Subject: Re: [OSPF] IETF OSPF YANG and BFD Configuration

From: Jeffrey Haas <[email-masked]>
Date: Mon, 19 Jun 2017 14:57:16 -0400

[Long delayed response.]

Reshad picked up the key points: Some things may make sense in the
per-client (protocol) users of BFD, some things perhaps do not.  And some
come down to questions for timer granularity.

The OSPF and ISIS models both make use of BFD simply by providing a boolean
that says "I'm using BFD or not".

Where we run into some issues are the cases highlighted: when the sessions
don't share common properties, how should the protocol pick what BFD session
to use?  

The current BFD yang model only permits a single IP single-hop session
to be configured.  (Key is interface/dst-ip)  This means that if different
parameters *were* desired, the BFD model won't permit it today.  However,
BFD sessions for many protocols tend not to be configured, but may spring
forth from protocol state, such as IGP adjacencies.  Thus, it's not
"configured" - it's solely operational state.  However, the BFD yang model
doesn't really make good provision for that as an "on".

Where all endpoint state is known a priori, config state makes better sense.

To pick the example of Juniper's configuration, if OSPF and eBGP were using
BFD, both can choose differing timers.  This represents two pieces of
configuration state for the same endpoints.  Additionally, only one BFD
session is formed using the most aggressive timers.

I partially point out the situation of multiple timers since there have been
prior list discussions on the situation where clients have different timing
requirements.  I don't think we handle this operationally in the BFD
protocol in the cleanest fashion right now - the session will go to Down
when the aggressive timers fail and there's no clean way to renegotiate to
the less aggressive timers.

-- Jeff

On Fri, May 19, 2017 at 02:31:38AM +0000, Reshad Rahman (rrahman) wrote:
> We started off with the intent of having BFD parameters in the applications/protocols which make use of BFD. For timer/multiplier this is pretty straight-forward, although the discussion of what to do when not all applications have the same BFD parameters for the same session (e.g. Go with most aggressive etc). Then we started looking at authentication parameters and having BFD authentication parms in OSPF/ISIS etc is not intuitive. And what do we do if applications have different BFD authentication parms. We concluded that the BFD authentication parms were better off in BFD. And once we did that, the timer/multiplier followed....
> 
> I may not recall all the details/discussons, but I do recall that we went back and forth on this and it took some time to make the decision.
> 
> Regards,
> Reshad (as individual contributor).
> 
> From: Mahesh Jethanandani <[email-masked]<mailto:[email-masked]>>
> Date: Thursday, May 18, 2017 at 5:34 PM
> To: "Acee Lindem (acee)" <[email-masked]<mailto:[email-masked]>>
> Cc: Jeffrey Haas <[email-masked]<mailto:[email-masked]>>, OSPF WG List <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
> Subject: Re: IETF OSPF YANG and BFD Configuration
> Resent-From: <[email-masked]<mailto:[email-masked]>>
> Resent-To: <[email-masked]<mailto:[email-masked]>>, Reshad <[email-masked]<mailto:[email-masked]>>, <[email-masked]<mailto:[email-masked]>>, <[email-masked]<mailto:[email-masked]>>, <[email-masked]<mailto:[email-masked]>>
> Resent-Date: Thursday, May 18, 2017 at 5:40 PM
> 
> Resending with correct BFD WG address.
> 
> On May 18, 2017, at 2:33 PM, Mahesh Jethanandani <[email-masked]<mailto:[email-masked]>> wrote:
> 
> Agree with Acee's assessment. After much debate, we decided that we should leave BFD parameter configuration in the BFD model itself, and have any IGP protocol reference the BFD instance in BFD itself. This makes sense specially if multiple protocols fate-share the BFD session.
> 
> Cheers.
> 
> On May 18, 2017, at 12:27 PM, Acee Lindem (acee) <[email-masked]<mailto:[email-masked]>> wrote:
> 
> Hi Jeff,
> 
> At the OSPF WG Meeting in Chicago, you suggested that we may want to provide configuration of BFD parameters within the OSPF model (ietf-ospf.yang). We originally did have this configuration. However, after much discussion and coordination with the BFD YANG design team, we agreed to leave the BFD session parameters in BFD and only enable BFD within the OSPF and IS-IS models.
> 
> We did discuss the fact that vendors (notably Cisco IOS-XR and Juniper JUNOS) do allow configuration within the IGPs. However, the consensus was to leave the BFD configuration in the BFD model. The heuristics to determine what parameters to use when the same BFD endpoint was configured with different parameters in different protocols were proprietary and somewhat of a hack.
> 
> I may have not remembered all the details so I'd encourage others to chime in.
> 
> Thanks,
> Acee
> 
> Mahesh Jethanandani
> [email-masked]<mailto:[email-masked]>
> 
> 
> 
> 
> Mahesh Jethanandani
> [email-masked]<mailto:[email-masked]>
> 
> 
>

