Network Working Group                                         S. Hartman
Internet-Draft                                         Painless Security
Intended status: Informational                                  D. Zhang
Expires: October 8, 2011                                          Huawei
                                                           April 6, 2011

                   Operations Model for Router Keying


   Developing an operational and management model for routing protocol
   security that works across protocols will be critical to the success
   of routing protocol security efforts.  This document discusses issues
   and begins to consider development of these models.

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
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   This Internet-Draft will expire on October 8, 2011.

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   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  4
   3.  Breakdown of KARP configuration  . . . . . . . . . . . . . . .  5
     3.1.  Integrity of the Key Table . . . . . . . . . . . . . . . .  6
     3.2.  Management of Key Table  . . . . . . . . . . . . . . . . .  6
     3.3.  Protocol Limitations from the Key Table  . . . . . . . . .  7
     3.4.  VRFs . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Credentials and Authorization  . . . . . . . . . . . . . . . .  8
     4.1.  Preshared Keys . . . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Asymmetric Keys  . . . . . . . . . . . . . . . . . . . . . 11
     4.3.  Public Key Infrastructure  . . . . . . . . . . . . . . . . 11
     4.4.  The role of Central Servers  . . . . . . . . . . . . . . . 12
   5.  Grouping Peers Together  . . . . . . . . . . . . . . . . . . . 13
   6.  Administrator Involvement  . . . . . . . . . . . . . . . . . . 15
     6.1.  Enrollment . . . . . . . . . . . . . . . . . . . . . . . . 15
     6.2.  Handling Faults  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Upgrade Considerations . . . . . . . . . . . . . . . . . . . . 17
   8.  Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 18
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     11.2. Informative References . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22

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1.  Introduction

   The KARP working group is designing improvements to the cryptographic
   authentication of IETF routing protocols.  These improvements include
   improvements to how integrity functions are handled within each
   protocol as well as designing an automated key management solution.

   This document discusses issues to consider when thinking about the
   operational and management model for KARP.  Each implementation will
   take its own approach to management; this is one area for vendor
   differentiation.  However, it is desirable to have a common baseline
   for the management objects allowing administrators, security
   architects and protocol designers to understand what management
   capabilities they can depend on in heterogeneous environments.
   Similarly, designing and deploying the protocol will be easier with
   thought paid to a common operational model.  This will also help with
   the design of NetConf schemas or MIBs later.

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2.  Requirements notation

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

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3.  Breakdown of KARP configuration

   There are multiple ways of structuring configuration information.
   One factor to consider is the scope of the configuration information.
   Several protocols are peer-to-peer routing protocols where a
   different key could potentially be used for each neighbor.  Other
   protocols require the same group key to be used for all nodes in an
   administrative domain or routing area.  In other cases, the same
   group key needs to be used for all routers on an interface, but
   different group keys can be used for each interface.

   Within situations where a per-interface, per-area or per-peer key can
   be used for manually configured long-term keys, that flexibility may
   not be desirable from an operational standpoint.  For example
   consider OSPF [RFC2328].  Each OSPF link needs to use the same
   authentication configuration, including the set of keys used for
   reception and the set of keys used for transmission, but may use
   different keys for different links.  The most general management
   model would be to configure keys per link.  However for deployments
   where the area uses the same key it would be strongly desirable to
   configure the key as a property of the area.  If the keys are
   configured per-link, they can get out of sync.  In order to support
   generality of configuration and common operational situations, it
   would be desirable to have some sort of inheritance where default
   configurations are made per-area unless overridden per-interface.

   As described in [I-D.housley-saag-crypto-key-table], the
   cryptographic keys are separated from the interface configuration
   into their own configuration store.  This document should specify how
   key selection interacts with the key table.  One possible approach
   would be to assume that all keys that permit use on a given interface
   would be used on that interface.  This model would need to be
   expanded in cases where keys are configured per-area or per-domain.
   It's not clear why "all" is permitted as an interface specification
   in this model; it seems unlikely that it would be desirable to use
   the same set of keys for two different instances of an IGP or across
   autonomous system boundaries.

   Another model is that the interface specification in the key table is
   a restriction.  Then a set of keys from the key table is attached to
   an interface, area or routing domain using an additional
   configuration step.  This avoids the previous problems at the expense
   of significant complexity of configuration.

