| Internet-Draft | PIM Join Attributes for LISP Mcast | February 2021 |
| Govindan | Expires 25 August 2021 | [Page] |
This document specifies an extension to PIM Join/ Prune messages. This document defines one PIM Join/ Prune attribute that support the construction of multicast distribution trees where the root and receivers are located in different Locator/ID Separation Protocol (LISP) sites using underlay IP Multicast. This attribute allows the receiver site to signal the underlay multicast group to the control plane of the root ITR (Ingress Tunnel Router).¶
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The construction of multicast distribution trees where the root and receivers are located in different LISP sites [RFC6830] is defined in [RFC6831].¶
[RFC6831] specifies that (root-EID,G) data packets are to be LISP- encapsulated into (root-RLOC,G) multicast packets. This document defines a TLV that facilitates the construction of trees for (root-RLOC, G).¶
Specifically, the assignment of the underlay multicast group needs to be done in consonance with the downstream xTR nodes and avoid unnecessary replication or traffic hairpinning.¶
Since the Receiver RLOC Attribute TLV defined in [RFC8059] only addresses the Ingress Replication case, an additional TLV is defined by this draft to include scenarios where the underlay uses Multicast transport. The TLV definition proposed here complies with the base specification [RFC5384].¶
This document uses terminology defined in [RFC6830], such as EID, RLOC, ITR, and ETR.¶
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 RFC 2119 [RFC2119].¶
When LISP based Multicast trees are built using IP Multicast in the underlay, the mapping between the overlay group address and the underlay group address becomes a very crucial. It is possible that under certain circumstances, differnt subsets of xTRs subscribing to the same overlay multicast stream would be constrained to use different underlay multicast mapping ranges. This definitely involves a trade-off between replication and the flexibility in assigning address ranges and could be required in certain situations as below:¶
Editorial Note: Comments from Stig: There should be some text indicating that the group address used should ideally only be used for LISP encapsulation (if ASM), and perhaps that it is preferrable to use an SSM group. Also, that the group obviously must be a group that the underlay supports/allows. I think it is also worth noting that ideally, different ETRs should request the same group.¶
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|F|E|Type=TBD | Length | Addr Family | Receiver Group
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
The authors would like to thank Stig Venaas for his valuable comments.¶
This memo includes the following request to IANA: One new PIM Join/ Prune attribute types have been requested: value TBD for the Receiver Group Attribute.¶
There is perhaps a new attack vector where an attacker can send a bunch of joins with different group addresses. It may interfere with other multicast traffic if those group addresses overlap. Also, it may take up a lot of resources if replication for thousands of groups are requested. However PIM authentication (?) should come to the rescue here. TBD Since explicit tracking would be done, perhaps it is worth enforcing that for each ETR RLOC (the RLOC used as the source of the overlay join), there should be only one group, whatever is in the last join would override what was there earlier? Or is it to strict to only allow a single group? Might there be reasons to maybe split different LISP payload into different groups in some cases. TBD.¶
Ed Note: To be addressed - Comments from Stig: Regarding security considerations and PIM authentication. The only solution we have here is to use IP-Sec to sign the J/P messages. I don't know if anyone has tried to us IPSec between LISP RLOCs. Are there any LISP security mechanisms that would help here for authenticating LISP encapsulated messages between xTRs?¶