Re: [Idr] [Responses for the comments during the IETF108] New Version Notification for draft-wang-idr-rd-orf-01.txt

Aijun Wang <> Fri, 07 August 2020 01:20 UTC

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From: "Aijun Wang" <>
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Date: Fri, 7 Aug 2020 09:19:59 +0800
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Subject: Re: [Idr] [Responses for the comments during the IETF108] New Version Notification for draft-wang-idr-rd-orf-01.txt
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Hi, Robert and Gyan:


The problem is similar as that for “BGP Maximum-Prefix” and should be control plane related issue.

No matter what’s the capabilities of the router, there is always the roof for its performance.  

And in large network deployment, there still exist the possibility that one or some PEs are misconfigured/attacked etc.  

We should not only control the PE behavior at network edge(for example, using BGP Maximum-Prefix feature), but also need to consider the risk within the network.   


RTC is one kind of method to control the routes propagation within the network, but it is not enough. 

RTC can filter the VRF routes it doesn’t want to, but it can’t suppress the VPN routes it wants.  Using RD-ORF can control the VPN routes limits within each VRF. 



Best Regards


Aijun Wang

China Telecom


From: Robert Raszuk [] 
Sent: Friday, August 7, 2020 7:05 AM
To: Aijun Wang <>cn>;
Cc: Keyur Patel <>om>; idr <>rg>; Gyan Mishra <>
Subject: Re: [Idr] [Responses for the comments during the IETF108] New Version Notification for draft-wang-idr-rd-orf-01.txt




I think we need to step back and first understand what is the problem. 


Statements "overload of the PE" .. "overwhelmed PE" etc ... are really not helpful. Neither are sufficient to justify this work based on the statement "we need more then one solution" etc .... 


What exactly is being considered a problem here ? 


1. Running out of RAM in control plane ? 

2. Running out of CPU in control plane ? 

3. Not being able to import VPNv4 routes to a VRFs due to not enough control plane memory ? 

4. Not being able to import VPNv4 routes to a VRFs due to not enough data plane memory ?   


And please do not say "all of the above" as it will also not much productive. 


While stating the above please indicate which vendors have been tested and do not meet feature wise sufficient protection. 


Many thx,





On Fri, Aug 7, 2020 at 12:50 AM Gyan Mishra < <> > wrote:



On Thu, Aug 6, 2020 at 7:29 AM Aijun Wang < <> > wrote:

Hi, Gyan and Robert:


Maximum Prefix Limit is one method to control the routes between PE and CE, but we should not depend only on it. 


   You can use maximum prefix along with an inbound filter prefix list or as path or community match for whatever style routing control desired.


>From a PE standpoint you have not explained why using the per VRF prefix limit to limit the size of the per VRF rib.  Please explain why that does not solve the problem.


RD-ORF can limit the influence scope of misbehavior PE as small as possible.


    I don’t think you want to use RD-ORF as that would drop all routes from a PE and RTC does the job well only advertising RTs imported on the PE.  I think it would be rare if ever that anyone would ever filter on RD.


RT-ORF can suppress the routes from unwanted VRFs, but can’t suppress the overflow routes in VRF that it is interested.




More details responses are inline below.

Aijun Wang

China Telecom

On Aug 6, 2020, at 18:02, Gyan Mishra < <> > wrote:


Hi Robert 


I am in agreement as you stated that most service providers from my experience use the per VRF prefix limit to protect resources.  Problem solved as you said 20+ years ago.  


That is a general rule of thumb for any service providers to perform due diligence on their PE memory resource carving per VRF and set it appropriately based on platform and total number of VRFs to account for.  


Problem solved on the SP end.


On the customer end, they can also use the maximum prefix peer command as well to prevent flood of routes in case of unwanted advertisements from unintentional VRF leaking by providers.


Kind Regards 





On Thu, Aug 6, 2020 at 5:49 AM Robert Raszuk < <> > wrote:

Hi Gyan,


Thank you for your comments - all very valid observations. 


Just to perhaps clarify one thing ... Problem authors are attempting to address - the way I understand it - is that given resource may be suffering from actually legitimate VPN routes hence to use RTC indeed a lot of additional RTs would have to be applied. 


But I do not understand why authors fail to recognize that solution for their problem has been invented and implemented over 20 years ago already. The solution is to control on a per *ingress* VRF basis number of VPN routes customer is authorized to inject into his VPN with eBGP PE-CE prefix limit. 


