Re: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type

Peter,

Please see inline. 

> -----Original Message-----
> From: Peter Psenak [mailto:ppsenak@cisco.com] 
> Sent: Tuesday, November 23, 2010 2:14 PM
> To: Jeffrey (Zhaohui) Zhang
> Cc: ospf@ietf.org
> Subject: Re: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type
> 
> Hi Jeffrey,
> 
> please see inline:
> 
> On 23.11.2010 19:29, Jeffrey (Zhaohui) Zhang wrote:
> > Peter,
> >
> > I think I understand the potential issue you mentioned, but 
> not quite clear about your solution.
> >
> > The draft mentions that the metrics could be dynamically 
> learned if the underlying network support it (in that case 
> the l2 and l3 should match). However that is outside the 
> scope the draft, which assumes that the metrics is obtained 
> by some means. Indeed if it is statically configured then the 
> operator needs to be careful.
> 
> dynamically updating L3 metrics based on the L2 topology is a 
> problem of 
> it own. The consequence is that L2 network changes that 
> mostly used to 
> be hidden to the L3 now becomes propagated to the L3 network.

If L2 network changes lead to L3 metric change, then it should not be hidden though?

I agree that the propogation of the changes needs to be rate limited, and a balance needs to be kept between routing stability and routing optimization.

Also about your original concern with l2/l3 mismatch - I don't think it is unique with this proposal. When you assign an interface metric for a regular interface (or neighbor in p2mp case) you also need to make sure that the metric reflects the l2 characteristics.

> 
> >
> > You mentioned creating p2p l2 connections. Does that mean 
> there will be correponding l3 p2p interfaces? If yes isn't it 
> no longer a bcast/p2mp hybrid? If not can you elaborate?
> 
> yes, some form of a sub-interface using the VLAN technology. That is 
> typically a p2p connection between the two OSPF speakers.

The very purpose of the proposal is to use the hybrid interface type to avoid the inefficiency with p2p/p2mp links when it comes to adjaceny and db synchronization, while being able to advertise different metrics per neighbor.

Thanks.
Jeffrey

> 
> thanks,
> Peter
> >
> > Thanks.
> > Jeffrey
> >
> >> -----Original Message-----
> >> From: Peter Psenak [mailto:ppsenak@cisco.com]
> >> Sent: Tuesday, November 23, 2010 1:11 PM
> >> To: Jeffrey (Zhaohui) Zhang
> >> Cc: ospf@ietf.org
> >> Subject: Re: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type
> >>
> >> Hi Jeffrey,
> >>
> >> one potential issue with this approach is the possible suboptimal
> >> traffic path if the L3 p2p topology created as you described do not
> >> match the L2 forwarding topology. With large L2 domains it 
> may be be
> >> nontrivial to assign L3 metric correctly so that the L2/L3
> >> forwarding match.
> >>
> >> One possible method to address the problem in hand is to create p2p
> >> connections between the routers via the L2 domain, using dedicated
> >> VLANs. This way the L2 forwarding is forced to match the L3
> >> p2p topology.
> >>
> >> thanks,
> >> Peter
> >>
> >> On 22.11.2010 17:36, Jeffrey (Zhaohui) Zhang wrote:
> >>> Hi,
> >>>
> >>> I presented the draft
> >> http://www.ietf.org/draft-nsheth-ospf-hybrid-bcast-and-p2mp-01
> >> .txt in Beijing (slides
> >> http://www.ietf.org/proceedings/79/slides/ospf-9.ppt) and it
> >> was deferred to the mailing list on whether the problem is
> >> worth the working group effort (some who reviewed the draft
> >> agreed that the proposed solution is reasonable for the problem).
> >>>
> >>> I'd like to request folks to review the draft/slides and
> >> voice your opinion. We developed the solution for a real
> >> network situation and would like to see that it gets
> >> consensus and standardized so that more operators/vendors can
> >> benefit from this.
> >>>
> >>> Thanks.
> >>> Jeffrey
> >>> _______________________________________________
> >>> OSPF mailing list
> >>> OSPF@ietf.org
> >>> https://www.ietf.org/mailman/listinfo/ospf
> >>>
> >>
> >>
> >
> 
> 