| Internet-Draft | IGP discovery for PCEP Security | August 2021 |
| Lopez, et al. | Expires 22 February 2022 | [Page] |
When a Path Computation Element (PCE) is a Label Switching Router (LSR) participating in the Interior Gateway Protocol (IGP), or even a server participating in IGP, its presence and path computation capabilities can be advertised using IGP flooding. The IGP extensions for PCE discovery (RFC 5088 and RFC 5089) define a method to advertise path computation capabilities using IGP flooding for OSPF and IS-IS respectively. However these specifications lack a method to advertise PCEP security (e.g., Transport Layer Security (TLS), TCP Authentication Option (TCP-AO)) support capability.¶
This document defines capability flag bits for PCE-CAP-FLAGS sub-TLV that can be announced as an attribute in the IGP advertisement to distribute PCEP security support information. In addition, this document updates RFC 5088 and RFC 5089 to allow advertisement of Key ID or Key Chain Name Sub-TLV to support TCP-AO security capability. RFC 8231, RFC 8306, and RFC 8623 are also updated to reflect the movement of the IANA "PCE Capability Flags" registry.¶
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This Internet-Draft will expire on 22 February 2022.¶
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
As described in [RFC5440], PCEP communication privacy is one importance issue, as an attacker that intercepts a Path Computation Element (PCE) message could obtain sensitive information related to computed paths and resources.¶
Among the possible solutions mentioned in these documents, Transport Layer Security (TLS) [RFC8446] provides support for peer authentication, and message encryption and integrity while TCP Authentication Option (TCP-AO) [RFC5925] and Cryptographic Algorithms for TCP-AO [RFC5926] offer significantly improved security for applications using TCP. As specified in section 4 of [RFC8253], in order for a Path Computation Client (PCC) to establish a connection with a PCE server using TLS or TCP-AO, PCC needs to know whether PCE server supports TLS or TCP-AO as a secure transport.¶
[RFC5088] and [RFC5089] define a method to advertise path computation capabilities using IGP flooding for OSPF and IS-IS respectively. However these specifications lack a method to advertise PCEP security (e.g., TLS) support capability.¶
This document defines capability flag bits for PCE-CAP-FLAGS sub-TLV that can be announced as attributes in the IGP advertisement to distribute PCEP security support information. In addition, this document updates RFC5088 and RFC5089 to allow advertisement of Key ID or Key Chain Name Sub-TLV to support TCP-AO security capability.¶
Note that the PCEP Open message exchange is another way to discover PCE capabilities information, but in this instance, the TCP security related key parameters need to be known before the PCEP session is established and the PCEP Open messages are exchanged. Thus, the use of the PCE discovery and capabilities advertisement of the IGP needs to be leveraged.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
[RFC5088] defines a PCE Discovery (PCED) TLV carried in an OSPF Router Information Link State Advertisement (LSA) as defined in [RFC7770] to facilitate PCE discovery using OSPF. This document defines two capability flag bits in the OSPF PCE Capability Flags to indicate TCP Authentication Option (TCP-AO) support [RFC5925][RFC5926] and PCEP over TLS support [RFC8253] respectively.¶
Similarly, [RFC5089] defines the PCED sub-TLV for use in PCE discovery using IS-IS. This document will use the same flag for the OSPF PCE Capability Flags sub-TLV to allow IS-IS to indicate TCP Authentication Option (TCP-AO) support, PCEP over TLS support respectively.¶
The IANA assignments for shared OSPF and IS-IS Security Capability Flags are documented in Section 8.1 ("OSPF PCE Capability Flags") of this document.¶
TCP-AO, PCEP over TLS support flag bits are advertised using IGP flooding.¶
If PCE supports multiple security mechanisms, it SHOULD include all corresponding flag bits in IGP advertisement.¶
If the client is restricted to a PCE server with TCP-AO support, the client MUST check if TCP-AO support flag bit in the PCE- CAP-FLAGS sub-TLV is set. If not, the client SHOULD NOT consider this PCE. If the client is restriced to a PCE server using TLS, the client MUST check if PCEP over TLS support flag bit in the PCE-CAP-FLAGS sub-TLV is set. If not, the client SHOULD NOT consider this PCE. Note that this can be overridden based on a local policy at the PCC.¶
The KEY-ID sub-TLV specifies a key that can be used by the PCC to identify the TCP-AO key [RFC5925].¶
The KEY-ID sub-TLV MAY be present in the PCED sub-TLV carried within the IS-IS Router Information Capability TLV when the capability flag bit of PCE-CAP-FLAGS sub-TLV in IS-IS is set to indicate TCP Authentication Option (TCP-AO) support. Similarly, this sub-TLV MAY be present in the PCED TLV carried within OSPF Router Information LSA when the capability flag bit of PCE-CAP-FLAGS sub-TLV in OSPF is set to indicate TCP-AO support.¶
The KEY-ID sub-TLV has the following format:¶
The KEY-CHAIN-NAME sub-TLV specifies a keychain name that can be used by the PCC to identify the keychain [RFC8177].¶
