits to make them unique and can be
centrally managed. So MPLS-VPN is only there to provide a consistent dual-stack environment
for customers testing.
Example of lab 6VPE related configuration basic commands. For the sake of simplicity in this
configuration the two CEs from the same VRF have different AS numbers but it is possible
with additional configuration to keep the same AS number for all the sites of the same VRF.
The egress 6VPE will replace the original AS number with twice the backbone number so the
CE will accept the BGP update. Otherwise if a BGP CE which receives a BGP update with its
own AS in it BGP would reject it as a routing loop prevention mechanism.
6VPE1
vrf definition acme
rd 10:11

7. address­family ipv6
route­target export 100:1
route­target import 100:1
!
int lo0
ip address 10.100.0.1 255.255.255.255
int fa0/0
vrf forwarding acme
ipv6 address 2001:db8:100:100::1/64
int Gig0/0
mpls ip
ip address 10.10.0.1 255.255.255.0
!
router ospf 1
network 10.0.0.0 0.255.255.255
!
router bgp 100
neighbor 10.100.0.2 remote­as 100
neighbor 10.100.0.2 update­source lo0
address­family vpnv6
neighbor 10.100.0.2 activate
neighbor 10.100.0.2 send­label
address­family ipv6 vrf acme
neighbor 2001:db8:100:100:2 remote­as 68747
neighbor 2001:db8:100:100:2 activate
redistribute connected
6VPE2
vrf definition acme
rd 11:11
!
address­family ipv6
route­target export 100:1
route­target import 100:1
!

8. int lo0
ip address 10.100.0.2 255.255.255.255
int fa0/0
vrf forwarding acme
ipv6 address 2001:db8:100:101::1/64
int Gig0/0
mpls ip
ip address 10.10.0.2 255.255.255.0
!
router ospf 1
network 10.0.0.0 0.255.255.255
!
router bgp 100
neighbor 10.100.0.1 remote­as 100
neighbor 10.100.0.1 update­source lo0
address­family vpnv6
neighbor 10.100.0.1 activate
neighbor 10.100.0.1 send­label
address­family ipv6 vrf acme
neighbor 2001:db8:100:101:2 remote­as 68748
neighbor 2001:db8:100:101:2 activate
redistribute connected
CE1
int lo0
ip address 2001:db8:100:115::1/128
int fa0/0
ipv6 address 2001:db8:100:100::2/64
ipv6 router rip fred enable
!
router bgp 68747
neighbor 2001:db8:100:100:1 remote­as 100
address­family ipv6
neighbor 2001:db8:100:100:1 activate
redistribute connected