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6400cl limit: 8,000 Downstream Hosts. What are they?

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Jesse S_1
Occasional Advisor

6400cl limit: 8,000 Downstream Hosts. What are they?

Hi,

I'm considering using two 6400cl switches as XRRP routers for a site. 3-5 static routes for internal subnets, and a default route to our firewall (to the internet). Servers on our LAN would use the 6400cl's virtual router as their default gateway.

In 6400cl in IP Routing Overview section it states that the 6400cl supports 8,000 "Downstream Hosts". What is that defined as? When are they created? I'm trying to judge whether that's enough.

I'm unclear on how a router would define "downstream" at all. Does each connection between a web browser on the internet and a server behind the 6400cl count towards this 8,000? Does that mean we'd be limited to communicating with 8,000 internet hosts in a certain timewindow? Or does this only apply to our hosts within the same layer2 area? Does it matter whether hosts are over the default route vs static routes?

The 5300xl is listed as supported 192,000, so I'm guessing the limitation is relevant. I'd consider using a 5300xl but they don't seem to support jumbo frames.

Are there any other practical limits I may run into when trying to use the 6400cl as my router?

Clarification greatly appreciated from anyone who knows! Thanks.
11 REPLIES
Jesse S_1
Occasional Advisor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Additionally, how does the "Network Subnet Addresses" limitation of 1,000 apply? We don't know the subnet of internet hosts (they're all unicast, 255.255.255.255 to us...)
Matt Hobbs
Honored Contributor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Hi Jesse,

Can you possibly get in touch with a local HP ProCurve technical consultant? I recommend you do as they should hopefully be able to provide you with this type of information.

The routing architecture between the 6400's and 5300's is quite different - although the 5300 has more 'downstream hosts' support, it does not have a network route table like the 6400. In effect, the 6400's tables get filled more slowly than that of the 5300's.

With either product though, for the fairly typical network that you are describing it's very unlikely that you will fill those tables.

Personally I'd recommend you seriously consider the 5400's. You've got a lot more future proofing built in that way.

Matt
Jesse S_1
Occasional Advisor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Thanks for your help Matt. Can you share any insight into what a 'downstream host' is? Is it any out-of-subnet (including internet/default route) IPs communicated with? How is the network route table used and how does it modify the host table behavior?

I understand if you don't have full details but any light you can cast on it would be helpful.

As for the 5400's... the docs on them seem to contain even less info as to what their limitations are! The switching speed specs look impressive, but like the 6400cl, that's not the concern... hard limitations like table sizes seem like they would be a concern first.

I may be able to get my hands on some 6400cl's to try out, but without knowing what the revelant resource limits are (and what they mean), it may be hard to even generate a test load!

Under a lot of conditions, 8,000 IPs might be fine, but under other conditions, one user with a bittorrent client can easily be talking to 400 IPs. Whether that's 400 out of 8000, I'd like to understand. Also what it does when it runs out of room in the table. Does it break, or does it just expire entries faster, resulting in more CPU usage? (from repeated lookups)

Thanks.

Matt Hobbs
Honored Contributor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

This is my understanding of how the two products differ, I'd recommend you still check from an official source if possible.

With the 6400, a downstream host is a device that is connected to one of it's own VLANs.

The network route table, is for your static and dynamically learned routes (RIP, OSPF).

In your example with just the default route, that would take up one entry in the network route table - so with with your bittorrent question, if you had one host talking to 400 IP addresses on the Internet, it would take up one entry in the host route table, and one entry in the network route table. Pretty efficient.

On the other hand, the 5300 uses source addresses and destination addresses in its host route table. As far as I can know this could use up to 401 host route entries on the switch. This does have one advantage which is that it allows the connection rate filtering (virus throttling) which is available on the 5300's.

If the hardware tables are filled, the switches will start routing in software instead.

Definitely evaluate the switches if you can and also see if you can speak to someone from HP on this topic.

Jesse S_1
Occasional Advisor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Thanks, that helps a lot. I'll definitely be trying to confirm this with HP. If that is the case, then 8,000 would be plenty.

One last bit I suppose. If I get my hands on some to evaluate, do you know of a way to see the size of the host route and network route tables? To confirm how many are being used in various situations. Perhaps a show command, or an SNMP OID?

Thanks much.
Matt Hobbs
Honored Contributor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

At this point in time I don't believe there is any user level commands or OID's that will give you this information. Sure would be nice though.
Jesse S_1
Occasional Advisor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Here's what HP ProCurve Support (PCC-Americs) had to say, in summary.

"Downstream Hosts" is another way of saying "Host Route Table." The 6400cl can handle 8,000 concurrent routing sessions. The 5300xl series can handle 192,000.

If you have 3 vlans configured and a default route to the internet (or another off-subnet destination), and a client on vlan1 opens sessions with hosts on vlan2, vlan3, and the internet, then that client is using up 3 entries in the host routing table. So it'd be easy to hit 8,000 potentially, but this is mitigated somewhat by the fact that traffic flows for most routed sessions are momentary. The real impact comes frmo sustained sessions, such as streaming video, long downloads, remote desktop sessions, bittorrent, etc.

He recommended looking at the 5300xl series if there wre concerns about the 6400cl capacity. He didn't seem to indicate any difference in utilization of the host route table between the two, but I've asked for some clarification in that regards. Also as to jumbo frames supporting models with substantially higher host route table sizes than the 6400cl.

It seems weird that they stick such small tables on these things!
Rion Odenbach
Occasional Visitor
Solution

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Please do not consider this sales advice. Please consult your reseller for sales advice.

