draft-ietf-idr-flow-spec-09.txt		rfc5575.txt
	IDR Working Group P. Marques
	Internet-Draft N. Sheth
	Intended status: Standards Track R. Raszuk
	Expires: November 27, 2009 B. Greene
	Juniper Networks
	J. Mauch
	NTT America
	D. McPherson
	Arbor Networks
	May 26, 2009
	Dissemination of flow specification rules
	draft-ietf-idr-flow-spec-09
	Status of this Memo
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	Abstract
	This document defines a new BGP NLRI encoding format that can be used
	to distribute traffic flow specifications. This allows the routing
	system to propagate information regarding more-specific components of
	the traffic aggregate defined by an IP destination prefix.
	Additionally it defines two applications of that encoding format.
	One that can be used to automate inter-domain coordination of traffic
	filtering, such as what is required in order to mitigate
	(distributed) denial of service attacks. And a second application to
	traffic filtering in the context of a BGP/MPLS VPN service.
	The information is carried via the Border Gateway Protocol (BGP),
	thereby reusing protocol algorithms, operational experience and
	administrative processes such as inter-provider peering agreements.
	Table of Contents
	1. Definitions of Terms Used in this Memo . . . . . . . . . . . . 4
	2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Flow specifications . . . . . . . . . . . . . . . . . . . . . 6
	4. Dissemination of Information . . . . . . . . . . . . . . . . . 7
	5. Traffic filtering . . . . . . . . . . . . . . . . . . . . . . 13
	5.1. Order of traffic filtering rules . . . . . . . . . . . . . 14
	6. Validation procedure . . . . . . . . . . . . . . . . . . . . . 15
	7. Traffic Filtering Actions . . . . . . . . . . . . . . . . . . 16
	8. Traffic filtering in RFC2547bis networks . . . . . . . . . . . 18
	9. Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . 19
	10. Security considerations . . . . . . . . . . . . . . . . . . . 19
	11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
	12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
	13. Normative References . . . . . . . . . . . . . . . . . . . . . 22
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
	1. Definitions of Terms Used in this Memo
	NLRI - Network Layer Reachability Information
	RIB - Routing Information Base
	Loc-RIB - Local RIB
	AS - Autonomous System Number
	VRF - Virtual Routing and Forwarding instance
	PE - Provider Edge router
	2. Introduction
	Modern IP routers contain both the capability to forward traffic
	according to IP prefixes as well as to classify, shape, rate limit,
	filter or redirect packets based on administratively defined
	policies.
	These traffic policy mechanisms allow the router to define match
	rules that operate on multiple fields of the packet header. Actions
	such as the ones described above can be associated with each rule.
	The n-tuple consisting of the matching criteria defines an aggregate
	traffic flow specification. The matching criteria can include
	elements such as source and destination address prefixes, IP protocol
	and transport protocol port numbers.
	This document defines a general procedure to encode flow
	specification rules for aggregated traffic flows so that they can be
	distributed as a BGP [RFC4271] NLRI. Additionally, we define the
	required mechanisms to utilize this definition to the problem of
	immediate concern to the authors: intra and inter provider
	distribution of traffic filtering rules to filter (Distributed)
	Denial of Service (DoS) attacks.
	By expanding routing information with flow specifications, the
	routing system can take advantage of the ACL/firewall capabilities in
	the router's forwarding path. Flow specifications can be seen as
	more specific routing entries to an unicast prefix and are expected
	to depend upon the existing unicast data information.
	A flow specification received from an external autonomous-system will
	need to be validated against unicast routing before being accepted.
	If the aggregate traffic flow defined by the unicast destination
	prefix is forwarded to a given BGP peer, then the local system can
	safely install more specific flow rules which may result in different
	forwarding behavior, as requested by this system.
	The key technology components required to address the class of
	problems targeted by this document are:
	1. Efficient point to multi-point distribution of control plane
	information.
	2. Inter-domain capabilities and routing policy support.
	3. Tight integration with unicast routing, for verification
	purposes.