   Operational Requirements: KARP MUST support configuration of keys at
   the most general scope for the underlying protocol; protocols
   supporting per-peer keys MUST permit configuration of per-peer keys,
   protocols supporting per-interface keys MUST support configuration of

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   per-interface keys, and so on.  KARP MUST NOT permit configuration of
   an inappropriate key scope.  For example, configuration of separate
   keys per interface MUST NOT be supported for a protocol requiring
   per-area keys.

3.1.  Integrity of the Key Table

   The routing key table [I-D.housley-saag-crypto-key-table] provides a
   very general mechanism to abstract the storage of keys for routing
   protocols.  To avoid misconfiguration and simplify problem
   determination, the router MUST verify the internal consistency of
   entries added to the table.  At a minimum, the router MUST verify:

   o  The cryptographic algorithms are valid for the protocol.

   o  The key derivation function is valid for the protocol.

   o  The direction is valid for the protocol; for example protocols
      that require the same session key be used in both directions MUST
      have a direction of both.

   o  The peer and interface specification is consistent with the

   Other checks are possible.  For example the router could verify that
   if a key is associated with a peer, that peer is a configured peer
   for the specified protocol.  However, this may be undesirable.  It
   may be desirable to load a key table when some peers have not yet
   been configured.  Also, it may be desirable to share portions of a
   key table across devices even when their current configuration does
   not require an adjacency with a particular peer in the interest of
   uniform configuration or preparing for fail-over.

3.2.  Management of Key Table

   Several management operations will be quite common.  For service
   provider deployments the configuration management system can simply
   update the key table.  However, for smaller deployments, efficient
   management operations are important.

   As part of adding a new key it is typically desirable to set an
   expiration time for an old key.  The management interface SHOULD
   provide a mechanism to easily update the expiration time for a
   current key used with a given peer or interface.  Also when adding a
   key it is desirable to push the key out to nodes that will need it,
   allowing use for receiving packets then later enabling transmit.
   This can be accomplished automatically by providing a delay between
   when a key becomes valid for reception and transmission.  However,

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   some environments may not be able to predict when all the necessary
   changes will be made.  In these cases having a mechanism to enable a
   key for sending is desirable.

3.3.  Protocol Limitations from the Key Table

   The format of the key table imposes a few limitations on routing
   protocols.  The first is that the key ID is 16 bits; some routing
   protocols have 32-bit key identifiers.  A key mapping table as
   discussed in 4.1 of [I-D.polk-saag-rtg-auth-keytable] could be used
   to map to the larger key identifier.  However it's probably desirable
   to either decide that only 16 bits of the key ID space is to be used
   or to expand the identifier space in the key table.  From a
   management standpoint we need to make concrete requirements around
   whether a key ID is per-protocol or whether subspaces in the key ID
   space are reserved for each protocol.  This is necessary so that
   implementations from different vendors can be managed consistently.

   The second requirement that the key table places is that the key ID
   is scoped fairly broadly.  At least within some protocols such as
   OSPF, the key ID might only need to be unique per-link or per-peer.
   That is, packets sent on two different interfaces could use key ID 32
   even if the keys were different for these interfaces.  An
   implementation could use the interface and the key ID as a lookup to
   find the right key.  However, the key table draft requires that a key
   ID be sufficient to look up a key, meaning that the key ID is a
   globally scoped identifier.  There is nothing wrong with this
   restriction, but it does need to be noted when assigning key IDs for
   a domain.

   Consideration is required for how an automated key management
   protocol will assign key IDs for group keys.  All members of the
   group may need to use the same key ID.  This requires careful
   coordination of global key IDs.  Interactions with the peer key ID
   field may make this easier; this requires additional study.

3.4.  VRFs

   Many core and enterprise routers support multiple routing instances.
   For example a router serving multiple VPNs is likely to have a
   forwarding/routing instance for each of these VPNs.  We need to
   decide how the key table and other configuration information for KARP
   interacts with this.  The obvious first-order answer is that each
   routing instance gets its own key table.  However, we need to
   consider how these instances interact with each other and confirm
   this makes sense.

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4.  Credentials and Authorization

   Several methods for authentication have been proposed for KARP.  The
   simplest is preshared keys used directly as traffic keys.  In this
   mode, the traffic integrity keys are directly configured.  This is
   the mode supported by today's routing protocols.

