draft-ietf-idr-bgp-flowspec-oid-06.txt   draft-ietf-idr-bgp-flowspec-oid-07.txt 
Network Working Group J. Uttaro Network Working Group J. Uttaro
Internet-Draft AT&T Internet-Draft AT&T
Updates: 5575 (if approved) J. Alcaide Updates: 5575 (if approved) J. Alcaide
Intended status: Standards Track C. Filsfils Intended status: Standards Track C. Filsfils
Expires: October 28, 2018 D. Smith Expires: May 9, 2019 D. Smith
Cisco Cisco
P. Mohapatra P. Mohapatra
Sproute Networks Sproute Networks
April 26, 2018 November 5, 2018
Revised Validation Procedure for BGP Flow Specifications Revised Validation Procedure for BGP Flow Specifications
draft-ietf-idr-bgp-flowspec-oid-06 draft-ietf-idr-bgp-flowspec-oid-07
Abstract Abstract
This document describes a modification to the validation procedure This document describes a modification to the validation procedure
defined in RFC 5575 for the dissemination of BGP flow specifications. defined in RFC 5575 for the dissemination of BGP flow specifications.
RFC 5575 requires that the originator of the flow specification RFC 5575 requires that the originator of the flow specification
matches the originator of the best-match unicast route for the matches the originator of the best-match unicast route for the
destination prefix embedded in the flow specification. This allows destination prefix embedded in the flow specification. This allows
only BGP speakers within the data forwarding path (such as autonomous only BGP speakers within the data forwarding path (such as autonomous
system border routers) to originate BGP flow specifications. Though system border routers) to originate BGP flow specifications. Though
skipping to change at page 1, line 47 skipping to change at page 1, line 47
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 28, 2018. This Internet-Draft will expire on May 9, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 4, line 7 skipping to change at page 4, line 7
Figure 1 Figure 1
It is highly desirable that each ASN is able to protect itself It is highly desirable that each ASN is able to protect itself
independently from network security attacks using the BGP flow independently from network security attacks using the BGP flow
specification NLRI for intra-domain purposes only. Network operators specification NLRI for intra-domain purposes only. Network operators
often deploy a dedicated Security Operations Center (SOC) within often deploy a dedicated Security Operations Center (SOC) within
their ASN to monitor and detect such security attacks. To mitigate their ASN to monitor and detect such security attacks. To mitigate
attacks in a scalable intra-domain manner, operators require the attacks in a scalable intra-domain manner, operators require the
ability to originate intra-domain flow specification NLRIs from a ability to originate intra-domain flow specification NLRIs from a
central BGP route controller (or router reflector per [RFC4456]) that central BGP route controller that is not within the data forwarding
is not within the data forwarding plane. In this way, operators can plane. In this way, operators can direct border routers within their
direct border routers within their ASN with specific attack ASN with specific attack mitigation actions (drop the traffic,
mitigation actions (drop the traffic, forward to a clean-pipe center, forward to a clean-pipe center, etc.). To originate a flow
etc.). To originate a flow specification NLRI, a central BGP route specification NLRI, a central BGP route controller must set itself as
controller (or route reflector) must set itself as the originator in the originator in the flowspec NLRI. This is necessary given the
the flowspec NLRI. This is necessary given the route controller is route controller is originating the flow specification not reflecting
originating the flow specification not reflecting it, and to avoid it, and to avoid the complexity of having to determine the egress
the complexity of having to determine the egress border router whose border router whose path was chosen as the best in each of the
path was chosen as the best in each of the ingress border routers. ingress border routers. It thus becomes necessary to modify step (a)
It thus becomes necessary to modify step (a) of the RFC 5575 of the [RFC5575] validation procedure such that an IBGP peer that is
validation procedure such that an IBGP peer that is not within the not within the data forwarding plane may originate flow specification
data forwarding plane may originate flow specification NLRIs. NLRIs.
3. Introduction 3. Introduction
RFC 5575 defined a new BGP capability that can be used to distribute [RFC5575] defined a new BGP capability that can be used to distribute
traffic flow specifications amongst BGP speakers in support of traffic flow specifications amongst BGP speakers in support of
traffic filtering. The primary intention of RFC 5575 is to enable traffic filtering. The primary intention of [RFC5575] is to enable
downstream autonomous systems to signal traffic filtering policies to downstream autonomous systems to signal traffic filtering policies to
upstream autonomous systems. In this way, traffic is filtered closer upstream autonomous systems. In this way, traffic is filtered closer
to the source and the upstream autonomous system(s) avoid carrying to the source and the upstream autonomous system(s) avoid carrying
the traffic to the downstream autonomous system only to be discarded. the traffic to the downstream autonomous system only to be discarded.
