What machine do I need to do full BGP?

Answered Question
May 15th, 2007
User Badges:

Hi all,

My company is planning to do full BGP with two providers with which we are now using default routing for the out packets mixed with BGP for announcing our prefix. My concern is that I'm uncapable to determine the correct machine to do it. I presume that anything less than a 7600 or 6500 is unuseful, but even with that gear, I'm not sure if it's better a 6500 or a 7600. I can't get the differences between them for us. Worse, which supervisor is the minimum for support the 250000+ BGP routes? 32, 720 (which incarnation?)? I'm lost :O

By the way, we're a hosting company and all of our connections are FastEthernet or GigaEthernet (with providers and the other switches)

Correct Answer by Darren Ramsey about 10 years 1 week ago

Don't bother with the 2800 or 3800. I'd go with a 7200 series. Either the new 7201 which is a sweet little box http://www.cisco.com/en/US/products/ps7253/index.html

or a 7204/7206 VXR bundle. You'll want the NPE-G2 with 1Gig ram. The Sup720-3BXL will work, but as stated in a previous post, it's way too much hardware just to hold the BGP table.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3.7 (6 ratings)
Danilo Dy Tue, 05/15/2007 - 04:18
User Badges:
  • Blue, 1500 points or more


For full BGP, the minimum requirement is 256MB DRAM. Therefore you need a router that can support 512MB DRAM.

A 3800 Series router is a good choice. A 3845 Router can support multiple NM/WIC on its 4 NM Slots and it comes integrated with 2GE and 2SFP Port with redundant power module and is upgradeable to 1GB DRAM.





laloperez Tue, 05/15/2007 - 07:41
User Badges:

And is it capable of handling a 100+Mbps conection to internet and the bgp table? What about a 2821 with 1Gig that we already owns?

We expect to need to route 250Mbps in a year from now and want to maximize our investiment, but don't want to oversize the machine. And, of course, inmediate expenses are important, too.

If you want to handle full Internet routing table than you have to first consider the memory available on you router as you routing and bgp table will become huge.

The number of prefixes received affect the memory and not the cpu. If you have many bgp peers than you have to consider the cpu as well. I think in this case choose the box with higher memory.

Anyway if you provide hosting services it is also wise to consider the packet forwarding performance of your box.

Here you can find some info about the performance of various products:


Pls rate if helps,


laloperez Tue, 05/15/2007 - 07:37
User Badges:

But I need traffic going towards the Internet at 100+ Mbps. I thought that the "traditional" routers can't barely handle such traffic and the bgp thing at the same time. If that's not the problem, a 2821 with 1Gig DRAM would be enough, wouldn't it?


If you take a look at the link I have posted earlier than you will see the 2821 has about 87M capability. If you plan to route this kind of large traffic than I think at leat 3800 series can be suitable. If you have to invest in new equipment as it looks than consider multilayer switch. They are also able to run BGP, OSPF (with appropriate image) and have much better performance.

Please rate if helps,


laloperez Tue, 05/15/2007 - 08:13
User Badges:

Thank you, I didn't see the item about 2821 until later. What puzzles me is that when you go for multilayer, things get complicated. We are using a pair of 4948 and they're fantastic for LAN switching and routing. But are limited to 32000 entries in the routing table 'cause of CEF, which is no possible to disable.

I'm going to check the 3800.

Danilo Dy Tue, 05/15/2007 - 17:23
User Badges:
  • Blue, 1500 points or more


For full BGP, the order of importance are;

1. Memory Capability

- 256 Minimum upgradeable to 512MB and above

2. Interface and Modules

- Thus it support your LAN/WAN Interface?

- Would there be slots available for future expansion?

3. Performance

- Do you need high performance?

- What where you hosting anyway to need such performance?

- Are you a big ISP with thousands of subscribers, multiple hosting, AS transit, or just a small to medium Data Centre

Though it would be nice to choose the biggest router available, but big is not always the best choice in terms of cost (one-time and recurring). A true solution architect will look for the suitable router, not always the big router - that's why companies employed network professional, else they can just call a sales representative from a vendor.


nikolasgeyer Tue, 05/15/2007 - 16:23
User Badges:
  • Bronze, 100 points or more

Hi there,

Reading your original and follow up posts, from what I can gather you need a router to provide;

- Full BGP routing

- Capable of 250Mbps+ sustained transfer

- Value for money.

The 3845 will do what you are after, however it maxes out ~250Mbps (using CEF switching). While it is a great value router, if you really are going to be doing 250Mbps+ then I would look at something a little bigger.