   As discussed in [I-D.polk-saag-rtg-auth-keytable], preshared keys can
   be used as the input to a key derivation function (KDF) to generate
   traffic keys.  For example the TCP Authentication Option (TCP-AO)
   [RFC5925] derives keys based on the initial TCP session state.
   Typically a KDF will combine a long-term key with public inputs
   exchanged as part of the protocol to form fresh session keys. a KDF
   could potentially be used with some inputs that are configured along
   with the long-term key.  Also, it's possible that inputs to a KDF
   will be private and exchanged as part of the protocol, although this
   will be uncommon in KARP's uses of KDFs.

   Preshared keys could also be used by an automated key management
   protocol.  In this mode, preshared keys would be used for
   authentication.  However traffic keys would be generated by some key
   agreement mechanism or transported in a key encryption key derived
   from the preshared key.  This mode may provide better replay
   protection.  Also, in the absence of active attackers, key agreement
   strategies such as Diffie-Hellman can be used to produce high-quality
   traffic keys even from relatively weak preshared keys.

   Public keys can be used for authentication.  The design guide
   [I-D.ietf-karp-design-guide] describes a mode in which routers have
   the hashes of peer routers' public keys.  In this mode, a traditional
   public-key infrastructure is not required.  The advantage of this
   mode is that a router only contains its own keying material, limiting
   the scope of a compromise.  The disadvantage is that when a router is
   added or deleted from the set of authorized routers, all routers that
   peer need to be updated.  Note that self-signed certificates are a
   common way of communicating public-keys in this style of

   Certificates signed by a certification authority or some other PKI
   could be used.  The advantage of this approach is that routers may
   not need to be directly updated when peers are added or removed.  The
   disadvantage is that more complexity and cost is required.

   Each of these approaches has a different set of management and
   operational requirements.  Key differences include how authorization
   is handled and how identity works.  This section discusses these

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4.1.  Preshared Keys

   In the protocol, manual preshared keys are either unnamed or named by
   a small integer (typically 16 or 32 bits) key ID.  Implementations
   that support multiple keys for protocols that have no names for keys
   need to try all possible keys before deciding a packet cannot be
   validated [RFC4808].  Typically key IDs are names used by one group
   or peer.

   Manual preshared keys are often known by a group of peers rather than
   just one peer.  This is an interesting security property: it is
   impossible to identify the peer sending a message cryptographically;
   it is only possible to identify a group of peers using cryptographic
   means.  Within the routing threat model the peer sending a message
   can be identified only because peers are trusted and thus can be
   assumed to correctly label the packets they send.  This contrasts
   with a protocol where cryptographic means such as digital signatures
   are used to verify the origin of a message.  As a consequence,
   authorization is typically based on knowing the preshared key rather
   than on being a particular peer.  Note that once an authorization
   decision is made, the peer can assert its identity; this identity is
   trusted just as the routing information from the peer is trusted.
   However, for the process of authorization, it would be more
   complicated to identify peers this way and would not gain a security
   benefit in most deployments.

   Preshared keys used with key derivation function similarly to manual
   preshared keys.  However to form the actual traffic keys, session or
   peer specific information is combined with the key.  From an
   authorization standpoint, the derivation key works the same as a
   manual key.  An additional routing protocol step or transport step
   forms the key that is actually used.

   Preshared keys that are used via automatic key management have not
   been specified.  Their naming and authorization may differ.  In
   particular, such keys may end up being known only by two peers.
   Alternatively they may also be known by a group of peers.
   Authorization could potentially be based on peer identity, although
   it is likely that knowing the right key will be sufficient.  There
   does not appear to be a compelling reason to decouple the
   authorization of a key for some purpose from authorization of peers
   holding that key to perform the authorized function.

   Care needs to be taken when symmetric keys are used for multiple
   purposes.  Consider the implications of using the same preshared key
   for two interfaces: it becomes impossible to distinguish a router on
   one interface from a router on another interface.  So, a router that
   is trusted to participate in a routing protocol on one interface

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   becomes implicitly trusted for the other interfaces that share the
   key.  For many cases, such as link-state routers in the same routing
   area, there is no significant advantage that an attacker could gain
   from this trust within the KARP threat model.  However, distance-
   vector protocols, such as BGP and RIP, permit routes to be filtered
   across a trust boundary.  For these protocols, participation in one
   interface might be more advantageous than another.  Operationally,
   when this trust distinction is important to a deployment, different
   keys need to be used on each side of the trust boundary.  Key
   derivation can help prevent this problem in cases of accidental
   misconfiguration.  However, key derivation cannot protect against a
   situation where a system was incorrectly trusted to have the key used
   to perform the derivation.  To the extent that there are multiple
   zones of trust and a routing protocol is determining whether a
   particular router is within a certain zone, the question of untrusted
   actors is within the scope of the routing threat model.

