IDR Working Group S. Hares
Internet-Draft Huawei
Obsoletes: 5575 (if approved) R. Raszuk
Updates: 7674 (if approved) Bloomberg LP
Intended status: Standards Track D. McPherson
Expires: August 18, 2017 Verisign
C. Loibl
Next Layer Communications
M. Bacher
T-Mobile Austria
February 14, 2017
Dissemination of Flow Specification Rules
draft-hr-idr-rfc5575bis-03.txt
Abstract
This document updates RFC5575 which defines a Border Gateway Protocol
Network Layer Reachability Information (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. This draft specifies IPv4 traffic flow
specifications via a BGP NLRI which carries traffic flow
specification filter, and an Extended community value which encodes
actions a routing system can take if the packet matches the traffic
flow filters. The flow filters and the actions are processed in a
fixed order. Other drafts specify IPv6, MPLS addresses, L2VPN
addresses, and NV03 encapsulation of IP addresses.
This document updates RFC5575 to correct unclear specifications in
the flow filters and to provide rules for actions which interfere
(e.g. redirection of traffic and flow filtering).
Applications which use the bgp flow specification are: 1) application
which automate of inter-domain coordination of traffic filtering,
such as what is required in order to mitigate (distributed) denial-
of-service attacks; 2) application which control traffic filtering in
the context of a BGP/MPLS VPN service, and 3) applications with
centralized control of traffic in a SDN or NFV context. Some of
deployments of these three applications can be handled by the strict
ordering of the BGP NLRI traffic flow filters, and the strict actions
encoded in the Extended Community Flow Specification actions.
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Status of This Memo
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
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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 August 18, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions of Terms Used in This Memo . . . . . . . . . . . 5
3. Flow Specifications . . . . . . . . . . . . . . . . . . . . . 6
4. Dissemination of IPv4 FLow Specification Information . . . . 6
4.1. Length Encoding . . . . . . . . . . . . . . . . . . . . . 7
4.2. NLRI Value Encoding . . . . . . . . . . . . . . . . . . . 7
4.2.1. Type 1 - Destination Prefix . . . . . . . . . . . . . 8
4.2.2. Type 2 - Source Prefix . . . . . . . . . . . . . . . 8
4.2.3. Type 3 - IP Protocol . . . . . . . . . . . . . . . . 8
4.2.4. Type 4 - Port . . . . . . . . . . . . . . . . . . . . 10
4.2.5. Type 5 - Destination Port . . . . . . . . . . . . . . 10
4.2.6. Type 6 - Source Port . . . . . . . . . . . . . . . . 10
4.2.7. Type 7 - ICMP type . . . . . . . . . . . . . . . . . 10
4.2.8. Type 8 - ICMP code . . . . . . . . . . . . . . . . . 11
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4.2.9. Type 9 - TCP flags . . . . . . . . . . . . . . . . . 11
4.2.10. Type 10 - Packet length . . . . . . . . . . . . . . . 12
4.2.11. Type 11 - DSCP (Diffserv Code Point) . . . . . . . . 12
4.2.12. Type 12 - Fragment . . . . . . . . . . . . . . . . . 12
4.3. Examples of Encodings . . . . . . . . . . . . . . . . . . 12
5. Traffic Filtering . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Ordering of Traffic Filtering Rules . . . . . . . . . . . 14
6. Validation Procedure . . . . . . . . . . . . . . . . . . . . 16
7. Traffic Filtering Actions . . . . . . . . . . . . . . . . . . 17
7.1. Traffic Rate in Bytes (sub-type 0x06) . . . . . . . . . . 18
7.2. Traffic Rate in Packets (sub-type TBD) . . . . . . . . . 19
7.3. Traffic-action (sub-type 0x07) . . . . . . . . . . . . . 19
7.4. IP Redirect (sub-type 0x08) . . . . . . . . . . . . . . . 19
7.5. Traffic Marking (sub-type 0x09) . . . . . . . . . . . . . 20
7.6. Rules on Traffic Action Interference . . . . . . . . . . 20
7.6.1. Examples . . . . . . . . . . . . . . . . . . . . . . 21
8. Dissemination of Traffic Filtering in BGP/MPLS VPN Networks . 21
8.1. Validation Procedures for BGP/MPLS VPNs . . . . . . . . . 22
8.2. Traffic Actions Rules . . . . . . . . . . . . . . . . . . 22
9. Limitations of Previous Traffic Filtering Efforts . . . . . . 22
9.1. Limitations in Previous DDoS Traffic Filtering Efforts . 22
9.2. Limitations in Previous BGP/MPLS Traffic Filtering . . . 23
10. Traffic Monitoring . . . . . . . . . . . . . . . . . . . . . 23
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
11.1. AFI/SAFI Definitions . . . . . . . . . . . . . . . . . . 24
