draft-ietf-ospf-ospfv2-hbit-08.txt   draft-ietf-ospf-ospfv2-hbit-09.txt 
OSPF K. Patel OSPF K. Patel
Internet-Draft Arrcus Internet-Draft Arrcus
Updates: 2328,6987 (if approved) P. Pillay-Esnault Updates: 6987 (if approved) P. Pillay-Esnault
Intended status: Standards Track Futurewei Intended status: Standards Track PPE Consulting
Expires: January 9, 2020 M. Bhardwaj Expires: March 16, 2020 M. Bhardwaj
S. Bayraktar S. Bayraktar
Cisco Systems Cisco Systems
July 8, 2019 September 13, 2019
Host Router Support for OSPFv2 Host Router Support for OSPFv2
draft-ietf-ospf-ospfv2-hbit-08 draft-ietf-ospf-ospfv2-hbit-09
Abstract Abstract
The OSPFv2 specifies an SPF algorithm that identifies transit The Open Shortest Path First Version 2 (OSPFv2) does not have a
vertices based on their adjacencies. Therefore, OSPFv2 does not have mechanism for a node to repel transit traffic if it is on the
a mechanism to prevent traffic transiting a participating node if it shortest path. This document assigns a new bit (Host-bit) in the
is a transit vertex in the only existing or shortest path to the OSPF Router-LSA bit registry and in the OSPF Router Informational
destination. The use of metrics to make the node undesirable can Capability Bits Registry that enables a host router to advertise that
only help to repel traffic if an alternative better route exists. it is a non-transit router. It also describes the changes needed to
This document defines the Host-bit functionality to prevent other support the Host-bit in the domain. In addition, this document
OSPFv2 routers from using the router for transit traffic in OSPFv2 updates OSPF Stub Router Advertisement (RFC6987) to advertise for
routing domains. This document updates the Open Shortest Path First type-2 External and NSSA LSAs with a high cost in order to repel
v2 specification (OSPFv2 rfc2328) by assigning a new bit (Host-bit) traffic effectively.
in the OSPF Router-LSA bit registry. In addition, if the Host-bit is
set, the calculation of the shortest-path tree for an area, as
described in OSPFv2, is modified by including a new check to verify
that transit vertices have the Host-bit clear. In addition, this
document updates OSPF Stub Router Advertisement (rfc6987) to
advertise for type-2 External and NSSA LSAs with a high cost in order
to repel traffic effectively.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 January 9, 2020.
This Internet-Draft will expire on March 16, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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
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7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
The OSPFv2 specifies an SPF algorithm that identifies transit The OSPFv2 specifies a Shortest Path First (SPF) algorithm that
vertices based on their adjacencies. Therefore, OSPFv2 does not have identifies transit vertices based on their adjacencies. Therefore,
a mechanism to prevent traffic transiting a participating node if it OSPFv2 does not have a mechanism to prevent traffic transiting a
is a transit vertex in the only existing or shortest path to the participating node if it is a transit vertex in the only existing or
destination. The use of metrics to make the node undesirable can shortest path to the destination. The use of metrics to make the
only help to repel traffic if an alternative better route exists. node undesirable can help to repel traffic only if an alternative
better route exists.
This functionality is particularly useful for a number of use cases: This functionality is particularly useful for a number of use cases:
1. To isolate a router to avoid blackhole scenarios when there is a 1. To isolate a router to avoid blackhole scenarios when there is a
reload and possible long reconvergence times. reload and possible long reconvergence times.
2. Closet Switches are usually not used for transit traffic but need 2. Closet Switches are usually not used for transit traffic but need
to participate in the topology. to participate in the topology.
3. Overloaded routers could use such a capability to temporarily 3. Overloaded routers could use such a capability to temporarily
repel traffic until they stabilize. repel traffic until they stabilize.
