Re: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt

Aijun Wang <wangaijun@tsinghua.org.cn> Tue, 27 July 2021 04:04 UTC

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From: "Aijun Wang" <wangaijun@tsinghua.org.cn>
To: "'Susan Hares'" <shares@ndzh.com>, <pce@ietf.org>
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Subject: Re: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt
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Hi, Susan:

 

Thanks for your reviews, let me first address your current questions and
wait for the further discussions on the overall solution.

 

Best Regards

 

Aijun Wang

China Telecom

 

From: pce-bounces@ietf.org <pce-bounces@ietf.org> On Behalf Of Susan Hares
Sent: Tuesday, July 27, 2021 7:19 AM
To: pce@ietf.org
Cc: 'idr-chairs' <idr-chairs@ietf.org>rg>; 'pce-chairs' <pce-chairs@ietf.org>
Subject: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt

 

Greetings: 

 

Thank you for your work on draft-ietf-pce-pcep-extension-native-ip-14.txt.


This comment should be consider feedback from me as a WG member of IDR and
PCE.  I have posted this information also on the  

 

This draft takes a step toward auto-configuration of BGP peers.  IDR has
created a set of requirements for BGP auto-configuration for Data Centers
at: 

https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-autoconf-considerations/

[WAJ] Yes, I have also reviewed this document and attended some discussions
on it. The autoconf document tries to build the BGP from scratch without 3rd
party(for example, PCE) assistance. It considers mainly the direct connected
BGP peer setup process automatically and does not involve the prefix
advertisement and explicit route setup. 

I think the aim of these two drafts is different but we can refer to some
designed considerations from it.

 

 

I¡¯ve put a copy of these comments at: 

https://trac.ietf.org/trac/idr/wiki/pce-pcep-extension-native-ip%20Hares%20c
omments

 

 

Cheers, Sue 

 

Comments on draft-ietf-pce-pcep-extension-native-ip-14

=================================================

Overview of errors 

1) section 6 description of BGP routers needs clarification 

(sections 6.1, 6.2, and 6.3) for RR and RR Clients 

[WAJ] Please see the replies inline below.

 

2) BGP Session Establish Procedures ¨C are these restrict to RR and RR
Clients?  

[WAJ] Yes. The BGP session is established between RR and its clients in
large network. It can also be established between two nodes directly.(as
described in
https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-autoconf-considerations/
)

 

3) Explicit routes [section 6.2] ¨C Is ECMP support as well as 1 prefix/1
next Hop?  

[WAJ] Yes, ECMP is supported. PCE needs to send two EPR(Explicit Peer Route)
objects, with the same ¡°Destination Adress¡± and ¡°Route Priority¡±, but
different ¡°Next Hop Address¡±

 

4) IPv4/IPv6 restrictions [section 6.3] ¨C are you restricting the peer
session or the AFI/SAFI supported by the Peer session? 

[WAJ] AFI/SAFI supported by the peer session.

 

5) Sections 7, 9, and 10 ¨C may need to change based on your answers to
questions 1-4? 

 

Detailed questions 

---------------------

1. Section 6 ¨C sub sections 6.1, 6.2 and 6.3. 

 

Problem: 

The text that describe the BGP peers and the diagram needs clarification on
the BGP peering between BGP peers:  R1, R7, and R3. If R1 and R7 are Route
Reflector clients (RR clients) are attached to the R3 then it is important
to indicate this point. 

[WAJ] Yes, R1 and R7 is RR clients.

If you are using classic route reflection, then R1, R3 and R7 would need to
be in the same Autonomous system. 

[WAJ] Yes, certainly.

 

The RR (R3) determines what routes are sent to the RR clients.  

 

This problem impacts the text in section 6.1, 6.2, and 6.3 

 

2.) Text change for Section 6.1 ¨C if R1 and R7 are RR clients. 

 

Here¡¯s a change if R1 and R7 are Router Reflector Clients.  

 

Current text: /

   The PCInitiate message should be sent to PCC which acts as BGP router

  and route reflector(RR).  In the example in Figure 1, it should be

   sent to R1(M1), R3(M2 & M3) and R7(M4), when R3 acts as RR./

 

Improved text: /

   The PCInitiate message should be sent to PCC which acts as 

    BGP router reflector or a route reflector client. In the 

   example in Figure 1, it should be

   sent to the route reflector clients R1(M1) and R7 (M4), and 

  the route reflector R3 (M1 or M4).    /

[WAJ] Has updated the draft with the following contents(almost same as your
suggestions):

The PCInitiate message should be sent to PCC which acts as BGP router and/or
route reflector(RR). In the example in Figure 1, it should be sent to route
reflector clients R1(M1) and R7(M4), and the route reflector R3(M2 & M3)
when R3 acts as RR. PCInitiate message creates an auto-configuration
function for these BGP peers providing the indicated Peer AS and the
Local/Peer IP Address.