The KEY-CHAIN-NAME sub-TLV MAY be present in the PCED sub-TLV carried within the IS-IS Router Information Capability TLV when the capability flag bit of PCE-CAP-FLAGS sub-TLV in IS-IS is set to indicate TCP Authentication Option (TCP-AO) support. Similarly, this sub-TLV MAY be present in the PCED TLV carried within OSPF Router Information LSA when the capability flag bit of PCE-CAP-FLAGS sub-TLV in OSPF is set to indicate TCP-AO support.¶
The KEY-CHAIN-NAME sub-TLV has the following format:¶
Section 4 of [RFC5088] states that no new sub-TLVs will be added to the PCED TLV, and no new PCE information will be carried in the Router Information LSA. This document updates [RFC5088] by allowing the two sub-TLVs defined in this document to be carried in the PCED TLV advertised in the Router Information LSA.¶
Section 4 of [RFC5089] states that no new sub-TLVs will be added to the PCED TLV, and no new PCE information will be carried in the Router CAPABLITY TLV. This document updates [RFC5089] by allowing the two sub-TLVs defined in this document to be carried in the PCED TLV advertised in the Router CAPABILITY TLV.¶
The introduction of the additional sub-TLVs should be viewed as an exception to the [RFC5088][RFC5089] policy justified by the requirements to discover the PCEP security support prior to establishing a PCEP session. The restrictions defined in [RFC5089][RFC5089] should still be considered to be in place.¶
The registry for the PCE Capability Flags assigned in section 8.2 of [RFC8231], section 6.9 of [RFC8306], and section 11.1 of [RFC8623] has changed to the IGP Parameters "Path Computation Element (PCE) Capability Flags" registry created in this document.¶
An LSR that does not support the IGP PCE capability bits specified in this document silently ignores those bits.¶
An LSR that does not support the KEYNAME sub-TLV specified in this document silently ignores the sub-TLV.¶
IGP extensions defined in this document do not introduce any new interoperability issues.¶
A configuration option may be provided for advertising and withdrawing PCEP security capability via OSPF and IS-IS.¶
Security considerations as specified by [RFC5088] and [RFC5089] are applicable to this document.¶
The information related to PCEP security is sensitive and due care needs to be taken by the operator. This document defines new capability bits that are susceptible to a downgrade attack by toggling them. The content of Key ID or Key Chain Name Sub-TLV can be tweaked to enable a man-in-the-middle attack. Thus before advertising the PCEP security parameters, using the mechanism described in this document, the IGP MUST be known to provide authentication and integrity for the PCED TLV using the mechanisms defined in [RFC5304], [RFC5310] or [RFC5709].¶
Moreover, as stated in [RFC5088] and [RFC5089], if the IGP does not provide any encryption mechanisms to protect the secrecy of the PCED TLV, then the operator must ensure that no private data is carried in the TLV, e.g. that key-ids or key-chain names do not reveal sensitive information about the network.¶
IANA is requested to move the "PCE Capability Flags" registry from "Open Shortest Path First v2 (OSPFv2) Parameters" to under the IANA Common IGP parameters registry and allocate new bits assignments for the IGP Parameters "Path Computation Element (PCE) Capability Flags" registry.¶
Bit Meaning Reference
xx TCP-AO Support [This.I.D]
xx PCEP over TLS support [This.I.D]
¶
The registry is located at: https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml¶
The PCED sub-TLVs were defined in [RFC5088] and [RFC5089], but they did not create a registry for it. This document requests IANA to create a new subregistry called "PCED sub-TLV type indicators" under the "Interior Gateway Protocol (IGP) Parameters" registry. The registration policy for this subregistry is "IETF Review" [RFC8126]. Values in this subregistry come from the range 0-65535.¶
This subregistry should be populated with:¶
Value Description Reference
0 Reserved [This.I.D][RFC5088]
1 PCE-ADDRESS [This.I.D][RFC5088]
2 PATH-SCOPE [This.I.D][RFC5088]
3 PCE-DOMAIN [This.I.D][RFC5088]
5 PCE-CAP-FLAGS [This.I.D][RFC5088]
4 NEIG-PCE-DOMAIN [This.I.D][RFC5088]
6 KEY-ID [This.I.D]
7 KEY-CHAIN-NAME [This.I.D]
¶
This registry is located at: https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml and used by both OSPF PCED TLV and IS-IS PCED sub-TLV.¶
The authors of this document would also like to thank Acee Lindem, Julien Meuric, Les Ginsberg, Ketan Talaulikar, Yaron Sheffer, Tom Petch, Aijun Wang, Adrian Farrel for the review and comments.¶
The authors would also like to speical thank Michale Wang for his major contributions to the initial version.¶
To be compliant with Section 10.2 of RFC5440, this document doesn't consider adding capability for TCP-MD5. Therefore by default, a PCEP Speaker supports the capability for TCP-MD5 (See section 10.2, [RFC5440]). A method to advertise TCP-MD5 Capability support using IGP flooding is not required. If the client is looking for a PCE server with other Security capability support (e.g., TLS support) than TCP-MD5, the client MUST check if the corresponding flag bit in the PCE-CAP-FLAGS sub-TLV is set (See section 3.1). Irrespective of which security capability (e.g., TCP-MD5) is selected, the same key-ids or key-chain names on the PCC and PCE server should be configured.¶