Don't use a 2626 for routing!

[Mathias Sundman]

I started the tread "Switch loop" a while ago because I were having problems with my network. After a lot of troubleshoting and discussions with HP tech support it turned out to have nothing with these potential loops but rather with the 2626 routing performance.

We have been using a number of 2626s todo routing in our network. It turned out to be a really bad idea!

A few months ago we started to notice the CPU utilization in these switches seemed to be very high 40-100% from time to time.

So last week I took an unused one and put it up for some throughput testing and found out that I were able to route about 900 Mbps (max packet size, measured with NPtcp) through it without the CPU utilization increasing more than a few procents. 900 Mbps was the same number as I were able to push between my two test-pc's with a crossover cable as well, so there was pratically no performance loss in routing it over the switch.

So, I then I moved on and tried to run the same test across my production network and were only able to push about 15 Mbps and the CPU utilization went up to about 80%!

So, I couldn't understand why my production switches were performing so badly when it performed so well in my lab. I got the answer from HP tech support last week:

I was under the impression that all routing were done in software (by the CPU) in the 2626, but that wasn't true.

The 2626 can route in the ASIC but it only has a host table with room for 128 hosts. That means that in my lab where only two pc's were connected the routing were done in the ASIC, but in my production switches the host tables are constantly filled up so my thoughput tests were therefor routed by the CPU and thous performs bad and shows high CPU utilization.

So, friday night I got a new 3400 installed in place of three 2626. To get more ports I reused two of the 2626s as layer two swithes with 24 VLANS defined, one for each 100Mbps port, and then a tagged gigabit port with all VLANS to the 3400. That way I got 24 100 Mbps ports out of ONE gigabit port on the 3400, all with diffrent IP subnets, but the routing now moved to the 3400 instead of 2626 that used todo the routing.

and WOW! What a diffrence! I can now push my 90 Mbps over the 100 Mpbs ports as I should, and my pings across my network are stable below 2 ms. They used to be jumpy between a few ms and up to 50 ms from time to time.

So it's like a brand new network! So this is just a warning to everyone else. Don't use 2626's for routing!

FYI: the 3400 has a host table with room for 64.000 hosts so it's much more cabable of doing real routing.

When reading the 2626 specs it seemed to me that the biggest routing limitations were that it could only handle 16 static routes and not dynamic routing protocols. None of these were of any concern for us, that's why we got the 2626's it the first place. I think the specs should be clear about this 128 entry host table as well as it's a very big limitation! That's not even mentioned...

//Mathias

[DataSquid]

Thank you! This was very helpful information.

[timmy b.]

Mathias,
Thanks for the detailed posting, it's nice to hear your success story!

[asdf_44]

Have you looked into the 2800?

[Mathias Sundman]

Yes, as always, to late I discovered that the 2800 series seems to be a quite capable router compared to the 2600. The specs for these swithes are a little un-clear though so I've opened a support case at HP to get an answer to the size of the host routing table on 2600, 2800, 3400 and 5300 and exactly how the host routing table is populated.

The HP support tech couldn't answer my questions either so I'm waiting for him to get some answer from the "next level of support" :-)

As soon as I know more details, I'll post them here.

[Peter Andersén]

Hi
I experinced the same problem but since i could trace how many host routes entries i got it is about 20.000 and my traffice is 25 Mbit/s.
So the only product that you can use from the above is 5300.
Why ?
There is so poor routing capacity in the software so if you can not use the ASIC none of the above switches handles 25 Mbit/s of traffice and this is not high performance stuff.
If you have not recieved information on how many host route entries there are.
2626 128
2824 4K
3400 8K
5300 128K/modul max in system 192K

So in my case it only works with 5300 and that is not because it is a faster product.
The only thing that makes it tick is that it has 128K of host route tables, but this will soon be full and then we would se what happens.

Peter

[Sergej Gurenko]

Is there any commands to how much "host route entries" are currently in use?

[Peter Andersén]

It does not look so, have not found any according to the manual the software should support listing of it but i have not found it thru SNMP and the CLI.
The hunt goes on.....


Peter

[T. Joebstl_1]

Anyone knows the limit of the routing table on the 4100gl series?

Regards,
Thomas

[Preston Gallwas]

Yeah, we've got a 4104gl, which I sold to management as the greatest thing since sliced bread for saving money by using it to route to a subnet... :|