---

From: "Acee Lindem (acee)" <[email-masked]>
Date: Mon, 19 Jun 2017 22:10:43 +0000

Hi Jeff, 

I don’t really feel there is a strong requirement to support different
timers values per protocol even though several implementations allow
different protocol specific values to be configured (with varying
behaviors). 

If there were such a requirement, I would think it would be better
satisfied by extending the BFD model session key with an additional
identifier, e.g., <interface/dst-ip/instance>. IMO, this would be
preferable to allowing the details of BFD to permeate into all the other
protocol models. This would require configuration of the instance rather
than a boolean in the protocols.

Thanks,
Acee 

On 6/19/17, 2:57 PM, "Jeffrey Haas" <[email-masked]> wrote:

>> We started off with the intent of having BFD parameters in the
>>applications/protocols which make use of BFD. For timer/multiplier this
>>is pretty straight-forward, although the discussion of what to do when
>>not all applications have the same BFD parameters for the same session
>>(e.g. Go with most aggressive etc). Then we started looking at
>>authentication parameters and having BFD authentication parms in
>>OSPF/ISIS etc is not intuitive. And what do we do if applications have
>>different BFD authentication parms. We concluded that the BFD
>>authentication parms were better off in BFD. And once we did that, the
>>timer/multiplier followed....
>> 
>> I may not recall all the details/discussons, but I do recall that we
>>went back and forth on this and it took some time to make the decision.
>> 
>> Regards,
>> From: Mahesh Jethanandani
>><[email-masked]<mailto:[email-masked]>>
>> Cc: Jeffrey Haas <[email-masked]<mailto:[email-masked]>>, OSPF WG
>>List <[email-masked]<mailto:[email-masked]>>,
>>"[email-masked]<mailto:[email-masked]>"
>><[email-masked]<mailto:[email-masked]>>,
>>"[email-masked]<mailto:[email-masked]>"
>><[email-masked]<mailto:[email-masked]>>,
>>"[email-masked]<mailto:[email-masked]>"
>><[email-masked]<mailto:[email-masked]>>
>> Resent-To: <[email-masked]<mailto:[email-masked]>>,
>>Reshad <[email-masked]<mailto:[email-masked]>>,
>><[email-masked]<mailto:[email-masked]>>,
>><[email-masked]<mailto:[email-masked]>>,
>><[email-masked]<mailto:[email-masked]>>
>> On May 18, 2017, at 2:33 PM, Mahesh Jethanandani
>><[email-masked]<mailto:[email-masked]>> wrote:
>> 
>> Agree with Acee's assessment. After much debate, we decided that we
>>should leave BFD parameter configuration in the BFD model itself, and
>>have any IGP protocol reference the BFD instance in BFD itself. This
>>makes sense specially if multiple protocols fate-share the BFD session.
>> 
>> Cheers.
>> 
>> On May 18, 2017, at 12:27 PM, Acee Lindem (acee)
>><[email-masked]<mailto:[email-masked]>> wrote:
>> 
>> Hi Jeff,
>> 
>> At the OSPF WG Meeting in Chicago, you suggested that we may want to
>>provide configuration of BFD parameters within the OSPF model
>>(ietf-ospf.yang). We originally did have this configuration. However,
>>after much discussion and coordination with the BFD YANG design team, we
>>agreed to leave the BFD session parameters in BFD and only enable BFD
>>within the OSPF and IS-IS models.
>> 
>> We did discuss the fact that vendors (notably Cisco IOS-XR and Juniper
>>JUNOS) do allow configuration within the IGPs. However, the consensus
>>was to leave the BFD configuration in the BFD model. The heuristics to
>>determine what parameters to use when the same BFD endpoint was
>>configured with different parameters in different protocols were
>>proprietary and somewhat of a hack.
>>

---

From: Mahesh Jethanandani <[email-masked]>
Date: Mon, 19 Jun 2017 15:11:25 -0700

> On Jun 19, 2017, at 11:57 AM, Jeffrey Haas <[email-masked]> wrote:
> 
> [Long delayed response.]
> 

The issue that I hear most is the timer granularity. Is there something else?