RFC 5575 also enables more granular traffic filtering based upon [RFC5575] also enables more granular traffic filtering based upon
upper layer protocol information (e.g., protocol port numbers) as upper layer protocol information (e.g., protocol port numbers) as
opposed to coarse IP destination prefix-based filtering. Flow opposed to coarse IP destination prefix-based filtering. Flow
specification NLRIs received from a BGP peer are subject to validity specification NLRIs received from a BGP peer are subject to validity
checks before being considered feasible and subsequently installed checks before being considered feasible and subsequently installed
within the respective Adj-RIB-In. The validation procedure defined within the respective Adj-RIB-In. The validation procedure defined
within RFC 5575 requires that the originator of the flow within [RFC5575] requires that the originator of the flow
specification NLRI matches the originator of the best-match unicast specification NLRI matches the originator of the best-match unicast
route for the destination prefix embedded in the flow specification. route for the destination prefix embedded in the flow specification.
This allows only BGP speakers [RFC4271] within the data forwarding This allows only BGP speakers [RFC4271] within the data forwarding
path (such as autonomous system border routers) to originate BGP flow path (such as autonomous system border routers) to originate BGP flow
specification NLRIs. Though it is possible to disseminate such flow specification NLRIs. Though it is possible to disseminate such flow
specification NLRIs directly from border routers, it may be specification NLRIs directly from border routers, it may be
operationally cumbersome in an autonomous system with a large number operationally cumbersome in an autonomous system with a large number
of border routers having complex BGP policies. This document of border routers having complex BGP policies. This document
describes a modification to the RFC 5575 validation procedure describes a modification to the [RFC5575] validation procedure
allowing flow specification NLRIs to be originated from a centralized allowing flow specification NLRIs to be originated from a centralized
BGP route controller within the local autonomous system that is BGP route controller within the local autonomous system that is not
neither in the data forwarding path nor serving as a BGP route in the data forwarding path. While the proposed modification cannot
reflector [RFC4456]. While the proposed modification cannot be used be used for inter-domain coordination of traffic filtering, it
for inter-domain coordination of traffic filtering, it greatly greatly simplifies distribution of intra-domain traffic filtering
simplifies distribution of intra-domain traffic filtering policies in policies in an autonomous system with a large number of border
an autonomous system with a large number of border routers having routers having complex BGP policies. By relaxing the validation
complex BGP policies. By relaxing the validation procedure for IBGP, procedure for IBGP, the proposed modification allows flow
the proposed modification allows flow specifications to be specifications to be distributed in a standard and scalable manner
distributed in a standard and scalable manner throughout an throughout an autonomous system.
autonomous system.
4. Revised Validation Procedure 4. Revised Validation Procedure
Step (a) of the validation procedure specified in RFC 5575, section 6 Step (a) of the validation procedure specified in [RFC5575], section
is redefined as follows: 6 is redefined as follows:
a. One of the following conditions MUST hold true. a. One of the following conditions MUST hold true.
* The originator of the flow specification matches the * The originator of the flow specification matches the
originator of the best-match unicast route for the destination originator of the best-match unicast route for the destination
prefix embedded in the flow specification. prefix embedded in the flow specification.
* The AS_PATH attribute of the flow specification does not * The AS_PATH attribute of the flow specification does not
contain AS_SET and AS_SEQUENCE segments. contain AS_SET and/or AS_SEQUENCE segments.
An AS_PATH without AS_SET and AS_SEQUENCE segments indicates that the An AS_PATH without AS_SET and/or AS_SEQUENCE segments indicates that
flow specification was originated inside the local AS [RFC4271] or the flow specification was originated inside the local AS [RFC4271]
inside the local confederation (in the case that the local AS belongs or inside the local confederation (in the case that the local AS
to a confederation of ASes) [RFC5065]. With this modification to the belongs to a confederation of ASes) [RFC5065]. With this
RFC 5575 validation procedure, it is now possible for an IBGP peer modification to the [RFC5575] validation procedure, it is now
that is not within the data forwarding path to originate flow possible for an IBGP peer that is not within the data forwarding path
specification NLRIs. This applies whether the AS belongs or not to a to originate flow specification NLRIs. This applies whether the AS
confederation of ASes. Checking the (newly introduced) second belongs or not to a confederation of ASes. Checking the (newly
condition above MAY be disabled by configuration on a BGP speaker. introduced) second condition above MAY be disabled by configuration
However, it SHOULD be enabled by default. Disabling the condition on a BGP speaker. However, it SHOULD be enabled by default.
