1. MPLS VPN Security assessment
C. Anselme-Moizan

2. Agenda MPLS VPN technology overview security concerns what to check ?
how to check it ?
conclusion
MPLS VPN security assessment

3. MPLS VPN
we consider here L3VPN (MPLS also supports L2VPN e.g. : EoMPLS, VPLS, …)
network based VPN (vs. CE based VPN)
any to any
no ciphering
VPN depends on whole core network configuration
RFC > RFC 4364
MPLS VPN security assessment

4. MPLS VPN vs. FR full mesh
MPLS VPN security assessment

5. MPLS RFC 3031 Multi-protocol label switching
Cisco : tag-switching (TDP -> LDP)
MPLS header contains a (stack of) label(s)
no CE participates to tag/label switching
MPLS VPN security assessment

6. MPLS : label distribution (LDP)In
Tag
Prefix
Out
Iface 9
128.89 -
….. …. In
Tag
Prefix
Out
Iface 4
128.89 9 5
171.69 1 7
….. …. In
Tag
Prefix
Out
Iface -
128.89 1 4
171.69 5
….. ….
128.89
Label 9 for PE CE 1
Label 4 for
Label 5 for 1 PE P
Label 7 for
171.69 PE CE
MPLS VPN security assessment

7. MPLS : label switching (no VPN)
Tag
Prefix
Out
Iface 9
128.89 -
….. …. In
Tag
Prefix
Out
Iface 4
128.89 9 5
171.69 1 7
….. …. In
Tag
Prefix
Out
Iface -
128.89 1 4
171.69 5
….. …. CE
128.89 PE 1
data 9
data 4
data 1 PE P
data CE
171.69 PE CE
MPLS VPN security assessment

8. VRF Virtual Routing and Forwarding instance
local to the PE, it contributes to the VPN but it is not the VPN
Route Distinguisher RD (64 bits) => RD
IPV4 addresses of two VPN can overlap, VPN-IPV4 addresses are distinct
Interface to “red CE” is associated to “red VRF” :
Interface does not accept labeled packets, only IPV4
Ingress traffic is routed through the associated VRF
Egress traffic could be routed to an interface not associated with the VRF
PE interface to the CE can be considered as “VPN edge”
Using VRF, each VPN has its own routing table on PE. Now, how is the VPN built across the network ?
MPLS VPN security assessment

9. MP-iBGP Part of Multiprotocol Extensions for BGP-4 (RFC 4760)
Extension to BGP in order to advertise VPN-IPV4 routes
A MP-iBGP update contains :
VPN-IPV4 address
Standard BGP attributes (loc.prf, MED, NH, AS path..)
Site Of Origin (identifies the originating PE)
Route Target (defines route propagation across VRFs)
Route Origin (identifies the originating CE)
Associated external label (set by originating PE)
no CE participates to MPiBGP
MPLS VPN security assessment

10. VRF configuration example
VRF configuration determines :
Route distinguisher
Route Target (RT) attribute(s) to be added to route update
Route Target (RT) to import i.e. a MP-iBGP update is accepted only if RT is imported by the VRF
ip vrf I_SIMPLE320
rd 9999:
route-target import 9999:
route-target export 9999:
maximum routes !
MPLS VPN security assessment

11. VRF configuration example
RD identifies the VRF, RT identifies the VPN (simple case)
VRF name could be different on each PE, it is only a convention to have the same name
VRF of a same VPN on distant PE exchange routes using MPiBGP. Now, how is the VPN enforced in the MPLS core ?
MPLS VPN security assessment

12. MPLS/VPN 2 levels of label :
Internal label : to transport packet to egress PE in MPLS core
External label : to identify the VRF on egress PE
P routers only handle internal label, they don’t know VPNs
On Ingress PE, the VRF determines which external label has to be added to the packet, and which egress PE is targeted. According to egress PE targeted, the internal label is added above the external one on label stack.
On egress PE, internal label is discarded, external label determines by which VRF the packet must be forwarded, external label is discarded and packet is processed “by” the VRF
MPLS VPN security assessment

13. Route Reflector RFC 4456 BGP route reflection avoid peering meshing
RR knows RD, RT, but not each VRF content (VRF is local and depends on RT import in VRF) RR RR PE PE PE PE PE PE PE PE PE PE PE PE
MPLS VPN security assessment

14. Extranet Extranet is when two VPN exchange routing information
Use of route import/export between VRF
For some customers, VPN is built with several VRFs exchanging routes (to reflect customer organization)
A VRF can learn routes from another without exporting routes to this other VRF and vice versa
i.e. main customer site may know routes to each branch but each branch does not know routes to other branches
MPLS VPN security assessment

