overview of MPLS, BGP, Frame relay,

Posted on 2013-02-04
Last Modified: 2013-02-22
If I understand Interior gateway protocols (RIP,OSPF,EIGRP) are used within companies network to route packets between different subnets.

BGP is commonly used by ISP : I may say it is used to route (IGPs) between different Autonomous systems on the internet...I could be wrong...please correct me

BGP is also used by companies, in case they have 2 primary connections to 2 different ISPs.
but in this case, I am not sure what the company will route through BGP...considering if the company has just one connection to a single ISP, then all that the company is doing is connecting to internet....Please correct me

Frame Relay allows company sites to be connected just like they are one site... if each site is using IGPs then ...I may say IGPs (Layer3) are tunnelled through FR(Layer2)..please correct me on this

MPLS is similar to FR ...but I wonder if it does  tunnel each company site IGPs(Layer3) through MPLS.
MPLS works at layer 2.5.

Any clarification will be appreciated.

Question by:jskfan
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Alexios earned 500 total points
ID: 38850237

BGP = your are correct
Further information easy to understand (without many technical details)

BGP is also used by companies, in case they have 2 primary connections to 2 different ISPs.
Also correct.
An example, 2 different ISPs,
1. an original ISP company like Verizon,
2. a university network

From the university network all commercial internet activity is forbitten (you cannot have a n eshop server hosted by this line) but you can access Google

So you configure BGP table for that particular traffic, all the actions going to Google map to a route through the university network, all actions for the website (eshop) via Verizon
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Frame Relay = almost correct

What is Frame-Relay?

Frame Relay is a Layer 2 protocol and commonly known as a service from carriers. For example, people will say “I ordered a frame-relay circuit”. Frame relay creates a private network through a carrier’s network. This is done with permanent virtual circuits (PVC). A PVC is a connection from one site, to another site, through the carrier’s network. This is really just a configuration entry that a carrier makes on their frame relay switches.

Obtaining a frame-relay circuit is done by ordering a T1 or fractional T1 from the carrier. On top of that, you order a frame-relay port, matching the size of the circuit you ordered. Finally, you order a PVC that connects your frame relay port to another of your ports inside the network.

The benefits to frame-relay are:

Ability to have a single circuit that connects to the “frame relay cloud” and gain access to all other sites (as long as you have PVCs). As the number of locations grow, you would save more and more money because you don’t need as many circuits as you would if you were trying to fully-mesh your network with point to point leased lines.

Improved disaster recovery because all you have to do is to order a single circuit to the cloud and PVC’s to gain access to all remote sites.

By using the PVCs, you can design your WAN however you want. Meaning, you define what sites have direct connections to other sites and you only pay the small monthly PVC fee for each connection.

Some other terms you should know, concerning frame relay are:

LMI = local management interface. LMI is the management protocol of frame relay. LMI is sent between the frame relay switches and routers to communicate what DLCI’s are available and if there is congestion in the network.

DLCI = data link connection identifier. This is a number used to identify each PVC in the frame relay network.

CIR = committed information rate. This is the amount bandwidth you pay to guarantee you will receive, on each PVC. Generally you have much less CIR than you have port speed. You can, of course, burst above your CIR to your port speed but that traffic is marked DE.

DE = discard eligible. Traffic marked DE (that was above your CIR) CAN be discarded by the frame-relay network if there is congestion.

FECN & BECN = forward explicit congestion notification & backward explicit congestion notification. These are bits set inside LMI packets to alert the frame-relay devices that there is congestion in the network.
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Author Comment

ID: 38862970
--The reason a comapny will user Frame Relay and MPLS so that the mentioned protocols will carry the internal gateway protocols (EIGRP,OSPF,RIP,STATIC Routes) to another remote site.


--what does BGP carry from the company? if you say IGPs means BGP is used by companies that have remote sites and the Traffic will go through ISP to reach the other site...just like Site to Site VPN...

So,, I wanted to knwo what [FR, MPLS,BGP] carry from a Company Network
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BGP relies on IGP, whether you're using a routing protocol, or static routing. If the route isn't already in the table, BGP won't announce it.

In a traditional implementation, IGP is used in an administrative domain where you have full control of the routing. Every device, every hop, you can make the decision for.

BGP is for when you need to connect to others who aren't inside your administrative domain. You can still have end to end connectivity, but your control of that connectivity ends t your border.

Which if you think about it, is practical. I do not want route announcements from another company having any effect on my internal routing at all, which is what you'd have if two different entities did their interconnection through an IGP. A misconfiguration at Company B could seriously screw up Company A if they were interconnected through, say, OSPF, and someone at Company B screwed up.

So by seperating the routing domains, if Company A is peering with Company B via BGP, then Company B's screwup could certainly effect Company A, but it would be limited to traffic that was leaving Company A. Company B isn't likely to be able to screw with Company A's routing to the point where mail traffic would be delivered to Company B's Exchange server instead of Company A's, for example (this assumes the BGP administrator has taken basic precautions, like making sure Company B can't advertise RFC1918 space, or advertise Company A's own prefixes back to them, for example).

So IGP and EGP have very different functions.

Now, with that being said - BGP can and has been used in an IGP style within companies, and quite successfully. Given that BGP was designed to scale, for very large companies, or those with many sites, using BGP to transport routing data across the enterprise can be very advantageous. I know one company that, once they grew to a point where OSPF's requirements to connect back to area 0 became a very annoying prohibition, just converted all their sites to use BGP when transferring data between sites, and only used OSPF internally at a given site, and it has worked very well.

Author Comment

ID: 38867144
I worked for a company that does some faxing services for other client the company DNS server has all records for other Client companies.
The company I worked for has 4 remote sites, the company used Site to Site VPN, so no Frame relay , No MPLS, maybe because of the cost. I remember they used BGP too since they have more than one connection to their ISPs.

Now, if I understand Site to Site VPN will carry all data between sites including the routing tables they have in each site.

But role will BGP play in this case? is it to announce the routes for other client companies???I doubt it...that 's wher I get confused..

You said BGP announces routes to other companies.. how do you explain it in the case of the company I worked for?

Thank you for your patience
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Alexios earned 500 total points
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Read this and you will understand it (don't bother with commands, just the theory part)

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Expert Comment

ID: 38917111
Glad to help

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