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Home > Archive > CCNP > April 2001 > MLS-RP requirement
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MLS-RP requirement
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| Just for fun I started to read about Multilayer Switching in chapter 6 of the BCMSN book. I am now left with two questions, one of which I will present here.
Multilayer switching (MLS) requires a special Switching Engine (MLS-SE) and an internal or external router (MLS-RP). It is obvious that the MLS-SE needs to be special and therefore a little more expensive than a basic layer 2 switch. It is the requirement for the MLS-RP that puzzels me. Why can only high-end routers be used? I would think that given the "route once" nature of the MLS-RP task, a low-end router would be adequate for many installations where traffic volume is high but connection rate is low. Is there any technical reason why only a high-end router can do the job? Why not e.g. a 1600 with proper software (and enough memory to store it)?
Or is the only reason Ciscos need to "push you up the price list"?  (thanks to doctorcisco for the price list expression)
Your views appreciated.
Terje | |
| BlueBaron 2001-04-26, 10:05 am |
| Well, consider this. If you have a 6509, fully populated (you should have the internal RP anyway), you're going to have a LOT of flows to contend with. On top of that, you have whatever routing your router is already doing.
Of course, I wouldn't put it past Cisco to say that with the express purpose for revenue either.  | |
| Terje 2001-04-26, 10:29 am |
| MLS can be done with lesser equipment than the 6509, can't it? Could I use the 2900G and 5000 series for MLS?
Anyway, let's imagine I don't do (much) WAN traffic and that most of the inter-(V)LAN traffic is large (long-lived) file transfers. I would then think that the "switch many" event would happend frequently and therefore justify an efficient MLS-SE. The "route once" event would happend seldom so that I could get away with a slow but otherwise capable eksternal MLS-RP. Am I getting it right?
Of course there could be situations where connections are established and broken at high frequency and therefore justifying a high performance router.
Think about it while I write my next question.
Terje | |
| BlueBaron 2001-04-26, 10:38 am |
| 5000 yes . . . 2900 no. You need a Sup module to implement MLS.
I see where you're coming from, and I agree. I wish I had the gear to test this out right now (I will soon). I would bet, however, that you could probably get away with a lower end router . . . I don't think I would go for a 1600 . . . 3640 maybe. | |
| Terje 2001-04-26, 10:52 am |
| quote:
Originally posted by BlueBaron
5000 yes . . . 2900 no. You need a Sup module to implement MLS.
This is what I found at http://www.cisco.com/univercd/cc/td/doc/pcat/ca2926.htm :
"multilayer switching with the Catalyst 2926GS and Catalyst 2926GL". Didn't study this thoroughly though. I am new to MLS
quote:
gear to test this out right now (I will soon).
If they could supply the software that is...
Thanks for your input BlueBaron. I appreciate it. Nice to have some technical discussions in this forum...
Terje | |
| BlueBaron 2001-04-26, 10:54 am |
| DOH!! Don't I look like a bafoon. <=) Yes, it is indeed nice to have some technical discussions again. | |
| MadChef 2001-04-26, 11:48 am |
| quote:
Originally posted by BlueBaron
Well, consider this. If you have a 6509, fully populated (you should have the internal RP anyway), you're going to have a LOT of flows to contend with.
Not only that, but those flows are going to age fairly quickly since the flow cache is of limited size. Even though it's going to be doing a "route once," the router is still going to be making a lot of route lookups.
In the scenario given by Terje, it might not, but that's a very limited scope in which it would work.
I still don't like the router on a stick concept. In this day when you could put layer 3 functionality on a 4000 (which would give you a 2 gig connection between SE and RP) why would you want to limit yourself to a FastE connection to your RP? (My answer to that question would be "Because I CAN," but that's still not a good answer. )
MadChef | |
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| creamy_stew 2001-04-26, 6:31 pm |
| You know, I'm not sure if this is a pipe dream or not, but I seem to remember something about the RSM (MLS-RP?) in the 6509 being very similar to a 2500.
The reason I remember it is that, when I read it, I hadn't grasped the route-once-switch-many concept and so I thought, the other way around from Terje, Huh? A 2500 doing the routing for a fully populated 6509?
Now if I could only remember where I read that, it would lend some sense of credibility to my story.
Will try
/creamy |
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