> doesn't really make good provision for that as an "on”.

The idea is that a BFD session is configured a priori and before a IGP session is configured with the most aggressive timer. IGP sessions then refer to the BGP session configured. If a IGP session is added that requires a more aggressive timer, we would have to renegotiate the more aggressive timer value.
 
> session is formed using the most aggressive timers.

That is what we are suggesting also.

> the less aggressive timers.

A BFD session would fail more likely because there is a real network failure than because the timer was more aggressive than what IGP had requested. 

>> [email-masked]<mailto:[email-masked]>

Mahesh Jethanandani
[email-masked]

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 20 Jun 2017 10:16:39 -0400

Mahesh,

> The issue that I hear most is the timer granularity. Is there something else?

Potentially mode (async vs. echo) and authentication.  However, I believe
timer granularity is the biggest one.

> The idea is that a BFD session is configured a priori and before a IGP session is configured with the most aggressive timer. IGP sessions then refer to the BGP session configured. If a IGP session…

Consider a broadcast network segment such as Ethernet.
Consider a few dozen routers on such a segment.

Is it your expectation that an IGP would require each of those routers to be
manually configured in the Yang module a priori?  That is, after all, much
of the point of an IGP: automatic discovery.

> That is what we are suggesting also.

The distinguishing point is configuration vs. operational state.  The
current model doesn't permit more than one set of parameters to be
provisioned even if the implementation may choose to instantiate exactly one
session.

> A BFD session would fail more likely because there is a real network failure than because the timer was more aggressive than what IGP had requested. 

Please note that I raise this point mostly because of prior discussion.  I'm
well aware of the headaches this currently causes:

Different protocols have different survivability requirements.  An IGP may
very well want sub-second timers, potentially for repair behaviors.  BGP may
want fast failover, but may be fine with second level granularity.  This is
particularly true since the cost of too aggressively flapping BGP is of
significantly greater impact to the network and the router.

But moving to what *is* rather than what should be, if there are two
different timing setups for the same endpoint: If you deprovision the more
aggressive timer, the session should likely renegotiate to the less
aggressive one rather than drop.

-- Jeff

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 20 Jun 2017 10:20:56 -0400

Acee,

On Mon, Jun 19, 2017 at 10:10:43PM +0000, Acee Lindem (acee) wrote:
> identifier, e.g., <interface/dst-ip/instance>.

I suspect multi-instancing may be where this conversation goes.

> IMO, this would be

My lingering concern is whether the client protocol may have preferences
about what session to use when such multi-instancing is permitted.
Minimally this would require some sort of Yang reference to the specific
instance.

As I'm noting in the other response, do we really expect BFD Yang model
users to pre-provision every single OSPF/ISIS adjacency in the config
stanza?  Likely, no.

What I tend to expect is a template being used for a service profile.  We
don't currently have such a thing.

-- Jeff

---

From: "Acee Lindem (acee)" <[email-masked]>
Date: Tue, 20 Jun 2017 14:14:28 +0000

Hi Jeff, Mahesh, 

See a couple inlines.

On 6/20/17, 10:16 AM, "Jeffrey Haas" <[email-masked]> wrote:

>> The idea is that a BFD session is configured a priori and before a IGP
>>session is configured with the most aggressive timer. IGP sessions then
>>refer to the BGP session configured. If a IGP session is added that
>>requires a more aggressive timer, we would have to renegotiate the more
>>aggressive timer value.
>

I think the BFD model should support a wildcard for destination IP address
to avoid this problem.

>provisioned even if the implementation may choose to instantiate exactly

This could be supported with extensions to the BFD model.

Thanks,
Acee 
>> A BFD session would fail more likely because there is a real network
>>failure than because the timer was more aggressive than what IGP had
>>requested. 
>

---

From: "Acee Lindem (acee)" <[email-masked]>
Date: Tue, 20 Jun 2017 14:18:14 +0000

Jeff, 

>Minimally this would require some sort of Yang reference to the specific

Right - this is what I just said.
>users to pre-provision every single OSPF/ISIS adjacency in the config

Agreed. 
>don't currently have such a thing.