15. Admin/Service VPN
How to reach customer devices from operator’s management network without exchanging routes between customers ?
assymetric RT
Hub and spoke topology
2 types of access to such a VPN :
client : knows only routes to servers
server : knows routes to clients and servers
ip vrf I_SIMPLE320 ip vrf MGT
rd 9999: rd 9999:20001
route-target import 9999: route-target import 9999:30000
route-target import 9999: route-target export 9999:20000
route-target export 9999: maximum routes
route-target export 9999: !
maximum routes !
MPLS VPN security assessment

16. Admin/Service VPN Management 9999:30000 9999:30000 9999:20000
Red
Green
9999:0001
9999:0002
MPLS VPN security assessment

17. Import map, Export map Not all import/export are declared statically
Use of import and/or export map that define rules for setting route targets in routing updates
For example :
ip vrf I_SIMPLE320
rd 9999:
export map VPN-export
route-target import 9999:20000
route-target import 9999:
route-target export 9999:
maximum routes !
MPLS VPN security assessment

18. Import map, Export map
route-map VPN-export permit 30
match tag 9000
set community 9999:20103
set extcommunity rt 9999:30000 !
ip route vrf I_SIMPLE ATM2/0/1.271 tag 9000
Allow to choose routes that are exported to management network (not all customer addresses, only management addresses)
MPLS VPN security assessment

19. Security concerns
MPLS/VPN security is reputed to be comparable to FR/ATM security assuming that :
Attacker cannot gain access to the core
Mistakes (or unwanted changes) in configurations are avoided
a VPN configuration depends on whole network configuration (not only configuration of VRF on the access PE for that VPN)
=> to check one VPN, you must check the whole network
MPLS VPN security assessment

20. Security concerns Then, following points are mandatory :
PE and P are in operator premises and physically protected
Each node (P/PE) is protected against intrusion
Only PE and P participate in tag switching
Only PE participate in MPiBGP (no CE)
Each VPN configuration on each PE must be correct
All the above points must be regularly checked
It is important that provisioning process is fully reliable
It is important to be able to check the whole network configuration for all VPN
MPLS VPN security assessment

21. What to check about MPLS/VPN configuration ?
VPN access points
PE interfaces
VRF configuration
RD presence
RD uniqueness
Max route
VPN connectivity
RT Import/Export
Routes/VRF consistency (do we route to an interface which do not belong to the VRF ?)
Admin/Service VPN security
RT use
Routes use
Compliance with provisioning/ressource allocation
MPLS VPN security assessment

22. How to check SAFE (OBS security assessment tool) feature
Collect periodically VPN related information in all VPN aware (PE) routers configurations :
VRF name RD
RT import/export
Static
Through route-map
Interfaces in VRF
Static routes
MPLS VPN security assessment

23. How to check Get information from ressource allocation tool VRF name
VPN id (RD and main RT are built from VPN id)
Interfaces
RT import
RT export
MPLS VPN security assessment

24. How to check Store information in order to be able to :
Provide information on VPN perimeter
Provide details where problems occur
Check consistency (what is referenced is declared and vice-versa)
Check compliancy of configuration data with allocation tool data
Check service/admin RT use
Check service/admin routes use
Check RD presence and uniqueness
Check static routes/interface consistency
MPLS VPN security assessment

25. Results exploitation
Even if we keep information for each PE, results are provided for the whole VPN.
i.e. VPN A export to VPN B means that there is at least one PE where VRF A exports at least one route with a route target imported by VRF B on at least one PE. This does not mean that all routes known in VPN A are known in VPN B.
Results are provided by VPN
Two type of results :
Obvious errors don’t depend on customer VPN architecture : ex: RD uniqueness, admin/service routes/RT use
VPN perimeter problem : noncompliance with allocation tool
Tool provides statistics
MPLS VPN security assessment

26. Results exploitation Who may use the tool ? Depends on error type
Backbone ops : operate the backbone (PE and P global configuration)
VPN owner : is responsible for one (or more) VPN (Customer access
Depends on error type
Obvious errors :
Can be identified by backbone ops
All obvious errors are reported in dashboards (excel files)
May require VPN owner action/validation
VPN perimeter problem :
can only be confirmed by VPN owner (knowledge of customer VPN architecture is needed)
MPLS VPN security assessment

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31. Conclusion A tool to keep an eye on VPN configurations
Other tools may also contribute (production tools, routing supervision tools)
But tool does not all the job, it is part of a whole set of security actions :
provisioning tools are designed to minimize errors in configurations
VPN owner checks his VPN perimeter (using his knowledge of customer network architecture)
Network architects follow design rules (no CE involved in MPi-BGP, no PE out of AS)
Backbone operators enforce PE and P protection against intrusion and check configurations for this protection periodically (also automated with a tool)
MPLS VPN security assessment