| Network Working Group | M. Boucadair |
| Internet-Draft | C. Jacquenet |
| Intended status: Standards Track | France Telecom |
| Expires: December 30, 2013 | R. Parker |
| Affirmed Networks | |
| D. R. Lopez | |
| Telefonica I+D | |
| P. Yegani | |
| Juniper Networks | |
| June 28, 2013 |
Differentiated Network-Located Function Chaining Framework
draft-boucadair-network-function-chaining-01
IP networks rely more and more on the combination of advanced functions (besides the basic routing and forwarding functions). This document defines a solution to enforce Network-Located Function Chaining (NLFC) with minimum requirements on the underlying network.
The proposed solution allows for Differentiated Forwarding (DiffForward): packets are classified at the entry point of an NLFC-enabled network, and are then forwarded on a per NLFC map basis.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on December 30, 2013.
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IP networks rely more and more on the combination of advanced functions (besides the basic routing and forwarding functions). Typical examples of such functions include firewall (e.g., [RFC6092]), DPI (Deep Packet Inspection), LI (Lawful Intercept) module, NAT44 [RFC3022], NAT64 [RFC6146], DS-Lite AFTR [RFC6333], NPTv6 [RFC6296], HOST_ID injection, HTTP Header Enrichment function, TCP tweaking and optimization functions, transparent caching, charging function, load-balancer, etc.
Such advanced functions are denoted NLF (Network-Located Function) in this document.
The major concern is how to provide differentiated forwarding for packets entering a network enabling advanced network functions. Differentiation is ensured by tweaking the set of network functions to be invoked. How to bind a packet to a forwarding plane is policy-based.
This document defines a framework to enforce Network-Located Function Chaining (NLFC) with minimum requirements on the underlying network. The proposed solution allows for Differentiated Forwarding (DiffForward): packets are classified at the entry point of an NLFC-enabled network, and are then forwarded on a per NLFC map basis.
This document does not make any assumption on the deployment context. The proposed framework covers both fixed and mobile networks (e.g., to rationalize the proliferation of advanced features at the Gi Interface [RFC6459]).
The main objectives of the proposed framework are as follows:
The following assumptions are made:
Given the assumptions listed in Section 1.4, the rationale of the framework is as follows:
This document makes use of the following terms:
The administrative entity that operates a NLFC-enabled domain maintains a local repository that lists the enabled NLFs. This administrative entity assigns a unique NLF identifier for each NLF.
NLF identifiers can be structured as strings or any other format. The main constraint on the format is that two NLFs MUST be assigned with different identifiers. NLF identifiers are case-sensitive.
A NLF may be embedded in one or several NLF Nodes. The NLF locator is typically the IP address or the FQDN to reach a given NLF Node.
The use of an IP address is RECOMMENDED to ovoid overloading NLF Nodes with name resolution capabilities. Resolution capabilities (together with advanced traffic engineering functions) are supported by the PDP (Policy Decision Point). In the rest of the document, we assume a NLF locator is structured as an IP address (IPv4 or IPv6).
A NLF can be multi-instantiated; as such one or more locators may be bound to the same NLF.
Added-value services delivered to end-user rely on the invocation of several NLFs. For each of these services, the administrative entity that operates an NLFC-enabled domain builds one or several NLFC Maps. Each of these maps characterizes the list of NLFs to be invoked with their exact invocation order.
Each NLFC Map is unambiguously identified with a unique identifier called NLFC Map Index. The NLFC Map Index MUST be expressible as an unsigned integer.
Distinct chains can be applied for inbound and outbound traffic. The direction of the traffic is not included as an attribute of the NLFC Map, but directionality may be implemented using two chains: i.e., two NLFC Maps are installed in the NLFC Policy Table. In such case, incoming packets are marked with Index_1 while outgoing packets will be forwarded according to a distinct NLFC Map identified with Index_2.
An example of NLFC Map to handle IPv6 traffic destined to an IPv4 remote server is defined as follows:
To handle incoming packets destined to the same IPv6 host, the following NLFC Map can be defined:
A PDP (Policy Decision Point, [RFC2753]) is the central entity which is responsible for maintaining NLFC Policy Tables, and enforcing appropriate policies in NLF Nodes and NLFC Boundary Nodes (see Figure 1). Policy enforcement can be achieved using a variety of protocols (e.g., NETCONF [RFC6241]).
One or multiple NLFC-enabled domains may be under the responsibility of the same PDP. Delimiting the scope of each NLFC-enabled domain is under the responsibility of the administrative entity operating the network.
o . . . . . . . . . . . . . . . . . . . . . . . o . NLFC Policy Enforcement . . +-------+ . . | |-----------------+ . . +-------| PDP | | . . | | |-------+ | . . | +-------+ | | . o . . | . . . . . | . . . . . | . . . . | . . . o o . . | . . . . . | . . . . . | . . . . | . . . o . | | | | . . v v v v . . +---------+ +---------+ +-------+ +-------+ . . |NLFC_BN_1| |NLFC_BN_n| | NLF_1 | | NLF_m | . . +---------+ +---------+ +-------+ +-------+ . . NLFC-enabled Domain . o . . . . . . . . . . . . . . . . . . . . . . . o
Figure 1: NLFC Policy Enforcement
The NLF Node MUST be provisioned with the following information:
Likewise, the NLFC Boundary Node MUST be provisioned with the following information:
In addition to the NLFC Policy Table, other NLF-specific policies can be installed by the PDP (e.g., configure distinct users profiles).
