WS-C4948E-S 10G/LACP Capabilities

[josepr]

Can I connect two servers with Dual 10Gbps NICs to the 10G ports on the switch and set up lacp for both using a src-dst-port (Load distribution on the source XOR destination TCP/UDP port) algorithm.

At the end each server should be able to communicate with each other at 20G and with all other clients on the 1G ports?

[dbeattie]

Yes, this should be possible. The 10Gbps ports are considered uplinks, but there is nothing special about them and they can be used as you suggest. Obviously, relevant L2 and L3 config has to be correct. Please also note the usual port-channel limitation that any one flow can only go over one link, so one connection (e.g. an ftp transfer) will only get to 10Gbps, not 20Gbps.

Hope this helps.

[josepr]

Thanks,

I wanted to make sure the 4948E supported src-dst-port lacp in the 10G ports so that connections running between different ports on the two servers would be distributed across the two links.

[dbeattie]

I can't say that I specifically remember put that command into a 4948E, but the command references can be found here:

https://www.cisco.com/c/en/us/support/switches/catalyst-4900-series-switches/products-command-reference-list.html

... and the latest one shows that "port-channel load-balance src-dst-port" is supported. I haven't checked earlier versions.

Hope this helps.

[nixpengu1n]

Hello,

Load-balancing method is a matter of IOS features and ether-channel configuration. More details could be found here:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swethchl.html

Also you may need to look at specific IOS release notes (depends what version you are using):

https://www.cisco.com/c/en/us/support/switches/catalyst-4900-series-switches/products-command-reference-list.html

Also, keep in mind that total throughput for both servers would be 20 Gbps, however one TCP stream will not exceed 10 Gbps speed. If rest of your clients are connected to the same switch with 1 Gbps uplinks, yes it is possible, however keep in mind that in best case scenario there could be no more that 20 clients utilizing 1 Gbps connection speed per server.

[Joseph W. Doherty]

". . . however keep in mind that in best case scenario there could be no more that 20 clients utilizing 1 Gbps connection speed per server."

Yes, although as clients generally are not busy 100% of the time, understand the increased aggregate bandwidth wouldn't only be useful to just 20 clients.

Also, as I noted in my other post, it's unlikely 20 clients would hash all their flows evenly across both links (an ideal best case). More likely, one link would become oversubscribed, while the other has excess bandwidth.

Lastly, when you have one host with 10x the bandwidth of the other host, often there will be transient egress drops upon egress to the lessor bandwidth host (this is a typical problem on the 3K switches, but your 4948 should behave better - you might also consider using your 4948's DBL feature if you do see egress drops).

[Joseph W. Doherty]

In addition to what the other posters have noted, also keep in mind your server will need to be configured to support LACP and the load balancing algorithm on the switch won't directly impact how the server will load balance it's egress to the LACP bundle. I.e. the switch will only load balance its egress traffic to the LACP bundle.

Also keep in mind, Etherchannel doesn't track how busy a link is, so a dual channel, on average, provides about a 50% boost over a single link. I.e. at best, expect your aggregate bandwidth to be 15 Gbps not 20 Gbps.