Network Working Group J. Luo, Ed.
Internet-Draft ZTE
Updates: 4379 (if approved) L. Jin, Ed.
Intended status: Standards Track
Expires: August 18, 2014 T. Nadeau, Ed.
Lucidvision
G. Swallow, Ed.
Cisco
February 14, 2014
Relayed Echo Reply mechanism for LSP Ping
draft-ietf-mpls-lsp-ping-relay-reply-02
Abstract
In some inter autonomous system (AS) and inter-area deployment
scenarios for Label Switched Path (LSP) Ping and Traceroute, a
replying LSR may not have the available route to the initiator, and
the Echo Reply message sent to the initiator would be discarded
resulting in false negatives or complete failure of operation of LSP
Ping and Traceroute. This document describes extensions to LSP Ping
mechanism to enable the replying Label Switching Router (LSR) to have
the capability to relay the Echo Response by a set of routable
intermediate nodes to the initiator.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 18, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Relayed Echo Reply message . . . . . . . . . . . . . . . . 5
3.2. Relay Node Address Stack . . . . . . . . . . . . . . . . . 5
3.3. New Return Code . . . . . . . . . . . . . . . . . . . . . 7
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Sending an Echo Request . . . . . . . . . . . . . . . . . 7
4.2. Receiving an Echo Request . . . . . . . . . . . . . . . . 7
4.3. Originating an Relayed Echo Reply . . . . . . . . . . . . 8
4.4. Relaying an Relayed Echo Reply . . . . . . . . . . . . . . 9
4.5. Sending an Echo Reply . . . . . . . . . . . . . . . . . . 9
4.6. Receiving an Echo Reply . . . . . . . . . . . . . . . . . 9
5. LSP Ping Relayed Echo Reply Example . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. New Message Type . . . . . . . . . . . . . . . . . . . . . 12
8.2. New TLV . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.3. New Return Code . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 13
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This document describes the extensions to the Label Switched Path
(LSP) Ping as specified in [RFC4379], by adding a relayed echo reply
mechanism which could be used to detect data plane failures in inter
autonomous system (AS) and inter-area LSPs. Without this extension,
the ping functionality provided by [RFC4379] would fail in many
deployed inter-AS scenarios, since the replying LSR in one AS may not
have the available route to the initiator in the other AS. The
mechanism in this draft defines a new message type referred as
"Relayed Echo Reply message", and a new TLV referred as "Relay Node
Address Stack TLV".
1.1. Conventions Used in This Document
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].
2. Motivation
LSP Ping [RFC4379] defines a mechanism to detect data plane failures
and localize faults. The mechanism specifies that the Echo Reply
should be sent back to the initiator usig an UDP packet with the
IPv4/ IPv6 address of the originating LSR. This works in
administrative domains allowing IP address reachability and routing
back to the originating LSR. However, in practice, this is often not
the case due to intra-provider routing policy, route hiding, network
address translation at autonomous system border routers (ASBR), and
etc. In fact, it is almost uniformly the case that in inter-AS
scenarios, it is not allowed the distribution or direct routing to
the IP addresses of any of the nodes other than the ASBR.
Figure 1 demonstrates a case where one LSP is set up between PE1 and
PE2. If private addresses were in use within AS2, a traceroute from
PE1 directed to PE2 could fail if the fault exists somewhere between
ASBR2 and PE2. Because P2 cannot forward packets back to PE1 given
that it is a private address within AS1. In this case, PE1 would
detect a path break, as the Echo Request messages would not be sent
back; however, localization of the actual fault would not be
possible.
