Hi Anton
Since the IGP shortcut use case you reference does, in fact, use the
TED populated by an instance of one protocol (OSPFv2 or OSPFv3) in an
instance of the other protocol (OSPFv3 or OSPFv2), I don’t think we
want to say anything about instances in the backward compatibility
section. I think we can reduce the text you provided below to:
X-AF only requires the head-end and the tail-end of the
advertised TE tunnels to support
X-AF advertisement and usage as described herein.
Intermediate OSPF Routers on the TE
tunnel path need not support X-AF functionality.
Thanks,
Acee
*From: *Lsr <lsr-boun...@ietf.org> on behalf of Acee Lindem
<a...@cisco.com>
*Date: *Thursday, April 19, 2018 at 5:29 PM
*To: *"Anton Smirnov (asmirnov)" <asmir...@cisco.com>,
"draft-ietf-ospf-xaf...@ietf.org" <draft-ietf-ospf-xaf...@ietf.org>
*Cc: *"lsr@ietf.org" <lsr@ietf.org>
*Subject: *Re: [Lsr] OSPF Routing with Cross-Address Family MPLS
Traffic Engineering Tunnels
Hi Anton,
I guess I see the use case described below as only one of the
potential use cases for the X-AF tunnels. It seems that path
computation, either head-end or PCE, could also use the dual-stack
endpoint information. Note that the OSPF doesn’t establish the LSPs or
even advertise the LSPs themselves– it merely populates the TE
Database. I know that you know this but you want to assure your text
doesn’t imply otherwise. Do you disagree? You can certainly keep this
use case but I’d reference RFC 3906 (informational reference) and
state that there could alternate use cases. Perhaps, your fellow
author Alvaro (of OSPF TTZ fame) could help with some generic text
preceding the specific IGP Shortcut use case.
Let me see if I can massage the backward compatibility text. I’m
requested a Routing Directorate review and I’m going to start the LSR
WG last call shortly.
Thanks,
Acee
*From: *"Anton Smirnov (asmirnov)" <asmir...@cisco.com>
*Organization: *Cisco Systems
*Date: *Saturday, April 14, 2018 at 6:48 PM
*To: *Acee Lindem <a...@cisco.com>, "draft-ietf-ospf-xaf...@ietf.org"
<draft-ietf-ospf-xaf...@ietf.org>
*Cc: *"lsr@ietf.org" <lsr@ietf.org>
*Subject: *Re: OSPF Routing with Cross-Address Family MPLS Traffic
Engineering Tunnels
Hi Acee,
sorry for my slow response.
Before answering questions lets establish 'prerequisites' of the
problem.
- Network is dual stack, OSPFv2 is used to route IPv4, OSPFv3 is used
to route IPv6
- TE LSAs are originated as per [RFC3630] and flooded in OSPFv2
- 'Endpoint' of each MPLS TE tunnel is IPv4 address
- There is a desire to make OSPFv3 to compute IPv6 routes over TE
tunnels - of which OSPFv3 has no topological information
> 3. In the section 3 mapping algorithm, why do you walk
the X-AF
> endpoints from all connected areas? Why not just the
area of local
> IP address?
Idea behind this wording is to cater for cases when area
borders are
laid differently in OSPFv2 and OSPFv3. It's even possible that
router is
ABR in OSPFv2 but not OSPFv3. From network design perspective
this, of
course, is a terrible thing to do - but not impossible.
I guess I still don't understand. Are you implying that you are
advertising TE LSAs using both OSPFv2 and OSPFv3 and aggregating the
TED and since the area boundaries may be different, you need to
search all the areas LSP endpoints? I don't think this deployment
model makes sense and I don't think this should be supported.
No, TE LSAs are advertised only in OSPFv2.
Consider information available to OSPFv3 on tunnel headend router.
Endpoint address of TE tunnel is IPv4 address, say 7.7.7.7 (this
address is what tunnel tailend router advertises in OSPFv2 TE LSA in
the Router Address TLV). OSPFv3 needs to find what router in what area
corresponds to router that advertises that TE LSA in OSPFv2.
That is, OSPFv3 has no its own TE information and not even a hint
to which area may belong the tailend router.
> 4. In the backward compatibility section, can you also
discuss the
> requirements for backward compatibility of the
endpoints? Also state
> that the X-AF tunnel will not be recognized unless the
endpoints are
> advertised by the same protocol (OSPFv2 or OSPFv3); or
describe the
> behavior if this is not the intension.
We can add paragraph saying something like:
"In order for XAF computation to work tunnel tailend routers
MUST
advertise XAF Node Local Address sub-TLVs in OSPF instance that
will
perform XAF computation. Thus only tunnel endpoints (both
tunnel headend
and tailend routers) and only OSPF protocol instance performing
XAF
routing must implement XAF as described in this document. Other
routers
in the network do not need to implement XAF algorithm or
interpret Node
Local Address sub-TLVs. For example, if network uses TE tunnels
signaled
by OSPFv2 [RFC3630] and intends to use cross-AF route
computation in
OSPFv3 then only OSPFv3 implementation on routers that serve as
tunnel
endpoints in OSPFv2 needs to be compliant with this
specification."
