Routing Area Working Group                                  S. Litkowski
Internet-Draft                                                    Orange
Intended status: Standards Track                              A. Simpson
Expires: November 19, December 10, 2016                                Alcatel Lucent
                                                                K. Patel
                                                                 J. Haas
                                                        Juniper Networks
                                                            May 18,
                                                            June 8, 2016

        Applying BGP flowspec rules on a specific interface set


   BGP Flow-spec is an extension to BGP that allows for the
   dissemination of traffic flow specification rules.  The primary
   application of this extension is DDoS mitigation where the flowspec
   rules are applied in most cases to all peering routers of the

   This document will present another use case of BGP Flow-spec where
   flow specifications are used to maintain some access control lists at
   network boundary.  BGP Flowspec is a very efficient distributing
   machinery that can help in saving OPEX while deploying/updating ACLs.
   This new application requires flow specification rules to be applied
   only on a specific subset of interfaces and in a specific direction.

   The current specification of BGP Flow-spec ([RFC5575]) introduces the
   notion of flow specification (which describes the matching criterion)
   and traffic filtering actions.  The flow specification is encoded as
   part of the NLRI while the traffic filtering actions are encoded as
   extended communities.  The combination of a flow specification and
   one or more actions is known as a flow specification rule.  [RFC5575]
   does not detail where the flow specification rules need to be


   Besides the flow specification and traffic filtering actions, this
   document presents introduces the notion of traffic filtering scope in order to
   drive where a new interface-set flowspec action particular rule must be applied.  In particular, this
   document introduces the "interface-set" traffic filtering scope that will
   could be used in complement parallel of other traffic filtering actions (marking,
   rate-limiting ...).  The purpose of this extension is to inform
   remote routers on about groups of interfaces where to
   apply the flow specification. rule must be

   This extension can also be used in a DDoS mitigation context where a
   provider wants to apply the filtering only on specific peers.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Use case  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Specific filtering for DDoS . . . . . . . . . . . . . . .   3
     1.2.  ACL maintenance . . . . . . . . . . . . . . . . . . . . .   4
   2.  Collaborative filtering and managing filter direction . . . .   5
   3.  Traffic filtering scope . . . . . . . . . . . . . . . . . . .   6
   4.  Interface specific filtering using BGP flowspec . . . . . . .   6
   5.  Interface-set extended community  . . . . . . . . . . . . . .   7
   5.   8
   6.  Interaction with permanent traffic actions  . . . . filtering rules  . . . . .   8
     5.1.   9
     6.1.  Interaction with interface ACLs . . . . . . . . . . . . .   9
     6.2.  Interaction with flow collection  . . . . . . . . . . . .  10
   6.  11
   7.  Scaling of per interface rules  . . . . . . . . . . . . . . .  10
   7.  11
   8.  Deployment considerations . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  12
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  13
     12.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Use case

1.1.  Specific filtering for DDoS

                       -----------------    --- (ebgp) - Peer3 (BW 10G)
                      /                  \/
                     |                   /|
                     |                PE --- (ebgp) - Transit1(BW 4x10G)
 Cust1 --- (ebgp) --- PE                  |
                     |                PE ---- (ebgp) - Peer2 (BW 4*10G)
                     |                   \|
 Cust2 --- (ebgp) --- PE                  |----- (ebgp) - Customer3
                    /|                    |
 Peer1(BW10G)-(ebgp) |                PE --- (ebgp) - Transit2(BW 4x10G)
                     |                    |
                      \                  /

                                    Figure 1

   The figure 1 above displays a typical service provider Internet
   network owing Customers, Peers and Transit.  To protect pro actively
   against some attacks (e.g.  DNS, NTP ...), the service provider may
   want to deploy some rate-limiting of some flows on peers and transit
   links.  But depending on link bandwidth, the provider may want to
   apply different rate-limiting values.

   For 4*10G links peer/transit, it may want to apply a rate-limiting of
   DNS flows of 1G, while on 10G links, the rate-limiting would be set
   to 250Mbps.  Customer interfaces must not be rate-limited.