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+-------+ +-------+ +------+ +------+ +------+ +------+
| | | | | | | | | | | |
| PE1 +---+ P1 +---+ ASBR1+---+ ASBR2+---+ P2 +---+ PE2 |
| | | | | | | | | | | |
+-------+ +-------+ +------+ +------+ +------+ +------+
<---------------AS1-------------><---------------AS2------------>
<---------------------------- LSP ------------------------------>
Figure 1: Simple Inter-AS LSP Configuration
A second example that illustrates how [RFC4379] would be insufficient
would be the inter-area situation in a Seamless MPLS architecture
[I-D.ietf-mpls-seamless-mpls] as shown below in Figure 2. In this
example P nodes the in core network would not have IP reachable route
to any of the ANs. When tracing an LSP from AN to remote AN, the
LSR1/LSR2 node could not make a response to the Echo Request either,
like P2 node in the inter-AS scenario in Figure 1.
+-------+ +-------+ +------+ +------+
| | | | | | | |
+--+ AGN11 +---+ AGN21 +---+ ABR1 +---+ LSR1 +--> to AGN
/ | | /| | | | | |
+----+/ +-------+\/ +-------+ +------+ /+------+
| AN | /\ \/
+----+\ +-------+ \+-------+ +------+/\ +------+
\ | | | | | | \| |
+--+ AGN12 +---+ AGN22 +---+ ABR2 +---+ LSR2 +--> to AGN
| | | | | | | |
+-------+ +-------+ +------+ +------+
static route ISIS L1 LDP ISIS L2 LDP
<-Access-><--Aggregation Domain--><---------Core--------->
Figure 2: Seamless MPLS Architecture
This document describes extensions to the LSP Ping mechanism to
facilitate a response from the replying LSR, by defining a simple
mechanism that uses the relay node (e.g, ASBR) to relay the message
back to the initiator. This approach will work because every
designated or learned relay node must have an IP route back to the
initiator. Using a recursive approach, relay node could relay the
message to the next relay node until the initiator is reached.
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3. Extensions
[RFC4379] describes the basic MPLS LSP Ping mechanism, which defines
two message types, Echo Request and Echo Reply message. This draft
defines a new message, Relayed Echo Reply message. This new message
is used to replace Echo Reply message which is sent from the replying
LSR to a relay node or from a relay node to another relay node.
A new TLV named Relay Node Address Stack TLV is defined in this
draft, to carry the IP addresses of the possible relay nodes for the
replying LSR.
In addition, a new Return Code is defined to notify the initiator
that the packet length was exceeded unexpected by the Relay Node
Address Stack TLV.
It should be noted that this document focuses only on detecting the
LSP which is set up using a uniform type of IP address. That is, all
hops between the source and destination use one address type of their
control planes. This does not preclude nodes that support both IPv6
and IPv4 addresses simultaneously, but the entire path must be
addressable using only one address family type. Supporting for mixed
IPv4-only and IPv6-only is beyond the scope of this document.
3.1. Relayed Echo Reply message
The Relayed Echo Reply message is a UDP packet, and the UDP payload
has the same format with Echo Request/Reply message. A new message
type is requested from IANA.
New Message Type:
Value Meaning
----- -------
TBD MPLS Relayed Echo Reply
The TCP and UDP port number 3503 has been allocated in [RFC4379] by
IANA for LSP Ping messages. The Relayed Echo Reply message will use
the same port number.
3.2. Relay Node Address Stack
The Relay Node Address Stack TLV is an optional TLV. It MUST be
carried in the Echo Request, Echo Reply and Relayed Echo Reply
messages if the echo reply relayed mechanism described in this draft
is required. Figure 3 illustrates the TLV format.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiator Source Port | Number of Relayed Addresses |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Stack of Relayed Addresses ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Relay Node Address Stack TLV
- Type: to be assigned by IANA. A suggested value is assigned from
32768-49161 as suggested by RFC4379 Section 3.
- Length: The Length of the Value field in octets.
- Initiator Source Port: The port that the initiator sends the Echo
Request message, and also the port that expected to receive the
Echo Reply message.
- Number of Relayed Addresses: An integer indicating the number of
relayed addresses in the stack.
- Stack of Relayed Addresses: A list of relay node addresses.
The format of each relay node address is as below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | Address Length| Reserved |K|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Relayed Address (0, 4, or 16 octects) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type# Address Type Address Length
---- ------------ ------------
0 Unspecified 0
1 IPv4 4
2 IPv6 16
Reserved: This field is reserved for future use and MUST be set to
zero.