11.2. Flow Component definitions . . . . . . . . . . . . . . . 24
11.3. Extended Community Flow Specification Actions . . . . . 25
12. Security Considerations . . . . . . . . . . . . . . . . . . . 26
13. Original authors . . . . . . . . . . . . . . . . . . . . . . 27
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
15.1. Normative References . . . . . . . . . . . . . . . . . . 27
15.2. Informative References . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. 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
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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 [RFC5575] 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 (Access Control List) or
firewall capabilities in the router's forwarding path. Flow
specifications can be seen as more specific routing entries to a
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 that 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-multipoint 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 specify 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 BGP, 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
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extensions, service providers will be careful to keep information
levels below the maximum capacity of their devices.
In many deployments of BGP Flow Specification, the flow specification
information has replace existing host length route advertisements.
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, this solution has been utilized in deployments because of
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 that 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 such
as IPv6 families [I-D.ietf-idr-flow-spec-v6],
2. 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.
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PE - Provider Edge router
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 [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 (Address Family
Identifier, Subsequent Address Family Identifier (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 as well as community matching and manipulation, MUST apply to
the Flow specification defined NLRI-type, especially in an inter-
domain environment. 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 IPv4 FLow Specification Information
We define a "Flow Specification" NLRI type (Figure 1) that may
include several components such as destination prefix, source prefix,
protocol, ports, and others (see Section 4.2 below). This NLRI is
treated as an opaque bit string prefix by BGP. Each bit string
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identifies a key to a database entry with which a set of attributes
can be associated.
This NLRI information is encoded using MP_REACH_NLRI and
MP_UNREACH_NLRI attributes as defined in [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) |
+------------------------------+
Figure 1: Flow-spec NLRI for IPv4
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]. 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.
4.1. Length Encoding
o If the NLRI length value is smaller than 240 (0xf0 hex), the
length field can be encoded as a single octet.
o Otherwise, it is encoded as an extended-length 2-octet value in
which the most significant nibble of the first byte is all ones.
In figure 1 above, values less-than 240 are encoded using two hex
digits (0xnn). Values above 239 are encoded using 3 hex digits
(0xfnnn). The highest value that can be represented with this
encoding is 4095. The value 241 is encoded as 0xf0f1.
4.2. NLRI Value Encoding
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.
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The encoding of each of the NLRI components begins with a type field
(1 octet) followed by a variable length parameter. Section 4.2.1 to
Section 4.2.12 define component types and parameter encodings for the
IPv4 IP layer and transport layer headers. IPv6 NLRI component types
are described in [I-D.ietf-idr-flow-spec-v6].
Flow specification components must follow strict type ordering by
increasing numerical order. 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 allow for future
extensibility.
4.2.1. 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.
4.2.2. Type 2 - Source Prefix
Encoding: <type (1 octet), prefix-length (1 octet), prefix>
Defines the source prefix to match.
4.2.3. Type 3 - IP Protocol
Encoding:<type (1 octet), [op, value]+>
Contains a set of {operator, value} pairs that are used to match
the IP protocol value byte in IP packets.
