Network Working Group Eric C. Rosen
Internet Draft Cisco Systems, Inc.
Expiration Date: December 2001
Jeremy De Clercq
Olivier Paridaens
Yves T'Joens
Alcatel
Chandru Sargor
Cosine Communications
June 2001
Use of PE-PE IPsec in RFC2547 VPNs
draft-rosen-ppvpn-ipsec-2547-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This draft describes a variation of RFC2547 [RFC2547bis] in which the
outermost MPLS label of a VPN packet is replaced with an IPsec
encapsulation. This enables the VPN packets to be carried over non-
MPLS networks, and allows the IPsec authentication and encryption
functions to be used to protect VPN packets.
Rosen, et al. [Page 1]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
Table of Contents
1 Introduction ........................................... 2
1.1 Issue: MPLS Infrastructure Required .................... 3
1.2 Issue: Protection Against Misbehavior by Transit Nodes . 4
1.3 Issue: Limitations on Multi-Provider Misconfigurations . 4
1.4 Issue: Privacy for VPN Data ............................ 5
1.5 Non-Issue: General Protection against Misconfiguration . 6
1.6 Conclusion ............................................. 6
2 Specification .......................................... 6
2.1 Technical Approach ..................................... 6
2.2 Selecting the Security Policy .......................... 7
2.3 BGP Label, Route, and Policy Distribution .............. 7
2.4 MPLS-in-IP Encapsulation by Ingress PE ................. 9
2.5 PE-PE IPsec (Application of IPsec by Ingress PE) ....... 10
2.6 Application of IPsec by Egress PE ...................... 11
3 Comparison with Using Part of SPI Field as a Label ..... 13
4 Summary for Sub-IP Area ................................ 14
4.1 Summary ................................................ 14
4.2 Where does it fit in the Picture of the Sub-IP Work .... 14
4.3 Why is it Targeted at this WG .......................... 14
4.4 Justification .......................................... 14
5 Authors' Addresses ..................................... 14
6 References ............................................. 15
1. Introduction
In "conventional" RFC2547 VPNs, when a PE router receives a packet
from a CE router, it looks up the packet's destination IP address in
a VRF. As a result of this lookup, it obtains an MPLS label stack, a
data link header, an output interface. The label stack is prepended
to the packet, the data link header is prepended to that, and the
resulting frame is queued for the output interface.
The bottom label on the MPLS label stack is always a label which will
not be seen until the packet reaches its point of egress from the
network. This label represents a particular route within the packet's
VPN. The purpose of the upper labels is to cause the packet to be
delivered to the router which understands the bottom label.
What we discuss here are procedures creating an MPLS packet which
Rosen, et al. [Page 2]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
carries ONLY the bottom label, and then using an IPsec encapsulation
to carry that MPLS packet (authenticated and/or encrypted) across the
network. That is, the upper labels are replaced with an IP header and
an IPsec header. The two endpoints of the IPsec Security Association
will be the ingress PE router and the egress PE router.
This note is inspired by [VPN-SPI], and originated as an attempt to
improve upon it.
The remainder of section 1 outlines a number of issues which can be
addressed by the use of IPsec.
1.1. Issue: MPLS Infrastructure Required
"Conventional" RFC2547 VPNs require that there be an MPLS Label
Switched Path (LSP) between a packet's ingress PE router and its
egress PE router. This means that an RFC2547 VPN cannot be
implemented if there is a part of the path between the ingress and
egress PE routers which does not support MPLS.
In order to enable RFC2547 VPNs to be deployed even when there are
non-MPLS router along the path between the ingress and egress PE
routers, it is desirable to have an alternative which allows the
upper labels to be replaced with an IP header. This encapsulating IP
header would encapsulate an MPLS packet containing only a bottom
label. The encapsulation header would have the address of the egress
PE in its destination IP address field, and this would cause the
packet to be delivered to the egress PE.
