draft-ietf-idr-bgp-flowspec-oid-03.txt   draft-ietf-idr-bgp-flowspec-oid-04.txt 
Network Working Group James Uttaro
Internet Draft AT&T Network Working Group J. Uttaro
Updates: 5575 Clarence Filsfils Internet-Draft AT&T
Intended Status: Proposed Standard David Smith Updates: 5575 (if approved) J. Alcaide
Expiration Date: September 21, 2016 Juan Alcaide Intended status: Standards Track C. Filsfils
Expires: September 14, 2017 D. Smith
Cisco Cisco
Pradosh Mohapatra P. Mohapatra
Sproute Networks Sproute Networks
March 21, 2016 March 13, 2017
Revised Validation Procedure for BGP Flow Specifications Revised Validation Procedure for BGP Flow Specifications
draft-ietf-idr-bgp-flowspec-oid-03 draft-ietf-idr-bgp-flowspec-oid-04
Abstract Abstract
This document describes a modification to the validation procedure This document describes a modification to the validation procedure
defined in RFC 5575 for the dissemination of BGP flow specifications. defined in RFC 5575 for the dissemination of BGP flow specifications.
RFC 5575 requires that the originator of the flow specification RFC 5575 requires that the originator of the flow specification
matches the originator of the best-match unicast route for the matches the originator of the best-match unicast route for the
destination prefix embedded in the flow specification. This allows destination prefix embedded in the flow specification. This allows
only BGP speakers within the data forwarding path (such as autonomous only BGP speakers within the data forwarding path (such as autonomous
system border routers) to originate BGP flow specifications. Though system border routers) to originate BGP flow specifications. Though
it is possible to disseminate such flow specifications directly from it is possible to disseminate such flow specifications directly from
border routers, it may be operationally cumbersome in an autonomous border routers, it may be operationally cumbersome in an autonomous
system with a large number of border routers having complex BGP system with a large number of border routers having complex BGP
policies. The modification proposed herein enables flow policies. The modification proposed herein enables flow
specifications to be originated from a centralized BGP route specifications to be originated from a centralized BGP route
controller. controller.
Status of this Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1 Specification of Requirements ...................... 3 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
2 Motivation ......................................... 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 2
3 Introduction ....................................... 5 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Revised Validation Procedure ....................... 6 4. Revised Validation Procedure . . . . . . . . . . . . . . . . 5
5 Security Considerations ............................ 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6 IANA Considerations ................................ 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7 Normative References ............................... 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8 Acknowledgements ................................... 8 8. Normative References . . . . . . . . . . . . . . . . . . . . 7
9 Authors' Addresses ................................. 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Specification of Requirements 1. 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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Motivation 2. Motivation
Step (a) of the validation procedure in [RFC5575], section 6 is Step (a) of the validation procedure in [RFC5575], section 6 is
defined with the underlying assumption that the flow specification defined with the underlying assumption that the flow specification
NLRI traverses the same path, in the inter-domain and intra-domain NLRI traverses the same path, in the inter-domain and intra-domain
route distribution graph, as that of the longest-match unicast route route distribution graph, as that of the longest-match unicast route
for the destination prefix embedded in the flow specification. for the destination prefix embedded in the flow specification.
In the case of inter-domain traffic filtering, for example, the flow In the case of inter-domain traffic filtering, for example, the flow
specification originator at the egress border routers of ASN1 (RTR-D specification originator at the egress border routers of ASN1 (RTR-D
and RTR-E in figure 1) matches the EBGP neighbor that advertised the and RTR-E in figure 1) matches the EBGP neighbor that advertised the
longest match destination prefix (RTR-F and RTR-G respectively). longest match destination prefix (RTR-F and RTR-G respectively).
Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in
figure 1), the flow specification originator matches the egress IBGP figure 1), the flow specification originator matches the egress IBGP
border routers that had advertised the unicast route for the best- border routers that had advertised the unicast route for the best-
match destination prefix (RTR-D and RTR-E respectively). This is true match destination prefix (RTR-D and RTR-E respectively). This is
even when ingress border routers select paths from different egress true even when ingress border routers select paths from different
border routers as best path based upon IGP distance (as an example, egress border routers as best path based upon IGP distance (as an
RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as the best example, RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as
path). the best path).
