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

Susan Hares <> Thu, 29 July 2021 21:50 UTC

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From: "Susan Hares" <>
To: "'Aijun Wang'" <>, <>
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Subject: Re: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt---with HyperLink Correction
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I apologize for missing PCE session today.  I re-injured a knee just before
the session.  Let me provide you suggestions for sections 6.1, 6.2, and 6.3
that may resolve some of the issues.  


This specification provides one mechanism for BGP auto-configuration.  I¡¯m
happy to continue to review this draft and provide suggestions.  


Cheerily, Susan Hares



Section 6.1


Old text:/

    The procedures for establishing the BGP session between two peers

     By using the PCInitiate and PCRpt message pair is show below: /


New text:/

    The PCInitiate message can be used to configure the parameters for 

    a BGP peer session using the PCInitiate and PCRpt message pair.

    This pair of PCE messages is exchanged with a PCE function 

    Attached to each BGP peer which needs to be configured.  

    After the BGP peer session has been configured 

    via this pair of PCE messages the BGP session establishment process 

    operates in a normal fashion.  


    All BGP peers are configured for peer to peer communication whether the

    peers are E-BGP peers or I-BGP peers.   One of the IBGP topologies

    that multiple I-BGPs peers operate in a route-reflector I-BGP peer

    The example below shows 2 I-BGP route reflector clients interacting

    with one Route Reflector (RR), but Route Reflector topologies may have

    up to 100s of clients.  Centralized configuration via PCE provides 

    mechanisms to scale auto-configuration of small and large topologies.  


old text:/

    In the example in Figure 1, if the routers R1 and R7 are within one AS

    and R3 acts as a router reflector.  PCInitiate message should be sent 

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

    clients (R3 M2 & M3) respectively.  For inter-AS scenario, such message

    can be sent directly to ASBR router to build EBGP session./ 


New text:/

    The route reflector topology for a single AS is shown in Figure 1. 

    The BGP routers R1, R3, and R7 are within a single AS.  R1 and R7

    are BGP router-reflector clients, and R3 is a Route Reflector. 


     The PCInitiate message should be sent all of the BGP routers that

     need to be configured R1 (M3), R3 (M2 & M3), and R7 (M4). / 



Section 6.2.  


My understanding for your email is that the explicit route 

establishment procedures are installing a static route 

which is not to be redistributed via BGP peer. 


If this understanding is correct, please clearly state this 

fact and modify the diagrams to indicate a static route

A suggestion for text for this case is: 


Old text: /

The detail procedures for the explicit route establishment

procedures are show below. / 


New text: /

The explicit route establishment procedures can be used

to install a route via PCE in the PCC/BGP Peer.

Based on BGP policy, these routes may or may not 

be redistributed by the BGP peers.  PCE explicit routes 

operate similar to static routes installed

by network management protocols (netconf/restconf) 

but the  routes are associated with the PCE routing module.   


An example of the use case where the of the use case where 

explicit route installed by PCE is redistributed by BGP is 

described in section 6.3.  An example of the procedure 

where the explicit route installed by PCE is not redistributed

by BGP is described in this section (see figure 2 below for the 

topology).   Explicit route installations (like NM static routes) 

must carefully install and uninstall static routes in an specific

order so that the pathways are established without loops. /


Section 6.3 

Old text:/

The detailed procedures for BGP prefix advertisement are shown 

Below using PCInitiate and PCRpt message pair./


New Text:/

The explicit route establishment procedures can be used

to install a route via PCE in the router that is both

a PCC and BGP Peer.  Based on BGP policy, these routes   

may be redistributed by the BGP peers (or may not be distributed).  


This section provides an example  of the 

PCInitiate and PCRpt messages for the use case when 

routes installed via PCE are redistributed within an IBGP 

cloud with RR and RR clients when a I-BGP policy allows

PCE explicit routes to be originated within the I-BGP cloud. 

The E-BGP use case and the IBGP use case without

route reflectors are not shown in this example.  


The redistribution via BGP of PCE explicit routes

based on the BGP policy is similar to redistribution 

of static routes installed by network management 

protocols (netconf/restconf) are redistributed by BGP.  

However, in this use case configured routes are 

associated with the PCE routing module and BGP 

policy must handle the redistribution of these routes. / 









From: Aijun Wang [] 
Sent: Wednesday, July 28, 2021 3:42 AM
To: 'Susan Hares';
Cc: 'idr-chairs'; 'pce-chairs'
Subject: RE: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt---with
HyperLink Correction


Hi, Susan, Mike and All other experts:


I have just upload the updated version of this draft, would you like to
review it again to refine it?

And you can also refer the presentation on this IETF meeting for additional

Thanks in advance.



Best Regards


Aijun Wang

China Telecom


From: Susan Hares <> 
Sent: Wednesday, July 28, 2021 5:58 AM
To: 'Aijun Wang' <>cn>;
Cc: 'idr-chairs' <>rg>; 'pce-chairs' <>
Subject: RE: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt---with
HyperLink Correction




Thank you for your quick response.  


I¡¯ve answered questions below.  Would you let me know when you update your
draft?  I¡¯ll re-read the sections that changed and make additional
suggestions.  If you think it would be useful to add 2 (or more) next hops
per EPR, please let me know. 

[WAJ] Adding 2 (or more) next hops per EPR is one viable solution to achieve
the ECMP effects, but it seems that the current format is more flexible and
extensible? For example, if we want to add the UCMP features, as Mike
proposed, we can add some information within the ¡°Optional TLV¡± field of
the EPR to indicate what percentage traffic should be allocated to each


I¡¯m glad to keep reviewing your changes. 