   Key derivation can be part of a management solution to a desire to
   have multiple keys for different zones of trust.  A master key could
   be combined with peer, link or area identifiers to form a router-
   specific preshared key that is loaded onto routers.  Provider that
   the master key lives only on the management server and not the
   individual routers, trust is preserved.  However in many cases,
   generating independent keys for the routers and storing the result is
   more practical.  If the master key were somehow compromised, all the
   resulting keys would need to be changed.  However if independent keys
   are used, the scope of a compromise may be more limited.

   More subtle problems with key separation can appear in protocol
   design.  Two protocols that use the same traffic keys may work
   together in unintended ways permitting one protocol to be used to
   attack the other.  Consider two hypothetical protocols.  Protocol A
   starts its messages with a set of extensions that are ignored if not
   understood.  Protocol B has a fixed header at the beginning of its
   messages but ends messages with extension information.  It may be
   that the same message is valid both as part of protocol A and
   protocol B. An attacker may be able to gain an advantage by getting a
   router to generate this message with one protocol under situations
   where the other protocol would not generate the message.  This
   hypothetical example is overly simplistic; real-world attacks
   exploiting key separation weaknesses tend to be complicated and
   involve specific properties of the cryptographic functions involved.
   The key point is that whenever the same key is used in multiple
   protocols, attacks may be possible.  All the involved protocols need
   to be analyzed to understand the scope of potential attacks.

   Key separation attacks interact with the KARP operational model in a
   number of ways.  Administrators need to be aware of situations where

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   using the same manual traffic key with two different protocols (or
   the same protocol in different contexts) creates attack
   opportunities.  Design teams should consider how their protocol might
   interact with other routing protocols and describe any attacks
   discovered so that administrators can understand the operational
   implications.  When designing automated key management or new
   cryptographic authentication within routing protocols, we need to be
   aware that administrators expect to be able to use the same preshared
   keys in multiple contexts.  As a result, we should use appropriate
   key derivation functions so that different cryptographic keys are
   used even when the same initial input key is used.

4.2.  Asymmetric Keys

   Outside of a PKI, public keys are expected to be known by the hash of
   a key or (potentially self-signed) certificate.  The Session
   Description Protocol provides a standardized mechanism for naming
   keys (in that case certificates) based on hashes (section 5
   [RFC4572]).  KARP SHOULD adopt this approach or another approach
   already standardized within the IETF rather than inventing a new
   mechanism for naming public keys.

   A public key is typically expected to belong to one peer.  As a peer
   generates new keys and retires old keys, its public key may change.
   For this reason, from a management standpoint, peers should be
   thought of as associated with multiple public keys rather than as
   containing a single public key hash as an attribute of the peer

   Authorization of public keys could be done either by key hash or by
   peer identity.  Performing authorizations by peer identity should
   make it easier to update the key of a peer without risk of losing
   authorizations for that peer.  However management interfaces need to
   be carefully designed to avoid making this extra level of indirection
   complicated for operators.

4.3.  Public Key Infrastructure

   When a PKI is used, certificates are used.  The certificate binds a
   key to a name of a peer.  The key management protocol is responsible
   for exchanging certificates and validating them to a trust anchor.

   Authorization needs to be done in terms of peer identities not in
   terms of keys.  One reason for this is that when a peer changes its
   key, the new certificate needs to be sufficient for authentication to
   continue functioning even though the key has never been seen before.

   Potentially authorization could be performed in terms of groups of

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   peers rather than single peers.  An advantage of this is that it may
   be possible to add a new router with no authentication related
   configuration of the peers of that router.  For example, a domain
   could decide that any router with a particular keyPurposeID signed by
   the organization's certificate authority is permitted to join the
   IGP.  Just as in configurations where cryptographic authentication is
   not used, automatic discovery of this router can establish
   appropriate adjacencies.