The operator byte is encoded as:
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| e | a | len | 0 |lt |gt |eq |
+---+---+---+---+---+---+---+---+
Numeric operator
e - end-of-list bit. Set in the last {op, value} pair in the
list.
a - 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.
len - length of the value field for this operand encodes 1 (00) -
4 (11) bytes. Type 3 flow component values are always encoded as
single byte (len = 00).
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.
+----+----+----+----------------------------------+
| lt | gt | eq | Resulting operation |
+----+----+----+----------------------------------+
| 0 | 0 | 0 | true (independent of the value) |
| 0 | 0 | 1 | == (equal) |
| 0 | 1 | 0 | > (greater than) |
| 0 | 1 | 1 | >= (greater than or equal) |
| 1 | 0 | 0 | < (less than) |
| 1 | 0 | 1 | <= (less than or equal) |
| 1 | 1 | 0 | != (not equal value) |
| 1 | 1 | 1 | false (independent of the value) |
+----+----+----+----------------------------------+
Table 1: Comparison operation combinations
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4.2.4. Type 4 - Port
Encoding:<type (1 octet), [op, value]+>
Defines a list of {operator, value} pairs that matches source OR
destination TCP/UDP ports. This list is encoded using the numeric
operator format defined in Section 4.2.3. 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
Encapsulating Security Payload (ESP) NULL [RFC4303] encryption.
4.2.5. Type 5 - Destination Port
Encoding:<type (1 octet), [op, value]+>
Defines a list of {operator, value} pairs used to match the
destination port of a TCP or UDP packet. This list is encoded
using the numeric operator format defined in Section 4.2.3.
Values are encoded as 1- or 2-byte quantities.
4.2.6. Type 6 - Source Port
Encoding:<type (1 octet), [op, value]+>
Defines a list of {operator, value} pairs used to match the source
port of a TCP or UDP packet. This list is encoded using the
numeric operator format defined in Section 4.2.3. Values are
encoded as 1- or 2-byte quantities.
4.2.7. Type 7 - ICMP type
Encoding:<type (1 octet), [op, value]+>
Defines a list of {operator, value} pairs used to match the type
field of an ICMP packet. This list is encoded using the numeric
operator format defined in Section 4.2.3. Values are encoded
using a single byte.
The ICMP type specifiers evaluate to FALSE whenever the protocol
value is not ICMP.
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4.2.8. Type 8 - ICMP code
Encoding:<type (1 octet), [op, value]+>
Defines a list of {operator, value} pairs used to match the code
field of an ICMP packet. This list is encoded using the numeric
operator format defined in Section 4.2.3. Values are encoded
using a single byte.
The ICMP code specifiers evaluate to FALSE whenever the protocol
value is not ICMP.
4.2.9. Type 9 - TCP flags
Encoding:<type (1 octet), [op, bitmask]+>
Bitmask values can be encoded as a 1- or 2-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 32-bit 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.
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 |
+---+---+---+---+---+---+---+---+
Bitmask format
e, a, len - Most significant nibble: (end-of-list bit, AND bit, and
length field), as defined for in the numeric operator format in
Section 4.2.3.
not - NOT bit. If set, logical negation of operation.
m - Match bit. If set, this is a bitwise match operation defined
as "(data AND value) == value"; if unset, (data AND value)
evaluates to TRUE if any of the bits in the value mask are set in
the data
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4.2.10. Type 10 - Packet length
Encoding:<type (1 octet), [op, bitmask]+>
Defines a list of {operator, value} pairs used to match on the
total IP packet length (excluding Layer 2 but including IP
header). This list is encoded using the numeric operator format
defined in Section 4.2.3. Values are encoded using 1- or 2-byte
quantities.
