MPLS / MLS difference?

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Can someone tell me if MPLS (multi protocol layer switching) and MLS
(multi layer switching) are essentially the same thing?


Re: MPLS / MLS difference?
Multi-Layer Switching (MLS) has become a highly desired method of
accelerating routing performance through the use of dedicated
Application Specific Integrated Circuits (ASICs). Traditional routing
is done through a central CPU and software. MLS offloads a significant
portion of routing (packet rewrite) to hardware, and thus has also been
termed switching. MLS and Layer 3 switching are equivalent terms.


Multiprotocol Label Switching (MPLS) is a standards-approved technology
for speeding up network traffic flow and making it easier to manage.
MPLS involves setting up a specific path for a given sequence of
packets, identified by a label put in each packet, thus saving the time
needed for a router to look up the address to the next node to forward
the packet to. MPLS is called multiprotocol because it works with the
Internet Protocol (IP), Asynchronous Transport Mode (ATM), and frame
relay network protocols. With reference to the standard model for a
network (the Open Systems Interconnection, or OSI model), MPLS allows
most packets to be forwarded at the layer 2 (switching) level rather
than at the layer 3 (routing) level. In addition to moving traffic
faster overall, MPLS makes it easy to manage a network for quality of
service (QoS). For these reasons, the technique is expected to be
readily adopted as networks begin to carry more and different mixtures
of traffic.


AT&T has rolled-out MPLS Private Network Transport - PNT

Hope this helps.

Brad Reese
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Re: MPLS / MLS difference?

www.BradReese.Com wrote:
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Thanks Brad. In some statements I've read, MLS is defined as the
explanation you've given for MPLS, i.e. treating packets from the same
flow the same by labelling each packet and imitating what was done to
the first packet. The first packet has to go through the router, but
subsequent packets in the same flow bypass the router and are handled
by the switch only.

In this definition for MLS, only IP is mentioned though. So would it be
correct to say that MLS using different protocols, such as ATM or FR,
is MPLS?


Re: MPLS / MLS difference?
You may have MPLS confused with MLSP.


The three major components of MLS are:

1. MLS route processor (MLS-RP)

2. MLS switching engine (MLS-SE)

3. Multilayer Switching Protocol (MLSP)


To determine the best path is the primary function of routing
protocols, and this can be a CPU-intensive process.

Thus, there is a significant performance increase with the offload of a
portion of this function to switching hardware.

This performance increase is the goal of the MLS feature.

Two of the three major components of MLS are the MLS route processor
(MLS-RP) and the MLS switching engine (MLS-SE).

The MLS-RP is the MLS-enabled router, which performs the traditional
function of routing between subnets/VLANs.

The MLS-SE is a MLS-enabled switch, which normally requires a router to
route between subnets/VLANs.

However, with special hardware and software, MLS-SE can handle the
rewrite of the packet.

When a packet transverses a routed interface, the change (rewrite) of
non-data portions of the packet occurs as the packet heads to the
destination, hop by hop.

Confusion can arise here because a Layer 2 device appears to take on a
Layer 3 task.

Actually, the switch only rewrites Layer 3 information and "switches"
between subnets/VLANs.

The router is still responsible for standards-based route calculations
and best-path determination.

You can avoid much of this confusion if you mentally keep the routing
and switching functions separate, especially when they are within the
same chassis (as with an internal MLS-RP).

Think of MLS as a much more advanced form of route cache, with a
separation of the cache from the router on a switch.

MLS requires both the MLS-RP and the MLS-SE, along with respective
hardware and software minimums.

The MLS-RP can be internal (installation in a switch chassis) or
external (connection via a cable to a trunk port on the switch).

Examples of internal MLS-RPs are the Route Switch Module (RSM) and the
Route Switch Feature Card (RSFC).


The third major component of MLS is the Multilayer Switching Protocol

You must understand the basics of MLSP to get at the heart of MLS and
perform effective MLS troubleshoot procedures.

MLS-RP and MLS-SE use MLSP to communicate with one another.

