What machine do I need to do full BGP?

[laloperez]

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)

[djankovic]

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]

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.

[kerek]

Hi,

I think the last question implied the fact even if you have multiple upstream providers (using bgp) the routing table size won't be multiplied but the bgp table will have more entries.

Krisztian

[djankovic]

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]

Hello

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.

hth

[laloperez]

Hello,

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]

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]

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]

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 :))