   Assuming that potentially self-signed certificates are used by
   routers that wish to use public keys but that do not need a PKI, then
   PKI and the infrastructureless mode of public-key operation described
   in the previous section can work well together.  One router could
   identify its peers based on names and use certificate validation.
   Another router could use hashes of certificates.  This could be very
   useful for border routers between two organizations.  Smaller
   organizations could use public keys and larger organizations could
   use PKI.

4.4.  The role of Central Servers

   An area to explore is the role of central servers like RADIUS or
   directories.  As discussed in the design-guide, a system where keys
   are pushed by a central management system is undesirable as an end
   result for KARP.  However central servers may play a role in
   authorization and key rollover.  For example a node could send a hash
   of a public key to a RADIUS server.

   If central servers do play a role it will be critical to make sure
   that they are not required during routine operation or a cold-start
   of a network.  They are more likely to play a role in enrollment of
   new peers or key migration/compromise.

   Another area where central servers may play a role is for group key
   agreement.  As an example, [I-D.liu-ospfv3-automated-keying-req]
   discusses the potential need for key agreement servers in OSPF.
   Other routing protocols that use multicast or broadcast such as IS-IS
   are likely to need a similar approach.

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5.  Grouping Peers Together

   One significant management consideration will be the grouping of
   management objects necessary to determine who is authorized to act as
   a peer for a given routing action.  As discussed previously, the
   following objects are potentially required:

   o  Key objects are required.  Symmetric keys may be preshared.
      Asymmetric public keys may be used directly for authorization as
      well.  During key transitions more than one key may refer to a
      given peer.  Group preshared keys may refer to multiple peers.

   o  A peer is a router that this router might wish to communicate
      with.  Peers may be identified by names or keys.

   o  Groups of peers may be authorized for a given routing protocol.

   Establishing a management model is difficult because of the complex
   relationships between each set of objects.  As discussed there may be
   more than one key for a peer.  However in the preshared key case,
   there may be more than one peer for a key.  This is true both for
   group security association protocols such as an IGP or one-to-one
   protocols where the same key is used administratively.  In some of
   these situations, it may be undesirable to explicitly enumerate the
   peers in the configuration; for example IGP peers are auto-discovered
   for broadcast links but not for non-broadcast multi-access links.

   Peers may be identified either by name or key.  If peers are
   identified by key it is probably strongly desirable from an
   operational standpoint to consider any peer identifiers or name to be
   a local matter and not require the names or identifiers to be
   synchronized.  Obviously if peers are identified by names (for
   example with certificates in a PKI), identifiers need to be
   synchronized between the authorized peer and the peer making the
   authorization decision.

   In many cases peers will explicitly be identified.  In these cases it
   is possible to attach the authorization information (keys or
   identifiers) to the peer's configuration object.  Two cases do not
   involve enumerating peers.  The first is the case where preshared
   keys are shared among a group of peers.  It is likely that this case
   can be treated from a management standpoint as a single peer
   representing all the peers that share the keys.  The other case is
   one where certificates in a PKI are used to introduce peers to a
   router.  In this case, rather than configuring peers, , the router
   needs to be configured with information on what certificates
   represent acceptable peers.

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   Another consideration is what routing protocols share peers.  For
   example it may be common for LDP peers to also be peers of some other
   routing protocol.  Also, RSVP-TE may be associated with some TE-based
   IGP.  In some of these cases it would be desirable to use the same
   authorization information for both routing protocols.

   In order to develop a management model for authorization, the working
   group needs to consider several questions.  What protocols support
   auto-discovery of peers?  What protocols require more configuration
   of a peer than simply the peer's authorization information and
   network address?  What management operations are going to be common
   as security information for peers is configured and updated?  What
   operations will be common while performing key transitions or while
   migrating to new security technologies?

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6.  Administrator Involvement

   One key operational question is what areas will administrator
   involvement be required.  Likely areas where involvement may be
   useful includes enrollment of new peers.  Fault recovery should also
   be considered.

