| Internet-Draft | PIM Null-Register packing | February 2023 |
| Kamath, et al. | Expires 10 August 2023 | [Page] |
In PIM-SM networks PIM Null-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 [RFC7761] sent from the 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 multiple Multicast source and group information in a single PIM message. This document refers to the new messages as the PIM Packed Null-Register message and PIM Packed Register-Stop message.¶
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 10 August 2023.¶
Copyright (c) 2023 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
The DR periodically sends PIM Null-Registers to keep the state of existing multicast sources active on the RP. 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 the DR.¶
This draft proposes a method to efficiently pack multiple PIM Null-Registers [RFC7761] and Register-Stops [RFC7761] into a single message as these packets do not contain encapsulated data.¶
The draft also discusses interoperability between PIM routers that do not understand PIM Packed Null-Register and PIM Packed Register-Stop messages.¶
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] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This section allocates a bit in the PIM Register-Stop message Flag Bits field for the RP to indicate its ability to receive PIM Packed Null-Register messages (Section 3), and send PIM Packed Register-Stop messages (Section 4).¶
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|6 5 4 3 2 1 0| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PIM Packed Null-Register message format includes a Count field 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 | Flag Bits | 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
¶
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 | Flag Bits | 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
¶
The PIM Packed Null-Register packet format should be enabled only if it is supported by all the routers in the Anycast-RP set ([rfc4610]). This consideration applies to PIM Anycast RP with MSDP [RFC3446] as well.¶
A router (DR) can decide to pack multiple Null-Register messages based on the capability received from the RP as part of the PIM Register-Stop. This ensures compatibility with routers that do not support processing of the new packet format. The capability information can be indicated by the RP via the PIM Register-Stop message sent to the DR. Thus a DR will switch to the new packet format only when it learns that the RP is capable of handling the PIM Packed Null-Register messages.¶
Conversely, a DR that does not support the packed format can continue generating the PIM Null-Register as defined in [RFC7761] (Section 4.4).¶
Consider a PIM RP router that supports PIM Packed Null-Registers and PIM Packed Register-Stops. When this router downgrades to a software version which does not support PIM Packed Null-Registers and PIM Packed Register-Stops, the DR that sends the PIM Packed Null-Register message will not get a PIM Register-Stop message back from the RP. In such scenarios the DR can send an unpacked PIM Null-Register and check the PIM Register-Stop to see if the capability bit (P-bit) for PIM Packed Null-Register is set or not. If it is not set then the DR will continue sending unpacked PIM Null-Register messages.¶
In case the network manager disables the packed capability at the RP, or in other words, unconfigures the feature from the RP, the router should not advertise the capability. However, an implementation MAY choose to still parse any packed registers if they are received. This may be particularly useful in the transitional period after the network manager disables it.¶
When building a PIM Packed Null-Register message or PIM Packed Register-Stop message, 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 by the MTU of the outgoing interface.¶
The Security Considerations from [RFC7761] apply to this document. In particular, the effect of forging a PIM Packed Null-Register or Register-Stop message would be amplified to all the records included and not a single source/group pair.¶
By forging a PIM Register-Stop message and setting the P-bit, an attacker can trigger the use of PIM Packed Null-Register messages by a DR thus creating unnecessary churn in the network.¶
The authors would like to thank Stig Venaas, Alvaro Retana, Anish Peter, Zheng Zhang and Umesh Dudani for their helpful comments on the draft.¶