4. BGP Route reflectors known as virtual Route Reflectors (vRRs), 4. BGP Route reflectors known as virtual Route Reflectors (vRRs),
that are not in the forwarding path but are in central locations that are not in the forwarding path but are in central locations
such as data centers. Such Route Reflectors typically are used such as data centers. Such Route Reflectors typically are used
for route distribution and are not capable of forwarding transit for route distribution and are not capable of forwarding transit
traffic. However, they need to learn the OSPF topology to traffic. However, they need to learn the OSPF topology to
perform spf computation for optimal routes and reachbility perform SPF computation for optimal routes and reachability
resolution for its clients resolution for its clients
[I-D.ietf-idr-bgp-optimal-route-reflection]. [I-D.ietf-idr-bgp-optimal-route-reflection].
This document defines the Host-bit (H-Bit)functionality to prevent This document describes the Host-bit (H-Bit)functionality that
other OSPFv2 routers from using the router for transit traffic in prevents other OSPFv2 routers from using the router for transit
OSPFv2 routing domains. This document updates the [RFC2328] by - traffic in OSPFv2 routing domains. This document defines the Host-
assigning the Host-bit in the OSPFv2 Router Properties Registry - if bit in the OSPFv2 Router Properties Registry and if the host-bit is
the host-bit is set then the calculation of the shortest-path tree set then the calculation of the shortest-path tree for an area, as
for an area, as described in section 16.1 of [RFC2328], is modified described in section 16.1 of [RFC2328], is modified by including a
by including a new check to verify that transit vertices DO NOT have new check to verify that transit vertices DO NOT have the host-bit
the host-bit set. set.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Host-bit Support 3. Host-bit Support
This document defines a new router-LSA bit known as the Host Bit or This document defines a new router-LSA bit known as the Host Bit or
the H-bit. An OSPFv2 router advertising a router-LSA with the H-bit the H-bit. An OSPFv2 router advertising a router-LSA with the H-bit
set indicates to other OSPFv2 routers in the area supporting the set indicates that it MUST NOT be used as a transit router (see
functionality that it MUST NOT be used as a transit router (see section 4) by other OSPFv2 routers in the area supporting the
section 4). functionality.
If the host-bit is NOT set routers MUST act transit routers as If the host-bit is NOT set routers MUST act transit routers as
described in [RFC2328] ensuring backward compatibility. described in [RFC2328] ensuring backward compatibility.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 1 | | LS age | Options | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID | | Link State ID |
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| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | 0 | TOS metric | | TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID | | Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data | | Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
Host Bit in router-LSA Figure 1
Host Bit in Router-LSA
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|H|0|0|N|W|V|E|B| |H|0|0|N|W|V|E|B|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Host Bit Host Bit
Bit H is the high-order bit of the OSPF as shown above. When set, an Bit H is the high-order bit of the OSPF as shown above. When set, an
OSPFv2 router is a Host (non-transit) router and is incapable of OSPFv2 router is a Host (non-transit) router and is incapable of
forwarding transit traffic. forwarding transit traffic. In this mode, the other OSPFv2 routers
in the area MUST NOT use the host router for transit traffic, but use
the host router only for its local destinations.
An OSPFv2 router originating a router-LSA with the H-bit set MUST An OSPFv2 router originating a router-LSA with the H-bit set MUST
advertise all its router links with a link cost of MaxLinkMetric advertise all its router links with a link cost of MaxLinkMetric
[RFC6987]. This is to increase the applicability of the H-bit to [RFC6987]. This is to increase the applicability of the H-bit to
partial deployments where it is the responsibility of the operator to partial deployments where it is the responsibility of the operator to
ensure that OSPFv2 routers not supporting the H-bit do not install ensure that OSPFv2 routers not supporting the H-bit do not install
routes causing routing loops. routes causing routing loops.
When the H-bit is set, an Area Border Router (ABR) MUST advertise the When the H-bit is set, an Area Border Router (ABR) MUST advertise the
same H-bit setting in its self-originated router-LSAs for all same H-bit setting in its self-originated router-LSAs for all
attached areas. The consistency of the setting will prevent inter- attached areas. The consistency of the setting will prevent inter-
area traffic transiting through the router by suppressing the area traffic transiting through the router by suppressing
suppressing advertisement of prefixes from other routers in the area advertisement of prefixes from other routers in the area in its
in its summary LSAs. ONLY IPv4 prefixes associated with its local summary LSAs. Only IPv4 prefixes associated with its local
interfaces MAY be advertised in summary LSAs to provide reachability interfaces MUST be advertised in summary LSAs to provide reachability
to end hosts attached behind a router with the H-bit set. to end hosts attached behind a router with the H-bit set.