The 3400 and 6400 have a similar architecure. The 4200 and 5300 also have a similar architecture. Let me clarify the documentation.

The 4200/5300 have a host route table. In user mode you cannot see this host route table. The host route table keeps track of both Source Address and Destination address. The chassis limit for this is 192k and the module limit is 128k. Each _flow_ will have its own entry. Each SA/DA pair will take up one entry in the host route table.

The 3400/6400 have both a host route table and a network route table. However, the Host Route Table on a 3400 only keeps track of the destination address. The HRT size is 8K entries and the NRT size is 1K. Depending upon where the frame is to be delivered the HRT could be used or the NRT could be used to deliver it to its destination. If the frame is to be delivered to a MAC that is directly connected, then the HRT is used. If the frame is to be deliver to a host/network that is another router hop away, then the NRT is used.

The number of routing table entries on a 3400 is smaller, however since it does not record source address, it does not fill as quickly.
Jesse S_1
Occasional Advisor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Rion,
Thanks for the additional input. If it works as you describe on the 6400cl, that would result in a significant reduction in host table entries used.

The main thing that I'd like to confirm in that arrangement. All traffic to the default route consists of one network route table entry (as opposed to trying to arbitrarily divide it out into /24's or something silly).

So if we had a network like this: 6400cl (router A), with a default route via router B (internet access), and a static route to 10.67.0.0/16 via gateway router C.

Then if we have two hosts connected to the 6400cl... host1 communicating with 100 IPs in the 10.67.0.0/16 range, host2 communicating with 100 IPs on the internet, and host1 and host2 talking to each other, then the table usage would be like this:

1 host route entry used for destination host1.
1 host route entry used for destination host2.
1 network route entry used for default route/internet access via router B.
1 network route entry used for 10.67.0.0/16 (via router C).

Does that sound right? In this case you can support communication with roughly 8000 local hosts, and up to 1000 subnets routed through another gateway (where the default route is treated as one entry also).

Thanks.
Rion Odenbach
Occasional Visitor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

This is not sales advice.

When host1 communicates with any device that has a mac directly connected to your 6400 switch, it will use a host route. If host 1 communicates with 400 hosts that are directly connected to the 6400, then 400 host routes will be created (if they do not exist already). Communications to endpoints that exist another router hop away will use a network route. Realistically, most customers will not have a problem with this. If you have more than 8000 attached hosts (that all talk to each other) at your site or if you have more than 1000 network routes, you need to get one of our bigger boxes.

You do realize that a 6400 is a 10gig only aggregation box, right? It needs to have switches that uplink at 10 gig. The 5300 is not 10 gig, and is a chassis. They are apples and oranges.

As others have sugguested, you should look at the 3500/5400 series. The reviewers guide with great information is located here:

http://www.hp.com/rnd/pdfs/ProCurve_Switch_5400zl_Series_Reviewers_Guide.pdf

Jesse S_1
Occasional Advisor

Re: 6400cl limit: 8,000 Downstream Hosts. What are they?

Yes, I realize that the 6400cl is a 10gig aggregation unit. That positions it well to potentially be a routing point. I'm not interested in obtaining 5300 series as it's neither 10gig nor does it have jumbo frame support. Any discussion of the 5300 limits is just as a comparison in routing table behavior. My interest is in developing a sense of what routing limitations the 6400, 3400, 5400, and 3500 units have. Unfortunately the very sparse and inconsistent documentation (and varied responses from sales support) make this difficult. Thankyou Rion and Matt for all your patience and assistance.

I am particularly interested in the 6400/3400 details because outside the L3 routing uncertainty (across all models), they seem to provide all the features we'd need at about 1/3rd the cost of the 5400/3500 setup. The 5400 provides a lot of expansion capability and features like PoE that we don't need. Also physically it's a lot more flexible for me to deal with 1U units than 3U and 5U chassis.

My main question there was how communication for a host on a 6400cl with 400 non-directly attached hosts (i.e. internet) would be treated. I understand it'll use a network route, but I'm looking for confirmation it will use only 1 network route table entry rather than some arbitrary division, such as one route per /24.

In the setup I'd like to use the switches in, there are only a few hundred hosts in the local L2 broadcast domain, but there are likely to be several thousand connections to internet hosts over the default route. So whether they use one network route entry per source IP-dest IP pair, or one route IP per destination IP, or one route IP per /24 of destination IPs, or one route total for all IP reached over the default route, makes a multiplicative difference in the numbers of routes I'd expect to use.

The reviewer's guides are very interesting documents. Looked at the one for the 5400 and the 5300 also (just for comparison of how they discuss layer 3 routing tables). Couldn't find one for the 3400/6400. Is there one hidden away somewhere?

I don't mean to be dense here, but the documents are very inconsistent in the terms and numbers they use within their own pages, or conflicting with other published specs, making the information confidence level low.

The 5300 reviewer's guide also indicates the the 5300 has a network route table, but statements have been made that the 5300 doesn't have a network route table, and the specs list it as supporting "192,000 downstream hosts". But both the 5300xl and 5400zl reviewer's guide list them as having "65,536 L3 host address routes" and "10,000 network address routes".

The 6400cl Advanced Traffic Management manual says the 3400cl/6400cl have "8000 downstream hosts" and "1000 network subnet addresses". The 6400cl specifications sheet says "Routing table size: 16000 entries". The 3400cl specification sheet says "Routing table size: 64000 entries."

Thanks again and have a good day.