Richard Burts Thu, 11/06/2008 - 19:49
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If we knew more about your situation and your requirements then we could give better advice. For example how heavily loaded do you expect the 100 Mbps link to be? If the average load is about 10 I might recommend one router but if the average load is about 70 then I might recommend something different. It also would make some difference what you expect the router to do. It is one thing if the router is only going to route between an inbound and an outbound interface. But if it is going to do packet inspection, or firewall functions, or address translation, or other services then a different router might be called for.

On the light end of the load I might recommend something like an 1841. If you expect medium range of loading then I would suggest something like a 2821 or 2851. And if you expect the load to be pretty heavy then I would suggest a 3825.



tcordier Fri, 11/07/2008 - 02:58
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As Ron suggest it depends very much on the load you expect on the line, and the additional services (encryption, NAT, or QoS). If you expect a link usage of more than 50MB, I personally would hit a little higher and recommend 72xx series routers. The 3845 will not offer full line rates for more than 50MB. Especially when you plan to use additional services and you have traffic rates higher than 50Mb, the 72xx (G1 or G2) is needed. If you need only FastEthernet ports, and no additional cards, you will also find that the 72xx G1/G2 is only a little more expensive than the 3845.

HTH, Thomas

Joseph W. Doherty Fri, 11/07/2008 - 04:49
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As the other posters have already noted, router sizing depends much on how hard you'll actually push your 100 Mbps link and also on what features you might enable. It also can depend on your average packet size, since smaller packets are more demanding, and might depend very much on what the packets contain especially when using additional router featues.

Surprisingly to many, many of the smaller software routers, although they may be equiped with gig Ethernet interfaces, often struggle with actual traffic rates beyond 10 Mbps. However, if you keep in mind they are often oriented for WAN routing, where a T1s or E1s are common, their performance is fine.

If you really needed to be able to substain 100 Mbps (duplex), your choices start with the 3845 and then jump to the 7200/7300 series using a G1 or G2 (or NSE) engine.

What you might also consider, if their features are sufficient, is usage of a 3560 or 3750 switch; or the 3750 Metro switch (a bit software feature richer than LAN 3750).


Thomas notes the 3845 does not offer more than 50 Mbps. It's true, Cisco doesn't recommend the 3845 for more than one T3 (45 Mbps), but they note the router's Fast/CEF switching performance as 500 Kpps and 256 Mbps for 64 byte size packets. Given these specs, the 3845 should manage 100 Mbps (duplex) Ethernet unless you drop into process switching, which enough of, will bring down a G1 or G2 below 100 Mbps altough you start with more reserve capacity with those.

sunjoseph Fri, 11/07/2008 - 08:46
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I don't need any of the integrated services, just need to set up vlans. I want to know if much benchmark testing has been done with out the integrated services.

Joseph W. Doherty Fri, 11/07/2008 - 10:25
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Sometimes Cisco lists outside benchmarks (Miercom's?) they've (I assume) have purchased. However, I've also attached Cisco references for the performance of various routers and switches.

sunjoseph Fri, 11/07/2008 - 10:32
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What do you think about the 1811 and 100Mbps when all we're doing is basic internet services and online database access?

Joseph W. Doherty Fri, 11/07/2008 - 10:49
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An 1811 appears to be rated at 70 Kpps, which is rather light if you need to fully drive 100 Mbps. However, as Rick noted, if your actually traffic usage volume is very light, an 1811 might be fine.

sunjoseph Fri, 11/07/2008 - 10:57
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Most of the traffic is database access which uses a 1460 bytes packet size by default (Sybase SQL Server Anywhere). By our calculation the packet per second required is 3069.

Does this seem reasonable?

Thanks for your posts.

sunjoseph Fri, 11/07/2008 - 11:00
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We are going to max out the memory, hopefully this will help in processing packets. By default it comes with 128MB and we are going to expand it to 384MB.

Joseph W. Doherty Fri, 11/07/2008 - 11:07
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Additional memory is most helpful for newer, and larger, IOS images, or huge route tables, e.g. Internet, but extra memory, I believe, doesn't often offer much benefit otherwise.


Realize routers are not like typical hosts where extra RAM might reduce virtual memory paging or increase a disk/file cache.

Joseph W. Doherty Fri, 11/07/2008 - 11:12
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Reasonable? In what way? Your numbers would generate about 36 Mbps, which, I would think would be a rather busy SQL server. Depending on the nature of the SQL interaction, lots of full sized packets might be suspect. I would expect SQL queries to be smaller, as I also would for SQL transactions.

sunjoseph Fri, 11/07/2008 - 11:19
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I'm using "Mbps calculated by pps * 64bytes * 8bits/byte" from the document regarding the performance of the 1811 which provides 70kpps. we are calculating it based on Sybase's default packet size of 1460 byte it should still be able to maximize that connection. Speed is dependent on packet size from the document.

Joseph W. Doherty Fri, 11/07/2008 - 14:57
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The PPS rate falls as the packet size increases for the same bandwidth.

For example, 100 Mbps Ethernet line-rate requires about 149 Kpps for 64 byte frames but only about 8 Kpps for 1518 byte frames.

Given that the performance of the 1811 is 70 Kpps for 64, we can see it falls far short of 100 Mbps, but you can't assume is will also deliver 70 Kpps for 1518 bytes frames, which if it could would provide about 875 Mbps. However, the PPS rate usually decreases slower then the packet rate size increases which means an effective increase in bandwidth. If the 1811 could deliver 16 Kpps for 1518 sized frames, it could push 200 Mbps.

I doubt Sybase's default packet size is 1460, more likely that's it's maximum segment size.

roger.sambora Mon, 01/10/2011 - 10:40
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Had a question for you: Would a Cisco 3845 work better as a head-end router for terminating IPSec sessions from remote sites over a Cisco 7206..or ther other way around, using a VSA IPsec card on the 7206 router?

Basically, this router will be using 1 dynamic crypto for remote-sites establishing ipsec sessions to it only - no routing traffic or user traffic over these dynamic tunnels - just basic snmp traffic for mgmt.



paolo bevilacqua Mon, 01/10/2011 - 11:38
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You should open new thread for new discussion.

You should also state you circuit speed and expected utilization.


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