When the H-bit is set cannot act as an AS Boundary Router (ASBR), as When the H-bit is set the host router cannot act as an AS Boundary
ASBR are transit routers to prefixes that are typically imported Router (ASBR). Indeed, ASBR are transit routers to prefixes that are
through redistribution of prefixes of other routing protocols. typically imported through redistribution of prefixes of other
Therefore, non-local IPv4 prefixes, e.g., those exported from other routing protocols. Therefore, non-local IPv4 prefixes, e.g., those
routing protocols, MUST NOT be advertised in AS-external-LSAs for exported from other routing protocols, MUST NOT be advertised in AS-
routers acting permanly as a host. However, in use cases such as an external-LSAs for routers acting permanently as a host. However, in
overloaded router or a router being gracefully isolated, these use cases such as an overloaded router or a router being gracefully
routers are only temporarily acting as host routers and therefore isolated, these routers are only temporarily acting as host routers
should continue to advertise their External LSAs but ensure they do and therefore SHOULD continue to advertise their External LSAs but
not attract traffic. In addition to the procedure described above, ensure that they do not attract traffic. In addition to the
temporary host routers advertising type 2-metric External LSAs MUST procedure described above, temporary host routers advertising type
set the metrics to LSInfinity to repel traffic.(see Section 6 of this 2-metric External LSAs MUST set the metrics to LSInfinity to repel
document). traffic.(see Section 6 of this document).
4. SPF Modifications 4. SPF Modifications
The SPF calculation described in section 16.1 [RFC2328] will be The SPF calculation described in section 16.1 [RFC2328] will be
modified to ensure that the routers originating router-LSAs with the modified to ensure that the routers originating router-LSAs with the
H-bit set will not be used for transit traffic. Step 2 is modified H-bit set will not be used for transit traffic. Step 2 is modified
as follows: as follows:
2) Call the vertex just added to the 2) Call the vertex just added to the
tree vertex V. Examine the LSA tree vertex V. Examine the LSA
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TransitCapability to TRUE. In any case, TransitCapability to TRUE. In any case,
each link described by the LSA gives each link described by the LSA gives
the cost to an adjacent vertex. For the cost to an adjacent vertex. For
each described link, (say it joins each described link, (say it joins
vertex V to vertex W): vertex V to vertex W):
5. Auto Discovery and Backward Compatibility 5. Auto Discovery and Backward Compatibility
To avoid the possibility of any routing loops due to partial To avoid the possibility of any routing loops due to partial
deployment, this document defines a OSPF Router Information (RI) LSA deployment, this document defines a OSPF Router Information (RI) LSA
[RFC7770] with and area flooding scope and a new bit assigned in the [RFC7770] with and an area flooding scope and a new bit assigned in
OSPF Router Informational Capability Bits Registry. Bit: the OSPF Router Informational Capability Bits Registry. Bit:
Bit Capabilities Bit Capabilities
7 Host Router Support capability 7 Host Router Support capability
Auto Discovery via announcement of the Host Support Functional Auto Discovery via announcement of the Host Support Functional
Capability ensures that the H-bit functionality and its associated Capability ensures that the H-bit functionality and its associated
SPF changes MUST only take effect if all the routers in a given OSPF SPF changes MUST only take effect if all the routers in a given OSPF
area support this functionality. area support this functionality.
In normal operations, there is no guarantee that the RI LSA will In normal operations, there is no guarantee that the RI LSA will
reach all routers in an area in a timely manner which may result in reach all routers in an area in a timely manner that may result in
rooting loops in partial deployments. For example, in a new router rooting loops in partial deployments. For example, in a new router
joins an area which previous had only H-bit capable routers with joins an area which previous had only H-bit capable routers with
H-bit set then it may take some time for the RI to propagate to all H-bit set then it may take some time for the RI to propagate to all
routers. routers.