In this procedure, the ingress and egress PEs themselves must support
MPLS, but that is not an issue, as those routers must necessarily
have RFC2547 VPN support, whereas the transit routers arguably should
be able to be "vanilla" routers with no special MPLS or VPN support.
This is most likely to be of import when VPN traffic must transit
through multiple providers.
It should be noted that if the upper MPLS labels are replaced with an
unsecured IP encapsulation, it becomes more difficult to protect the
VPNs against spoofed packets. A Service Provider (SP) can protect
against spoofed MPLS packets by the simple expedient of not accepting
MPLS packets from outside its own boundaries (or more generally by
keeping track of which labels are validly received over which
interfaces, and discarding packets which arrive with labels that are
not valid for their incoming interfaces). Protection against spoofed
IP packets requires having all the boundary routers perform
filtering; either filtering out packets from "outside" which are
addressed to PE routers, or filtering out packets from "outside"
Rosen, et al. [Page 3]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
which have source addresses that belong "inside". The maintenance of
these filter lists can be management-intensive, and the their use at
all border routers can affect the performance seen by all traffic
entering the SP's network.
If an IPsec encapsulation is used, however, this filtering at the
border can be eliminated, and the spoofing protection can be managed
at the ingress and egress PE routers, transparently to the border
routers. IPsec does have its own management and performance
implications, of course.
1.2. Issue: Protection Against Misbehavior by Transit Nodes
Authentication applied by the ingress PE on a PE-to-PE basis can
protect against the misrouting or modification (intentional or
accidental) of packets by the transit nodes. Packets which get
forwarded to the "wrong" egress PE will not pass authentication, nor
will packets which have been modified. In particular, the
authentication should guarantee the integrity of whatever MPLS labels
are carried by the packet.
1.3. Issue: Limitations on Multi-Provider Misconfigurations
Sometimes a VPN will have some sites which connect to one SP (SP1),
and some other sites which connect to another SP (SP2).
Consider a case in which VPN V1 has sites attaching to SP1 and SP2,
but VPN V2 has all of its sites attaching only to SP2.
SP2 would like to ensure that nothing done by SP1 can cause V1 to get
illegitimately cross-connected to V2. Since V2 has no sites in SP1,
it should be immune to the effects of any misconfigurations within
SP1.
This assurance can be achieved if the egress PE (in SP2) can
determine, for each VPN packet, whether that packet came from SP1,
and if so, whether it carries an MPLS label which corresponds to a
VPN route that was actually distributed to SP1. (That is, packets
originating from SP1 destined for VPNs in SP2 would be checked if
they are for VPNs which really have sites in SP1.) SP2's egress PEs
could be configured with the knowledge of which VPNs have sites
attached to SP1. Cryptographic authentication could then be used to
determine that a particular packet did indeed originate in SP1.
In general, if an egress PE knows which labels may be validly applied
by which ingress PEs, IPsec authentication can be used to ensure that
Rosen, et al. [Page 4]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
a given ingress PE has not applied a label that it has no right to
use. However, the scalability of the VPN scheme would be severely
compromised if an egress PE had to distribute a different set of
labels to each ingress PE, so we will not pursue this general case,
but will only pursue label authentication in the inter-provider case.
1.4. Issue: Privacy for VPN Data
IPsec Security Associations that associate ingress PE routes with
egress PE routers do not ensure privacy for VPN data. The data is
exposed on the PE-CE access links, and is exposed in the PE routers
themselves. Complete privacy requires that the encryption/decryption
be performed within the enterprise, not by the SP. So the use of
PE-PE IPsec encryption within the network of a single SP will perhaps
be of less import than the use of IPsec authentication. On the other
hand, if an SP is trusted to properly secure its routers, but the
transmission media used by the SP are not trusted, then PE-PE
encryption does provide the necessary privacy.
There may be a need for encryption if a VPN has sites attached to
different trusted SPs, but some of the transit traffic needs to go
through the "public Internet". In this case, it may be necessary to
encrypt the VPN data traffic as it crosses the public Internet.