/ - - - - - - - - - - - - - - / - - - - - - - - - - - - - -
| ASN1 | | ASN1 |
+-------+ +-------+ +-------+ +-------+
| | | | | | | | | | | |
| RTR-A | | RTR-B | | RTR-A | | RTR-B |
| | | | | | | | | | | |
+-------+ +-------+ +-------+ +-------+
| \ / | | \ / |
IBGP \ / IBGP IBGP \ / IBGP
| \ / | | \ / |
+-------+ +-------+
| | | | | | | |
| RTR-C | | RTR-C |
| | RC | | | | RC | |
+-------+ +-------+
| / \ | | / \ |
/ \ / \
| IBGP / \ IBGP | | IBGP / \ IBGP |
+-------+ +-------+ +-------+ +-------+
| | RTR-D | | RTR-E | | | | RTR-D | | RTR-E | |
| | | | | | | |
| | | | | | | | | | | |
+-------+ +-------+ +-------+ +-------+
| | | | | | | |
- - -|- - - - - - - - -|- - -/ - - -|- - - - - - - - -|- - -/
| EBGP EBGP | | EBGP EBGP |
- - -|- - - - - - - - -|- - -/ - - -|- - - - - - - - -|- - -/
| | | | | | | |
+-------+ +-------+ +-------+ +-------+
| | | | | | | | | | | |
| RTR-F | | RTR-G | | RTR-F | | RTR-G |
| | | | | | | | | | | |
+-------+ +-------+ +-------+ +-------+
| ASN2 | | ASN2 |
/ - - - - - - - - - - - - - - / - - - - - - - - - - - - - -
Figure 1 Figure 1
It is highly desirable that each ASN is able to protect itself It is highly desirable that each ASN is able to protect itself
independently from network security attacks using the BGP flow independently from network security attacks using the BGP flow
specification NLRI for intra-domain purposes only. Network operators specification NLRI for intra-domain purposes only. Network operators
often deploy a dedicated Security Operations Center (SOC) within often deploy a dedicated Security Operations Center (SOC) within
their ASN to monitor and detect such security attacks. To mitigate their ASN to monitor and detect such security attacks. To mitigate
attacks in a scalable intra-domain manner, operators require the attacks in a scalable intra-domain manner, operators require the
ability to originate intra-domain flow specification NLRIs from a ability to originate intra-domain flow specification NLRIs from a
central BGP route controller (or router reflector per [RFC4456]) that central BGP route controller (or router reflector per [RFC4456]) that
is not within the data forwarding plane. In this way, operators can is not within the data forwarding plane. In this way, operators can
direct border routers within their ASN with specific attack direct border routers within their ASN with specific attack
mitigation actions (drop the traffic, forward to a clean-pipe center, mitigation actions (drop the traffic, forward to a clean-pipe center,
etc.). To originate a flow specification NLRI, a central BGP route etc.). To originate a flow specification NLRI, a central BGP route
controller (or route reflector) must set itself as the originator in controller (or route reflector) must set itself as the originator in
the flowspec NLRI. This is necessary given the route controller is the flowspec NLRI. This is necessary given the route controller is
originating the flow specification not reflecting it, and to avoid originating the flow specification not reflecting it, and to avoid
the complexity of having to determine the egress border router whose the complexity of having to determine the egress border router whose
path was chosen as the best in each of the ingress border routers. It path was chosen as the best in each of the ingress border routers.
thus becomes necessary to modify step (a) of the RFC 5575 validation It thus becomes necessary to modify step (a) of the RFC 5575
procedure such that an IBGP peer that is not within the data validation procedure such that an IBGP peer that is not within the
forwarding plane may originate flow specification NLRIs. data forwarding plane may originate flow specification NLRIs.
3. Introduction 3. Introduction
RFC 5575 defined a new BGP capability that can be used to distribute RFC 5575 defined a new BGP capability that can be used to distribute
traffic flow specifications amongst BGP speakers in support of traffic flow specifications amongst BGP speakers in support of
traffic filtering. The primary intention of RFC 5575 is to enable traffic filtering. The primary intention of RFC 5575 is to enable
downstream autonomous systems to signal traffic filtering policies to downstream autonomous systems to signal traffic filtering policies to
upstream autonomous systems. In this way, traffic is filtered closer upstream autonomous systems. In this way, traffic is filtered closer
to the source and the upstream autonomous system(s) avoid carrying to the source and the upstream autonomous system(s) avoid carrying
the traffic to the downstream autonomous system only to be discarded. the traffic to the downstream autonomous system only to be discarded.