Cheers, Sue 


From: Aijun Wang [] 
Sent: Tuesday, July 27, 2021 3:19 AM
To: 'Susan Hares';
Cc: 'idr-chairs'; 'pce-chairs'
Subject: RE: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt---with
HyperLink Correction


Hi, Susan and all:


Update one hyperlink on the contents, please refer to this mail for comments


From: <> On Behalf Of Aijun Wang
Sent: Tuesday, July 27, 2021 12:04 PM
To: 'Susan Hares' <>om>;
Cc: 'idr-chairs' <>rg>; 'pce-chairs' <>
Subject: Re: [Pce] draft-ietf-pce-pcep-extension-native-ip-14.txt


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




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

[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.


[Sue] You have understood that the bgp auto-configuration works on peer

          I simply wanted you to know that your PCE work linked that that
work in BGP. 


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



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

[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


The point ¨Cto-point (P2P) Peering was clear in RFC8821. 

[Sue] It would be useful to revise the draft to clearly define this is a
single AS,

RR location, and RR client locations. 

[WAJ] Has added some text as below. Actually, the procedures described in
this draft is not limited to one AS, it can be applied to inter-AS scenario

¡°In the example in Figure 1, if the router R1 and R7 are within one AS and
R3 acts as the route reflector, PCInitiate message should be sent to route
reflector clients R1(M1) and R7(M4), and the route reflector R3(M2 & M3)
respectively. For inter-AS scenario, such message can be sent directly to
the ASBR router to build EBGP session.¡±


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¡±

[Sue] ¨C it is possible to be more effective in the EPR by including 2 (or

Next Hops.  Have you consider this choice in PCE? 

[WAJ] As I answered in the begin of this email, it seems to encode one
single hop per EPR is more clear, extensible and flexible?


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.

[Sue] Again ¨C it would be helpful to clearly state AFI/SAFI. 

[WAJ] Has updated the draft accordingly, as ¡°The allowed AFI/SAFI for the
IPv4 BGP session should be 1/1(IPv4 prefix) and the allowed AFI/SAFI for the
IPv6 BGP session should be 2/1(IPv6 prefix). If mismatch occur, an
error(Error-type=TBD6, Error-value=TBD18, BPI/PPR address family mismatch)
should be reported via PCErr message.¡±


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. 



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.

[Sue] Please make this fact clear in your next revision. 

[WAJ] Done


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

[WAJ] Yes, certainly.

[Sue] Please make that clear in your document. 

[WAJ] Done


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

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.

[Sue] Thank you.  Did you submit your updated draft? 

[WAJ] Done


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.

[Sue]: If you use the PCEInitiate message with another structure, it would
be useful

To include an example in your document of multiple peers. 

[WAJ] The BPI(BGP Peer Info) object is sent only to the two BGP peers, will
not be sent to multiple peers (>2) simultaneously. 

          The PPA(Peer Prefix Advertisement) object is sent only to the
prefixes source node(for example, R1 or R7 in Figure 4). The RR needs not
receive such instructions. RR will receive the advertised prefix and forward
it to its other clients, based on the normal RR behavior.

Then, there is no differences for the BPI and PPA messages to RR, or its


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

[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]) ¨¤ R7] [note my error]  


                [Sue] If a route is installed in the RR clients, why is it
not updated to the BGP

               Peer web (R1-RR-R7). I thought the purpose of adding it to
the RR client. 

                If it is not the purpose, why is this included in the BGP

[WAJ] EPR object is different with BPI and PPA objects.  EPR object is just
used to indicate/influence how to get the BGP nexthop.  Such information
does not spread via the BGP mechanism, it is deployed by the PCEP protocol



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.


[Sue] Then is the purpose to send it from 1 RR client (for example R1), and 

 Have it redistribute to R3 (RR) and R7 (RR client). 

[WAJ] No, it is not redistribute to R3. EPR object is deployed directly via
the PCEP protocol. The spread of such information is different from PPA,
which is via the BGP control plane.


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.

[Sue] Thank you.  At least I got one detail correct [smile]. 

[WAJ] It¡¯s my responsibility to describe the mechanism more clearly.


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

[Sue] Thank  you for the explanation.  Do you think it is useful to allow 2

 In the same EPR object. 

[WAJ] Currently, I think one next-hop per EPR maybe more clear, extensible
and flexible. If there is any other strong advantages, we can modify it


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

[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¡­ ¡­¡£

[Sue]:  This is a wonderful addition. 


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

[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.

[Sue] If you have trio of 2 RR clients and RR, then simply indicate you
follow RR-RRclient rules. 

[WAJ] The PPA(Peer Prefixes Advertisement) object need only be sent to the
source node, then such prefixes information will be flooded based on the
regular BGP RR mechanism. We need not send PPA object to all of the RR¡¯s


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


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).

                 [Sue]: Why did you make this restriction?  Is it from PCE

[WAJ] Just want to simplify the management of network and less error-prune.


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


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


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.

[Sue] What prevents the EPR object from being sent to the RR via BGP. 

Is the EPR object not installed in the BGP RIBs to be sent? 

[WAJ] EPR object is deployed along the optional path via PCEP protocol, it
will be installed in the RIB of node, but not the BGP RIB of the node.

I think I am missing something simple here. 

[WAJ] The EPR object is described between BPI and PPA object section, maybe
this lead to your impression that it is also related to the BGP. If
necessary, we can adjust the description sequences of these objects later.


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

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


[Sue] Thank you for the discussion.  Could you provide updates