	Items 1 and 2 have already been addressed using BGP for other types
	of control plane information. Close integration with BGP also makes
	it feasible to specific a mechanism to automatically verify flow
	information against unicast routing. These factors are behind the
	choice of BGP as the carrier of flow specification information.
	As with previous extensions to the BGP protocol, this specification
	makes it possible to add additional information to Internet routers.
	These are limited in terms of the maximum number of data elements
	they can hold as well as the number of events they are able to
	process in a given unit of time. The authors believe that, as with
	previous extensions, service providers will be careful to keep
	information levels bellow the maximum capacity of their devices.
	It is also expected that in many initial deployments flow
	specification information will replace existing host length route
	advertisements rather than add additional information.
	Experience with previous BGP extensions has also shown that the
	maximum capacity of BGP speakers has been gradually increased
	according to expected loads. Taking into account Internet unicast
	routing as well as additional applications as they gain popularity.
	From an operational perspective, the utilization of BGP as the
	carrier for this information allows a network service provider to
	reuse both internal route distribution infrastructure (e.g.: route
	reflector or confederation design) and existing external
	relationships (e.g.: inter-domain BGP sessions to a customer
	network).
	While it is certainly possible to address this problem using other
	mechanisms, the authors believe that this solution offers the
	substantial advantage of being an incremental addition to already
	deployed mechanisms.
	In current deployments, the information distributed by the flow-spec
	extension is originated both manually as well as automatically. The
	latter by systems which are able to detect malicious flows. When
	automated systems are used care should be taken to ensure their
	correctness as well as to limit the number and advertisement rate of
	flow routes.
	This specification defines required protocol extensions to address
	most common applications of IPv4 unicast and VPNv4 unicast filtering.
	The same mechanism can be reused and new match criteria added to
	address similar filtering needs for other BGP address families (for
	example IPv6 unicast). Authors believe that those would be best to
	be addressed in a separate document.
	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].
	3. Flow specifications
	A flow specification is an n-tuple consisting of several matching
	criteria that can be applied to IP traffic. A given IP packet is
	said to match the defined flow if it matches all the specified
	criteria.
	A given flow may be associated with a set of attributes, depending on
	the particular application, such attributes may or may not include
	reachability information (i.e. NEXT_HOP). Well-known or AS-specific
	community attributes can be used to encode a set of predetermined
	actions.
	A particular application is identified by a specific (AFI, SAFI) pair
	[RFC4760] and corresponds to a distinct set of RIBs. Those RIBs
	should be treated independently from each other in order to assure
	non-interference between distinct applications.
	BGP itself treats the NLRI as an opaque key to an entry in its
	databases. Entries that are placed in the Loc-RIB are then
	associated with a given set of semantics which is application
	dependent. This is consistent with existing BGP applications. For
	instance IP unicast routing (AFI=1, SAFI=1) and IP multicast reverse-
	path information (AFI=1, SAFI=2) are handled by BGP without any
	particular semantics being associated with them until installed in
	the Loc-RIB.
	Standard BGP policy mechanisms, such as UPDATE filtering by NLRI
	prefix and community matching, SHOULD apply to the newly defined
	NLRI-type. Network operators can also control propagation of such
	routing updates by enabling or disabling the exchange of a particular
	(AFI, SAFI) pair on a given BGP peering session.
	4. Dissemination of Information
	We define a "Flow Specification" NLRI type that may include several
	components such as destination prefix, source prefix, protocol,
	ports, etc. This NLRI is treated as an opaque bit string prefix by
	BGP. Each bit string identifies a key to a database entry which a
	set of attributes can be associated with.
	This NLRI information is encoded using MP_REACH_NLRI and
	MP_UNREACH_NLRI attributes as defined in RFC4760 [RFC4760]. Whenever
	the corresponding application does not require Next Hop information,
	this shall be encoded as a 0 octet length Next Hop in the
	MP_REACH_NLRI attribute and ignored on receipt.
	The NLRI field of the MP_REACH_NLRI and MP_UNREACH_NLRI is encoded as
	a 1 or 2 octet NLRI length field followed by a variable length NLRI
	value. The NLRI length is expressed in octets.
