Routing Area Working Group S. Litkowski
Internet-Draft Orange
Intended status: Standards Track A. Simpson
Expires: June 25, 2015 Alcatel Lucent
K. Patel
Cisco
J. Haas
Juniper Networks
December 22, 2014
Applying BGP flowspec rules on a specific interface set
draft-litkowski-idr-flowspec-interfaceset-01
Abstract
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
network.
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 does not detail where the
flow specification rules need to be applied.
This document presents a new interface-set flowspec action that will
be used in complement of other actions (marking, rate-limiting ...).
The purpose of this extension is to inform remote routers on where to
apply the flow specification.
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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Status of This Memo
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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. Interface specific filtering using BGP flowspec . . . . . . . 6
4. Interface-set extended community . . . . . . . . . . . . . . 6
5. Interaction with interface ACLs . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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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 proactively
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
interfaces.
Section Section 3 will detail a solution to address this use case
using BGP Flowspec.
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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. Maintaing
and deploying ACLs on hundreds/thousands of routers is really painful
and time consuming and a service provider would be interrested 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 can imagine two cases :
o Maintaining complete ACLs using flowspec : in this case all the
ingress ACL are maintained and deployed using BGPFlowspec. See
section Section 6 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
provisionning, 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 permanentely in
BGP Flowspec or update its ACL or remove the entry (in case
equipments are not vulnerable anymore).
Section Section 3 will detail a solution to address this use case
using BGP Flowspec.
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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 permits to
apply traffic action one step before and so may permit 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 destinated to MyAS. 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.
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3. Interface specific filtering using BGP flowspec
The use case detailled above requires application of different BGP
Flowspec rules on different set of interfaces. The basic
specification detailled in [RFC5575] does not address this and does
not give any detail on where the FlowSpec filter need to be applied.
We propose to introduce an identification of interfaces within BGP
Flowspec. All interfaces may be associated to one or more group-
identifiers and a BGP Flowspec rule may also be associated with one
or more group-identifiers including a filtering direction
(input/output/both) , so the FlowSpec rule will be applied only on
interfaces belonging the the group identifier included in the BGP
FlowSpec update.
Considering figure 2, we can imagine the following design :
o Internet customer interfaces are associated with group-identifier
1.
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
direction.
4. Interface-set extended community
This document proposes a new BGP extended community called "flow spec
interface-set". This new BGP extended community is part of
TRANSITIVE FOUR-OCTET AS-SPECIFIC EXTENDED COMMUNITY and has subtype
TBD.
The Global Administrator field of this community MUST be set to the
ASN of the originating router. The Local Administrator field is
encoded as follows :
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| O | I | Group Identifier :
+---+---+---+---+---+---+---+---+
: Group Identifier (cont.) |
+---+---+---+---+---+---+---+---+
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-
identifier.
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.
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.
5. 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
behavior. In order, to keep a deterministic and well known
behaviour, an implementation SHOULD process the BGP FlowSpec ACL as
follows :
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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 10.0.0.1/32 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 10.0.0.1 to 11.0.0.2 on port 53 will be rejected
because the dynamic ACL rejects it.
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o a UDP flow from 10.0.0.2 to 11.0.0.2 on port 53 will be accepted
because both ACLs accept it.
o a TCP flow from 10.0.0.2 to 11.0.0.2 on port 80 will be rejected
because permanent ACL rejects it.
6. 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
down.
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
retained.
7. Acknowledgements
Authors would like to thanks Wim Hendrickx for his valuable comments.
8. IANA Considerations
This document requests a new sub-type from the "TRANSITIVE FOUR-OCTET
AS-SPECIFIC EXTENDED COMMUNITY SUB-TYPES" extended community
registry. The sub-type name shall be 'Flow spec interface-set'.
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9. Normative References
[I-D.uttaro-idr-bgp-persistence]
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
2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, August 2009.
Authors' Addresses
Stephane Litkowski
Orange
Email: stephane.litkowski@orange.com
Adam Simpson
Alcatel Lucent
Email: adam.simpson@alcatel-lucent.com
Keyur Patel
Cisco
Email: keyupate@cisco.com
Jeff Haas
Juniper Networks
Email: jhaas@juniper.net
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