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K bit: If the K bit is set to 1, then this sub-TLV SHOULD be kept in
Relay Node Address Stack, SHOULD not be deleted in compress process
of section 4.2. The K bit may be set by ASBRs which address would be
kept in the stack if necessary.
If the K bit is set to 0, then this sub-TLV SHOULD be processed
normally according to section 4.2.
Relayed Address: This field specifies the node address, either IPv4
or IPv6.
3.3. New Return Code
A new Return Code is used by the replying LSR to notify the initiator
that the packet length was exceeded unexpected by the Relay Node
Address Stack TLV.
New Return Code:
Value Meaning
----- -------
TBD Response Packet length was exceeded by the Relay Node
Address Stack TLV unexpected
4. Procedures
4.1. Sending an Echo Request
In addition to the procedures described in Section 4.3 of [RFC4379],
a Relay Node Address Stack TLV MUST be carried in the Echo Request
message for facilitate the relay functionality.
When the Echo Request is first sent by initiator supporting these
extensions, a Relay Node Address Stack TLV with the initiator address
in the stack and its source port MUST be included. That will ensure
that the first relay node address in the stack will always be the
initiator address.
For the subsequent Echo Request messages, the initiator would copy
the Relay Node Address Stack TLV from the received Echo Reply
message.
4.2. Receiving an Echo Request
In addition to the processes in Section 4.4 of [RFC4379], the
procedures of the Relay Node Address Stack TLV are defined here.
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Upon receiving a Relay Node Address Stack TLV of the Echo Request
message, the receiver MUST check the addresses of the stack in
sequence from top to bottom (the first address in the stack ==== will
be first one to be checked), to find out the first public routable IP
address. Those address entries behind of the first routable IP
address in the address list with K bit set to 0 MUST be deleted, and
the address entry of the replying LSR MUST be added at the bottom of
the stack. Those address entries with K bit set to 1 MUST be kept in
the stack. The updated Relay Node Address Stack TLV MUST be carried
in the response message.
If the replying LSR wishes to hide its routable address information,
the address entry added in the stack SHOULD be a blank entry with
Address Type set to unspecified. The blank address entry in the
receiving Echo Request SHOULD be treated as an unroutable address
entry.
If the packet length was exceeded unexpectedly by the Relay Node
Address Stack TLV, the TLV SHOULD be returned back unchanged in the
echo response message. And the new return code SHOULD help to notify
the initiator of the situation.
If the first routable IP address is the first address in the stack,
the replying LSR SHOULD respond an Echo Reply message to the
initiator.
If the first routable IP address is of an intermediate node, other
than the first address in the stack, the replying LSR SHOULD send an
Relayed Echo Reply instead of an Echo Reply in response.
An LSR not recognize the Relay Node Address Stack TLV, SHOULD ignore
it according to section 3 of RFC4379.
4.3. Originating an Relayed Echo Reply
When the replying LSR received an Echo Request with the initiator IP
address in the Relay Node Address Stack TLV is IP unroutable, the
replying LSR SHOULD send an Relayed Echo Reply message to the first
routable intermediate node. The processing of Relayed Echo Reply is
the same with the procedure of the Echo Reply described in Section
4.5 of RFC4379, except the destination IP address and the destination
UDP port of the message part. The destination IP address of the
Relayed Echo Reply is set to the first routable IP address from the
Relay Node Address Stack TLV, and both the source and destination UDP
port is set to 3503.
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4.4. Relaying an Relayed Echo Reply
Upon receiving an Relayed Echo Reply message with its address as the
destination address in the IP header, the relay node should check the
address items in Relay Node Address Stack TLV in sequence from top to
down, and find the first routable node address.
If the first routable address is the top one of the address list,
e.g, the initiator address, the relay node SHOULD send an Echo Reply
message to the initiator containing the same payload with the Relayed
Echo Reply message received. See section 4.5 for detail.