However, while PE-PE encryption is the one way to handle this, it is
not the only way. An alternative would be to use an encrypted tunnel
to connecting a border router of one trusted SP to a border router of
another. Then the two trusted domains could be treated as immediate
neighbors, adjacent over the tunnel. This would keep the
encryption/decryption at the few locations where it is actually
needed. On the other hand, there may be performance and scalability
advantages to spreading the cost of the cryptography among a larger
set of routers, viz., the ingress and egress PEs.
The scenario of having VPN traffic go from a trusted domain through
an untrusted domain to another trusted domain may not be completely
realistic, though, due to the difficulty of supporting the necessary
Service Level Agreements through the public Internet. (This is an
issue of some controversy.)
Rosen, et al. [Page 5]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
1.5. Non-Issue: General Protection against Misconfiguration
In general, the integrity of an RFC2547 VPN depends upon the SP
having properly configured the PE routers. There is no way of
preventing an SP from creating a bogus VPN that contains sites which
aren't supposed to communicate with each other. It is the SP's
responsibility to get this right.
It is sometimes thought one can obtain protection against
misconfigurations by having the PE routers apply cryptographic
authentication to the VPN packets. This is not the case. If an
ingress PE router has been misconfigured so as to assign a particular
site to the wrong VPN, likely as not the PE has been misconfigured to
apply that VPN's authenticator to packets to/from that site.
Protection against misconfiguration on the part of the SP requires
that the authentication procedure be applied before the ingress PE
router sees the packets, and after the egress PE router forwards
them, and cannot be dealt with by PE-PE IPsec.
1.6. Conclusion
Taken together, the above set of issues suggest that there are
situations in which using PE-PE IPsec as the tunneling protocol for
RFC2547 VPNs does have value. In the next section, we specify the
necessary procedures for incorporating PE-PE IPsec as a tunneling
option for RFC2547 VPNs.
2. Specification
2.1. Technical Approach
In short, the technical approach specified here is:
1. Continue to use MPLS to identify a VPN-IP route, by continuing
to add an MPLS label stack to the VPN packets. However, the
label stack will carry only one label, the current "bottom
label."
2. An MPLS-in-IP encapsulation will be used to turn the above MPLS
packet back into an IP packet. This in effect creates an IP
tunnel between the ingress PE router and the egress PE router.
Rosen, et al. [Page 6]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
3. IPsec Transport Mode will be used to secure the above-mentioned
IP tunnels.
The net effect is that an MPLS packet gets sent through an IPsec-
secured IP tunnel.
The following sub-sections attempt to flesh this out in more detail.
2.2. Selecting the Security Policy
One might think that a given SP (or set of cooperating SPs) will
decide either that they need to use IPsec for ALL PE-PE tunnels, or
else that PE-PE IPsec is not needed at all. But this simple "all or
nothing" strategy does not really capture the set of considerations
discussed in the Introduction. For example, a very reasonable policy
might be to use IPsec only for inter-provider PE-PE tunnels, while
using MPLS for intra-provider PE-PE tunnels. Or one might decide to
use IPsec only for certain inter-provider tunnels. Or one might
decide to use IPsec for certain intra-provider tunnels.
In an RFC2547 VPN environment, it makes most sense to place control
of the policies with the egress PE router. It is the egress PE which
needs to know that it wants to process certain packets ONLY if they
come through encrypted tunnels, and that it wants to discard those
same packets if they don't come through encrypted tunnels. This means
that we need to be able to configure a policy into the egress PE, and
have it signal that policy to the ingress PE. RFC2547 already
provides an egress-to-ingress signaling capability via BGP, and we
will specify how to extend this to the signalling of security policy.
Of course, there is nothing to stop an ingress PE router from being
configured to use IPsec even if the egress PE has not signalled its
desire for IPsec. This should work, as long as the necessary IPsec
infrastructure is in place. (However, in this sort of application
the ingress PE and the egress PE are NOT really independent entities
which might conceivably have different security policies.)