RFC 5575 also enables more granular traffic filtering based upon RFC 5575 also enables more granular traffic filtering based upon
upper layer protocol information (e.g., protocol port numbers) as upper layer protocol information (e.g., protocol port numbers) as
opposed to coarse IP destination prefix-based filtering. Flow opposed to coarse IP destination prefix-based filtering. Flow
specification NLRIs received from a BGP peer are subject to validity specification NLRIs received from a BGP peer are subject to validity
checks before being considered feasible and subsequently installed checks before being considered feasible and subsequently installed
within the respective Adj-RIB-In. The validation procedure defined within the respective Adj-RIB-In. The validation procedure defined
within RFC 5575 requires that the originator of the flow within RFC 5575 requires that the originator of the flow
specification NLRI matches the originator of the best-match unicast specification NLRI matches the originator of the best-match unicast
route for the destination prefix embedded in the flow specification. route for the destination prefix embedded in the flow specification.
This allows only BGP speakers [RFC4271] within the data forwarding This allows only BGP speakers [RFC4271] within the data forwarding
path (such as autonomous system border routers) to originate BGP flow path (such as autonomous system border routers) to originate BGP flow
specification NLRIs. Though it is possible to disseminate such flow specification NLRIs. Though it is possible to disseminate such flow
specification NLRIs directly from border routers, it may be specification NLRIs directly from border routers, it may be
operationally cumbersome in an autonomous system with a large number operationally cumbersome in an autonomous system with a large number
of border routers having complex BGP policies. This document of border routers having complex BGP policies. This document
describes a modification to the RFC 5575 validation procedure describes a modification to the RFC 5575 validation procedure
allowing flow specification NLRIs to be originated from a centralized allowing flow specification NLRIs to be originated from a centralized
BGP route controller within the local autonomous system that is BGP route controller within the local autonomous system that is
neither in the data forwarding path nor serving as a BGP route neither in the data forwarding path nor serving as a BGP route
reflector [RFC4456]. While the proposed modification cannot be used reflector [RFC4456]. While the proposed modification cannot be used
for inter-domain coordination of traffic filtering, it greatly for inter-domain coordination of traffic filtering, it greatly
simplifies distribution of intra-domain traffic filtering policies in simplifies distribution of intra-domain traffic filtering policies in
an autonomous system with a large number of border routers having an autonomous system with a large number of border routers having
complex BGP policies. By relaxing the validation procedure for IBGP, complex BGP policies. By relaxing the validation procedure for IBGP,
the proposed modification allows flow specifications to be the proposed modification allows flow specifications to be
distributed in a standard and scalable manner throughout an distributed in a standard and scalable manner throughout an
autonomous system. autonomous system.
4. Revised Validation Procedure 4. Revised Validation Procedure
Step (a) of the validation procedure specified in RFC 5575, section 6 Step (a) of the validation procedure specified in RFC 5575, section 6
is redefined as follows: is redefined as follows:
a) One of the following conditions MUST hold true: a. One of the following conditions MUST hold true.
o The originator of the flow specification matches the
originator of the best-match unicast route for the
destination prefix embedded in the flow specification.
o The AS_PATH and AS4_PATH attribute of the flow
specification are empty.
o The AS_PATH and AS4_PATH attribute of the flow
specification does not contain AS_SET and AS_SEQUENCE
segments.
An empty AS_PATH and AS4_PATH attribute indicates per [RFC4271] that * The originator of the flow specification matches the
the flow specification NLRI originated in the same autonomous system originator of the best-match unicast route for the destination
as the local BGP speaker. Similarly, lack of AS_SET and AS_SEQUENCE prefix embedded in the flow specification.
segments within an AS_PATH and AS4_PATH attribute that is not empty
indicates that the flow specification NLRI originated in the same * The AS_PATH attribute of the flow specification does not
autonomous system as the local BGP speaker but that the autonomous contain AS_SET and AS_SEQUENCE segments.
system includes a BGP confederation [RFC5065]. With this proposed
modification to the RFC 5575 validation procedure, it is now possible An AS_PATH without AS_SET and AS_SEQUENCE segments indicates that the
for an IBGP peer that is not within the data forwarding path to flow specification was originated inside the local AS [RFC4271] or
originate flow specification NLRIs. This applies with and without the inside the local confederation (in the case that the local AS belongs
presence of a BGP confederation within the autonomous system. to a confederation of ASes) [RFC5065]. With this modification to the
RFC 5575 validation procedure, it is now possible for an IBGP peer
that is not within the data forwarding path to originate flow
specification NLRIs. This applies whether the AS belongs or not to a
confederation of ASes. Checking the (newly introduced) second
condition above MAY be disabled by configuration on a BGP speaker.