4.2.11. Type 11 - DSCP (Diffserv Code Point)
Encoding:<type (1 octet), [op, value]+>
Defines a list of {operator, value} pairs used to match the 6-bit
DSCP field [RFC2474]. This list is encoded using the numeric
operator format defined in Section 4.2.3. Values are encoded
using a single byte. The two most significant bits are zero and
the six least significant bits contain the DSCP value.
4.2.12. Type 12 - Fragment
Encoding:<type (1 octet), [op, bitmask]+>
Uses bitmask operand format defined in Section 4.2.9.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Reserved |LF |FF |IsF|DF |
+---+---+---+---+---+---+---+---+
Bitmask values:
Bit 7 - Don't fragment (DF)
Bit 6 - Is a fragment (IsF)
Bit 5 - First fragment (FF)
Bit 4 - Last fragment (LF)
4.3. Examples of Encodings
An example of a flow specification encoding for: "all packets to
10.0.1/24 and TCP port 25".
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+------------------+----------+----------+
| 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
10.1.1/24 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 | "AND", value size=1, <= |
| 0x8b | value | 139 |
| 0x91 | operator | end-of-list, value-size=2, = |
| 0x1f90 | value | 8080 |
+--------+----------+------------------------------+
This constitutes an NLRI with an NLRI length of 16 octets.
5. Traffic Filtering
Traffic filtering policies have been traditionally considered to be
relatively static. Limitations of the static mechanisms caused this
mechanism to be designed for the three new applications of traffic
filtering (prevention of traffic-based, denial-of-service (DOS)
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attacks, traffic filtering in the context of BGP/MPLS VPN service,
and centralized traffic control for SDN/NFV networks) requires
coordination among service providers and/or coordination among the AS
within a service provider. Section 8 has details on the limitation
of previous mechanisms and why BGP Flow Specification version 1
provides a solution for to prevent DOS and aid BGP/MPLS VPN filtering
rules.
This flow specification NLRI defined above to convey information
about traffic filtering rules for traffic that should be discarded or
handled in manner specified by a set of pre-defined actions (which
are defined in BGP Extended Communities). 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, this draft specifies two application
specific NLRI identifiers that provide traffic filters, and a set of
actions encoding in BGP Extended Communities. The two application
specific NLRI identifiers are:
o IPv4 flow specification identifier (AFI=1, SAFI=133) along with
specific semantic rules for IPv4 routes, and
o BGP NLRI type (AFI=1, SAFI=134) value, which can be used to
propagate traffic filtering information in a BGP/MPLS VPN
environment.
Distribution of the IPv4 Flow specification is described in section
6, and distibution of BGP/MPLS traffic flow specification is
described in section 8. The traffic filtering actions are described
in section 7.
5.1. Ordering 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 specification's rules and must be
consistent 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) than the rule that doesn't contain that
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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 the 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) < component_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;
}
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6. Validation Procedure
Flow specifications received from a BGP peer that 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 has 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.
BGP implementations MUST also enforce that the AS_PATH attribute of a
route received via the External Border Gateway Protocol (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.
The best-match unicast route may change over the time independently
of the flow specification NLRI. Therefore, a revalidation of the
flow specification NLRI MUST be performed whenever unicast routes
change. Revalidation is defined as retesting that clause a and
clause b above are true.
Explanation:
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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 neighboring 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.
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.
Additional actions can be defined as either requiring standards or as
vendor specific.
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.
This document defines the following extended communities values shown
in Table 2 in the form 0x8xnn where nn indicates the sub-type.
Encodings for these extended communities are described below.
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+--------+----------------------+-----------------------------------+
| type | extended community | encoding |
+--------+----------------------+-----------------------------------+
| 0x8006 | traffic-rate-bytes | 2-byte ASN, 4-byte float |
| 0x8007 | traffic-action | bitmask |
| 0x8008 | redirect AS-2byte | 2-octet AS, 4-octet value |
| 0x8108 | redirect IPv4 | 4-octet IPv4 addres, 2-octet |
| | | value |
| 0x8208 | redirect AS-4byte | 4-octet AS, 2-octet value |
| 0x8009 | traffic-marking | DSCP value |
| TBD | traffic-rate-packets | 2-byte ASN, 4-byte float |
+--------+----------------------+-----------------------------------+
Table 2: Traffic Action Extended Communities
Some traffic action communities may interfere with each other.
