Network Working Group V. Kamath
Internet-Draft VMware
Intended status: Standards Track R. Chokkanathapuram Sundaram
Expires: May 4, 2021 Cisco Systems, Inc.
R. Banthia
Apstra
A. Gopal
Cisco Systems, Inc.
October 31, 2020
PIM Null-Register packing
draft-ietf-pim-null-register-packing-06
Abstract
In PIM-SM networks PIM Register messages are sent by the Designated
Router (DR) to the Rendezvous Point (RP) to signal the presence of
Multicast sources in the network. There are periodic PIM Null-
Registers sent by a DR to the RP to keep the state alive at the RP as
long as the source is active. The PIM Null-Register message carries
information about a single Multicast source and group.
This document defines a standard to send information about multiple
multicast sources and multicast groups in a single PIM Null-Register
message, in a packed format. This document also discusses the
interoperability between PIM routers that support the new packed
message format and PIM routers that do not support the new format.
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 https://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 May 4, 2021.
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Copyright Notice
Copyright (c) 2020 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
(https://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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Packed Register Capability . . . . . . . . . . . . . . . . . 3
3. PIM Packed Null-Register message . . . . . . . . . . . . . . 4
4. PIM Packed Register-Stop message format . . . . . . . . . . . 5
5. Protocol operation . . . . . . . . . . . . . . . . . . . . . 6
6. PIM Anycast RP considerations . . . . . . . . . . . . . . . . 6
7. PIM RP router version downgrade . . . . . . . . . . . . . . . 7
8. Fragmentation consideration . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
12. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
PIM Null-Registers are sent by a DR periodically for Multicast
streams to keep the states active on the RP, as long as the source is
active. As the number of multicast sources increases, the number of
PIM Null-Register messages that are sent also increases. This
results in more PIM packet processing at the RP and at the DRs.
The control plane policing (COPP), monitors the packets that are
processed by the control plane. Due to the high rate at which Null-
Registers are received at the RP, this can lead to COPP drops of
Multicast PIM Null-Register messages. This document defines a method
to efficiently pack multiple PIM Null-Registers [[RFC7761]
(Section 4.4)] and Register-Stops [[RFC7761] (Section 3.2)] into a
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single message as these packets anyway do not contain encapsulated
data.
The document also discusses interoperability with PIM routers that do
not understand the new packet format.
1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] when, and only when, they appear in all capitals, as
shown here.
1.2. Terminology
RP: Rendezvous Point
DR: Designated Router
2. Packed Register Capability
To ensure compatibility with routers that do not support processing
of the packed format, A router (DR) can decide to pack multiple Null-
Register messages based on the capability received from the RP as
part of Register-Stop. Thus a DR will switch to the packed format
only when it learns RP is capable of handling the packed Null-
Register messages.
Conversely, a DR that does not support the new format can continue
generating the PIM Null-Register using the current format. To
exchange the capability information in the Register-Stop message, the
"reserved" field is used to indicate this capability in those
Register-Stop messages. One bit of the reserved field is used to
indicate the "packing" capability (P bit). The rest of the bits in
the "Reserved" field will be retained for future use.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type |P| Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PIM Register-Stop message with capability option
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PIM Version, Type, Checksum, Group Address, Source Address:
Same as [RFC7761] (Section 4.9.4)
P:
Capability bit (flag bit 7) used to indicate support for the
Packed-Register Capability
3. PIM Packed Null-Register message
PIM Packed Null-Register message format includes a count to indicate
the number of Null-Register records in the message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type |Subtype| FB | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Count | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address[1] (Encoded-Group format) |
| Source Address[1] (Encoded-Unicast format) |
. .
. .
. .
. .
. Group Address[N] .
| Source Address[N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PIM Packed Null-Register message format
PIM Version, Reserved, Checksum:
Same as [RFC7761] (Section 4.9.3)
Type, SubType:
The new packed Null-Register Type and SubType values TBD.
[RFC8736]
Count:
The number of packed Null-Register records. A record consists of
a Group Address and Source Address pair.
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Group Address, Source Address:
Same as [RFC7761] (Section 4.9.4)
4. PIM Packed Register-Stop message format
The PIM Packed Register-Stop message includes a count to indicate the
number of records that are present in the message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type |Subtype| FB | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Count | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address[1] (Encoded-Group format) |
| Source Address[1] (Encoded-Unicast format) |
. .
. .
. .
. .
. Group Address[N] .
| Source Address[N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PIM Packed Register-Stop message format
PIM Version, Reserved, Checksum:
Same as [RFC7761] (Section 4.9.4)
Type:
The new Register Stop Type and SubType values TBD
Count:
The number of packed Register-Stop records. A record consists of
a Group Address and Source Address pair.
Group Address, Source Address:
Same as [RFC7761] (Section 4.9.4)
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5. Protocol operation
The following combinations are possible:
1. DR and RP both support the PIM Packed Register format
* As specified in [[RFC7761]], the DR sends PIM Register
messages towards the RP when a new source is detected.
