load sharing per packet vs multilink

Unanswered Question
Nov 26th, 2007

Dear all,

i had confusion as what is the difference between load sharing per packet and multilink

Pl. explain or give me link to document

mahesh

I have this problem too.
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guruprasadr Tue, 11/27/2007 - 04:05

HI Mahesh, [Do Rate all HELPFUL POSTS]

In addition to the Link Provided by BVS:

In definition:

Load Sharing (Per Packet):

Per-packet load balancing allows the router to send successive packets over each Link configured for Load Sharing.

It works with the Logic of round-robin method to see which path each packet takes to the destination.

==> Refer Link in POST of BVS.

MLPPP:

2 - Circuits of equal TYPE and Bandwidth are Bundled togther for Load Sharing. It doesn't follow the per-packet / per-destination techniq whereas the overall Usage is Balanced across the Circuits.

Anyway, in MLPPP its quiet difficult to track for any Circuit Changes(Up / Down).

==> Refer Link in POST of BVS.

Do Rate all HELPFUL POSTS

Best Regards,

Guru Prasad R

bvsnarayana03 Tue, 11/27/2007 - 05:16

Guru bhai,

Thanks for addition. Generally answers posted from office are too short & to the point bcoz of the load, but no matter what the load, i cant resist from checking the forum.

guruprasadr Tue, 11/27/2007 - 21:16

HI Narayan,

Good Day ! !

Normally i feel difficult to provide Links in my Replies becoz i have to maintain the habit of consolidating the cisco useful links.

Its always nice to see U active on the Forum.

:-) I appreciate your answer with regards to the Question on Split-Horizon

Best Regards,

Guru Prasad R

mahesh-gohil Wed, 11/28/2007 - 01:16

Thanks all,

dear Guru,

i am much clear about load sharing per packet.

But not about mlppp as how traffic will be shared among two links of multilink

is it like if i have two links bundled to mlppp.. and in such cases before passing traffic router will decide to send half of traffic to one link and rest to another ?

pl. make it more clear to me

regards

Mahesh

bvsnarayana03 Wed, 11/28/2007 - 02:03

The Multilink Protocol (MLP) uses packet fragmentation and a round-robin link assignment technique to distribute portions of data traffic over the various links within a bundle.

A router at one end of the bundle separates a long IP packet into two or more fragments and adds an MLP sequence header to each fragment. The load-balancing algorithm distributes the fragments taken from each packet over an appropriate number of the links, to allow parallel transmission through the bundle. In this manner, packets from a particular flow actually utilize any or all of the links in the bundle.

The communications over parallel links may encounter different delays in transmission. Fragments of one packet or succeeding packets may arrive at the receiver in a different order than when sent out over the multilink bundle. The PPP Multilink Protocol therefore uses packet sequencing to order fragments and packets. Specifically, a sequence number included in the header of each fragment of a packet allows the receiver to properly reorder the fragments and packets as they arrive over different links in the bundle.

The use of the sequence numbers, the differences in transit time through the links and the subsequent reordering all add delay and processing time.

guruprasadr Wed, 11/28/2007 - 02:04

Dear Mahesh, [Pls Rate all Helpful POSTS]

Traffic across the links in a multilink should get equally loadbalanced as the packets are equally fragmented across each link rather than each packet on each link .

So , even with the BW configured differently traffic would be distributed equally and if link capacity is less when compared with others , there would be drops and it would in turn affect others as the packets are fragemented equally across the links.

Consider 2 - T1s into a multilink bundle. This treats both physical links as part of a single logical interface. All Traffic (to and fro) are only via the Logical MLPPP Interface.

Do Rate ALL HELPFUL POSTS.

Best Regards,

Guru Prasad R

mahesh-gohil Wed, 11/28/2007 - 21:52

Ok,

Now what happens if I configure

no ppp multilink fragmentation

and how will be result if one link is down or is less reliable

does mlppp considers these parameters to provide better result

Regards

Mahesh

guruprasadr Wed, 11/28/2007 - 23:19

Dear Mahesh, [Do Rate if HELPS]

As told before, its Quiet difficult to track the Link Changes like Up / Down in case of MLPPP where the links are Bundled each-other and considered as single logical path.

MLPPP is best suited for environment where both the Links in Bundle are of Equal Capacity. Because during packet fragmentation (with MLPPP) on un-equal links the possibility of Packet losses since the MLPPP fragmentation of Packet is equal among the Links.

Dont worry, If one Link is DOWN all traffic will be re-routed via another link. After the restoration again the normal B/W sharing happens.

If the Link is UP with some reliability Issue faced means, please go-ahead and disable the Link unless the reliability is restored to avoid the packet drops.

Pls RATE if HELPS

Best Regards,

Guru Prasad R

bvsnarayana03 Thu, 11/29/2007 - 00:12

Enabling fragmentation reduces the delay latency among bundle links, but adds some load to the CPU. Disabling fragmentation may result in better throughput.

If your data traffic is consistently of a similar size, it is recommended disabling fragmentation. In this case, the benefits of fragmentation may be outweighed by the added load on the CPU.

bvsnarayana03 Thu, 11/29/2007 - 23:51

Also refer to the below link which had discussion on multilink. Refer to the 3 post from last for understanding how load-balancing works.

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddc720b/18#selected_message

pls rate if helped.

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