	+------------------------------+
	| length (0xnn or 0xfn nn) |
	+------------------------------+
	| NLRI value (variable) |
	+------------------------------+
	flow-spec NLRI
	If the NLRI length value is smaller than 240 (0xf0 hex), the length
	field can be encoded as a single octet. Otherwise, it is encoded as
	a extended length 2 octet value in which the most significant nibble
	of the first byte is all ones.
	The Flow Specification NLRI-type consists of several optional
	subcomponents. A specific packet is considered to match the flow
	specification when it matches the intersection (AND) of all the
	components present in the specification.
	The following component types are defined:
	Type 1 - Destination Prefix
	Encoding: <type (1 octet), prefix length (1 octet), prefix>
	Defines the destination prefix to match. Prefixes are encoded
	as in BGP UPDATE messages, a length in bits is followed by
	enough octets to contain the prefix information.
	Type 2 - Source Prefix
	Encoding: <type (1 octet), prefix-length (1 octet), prefix>
	Defines the source prefix to match.
	Type 3 - IP Protocol
	Encoding: <type (1 octet), [op, value]+>
	Contains a set of {operator, value} pairs that are used to
	match IP protocol value byte in IP packets.
	The operator byte is encoded as:
	0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+
	| e | a | len | 0 |lt |gt |eq |
	+---+---+---+---+---+---+---+---+
	Numeric operator
	* End of List bit. Set in the last {op, value} pair in the list.
	* AND bit. If unset the previous term is logically ORed with the
	current one. If set the operation is a logical AND. It should
	be unset in the first operator byte of a sequence. The AND
	operator has higher priority than OR for the purposes of
	evaluating logical expressions.
	* The length of value field for this operand is given as (1 <<
	len).
	* Lt - less than comparison between data and value.
	* gt - greater than comparison between data and value.
	* eq - equality between data and value.
	* The bits lt, gt, and eq can be combined to produce "less or
	equal", "greater or equal" and inequality values.
	Type 4 - Port
	Encoding: <type (1 octet), [op, value]+>
	Defines a list of {operation, value} pairs that matches source
	OR destination TCP/UDP ports. This list is encoded using the
	numeric operand format defined above. Values are encoded as 1
	or 2 byte quantities.
	Port, source port and destination port components evaluate to
	FALSE if the IP protocol field of the packet has a value other
	than TCP or UDP, if the packet is fragmented and this is not
	the first fragment or if the system in unable to locate the
	transport header. Different implementations may or may not be
	able to decode the transport header in the presence of IP
	options or ESP NULL [RFC4303] encryption.
	Type 5 - Destination port
	Encoding: <type (1 octet), [op, value]+>
	Defines a list of {operation, value} pairs used to match the
	destination port of a TCP or UDP packet. Values are encoded as
	1 or 2 byte quantities.
	Type 6 - Source port
	Encoding: <type (1 octet), [op, value]+>
	Defines a list of {operation, value} pairs used to match the
	source port of a TCP or UDP packet. Values are encoded as 1 or
	2 byte quantities.
	Type 7 - ICMP type
	Encoding: <type (1 octet), [op, value]+>
	Defines a list of {operation, value} pairs used to match the
	type field of an icmp packet. Values are encoded using a
	single byte.
	The ICMP type and code specifiers evaluate to FALSE whenever
	the protocol value is not ICMP
	Type 8 - ICMP code
	Encoding: <type (1 octet), [op, value]+>
	Defines a list of {operation, value} pairs used to match the
	code field of an icmp packet. Values are encoded using a
	single byte.
	Type 9 - TCP flags
	Encoding: <type (1 octet), [op, bitmask]+>
	Bitmask values can be encoded as a one or two byte bitmask.
	When a single byte is specified it matches byte 13 of the TCP
	header [RFC0793] which contains bits 8 though 15 of the 4th
	32bit word. When a 2 byte encoding is used it matches bytes 12
	and 13 of the TCP header with the data offset field having a
	"don't care" value.
	As with port specifiers, this component evaluates to FALSE for
	packets that are not TCP packets.
