Re: PBR

From: Andrew Metcalf (prelude@mindspring.com)
Date: Thu Aug 02 2001 - 17:18:09 EDT


Whatcha all talkin' bout? Can't make no sense of it... PBRs a great beer!
Smooth, cheap....and made in America! It ain't fancy, but neither's I.

andrew
(who lives in the deep south)

----- Original Message -----
From: "David Sinn" <dsinn@microsoft.com>
To: "Kinczli Zoltán" <Zoltan.Kinczli@Synergon.hu>; "Fillet Platoon"
<fplatoon@yahoo.com>
Cc: <cisco-nsp@puck.nether.net>
Sent: Thursday, August 02, 2001 4:56 PM
Subject: RE: PBR

By default CEF, and fast/optimum switching does per-flow load-balancing.
You have to explicitly turn on per-packet load-balancing with the "ip
load-sharing per-packet" command. Regardless of what Cisco, or the
documentation call's it, by default it is per-flow (actually
per-destination which means that a flow will follow the same link).
Engine 2 LC's on GSR can not do per-packet load-balancing, regardless of
whether you can enter the command or not.

David

-----Original Message-----
From: Kinczli Zoltán [mailto:Zoltan.Kinczli@Synergon.hu]
Sent: Wednesday, August 01, 2001 7:49 AM
To: David Sinn; Fillet Platoon
Cc: cisco-nsp@puck.nether.net
Subject: RE: PBR

David,

   Most of our customers do use CEF. Many of them are using
it because the per-packet load-sharing feature. (Others do have
really huge routing tables, where other route caches are not
really effective.) They tipically share the load between 4 2Mbps lines.
(They could as well use more links...)

   According to the i/f counters the pps values, and the load,
calculated over 30 sec, are almost exactly the same on the links.

   Ok, not all the packets are of equal size, so you are right
to tell us, it's not a strict load sharing algorithm. The load
on the link is the number of bytes transmitted, not the number of
packets, perfectly true.

    An algorithm, you desire, would be such complex one, which would
- i guess - cause the traffic to be process switched. Are you sure
it would worth the effort/overhead/etc??

--Zoltan

PS: and i'm sorry to argue, but a given flow it not using the same
link out of a given router, or else it would not be called per-packet
load sharing

-----Eredeti üzenet-----
Feladó: David Sinn [mailto:dsinn@microsoft.com]
Küldve: 2001. augusztus 1. 3:35
Címzett: Fillet Platoon
Másolatot kap: cisco-nsp@puck.nether.net
Tárgy: RE: PBR

The simple answer is "no", but you have other options.

Cisco's load balancing is not intelligent, and is not balancing. It is
a fixed hash over the given number of links that cause a given flow to
always use the same link out of a given router. There is no feedback
mechanism. Thus you can have very clumpy traffic (especially on slower
speed links).

If you aren't on a GSR, then you could turn on CEF per-packet load
balancing but this means you need to run CEF, and very few people do
this, so you mileage will vary (i.e.. If you don't want to run CEF you
can turn off all route-caching and the router will per-packet load
balance by default. This method is not very elegant, but depending on
load MIGHT be acceptable. Either way you are telling the router to load
balance the traffic on a per-packet basis across the parallel links.
This can result in out-of-order delivery of traffic, so consider if that
is important to you. Also it is not a guarantee that the traffic will
still be well balanced, but is a better shot then having the flow based
load balancing you have now and resulting in the clumpy traffic you are
seeing.

You can also consider more L2 load balancing such as MLPPP or ATM-IMA.

ATM-IMA can work if you are talking about T-1's, and last I checked the
PA/NM's supported 8 T1's. It does mean you have to run ATM, which is
mostly considered a four letter word, so think about it deeply before
you jump. You also loose a fair amount total throughput due to
overhead, so you have even more to consider if you are on slow links.

MLPPP could also be an option, and is possibly your best if you control
both ends, and can take the CPU hit that it creates.

All in all it depends on what box you are on, and how much pain you can
endure.

David

-----Original Message-----
From: Fillet Platoon [mailto:fplatoon@yahoo.com]
Sent: Monday, July 30, 2001 8:39 PM
To: cisco-nsp@puck.nether.net
Subject: PBR

hello guys,

    my goal is to load balanced my point-to-point
links that have 8 parallel serial connection, so i
used EIGRP as my routing protocol and i used MHSRP
along with PBR on some of my selective source address.
Is there a routing protocol that intelligent enough to
detect that my Serial 0 connection is congested and i
will automatically redirect it to serial 1 or Serial 2
that is not congested? If not is there a way to solve
it? Is there a features in Cisco IOS that
automatically detect that the link is congested and
automatically redirect it to another link that is not
congested?

rgds,
fillet

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