Network Working Group J. Luo, Ed.
Internet-Draft ZTE
Updates: 4379 (if approved) L. Jin, Ed.
Intended status: Standards Track Individual
Expires: January 7, 2016 T. Nadeau, Ed.
Lucidvision
G. Swallow, Ed.
Cisco
July 6, 2015
Relayed Echo Reply mechanism for LSP Ping
draft-ietf-mpls-lsp-ping-relay-reply-10
Abstract
In some inter autonomous system (AS) and inter-area deployment
scenarios for RFC 4379 "Label Switched Path (LSP) Ping and
Traceroute", a replying Label Switching Router (LSR) may not have the
available route to an 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 LSR to have the capability to relay the Echo Response by a
set of routable intermediate nodes to the initiator. This document
updates RFC 4379.
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-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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 January 7, 2016.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . 6
3.3. MTU Exceeded Return Code . . . . . . . . . . . . . . . . 8
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Sending an Echo Request . . . . . . . . . . . . . . . . . 8
4.2. Receiving an Echo Request . . . . . . . . . . . . . . . . 9
4.3. Originating an Relayed Echo Reply . . . . . . . . . . . . 10
4.4. Relaying an Relayed Echo Reply . . . . . . . . . . . . . 10
4.5. Sending an Echo Reply . . . . . . . . . . . . . . . . . . 11
4.6. Sending Subsequent Echo Requests . . . . . . . . . . . . 11
4.7. Impact to Traceroute . . . . . . . . . . . . . . . . . . 12
5. LSP Ping Relayed Echo Reply Example . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8.1. New Message Type . . . . . . . . . . . . . . . . . . . . 14
8.2. New TLV . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.3. MTU Exceeded Return Code . . . . . . . . . . . . . . . . 15
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 15
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
This document describes extensions to the Label Switched Path (LSP)
Ping as specified in [RFC4379], by adding a relayed echo reply
mechanism which could be used to report data plane failures for inter
autonomous system (AS) and inter-area LSPs. Without these
extensions, the ping functionality provided by [RFC4379] would fail
in many deployed inter-AS scenarios, since the replying Label
Switching Router (LSR) in one AS may not have an available route to
the initiator in the other AS. The mechanism in this document
defines a new message type referred as "Relayed Echo Reply message",
and a new TLV referred as "Relay Node Address Stack TLV".
This document is also to update [RFC4379], include updating of Echo
Request sending procedure in section 4.3 of [RFC4379], Echo Request
receiving procedure in section 4.4 of [RFC4379], Echo Reply sending
procedure in Section 4.5 of [RFC4379], Echo Reply receiving procedure
in section 4.6 of [RFC4379].
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 using an UDP packet with the
IPv4/IPv6 destination address set to an address of the LSR that
originated the Echo Request. This works in administrative domains
where IP address reachability is allowed among LSRs, and every LSR is
able to route back to the originating LSR. However, in practice,
this is often not the case due to intra-provider routing policy,
route hiding, and network address translation at autonomous system
border routers (ASBR). In fact, it is almost always the case that in
inter-AS scenarios the only node in one AS to which direct routing is
allowed from the other AS is the ASBR, and routing information from
within one AS is not distributed into another AS.
Figure 1 demonstrates a case where an LSP is set up between PE1 and
PE2. If PE1's IP address is not distributed to AS2, a traceroute
from PE1 directed towards PE2 can result in a failure because an LSR
in AS2 may not be able to send the Echo Reply message. E.g., P2
cannot forward packets back to PE1 given that it is an routable IP
address in AS1 but not routable in AS2. In this case, PE1 would
detect a path break, as the Echo Reply messages would not be
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received. Then localization of the actual fault would not be
possible.
Note that throughout the document, routable address means that it is
possible to route an IP packet to this address using the normal
information exchanged by the IGP operating in the AS.