Section 7.6 of this specification provides rules for handling
interference between specific types of traffic actions, and error
handling based on [RFC7606]. Any additional definition of a traffic
actions specified by additional standards documents or vendor
documents MUST specify if the traffic action interacts with an
existing traffic actions, and provide error handling per [RFC7606].
The traffic actions are processed in ascending order of the sub-type
found in the BGP Extended Communities. All traffic actions are
specified in transitive BGP Extended Communities.
7.1. Traffic Rate in Bytes (sub-type 0x06)
The traffic-rate-bytes extended community uses the following extended
community encoding:
The first two octets carry the 2-octet id, which can be assigned from
a 2-byte AS number. When a 4-byte AS number is locally present, the
2 least significant bytes of such an AS number can be used. This
value is purely informational and should not be interpreted by the
implementation.
The remaining 4 octets carry the maximum 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.
Interferes with: Traffic Rate in packets (traffic-rate-packets).
Process traffic rate in bytes (sub-type 0x06) action before traffic
rate in packets action (sub-type TBD).
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7.2. Traffic Rate in Packets (sub-type TBD)
The traffic-rate-packets extended community uses the same encoding as
the traffic-rate-bytes extended community. The floating point value
carries the maximum packet rate in packets per second. A traffic-
rate-packets of 0 should result in all traffic for the particular
flow to be discarded.
Interferes with: Traffic Rate in bytes (traffic-rate-bytes). Process
traffic rate in bytes (sub-type 0x06) action before traffic rate in
packets action (sub-type TBD).
7.3. Traffic-action (sub-type 0x07)
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.
40 41 42 43 44 45 46 47
+---+---+---+---+---+---+---+---+
| reserved | S | T |
+---+---+---+---+---+---+---+---+
where S and T are defined as:
o T: Terminal Action (bit 47): 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.
o S:Sample (bit 46): Enables traffic sampling and logging for this
flow specification.
Interferes with: No other BGP Flow Specification traffic action in
this document.
7.4. IP Redirect (sub-type 0x08)
The redirect extended community allows the traffic to be redirected
to a VRF routing instance that lists 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].
It should be noted that the low-order nibble of the Redirect's Type
field corresponds to the Route Target Extended Community format field
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(Type). (See Sections 3.1, 3.2, and 4 of [RFC4360] plus Section 2 of
[RFC5668].) The low-order octet (Sub-Type) of the Redirect Extended
Community remains 0x08 for all three encodings of the BGP Extended
Communities (AS 2-byte, AS 4-byte, and IPv4 address).
Interferes with: All other redirect functions. All redirect
functions are mutually exclusive. If this redirect function exists,
then no other redirect functions can be processed.
7.5. Traffic Marking (sub-type 0x09)
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.
Interferes with: No other action in this document.
7.6. Rules on Traffic Action Interference
Traffic actions may interfere with each other. If interfering
traffic actions are present for a single flow specification NLRI the
entire flow specification (irrespective if there are any other non
conflicting actions associated with the same flow specification)
SHALL be treated as BGP WITHDRAW.
This document defines 7 traffic actions which are interfering in the
following way:
1. Redirect-action-communities (0x8008, 0x8108, 0x8208):
The three redirect-communities are mutually exclusive. Only a
single redirect community may be associated with a flow
specification otherwise they are interfering.
2. All traffic-action communities (including redirect-actions):
Multiple occurences of the same (sub-type and type) traffic-
action associated with a flow specification are always
interfering.