2.3. BGP Label, Route, and Policy Distribution
Distribution of labeled VPN-IP routes by BGP is done exactly as at
present, except that some additional BGP attributes are needed for
each distributed VPN-IP route.
A given egress PE will be configurable to indicate whether it expects
to receive all, some, or none of its VPN traffic through an IPsec-
secured IP tunnel. In general, an ingress PE will not have to know
Rosen, et al. [Page 7]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
in advance whether any of the egress PEs for its VPNs require their
VPN traffic to be sent through an IPsec-secured IP tunnel; this will
be signaled from the egress PE. The obvious way to do this is the
following. If an egress PE wants to receive traffic for a particular
VPN-IP route through an IPsec-secured IP tunnel, it adds a new BGP
Extended Community attribute to the route. This attribute will then
get distributed along with the route to the ingress PEs.
Let's call this attribute the "IPsec Extended Community". (It is
possible that this will actually be encoded as a particular value or
set of values of a more general "Tunnel Type Extended Community"; for
the purposes of this draft, however, we will continue to refer to it
as the "IPsec Extended Community".)
It is conceivable that an egress PE in a particular SP's network will
only want to receive IPsec-secured IP-tunneled traffic for those VPNs
which have sites that are attached to other SPs. In this case, one
would want to be able to configure, on a per-VRF basis, whether
routes exported from that VRF should have an IPsec Extended Community
attribute or not.
A more complex situation would arise if it were only desired to
receive IPsec-secured IP-tunneled traffic for a particular VPN if
that traffic has originated from a site which is attached to a
different SP's network. That is, one might want to receive inter-
provider traffic through an IPsec-secured IP tunnel, but to receive
intra-provider traffic through an unsecured MPLS LSP. As long as an
SP has a policy of never accepting MPLS packets from other SPs, this
may provide the necessary security while minimizing the amount of
cryptography that actually has to be used.
One way to do this would be to map each exportable IP address prefix
into two different VPN-IP prefixes, using two different RDs (say RD1
and RD2). Then two different RTs (say RT1 and RT2) would be used,
one of which causes intra-provider distribution, and one of which
causes inter-provider distribution. The prefixes with RD1 would be
given RT1 as a route target; the prefixes with RD2 would be given RT2
as a route target. If RT2 is the route target that causes inter-
provider distribution, then only the routes with RT2 would carry the
IPsec Extended Community.
A simpler approach, perhaps, would be to use only a single set of
VPN-IP prefixes, but to have a value of the IPsec Extended Community
which encodes an SP identifier, and which means "only use IPsec if
the ingress PE is in a different SP network than the one which is
identified here". (Again, the assumption is that MPLS packets are not
accepted from other SPs.)
Rosen, et al. [Page 8]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
It is conceivable that an egress PE will want some of its IPsec-
secured IP-tunneled VPN traffic to be encrypted, but will want some
to be authenticated and not encrypted. It is even conceivable that it
will want some traffic to arrive through an IPsec tunnel without
being either encrypted or authenticated. The IPsec Extended Community
attribute should have a value which specifies which of these are
required.
It may be desirable to allow the IPsec Extended Community to specify
a set of policies, so that the ingress PE can choose from among them.
2.4. MPLS-in-IP Encapsulation by Ingress PE
When a PE receives a packet from a CE, it looks up the packet's IP
destination address in the VRF corresponding to that CE. This enables
it to find a VPN-IP route. The VPN-IP route will have an associated
MPLS label and an associated BGP Next Hop. The label is pushed on the
packet. Then, if (and only if) the VPN-IP route has an IPsec Extended
Community attribute, an IP encapsulation header is prepended to the
packet, creating an MPLS-in-IP encapsulated packet. The IP source
address field of the encapsulation header will be an address of the
ingress PE itself. The IP destination address field of the
encapsulation header will contain the value of the associated BGP
Next Hop attribute; this will be an IP address of the egress PE.