If the first routable address is not the top one of the address list,
e.g, another intermediate relay node, the relay node SHOULD send an
Relayed Echo Reply message to this relay node with the payload
unchanged.
Note, the replying LSR SHOULD send a Relayed Echo Reply message to
the first relay node found in Relay Node Address Stack TLV that is
routable by the router. The routable address MUST be located before
the source IP address of the received Relayed Echo Reply which must
be also in the stack, otherwise the Relayed Echo Reply should not be
sent, so as to avoid potential loop.
4.5. Sending an Echo Reply
The Echo Reply is sent in two cases:
1. When the replying LSR received an Echo Request with the initiator
IP address in the Relay Node Address Stack TLV is IP routable, the
replying LSR would send an Echo Reply to the initiator. In addition
to the procedure of the Echo Reply described in Section 4.5 of
RFC4379, the Relay Node Address Stack TLV would be carried in the
Echo Reply.
2. When the intermediate relay node received an Relayed Echo Reply
with the initiator IP address in the Relay Node Address Stack TLV IP
routable, the intermediate relay node would send the Echo Reply to
the initiator with the payload unchanged other than the Message Type
field. The destination IP address of the Echo Reply is set to the
initiator IP address, and the destination UDP port would be copied
from the Initiator Source Port field of the Relay Node Address Stack
TLV. The source UDP port should be 3503.
4.6. Receiving an Echo Reply
In addition to the processes in Section 4.6 of [RFC4379], the
initiator would copy the Relay Node Address Stack TLV received in the
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Echo Reply to the next Echo Request.
5. LSP Ping Relayed Echo Reply Example
Considering the inter-AS scenario in Figure 4 below.
+-------+ +-------+ +------+ +------+ +------+ +------+
| | | | | | | | | | | |
| PE1 +---+ P1 +---+ ASBR1+---+ ASBR2+---+ P2 +---+ PE2 |
| | | | | | | | | | | |
+-------+ +-------+ +------+ +------+ +------+ +------+
<---------------AS1-------------><---------------AS2------------>
<--------------------------- LSP ------------------------------->
Figure 4: Example Inter-AS LSP
In the example, an LSP has been created between PE1 to PE2. When
performing LSP traceroute on the LSP, the first Echo Request sent by
PE1 with outter-most label TTL=1, contains the Relay Node Address
Stack TLV with the only address of PE1.
After processed by P1, P1's address will be added in the Relay Node
Address Stack TLV address list following PE1's address in the Echo
Reply.
PE1 copies the Relay Node Address Stack TLV into the next Echo
Request when receiving the Echo Reply.
Upon receiving the Echo Request, ASBR1 checks the address list in the
Relay Node Address Stack TLV in sequence, and finds out that PE1
address is routable. Then deletes P1 address, and adds its own
address following PE1 address. As a result, there would be PE1
address followed by ASBR1 address in the Relay Node Address Stack TLV
of the Echo Reply sent by ASBR1.
PE1 then sends an Echo Request with outer-most label TTL=3,
containing the Relay Node Address Stack TLV copied from the received
Echo Reply message. Upon receiving the Echo Request message, ASBR2
checks the address list in the Relay Node Address Stack TLV in
sequence, and finds out that PE1 address is IP route unreachable, and
ASBR1 address is the first routable one in the Relay Node Address
Stack TLV. ASBR2 adds its address as the last address item following
ASBR1 address in Relay Node Address Stack TLV, sets ASBR1 address as
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the destination address of the Relayed Echo Reply, and sends the
Relayed Echo Reply to ASBR1.
Upon receiving the Relayed Echo Reply from ASBR2, ASBR1 checks the
address list in the Relay Node Address Stack TLV in sequence, and
finds out that PE1 address is first routable one in the address list.
Then ASBR1 send an Echo Reply to PE1 with the payload of received
Relayed Echo Reply no changes other than the Message Type field.