+-------+ +-------+ +------+ +------+ +------+ +------+
| | | | | | | | | | | |
| 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 LSRs in the core network would not have IP reachable route to
any of the ANs. When tracing an LSP from one access node (AN) to the
remote AN, the LSR1/LSR2 node cannot send the Echo Reply either, like
the 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 mechanism
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that uses a relay node (e.g, ASBR) to relay the message back to the
initiator. Every designated or learned relay node must be reachable
to the next relay node or to the initiator. Using a recursive
approach, relay node could relay the message to the next relay node
until the initiator is reached.
The LSP Ping relay mechanism in this document is defined for unicast
case. How to apply the LSP Ping relay mechanism in multicast case is
out of the scope.
3. Extensions
[RFC4379] describes the basic MPLS LSP Ping mechanism, which defines
two message types, Echo Request and Echo Reply message. This
document 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
document, to carry the IP addresses of the relay nodes for the
replying LSR.
In addition, MTU (Maximum Transmission Unit) Exceeded Return Code is
defined to indicate to the initiator that one or more TLVs will not
be returned due to MTU size.
It should be noted that this document focuses only on detecting the
LSP which is set up using a uniform IP address family type. That is,
all hops between the source and destination node use the same address
family type for their LSP ping 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
----- -------
TBD1 MPLS Relayed Echo Reply
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The use of TCP and UDP port number 3503 is described in [RFC4379] and
has been allocated 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
document is required. Figure 3 illustrates the TLV format.
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 | Reply Add Type| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address of Replying Router (0, 4, or 16 octects) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address Offset | Number of Relayed Addresses |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Stack of Relayed Addresses ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Relay Node Address Stack TLV
- Type: value is TBD2. The value should be assigned by IANA from
32768-49161 as suggested by [RFC4379] Section 3.
- Length: the length of the value field in octets.
- Initiator Source Port: the source UDP port that the initiator uses
in the Echo Request message, and also the port that is expected to
receive the Echo Reply message.
- Reply Address Type: address type of replying router. This value
also implies the length of the address field as shown below.
Type# Address Type Address Length
---- ------------ ------------
0 Null 0
1 IPv4 4
2 IPv6 16
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- Reserved: This field is reserved and MUST be set to zero.
- Source Address of Replying Router: source IP address of the
originator of Echo Reply or Replay Echo Reply message.
- Destination Address Offset: an offset (octets) to indicate the
position of the destination address of the Reply or Relayed Reply
message. The entry on the top of the Stack of Relayed Addresses
will have offset of 0.
- 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 |K| Reserved | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Relayed Address (0, 4, or 16 octects) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type# Address Type Address Length
---- ------------ ------------
0 Null 0
1 IPv4 4
2 IPv6 16
Reserved: The two fields are reserved and MUST be set to zero.
K bit: if the K bit is set to 1, then this address stack entry MUST
NOT be stripped from the Relay Node Address Stack during processing
described in Section 4.2. If the K bit is clear, the entry might be
stripped according to the processing described in Section 4.2.
Having the K bit set in the relay node address entry causes that
entry to be preserved in the Relay Node Address Stack TLV for the
entire traceroute operation. A responder node MAY set the K bit to
ensure its relay node address entry remains as one of the relay nodes
in the Relay Node Address Stack TLV. The address with K bit set will
always be a relay node address for the Relayed Echo Reply, see
section 4.3.
Relayed Address: this field specifies the node address, either IPv4
or IPv6.
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3.3. MTU Exceeded Return Code
Return Code is defined to indicate that one or more TLVs were omitted
from the Echo Reply or Relayed Echo Reply message to avoid exceeding
the message's effective MTU size. These TLVs MAY be included in an
Errored TLV's Object with their lengths set to 0 and no value. The
return sub-code MUST be set to the value that otherwise would have
been sent. For more detail, please refer to section 4.2.