(This description is not meant to specify an implementation strategy;
any implementation procedure which produces the same result is
acceptable.)
N.B.: If the ingress PE and the egress PE are not in the same
autonomous system, this requires that there be an EBGP connection
between a router in one autonomous system and a router in another. If
the two autonomous systems are not adjacent, this will need to be a
multi-hop EBGP connection.
The effect is to dynamically create an IP tunnel between the ingress
and egress PE routers. No apriori configuration of the remote tunnel
endpoints is needed. Note that these IP tunnels are NOT IGP-visible
links, and routing adjacencies are not supported across these tunnel.
Note also that the set of remote tunnel endpoints is NOT known in
advance, but is learned dynamically via the BGP distribution of VPN-
IP routes.
These IP tunneled packets will then be associated with an IPsec
Security Association (SA), and transported using IPsec transport
mode. This is described in more detail in the next sub-section.
Rosen, et al. [Page 9]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
2.5. PE-PE IPsec (Application of IPsec by Ingress PE)
A given ingress PE needs to have an IPsec SA with each PE router that
is an egress PE for traffic which the ingress PE receives from a CE.
In general, the set of egress PEs for a given ingress PE is not known
in advance. This is determined dynamically by the BGP distribution of
VPN-IP routes. This suggests that it will be very important to be
able to set up IPsec SAs dynamically, and that static keying will not
be a viable option. There will need to be a key distribution
infrastructure that supports multiple SPs, and IKE will need to be
used.
A number of different VPNs might need to have traffic carried from a
particular ingress PE to a particular egress PE. It is thus natural
to ask whether there should be one SA between the pair of PEs, or n
SAs between the pair of PEs, where n is the number of VPNs. Clearly,
scalability is improved by having only a single SA for each pair of
PEs. So the question is whether there is a significant security
advantage to having a distinct SA for each VPN. There does not appear
to be any such advantage. Since the SA is PE-to-PE, NOT CE-to-CE,
having a different SA for each VPN does not appear to provide any
additional protection.
It is conceivable that there might need to be two (or more) SAs
between a pair of PEs, e.g., one in which data encryption is used and
one in which authentication but not encryption is used. But this is
not the same as having a separate SA for each VPN.
We assume that the PE router will contain an IPsec module (either a
hardware or a software module) which is responsible for doing the key
exchange, for setting up the IPsec SAs as needed, and for doing the
cryptography.
As discussed in section 2.2, the PE router creates an MPLS-in-IP
encapsulated packet. It does not simply send that packet to its next
hop, rather, it delivers the packet, along with the corresponding
IPsec Extended Community value, to the IPsec module. (As an
implementation consideration, it is not really required to deliver an
MPLS-in-IP encapsulated packet to the IPsec module; all that really
needs to be delivered is the MPLS packet and the information (or
pointer thereto) that would be needed to create the IP encapsulation
header.)
The IPsec module will set up an IPsec SA to the packet's destination
address, if one does not already exist. It will then apply the
appropriate IPsec procedures, generating a packet with an IP header
followed by an IPsec header followed by an MPLS label stack followed
Rosen, et al. [Page 10]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
by the original data packet. The IPsec module then delivers this
packet, as if it were a brand new packet, to the routing module. The
routing module forwards it as an IP packet.
While the IPsec SA is being set up, packets cannot be delivered
through it. Packets may be dropped during this time, though a
sensible policy might be to queue the first packet and drop the rest
(as is commonly done in ARP implementations while awaiting an ARP
resolution).
We do assume here that the IPsec module is subsidiary to the PE
router, and does not function itself as an independent router in the
network. A solution could be designed to support the latter case, but
at a considerable increment in complexity.