   BGP Flow-spec infrastructure may already be present on the network,
   and all PEs may have a BGP session running flowspec address family.
   The Flowspec infrastructure may be reused by the service provider to
   implement such rate-limiting in a very quick manner and being able to
   adjust values in future quickly without having to configure each node
   one by one.  Using the current BGP flowspec specification, it would
   not be possible to implement different rate limiter on different
   interfaces of a same router.  The flowspec rule is applied to all
   interfaces in all directions or on some interfaces where flowspec is
   activated but flowspec rule set would be the same among all

   Section Section 3 4 will detail a solution to address this use case
   using BGP Flowspec.

1.2.  ACL maintenance

                              ---------------    --- (ebgp) - Cust4_VPN
                             /                \/
    Cust1_INT -- (ebgp) --- PE                /|
                            |              PE ------ (ebgp) - Transit1
    Cust3_VPN -- (ebgp) --- PE                 |
                            |              PE ------ (ebgp) - Peer2
                            |                 \|
    Cust2_INT -- (ebgp) --- PE                 |----- (ebgp) - Cust4_INT
                           /|                  |
    Peer1 ------ (ebgp) --  |              PE ------ (ebgp) - Transit2
                            |                  |
                             \                /

                                       Figure 2

   The figure 1 above displays a typical service provider multiservice
   network owing Customers, Peers and Transit for Internet, as well as
   VPN services.  The service provider requires to ensure security of
   its infrastructure by applying ACLs at network boundary.  Maintaining
   and deploying ACLs on hundreds/thousands of routers is really painful
   and time consuming and a service provider would be interested to
   deploy/updates ACLs using BGP Flowspec.  In this scenario, depending
   on the interface type (Internet customer, VPN customer, Peer, Transit
   ...) the content of the ACL may be different.

   We foresee two main cases :

   o  Maintaining complete ACLs using flowspec : in this case all the
      ingress ACL are maintained and deployed using BGPFlowspec.  See
      section Section 8 9 for more details on security aspects.

   o  Requirement of a quick deployment of a new filtering term due to a
      security alert : new security alerts often requires a fast
      deployment of new ACL terms.  Using traditional CLI and hop by hop
      provisioning, such deployment takes time and network is
      unprotected during this time window.  Using BGP flowspec to deploy
      such rule, a service provider can protect its network in few
      seconds.  Then the SP can decide to keep the rule permanently in
      BGP Flowspec or update its ACL or remove the entry (in case
      equipments are not vulnerable anymore).

   Section Section 3 4 will detail a solution to address this use case
   using BGP Flowspec.

2.  Collaborative filtering and managing filter direction

   [RFC5575] states in Section 5. : "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 case of networks collaborating in filtering, there is a use case
   for performing outbound filtering.  Outbound filtering allows to
   apply traffic action one step before and so may allow to prevent
   impact like congestions.

           /                        \
           |   Upstream provider     |
           \                        /
               |                |
               |P2              |P1
           /                        \
           |        MyAS             |
           \                        /

                   Figure 3

   In the figure above, MyAS is connected to an upstream provider.  If a
   malicious traffic comes in from the upstream provider, it may
   congestion P1 or P2 links.  If MyAS apply inbound filtering on P1/P2
   using BGP Flowspec, the congestion issue will not be solved.

   Using collaborative filtering, the upstream provider may propose to
   MyAS to filter malicious traffic sent to it.  We propose to enhance
   [RFC5575] to make myAS able to send BGP FlowSpec updates (on eBGP
   sessions) to the upstream provider to request outbound filtering on
   peering interfaces towards MyAS.  When the upstream provider will
   receive the BGP Flowspec update from MyAS, the BGP flowspec update
   will contain request for outbound filtering on a specific set of
   interfaces.  The upstream provider will apply automatically the
   requested filter and congestion will be prevented.

3.  Interface specific  Traffic filtering using BGP flowspec

   The scope

   We see with the use case detailed described above requires application of different that some BGP
   Flowspec flowspec rules
   may need to be applied only on different set specific elements of interfaces. the network
   (interfaces, nodes ...).  The basic specification detailed in
   [RFC5575] does not address this and does not give any detail on where
   the FlowSpec filter traffic filtering rule need to be applied.

