Re: [tsvwg] TSVWG WGLC: draft-ietf-tsvwg-rfc5405bis-06
"Black, David" <david.black@emc.com> Mon, 12 October 2015 23:06 UTC
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From: "Black, David" <david.black@emc.com>
To: "tsvwg@ietf.org" <tsvwg@ietf.org>
Thread-Topic: TSVWG WGLC: draft-ietf-tsvwg-rfc5405bis-06
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Date: Mon, 12 Oct 2015 23:06:40 +0000
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Subject: Re: [tsvwg] TSVWG WGLC: draft-ietf-tsvwg-rfc5405bis-06
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<WG chair hat OFF> Ok, I'm slightly late, but here are the rest of my comments on this draft. I've tagged each as technical vs. editorial, and with my chair hat off, these are open to discussion by the authors and anyone else interested (e.g., they are not to be viewed as "MUST do this" WG chair comments) Section 3, last paragraph: Technical If used correctly, these more fully-featured transport protocols are not as "heavyweight" as often claimed. That responds to one frequent objection to use of congestion-controlled IETF protocols. Another objection that ought to be acknowledged is that there is quite a bit of deployed Internet gear that doesn't support transport protocols other than TCP or UDP. For example, a frequent rationale for use of UDP in encapsulations is that TCP's reliable delivery functionality is not wanted and other protocols (e.g., DCCP) aren't supported by common ECMP implementations at layer 2 and layer 3. This "running code" objection should at least be acknowledged. It (unfortunately) also applies to discussion of UDP-Lite in 3.4.1, and is noted at the end of that section. End of 3.1.4: Editorial to reduce the probability that all three packets will be lost due to the same congestion event. I suggest: "same congestion event." -> "same congestion (or other) event." An example of an "other" event is a burst of radio interference on a wireless link or network that is not compensated for by link measures (e.g., link retransmission or link FEC). 3.1.5, p.11: Typos and ETC(0)/Not-ECT packets ETC -> ECT ... and discipline the spelling corrector that was responsible ;-). [RFC6679] provides guidance an example of this support, by describing a method to allow ECN to be for UDP-based applications using the Real-Time Protocol (RTP). "ECN to be for" -> "ECN to be used for" 3.1.5: Technical Something about this sentence is odd: Applications that can provide this set of mechanisms, but wish to gain the benefits of using ECN, are encouraged to use a transport protocol that already supports ECN (such as TCP). Was "can" -> "cannot" intended in the first line? 3.1.6: Editorial Normally a UDP source/ destination port pair will set a single DSCP value for all packets belonging to a flow. At end of sentence, insert "but multiple DSCPs can be used as described later in this section" to set up 3rd paragraph in this section on the DART draft. 3.1.7: Technical Some UDP applications are only expected to be deployed over network paths that use preprovisioned capacity or capacity reserved using dynamic provisioning, e.g., through the Resource Reservation Protocol (RSVP). Multicast applications are also used with preprovisioned capacity (e.g., IPTV deployments within access networks). These applications MAY choose not to implement any congestion control mechanism and instead rely on transmitting only on paths where the capacity is provisioned and reserved for this use. I've seen attempts to "drive a Mack truck" through that "MAY" by ignoring congestion control entirely (e.g., by writing a sentence that parrots "preprovisioned capacity or capacity reserved using dynamic provisioning"). That needs to be discouraged ;-). I'd like to see some text added what an IETF protocol RFC SHOULD do in order to take advantage of that MAY - RFC 7510 (MPLS over UDP) may be a useful example to cite. I'm tempted to ask for "MUST do" here, but "SHOULD do" seems appropriate, with the potential wrath of the IESG and/or the IETF community being possible consequences of disregarding that "SHOULD" ;-). 3.1.9: Technical A tunnel SHOULD provide mechanisms to restrict the types of flows that may be carried by the tunnel. For instance, a UDP tunnel designed to carry IP, needs to filter non-IP traffic at the ingress. This is particularly important when a generic tunnel encapsulation is used (e.g., one that encapsulates using an EtherType value). This looks like an implicit recommendation that future encapsulation protocol specifications that use EtherType SHOULD explicitly limit the allowed EtherType values. That's important enough that it should be explicitly stated. 3.2: Technical Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821] does not rely upon network support for ICMP messages and is therefore considered more robust than standard PMTUD. This should express a stronger caution about relying on ICMP "Packet Too Big" messages. Firewalls have a nasty proclivity to drop these, they may not make it through NATs, and tunnel ingress nodes will often discard them when generated within a tunnel. For tunnels, PLPMTUD can be problematic, as adding probe packets can easily force the tunnel into congestion case 3 in Section 3.1.9 (tunnel protocol designers tend to not want to go there), as well as complicate the data path at the tunnel decapsulator. Something ought to be said about this, as tunnels are in a significantly worse position wrt this concern by comparison to non-encapsulating UDP applications. 4.1: Editorial Two styles of congestion control have been defined in the RFC-series: I don't see citations of RFCs as examples of these two styles - they should be added to the bullets introduced by the above text. 5.1: Technical The discussion of "randomized" source ports should recommend (lower case "should" or "recommend" is ok, IMHO) that they come from the Dynamic Ports, also known as the Private or Ephemeral Ports, 49152-65535 (cite RFC 6335 section 6). 5.2: Technical Analogous to Section 3.2, this section should also strongly caution against relying ICMP messages for anything. See above comment on section 3.2 for why. 6: Editorial UDP applications SHOULD provide protection from off-path data injection attacks using a pseudo-random source port or equivalent technique (see Section 5.1). "pseudo-random" -> "randomized" to match term used in Section 5.1. Some of the changes suggested above may affect the summary table in Section 7. 10.2 Informative References: Technical Should the following be normative?: [I-D.ietf-dart-dscp-rtp] [I-D.ietf-tsvwg-circuit-breaker] The dart-dscp draft would be a downref, if normatively cited. </WG chair hat OFF> Thanks, --David ---------------------------------------------------- David L. Black, Distinguished Engineer EMC Corporation, 176 South St., Hopkinton, MA 01748 +1 (508) 293-7953 FAX: +1 (508) 293-7786 david.black@emc.com Mobile: +1 (978) 394-7754 ----------------------------------------------------
- [tsvwg] TSVWG WGLC: draft-ietf-tsvwg-rfc5405bis-06 Black, David
- Re: [tsvwg] TSVWG WGLC: draft-ietf-tsvwg-rfc5405b… Black, David