3750 vs. 2821

Answered Question
Feb 25th, 2008
User Badges:

We have been recommended to move our routing services from a pair of 2821 routers to a pair of 3750 switches (with IPSERVICES). I was wondering if anyone has any statistics as to the throughput of the two?

I realize that there are many variables to consider, but I cannot seem to find any comparisons between the routing capabilities of these two products.

Thanks in advance for any input.

Correct Answer by Richard Burts about 9 years 1 month ago

Dave


I recently went through a similar discussion with a customer about whether to utilize 3750s to do intervlan routing or to use an external router. One aspect became important in our discussion and may be important in your situation as well and it depends on understanding your traffic patterns. If most of the traffic will be "internal" or inter-vlan traffic then there are advantages to using the 3750 to do the routing. If you use the router then you are sending a packet over a physical link to a different box, waiting for the box to make its routing decision, and sending the packet back over the same link so it can be forwarded to the destination VLAN. Now you have the performance of the link as well as the routing performance of the other box impacting the routing performance. If the routing is done by the 3750 then we eliminate 2 trips over the physical link and move data at backplace speeds instead of LAN speeds. If most of the traffic will be "external" (to and from outside addresses) then there may be advantages to having the external router to do the routing since it will need to handle the traffic anyway.


So what kind of traffic pattern do you think you are dealing with?


HTH


Rick

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4 (1 ratings)
Loading.
Edison Ortiz Mon, 02/25/2008 - 08:53
User Badges:
  • Super Bronze, 10000 points or more
  • Hall of Fame,

    Founding Member

The 2821's throughput is about 87Mbps (see attached file for more info).


Personally, I wouldn't move from a 2821 router to a 3750 switch for 'routing' purposes. You do lose some cool features that are part of the router architecture such as: Advanced QoS, NBAR among other things.


I would use the 3750 if you needed port density and routing all in one box.


HTH,


__


Edison.



dmcushing Mon, 02/25/2008 - 09:40
User Badges:

The reasoning behind moving to the 3750's is to improve performance and throughput. It has been recommended by a consultant as part of a VoIP initiative. They feel that the two 2821 routers in our environment don't provide enough horsepower to guarantee adequate VoIP performance. Mind you, no one (including ourselves) have done a network assessment to prove whether this is true one way or the other at the moment.


I just would like to have some sort of raw numbers on throughput comparing the two to see if the 2821 is really that much inferior to the 3750 for routing.


Thanks for the input regarding NBAR and QoS, it provides some additional fodder :)

srue Mon, 02/25/2008 - 09:50
User Badges:
  • Blue, 1500 points or more

without knowing anything about your environment, is it feasible to keep the 2821's for routing purposes and use the 3750(s) for switching only?

dmcushing Mon, 02/25/2008 - 09:59
User Badges:

Yes, I thought it would be feasible, but the consultants were touting the superiority of the 3750s over the 2821s. They have stated that the 3750's will provide superior throughput and reduce the overall latency. Their view of the 2821s were as a low-end router, while the 3750 would provide superior routing capabilities. I have my doubts since they will be switching + routing, as opposed to just routing on the 2821's.


However, I can't find any statistics on the 3750's routing metrics (throughput, etc.) in comparison to the 2821's, so I cannot demonstrate anything one way or the other.


As part of the re-architecture, we are also moving a lot of the routing to the multi-layer switches in our closets (3560's). That would make the 3750's our 'core' routers. We are a fairly small campus with about 1500 workstations.

lamav Mon, 02/25/2008 - 10:22
User Badges:
  • Blue, 1500 points or more

Hey, DM:


You know what...? Its great that you want to support your own cause, but you should be asking these consultants to prove their case by providing you with comparable statistics. It is their job to present you with enough information for you to be able to make an informed decision.


You should not have to search frantically for stats when you are paying top dollar (Im sure) for consultants to do that for you.