6.1.  Enrollment

   One area where the management of routing security needs to be
   optimized is the deployment of a new router.  In some cases a new
   router may be deployed on an existing network where routing to
   management servers is already available.  In other cases, routers may
   be deployed as part of connecting or creating a site.  Here, the
   router and infrastructure may not be available until the router has
   securely authenticated.  This problem is similar to the problem of
   getting initial configuration of routing instances onto the router.
   However, especially in cases where asymmetric keys or per-peer
   preshared keys are used, the configuration of other routers needs to
   be modified to bring up the security association.  Also, there has
   been discussion of generating keys on routers and not allowing them
   to leave devices.  This also impacts what strategies are possible.
   For example this might mean that routers need to be booted in a
   secure environment where keys can be generated, and public keys
   copied to a management server to push out the new public key to
   potential peers.  Then, the router needs to be packaged, moved to
   where it will be deployed and set up.Alternatives are possible; it is
   critical that we understand how what we propose impacts operators.

   We need to work through examples with operators familiar with
   specific real-world deployment practices and understand how proposed
   security mechanisms will interact with these practices.

6.2.  Handling Faults

   Faults may interact with operational practice in at least two ways.
   First, security solutions may introduce faults.  For example if
   certificates expire in a PKI, previous adjacencies may no longer
   form.  Operational practice will require a way of repairing these
   errors.  This may end up being very similar to deploying a router
   that is connecting a new site as the security fault may have
   partitioned the network.  However, unlike a new deployment, the event
   is unplanned.  Strategies such as configuring a router and shipping
   it to a site may not be appropriate for recovering a fault even
   though they may be more useful for new deployments.

   Monitoring will play a critical role in avoiding security faults such
   as certificate expiration.  However, the protocols MUST still have

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   adequate operational mechanisms to recover from these situations.
   Also, some faults, such as those resulting from a compromise or
   actual attack on a facility are inherent and may not be prevented.

   A second class of faults is equipment faults that impact security.
   For example if keys are stored on a router and never moved from that
   device, failure of a router implies a need to update security
   provisioning on the replacement router and its peers.

   To address these operational considerations, we should identify
   circumstances surrounding recovery from today's faults and understand
   how protocols will impact mechanisms used today.

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7.  Upgrade Considerations

   It needs to be possible to deploy automated key management in an
   organization without either having to disable existing security or
   disrupting routing.  As a result, it needs to be possible to perform
   a phased upgrade from manual keying to automated key management.

   For peer-to-peer protocols such as BGP, this is likely to be
   relatively easy.  First, code that supports automated key management
   needs to be loaded on both peers.  Then the adjacency can be
   upgraded.  The configuration can be updated to switch to automated
   key management when the second router reboots.

   The situation is more complicated for multicast protocols.  It's
   probably not reasonable to bring down an entire link to reconfigure
   it as using automated key management.  Two approaches should be
   considered.  One is to support key table rows from the automated key
   management and manually configured for the same link at the same
   time.  Coordinating this may be tricky.  Another possibility is for
   the automated key management protocol to actually select the same
   traffic key that is being used manually

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8.  Related Work

   Discuss draft-housley-saag-*, draft-polk-saag-*, the discussions in
   the KARP framework, etc.

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9.  Security Considerations

   This document does not define a protocol.  It does discuss the
   operational and management implications of several security

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10.  Acknowledgments

   Funding for Sam Hartman's work on this memo is provided by Huawei.

   The authors would like to thank Gregory Lebovitz, Russ White and Bill
   Atwood for valuable reviews.

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11.  References

11.1.  Normative References

              Housley, R. and T. Polk, "Database of Long-Lived Symmetric
              Cryptographic Keys",
              draft-housley-saag-crypto-key-table-04 (work in progress),
              October 2010.

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

11.2.  Informative References

              Lebovitz, G. and M. Bhatia, "Keying and Authentication for
              Routing Protocols (KARP) Design Guidelines",
              draft-ietf-karp-design-guide-02 (work in progress),
              March 2011.

              Liu, Y., "OSPFv3 Automated Group Keying Requirements",
              draft-liu-ospfv3-automated-keying-req-01 (work in
              progress), July 2007.

              Polk, T. and R. Housley, "Routing Authentication Using A
              Database of Long-Lived Cryptographic Keys",
              draft-polk-saag-rtg-auth-keytable-05 (work in progress),
              November 2010.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572, July 2006.

   [RFC4808]  Bellovin, S., "Key Change Strategies for TCP-MD5",
              RFC 4808, March 2007.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

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Authors' Addresses

   Sam Hartman
   Painless Security


   Dacheng Zhang


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