   In addition to the flow specification (flow matching criterion) and
   traffic filtering actions described in [RFC5575], this document
   introduces the notion of traffic filtering scope.  The traffic
   filtering scope will describe where a particular flow specification
   rule must be applied.

   Using a traffic filtering scope in a BGP Flow spec rule is optional.
   When a rule does not contain any traffic filtering scope parameter,
   [RFC5575] applies.

4.  Interface specific filtering using BGP flowspec

   The use case detailed above requires application of different BGP
   Flowspec rules on different set of interfaces.

   We propose to introduce, within BGP Flowspec, an identification a traffic filtering
   scope that identifies a group of interfaces where a particular filter
   should apply on.  Identification of interfaces within BGP Flowspec
   will be done through group identifiers.  A group identifier marks a
   set of interfaces sharing a common administrative property.  Like a
   BGP community, the group identifier itself does not have any
   significance.  It is up to the network administrator to associate a
   particular meaning to a group identifier value (e.g. group ID#1
   associated to Internet customer interfaces).  The group identifier is
   a local interface property.  Any interface may be associated with one
   or more group identifiers using manual configuration.

   When a filtering rule advertised through BGP Flowspec must be applied
   only to particular sets of interfaces, the BGP Flowspec BGP update
   will contain the identifiers associated with the relevant sets of
   interfaces.  In addition to the group identifiers, it will also
   contain the direction the filtering rule must be applied in (see
   Section 4). 5).

   Configuration of group identifiers associated to interfaces may
   change over time.  An implementation MUST ensure that the filtering
   rules (learned from BGP Flowspec) applied to a particular interface
   are always updated when the group identifier mapping is changing.

   Considering figure 2, we can imagine the following design :

   o  Internet customer interfaces are associated with group-identifier

   o  VPN customer interfaces are associated with group-identifier 2.

   o  All customer interfaces are associated with group-identifier 3.

   o  Peer interfaces are associated with group-identifier 4.

   o  Transit interfaces are associated with group-identifier 5.

   o  All external provider interfaces are associated with group-
      identifier 6.

   o  All interfaces are associated with group-identifier 7.

   If the service provider wants to deploy a specific inbound filtering
   on external provider interfaces only, the provider can send the BGP
   flow specification using group-identifier 6 and including inbound

   There are some cases where nodes are dedicated to specific functions
   (Internet peering, Internet Edge, VPN Edge, Service Edge ...), in
   this kind of scenario, there is an interest for a constrained
   distribution of filtering rules that are using the interface specific
   filtering.  Without the constrained route distribution, all nodes
   will received all the filters even if they are not interested in
   those filters.  Constrained route distribution of flowspec filters
   would allow for a more optimized distribution.


5.  Interface-set extended community

   This document proposes a new BGP Route Target extended community
   called "flowspec interface-set".  This document so expands the
   definition of the Route Target extended community to allow a new
   value of high order octet (Type field) to be TBD (in addition to the
   values specified in [RFC4360]).

   In order to ease intra-AS and inter-AS use cases, this document
   proposes to have a transitive as well as a non transitive version of
   this extended community.

   This new BGP Route Target extended community is encoded as follows :

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |  Type (TBD)   |      0x02     |    Autonomous System Number   :
      :     AS Number (cont.)         |O|I|      Group Identifier     |

   The flags are :

   o  O : if set, the flow specification rule MUST be applied in
      outbound direction to the interface set referenced by the
      following group-identifier.

   o  I : if set, the flow specification rule MUST be applied in input
      direction to the interface set referenced by the following group-

   Both flags can be set at the same time in the interface-set extended
   community leading to flow rule to be applied in both directions.  An
   interface-set extended community with both flags set to zero MUST be
   treated as an error and as consequence, the FlowSpec update MUST be
   discarded.  As having no direction indicated as no sense, there is no
   need to propagate the filter informations in the network.

   The Group Identifier is coded as a 14-bit number (values goes from 0
   to 16383).

   Multiple instances of the interface-set community may be present in a
   BGP update.  This may appear if the flow rule need to be applied to
   multiple set of interfaces.