My reccomendation would be for the Cisco 7206VXR with NPE-G1. The NPE has 3 built in gigabit ethernet ports, it will handle 256000 routes and can support ~520Mbps of traffic using CEF switching. They are great value as well either brand new or second hand from an authorized reseller. The good thing about it as well is it performance starts to become an issue, you can throw in an NPE-G2 which supports ~1Gbps. Its also extremely modular and supports a range of cards if required(ethernet, pos, atm etc).

To answer your question about the 6500/7600's and route table sizes etc, the Sup720 and Sup720-3B both support 256,000 routes and the Sup720-3BXL supports 1,000,000 routes. The Sup720 supports ~15Gbps of throughput using DFC cards and ~7.5Gbps using non DFC cards.

As above, personally I would look towards the 7206VXR with NPE-G1 (or 7301 which is essentially the same thing but in a smaller box which is conveniant if you dont see yourself adding lots of cards in) based on value and requirements. The 6500/7600 seems overkill for this application unless you are also going to do something else with it.


Correct Answer
Darren Ramsey Tue, 05/15/2007 - 16:37
User Badges:
  • Silver, 250 points or more

Don't bother with the 2800 or 3800. I'd go with a 7200 series. Either the new 7201 which is a sweet little box http://www.cisco.com/en/US/products/ps7253/index.html

or a 7204/7206 VXR bundle. You'll want the NPE-G2 with 1Gig ram. The Sup720-3BXL will work, but as stated in a previous post, it's way too much hardware just to hold the BGP table.

laloperez Wed, 05/16/2007 - 00:03
User Badges:

Will it be safe to use a machine capable of 256000 routes, if the internet table is now more than 200000 entries? That's the fear I have, cause all this machines with CEF are blazing fast, but die quickly if the FIB gets exhausted, and I don't know if a 7200 will run out of FIB space in a year.

laloperez Wed, 05/16/2007 - 01:43
User Badges:

I've just read the characteristics of the new 7201 and I think it's perfect!

Thank you!

djankovic Thu, 08/30/2007 - 05:59
User Badges:

What about Catalyst 6509 with SUP-32 engine? Does it support 256k routes? Will it's processor be enough if I have 3 Internet uplinks? How much traffic can I expect for it to support?

laloperez Thu, 08/30/2007 - 06:53
User Badges:

As you can read through the rest of the thread, it depends on your needs. The Sup-32 supports 256k routes on CEF, but if you need to support 3 uplinks, it may be not enough. What kind of interfaces are those uplinks? Basically, if you need high speed in many interfaces (>=1Gbps) you'll use a 6500 or 7600 (or greater). If you need moderate traffic rates (total throughput less than 2Gbps) and full BGP you'll done with a 7200 and a NP-GE1 or 2 processor. If you need full speed but just partial BGP, you can use the Sup-32 or the basic Sup-720.

But, if you need full speed AND full BGP, chances are that you'll need a latest Sup-720 in a 6500 or 7600, OR go for a 12000 series.

IMHO, 256k maximum routes support is a bit risky these days if you need full BGP (even riskier if you need to peer with more than one provider)

djankovic Thu, 08/30/2007 - 09:30
User Badges:

What exactly is limitation of Sup-32. Is it the fact that is supports 256k routes in CEF? Is it the CPU or memory? Aggregate traffic is around 1Gbps. Why is it riskier if I have more than one upstream? Routing table should have almost the same number of networks?

laloperez Thu, 08/30/2007 - 23:46
User Badges:

Well, Sup32, as well as Sup720 uses CEF to switch packets. The size of the CEF hardware "pipes" limits how many simultaneous switched routes you can have. If there are more than that number, it uses CPU and main memory to process the packets, and performance dies (and performance is why you buy a 6500 in first instance). It's not a main memory nor a cpu issue, just a limit of the ASICs that make the CEF architecture.

If you have more than one upstream, CEF must aggregate information from all the upstreams in order for BGP to calculate the paths. Today there are more than 233000 entries in the BGP table, and growing. So I think it's a bit close to the Sup32 (or "low-end" Sup720) limit. It's not a cheap system to invest in if in a year may be obsolete.

By the other way, for 1G of aggregate traffic, you could perfectly use a 7200 series with the latest processor card that gives you 2Gbps and has no problems with the BGP table.

I don't understand your last question, sorry.

djankovic Fri, 08/31/2007 - 00:56
User Badges:

So CEF would become an issue if routing table grows over 256k entries, but for now it would work fine. What about 7200? What is his maximum number of IPv4 routes? I can't find this information on web. What about other resources on SUP32 system? It has 300Mhz processor. Do you think it can become an issue?

agugger Fri, 08/31/2007 - 02:18
User Badges:


It?s a little strange discussion. What do you understand under full BGP?