may be a good practice when the administrator knows with certainty Disabling the condition may be a good practice when the administrator
that there are not flow specification NLRI originated inside the knows with certainty that there are not flow specification NLRI
local AS (or local confederation). Optionally, an implementation originated inside the local AS (or local confederation). The default
could be configured to allow only flow specification NLRIs containing behavior is thus to validate an empty AS_PATH. In this context, an
only a subset of ASes. This could be useful, for example, with empty AS_PATH means that it does not have AS_SET and/or AS_SEQUENCE
networks that consist of multiple ASes that operate under the same segments. Optionally, an implementation MAY also validate a specific
administrative domain. non-empty AS_PATH. For instance, it could validate a flowspec NLRI
whose AS_PATH contains only an AS_SEQUENCE of ASes known (via
configuration) to belong to the same administrative domain.
Further, RFC 5575 states that "BGP (flow specification) Further, [RFC5575] states that "BGP (flow specification)
implementations MUST also enforce that AS_PATH attribute of a route implementations MUST also enforce that AS_PATH attribute of a route
received via the External Border Gateway Protocol (EBGP) contains the received via the External Border Gateway Protocol (EBGP) contains the
neighboring AS in the left-most position of the AS_PATH attribute". neighboring AS in the left-most position of the AS_PATH attribute".
This rule is not valid for all topologies. For example, it prevents This rule is not valid for all topologies. For example, it prevents
the exchange of BGP flow specification NLRIs at Internet exchanges the exchange of BGP flow specification NLRIs at Internet exchanges
with BGP route servers. Therefore, this document also redefines the with BGP route servers. Therefore, this document also redefines the
RFC 5575 AS_PATH validation procedure referenced above as follows. [RFC5575] AS_PATH validation procedure referenced above as follows:
BGP flow specification implementations MUST enforce that the last AS BGP flow specification implementations MUST enforce that the last AS
added within the AS_PATH attribute of a EBGP learned flow added within the AS_PATH attribute of a EBGP learned flow
specification NLRI MUST match the last AS added within the AS_PATH specification NLRI MUST match the last AS added within the AS_PATH
attribute of the best-match unicast route for the destination prefix attribute of the best-match unicast route for the destination prefix
embedded in the flow specification. This proposed modification embedded in the flow specification. This proposed modification
enables the exchange of BGP flow specification NLRIs at Internet enables the exchange of BGP flow specification NLRIs at Internet
exchanges with BGP route servers while at the same time, for security exchanges with BGP route servers while at the same time, for security
reasons, prevents an EBGP peer from advertising an inter-domain flow reasons, prevents an EBGP peer from advertising an inter-domain flow
specification for a destination prefix that it does not provide specification for a destination prefix that it does not provide
reachability information for. Note, comparing only the last ASes is reachability information for. Note, comparing only the last ASes
sufficient for EBGP learned flow specification NLRIs. Requiring a added is sufficient for EBGP learned flow specification NLRIs.
full AS_PATH match would limit origination of inter-domain flow Requiring a full AS_PATH match would limit origination of inter-
specifications to the origin (or first) AS of the best-match unicast domain flow specifications to the origin (or first) AS of the best-
route for the destination prefix embedded in the flow specification match unicast route for the destination prefix embedded in the flow
only. As such, a full AS_PATH validity check may prevent transit specification only. As such, a full AS_PATH validity check may
ASes from originating inter-domain flow specifications which is not prevent transit ASes from originating inter-domain flow
desirable. specifications, which is not desirable.
This document also clarifies proper handling when the BGP flow This document also clarifies proper handling when the BGP flow
specification does not embed a destination prefix component. The specification does not embed a destination prefix component. The
default behavior SHOULD be not to perform any validation procedure. default behavior SHOULD be not to perform any validation procedure.
Further, support for two-octet AS number space is out of the scope of Further, support for two-octet AS number space is out of the scope of
this document. this document.
In this context, AS_PATH attribute is defined as the reconstructed AS In this context, AS_PATH attribute is defined as the reconstructed AS
Path information (by combining AS_PATH and AS4_PATH attributes, if Path information (by combining AS_PATH and AS4_PATH attributes, if
the BGP speaker is a NEW speaker and receives the route from an OLD the BGP speaker is a NEW speaker and receives the route from an OLD
speaker), according to section 4.2.3 of RFC 6793. speaker), according to section 4.2.3 of [RFC6793].