   Multiple instances of the community in a BGP update MUST be
   interpreted as a "OR" operation : if a BGP update contains two
   interface-set communities with group ID 1 and group ID 2, the filter
   would need to be installed on interfaces belonging to Group ID 1 or
   Group ID 2.

   As using a Route Target, route distribution of flowspec NLRI with
   interface-set may be subject to constrained distribution as defined
   in [RFC4684].  Constrained route distribution for flowspec routes
   using interface-set requires discussion and will be addressed in a
   future revision of the document.


6.  Interaction with permanent traffic actions filtering rules

   [RFC5575] states that BGP Flowspec is primarily designed to allow
   upstream AS to perform inbound filtering in their ingress routers.
   This specification does not precise where this ingress filtering
   should happen in the packet processing pipe.

   This proposal enhances [RFC5575] in order to add action on rules for traffic
   coming from or going to specific interfaces.  Based on this
   enhancement, some new requirements come to implementations.

   An implementation SHOULD apply input actions (I bit set) within the
   input packet processing pipe.  An implementation SHOULD apply output
   actions (O bit set) within the output packet processing pipe.

   As input and output processing pipes may also involve already present
   static/permanent features that will manipulate the packet, the next
   sections will try to clarify how the static behaviors should interact
   will BGP flowspec actions.


6.1.  Interaction with interface ACLs

   Deploying interface specific filters using BGP FlowSpec (dynamic
   entries) may interfere with existing permanent interface ACL (static
   entries).  The content of the existing permanent ACL MUST NOT be
   altered by dynamic entries coming from BGP FlowSpec.  Permanent ACLs
   are using a specific ordering which is not compatible with the
   ordering of FS rules and misordering of ACL may lead to undesirable
   behaviour.  In order, to keep a deterministic and well known
   behaviour, an implementation SHOULD process the BGP FlowSpec ACL as
   follows :

   o  In inbound direction, the permanent ACL action is applied first
      followed by FlowSpec action.  This gives the primary action to the
      permanent ACL as it is done today.

   o  In outbound direction, FlowSpec action action is applied first followed
      by permanent ACL.  This gives the final action to the permanent
      ACL as it is done today.

                        Inbound filters                          Outbound filters
           ---------      -------      ----------      -------      ---------
          |Permanent| -> |Dynamic| -> |Forwarding| -> |Dynamic| -> |Permanent|

   In order for a flow to be accepted, the flow must be accepted by the
   two ACLs and a flow is rejected when one of the ACL rejects it as
   described in the table below :

   |   Permanent ACL entry   |    FlowSpec ACL entry    |    Result    |
   |          action         |          action          |    action    |
   |           Drop          |           Drop           |     Drop     |
   |           Drop          |          Accept          |     Drop     |
   |          Accept         |           Drop           |     Drop     |
   |          Accept         |          Accept          |    Accept    |

   Example :

   o  ACL permanent IN :

      *  Entry 1 : permit udp from 10/8 to 11/8 port 53

      *  Entry 2 : permit tcp from 10/8 to 11/8 port 22

      *  Entry 3 : deny ip from 10/8 to 11/8

   o  ACL dynamic FlowSpec IN :

      *  Entry 1 : deny udp from to 11/8 port 53

      *  Entry 2 : permit tcp from 10/8 to 11/8 port 80

   In the example above :

   o  a UDP flow from to on port 53 will be rejected
      because the dynamic ACL rejects it.

   o  a UDP flow from to on port 53 will be accepted
      because both ACLs accept it.

   o  a TCP flow from to on port 80 will be rejected
      because permanent ACL rejects it.


6.2.  Interaction with flow collection

   A router may activate flow collection features (used in collaboration
   with Netflow export).  Flow collection can be done at input side or
   output side.  As for ACL, an implementation SHOULD process :

   o  BGP FS rules after the inbound flow collection : in case of DDoS
      protection, it is important to keep monitoring of attack flows and
      so performing action, after collection.

   o  BGP FS rules before the outbound flow collection : purpose of
      outbound flow collection is really to track flows that are exiting
      the interface.  BGP FS rules should not interfere in this.