The procedure as specified above requires two routing lookups. Before
IPsec processing, The original packet's destination address is looked
up in a VRF. After IPsec processing, the IPsec packet's destination
address is looked up in the default routing table. It is worth
noting that the information obtained from the second lookup is really
available at the time of the first lookup. In some environments, it
might be advantageous to forward this information, along with the
packet, to the IPsec module; possibly this can be used to avoid the
need for the second lookup. However, in some environments, it will be
impossible to avoid the second lookup.
2.6. Application of IPsec by Egress PE
We assume that every egress PE is also an ingress PE, and hence has
the IPsec module which is mentioned in section 2.2. This module will
handle the necessary IKE functions, SA and tunnel maintenance, etc.,
etc, as well as handling arriving IPsec packets. The IPsec module
will apply the necessary IPsec procedures to arriving IPsec packets,
and will hence recover the contained MPLS-in-IP packets. The IPsec
module should then strip off the encapsulating IP header to recover
the MPLS packet, and should then deliver the resulting MPLS packet to
the routing function for ordinary MPLS switching. (Of course, as an
implementation matter, there is probably no need to put the
encapsulating IP header on only to then take it off immediately.)
There are subtle issues having to do with the proper handling of MPLS
packets (rather than IPsec packets) which the PE router receives from
P routers or from other PE routers. If the top label on a received
MPLS packet corresponds to an IP route in the "default" routing
table, "ordinary" MPLS switching is done. But if the top label on a
received MPLS packet corresponds to a VPN-IP route, there are a
number of different cases to consider:
Rosen, et al. [Page 11]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
a. The packet has just been removed from an IPsec SA by the IPsec
module. In this case, ordinary MPLS switching should be done.
(Well, ... see below for further qualifications.)
b. The packet arrived from a neighboring P or PE router as an MPLS
packet, with no IPsec encapsulation. Now we have some sub-
cases:
i. The packet's top label corresponds to a VPN-IP route
which was not exported with the IPsec Extended
Community attribute. In this case, ordinary MPLS
switching is applied.
ii. The packet's top label corresponds to a VPN-IP route
which was exported with the value of the IPsec Extended
Community attribute which indicates that IPsec is to be
used only when the ingress PE is in a different SP
network. In this case, we assume that MPLS packets are
not being accepted from other networks, so ordinary
MPLS switching is applied.
iii. The packet's top label corresponds to a VPN-IP route
which was exported with an IPsec Extended Community,
but case ii does not apply. In this case the packet
should be discarded; packets with this label are
supposed to be secured, but this packet was not
properly secured.
Providing this functionality requires the use of two separate label
lookup tables, one of which is used for packets that have been
removed from IPsec SAs, and one of which is used for other packets.
Labels which are only valid when they are carried within an IPsec
packet would only appear in the former lookup table. This does imply
that after a packet has been processed by the IPsec module, the
contained MPLS packet is not simply returned to the routing lookup
path; rather it must carry some indication of which label lookup
table must be used to switch that packet. This also presupposes that
there will be MPLS VPN code to properly populate the two different
lookup tables. Perhaps packets removed from IPsec SAs should appear,
to the routing module, to be arriving on a particular virtual
interface, rather than on the actual sub-interface over which they
really arrived. Then interface-specific label lookup tables could be
used.
In fact, it may be advantageous to have more than one label lookup
table that is used for packets that have been removed from IPsec SAs.
Certain VPN-IP routes will be exported to certain SPs, but not to
others. Security can thus be improved by having one label lookup
Rosen, et al. [Page 12]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
table for each such SP. The IPsec module would then have to say, for
each packet, which SP it came from. I think that given a proper
certificate authority infrastructure this can be inferred by the
IPsec module from the information which the IKE procedure makes
available to it. For this to work, the MPLS VPN code would have to be
able to properly populate the various lookup tables.
3. Comparison with Using Part of SPI Field as a Label
An alternative methodology that achieves similar results is the one
described in [VPN-SPI]. The proposal described above was in fact
inspired by that draft, and arose as a proposed improvement to it.