By the way, migrating to a routed access design is a good idea when you have a relatively small environment. Im sure you will not want a routed distribution layer to support inter-vlan routing, so migrating from L2 trunks to the core to L3 uplinks to the core minimzes the looped topology and keeps L2 traffic off your core, which is highly recommended.


Just my opinion...


HTH


Victor

srue Mon, 02/25/2008 - 10:25
User Badges:
  • Blue, 1500 points or more

so are the 2821's currently providing internal routing only then? is this some sort of routing on a stick scenario?

Correct Answer
Richard Burts Mon, 02/25/2008 - 10:35
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Dave


I recently went through a similar discussion with a customer about whether to utilize 3750s to do intervlan routing or to use an external router. One aspect became important in our discussion and may be important in your situation as well and it depends on understanding your traffic patterns. If most of the traffic will be "internal" or inter-vlan traffic then there are advantages to using the 3750 to do the routing. If you use the router then you are sending a packet over a physical link to a different box, waiting for the box to make its routing decision, and sending the packet back over the same link so it can be forwarded to the destination VLAN. Now you have the performance of the link as well as the routing performance of the other box impacting the routing performance. If the routing is done by the 3750 then we eliminate 2 trips over the physical link and move data at backplace speeds instead of LAN speeds. If most of the traffic will be "external" (to and from outside addresses) then there may be advantages to having the external router to do the routing since it will need to handle the traffic anyway.


So what kind of traffic pattern do you think you are dealing with?


HTH


Rick

dmcushing Mon, 02/25/2008 - 10:51
User Badges:

I would estimate that 70% of the traffic would be internal (inter-vlan) traffic. We have a large amount of Internet traffic (we are an educational institution), but the bulk of what I am looking at is inter-vlan.


Your explanation makes more sense to me than the 3750's being a superior choice as a router, thanks for the 'tweak' on my thinking cap!

Richard Burts Mon, 02/25/2008 - 11:02
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Dave


I am glad that I was able to enlarge the discussion. While comparing the performance of the boxes directly is intuitive and appealing it needs to be tempered with a "big picture" view of the processing environment.


Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forum more useful when people can read a question and can know that they will read responses that resolved the question.


HTH


Rick

dmcushing Mon, 02/25/2008 - 10:37
User Badges:

Your point is well taken. We are migrating to keep the L2 off the core and this migration from the 2821's to the 3750's was part of the recommendation.


I will see if they can provide stats, we have a design meeting coming up - I was hoping that I would be able to go to the meeting armed :)


I don't disagree with re-architecting in the manner that we are. In the long run I think it will be a superior model - I just don't want to find out that our bottleneck is going to be the 3750's which will be handling our core traffic along with core routing.

Joseph W. Doherty Mon, 02/25/2008 - 19:58
User Badges:
  • Super Bronze, 10000 points or more

With regard to raw performance, no comparison. 2821 is published in the pdf provided by Edison at 170 Kpps. The 3750 series varies per model but tops out around 38.7 Mpps. (About 227 times more performance.)


With regard to features, software routers like the 2821 are much richer.


What I've found effective is using 3750s for (branch) LAN routing (and the LAN gateway) but additionally use software routers for WAN routing, sized for the relevant WAN bandwidth. The richness of the software router is useful when you step down from gig speeds to typical WAN speeds. I.e. no router on the stick, instead (small) LAN routers AND (small) WAN routers.


PS:

For your description of 1500 LAN clients, I would consider the 3750 a bit lightweight for a "core" router. Better (more than 2x faster) would be the 3750-E series but even it has some subtle limitations. Possibly even better, although with the loss of stacking, are the 4900 series. Their not much faster (excluding the recent 4900M) than the 3750-Es but they are basically a 4500 without the chassis (i.e. industrial strength IOS).


PPS:

If you don't need multiple units, the 3560 series (also -Es) cost less than similar 3750(-E)s. Given the choice of a pair of routers, e.g. distribution/core, I would prefer stacking. Pros and cons, but Cisco recent VSS technology sort of endorses the advantages of one virtual device vs. separate pairs.

Actions

This Discussion