[c-nsp] jumbo frame over the VLAN

[Peter Rathlev]

On Thu, 2009-10-29 at 17:11 +0800, tseveendorj wrote:
> My problem is Guest OS couldn't access to MD3000i via mtu 9000.  May you 
> ask how to know. request timed out when I'm pinging from ESXi CLI with 
> vmkping -s 9000 IP address of MD3000i.
> 
> I think may be cisco 3560-E added VLAN header byte in front of packet 
> then mtu 9000 didn't match. If i'm wrong please correct me.

As far as I know ping utilities like "vmkping" use "-s" to specify
payload size, i.e. "-s 9000" means 9000 bytes payload and 28 bytes
header (ICMP + IP), resulting in something that needs a 9028 byte MTU.
You should probably test with "-s 8972" instead.

If the connection is a trunk you use 4 bytes for the 802.1q tag. Cisco
switches automagically make room for this, I don't know about VMware or
other equipment.

You could also try to adjust the MTU in the switch; the 3560E seems to
support up to 9198 bytes.

Bear in mind that "jumbo frames" isn't a standard in any way. (At least
yet.)

-- 
Peter