Policies managed and stored by the PDP may be configured to the PDP manually or be triggered by dynamic means (e.g., AAA).
In the event of any update (e.g., define a new NLFC Map, delete an NLFC Map, add a new NLF Locator, update classification policy), the PDP MUST enforce the updated policy configuration in all NLF Nodes and NLFC Boundary Nodes.
Load-balancing among several NLF Nodes supporting the same NLF can be driven by the PDP. Indeed, the PDP can generate multiple classification rules and NLFC Maps to meet load-balancing objectives.
The processing of packets by the nodes that belong to a NLFC-enabled domain does not necessarily require any interaction with the PDP, depending on the nature of the NLF supported by the nodes and the corresponding policies to be enforced. For example, traffic conditioning capabilities [RFC2475] are typical NLF functions that may require additional solicitation to the PDP for the NLF node to decide what to do with some out-of-profile traffic.
The behavior of each node of a NLFC-enabled domain is specified in the following sections. We assume that the provisioning operations discussed in Section 3 have succeeded.
NLFC Boundary Nodes act both as a NLFC Ingress Node and as a NLFC Egress Node for the respective directions of the traffic.
Traffic enters a NLFC-enabled domain at a NLFC Ingress Node (Section 4.3) and exists the domain at a NLFC Egress Node (Section 4.4).
The NLFC Classifier classifies packets based on (some of) the contents of the packet header. Concretely, it classifies packets based on the value of a combination of one or more header fields, such as source address, destination address, DS field, protocol ID, source port and destination port numbers, and any other information.
Each NLFC Map Classification Rule MUST be bound to one single NLFC Map (i.e., the classification rule must include only one NLFC Map Index).
When a packet is received through an interface of the NLFC Ingress Node that connects to the outside of the NLFC domain, the Ingress Node MUST:
As a result of this process, the packet will be sent to an NLF Node or an Intermediate Node.
When a packet is received through an interface that connects the NLFC Egress Node to its NLFC domain, the Egress Node MUST:
This section assumes the NLF Nodes does not embed a Classifier as discussed in Section 6.3.
When a packet is received by a NLF Node, the latter MUST:
An Intermediate Node is any node that does not support any NLF function and which is located within a NLFC-enabled domain.
No modification is required to intermediate nodes to handle incoming packets. In particular, routing and forwarding are achieved using legacy procedures.
This section discusses two main protocol issues to be handled in order to deploy DiffForward.
A NLFC Map Index is an integer that points to a NLFC Map.
In order to avoid all nodes of a NLFC-enabled domain to be NLF-aware, this specification recommends to undertake classifiers at boundary nodes while intermediate nodes forward the packets according to the NLFC Map Index conveyed in the packet (NLF Node) or according to typical forwarding policies (any NLF-unaware node).
An 8-bit field would be sufficient to accommodate deployment contexts with reasonable set of NLFC Maps. A 16-bit (or 32-bit) field would provide a comfortable solution (e.g., to accommodate the requirement discussed in Section 6.2).
Instead of injecting a Map Index, an alternate solution would be to use SSR IP option or any similar solution to indicate a loose or strict explicit route. This alternative was not considered because of the negative impact on the processing and potential fragmentation issues.
Injecting an 8-bit or even 16-bit field would minimize fragmentation issues.
NLFC Map Indexes can be conveyed in various locations of a packet:
A NLFC Ingress Node or an NLF Node MUST be able to forward a packet matching an existing NLFC Map to a NLF Node. The locator of the next NLF is retrieved from the NLFC Policy Table. In case the next NLF Node in the list is not an immediate neighbor, a solution to force the packet to cross that NLF Node MUST be supported. This document suggests the use of IP-in-IP encapsulation scheme. Other tunneling solutions can be considered in the future.
The following deployment considerations should be taken into account:
Some NLFs may be provisioned with a set of local differentiated policies (denoted as profiles). For example, an NLF realizing DPI may be configured to block Peer-to-Peer protocols for some group of users while authorize it for another group of users.
The profile selection policy can be local to a NLF or be controlled by the PDP. In the latter case, distinct NLF identifiers can be assigned for each profile. Doing so, the PDP conveys to the NLF the profile to be enforced for received traffic.
If NLF Nodes are also configured to behave as Classifiers, NLFC Map Index is not required to be explicitly signalled in each packet. Concretely, the NLFC Policy Table configured to the NLF Node includes also classification rules. These classification rules are enforced to determine whether the local NLF must be involved. If an incoming packet matches at least one classification rule pointing to an NLFC Map in which the NLF Identifier is listed, the NLF Node retrieves the next hop NLF from the NLF Map indicated in the classification rule, the packet is handled by the local NLF, and then the NLF Node forwards the packet to the next hop NLF. If not, the packet is forwarded to the next hop following legacy forwarding behavior.