	This type uses the bitmask operand format, which differs from
	the numeric operator format in the lower nibble.
	0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+
	| e | a | len | 0 | 0 |not| m |
	+---+---+---+---+---+---+---+---+
	* Most significant nibble: (End of List bit, AND bit and Length
	field), as defined for in the numeric operator format.
	* NOT bit. If set, logical negation of operation.
	* Match bit. If set this is a bitwise match operation defined as
	"(data & value) == value"; if unset (data & value) evaluates to
	true if any of the bits in the value mask are set in the data.
	Type 10 - Packet length
	Encoding: <type (1 octet), [op, value]+>
	Match on the total IP packet length (excluding L2 but including
	IP header). Values are encoded using as 1 or 2 byte
	quantities.
	Type 11 - DSCP
	Encoding: <type (1 octet), [op, value]+>
	Defines a list of {operation, value} pairs used to match the
	6-bit DSCP field [RFC2474]. Values are encoded using a single
	byte, where the two most significant bits are zero and the six
	least significant bits contain the DSCP value.
	Type 12 - Fragment
	Encoding: <type (1 octet), [op, bitmask]+>
	Uses bitmask operand format defined above.
	0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+
	| Reserved |LF |FF |IsF|DF |
	+---+---+---+---+---+---+---+---+
	Bitmask values:
	+ Bit 7 - Dont fragment
	+ Bit 6 - Is a fragment
	+ Bit 5 - First fragment
	+ Bit 4 - Last fragment
	Flow specification components must follow strict type ordering. A
	given component type may or may not be present in the specification,
	but if present it MUST precede any component of higher numeric type
	value.
	If a given component type within a prefix in unknown, the prefix in
	question cannot be used for traffic filtering purposes by the
	receiver. Since a Flow Specification has the semantics of a logical
	AND of all components, if a component is FALSE by definition it
	cannot be applied. However for the purposes of BGP route propagation
	this prefix should still be transmitted since BGP route distribution
	is independent on NLRI semantics.
	The <type, value> encoding is chosen in order to account for future
	extensibility.
	An example of a Flow Specification encoding for: "all packets to
	10.0.1/24 and TCP port 25".
	+------------------+----------+----------+
	| destination | proto | port |
	+------------------+----------+----------+
	| 0x01 18 0a 00 01 | 03 81 06 | 04 81 19 |
	+------------------+----------+----------+
	Decode for protocol:
	+-------+----------+------------------------------+
	| Value | | |
	+-------+----------+------------------------------+
	| 0x03 | type | |
	| 0x81 | operator | end-of-list, value size=1, = |
	| 0x06 | value | |
	+-------+----------+------------------------------+
	An example of a Flow Specification encoding for: "all packets to
	10.0.1/24 from 192/8 and port {range [137, 139] or 8080}".
	+------------------+----------+-------------------------+
	| destination | source | port |
	+------------------+----------+-------------------------+
	| 0x01 18 0a 01 01 | 02 08 c0 | 04 03 89 45 8b 91 1f 90 |
	+------------------+----------+-------------------------+
	Decode for port:
	+--------+----------+------------------------------+
	| Value | | |
	+--------+----------+------------------------------+
	| 0x04 | type | |
	| 0x03 | operator | size=1, >= |
	| 0x89 | value | 137 |
	| 0x45 | operator | &, value size=1, <= |
	| 0x8b | value | 139 |
	| 0x91 | operator | end-of-list, value-size=2, = |
	| 0x1f90 | value | 8080 |
	+--------+----------+------------------------------+
	This constitutes a NLRI with an NLRI length of 16 octets.
	Implementations wishing to exchange flow specification rules MUST use
	BGP's Capability Advertisement facility to exchange the Multiprotocol
	Extension Capability Code (Code 1) as defined in RFC4760 [RFC4760].
	The (AFI, SAFI) pair carried in the Multiprotocol Extension
	capability MUST be the same as the one used to identify a particular
	application that uses this NLRI-type.
	5. Traffic filtering
	Traffic filtering policies have been traditionally considered to be
	relatively static.
