Re: [MEXT] about draft-ietf-mext-flow-binding-02.txt
Hesham Soliman <hesham@elevatemobile.com> Sat, 16 May 2009 03:58 UTC
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Date: Sat, 16 May 2009 13:58:26 +1000
From: Hesham Soliman <hesham@elevatemobile.com>
To: marcelo bagnulo braun <marcelo@it.uc3m.es>, "Tsirtsis, George" <tsirtsis@qualcomm.com>, mext <mext@ietf.org>
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Subject: Re: [MEXT] about draft-ietf-mext-flow-binding-02.txt
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Thanks for the detailed review. Some answers inline On 16/05/09 9:46 AM, "marcelo bagnulo braun" <marcelo@it.uc3m.es> wrote: > Hi, > > Please find my comments about draft-ietf-mext-flow-binding-02.txt. > > > > Flow binding: An entry in the list of flow binding associated with > a given mobile node. > > circular definition, please rephrase. => ok. > > BID-PRI > > This is a 7-bit field placing each BID to a relative priority > with other registered BIDs. Value "0" is reserved for > implementation of [I-D.ietf-monami6-multiplecoa] that do not > support this specification. A higher number in this field > indicates lower priority, > > Why is that? Is there a reason for having the higher value of a field > called BID PRI to mean _lower_ priority or are we just trying hard to be > counter intuitive? => I think George added this in a way to be consistent with the PRI field, which you comment on below. Why is the PRI field that way? I don't know :) I guess I did that one day when I was feeling counter intuitive. We can reverse this > > same comment applies to: > > FID-PRI > > This is an 8-bit priority field to indicate the priority of a > particular option. This field is needed in cases where two > different flow descriptions in two different options overlap. > The priority field decides which policy should be in those > cases. A lower number in this field indicates a higher > priority. > > Later the drafts reads: > > The following values are reserved for the PRO field in this option: > > 0 Add a flow binding > > 1 Modify a flow binding > > I haven't read the whole draft yet, but wouldn't make sense to avoid > this option. I mean, if the FID is new, then we create a new binding and > if the FID already exists, then it is a modification. I mean, the > problem with doing the approach described is that it has the potential > of creating contradictory situations... for instance what happens if we > receive an option with a value of 0 in the PRO field but there is no > existing binding with the BID? => I think you mean 1 not 0. It would be an error, which illustrates the advantage of this, i.e. It catches any mismatch between the MN and HA. (I mean, i understand that the flow > binding messages are atomic i.e. that each time w new one is received it > not an incremental change from the previous one, but it contains the > complete information about the binding, correct? If that is the case, we > better simply create a new one, even if the sender thinks this is a > modifciation, since the msg actually provides all the information for > the creation of the flow binding, correct?) => It can be done this way if we don't care about catching mismatches. This orginally contained explicit deletes as well, which we removed. I know that it now seems redundant with only those two operations. > > > later on the draft reads: > > 1 Forward. This value indicates a request to forward a flow to > the address indicated in the Binding Reference sub-option. A > single BID MUST be associated with this Action. > ... > > 3 n-cast. This value indicates a request to replicate the flow to > several addresses indicated in the Binding Reference sub-option. > One or more BIDs MUST be associated with this Action. > > > What is the difference between a n-cast value with a single BID and a > Forward option? couldn't we just live with the n-cast option? (if it has > only one BID, it has the same behaviour as the forward option? => Yes we could. > > LAter on it reads: > > It should be noted that per-packet load balancing may have negative > impacts on TCP congestion avoidance mechanisms as it is desirable to > maintain order between packets belonging to the same TCP connection. > This behaviour is specified in RFC2702 [RFC2702]. Other negative > impacts are also foreseen for other types of real time connections > due to the potential variations in RTT between packets. Hence per- > packet load balancing is not currently supported in this extension. > > I fully agree with this, but i fail to see why this is the correct place > to mention this. It probably belongs to somewhere else. Probably, we > should make even a stronger statement, i.e. the flow bindings separating > the packets of a TCP connection SHOULD NOT be used. => Ok about placement. SHOULD NOT? I think this is a MUST NOT. Also, it affects any secure traffic with replay attack prevention. So it's not just TCP. That's why the entire option is not allowed in the draft. > > > The binding identifier option, defined in > [I-D.ietf-monami6-multiplecoa], registering a given BID which is then > indicated in the Binding Reference sub-option, MUST be either defined > in the same or earlier BU from the one including the binding > reference sub-option. > > I think what this sentence means, but I fail to parse it properly. I > would suggest rephrasing => ok. > > 4.3. Flow Identification Summary Mobility Option > > TBD > > I guess more text is needed here... > > later on... > > The BIDs included in a given entry point to a corresponding entry in > the binding cache for the purpose of identifying a care-of address. > > is there a verb missing in this sentence? => Yup needs rewording. > > later on > > Depending on the Action parameter in a given entry a valid BID is > required to make the entry "active". > > How is that dependent of the action paramter? > The text tha follows, seem to imply that an entry is active or inactvie > depending on the BID not on the actions... => Agreed, this is left over and erroneous. > > later on... > > BID-PRI BID CoA > --------- --- --- > 20 1 IP1 > 30 3 IP2 > 30 2 IP3 > > Ordered BID Entries > > I would suggest moving this table right after the table describing the > Ordered Flow Binding Entries => ok. > > 5.2. Mobile Node Considerations > > This specification allows the mobile node to maintain several > bindings in its home agent and to direct packets to different care-of > addresses according to flow bindings. > > I understnad that not only the HA maintains the bidnings but also the CN > and the MAPs, so i think this should be included here. => Agreed. > > The home agent list of flow bindings is manipulated by the mobile > node, via flow identification and flow summary options included in > binding update messages. > > similar comment here. It is not only the HA list of bindings, but also > the CN and MAP list of bindings, right? => Yes. > > All flow binding state MUST be refreshed in every binding update the > mobile node sends. Any previously registered flow binding that is > not included in a given binding update will be deleted. So, any flow > bindings that are not added or modified by a flow identification > option, but have previously registered and need to be maintained MUST > be included in a flow summary option. Only one flow summary option > can be included in a given binding update. > > So, i really fail to see why we need the PRO bits. I mean, if every tome > we sent a BU it will contain all the info about all the bindings, it is > irrelevant if the binding is being created or modified in the options, > since we are including all the information anyway. => Yeah, I think you have a point about this. Like I said earlier, it used to work different and contain more actions but I think you're right. > > Note that any inactive flow bindings, i.e., flow bindings without > associated BIDs that are marked as Inactive in the list of flow > binding entries (see Section 4.4, MUST also be refreshed, or > modified, to be maintained. If they are not included in a BU they > will be removed. > > closing bracket missing > > 5.2.4. Removing flow bindings > > Removal of flow binging entries is performed implicitly by omission > of a given FID from a binding update. > > To remove a flow binding the MN simply sends a binding update that > includes flow identification and flow summary options for all the > FIDs that need to be refreshed, modified, or added, and simply omits > any FIDs that need to be removed. > > what if the MN sneds a BUt wihtout the Flow binding option? are all the > flow bidings removed? => Without any FIDs? Yes they're all removed. > > - if the Action indicates 'n-cast', > > If the Binding reference sub-option is not included, the home > agent MUST reject this flow binding add request by copying the > flow identification option in the BA, and setting the Status field > to 129 (Flow identification option poorly formed). > > If the Binding Reference sub-option is present and includes BIDs > that are not present in the binding cache of the mobile node the > home agent MUST reject this flow binding add request by copying > the flow identification option in the BA, and setting the Status > field to TBD (BID not known). > > If the Binding Reference sub-option is present and includes one or > more BIDs, and the BIDs exist in the mobile node's binding cache, > > all the bods must exist? what if some exists and some don't? => What do you mean? You mean on a per FID or on aggregate? > > later on... > > If the value of any of the FID fields included in the flow summary > option is not present in the list of flow binding entries for this > mobile node, the home agent MUST reject this flow binding modify > request > > is this option only carried in a modify request? I understood that also > could be carried in an add request, correct? => Yes. Hesham >
- [MEXT] about draft-ietf-mext-flow-binding-02.txt marcelo bagnulo braun
- Re: [MEXT] about draft-ietf-mext-flow-binding-02.… Hesham Soliman
- Re: [MEXT] about draft-ietf-mext-flow-binding-02.… marcelo bagnulo braun