Tasks include:

The enable of MLS.

Installation of MLS flows (cache information).

Update or deletion of flows.

Management and export of flow statistics.

MLSP also allows the MLS-SE to:

Learn the Layer 2 MAC addresses of the MLS-enabled router interfaces

Check the flowmask of the MLS-RP.

Confirm that the MLS-RP is operational.

The MLS-RP sends out multicast "hello" packets every 15 seconds with
use of MLSP.

If the MLS-SE misses three of these intervals, the MLS-SE recognizes
that the MLS-RP has failed or that connectivity to the MLS-RP is lost.

The diagram above illustrates three essentials that you must complete
(with use of MLSP) to create a shortcut: the candidate, enable, and
cache steps.

The MLS-SE checks for the cache MLS entry.

If the MLS cache entry and packet information match (a "hit"), the
packet header rewrite occurs locally on the switch.

This rewrite is a shortcut or bypass of the router. The packet does not
forward to the router as normally occurs. Packets that do not match are
forwarded to the MLS-RP as candidate packets.

A local switch may occur for these packets. After the pass of the
candidate packet through the MLS flowmask and the rewrite of the
information in the packet header (without contact with the data
portion), the router sends the packet toward the next hop along the
destination path.

The packet is now an enabler packet. If the packet returns to the same
MLS-SE from which the packet left, a MLS shortcut is created and placed
into the MLS cache. Now, instead of the router software, the switch
hardware locally rewrites that packet and all similar packets that
follow (a "flow").

The same MLS-SE must see both the candidate and enabler packets for a
particular flow for the creation of a MLS shortcut. (This requirement
is why network topology is important to MLS.)

Remember, the purpose of MLS is to allow the communication path between
two devices in different VLANs, with connection off the same switch, to
bypass the router. This action enhances network performance.

With use of the flowmask, which is essentially an access list, the
administrator can adjust the degree of similarity of these packets. The
administrator can adjust the scope of these flows:

Destination address.

Destination and source addresses.

Destination, source, and Layer 4 information.

The first packet of a flow always passes through the router. From then
on, the flow is locally switched. Each flow is unidirectional.
Communication between PCs, for example, requires the setup and use of
two shortcuts. The main purpose of MLSP is to set up, create, and
maintain these shortcuts.

These three components (the MLS-RP, the MLS-SE, and MLSP) free up vital
router resources through the allowance of other network components to
take on some of the router functions. For certain topologies and
configurations, MLS provides a simple and highly effective method to
increase network performance in the LAN.


Brad Reese
BradReese.Com - Cisco Job Search

Re: MPLS / MLS difference? wrote:
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If you add a label, it *IS* MPLS.

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NO. That would still be MLS, it is only MPLS when a label gets attached and
THAT is used for the forwardimng decision. Multi Protocol LABEL switching.
Paul Matthews                 

Re: MPLS / MLS difference? wrote:

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They are way different.

Basically MPLS is the addition of a label to a packet such that only the label
need be read for a device to decide what to do with it. Initially this was to
try to speed things up as just a tag needed to be checked when routers did
stuff in CPU. The main advantage now is not performance as most ruters work in
hardware but separation. Through the MPLS network it is the label that needs to
be checked rather than the IP info.

That means an MPLS carrier could provide services to, say Microsoft and Cisco.
they could both use the same area of RFC1918 network addressing and be able to
function totally independantly.

MLS is Multi layer switching. The first packet in a flow will be processes in
CPU, and then a cache entry written to the switch engine so that subsequent
packets can be switched in hardware without having to trouble the CPU.
This is where thing like code red cause problems to the network. At the router
near the infected device traffic was being sent to random[1] addresses. These
were not previously in the cache and needed full lookup. If you had a router
with a large routing table *and* a default route the routing table was checked
then the packet was forwarded according to the default so it could cause the
same problem at the nest router. The real crippler was where a random address
hit a valid subnet within the network, and the taget router had to ARP for lots
of nonexistant addresses...

[1] I know it was not totlly random, but near enough...

Paul Matthews                 

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