	The popularity of traffic-based denial of service (DoS) attacks,
	which often requires the network operator to be able to use traffic
	filters for detection and mitigation, brings with it requirements
	that are not fully satisfied by existing tools.
	Increasingly, DoS mitigation, requires coordination among several
	Service Providers, in order to be able to identify traffic source(s)
	and because the volumes of traffic may be such that they will
	otherwise significantly affect the performance of the network.
	Several techniques are currently used to control traffic filtering of
	DoS attacks. Among those, one of the most common is to inject
	unicast route advertisements corresponding to a destination prefix
	being attacked. One variant of this technique marks such route
	advertisements with a community that gets translated into a discard
	next-hop by the receiving router. Other variants, attract traffic to
	a particular node that serves as a deterministic drop point.
	Using unicast routing advertisements to distribute traffic filtering
	information has the advantage of using the existing infrastructure
	and inter-as communication channels. This can allow, for instance, a
	service provider to accept filtering requests from customers for
	address space they own.
	There are several drawbacks, however. An issue that is immediately
	apparent is the granularity of filtering control: only destination
	prefixes may be specified. Another area of concern is the fact that
	filtering information is intermingled with routing information.
	The mechanism defined in this document is designed to address these
	limitations. We use the flow specification NLRI defined above to
	convey information about traffic filtering rules for traffic that
	should be discarded.
	This mechanism is primarily designed to allow an upstream autonomous
	system to perform inbound filtering, in their ingress routers of
	traffic that a given downstream AS wishes to drop.
	In order to achieve this goal, we define an application specific NLRI
	identifier (AFI=1, SAFI=133) along with specific semantic rules.
	BGP routing updates containing this identifier use the flow
	specification NLRI encoding to convey particular aggregated flows
	that require special treatment.
	Flow routing information received via this (afi, safi) pair is
	subject to the validation procedure detailed below.
	5.1. Order of traffic filtering rules
	With traffic filtering rules, more than one rule may match a
	particular traffic flow. Thus it is necessary to define the order at
	which rules get matched and applied to a particular traffic flow.
	This ordering function must be such that it must not depend on the
	arrival order of the flow specifications rules and must be constant
	in the network.
	The relative order of two flow specification rules is determined by
	comparing their respective components. The algorithm starts by
	comparing the left-most components of the rules. If the types
	differ, the rule with lowest numeric type value has higher precedence
	(and thus will match before) the rule that doesn't contain that
	component type. If the component types are the same, then a type
	specific comparison is performed.
	For IP prefix values (IP destination and source prefix) precedence is
	given to lowest IP value of the common prefix length; if the common
	prefix is equal then the most specific prefix has precedence.
	For all other component types, unless otherwise specified, the
	comparison is performed by comparing the component data as a binary
	string using the memcmp() function as defined by the ISO C standard.
	For strings of different lengths, the common prefix is compared. If
	equal the longest string is considered to have higher precedence than
	the shorter one.
	Pseudocode:
	flow_rule_cmp (a, b)
	{
	comp1 = next_component(a);
	comp2 = next_component(b);
	while (comp1 || comp2) {
	// component_type returns infinity on end-of-list
	if (component_type(comp1) < compnent_type(comp2)) {
	return A_HAS_PRECEDENCE;
	}
	if (component_type(comp1) > component_type(comp2)) {
	return B_HAS_PRECEDENCE;
	}
	if (component_type(comp1) == IP_DESTINATION || IP_SOURCE) {
	common = MIN(prefix_length(comp1), prefix_length(comp2));
	cmp = prefix_compare(comp1, comp2, common);
	// not equal, lowest value has precedence
	// equal, longest match has precedence
	} else {
	common = MIN(component_length(comp1), component_length(comp2));
	cmp = memcmp(data(comp1), data(comp2), common);
	// not equal, lowest value has precedence
	// equal, longest string has precedence
	}
	}
	return EQUAL;
	}
	6. Validation procedure
	Flow specifications received from a BGP peer and which are accepted
	in the respective Adj-RIB-In are used as input to the route selection
	process. Although the forwarding attributes of two routes for the
	same Flow Specification prefix may be the same, BGP is still required
	to perform its path selection algorithm in order to select the
	correct set of attributes to advertise.