MTU Exceeded Return Code:
Value Meaning
----- -------
TBD2 One or more TLVs not returned due to MTU size
Then section 4.4 of [RFC4379], step 7 will be updated to integrate
the processing of MTU Exceeded Return Code.The following text will be
added:
Before sending Echo Reply, the new packet size should be checked. If
Best-return-code is 3 ("Replying router is an egress for the FEC at
stack depth"), or 8 ("Label switched at stack-depth"), and if the
packet size exceeds MTU size, then Best-return-code is TBD3 ("One or
more TLVs not returned due to MTU size")
4. Procedures
In the following section, we describe the relay reply procedures with
traceroute operation. If operator has knowledge of the relay nodes,
the initiator could do LSP Ping by directly sending Echo Request with
Relay Node Address Stack TLV containing the already known relay
nodes.
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 if the relay functionality is required.
When the initiator sends the first Echo Request with a Relay Node
Address Stack TLV, the TLV MUST contain the initiator address as the
first entry of the stack of relayed addresses, the Destination
Address Offset set to this entry, and the source address of the
replying router set to null. The Initiator Source Port field MUST be
set to the source UDP port. Note that the first relay node address
in the stack will always be the initiator's address.
When sending subsequent Echo Request message, refer to section 4.6.
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4.2. Receiving an Echo Request
The Type of the Relay Node Address Stack TLV is chosen from the range
32768 to 49161 so that (per section 3 of [RFC4379]) an LSR that does
not recognize the TLV knows that the TLV is optional and can safely
ignore it.
In addition to the processes in section 4.4 of [RFC4379], the
procedures of the Relay Node Address Stack TLV are defined here.
Upon receiving a Relay Node Address Stack TLV in an Echo Request
message, the receiver updates the "Source Address of Replying
Router". The address MUST be same as the source IP address of Relay
Echo Reply (section 4.3) or Echo Reply message (section 4.5) being
sent.
Those address entries with K bit set to 1 MUST be kept in the stack.
The receiver MUST check the addresses of the stack in sequence from
bottom to top to find the last address in the stack with the K bit
set (or the top of the stack if no K bit was found). The receiver
then checks the stack beginning with this entry, proceeding towards
the bottom to find the first routable address IP address. The
Destination Address Offset MUST be set to this entry which is also
the resolved destination address. Address entries below the first
routable IP address MUST be deleted. At least one address entries of
the replying LSR MUST be added at the bottom of the stack. A second
or more address entries MAY also be added if necessary, depending on
implementation. The final address added MUST be an address that is
reachable through the interface that the Echo Request Message would
have been forwarded if it had not TTL expired at this node. The
updated Relay Node Address Stack TLV MUST be carried in the response
message.
If the replying LSR is configured to hide its routable address
information, the address entry added in the stack MUST be a NIL entry
with Address Type set to NULL.
If a node spans two addressing domains (with respect to this message)
where nodes on either side may not be able to reach nodes in the
other domain, then the final address added SHOULD set the K bit. One
example of spanning two address domains is the ASBR node. Other
cases are also possible, and out of the scope of this document.
K bit applies in the case of a NULL address, to serve as a warning to
the initiator that further Echo Request messages may not result in
receiving Echo Reply messages.
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If the full reply message would exceed the MTU size, the Relay Node
Address Stack TLV SHOULD be included in the Echo Reply message (i.e.,
other optional TLVs are excluded).
4.3. Originating an Relayed Echo Reply
The destination address determined in section 4.2 is used as the next
relay node address. If the resolved next relay node address is not
routable, then sending of Relayed Echo Reply or Echo Reply will fail.
If the first IP address in the Relay Node Address Stack TLV is not
the next relay node address, the replying LSR SHOULD send a Relayed
Echo Reply message to the next relay 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. The destination IP address of the Relayed
Echo Reply is set to the next relay node address from the Relay Node
Address Stack TLV, and both the source and destination UDP port are
set to 3503. The updated Relay Node Address Stack TLV described in
section 4.2 MUST be carried in the Relayed Echo Reply message. The
Source Address of Replying Router field is kept unmodified, and
Source IP address field of the IP header is set to an address of the
sending node.
When the next relay node address is the first one in the address
list, please refer to section 4.5.