However, it SHOULD be enabled by default. Disabling the condition
may be a good practice when the administrator knows with certainty
that there are not flow specification NLRI originated inside the
local AS (or local confederation). Optionally, an implementation
could be configured to allow only flow specification NLRIs containing
only a subset of ASes. This could be useful, for example, with
networks that consist of multiple ASes that operate under the same
administrative domain.
Further, RFC 5575 states that "BGP (flow specification) Further, RFC 5575 states that "BGP (flow specification)
implementations MUST also enforce that AS_PATH attribute of a route implementations MUST also enforce that AS_PATH attribute of a route
received via the External Border Gateway Protocol (eBGP) contains the received via the External Border Gateway Protocol (EBGP) contains the
neighboring AS in the left-most position of the AS_PATH attribute". neighboring AS in the left-most position of the AS_PATH attribute".
This rule is not valid for all topologies. For example, it prevents This rule is not valid for all topologies. For example, it prevents
exchange of BGP flow specification NLRIs at Internet exchanges with the exchange of BGP flow specification NLRIs at Internet exchanges
BGP route servers. Therefore, this document also redefines the RFC with BGP route servers. Therefore, this document also redefines the
5575 AS_PATH and AS4_PATH validation procedure referenced above as RFC 5575 AS_PATH validation procedure referenced above as follows.
follows.
BGP flow specification implementations MUST enforce that the last AS BGP flow specification implementations MUST enforce that the last AS
added within the AS_PATH and AS4_PATH attribute of a EBGP learned added within the AS_PATH attribute of a EBGP learned flow
flow specification NLRI MUST match the last AS added within the specification NLRI MUST match the last AS added within the AS_PATH
AS_PATH and AS4_PATH attribute of the best-match unicast route for attribute of the best-match unicast route for the destination prefix
the destination prefix embedded in the flow specification. This embedded in the flow specification. This proposed modification
proposed modification enables the exchange of BGP flow specification enables the exchange of BGP flow specification NLRIs at Internet
NLRIs at Internet exchanges with BGP route servers while at the same exchanges with BGP route servers while at the same time, for security
time, for security reasons, prevents an EBGP peer from advertising an reasons, prevents an EBGP peer from advertising an inter-domain flow
inter-domain flow specification for a destination prefix that it does specification for a destination prefix that it does not provide
not provide reachability information for. Note, comparing only the reachability information for. Note, comparing only the last ASes is
last ASNs is sufficient for EBGP learned flow specification NLRIs. sufficient for EBGP learned flow specification NLRIs. Requiring a
full AS_PATH match would limit origination of inter-domain flow
specifications to the origin (or first) AS of the best-match unicast
route for the destination prefix embedded in the flow specification
only. As such, a full AS_PATH validity check may prevent transit
ASes from originating inter-domain flow specifications which is not
desirable.
Requiring a full AS_PATH and AS4_PATH match would limit origination This document also clarifies proper handling when the BGP flow
of inter-domain flow specifications to the origin (or first) AS of specification does not embed a destination prefix component. The
the best-match unicast route for the destination prefix embedded in default behavior SHOULD be not to perform any validation procedure.
the flow specification only. As such, a full AS_PATH and AS4_PATH Further, support for two-octet AS number space is out of the scope of
validity check may prevent transit ASNs from originating inter-domain this document.
flow specifications which is not desirable.
5. Security Considerations In this context, AS_PATH attribute is defined as the reconstructed AS
Path information (by combining AS_PATH and AS4_PATH attributes, if
the BGP speaker is a NEW speaker and receives the route from an OLD
speaker), according to section 4.2.3 of RFC 6793.
RFC 5575 references "the best-match unicast route for the destination
prefix embedded in the flow specification". For clarity, this route
is defined hereby as the best path of the unicast network that covers
destination prefix embedded in the flow specification with the longer
prefix-length. In other words, we consider only the best-match
network and we do not consider unicast non-best paths (even if it is
received from the same peer than the flowspec route).