	The first step of the BGP Route Selection procedure (section 9.1.2 of
	[RFC4271]) is to exclude from the selection procedure routes that are
	considered non-feasible. In the context of IP routing information
	this step is used to validate that the NEXT_HOP attribute of a given
	route is resolvable.
	The concept can be extended, in the case of Flow Specification NLRI,
	to allow other validation procedures.
	A flow specification NLRI must be validated such that it is
	considered feasible if and only if:
	a) The originator of the flow specification matches the originator of
	the best-match unicast route for the destination prefix embedded
	in the flow specification.
	b) There are no more-specific unicast routes, when compared with the
	flow destination prefix, that have been received from a different
	neighboring AS than the best-match unicast route, which has been
	determined in step a).
	By originator of a BGP route, we mean either the BGP originator path
	attribute, as used by route reflection, or the transport address of
	the BGP peer, if this path attribute is not present.
	The underlying concept is that the neighboring AS that advertises the
	best unicast route for a destination is allowed to advertise flow-
	spec information that conveys a more or equally specific destination
	prefix. Thus, as long as there are no more-specific unicast routes,
	received from a different neighbor AS, which would be affected by
	that filtering rule.
	The neighboring AS is the immediate destination of the traffic
	described by the Flow Specification. If it requests these flows to
	be dropped that request can be honored without concern that it
	represents a denial of service in itself. Supposedly, the traffic is
	being dropped by the downstream autonomous-system and there is no
	added value in carrying the traffic to it.
	BGP implementations MUST also enforce that the AS_PATH attribute of a
	route received via eBGP contains the neighboring AS in the left-most
	position of the AS_PATH attribute. While this rule is optional in
	the BGP specification, it becomes necessary to enforce it for
	security reasons.
	7. Traffic Filtering Actions
	This specification defines a minimum set of filtering actions that it
	standardizes as BGP extended community values [RFC4360]. This is not
	meant to be an inclusive list of all the possible actions but only a
	subset that can be interpreted consistently across the network.
	Implementations should provide mechanisms that map an arbitrary BGP
	community value (normal or extended) to filtering actions that
	require different mappings in different systems in the network. For
	instance, providing packets with a worse than best-effort per-hop
	behavior is a functionality that is likely to be implemented
	differently in different systems and for which no standard behavior
	is currently known. Rather than attempting to define it here, this
	can be accomplished by mapping a user defined community value to
	platform / network specific behavior via user configuration.
	The default action for a traffic filtering flow specification is to
	accept IP traffic that matches that particular rule.
	The following extended community values can be used to specify
	particular actions.
	+--------+--------------------+--------------------------+
	| type | extended community | encoding |
	+--------+--------------------+--------------------------+
	| 0x8006 | traffic-rate | 2-byte as#, 4-byte float |
	| 0x8007 | traffic-action | bitmask |
	| 0x8008 | redirect | 6-byte Route Target |
	| 0x8009 | traffic-marking | DSCP value |
	+--------+--------------------+--------------------------+
	Traffic-rate The traffic-rate extended community is a non-transitive
	extended community across the Autonomous system boundary and uses
	following extended community encoding:
	The first two octets carry the 2 octet id which can be assigned
	from a 2 byte AS number. When 4 byte AS number is locally
	present 2 least significant bytes of such AS number can be
	used. This value is purely informational and should not be
	interpreted by the implementation.
	The remaining 4 octets carry the rate information in IEEE
	floating point [IEEE.754.1985] format , units being bytes per
	second. A traffic-rate of 0 should result on all traffic for
	the particular flow to be discarded.
	Traffic-action The traffic-action extended community consists of 6
	bytes of which only the 2 least significant bits of the 6th byte
	(from left to right) are currently defined.
	0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+
	| reserved | S | T |
	+---+---+---+---+---+---+---+---+
	* Terminal action (bit 7). When this bit is set the traffic
	filtering engine will apply any subsequent filtering rules (as
	defined by the ordering procedure). If not set the evaluation
	of the traffic filter stops when this rule is applied.