4.4. Relaying an Relayed Echo Reply
Upon receiving an Relayed Echo Reply message with its own address as
the destination address in the IP header, the relay node MUST
determine the next relay node address as described in section 4.2,
with the modification that the location of the received destination
address is used instead of the bottom of stack in the algorithm. The
Destination Address Offset in Relay Node Address Stack TLV will be
set to the next relay node address. Note that unlike section 4.2 no
changes are made to the Stack of Relayed Addresses.
If the next relay node address is not the first one in the address
list, i.e., another intermediate relay node, the relay node MUST send
an Relayed Echo Reply message to the determined upstream node with
the payload unchanged other than the Relay Node Address Stack TLV.
The TTL SHOULD be copied from the received Relay Echo Reply and
decremented by 1. The Source Address of Replying Router field is
kept unmodified, and Source IP address field of the IP header is set
to an address of the sending node.
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When the next relay node address is the first one in the address
list, please refer to section 4.5.
4.5. Sending an Echo Reply
The Echo Reply is sent in two cases:
1. When the replying LSR receives an Echo Request, and the first IP
address in the Relay Node Address Stack TLV is the next relay node
address (section 4.3), 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 updated Relay Node Address
Stack TLV described in section 4.2 MUST be carried in the Echo Reply.
If the receiver does not recognize the Relay Node Address Stack TLV,
as per section 3 and 4.5 of [RFC4379], it will send an Echo Reply
without including the TLV.
2. When the intermediate relay node receives a Relayed Echo Reply,
and the first IP address in the Relay Node Address Stack TLV is the
next relay node address (section 4.4), the intermediate relay node
would send the Echo Reply to the initiator, and update the Message
Type field from type of Relayed Echo Reply to Echo Reply. The
updated Relay Node Address Stack TLV described in section 4.4 MUST be
carried in the Echo Reply. The destination IP address of the Echo
Reply is set to the first IP address in the stack, 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. The TTL of the Echo Reply SHOULD be copied from the
received Relay Echo Reply and decremented by 1. The Source Address
of Replying Router field is kept unmodified, and Source IP address
field of the IP header is set to an address of the sending node.
4.6. Sending Subsequent Echo Requests
During a traceroute operation, multiple Echo Request messages are
sent. Each time the TTL is increased, the initiator SHOULD copy the
Relay Node Address Stack TLV received in the previous Echo Reply to
the next Echo Request. The Relay Node Address Stack TLV MUST NOT be
modified except as follows. A NIL entry with K bit unset MAY be
removed. A NIL entry with K bit serves as a warning that further
Echo Request messages are likely to not result in a reply. If,
however, the initiator decides to continue a traceroute operation,
the NIL entry with the K bit set MUST be removed. The Source Address
of Replying Router and Destination Address Offset fields may be
preserved or reset since these fields are ignored in received MPLS
Echo Request.
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4.7. Impact to Traceroute
Source IP address in Echo Reply and Relay Echo Reply is to be of the
address of the node sending those packets, not the original
responding node. Then the traceroute address output module will
print the source IP address as below:
if (Relay Node Address Stack TLV exists) {
Print the Source Address of Replying Router in
Relay Node Address Stack TLV;
} else {
Print the source IP address of Echo Reply message;
}
5. LSP Ping Relayed Echo Reply Example
Considering the inter-AS scenario in Figure 4 below. AS1 and AS2 are
two independent address domains. In the example, an LSP has been
created between PE1 to PE2, but PE1 in AS1 is not reachable by P2 in
AS2.
+-------+ +-------+ +------+ +------+ +------+ +------+
| | | | | | | | | | | |
| PE1 +---+ P1 +---+ ASBR1+---+ ASBR2+---+ P2 +---+ PE2 |
| | | | | | | | | | | |
+-------+ +-------+ +------+ +------+ +------+ +------+
<---------------AS1-------------><---------------AS2------------>
<--------------------------- LSP ------------------------------->
Figure 4: Example Inter-AS LSP
When performing LSP traceroute on the LSP, the first Echo Request
sent by PE1 with outer-most label TTL=1, contains the Relay Node
Address Stack TLV with PE1's address as the first relayed address.