[WAJ] we have mentioned prefix limit solutions in the draft and analysis its applicability scope.


Most SPs offering L3VPNs use prefix limit successfully to protect their shared resources for vast majority of customers and deployments. For VPN customers with unpredictable amount of routing CSC model should be used instead. 


By all means filtering and dropping accepted into SP network VPN route should not take place. 








On Thu, Aug 6, 2020 at 11:41 AM Gyan Mishra < <> > wrote:

Hi Aijun


I agree with Robert that you cannot filter by RD or you would drop all the routes and filtering must be done by RT.  Also the issue with RT ORF filter is as Robert mentioned that you may have the same prefix with two different RTs which is common unique by RD and so the ORF would drop the prefixes.  


[WAJ] Such situation can only happen at the extraVPN scenarios which should be designed carefully——one must keep the prefixes in these VRFs not overlap. But if the prefixes in these VRFs are not overlap, why do we need to separate them in different VRFs?

In conclusion, this is just corner case and should be avoided in design.




I am not sure I understand what problem you are trying to solve that is not already solved by RTC membership so that only RTs imported by the PE are what is advertised by the RR.  That is most effective way of cutting down the RT flooding that occurs in the RR to PE advertisement.  RT filtering is enabled by Default on all PEs and only if the RT is imported on the PE are the RTs accepted into the vpn rib. That works pretty well in cutting down RT advertisements by the RR.


As Robert mentioned each VRF has a maximum prefix which is defined on the PE RIBs per VRF and in general on most current or even hardware within the last 10 years is a minimum 1M prefixes per VRF is pretty standard with most vendors and platforms.  The vpn rib limit is much much higher on the higher end platforms.


You draft talks about inter-as issues solved with RT-ORF.  So when PE-PE inter-as option B by default all RTs are dropped due to default RT filtering and only RTs that are accepted are those RTS that are explicitly being imported on the PE ASBR.  There is an option for retain route-target all that disabled the default RT filtering so that all VPN routes can be accepted on the inter-as option B link.  However a RT filter can still be applied to the retian-route-target all so that only pertinent RTs are accepted inter domain.  That seems to work pretty well.


As far as inter-as option C, the PE-PE ASBRs do not maintain the VPN RIB.  BGP LU is enabled on the inter-as link for end to end LSP by importing the loopback between ASs for the end to end LSPto be built.   The RRs between the SPs have eBGP VPN IPv4 VPN IPV6 peer with next hop unchanged so the data plane gets built between the PEs.  The RR by default does not have RT filtering enabled by default as does the PE, so is able to reflect all the vpn routes learned to all PEs within each AS.  In the inter-as scenario as well RTC works very well with the RT membership to cut down on RR to PE vpn route advertisements.


Kind Regards 




On Wed, Aug 5, 2020 at 12:49 PM Aijun Wang < <> > wrote:

Hi, Robert:


Aijun Wang

China Telecom

On Aug 6, 2020, at 00:14, Robert Raszuk < <> > wrote:


[WAJ] The VPN routes imported in these VRFs can’t use the same RD, or else, the VPN prefixes in different VRFs will collision on RR.


Nothing will "collide" on RRs. 


NLRI = RD+Prefix  not just the RD. 


[WAJ] The prefix part can be overlap in different VRF. If the RD is same, RD+Prefix will also be overlap.

We must make sure different VRF use different RD to make the VPN prefixes unique within the domain.


So you may have completely different prefixes sourced by the same VRF going to completely different VRFs on same or different PEs. 



[WAJ] This situation is for extraVPN communication, and should be designed carefully to avoid the address collision.. 

If the address space in different VRF need to be considered in such manner, putting them in one VRF may be more straightforward.

Kind regards,







Idr mailing list <>



Gyan Mishra

Network Solutions Architect 

M 301 502-1347
13101 Columbia Pike <,+MD?entry=gmail&source=g>  
Silver Spring, MD <,+MD?entry=gmail&source=g> 




Gyan Mishra

Network Solutions Architect 

M 301 502-1347
13101 Columbia Pike <,+MD?entry=gmail&source=g>  
Silver Spring, MD <,+MD?entry=gmail&source=g> 




Gyan Mishra

Network Solutions Architect 

M 301 502-1347
13101 Columbia Pike 
Silver Spring, MD