This make sense if connect to two or more different Providers, probably in different cities.

The pure bandwidth (Mbps) and the Performance (Mpps/Kpps) are a secondary issue.

Think about the security needs with ACL etc. in such a Router.

If you would go to two Providers with the full Internet Routing table in your Machine then do you have the following choice:

-A classic 7206 with NPE-G1 or better NPE-G2 and enough Memory (more or less the Max).

-Or a 7600 Router with Supervisor 720BXL and no other supervisor, only the BXL have enough TCAM space.

To the difference C7600 and C6500 use most the same hardware but the IOS is more Provider oriented.

Routers below the 7200 need at least enough memory to handle the Internet in BGP and enough performance to handle the security needs.


laloperez Fri, 08/31/2007 - 03:38
User Badges:


With full BGP I meant the complete BGP table. Many providers let you do partial BGP with them, i.e., pass you their own routes and the ones from their customers. That can reduce the table from a 10 to more than 50% of the original size, depending on the size of the provider, and, eventhough it doesn't provide the best route election, may be enough for one needs.

I agree with the rest of your comments, but why do you consider the discussion strange? For one not familiar with the Cisco hardware portfolio and the CEF operation, sounds weird that a multi-thousand-dollar machine would have problems with BGP that a not-so-many-thousand one won't have. Maybe because CEF confuses things, and people doesn't realize that a switch, even with routing in it is mainly for LAN use, and if you go outside, you need a real router.

alfredos Fri, 08/31/2007 - 04:08
User Badges:

Hi. To summarize, you can maintain a full BGP table with two providers and its associated CEF table in a router with as little as 512 MB RAM. If you filter inbound announcements a bit (you don't really need your providers to do this for you, you can do it in your end), then you can get away with as little as 128 MB, but then you would loose the advantage of the full feed.

The problem with the 2800s is their switching performance. If you really need full BGP tables, then odds are that you will require a switching capacity of hundreds of thousands of packets per second and upwards; the 2800s will not reach that figure by far. The switching performance is often overlooked but is actually the most important difference between the multi-thousand-dollar box and the not-so-many-thousand one; so much so that it is what justifies much, if not most, of the price difference.

If you are not sure, then I would advise to either stay well clear of full BGP feeds and look at the problem you are trying to solve again; or to seek professional advice in building and maintaining everything (shameless plug here), because it is not trivial and a single bad operation on a minimalistic design (which is what you are doing) will effectively disconnect your whole network from the Internet for as much as hours.

laloperez Fri, 08/31/2007 - 06:52
User Badges:

Hola Alfredo ?Qu? tal? :)

I'm not sure who are you answering to, this is beginning to become a little mesh. What was in first instance a post for getting help for myself has became one to help djankovic. If you read the first posts, they are from May, but reappeared a few days ago. Since May I've learned a few things, and now I am pretty sure of the solution .In fact, we are implementing it: two 7204 NPE-G2 for external routing/BGP peering and the two 4948 for inter-vlan routing in a partial mesh topology with HSRP and such redundancy things. It's enough for our needs and much cheaper than a 7600/6500 with Sup 720XL. As I said to djankovic, the solution for him depends a lot in your particular needs, current topology, budget, growing previsions, etc.

laloperez Fri, 08/31/2007 - 03:18
User Badges:

As I said before, I'm not sure a Sup32 would be able to handle the complete BGP table at this moment. Take into account that for using BGP to be meningful it's necessary to have at least two upstream prividers, and the combined BGP information could exhaust the TCAM space in the 6500.

The 7200 has no problems with the BGP tables, because it stores all in system memory, and not depends on CEF restrictions. Its limits are in the performance area: you can't attach some fast or gigabit ethernet access switches to it and pretend to distribute packets between vlans at full speed. But for upstreams up to 1Gig with the NPE-G2 would be enough.

The performance of the Sup32 depends on many factors: the backplane (32Gbps shared between cards), the cards used (not all available can use the full bandwidth), and such. It's a real complex question. You need to review the characteristics of the different cards you'll use and see if they match your requisites.

Anyway, what's your network topology? What will you be using the 6500 for? It's not the same to use it for internal routing between vlans and let another router (a 7200, i.e.) to do the external, than to try to do all the work with it. As a rule of thumb, if you don't need multigigabit upstreams (>1Gbps aggregate) BUT need BGP and inter-vlan routing in your network, use a fast CEF multilayer switch for the inner LAN, and a traditional router for the external connection for BGP (unless you have all the money you want and can afford a 7600 with the last Sup 720 - the one with 1 million routes in CEF :))


This Discussion