Agreed. My point is that the BFD specific parameters should in the BFD
model rather than the protocol models.

Acee

---

From: "Les Ginsberg (ginsberg)" <[email-masked]>
Date: Tue, 20 Jun 2017 14:25:12 +0000

Jeff -

Inline.

> -----Original Message-----
> From: Rtg-bfd [mailto:[email-masked]] On Behalf Of Jeffrey Haas
> Sent: Tuesday, June 20, 2017 7:17 AM
> To: Mahesh Jethanandani
> Cc: Jeffrey Haas; Reshad Rahman (rrahman); OSPF WG List; draft-ietf-ospf-
> [email-masked]; [email-masked]; [email-masked]; Acee Lindem
> (acee)
> > > Where we run into some issues are the cases highlighted: when the
> > > sessions don't share common properties, how should the protocol pick
> > > what BFD session to use?
> >
> > > The current BFD yang model only permits a single IP single-hop
> > > session to be configured.  (Key is interface/dst-ip)  This means
> > > that if different parameters *were* desired, the BFD model won't
> > > permit it today.  However, BFD sessions for many protocols tend not
> > > to be configured, but may spring forth from protocol state, such as
> > > IGP adjacencies.  Thus, it's not "configured" - it's solely
> > > operational state.  However, the BFD yang model doesn't really make
> good provision for that as an "on”.
> >
> > The idea is that a BFD session is configured a priori and before a IGP session
> is configured with the most aggressive timer. IGP sessions then refer to the
> BGP session configured. If a IGP session is added that requires a more
> aggressive timer, we would have to renegotiate the more aggressive timer
> value.
> 
> manually configured in the Yang module a priori?  That is, after all, much of
> the point of an IGP: automatic discovery.
> 
> > > To pick the example of Juniper's configuration, if OSPF and eBGP
> > > were using BFD, both can choose differing timers.  This represents
> > > two pieces of configuration state for the same endpoints.
> > > Additionally, only one BFD session is formed using the most aggressive
> timers.
> >
> The distinguishing point is configuration vs. operational state.  The current
> model doesn't permit more than one set of parameters to be provisioned
> even if the implementation may choose to instantiate exactly one session.
> 
> > > I partially point out the situation of multiple timers since there
> > > have been prior list discussions on the situation where clients have
> > > different timing requirements.  I don't think we handle this
> > > operationally in the BFD protocol in the cleanest fashion right now
> > > - the session will go to Down when the aggressive timers fail and
> > > there's no clean way to renegotiate to the less aggressive timers.
> >
> > A BFD session would fail more likely because there is a real network failure
> than because the timer was more aggressive than what IGP had requested.
> 
> Please note that I raise this point mostly because of prior discussion.  I'm well
> aware of the headaches this currently causes:
> 
[Les:] The real issues here are false failures and proper use of dampening. No protocol - not even an IGP - wants to flap unnecessarily. If timers are set so aggressively that false failures are reported this is BAD.
Even worse is failure to dampen so that we get multiple false failures in a short period of time.

Arguing that the right way to solve this problem is to increase the number of sessions using different timer granularity seems likely to make any problems worse as you have now increased the number of BFD sessions with the associated costs.

   Les

> aggressive timer, the session should likely renegotiate to the less aggressive
> one rather than drop.
> 
> -- Jeff

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 20 Jun 2017 10:58:56 -0400

Les,

> Arguing that the right way to solve this problem is to increase the number of sessions using different timer granularity seems likely to make any problems worse as you have now increased the number…

I'm mildly amused you seem to think I'm not considering the cost of
additional sessions in the scaling matrix. :-)

I do think you're conflating the survivability requirements vs. timer
granularity.  However, I agree that the most commonly deployed form is to go
for single session with the most stable aggressive timer.

Again, the reason I raise this is there has been discussion regarding
behavior for different client timing requirements.  There are a few options
for how this is likely to play out in terms of BFD protocol implementation.
However, configuration and operational models tend to evolve much more
slowly.  (And I certainly don't need to tell you that.)  Thus, I'm prodding
at this space a bit to attempt to do some future proofing.

As we noted earlier in thread, this likely at least encourages configuration
to be multi-instanced, even if the session instantiation is not currently.
Key changes aren't something we can readily do, so getting that part right
early is necessary.