 

3) Section 6.1 ¨C BGP Session Establishment Procedure 

Question: Does the PCEInitiate (message and report) require the RR and RR
client structure? 

[WAJ] No. not necessary.  The BGP session setup procedures is same between
RR and its clients.

 

If so, the PCInitiate should have a parameter indicate what type of BGP peer
(RR or RR client) each receiving BGP peer should be.   

 

4) Section 6.2 ¨C Explicit Route Establishment Procedure 

 

Problem: It is unclear what the impact to the routing system of the setting
of explicit route.  

 

Basic Details: (1 Route with 1 Next Hop)

If R1 and R7 are RR clients and the Explicit route operates as static route
installed by the PCIntiate, then BGP peer will reflected these static routes
R3. 

[WAJ] No, the explicit route is only installed on the aimed PCC nodes and
such information will not be advertised via the BGP session between RR and
its clients.

[R1 (explicit route [static route]) ¨¤ R3] 

[R1 (explicit route [static route]) ¨¤ R3] 

 

Setting or clearing the Explicit route seem to map to a setting/clear a
static route on the node.  If this is true, then this section needs to be
rework to clear describe the process. 

[WAJ] Yes, it is similar with the static route on the node. The purpose of
these explicit routes are to influence the final recursive forwarding path
for prefixes advertised by BGP peer.

 

Your setting the route on the pathway hop by hop is similar to
netconf/restconf setting routes in a pathway.   

[WAJ] Yes, it is similar.

 

ECMP Details: (1 Route with multiple Next Hop) 

If the explicit route is a ECMP route with multiple next hop paths, the next
hop for a route installed in could be R5 or R2. 

[WAJ] Yes. For ECMP routes, the PCE needs to send two EPR objects to PCC(in
Figure2, on R1), with the ¡°Destination Address¡± are both set to R7, but
the ¡°Nexthop Address¡± is set differently(for example, R2, R5 as you
mentioned.).  The ¡°Route Priority¡± field in EPR object should also be the
same.

 

If ECMP is allowed, then you need to decide if:

a) adding this route allows the route to be installed if only some of the
next hops are valid (for example R5 is valid, but R2 is not)

b) delete routing allows the route to be deleted if both next hops were not
installed. 

[WAJ]  Adding the description ¡°The PCC should verify that the next hop
address is reachable.¡±  before the sentence ¡°Upon the error occurs, the
PCC SHOULD send the corresponding error via PCErr message, with an error
information¡­ ¡­¡£

 

5) Section 6.3 

 

Problem:  You do not clear indicate the status of BGP peer routers. 

 

If R1 and R7 are BGP route reflector clients, then R1 and R7 will send the
route to R3 which will reflect the route to other RR clients (if policy
allows). 

[WAJ] The propagation of BGP prefixes is the same as the traditional BGP
procedures. The ¡°Peer Address¡± in PPA objects indicates which peer the
prefixes will be sent to.

 

6.) Section 6.3 

Problem:  It is unclear why there is a restriction for IPv4 prefix to be
sent only via a IPv4 BGP section, and the IPv6 prefix only via a IPV6
section. 

 

Details: I think the author is trying to describe the peers support for a
particular set of AFI/SAFIS for NLRI sent rather than the peering.  However,
it is unclear. 

[WAJ] What we want to express is that the IPv4 BGP Peer session will
advertise/receive only IPv4 prefixes(AFI/SAFI is 1/1 ), and IPv6 BGP Peer
session will advertise/receive IPv6 prefixes(AFI/SAFI is 2/1)

 

7.) Sections 7.2 and 7.3 

All of these issues on the intent of the protocol need to be answered before
I can provide additional feedback on the PCEP objects.  

 

The initial shape of the PCE discussion are reasonable, but working through
the details requires clarity in sections 6.1 to 6.3.  For example, support
for ECMP in the explicit routes may cause sections 7.3 and 7.4 to be
rewritten. 

 

8.) Section 9 ¨C 

The error handling must consider the RR to RR client distribution of routes.


[WAJ] The route distribution process between the RR and RR clients is
unchanged.

 

Also, if one PCE overwrites another multiple route are sent from a RR client
to the RR.  The policy in the RR must be set-up to handle errors. 

[WAJ] The information from EPR object is not advertised by the RR client
back to the RR.

 

This section needs a bit of rethinking. 

 

8.) Section 10 - BGP Considerations -  

The content of the BGP consideration sections seems reasonable, but it
should be reviewed again after all the remainder of the document has been
clarified. 

[WAJ] Wish to receive your more through considerations for the current
solution.