Let consider the example shown in Figure 2. The local NLF Node embeds NLFa. After checking the classification rules and the NLFC Maps, the NLF Node concludes NLFa must be invoked only when a packet matches Rule 1 and Rule 3. If a packet matches Rule 1, the next NLF is NLFc. If a packet matches Rule 3, the next NLF is NLFh.
+-----------------------------------------------+
| NLFC Policy Table |
+-----------------------------------------------+
|Local NLF Identifier: NLFa |
+-----------------------------------------------+
|Classification Rules |
| Rule 1: If DEST=IP1; then NLFC_MAP_INDEX1 |
| Rule 2: If DEST=IP2; then NLFC_MAP_INDEX2 |
| Rule 3: IF DEST=IP3; then NLFC_MAP_INDEX3 |
+-----------------------------------------------+
|NLFC Maps |
| {NLFC_MAP_INDEX1, {NLFa, NLFc} |
| {NLFC_MAP_INDEX2, {NLFd, NLFb} |
| {NLFC_MAP_INDEX3, {NLFa, NLFh} |
+-----------------------------------------------+
Figure 2
NLF Nodes may be enabled in a NLFC-enabled domain so that each of them has a direct adjacency with other NLF Nodes. In such configuration, no additional encapsulation scheme is needed to exchange traffic between these nodes.
NLF Nodes use the NLFC Policy Table to detect whether the local NLF was already applied for the received packet (i.e., detect NLF Loop). The NLF Node MUST invoke the local NLF only if the packet is received from a NLFC Boundary Node or a NLF Node having an identifier listed before the local NLF in the NLF Map matched by the packet. NLF Loop detection SHOULD be a configurable feature.
Figure 3 shows an example of a NLFC Policy Table of a NLF Node embedding NLFa. If we consider a packet, received from Locb, matches Rule 2. NLFa must not be invoked because NLFb is listed after NLFa (see the NLFC Map list). That packet will be forwarded without invoking NLFa.
+-----------------------------------------------+
| NLFC Policy Table |
+-----------------------------------------------+
|Local NLF Identifier: NLFa |
+-----------------------------------------------+
|NLFC Maps |
| {NLFC_MAP_INDEX1, {NLFa, NLFc} |
| {NLFC_MAP_INDEX2, {NLFd, NLFa, NLFb, NLFh} |
+-----------------------------------------------+
|NLFC Locators |
| Locator_NLFb: Locb |
| Locator_NLFc: Locc |
| Locator_NLFd: Locd |
| Locator_NLFh: Loch |
+-----------------------------------------------+
Figure 3
The support of this feature is OPTIONAL.
If NLF loop detection is not activated in an NLFC-enabled domain, the PDP may provision to underlying nodes a lite NLFC Policy Table. Lite NLFC Policy Table is a subset of the full NLFC Policy Table which includes:
An example of lite NLFC Policy Table is shown in Figure 4.
+-----------------------------------------------+ | NLFC Policy Table | +-----------------------------------------------+ |Local NLF Identifier: NLFa | +-----------------------------------------------+ |Lite NLFC Maps | | NLFC_MAP_INDEX1, Next_Hop_NLF = NLFc | | NLFC_MAP_INDEX2, Next_Hop_NLF = NLFb | +-----------------------------------------------+ |NLFC Locators | | Locator_NLFb: Locb | | Locator_NLFc: Locc | +-----------------------------------------------+
Figure 4
Determination by the PDP of liveness of each NLF in the service chain provides a number of benefits. These include:
In order to determine liveness of any particular NLF Node, standard protocols such as ICMP or BFD (both single-hop [RFC5881] and multi-hop [RFC5883]) may be utilized between the PDP and the NLF Nodes.
For more sophisticated load-balancing support, protocols that allow for both liveness determination and the transfer of application-specific data, such as SNMP and NETCONF may be utilized between the PDP and the NLF Nodes.
The support of this feature is OPTIONAL.
Required IANA actions will be discussed in future version of the document.
Means to defend NLFC Boundary Nodes and NLF Nodes against broken NLFC Policy Table MUST be enabled. For example, authenticated means are to be used between a PDP and the underlying NLFC elements.
NLFC Boundary Nodes MUST strip any existing NLFC Map Index when handling an incoming packet. A list of authorized NLFC Map Indexes are configured to the underlying NLFC elements.
NETCONF-related security considerations are discussed in [RFC6146].
Means to defend against denial-of-service must be supported. Means to prevent NLF loops should be supported.
Nodes involved in the same NLFC-enabled domain MUST be provisioned with the same NLFC Policy Table. Inconsistencies in this tables will result in forwarding mis-behavior.
Many thanks to D. Abgrall, D. Minodier, Y. Le Le Goff, and D. Cheng for their review and comments.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC6241] | Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011. |