The likely impact on current IGP module BFD configuration may be a later
augmentation.  Thus, as long as the likely implications are understood,
there may be no further action needed at this time.  Determining that is
partially what this thread is attempting to shake out.

-- Jeff

---

From: "Acee Lindem (acee)" <[email-masked]>
Date: Tue, 20 Jun 2017 15:40:28 +0000

Hi Jeff, 

On 6/20/17, 10:58 AM, "Jeffrey Haas" <[email-masked]> wrote:

>> [Les:] The real issues here are false failures and proper use of
>>dampening. No protocol - not even an IGP - wants to flap unnecessarily.
>>If timers are set so aggressively that false failures are reported this
>>is BAD.
>> Arguing that the right way to solve this problem is to increase the
>>number of sessions using different timer granularity seems likely to
>>make any problems worse as you have now increased the number of BFD
>>sessions with the associated costs.
>

In the IGPs, we have a separate BFD container in the interface
configuration. Currently, it only contains the a boolean. This could
easily be augmented to reference the appropriate construct in the BFD
model. 

Thanks,
Acee

---

From: Mahesh Jethanandani <[email-masked]>
Date: Tue, 20 Jun 2017 10:50:15 -0700

> On Jun 20, 2017, at 8:40 AM, Acee Lindem (acee) <[email-masked]> wrote:
> 
> Hi Jeff, 
> 

Let me work with Reshad to suggest what IGP could suggest to BFD in their construct, and have BFP pick what it believes would be the right set of parameters to be able to support most of the IGPs over the given BFD session. Whether we add it in the current model or add it later as an augmentation could then be decided separately.

Mahesh Jethanandani
[email-masked]

---

From: Greg Mirsky <[email-masked]>
Date: Tue, 20 Jun 2017 12:55:58 -0500

Hi Jeff,
I'd like to hear from others who are familiar with implementations of BFD
that supports per protocol single-hop BFD multi-sessions between the same
pair of BFD systems. RFC 5881 does allow per protocol single-hop sessions
on the same interface, logical or physical, between the same pair of
systems. But it is not clear, in my opinion, how BFD does demultiplexing if
Your Discriminator == 0 per protocol (RFC 5881, section 3, last sentence)
if systems use the same IP addresses. And hence the question, Even though
it is allowed to have BFD single-hop sessions per application/protocol on
the same interface between the same pair of systems, is this real,
practical requirement?
Or am I missing the point completely?

Regards,
Greg

On Mon, Jun 19, 2017 at 1:57 PM, Jeffrey Haas <[email-masked]> wrote:

> applications/protocols which make use of BFD. For timer/multiplier this is
> pretty straight-forward, although the discussion of what to do when not all
> applications have the same BFD parameters for the same session (e.g. Go
> with most aggressive etc). Then we started looking at authentication
> parameters and having BFD authentication parms in OSPF/ISIS etc is not
> intuitive. And what do we do if applications have different BFD
> authentication parms. We concluded that the BFD authentication parms were
> better off in BFD. And once we did that, the timer/multiplier followed....
> >
> List <[email-masked]<mailto:[email-masked]>>, "[email-masked]<
> mailto:[email-masked]>" <[email-masked]<
> mailto:[email-masked]>>, "[email-masked]
> <mailto:[email-masked]>" <[email-masked]
> <mailto:[email-masked]>>, "[email-masked]<mailto:rtg-
> [email-masked]>" <[email-masked]<mailto:[email-masked]>>
> Reshad <[email-masked]<mailto:[email-masked]>>, <
> [email-masked]<mailto:[email-masked]>>, <
> [email-masked]<mailto:[email-masked]>>, <
> [email-masked]<mailto:[email-masked]>>
> > On May 18, 2017, at 2:33 PM, Mahesh Jethanandani <
> [email-masked]<mailto:[email-masked]>> wrote:
> >
> should leave BFD parameter configuration in the BFD model itself, and have
> any IGP protocol reference the BFD instance in BFD itself. This makes sense
> specially if multiple protocols fate-share the BFD session.
> >
> > Cheers.
> >
> (ietf-ospf.yang). We originally did have this configuration. However, after
> much discussion and coordination with the BFD YANG design team, we agreed
> to leave the BFD session parameters in BFD and only enable BFD within the
> OSPF and IS-IS models.
> >
> JUNOS) do allow configuration within the IGPs. However, the consensus was
> to leave the BFD configuration in the BFD model. The heuristics to
> determine what parameters to use when the same BFD endpoint was configured
> with different parameters in different protocols were proprietary and
> somewhat of a hack.
> >

