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Ask the Expert- MPLS Best Practices- Configuration & Troubleshooting

Cisco Moderador
Community Manager
Community Manager

This topic is a chance to discuss more about the Multi Protocol Label Switching (MPLS) technology and its typical applications. This session will cover all questions related to MPLS fundamentals including its supporting protocols (LDP, BGP), and its most common applications, such as BGP-less core networks, 6PE/6VPE migration mechanisms, L2 and L3 VPNs, both in intra-AS and inter-AS scope.


To participate in this event, please use theJoin the Discussion : Cisco Ask the Expertbutton below to ask your questions


Ask questions from Monday October 15th to Friday November 2nd, 2018


Featured expert

david.pngDavid Samuel Peñaloza Seijas works as a Senior Network Consulting Engineer at Verizon Enterprise Solutions in the Czech Republic. Previously, he worked as a Network Support Specialist in the IBM Client Innovation Center in the Czech Republic. David is an expert interested in all topics related to networks. However, he focuses mainly on data centers, enterprise networks, and network design, including software-defined networking (SDN). David has a long relationship with Cisco. He has been a Cisco Instructor for the Cisco Academy and was recognized as a Cisco Champion and a Cisco Designated VIP for 2017 and 2018. David holds a CCNP R&S, CCDP, CCNA Security, CCNA CyberOps and a CCNA SP certification. Currently, he is preparing for a CCDE. 


David might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation on the Service Providers community.

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31 Replies 31

Routing Policy to Match Incoming RD

On CISCO ASR 9K routers


an i have routing Policy to match the Incoming RD, and export the Routes based on the Incoming RD's. Basically I do not want to export certain routes to certain Incoming RD ( Router Distinguishers )

Though I could have Same Import RT and export  RT in those RD.



RD                             ( I would Like ASR to Export Routes to this RD  )

        iRT  65201:64

        eRT 65201:64 


RD                              ( I would Like the ASR not to export the Routes to this RD )

        iRT  65201:64

        eRT 65201:64 



Is it Possible! And can i have some configuration examples as references



The RD is a 64 bit value appended to NLRI and used per VRF, whose only objective is to give uniqueness to prefixes received from customers in a given VRF. Furthermore, import and export operations are performed in the VRF (which has an RD configured).


You cant import or export an RD, which makes me believe you are referring to Route Targets. Route Targets are extended communities and have a similar structure to RDs, that makes them prone to be confused with RDs.


Could you please clarify your requirement?



First of all thanks a Lot for your Reply.

Basically I have the following setup, and I do not have much control on the Quagga side.

So basically that means, people configuring the Quagga can configure anything they need.


So Problem here is I have a OAM Network,

and somehow we can configure the Quagga as below and we can hook on to the OAM network.


So, I want the OAM VRF routes to be exported only to the Specific RD in the Neighbor

So far, I do not find a Option in ASR to Export Routes from VRF based on Source RD!

So I am wondering what could be other ways.

Or that is that something I could do on Quagga side also please let me know.

How this could be made possible, either via Route Policy or some other means,




I am afraid we need to clarify a confusion about the RD, RT, and their purpose so we dont step on our toes.


The RD is configured under the VRF and is appended to the NLRI. The purpose of RD is only to help BGP distinguish between the same-looking networks from different VRFs - for instance: a BGP advertisement about in VRF B does not look like a BGP update of in VRF A.


This is where the task of RD ends. It is not used as a tool to decide what VRF can a route be imported to or exported from.


On the other hand, a Route Target is an extended community attribute that can be attached multiple times to a route and it allows control of the VPN membership. With them you manage which prefixes get advertised between VRFs and how your VPN topology would be (i.e. hub and spoke, full mesh). Their actions can be defined as follows:


Import: allow routes from the MPLS core to get into the VRF

Export: allow routes from the VRF to get out of the VRF to the MPLS core.


These operations are not dependent of an specific RD, they only depend on the RTs and the import/export actions.


There is a way to advertise your routes selectively (via a route map, tagging the prefixes with the extended community and removing the export statement in the VRF), but that would affect both VRFs importing them.


Now, on the Quagga side that you mentioned yourself you cannot configure, there are two distinct VRFs, both interested in the same set of routes since both use the same "route-target import". The moment you set that RT in a "route-target export" command, both VRFs on the Quagga side will receive those routes. There is no way you can make it more selective on the sender side, and RD will not help here because the Quagga is not use the RD for any route sorting or filtering purposes - in fact, no router would since this is not how BGP sorts routes into VRFs.


Sorry to disappoint, but in this case, there is no solution without cooperating with the Quagga administrators, and changing the RTs so that the two VRFs on the Quagga side potentially have a subset of non-overlapping RTs.
Please note that BGP as a protocol is still based on the mutual trust paradigm; if an administrator maliciously misconfigured his BGP to import routes into VRFs they should not be in, there is hardly anything you can do about it, apart from not advertising those routes to that router at all.



Hi David
I’m looking to install an MPLS domain controller attached to my LAN network. The issue I’m facing is that the MPLs has a different DNS to the LAN I’ve my DC installed. At this point my first query comes here, I’m unsure how to configure the DNS server since they are allocated differently
Could you please help here or share some insights?



Lets break it in pieces first to make it digestible


You need to deploy a DNS server that will be used by a MPLS infrastructure? In addition to that, you do have another DNS server inside your DC LAN side.


A domain controller for MPLS? Could you be referring to PCE? Is this reasoning correct?


What are you trying to achieve?


Excuse my questions, just trying to clarify the wording and your requirement so we can find the proper answer for your query. Many terms can cause confusion.





Hi I have a cisco smart switch 200 8 port the green light flash when you send info but it dose not reply and my PC can not find it .Try using findit program but all it dose is reinstall or repair can you help .

I have PTSD from Armed Forces , so find it difficult to keep my mind on thing  


Hello Richard


Have you tried the start-up guide? It explains how to set it up and the IP it has configured by default. Perhaps it can be useful for you.


Start-up Guide:


Also, I would recommend you to post your query here (Small Business Support Community):


Hope it helps



At my company we have implemented an internal MPLS network.  I am not very familiar with BGP and MPLS and was wondering if there was a "list" or recommendations to use for trouble-shooting purposes.  Thank you..


MPLS and BGP in their own are extensive topics, before any attempt to troubleshoot its recommended to understand the mechanisms that allow them to work together (otherwise troubleshooting wouldnt be successful or even feasible). There are many inner moving parts that integrate MPLS as a solution and also its interaction with BGP.


I would recommend to start from basics so foundations are properly placed.


MPLS fundamentals by Luc De Ghein would be an excellent way to start so MPLS mechanisms can be understood.

CCNP ROUTE 300-101 Official Certification Guide describes BGP up to a reasonable extent.


Maybe this blog post can also help you:


Hope it helps

Cisco Employee
Cisco Employee

wow, this would have a great session. I am interested and waiting for the session.


Thanks David

Hi @praverai

Welcome to this session, this is an online-forum event. Please feel free to post all your questions related to MPLS on this forum and tech matter expert David, will help you to solve them



I would like to join this session and explore the knowledge.





Hi @fortis007

Thanks for your interest in this session. To join you just simply need to click on “Reply” and post all the questions you have related to MPLS. Technology matter expert David will help you to solve all of them

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