Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt

Robert Raszuk <robert@raszuk.net> Sun, 16 April 2017 20:34 UTC

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Date: Sun, 16 Apr 2017 22:34:49 +0200
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To: "Rajiv Asati (rajiva)" <rajiva@cisco.com>
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Subject: Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt
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Rajiv,

I think that everyone fully agrees that in order to consider prefix as
valid the next hop to it should be reachable.

The only open question is how to detect it when you have no direct protocol
adj. established.

Jeff seems stuck with BFD .. but there is number of folks who see S-BFD as
much better fit to the problem. Yet UDP echo in some implementations
already does it today.

I think we need to evaluate pros and cons of all options before making any
more formal recommendation. At this point however I think 7880 fits best.

Kind regards,
R.



On Apr 16, 2017 10:12 PM, "Rajiv Asati (rajiva)" <rajiva@cisco.com>; wrote:

> Hi Jeff,
>
>
> >   But more importantly, you'll stop sending it toward your own peering
> and
> >   attracting blackholed traffic.
>
> Indeed. That’s key.
>
> And it could rely on the route resolvability condition to be appropriately
> modified, as described in
> https://tools.ietf.org/html/draft-ietf-idr-bgp-bestpath-selection-criteria
> .
>
> >    RS-BFD basically reinvents the same procedure in your draft, simply
> being
> >    specific about the use of BFD as the dataplane liveness check
> mechanism.
> >    However, as you note in the RS-BFD draft, we do leave the option for
> other
> >    mechanisms.
> >
> >    I suspect the other authors of RS-BFD aren't particular where we pick
> up our
> >    text for the resolvability condition.  However, if the suggestion is
> to make
> >   a reference to your draft, you'll need to bring it back from zombie
> state
> >    and progress it. :-)
>
> Agreed. It is alive (-07 version). https://tools.ietf.org/html/
> draft-ietf-idr-bgp-bestpath-selection-criteria-07
> It can be used as a normative reference in your draft.
>
> --
> Cheers,
> Rajiv Asati
> Distinguished Engineer, Cisco
>
> -----Original Message-----
> From: Jeffrey Haas <jhaas@pfrc.org>;
> Date: Tuesday, March 14, 2017 at 5:36 PM
> To: Rajiv Asati <rajiva@cisco.com>;
> Cc: "robert@raszuk.net"; <robert@raszuk.net>;, "idr@ietf.org"; <idr@ietf.org>;
> Subject: Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt
>
>     Rajiv,
>
>     On Tue, Mar 14, 2017 at 09:08:24PM +0000, Rajiv Asati (rajiva) wrote:
>     > Is the assumption here that the client routers have routing view
> limited to what’s provided by the Route Server? If not, then wouldn’t
> Client Routers benefit from having to invalidate the path learned from the
> remote client router as soon as the connectivity check failed?
>
>     This is what I believe the procedure says.  See section 6.
>
>     > Of course, Client Routers conveying the lack of NLRI reachability
> per NH to the Route Server, and expecting Route Server to provide a
> different NHs of the NLRIs, and expecting it to be functional, while still
> attracting the traffic for unreachable destinations since the Loc-RIB is
> still pointing to the unreachable NH for the affected NLRIs.
>
>     The thing that is somewhat different for a IXP environment running a
> route
>     server than normal eBGP is the low (to zero) likelihood of having a
> backup
>     path.  If 10/8 was learned from the route server for nexthop
> 192.0.2.1, and
>     you stop being able to reach that nexthop, removing it from your
> forwarding
>     (unreachable) is your only choice.
>
>     You *might* have a source of that path internally.  In that case, you
> can
>     use it.
>
>     But more importantly, you'll stop sending it toward your own peering
> and
>     attracting blackholed traffic.
>
>     > I wonder whether  https://tools.ietf.org/html/
> draft-ietf-idr-bgp-bestpath-selection-criteria be useful here.
>
>     In a sense of good timing, John Scudder had brought this to my
> attention
>     about an hour ago.
>
>     RS-BFD basically reinvents the same procedure in your draft, simply
> being
>     specific about the use of BFD as the dataplane liveness check
> mechanism.
>     However, as you note in the RS-BFD draft, we do leave the option for
> other
>     mechanisms.
>
>     I suspect the other authors of RS-BFD aren't particular where we pick
> up our
>     text for the resolvability condition.  However, if the suggestion is
> to make
>     a reference to your draft, you'll need to bring it back from zombie
> state
>     and progress it. :-)
>
>     -- Jeff
>
>
>