For the Echo Request with outer-most label TTL=4, P2 checks the
address list in the Relay Node Address Stack TLV in sequence, and
finds out that both PE1 and ASBR1 addresses are not IP routable, and
ASBR2 address is the first routable address. And P2 would send an
Relayed Echo Reply to ASBR2 with the Relay Node Address Stack TLV of
four addresses, PE1, ASBR1, ASBR2 and P2 address in sequence.
Then according to the process described in section 4.4, ASBR2 would
send the Relayed Echo Reply to ASBR1. Upon receiving the Relayed
Echo Reply, ASBR1 would send an Echo Reply to PE1 as PE1 address is
routable. And as relayed by ASBR2 and ASBR1, the echo response would
finally be sent to the initiator PE1.
For the Echo Request with outer-most label TTL=5, the echo response
would relayed to PE1 by ASBR2 and ASBR1, similar to the case of
TTL=4.
The Echo Reply from the replying node which has no reachable route to
the initiator is finally transmitted to the initiator by multiple
relay nodes.
6. Security Considerations
The Relayed Echo Reply mechanism for LSP Ping creates an increased
risk of DoS by putting the IP address of a target router in the Relay
Node Address Stack. These messages then could be used to attack the
control plane of an LSR by overwhelming it with these packets. A
rate limiter SHOULD be applied to the well-known UDP port on the
relay node as suggested in RFC4379. The node which acts as a relay
node SHOULD validate the relay reply against a set of valid source
addresses and discard packets from untrusted border router addresses.
An implementation SHOULD provide such filtering capabilities.
If an operator wants to obscure their nodes, it is RECOMMENDED that
they may replace the replying node address that originated the Echo
Reply with blank address in Relay Node Address Stack TLV.
Other security considerations discussed in [RFC4379], are also
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applicable to this document.
7. Backward Compatibility
When one of the nodes along the LSP does not support the mechanism
specified in this draft, the node will ignore the Relay Node Address
Stack TLV as described in section 4.2. Then the initiator may not
receive the Relay Node Address Stack TLV in Echo Reply message from
that node. In this case, an indication should be reported to the
operator, and the Relay Node Address Stack TLV in the next Echo
Request message should be copied from the previous Echo Request, and
continue the ping process. If the node described above is located
between the initiator and the first relay node, the ping process
could continue without interruption.
8. IANA Considerations
IANA is requested to assign one new Message Type, one new TLV and one
new Return Code.
8.1. New Message Type
New Message Type:
Value Meaning
----- -------
TBD MPLS Relayed Echo Reply
8.2. New TLV
New TLV: Routable Relay Node Address TLV
Type Meaning
---- --------
TBD Relay Node Address Stack TLV
A suggested value is assigned from 32768-49161 as suggested by
RFC4379 Section 3.
8.3. New Return Code
New Return Code:
Value Meaning
----- -------
TBD Response Packet length was exceeded by the Relay Node
Address Stack TLV unexpected
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9. Acknowledgement
The authors would like to thank Carlos Pignataro, Xinwen Jiao, Manuel
Paul, Loa Andersson, Wim Henderickx, Mach Chen, Thomas Morin and
Gregory Mirsky for their valuable comments and suggestions.
10. Contributors
Ryan Zheng
JSPTPD
371, Zhongshan South Road
Nanjing, 210006, China
Email: ryan.zhi.zheng@gmail.com
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
11.2. Informative References
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture",
draft-ietf-mpls-seamless-mpls-05 (work in progress),
January 2014.
Authors' Addresses
Jian Luo (editor)
ZTE
50, Ruanjian Avenue
Nanjing, 210012, China
Email: luo.jian@zte.com.cn
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Lizhong Jin (editor)
Shanghai, China
Email: lizho.jin@gmail.com
Thomas Nadeau (editor)
Lucidvision
Email: tnadeau@lucidvision.com
George Swallow (editor)
Cisco
300 Beaver Brook Road
Boxborough , MASSACHUSETTS 01719, USA
Email: swallow@cisco.com
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