The following recommendations will mitigate transient routing loops: The following recommendations will mitigate transient routing loops:
o Implementations are RECOMMENDED to provide a configuration o Implementations are RECOMMENDED to provide a configuration
parameter to manually override enforcement of the H-bit parameter to manually override enforcement of the H-bit
functionality in partial deployments where the topology guarantees functionality in partial deployments where the topology guarantees
skipping to change at page 8, line 19 skipping to change at page 8, line 19
Bit Number Capability Name Reference Bit Number Capability Name Reference
7 OSPF Host Router This Document 7 OSPF Host Router This Document
8. Security Considerations 8. Security Considerations
This document introduces the H-bit which is a capability that This document introduces the H-bit which is a capability that
restricts the use of a router for transit except for its local restricts the use of a router for transit except for its local
destinations. This is a subset of the operations of a normal router destinations. This is a subset of the operations of a normal router
and therefore should not introduce new security considerations beyond and therefore should not introduce new security considerations beyond
those already known in OSPF. The feature however does introduce the those already known in OSPF. The feature, however does introduce the
flooding of a capability information that allows discovery and flooding of a capability information that allows discovery and
verification that all routers in an area are capable before turning verification that all routers in an area are capable before turning
on the feature. In case. a rogue or buggy router advertise on the feature. In the event that a rogue or buggy router advertises
incorrectly its capability there are two possible cases: incorrectly its capability there are two possible cases:
o The router does not have the capability but send H-Bit set in its o The router does not have the capability but sends H-Bit set in its
LSAs: In this case, there is a possibility of a routing loop. LSAs: In this case, there is a possibility of a routing loop.
However this is mitigated by the fact that this router should be However this is mitigated by the fact that this router should be
avoided anyway. Moreover, the link metrics cost of this router avoided anyway. Moreover, the link metrics cost (MaxLinkMetric)
should be MaxLinkMetric and will mitigate this situation. In any of this router will mitigate this situation. In any case, a
case a router advertising the H-bit capability without its links router advertising the H-bit capability without its links cost
cost equal to MaxLinkMetric may be an indicator that this is a equal to MaxLinkMetric may be an indicator that this is a rogue
rogue router. router and to be avoided.
o The router has the capability but sends the H-Bit clear in its o The router has the capability but sends the H-Bit clear in its
LSAs: In this case, the router merely prevents support of other LSAs: In this case, the router merely prevents support of other
H-bit routers in the area and all the routers to run the modified H-bit routers in the area and all the routers to run the modified
SPF. The impact is also mitigated as other H-Bit routers in the SPF. The impact is also mitigated as other H-Bit routers in the
area also advertise MaxLinkMetric cost so they will still be area also advertise MaxLinkMetric cost so they will still be
avoided unless they are the last resort path. avoided unless they are the last resort path.
9. Acknowledgements 9. Acknowledgements
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>. <https://www.rfc-editor.org/info/rfc2328>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>. February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-idr-bgp-optimal-route-reflection] [I-D.ietf-idr-bgp-optimal-route-reflection]
Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K. Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K.
Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft- Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft-
ietf-idr-bgp-optimal-route-reflection-18 (work in ietf-idr-bgp-optimal-route-reflection-19 (work in
progress), April 2019. progress), July 2019.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
Authors' Addresses Authors' Addresses
Keyur Patel Keyur Patel
Arrcus Arrcus
Email: keyur@arrcus.com Email: keyur@arrcus.com
Padma Pillay-Esnault Padma Pillay-Esnault
Futurewei PPE Consulting
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: padma.ietf@gmail.com Email: padma.ietf@gmail.com
Manish Bhardwaj Manish Bhardwaj
Cisco Systems Cisco Systems
170 W. Tasman Drive 170 W. Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
Email: manbhard@cisco.com Email: manbhard@cisco.com
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