        Inbound                                                 Outbound
        Flow          BGP                           BGP         Flow
                collection    FS                            FS          collection
           ---------      -------      ----------      -------      ---------
          |Permanent| -> |Dynamic| -> |Forwarding| -> |Dynamic| -> |Permanent|


7.  Scaling of per interface rules

   Creating rules that are applied on specific interfaces may create
   forwarding rules that may be harder to share.

   An implementation SHOULD take care about trying to keep sharing
   forwarding structures as much as possible in order to limit the
   scaling impact.  How the implementation would do so is out of scope
   of the document.


8.  Deployment considerations

   There are some cases where a particular BGP Flowspec NLRI may be
   advertised to different interface groups with a different action.
   For example, a service provider may want to discard all ICMP traffic
   from customer interfaces to infrastructure addresses and want to
   rate-limit the same traffic when it comes from some internal
   platforms.  These particular cases require ADD-PATH to be deployed in
   order to ensure that all paths (NLRI+interface group+actions) (NLRI+interface-set group-id+actions)
   are propagated within the BGP control plane.  Without ADD-PATH, only
   a single "NLRI+interface group+actions" "NLRI+interface-set group-id+actions" will be propagated, so
   some filtering rules will never be applied.


9.  Security Considerations

   Managing permanent Access Control List by using BGP Flowspec as
   described in Section 1.2 helps in saving roll out time of such ACL.
   However some ACL especially at network boundary are critical for the
   network security and loosing the ACL configuration may lead to
   network open for attackers.

   By design, BGP flowspec rules are ephemeral : the flow rule exists in
   the router while the BGP session is UP and the BGP path for the rule
   is valid.  We can imagine a scenario where a Service Provider is
   managing the network boundary ACLs by using only FlowSpec.  In this
   scenario, if , for example, an attacker succeed to make the internal
   BGP session of a router to be down , it can open all boundary ACLs on
   the node, as flowspec rules will disappear due to the BGP session

   In reality, the chance for such attack to occur is low, as boundary
   ACLs should protect the BGP session from being attacked.

   In order to complement the BGP flowspec solution is such deployment
   scenario and provides security against such attack, a service
   provider may activate Long lived Graceful Restart
   [I-D.uttaro-idr-bgp-persistence] on the BGP session owning Flowspec
   address family.  So in case of BGP session to be down, the BGP paths
   of Flowspec rules would be retained and the flowspec action will be


10.  Acknowledgements

   Authors would like to thanks Wim Hendrickx and Robert Raszuk for his
   their valuable comments.


11.  IANA Considerations

   This document requests a new type from the "BGP Transitive Extended
   Community Types" extended community registry.  This type name shall
   be 'FlowSpec'.

   This document requests a new type from the "BGP Non-Transitive
   Extended Community Types" extended community registry.  This type
   name shall be 'FlowSpec'.

   This document requests creation of a new registry called "FlowSpec
   Extended Community Sub-Types".  This registry contains values of the
   second octet (the "Sub-Type" field) of an extended community when the
   value of the first octet (the "Type" field) is to one of those
   allocated in this document.

   Within this new registry, this document requests a new subtype
   (suggested value 0x02), this sub-type shall be named "interface-set".


12.  References


12.1.  Normative References

              Rosen, E., Patel, K., Haas, J., and R. Raszuk, "Route
              Target Constrained Distribution of Routes with no Route
              Targets", draft-ietf-idr-rtc-no-rt-05 (work in progress),
              May 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <>.

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
              R., Patel, K., and J. Guichard, "Constrained Route
              Distribution for Border Gateway Protocol/MultiProtocol
              Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
              Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
              November 2006, <>.

   [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,


12.2.  Informative References

              Uttaro, J., Chen, E., Decraene, B., and J. Scudder,
              "Support for Long-lived BGP Graceful Restart", draft-
              uttaro-idr-bgp-persistence-03 (work in progress), November

Authors' Addresses

   Stephane Litkowski

   Adam Simpson
   Alcatel Lucent


   Keyur Patel


   Jeff Haas
   Juniper Networks