When a traffic action is defined in a standards document the handling
of interaction with other/same traffic actions MUST be defined as
well. Invalid interactions between actions SHOULD NOT trigger a BGP
NOTIFICATION. All error handling for error conditions based on
[RFC7606].
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7.6.1. Examples
(redirect vpn-a, redirect vpn-b, traffic-rate-bytes 1Mbit/s)
Redirect vpn-a and redirect vpn-b are interfering: The BGP UPDATE
is treated as WITHDRAW.
(redirect vpn-a, traffic-rate-bytes 1Mbit/s, traffic-rate-bytes
2Mbit/s)
Duplicate traffic-rate-bytes are interfering: The BGP UPDATE is
treated as WITHDRAW.
(redirect vpn-a, traffic-rate-bytes 1Mbit/s, traffic-rate-packets
1000)
No interfering action communities: The BGP UPDATE is subject to
further processing.
8. Dissemination of Traffic Filtering in BGP/MPLS VPN Networks
Provider-based Layer 3 VPN networks, such as the ones using a BGP/
MPLS IP VPN [RFC4364] control plane, may have different traffic
filtering requirements than Internet service providers. But also
Internet service providers may use those VPNs for scenarios like
having the Internet routing table in a VRF, resulting in the same
traffic filtering requirements as defined for the global routing
table environment within this document. 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 above in section x of this document.
The NLRI length field shall include both the 8 bytes of the Route
Distinguisher as well as the subsequent flow specification.
+------------------------------+
| length (0xnn or 0xfn nn) |
+------------------------------+
| Route Distinguisher (8 bytes)|
+------------------------------+
| NLRI value (variable) |
+------------------------------+
Flow-spec NLRI for MPLS
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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.
8.1. Validation Procedures for BGP/MPLS VPNs
The validation procedures are the same as for IPv4.
8.2. Traffic Actions Rules
The traffic action rules are the same as for IPv4.
9. Limitations of Previous Traffic Filtering Efforts
9.1. Limitations in Previous DDoS Traffic Filtering Efforts
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 (commonly known as remote triggered blackhole RTBH).
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
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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 is
subject to modified forwarding behavior (actions). The actions are
defined as extended communities and include (but are not limited to)
rate-limiting (including discard), traffic redirection, packet
rewriting.
9.2. Limitations in Previous BGP/MPLS Traffic Filtering
Provider-based Layer 3 VPN networks, such as the ones using a BGP/
MPLS IP VPN [RFC4364] control plane, may 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.
But also Internet service providers may use those VPNs for scenarios
like having the Internet routing table in a VRF. Therefore,
limitations described in Section 9.1 also apply to this section.
The BGP Flow Specification version 1 addresses these limitations.
10. Traffic 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.
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o A mechanism to count the number of matches for a given flow
specification rule.
11. IANA Considerations
This section complies with [RFC7153]
11.1. AFI/SAFI Definitions
For the purpose of this work, IANA has allocated values for two
SAFIs: SAFI 133 for IPv4 dissemination of flow specification rules
and SAFI 134 for VPNv4 dissemination of flow specification rules.
11.2. Flow Component definitions
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.
IANA created and maintains a new registry entitled: "Flow Spec
Component Types". The following component types have been
registered:
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
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Type 13 - Bit Mask filter
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] | First Come First Served |
+--------------+-------------------------------+
The specification of a particular "flow component type" must clearly
identify what the criteria used to match packets forwarded by the
router is. 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
46 unused bits, which can be used to convey additional meaning. IANA
created and maintains a new registry entitled: "Traffic Action
Fields". These values should be assigned via IETF Review rules only.
The following traffic-action fields have been allocated:
47 Terminal Action
46 Sample
0-45 Unassigned
11.3. Extended Community Flow Specification Actions
The Extended Community FLow Specification Action types consists of
two parts: BGP Transitive Extended Community types and a set of sub-
types.
