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Contributor
Posts: 164
Registered: ‎11-14-2009
0

Some Basic MPLS Questions

Hello Community

 

Can some one please answer these questions

 

1-what is the differnece between traffic engineering
and mpls traffic engineering

1a-Are l3vpns possible without MPLS

2-what if we dont have a signaling protocol with MPLS

3-what benifit do we achieve by using MPLS tunnels

4-How do MPLS forms a tunnel

Thanks & Regards

Malik

Contributor
Posts: 34
Registered: ‎04-19-2010
0

Re: Some Basic MPLS Questions

Hi,

Replying quickly to Your question:

 

1) No differnece. Mpls path can use a way which is derived by algorithm  using TE like ospf with TE or is-is.  Generally traffic engineering it is a mechanism to calculate lsp path using certaim criteria like bandwith, link color etc.

 

1a) You can do it with gre or ipsec tunneling aswell

 

2)  Without signalling protocols there is no way to set up lsp automatically. Then You must set up lsp manually from ingress by transit to egress routers

 

3) Lot's of but 2 my opinion is traffic engineering  and services like l3 vpn, l2 vpn and vpls. With TE there is a method to send the traffic through the routers and interface which conform to certain criteria (ie. Bandwith avaiability). MPLS tunnel also separate customer traffic and make it possible to build vpns. There is also third very important think. There are mechnism like fast reroute which provide very fast convergence if problem occurs. This restoration may be even about 50 ms which is not possible in classic IP routing.

 

3) MPLS tunnell is a kind of abstract. From router point of view mpls is another type of decision making where to send a packet. Rsvp or ldp signalling is the way to inform  which labels will be used. In case of PE routers ldp or bgp signalls the end points the service they want to establish.

 

 

Hope it helps,

 

Regards,

 

Artur

Contributor
Posts: 164
Registered: ‎11-14-2009
0

Re: Some Basic MPLS Questions

Many Thank Artur

 

Can  you please tell me further

 

1-If we can use traffic engineering with IGP's such as OSPF or ISIS how is it deployed in JUNOS.

 

2-How can we compare IGP TE capability with MPLS-TE capability i mean if we can achieve TE with IGP in say case of l3vpn's then why use MPLS TE .

 

3-If we can do traffic engineering with IGP's then why do we use MPLS/RSVP TE.

 

4-Can we utilize CSPF to do TE with IGP only i mean without using RSVP.

 

5-1(a) If we can have l3vpn's with GRE tunnels then how will we do TE.

 

Thanks & Regards

Malik

Contributor
Posts: 34
Registered: ‎04-19-2010
0

Re: Some Basic MPLS Questions

Hi again,

1) For details please look at Junos docs. Is-is supports  TE by default. Using ospf You have to enable it with traffic-engineering command

 

 2) Mpls-te is the capability to establish  lsp path using some criteria provided by traffic enginnering and not only igp shortest path. Those criteria are provided by igp with TE enabled.

 

3) IGP only provides the information needed to set up lsp relevant to TE constraints

 

4) No. Only rsvp is using cspf database and TE information.

 

5)  If we use gre  we are not using TE at all. Only  rsvp signalled mpls lsp can use TE. 

 

Regars,

 

Artur

 

 

 

 

 

 

 

 

 

Contributor
Posts: 164
Registered: ‎11-14-2009
0

Re: Some Basic MPLS Questions

Thanks again Artur

 

I want to clear one last thing i.e. according to me TE is the capability to efficiently utlize the underutilized paths in the network that are ignored by IGP due to the metric & we also know that we may utilize ECMP,Policy based routing to efficeintly route the traffic and we may also utilize node-link protection to provide the fast-re route.

 

Now how is MPLS/TE differnet then IGP-TE?


Can MPLS/TE only be utilized to engineer the MPLS services i.e the traffic resolved via inet3.We also know that RSVP has the capabality to oversee the bandwidth along the path while normal IGP can not do this but what if IGP can not do this what benifit do we achieve when we oversee the bandwith automatic swithching in case of failure but IGP will also switch across in case of failure to the next best link

 

Now the question is can simple IGP also provide TE to the MPLS traffic if we dont define the constraints.

 

Things are sort of messed up on my mind Smiley Very Happy.I hope you dont mind.I feel that if we only rely on IGP TE capability then we will be able to Engineer VPN traffic as well without using CSPF.

 

Thanks & Regards

Malik

Contributor
Posts: 34
Registered: ‎04-19-2010
0

Re: Some Basic MPLS Questions

Hi again,

Please not that there  is no TE without  cspf. If You turn TE on (default for is-is)  constraints are announced automaticaly. Even if You do not create them. For instance interface bandwith.