In the current proposal, IPsec transport mode is applied to an MPLS-
in-IP encapsulation, where the MPLS-in-IP encapsulation carries the
BGP-distributed labels of RFC 2547. In [VPN-SPI], there is no MPLS-
in-IP encapsulation. Rather:
- IPsec tunnel mode is applied to the enduser's packet directly.
- A subfield of the IPsec SPI field is used to provide the function
of the BGP-distributed MPLS label. This either requires that BGP
distribute a different kind of label (one that can fit into the
SPI sub-field), or that an MPLS label be carried within the SPI
field.
The [VPN-SPI] proposal does have the advantage of making each packet
4 bytes shorter, since an entire entry in the MPLS label stack is
eliminated (replaced by the SPI sub-field).
The current proposal, unlike that in [VPN-SPI], does not in any way
alter the use or interpretation of the SPI field, and does not impact
the IPsec or IKE protocols and procedures in any way. The current
proposal also better preserves the distinction between fields that
are meaningful to IPsec and fields that are meaningful to
routing/forwarding. Failure to preserve this layering could
potentially lead to complications in the future (e.g., if BGP ever
needed to distribute a stack of two MPLS labels, or if some
enhancement to IPsec ever needed to reclaim the SPI sub-field used to
carry the label, etc., etc.). Keeping the MPLS VPN functionality in
the MPLS layer and out of the IPsec layer certainly seems worthwhile.
Rosen, et al. [Page 13]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
4. Summary for Sub-IP Area
4.1. Summary
The base specification for RFC2547 VPNs, i.e., draft-rosen-
rfc2547bis-03.txt, specifies the procedures for providing a
particular style of VPN, using MPLS label switched paths between
Provider Edge (PE) routers. The base specification does not discuss
other types of tunnels between PE routers.
This draft extends the base specification by specifying the
procedures for providing the RFC2547 style of VPN using IPsec tunnels
(rather than MPLS LSPs) between PE routers.
4.2. Where does it fit in the Picture of the Sub-IP Work
This work fits squarely in the PPVPN box.
4.3. Why is it Targeted at this WG
The WG is chartered with considering the RFC2547 style of VPN. This
draft specifies procedures to allow that style of VPN to run on
networks which do not implement MPLS in the core switches, and/or in
environments in which increased security is needed.
Thus the draft allows the RFC2547 style of VPN to meet additional
requirements that are not met by the base specification.
4.4. Justification
The WG should consider this document as it extends a style of VPN
explicitly called out in the charter so that (a) additional security
requirements can be met, (b) it becomes applicable to a wider range
of IP-based backbone environments.
5. Authors' Addresses
Eric C. Rosen
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA, 01824
Email: erosen@cisco.com
Rosen, et al. [Page 14]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
Jeremy De Clercq
Alcatel
Francis Wellesplein 1
2018 Antwerpen, Belgium
Phone: +32 3 240 4752
Email: jeremy.de_clercq@alcatel.be
Olivier Paridaens
Alcatel
Francis Wellesplein 1
2018 Antwerpen, Belgium
Phone: +32 3 240 9320
Email: olivier.paridaens@alcatel.be
Yves T'Joens
Alcatel
Francis Wellesplein 1
2018 Antwerpen, Belgium
Phone: +32 3 240 7890
Email: yves.tjoens@alcatel.be
Chandru Sargor
CoSine Communications
1200 Bridge Parkway
Redwood City, CA 94065
Email: csargor@cosinecom.com
6. References
[RFC2547bis] BGP/MPLS VPNs, Rosen et. al., draft-rosen-rfc2547bis-
03.txt, 2/01.
[VPN-SPI] BGP/IPsec VPN, De Clercq et. al., draft-declercq-bgp-
ipsec-vpn-01.txt, 2/01.
Rosen, et al. [Page 15]
Internet Draft draft-rosen-ppvpn-ipsec-2547-00.txt June 2001
Rosen, et al. [Page 16]