Note that, per RFC 5575, originator may refer to the BGP
ORIGINATOR_ID attribute or the transport address of the peer from
which we received the update. If the later, a network must be
designed so it has a congruent topology. Otherwise, using two
peering sessions between the same pair of BGP speakers, one for
unicast and one for flowspec, will cause the flowspec validation
procedure to fail. Consider, for example, the case where a BGP route
reflector receives the NLRIs from a route reflector client, thus not
receiving the ORIGINATOR_ID attribute. If the speaker belongs to a
confederation [RFC5065] and we are receiving a flowspec route from
different peers than its best match unicast route, the flowspec
validation procedure will fail as well. Consider also a
misconfiguration where flowspec address-family is not configured for
a particular peering between different member-AS (but it is
configured for unicast). Even if we receive the flowspec route via a
redundant peer, we may receive the unicast route and the flowspec
from different peers, and thus flowspec validation will fail. With
the (newly introduced) second condition above applied, uncongruent
topologies are supported.
5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
No new security issues are introduced by relaxing the validation No new security issues are introduced by relaxing the validation
procedure for IBGP learned flow specifications. With this proposal, procedure for IBGP learned flow specifications. With this proposal,
the security characteristics of BGP flow specifications remain the security characteristics of BGP flow specifications remain
equivalent to the existing security properties of BGP unicast equivalent to the existing security properties of BGP unicast
routing. Traffic flow specifications learned from IBGP peers are routing. Traffic flow specifications learned from IBGP peers are
trusted, hence, its not required to validate that the originator of trusted, hence, it is not required to validate that the originator of
an intra-domain traffic flow specification matches the originator of an intra-domain traffic flow specification matches the originator of
the best-match unicast route for the flow destination prefix. the best-match unicast route for the flow destination prefix.
Conversely, this proposal continues to enforce the validation Conversely, this proposal continues to enforce the validation
procedure for EBGP learned traffic flow specifications. In this way, procedure for EBGP learned traffic flow specifications. In this way,
the security properties of RFC 5575 are maintained such that an EBGP the security properties of RFC 5575 are maintained such that an EBGP
peer cannot cause a denial-of-service attack by advertising an peer cannot cause a denial-of-service attack by advertising an inter-
inter-domain flow specification for a destination prefix that it does domain flow specification for a destination prefix that it does not
not provide reachability information for. provide reachability information for.
6. IANA Considerations
This document has no actions for IANA. 7. Acknowledgements
7. Normative References The authors would like to thank Han Nguyen for his direction on this
work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen
and Shyam Sethuram for their review comments.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 8. Normative References
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Protocol 4 (BGP-4)", RFC 4271, March 2006. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4456] Bates, T., Chen, E., and Chandra, R., "BGP Route [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC Border Gateway Protocol 4 (BGP-4)", RFC 4271,
4456, April 2006. DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC5065] Traina, P., McPherson, D., and Scudder, J., "Autonomous [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
System Confederations for BGP", August 2007. Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
and McPherson, D., "Dissemination of Flow Specification Rules", RFC System Confederations for BGP", RFC 5065,
5575, August 2009. DOI 10.17487/RFC5065, August 2007,
<http://www.rfc-editor.org/info/rfc5065>.
8. Acknowledgements [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,
<http://www.rfc-editor.org/info/rfc5575>.
The authors would like to thank Han Nguyen for his direction on this [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen Autonomous System (AS) Number Space", RFC 6793,
and Shyam Sethuram for their review comments. DOI 10.17487/RFC6793, December 2012,
<http://www.rfc-editor.org/info/rfc6793>.
9. Authors' Addresses Authors' Addresses
James Uttaro James Uttaro
AT&T AT&T
200 S. Laurel Avenue 200 S. Laurel Ave
Middletown, NJ 07748 Middletown, NJ 07748
USA USA
Email: ju1738@att.com Email: ju1738@att.com
Juan Alcaide Juan Alcaide
Cisco Cisco
7100 Kit Creek Road 7100 Kit Creek Road
Research Triangle Park, NC 27709 Research Triangle Park, NC 27709
USA USA
Email: jalcaide@cisco.com Email: jalcaide@cisco.com
Clarence Filsfils Clarence Filsfils
Cisco Cisco
Brussels 1000
BE
Email: cf@cisco.com Email: cf@cisco.com
David Smith David Smith
Cisco Cisco
111 Wood Avenue South 111 Wood Ave South
Iselin, NJ 08830 Iselin, NJ 08830
USA USA
Email: djsmith@cisco.com Email: djsmith@cisco.com
Pradosh Mohapatra Pradosh Mohapatra
Sproute Networks Sproute Networks
Email: mpradosh@yahoo.com Email: mpradosh@yahoo.com
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