IANA has updated the following "BGP Transitive Extended Community
Types" registries to contain the values listed below:
0x80 - Generic Transitive Experimental Use Extended Community Part
1 (Sub-Types are defined in the "Generic Transitive Experimental
Extended Community Part 1 Sub-Types" Registry)
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0x81 - Generic Transitive Experimental Use Extended Community Part
2 (Sub-Types are defined in the "Generic Transitive Experimental
Extended Community Part 2 Sub-Types" Registry)
0x82 - Generic Transitive Experimental Use Extended Community Part
3 (Sub-Types are defined in the "Generic Transitive Experimental
Use Extended Community Part 3 Sub-Types" Registry)
RANGE REGISTRATION PROCEDURE
0x00-0xbf First Come First Served
0xc0-0xff IETF Review
SUB-TYPE VALUE NAME REFERENCE
0x00-0x05 unassigned
0x06 traffic-rate [this document]
0x07 traffic-action [this document]
0x08 Flow spec redirect IPv4 [RFC5575] [RFC7674]
[this document]
0x09 traffic-marking [this document]
0x0a-0xff Unassigned [this document]
12. 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 is 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.
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13. Original authors
Barry Greene, MuPedro Marques, Jared Mauch, Danny McPherson, and
Nischal Sheth were authors on [RFC5575], and therefore are
contributing authors on this document.
Note: Any original author of [RFC5575] who wants to work on this
draft can be added as a co-author.
14. Acknowledgements
The authors would like to thank Yakov Rekhter, Dennis Ferguson, Chris
Morrow, Charlie Kaufman, and David Smith for their comments for the
comments on the original [RFC5575]. Chaitanya Kodeboyina helped
design the flow validation procedure; and Steven Lin and Jim Washburn
ironed out all the details necessary to produce a working
implementation in the original [RFC5575].
Additional acknowledgements for this document will be included here.
The current authors would like to thank Alexander Mayrhofer and
Nicolas Fevrier for their comments and review.
15. References
15.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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,
DOI 10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
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[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <http://www.rfc-editor.org/info/rfc4364>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>.
[RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
<http://www.rfc-editor.org/info/rfc4761>.
[RFC4762] Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
<http://www.rfc-editor.org/info/rfc4762>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
<http://www.rfc-editor.org/info/rfc5575>.
[RFC5668] Rekhter, Y., Sangli, S., and D. Tappan, "4-Octet AS
Specific BGP Extended Community", RFC 5668,
DOI 10.17487/RFC5668, October 2009,
<http://www.rfc-editor.org/info/rfc5668>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482,
DOI 10.17487/RFC6482, February 2012,
<http://www.rfc-editor.org/info/rfc6482>.
[RFC7153] Rosen, E. and Y. Rekhter, "IANA Registries for BGP
Extended Communities", RFC 7153, DOI 10.17487/RFC7153,
March 2014, <http://www.rfc-editor.org/info/rfc7153>.
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[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<http://www.rfc-editor.org/info/rfc7606>.
15.2. Informative References
[I-D.ietf-idr-flow-spec-v6]
McPherson, D., Raszuk, R., Pithawala, B.,
akarch@cisco.com, a., and S. Hares, "Dissemination of Flow
Specification Rules for IPv6", draft-ietf-idr-flow-spec-
v6-07 (work in progress), March 2016.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
Authors' Addresses
Susan Hares
Huawei
7453 Hickory Hill
Saline, MI 48176
USA
Email: shares@ndzh.com
Robert Raszuk
Bloomberg LP
731 Lexington Ave
New York City, NY 10022
USA
Email: robert@raszuk.net
Danny McPherson
Verisign
USA
Email: dmcpherson@verisign.com
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Christoph Loibl
Next Layer Communications
Mariahilfer Guertel 37/7
Vienna 1150
AT
Phone: +43 664 1176414
Email: cl@tix.at
Martin Bacher
T-Mobile Austria
Rennweg 97-99
Vienna 1030
AT
Email: mb.ietf@gmail.com
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