---

From: "Acee Lindem (acee)" <[email-masked]>
Date: Tue, 20 Jun 2017 18:04:04 +0000

On 6/20/17, 1:50 PM, "Mahesh Jethanandani" <[email-masked]> wrote:

>>> granularity.  However, I agree that the most commonly deployed form is
>>>to
>>> go
>Let me work with Reshad to suggest what IGP could suggest to BFD in their
>construct, and have BFP pick what it believes would be the right set of
>parameters to be able to support most of the IGPs over the given BFD
>session. Whether we add it in the current model or add it later as an
>augmentation could then be decided separately.

Given that the IGP models are more mature and will soon be ready for
publication, I think it is a given that this will be done in an
augmentation. 

Thanks,
Acee

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 20 Jun 2017 15:00:09 -0400

Greg,

> Or am I missing the point completely?

Correct, 5881 procedures do not currently permit this.
As I mentioned, we've had prior discussions about this being potentially
problematic for clients that may have differing timing requirements.

Part of the point of this exercise is to provide necessary future-proofing
against the need to re-issue the Yang modules if such a mechanism is
developed.  (Somewhat analogous to the instructions to the design team that
MPLS-TP was out of scope for the module, but that its structure shouldn't
prevent its implementation in the future.)

Thus far, two points have sprung from the discussion that are likely
actionable:
- The single-hop configuration in the current BFD module isn't suitable for
  use by the IGPs.  Some form of wildcard of templating behavior is
  necessary.
- Multiple clients that might desire to configure a session with different
  parameters are unable to do so today.  This precludes some implementations
  that permit such configuration, potentially at protocol scope.  It also
  doesn't fit the future-proofing thought.

-- Jeff

---

From: Greg Mirsky <[email-masked]>
Date: Tue, 20 Jun 2017 14:48:51 -0500

Hi Jeff,
thank you for the great summary of the discussion, helps me to catch the
wave.
I'm skeptical that there's realistic scenario where two BFD systems will be
requested to run multiple BFD single-hop session between them over the same
interfaces (logical or physical). I believe that we should try to make
models future proof but to the level that is reasonable, practical.
Approach "if we can think of it, then we need to support it" may not be the
one.
RE: RFC 5881. I've referred to the following:
... any BFD packet from the remote machine with a zero value of Your
Discriminator MUST be associated with the session bound to the remote
system, interface, and protocol.
Unless we add out-band bootstrapping of BFD sessions like with LSP Ping, I
don't see how received BFD control packet with zero value in Your
Discriminator may be bound to not just any one of several protocols that
are trying to run BFD session on the same interface to the same remote
system but to the right one, the one that corresponds to the protocol on
whose behalf remote BFD peer sent the control packet. Hence my question Do
we have implementation(s) that use this and are asking for BFD data model
to accommodate them? Or we are just doing interesting intellectual exercise?

Regards,
Greg

On Tue, Jun 20, 2017 at 2:00 PM, Jeffrey Haas <[email-masked]> wrote:

> sessions
> have
> > > > On May 18, 2017, at 12:27 PM, Acee Lindem (acee) <[email-masked]
> <mailto:
> > > [email-masked]>> wrote:
> > > >
> > > > Hi Jeff,
> > > >
> after
> was
> configured

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 20 Jun 2017 16:26:39 -0400

> to accommodate them? Or we are just doing interesting intellectual exercise?

The constant iteration regarding "intellectual exercise" is getting
irritating.  See prior comments.

This distribution is too large to try to design the actual behavioral
change.  If you feel the need to pursue that thread, please reduce the scope
of the cc: list.  This will be my last reply to this topic on the expanded
distro.

To offer one example of how such a thing could be implemented, BFD
authentication can be used with different parameters for each session.  This
provides the necessary split for demultiplexing.  Such a hack is not unusual
operations trick when running OSPF for (partially) disjoint domains on the
same interface, although I suspect that the hack is no longer necessary with
multi-instance techs.  (This trick goes back to the 1990's.)

-- Jeff