[MBONED] Mail regarding draft-tissa-pim-mcastoam

[Ronald Bonica <[e-mail]>]

Tissa,

Currently, any station sourcing traffic to a multicast group can send an ICMP Echo message to that group. The ICMP Echo message elicits a response from each receiver subscribed to the group. This may not be desirable because the number of receivers, and therefore, the number of responses, may be very large.

draft-tissa-pim-mcastoam draft attempts to remedy that problem by appending an RFC 4884 extension to the ICMP Echo. The extension specifies which stations should respond and which should not.

This raises the following questions:

1) Backwards compatibility - Hosts running legacy software will not parse the new extension. They will respond to the ICMP Echo regardless of how it was scoped by the extension. So, the sender will not be protected from a barrage of responses.

2) ICMP Behavior - In your draft, the ICMP Echo elicits a response from all receivers and intermediate routers. Currently, routers do not respond unless they are also receivers. Are you recommending that the router should both process the PING message (as a receiver) and forward it (as a router)?

3) Security considerations - Could multicast PINGs be used as a DoS vector? In particular, what happens if the multicast source pings a group that has many, many receivers. The PING specifies a spoofed source address and is scoped to 0.0.0.0/0.

In all fairness, this condition exists today. 

4) ICMP Syntax -  The ICMP Echo / Response messages are not extensible. See RFC 4884, Section 4 for details.



--------------------------
Ron Bonica
vcard:       www.bonica.org/ron/ronbonica.vcf