MPLS Response

[zanub]

Hi,

One very basic question. We have a MPLS line to a remote site and a DSL line to the same remote site. When i ping these sites, we are getting almost the same response times for both the circuits. eg:320ms for MPLS and 390 for DSL. Shouldn't the MPLS repsonse be way better. Around how much can i expect?

Thanks

[n.nandrekar]

Hi Zanub,

It is a popular misconception that MPLS is "faster" than ip. It might have been when it was first implemented but now-a-days, almost all the routers implement routing in hardware by use of CEF or fast-switching. So as long as it is implemented in hardware, it doesnt make any difference if the forwarding decision is based on L3 or L2 & 1/2 (mpls). Both will take the same processing time ( almost wirespeed) .

The reason mpls became famous and widely deployed is not because it is fast, but because it is a very good service enabler. It enables the provisioning of many services like L3 vpns, vpls, eompls, atom, traffic engineering etc.

So the responsetime would be the same for mpls or ip but could vary based on any additional features/services implemented. As far as pure lookup and forwarding is concerned, it shopuld be the same if implemented in h/w.

Regards,

Niranjan

[shivlu jain]

niranjan

you are very much right, but I think whether the switching is prcess by hardware but still the lookpart is being decreased. Becasue without mpls routing table has to search for the route and correspondng next hop address but in mpls case it has to bind the label for the next hop.

regards

shivlu

[n.nandrekar]

hi Shivlu!

When implemented in hardware, it uses CEF which is implemented using TCAM. In this case, the nexthop as well as the mac address , qos params etc are all already discovered and created into a template. " sh mls cef x.x.x.x detail" will give you the adjacency entry and the specific adjacency entry will give you the outgoing interface and associated L2 and L3 params. These are just inserted on the packet and the packet is forwarded.

MPLS is also implemented in the same way. So your argument is invalid and the it should take the same time in hardware. there is no different search for next hop and it doesnot go serially.

Regards,

Niranjan

[shivlu jain]

niranjan thanks for your reply.

[n.nandrekar]

refer the following doc for how CEF works.

http://www.cisco.com/en/US/docs/ios/12_1/switch/configuration/guide/xcdcef.html

Regards,

niranjan

[zanub]

niranjan,

then why would i prefer mpls over dsl.i know it will gurantee a bandwidth..but i keep on hearing we cant use voip over dsl..but i see the same response times for both the circuits..my dsl 2mbps should have enough bandwidth for voip users(10 lets say)..pls advice..

thanks

[n.nandrekar · Accepted solution]

hi Zanub,

As I have mentioned, MPLS is mainly used as a service enabler. The advantage you could get for using MPLS is you can have better services like traffic engineering QoS, VPNs etc. So if you are comparing dsl and mpls without any service, they both would work the same. But with mpls, you might have better redundancy with features like Fast-reroute, traffic engineering to have guarantees etc.

If your service provider is not giving you any services, then dsl and mpls would be the same as far as response times are concerned. And you still can run voip over that too but the problem would be during congestion. It is the worst case scenarios that you pay for. May be during congestion times or when there are problems in the SP core, you could see the difference in the response times for mpls and regular DSL. And again if you are using the connection for VPNs, then mpls provides many more features. And moreover mpls can use traffic engineering which can help your traffic take lesser congested path or a specific path to maintain constant delay avoiding jitter. Hense, mpls.

Regards,

Niranjan