After processed by P1, P1's interface address facing ASBR1 without
the K bit set 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, and determines that PE1's address is
the next relay address. Then deletes P1's address, and adds its
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interface address facing ASBR2 with the K bit set. As a result,
there would be PE1's address followed by ASBR1's interface address
facing ASBR2 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, and
determines ASBR1's interface address is the next relay address in the
stack TLV. ASBR2 adds its interface address facing P2 with the K bit
set. Then ASBR2 sets the next relay address as 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, and determines that
PE1's address is the next relay node. Then ASBR1 sends an Echo Reply
to PE1.
For the Echo Request with outer-most label TTL=4, P2 checks the
address list in the Relay Node Address Stack TLV, and determines that
ASBR2's interface address is the next relay address. Then P2 sends
an Relayed Echo Reply to ASBR2 with the Relay Node Address Stack TLV
containing four addresses, PE1's, ASBR1's interface address, ASBR2's
interface address and P2's interface address facing PE2 in sequence.
Then according to the process described in section 4.4, ASBR2 sends
the Relayed Echo Reply to ASBR1. Upon receiving the Relayed Echo
Reply, ASBR1 sends an Echo Reply to PE1. And as relayed by ASBR2 and
ASBR1, the Echo Reply would finally be sent to the initiator PE1.
For the Echo Request with outer-most label TTL=5, the Echo Reply
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 IP reachable route
to the initiator is thus 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
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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 NIL address entry in Relay Node Address Stack TLV.
A receiver of an MPLS Echo Request could verify that the first
address in the Relay Node Address Stack TLV is the same address as
the source IP address field of the received IP header.
The Relay Node Address Stack TLV has the path information of the LSP,
and such information may be maliciously used by any uncontrolled LSR/
LER. We have two ways to reduce the path information in the TLV:
1. it is recommended to clear the K bit in the relay address entry
unless you have to.
2. it is encouraged to use NIL address entry to hide node information
if possible.
Other security considerations discussed in [RFC4379], are also
applicable to this document.
7. Backward Compatibility
When one of the nodes along the LSP does not support the mechanism
specified in this document, 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
Return Code.
8.1. New Message Type
This document requires allocation of one new message type from
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters" registry, the "Message Type" registry:
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Value Meaning
----- -------
TBD1 MPLS Relayed Echo Reply
The value should be assigned from the "Standards Action" range
(0-191), and using the lowest free value within this range.
8.2. New TLV
This document requires allocation of one new TLV from "Multi-Protocol
Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry, the "TLVs" registry:
Type Meaning
---- --------
TBD2 Relay Node Address Stack TLV
A suggested value should be assigned from "Standards Action" range
(32768-49161) as suggested by [RFC4379] Section 3, using the first
free value within this range.
8.3. MTU Exceeded Return Code
This document requires allocation of MTU Exceeded return code from
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters" registry, the "Return Codes" registry:
Value Meaning
----- -------
TBD3 One or more TLVs not returned due to MTU size
The value should be assigned from the "Standards Action" range
(0-191), and using the lowest free value within this range.
9. Acknowledgement
The authors would like to thank Carlos Pignataro, Xinwen Jiao, Manuel
Paul, Loa Andersson, Wim Henderickx, Mach Chen, Thomas Morin, Gregory
Mirsky, Nobo Akiya and Joel M. Halpern for their valuable comments
and suggestions.
10. Contributors
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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-07 (work in progress), June 2014.
Authors' Addresses
Jian Luo (editor)
ZTE
50, Ruanjian Avenue
Nanjing, 210012, China
Email: luo.jian@zte.com.cn
Lizhong Jin (editor)
Individual
Shanghai, China
Email: lizho.jin@gmail.com
Thomas Nadeau (editor)
Lucidvision
Email: tnadeau@lucidvision.com
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George Swallow (editor)
Cisco
300 Beaver Brook Road
Boxborough , MASSACHUSETTS 01719, USA
Email: swallow@cisco.com
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