* An RP supporting this specification SHOULD set the P-bit in
the corresponding Register-Stop messages.
* When a Register-Stop message with the P-bit set is received,
the DR SHOULD send Packed Null-Register messages (Section 3)
to the RP instead of multiple Register messages with the N-bit
set ([[RFC7761]]).
* The RP, after receiving a Packed Null-Register message SHOULD
start sending Packed Register-Stop messages (Section 4) to the
corresponding DR instead of individual Register-Stop messages.
2. DR supports but RP does not support PIM Packed Register format
* As specified in [[RFC7761]], DR sends PIM Register towards the
RP.
* RP sends a Register-Stop in the [[RFC7761]] without any
capability information.
* DR then sends Null-Registers in the [[RFC7761]] format.
3. RP supports but DR doesn't support the PIM Packed Register format
* As specified in [[RFC7761]], DR sends the PIM Register towards
the RP.
* RP sends a PIM Packed Register-Stop towards the DR that
includes capability information.
* Since the the DR doesn't support the PIM Packet Register
format, it will always send registers according to
[[RFC7761]].
6. PIM Anycast RP considerations
The PIM Packed Register format should be enabled only if it is
supported by all PIM Anycast RP [[RFC4610]] members in the RP set for
An RP address.
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7. PIM RP router version downgrade
Consider a PIM RP router that supports PIM Register Packing and then
downgrades to a software version which does not support PIM Register
Packing. The DR that sends the PIM Packed Register message will not
get a PIM Register-Stop message back. In such scenarios the DR MUST
send an unpacked PIM Register and check the PIM Register-Stop to see
if the capability bit (P-bit) for PIM Packed Register is set or not.
If it is not set then the DR will continue sending unpacked PIM
Register messages.
8. Fragmentation consideration
When building a PIM Packed Register message using the packed-register
format, a router should include as many records as possible based on
the path MTU towards RP, if path MTU discovery is done. Otherwise,
the number of records should be limited to the MTU of the outgoing
interface.
9. Security Considerations
General Register messages security considerations from [[RFC7761]]
apply. As mentioned in [[RFC7761]], Register messages and Register-
Stop messages are forwarded by intermediate routers to their
destination using normal IP forwarding. Without data origin
authentication, an attacker who is located anywhere in the network
may be able to forge a Register or Register-Stop message. We next
consider the effect of a forgery of each of these messages. By
forging a Register message, an attacker can cause the RP to inject
forged traffic onto the shared multicast tree.
By forging a Register-Stop message, an attacker can prevent a
legitimate DR from registering packets to the RP. This can prevent
local hosts on that LAN from sending multicast packets. The above
two PIM messages are not changed by intermediate routers and need
only be examined by the intended receiver. Thus, these messages can
be authenticated end-to-end. Attacks on Register and Register-Stop
messages do not apply to a PIM-SSM-only implementation, as these
messages are not required for PIM-SSM.
There is another case where a spoof Register can be sent to make it
appear that is is from the RP, and that the RP supports this new
packed capability when it does not. This can cause Null-Registers to
not be received by the RP. But standard methods to prevent spoofing
should take care of this case. Spoofing methods like uRPF, or on
domain boundary, filter out packets coming from the outside from
addresses that belong to routers inside.
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All these considerations apply equally to the [[RFC7761]] messages.
10. IANA Considerations
This document requires the assignment of "Capability bit" (P-bit),
flag bit 7 in the PIM Null-Register message.
This document requires the assignment of 2 new PIM message types
for the "PIM Packed Register" and "PIM Register Stop" in the PIM
Message Types registry.
11. Acknowledgments
The authors would like to thank Stig Venaas, Anish Peter, Zheng Zhang
and Umesh Dudani for their helpful comments on the draft.
12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610,
DOI 10.17487/RFC4610, August 2006,
<https://www.rfc-editor.org/info/rfc4610>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8736] Venaas, S. and A. Retana, "PIM Message Type Space
Extension and Reserved Bits", RFC 8736,
DOI 10.17487/RFC8736, February 2020,
<https://www.rfc-editor.org/info/rfc8736>.
Authors' Addresses
Vikas Ramesh Kamath
VMware
3401 Hillview Ave
Palo Alto CA 94304
USA
Email: vkamath@vmware.com
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Ramakrishnan Chokkanathapuram Sundaram
Cisco Systems, Inc.
Tasman Drive
San Jose CA 95134
USA
Email: ramaksun@cisco.com
Raunak Banthia
Apstra
333 Middlefield Rd STE 200
Menlo Park CA 94025
USA
Email: rbanthia@apstra.com
Ananya Gopal
Cisco Systems, Inc.
Tasman Drive
San Jose CA 95134
USA
Email: ananygop@cisco.com
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