	* Sample (bit 6). Enables traffic sampling and logging for this
	flow specification.
	Redirect The redirect extended community allows the traffic to be
	redirected to a VRF routing instance that list the specified
	route-target in its import policy. If several local instances
	match this criteria, the choice between them is a local matter
	(for example, the instance with the lowest Route Distinguisher
	value can be elected). This extended community uses the same
	encoding as the Route Target extended community [RFC4360]
	Traffic Marking The traffic marking extended community instructs a
	system to modify the DSCP bits of a transiting IP packet to the
	corresponding value. This extended community is encoded as a
	sequence of 5 zero bytes followed by the DSCP value encoded in the
	6 least significant bits of 6th byte.
	8. Traffic filtering in RFC2547bis networks
	Provider-based layer 3 VPN networks, such as the ones using an BGP/
	MPLS IP VPN [RFC4364] control plane, have different traffic filtering
	requirements than internet service providers.
	In these environments, the VPN customer network often has traffic
	filtering capabilities towards their external network connections
	(e.g. firewall facing public network connection). Less common is the
	presence of traffic filtering capabilities between different VPN
	attachment sites. In an any-to-any connectivity model, which is the
	default, this means that site to site traffic is unfiltered.
	In circumstances where a security threat does get propagated inside
	the VPN customer network, there may not be readily available
	mechanisms to provide mitigation via traffic filter.
	This document proposes an additional BGP NLRI type (afi=1, safi=134)
	value, which can be used to propagate traffic filtering information
	in a BGP/MPLS VPN environment.
	The NLRI format for this address family consists of a fixed length
	Route Distinguisher field (8 bytes) followed by a flow specification,
	following the encoding defined in this document. The NLRI length
	field shall include both the 8 bytes of the Route Distinguisher as
	well as the subsequent flow specification.
	Propagation of this NLRI is controlled by matching Route Target
	extended communities associated with the BGP path advertisement with
	the VRF import policy, using the same mechanism as described in "BGP/
	MPLS IP VPNs" [RFC4364] .
	Flow specification rules received via this NLRI apply only to traffic
	that belongs to the VRF(s) in which it is imported. By default,
	traffic received from a remote PE is switched via an mpls forwarding
	decision and is not subject to filtering.
	Contrary to the behavior specified for the non-VPN NLRI, flow rules
	are accepted by default, when received from remote PE routers.
	9. Monitoring
	Traffic filtering applications require monitoring and traffic
	statistics facilities. While this is an implementation specific
	choice, implementations SHOULD provide:
	o A mechanism to log the packet header of filtered traffic,
	o A mechanism to count the number of matches for a given Flow
	Specification rule.
	10. Security considerations
	Inter-provider routing is based on a web of trust. Neighboring
	autonomous-systems are trusted to advertise valid reachability
	information. If this trust model is violated, a neighboring
	autonomous system may cause a denial of service attack by advertising
	reachability information for a given prefix for which it does not
	provide service.
	As long as traffic filtering rules are restricted to match the
	corresponding unicast routing paths for the relevant prefixes, the
	security characteristics of this proposal are equivalent to the
	existing security properties of BGP unicast routing.
	Where it not the case, this would open the door to further denial of
	service attacks.
	Enabling firewall like capabilities in routers without centralized
	management could make certain failures harder to diagnose. For
	example, it is possible to allow TCP packets to pass between a pair
	of addresses but not ICMP packets. It is also possible to permit
	packets smaller than 900 or greater than 1000 bytes to pass between a
	pair of addresses, but not packets whose length is in the range 900-
	1000. Such behavior may be confusing and these capabilities should
	be used with care whether manually configured or coordinated through
	the protocol extensions described in this document.
	11. IANA Considerations
	A flow specification consists of a sequence of flow components, which
	are identified by a an 8-bit component type. Types must be assigned
	and interpreted uniquely. The current specification defines types 1
	though 12, with the value 0 being reserved.
	For the purpose of this work IANA has allocated values for two SAFIs:
	SAFI 133 for IPv4 and SAFI 134 for VPNv4 dissemination of flow
	specification rules.