 

Regards,

 

Artur

Super Contributor
Posts: 158
Registered: ‎04-20-2009
0

Re: Some Basic MPLS Questions

[ Edited ]

To add to the thread:

 

Your IGP populates the Traffic Engineering Database (TED)

 

jack@router> show ted database ?
Possible completions:
  <[Enter]>            Execute this command
  <system-id>          System ID or node ID
  brief                Display brief output (default)
  detail               Display detailed output
  extensive            Display extensive output
  |                    Pipe through a command

Then RSVP may use information from the TED.  You must specify which constraints for RSVP to use and set the limits to which it will utilize them.

 

ISIS --fill--> TED <--use--RSVP


 ISIS uses the extended IS reachability TLV (TLV type 22), which has sub-TLVs to describe different aspects of the network links.  OSPF uses the opaque LSA (type 10) which has a TLV payload describing the links.

 

Link-protection and FRR do not require TE unless you want to apply contraints to the detour/bypass LSPs  Also, explicit route objects (ERO) do not require TE, but will allow you to engineer the exact path your LSP will take.

Contributor
Posts: 164
Registered: ‎11-14-2009
0

Re: Some Basic MPLS Questions

Many Thanks Parks

 

I am trying to find out some very strong point that proves that IGP-TE cant provide what MPLS-TE can provide.

 

Can IGP-TE be used to optimize l3vpn traffic or other MPLS applications?why or why not?

 

I feel that IGP-TE can't reserve the bandwidth along the path and that is where MPLS-TE comes in to play what do you say.

 

Are RSVP-TE & MPLS-TE same things?

 

We use MPLS/RSVP TE using LSP to optimize the forwarding plane how can we optimize the control plane then ?

 

Is MPLS an umbrella term i.e. the combination of IGP & Signaling protocols (LDP/RSVP) define the MPLS.

 

How can we prove that L3Vpn is an MPLS application?

 

Thanks & Regards

Malik

 

Super Contributor
Posts: 158
Registered: ‎04-20-2009
0

Re: Some Basic MPLS Questions

I don't know of anyone using IGP-TE, most networks use MPLS-TE.  I think there is/was some work going on for crLDP which would might use IGP-TE information.  For all practical purposes, I would not worry about IGP-TE.  If you can provide a link to what your are researching for IGP-TE, I might be able to comment more.  I would just stick to MPLS-TE.

 

Please look at this FAQ concerning MPLS-TE: http://www.mplsrc.com/faq2.shtml#MPLS%20Traffic%20Engineering

 

Also, for VPN definitions check out: http://www.mplsrc.com/faq2.shtml#MPLS%20VPNs

 

MPLS is a term that encompases a transport technology (ie Label Switching), and VPNs are the services that ride on top of MPLS (ie L3VPN, VPLS).

 

 

Contributor
Posts: 164
Registered: ‎11-14-2009
0

Re: Some Basic MPLS Questions

Hello Parks

 

I recently came across a discussion on when IGP has TE capabilities then why do we use MPLS-TE as IGP can also provide fast reroute i.e. loop free alternates & ERO as well and i had no clear answer that is why i am into this discussion.

 

Is this arguable point at all ? if it is arguable then what provides the differnce i.e what IGP-TE cant provide that MPLS-TE can???

 

Thanks & Regards

Malik

Super Contributor
Posts: 158
Registered: ‎04-20-2009

Re: Some Basic MPLS Questions

I understand now.  This really comes down to LDP vs RSVP as a signaling method. 

 

The benefits of LDP are really simplicity.  It is a very plug and play protocol.  You turn it on and it just works.  For better failure detection and recovery, LDP relies on the IGP to provide those capabilities.  Like you mention, loop-free alternates, is a excellent additon to protect MPLS traffic when using LDP.

 

LDP is still very limited in it's TE capabilites (it relies on the IGP to do the work).  I wouldn't even call it traffic engineering.  RSVP, on the other hand, has many more options and capabilites.  LDP will never match RSVP capabilties.

 

If you want simple LSP (really a FEC) setup with basic failure detection and recovery, then LDP will be the best option.  For everything else, you need to use RSVP.  Larger networks combine the to singalling methods by using LDP at the edge of the network with RSVP in the core.  LDP tunnelling over RSVP LSP is also used.

Distinguished Expert
Posts: 1,507
Registered: ‎06-06-2011
0

Re: Some Basic MPLS Questions

I am getting ready to to take the JMV course and it seems like your questions may be covered by this course. So you might want to give it a shot. Here are the course objective. I have heard from a few people who have taken that course that it is quite comprehensive.

https://learningportal.juniper.net/juniper/user_activity_info.aspx?id=3799

Here is a document that may help you: http://www.juniper.net/techpubs/en_US/junos12.1/information-products/topic-collections/config-guide-...

I just pulled it down and have not looked through all of it, but the first chapter seem to be dealing with TE. Hopefully tis may help in the meantime.

[KUDOS PLEASE! If you think I earned it!
If this solution worked for you please flag my post as an "Accepted Solution" so others can benefit..]