Will this text work?
I think this could be a lot clearer if it were written from the
perspective of the head-end router performing the calculation. Also,
you lost me completely with the last sentence. We are uses a single
protocol, OSPFv2 or OSPFv3 to advertise TE LSAs. Since both IPv4 and
IPv6 traffic is tunneled over that LSP, there is no reason to
operate both protocols since traffic will take the path of the X-AF
LSP - correct?
But OSPFv2 does not produce IPv6 routes. Both protocols operate in the
network:
- OSPFv2 computes IPv4 routes and distributes TE database
- OSPFv3 computes IPv6 routes. If TE tunnels provide shortcut to
destination then OSPFv3 will point route into the tunnel.
---
Anton
On 04/07/18 23:06, Acee Lindem (acee) wrote:
Hi Anton,
On 4/6/18, 7:33 AM, "Anton Smirnov (asmirnov)"
<asmir...@cisco.com><mailto:asmir...@cisco.com>wrote:
Hi Acee,
my answers below (I didn't vet them with other authors, so
they may
express different opinions).
> 1. Have you considered a shorter name for the RFC? For
example: “OSPF
> Cross Address Family Traffic Engineering Tunnels”?
Your proposed variant drops two pieces: "Routing with" and
"MPLS".
Dropping mention to MPLS is fine with me. Dropping "Routing
with" seems
to me less correct because the draft is about ways to compute
routes and
not about setting up/managing tunnels.
But ultimately I have no strong feelings here and if there
is a
requirement to shorten document's name then that would be a
good candidate.
> 2. Can you change the requirements language text to the RFC
8174
version?
OK, we will publish new document revision when we agreed on
other
points.
> 3. In the section 3 mapping algorithm, why do you walk
the X-AF
> endpoints from all connected areas? Why not just the
area of local
> IP address?
Idea behind this wording is to cater for cases when area
borders are
laid differently in OSPFv2 and OSPFv3. It's even possible that
router is
ABR in OSPFv2 but not OSPFv3. From network design perspective
this, of
course, is a terrible thing to do - but not impossible.
I guess I still don't understand. Are you implying that you are
advertising TE LSAs using both OSPFv2 and OSPFv3 and aggregating the
TED and since the area boundaries may be different, you need to
search all the areas LSP endpoints? I don't think this deployment
model makes sense and I don't think this should be supported.
> 4. In the backward compatibility section, can you also
discuss the
> requirements for backward compatibility of the
endpoints? Also state
> that the X-AF tunnel will not be recognized unless the
endpoints are
> advertised by the same protocol (OSPFv2 or OSPFv3); or
describe the
> behavior if this is not the intension.
We can add paragraph saying something like:
"In order for XAF computation to work tunnel tailend routers
MUST
advertise XAF Node Local Address sub-TLVs in OSPF instance that
will
perform XAF computation. Thus only tunnel endpoints (both
tunnel headend
and tailend routers) and only OSPF protocol instance performing
XAF
routing must implement XAF as described in this document. Other
routers
in the network do not need to implement XAF algorithm or
interpret Node
Local Address sub-TLVs. For example, if network uses TE tunnels
signaled
by OSPFv2 [RFC3630] and intends to use cross-AF route
computation in
OSPFv3 then only OSPFv3 implementation on routers that serve as
tunnel
endpoints in OSPFv2 needs to be compliant with this
specification."
Will this text work?
I think this could be a lot clearer if it were written from the
perspective of the head-end router performing the calculation. Also,
you lost me completely with the last sentence. We are uses a single
protocol, OSPFv2 or OSPFv3 to advertise TE LSAs. Since both IPv4 and
IPv6 traffic is tunneled over that LSP, there is no reason to
operate both protocols since traffic will take the path of the X-AF
LSP - correct?
Thanks,
Acee
---
Anton
On 04/04/18 20:13, Acee Lindem (acee) wrote:
> Hi Anton, Alvaro, and Mike,
>
> In preparation for WG last call, I have a couple comments.
>
> 1. Have you considered a shorter name for the RFC? For
example: “OSPF
> Cross Address Family Traffic Engineering Tunnels”?
> 2. Can you change the requirements language text to the RFC
8174 version?
> 3. In the section 3 mapping algorithm, why do you walk the
X-AF
> endpoints from all connected areas? Why not just the area
of local
> IP address?
> 4. In the backward compatibility section, can you also
discuss the
> requirements for backward compatibility of the endpoints?
Also state
> that the X-AF tunnel will not be recognized unless the
endpoints are
> advertised by the same protocol (OSPFv2 or OSPFv3); or
describe the
> behavior if this is not the intension.
>
> Thanks,
>
> Acee
>