RFC 5575 references "the best-match unicast route for the destination [RFC5575] references "the best-match unicast route for the
prefix embedded in the flow specification". For clarity, this route destination prefix embedded in the flow specification". For clarity,
is defined hereby as the best path of the unicast network that covers this route is defined hereby as the best path of the unicast network
destination prefix embedded in the flow specification with the longer that covers destination prefix embedded in the flow specification
prefix-length. In other words, we consider only the best-match with the longer prefix-length. In other words, we consider only the
network and we do not consider unicast non-best paths (even if it is best-match network and we do not consider unicast non-best paths
received from the same peer than the flowspec route). (even if it is received from the same peer than the flowspec route).
Note that, per RFC 5575, originator may refer to the BGP Note that, per [RFC5575], originator may refer to the BGP
ORIGINATOR_ID attribute or the transport address of the peer from ORIGINATOR_ID attribute or the transport address of the peer from
which we received the update. If the later, a network must be which we received the update. If the later, a network must be
designed so it has a congruent topology. Otherwise, using two designed so it has a congruent topology. Otherwise, using two
peering sessions between the same pair of BGP speakers, one for peering sessions between the same pair of BGP speakers, one for
unicast and one for flowspec, will cause the flowspec validation unicast and one for flowspec, will cause the flowspec validation
procedure to fail. Consider, for example, the case where a BGP route procedure to fail. Consider, for example, the case where a BGP route
reflector receives the NLRIs from a route reflector client, thus not reflector receives the NLRIs from a route reflector client, thus not
receiving the ORIGINATOR_ID attribute. If the speaker belongs to a receiving the ORIGINATOR_ID attribute. If the speaker belongs to a
confederation [RFC5065] and we are receiving a flowspec route from confederation [RFC5065] and we are receiving a flowspec route from
different peers than its best match unicast route, the flowspec different peers than its best match unicast route, the flowspec
validation procedure will fail as well. Consider also a validation procedure will fail as well. Consider also a
misconfiguration where flowspec address-family is not configured for misconfiguration where flowspec address-family is not configured for
a particular peering between different member-AS (but it is a particular peering between different member-AS (but it is
configured for unicast). Even if we receive the flowspec route via a configured for unicast). Even if we receive the flowspec route via a
redundant peer, we may receive the unicast route and the flowspec redundant peer, we may receive the unicast route and the flowspec
from different peers, and thus flowspec validation will fail. With from different peers, and thus flowspec validation will fail. Thus,
the (newly introduced) second condition above applied, uncongruent with the (newly introduced) second condition above applied,
topologies are supported. incongruent topologies are supported.
Note that if the flowspec NLRI is learned from another AS (and thus
the AS_PATH is not empty), the original validation procedures defined
in [RFC5575] still apply and incongruent topologies may cause
validation rules to fail.
5. IANA Considerations 5. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
6. Security Considerations 6. Security Considerations
No new security issues are introduced by relaxing the validation No new security issues are introduced by relaxing the validation
procedure for IBGP learned flow specifications. With this proposal, procedure for IBGP learned flow specifications. With this proposal,
the security characteristics of BGP flow specifications remain the security characteristics of BGP flow specifications remain
equivalent to the existing security properties of BGP unicast equivalent to the existing security properties of BGP unicast
routing. Traffic flow specifications learned from IBGP peers are routing. Traffic flow specifications learned from IBGP peers are
trusted, hence, it is not required to validate that the originator of trusted, hence, it is not required to validate that the originator of
an intra-domain traffic flow specification matches the originator of an intra-domain traffic flow specification matches the originator of
the best-match unicast route for the flow destination prefix. the best-match unicast route for the flow destination prefix.
Conversely, this proposal continues to enforce the validation Conversely, this proposal continues to enforce the validation
procedure for EBGP learned traffic flow specifications. In this way, procedure for EBGP learned traffic flow specifications. In this way,
the security properties of RFC 5575 are maintained such that an EBGP the security properties of [RFC5575] are maintained such that an EBGP
peer cannot cause a denial-of-service attack by advertising an inter- peer cannot cause a denial-of-service attack by advertising an inter-
domain flow specification for a destination prefix that it does not domain flow specification for a destination prefix that it does not
provide reachability information for. provide reachability information for.
7. Acknowledgements 7. Acknowledgements
The authors would like to thank Han Nguyen for his direction on this The authors would like to thank Han Nguyen for his direction on this
work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen
and Shyam Sethuram for their review comments. and Shyam Sethuram for their review comments.
 End of changes. 22 change blocks. 
75 lines changed or deleted 81 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/