	The following traffic filtering flow specification rules are to be
	allocated by IANA from BGP Extended Communities Type - Experimental
	Use registry. Authors recommend the following type values:
	0x8006 - Flow spec traffic-rate
	0x8007 - Flow spec traffic-action
	0x8008 - Flow spec redirect
	0x8009 - Flow spec traffic-remarking
	Authors would like to ask IANA to create and maintain a new registry
	entitled: "Flow Spec Component Type". Authors recommend to allocate
	the following component types:
	Type 1 - Destination Prefix
	Type 2 - Source Prefix
	Type 3 - IP Protocol
	Type 4 - Port
	Type 5 - Destination port
	Type 6 - Source port
	Type 7 - ICMP type
	Type 8 - ICMP code
	Type 9 - TCP flags
	Type 10 - Packet length
	Type 11 - DSCP
	Type 12 - Fragment
	In order to manage the limited number space and accommodate several
	usages the following policies defined by RFC 5226 [RFC5226] are used:
	+--------------+-------------------------------+
	| Range | Policy |
	+--------------+-------------------------------+
	| 0 | Invalid value |
	| [1 .. 12] | Defined by this specification |
	| [13 .. 127] | Specification Required |
	| [128 .. 255] | Private Use |
	+--------------+-------------------------------+
	The specification of a particular "flow component type" must clearly
	identify what is the criteria used to match packets forwarded by the
	router. This criteria should be meaningful across router hops and
	not depend on values that change hop-by-hop such as ttl or layer-2
	encapsulation.
	The "Traffic-action" extended community defined in this document has
	6 unused bits which can be used to convey additional meaning.
	Authors would like to ask IANA to create and maintain a new registry
	entitled: "Traffic Action Fields". These values should be assigned
	via IETF Review rules only. Authors recommend to allocate the
	following traffic action fields:
	0 Terminal Action
	1 Sample
	2-47 Unassigned
	12. Acknowledgments
	The authors would like to thank Yakov Rekhter, Dennis Ferguson, Chris
	Morrow, Charlie Kaufman and David Smith for their comments.
	Chaitanya Kodeboyina helped design the flow validation procedure.
	Steven Lin and Jim Washburn ironed out all the details necessary to
	produce a working implementation.
	13. Normative References
	[IEEE.754.1985]
	Institute of Electrical and Electronics Engineers,
	"Standard for Binary Floating-Point Arithmetic",
	IEEE Standard 754, August 1985.
	[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
	RFC 793, September 1981.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
	"Definition of the Differentiated Services Field (DS
	Field) in the IPv4 and IPv6 Headers", RFC 2474,
	December 1998.
	[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
	Protocol 4 (BGP-4)", RFC 4271, January 2006.
	[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
	RFC 4303, December 2005.
	[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
	Communities Attribute", RFC 4360, February 2006.
	[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
	Networks (VPNs)", RFC 4364, February 2006.
	[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
	"Multiprotocol Extensions for BGP-4", RFC 4760,
	January 2007.
	[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
	IANA Considerations Section in RFCs", BCP 26, RFC 5226,
	May 2008.
	Authors' Addresses
	Pedro Marques
	Juniper Networks
	1194 N. Mathilda Ave.
	Sunnyvale, CA 94089
	US
	Email: roque@juniper.net
	Nischal Sheth
	Juniper Networks
	1194 N. Mathilda Ave.
	Sunnyvale, CA 94089
	US
	Email: nsheth@juniper.net
	Robert Raszuk
	Juniper Networks
	1194 N. Mathilda Ave.
	Sunnyvale, CA 94089
	US
	Email: raszuk@juniper.net
	Barry Greene
	Juniper Networks
	1194 N. Mathilda Ave.
	Sunnyvale, CA 94089
	US
	Email: bgreene@juniper.net
	Jared Mauch
	NTT America
	101 Park Ave
	41st Floor
	New York, NY 10178
	US
	Email: jared@us.ntt.net
	Danny McPherson
	Arbor Networks
	Email: danny@arbor.net
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