How do you test for the MTU between two filers to verify they can pass jumbo frames for SnapVault?
A standard method of determining whether your ethernet communications channel can transmit a particular MTU is to "Ping for the MTU"
The syntax to do this with Windows is shown below. Linux has similar capabilities to set a "do not fragment" bit, but I could find no such option in ONTAP.
What is the test method for ONTAP?
Ping for the MTU
================
Windows Ping Syntax:
ping -f -l 1472 4.2.2.2
-f = do not fragment
-l = set size in bytes
1472 = a common max frame size with DSL
4.2.2.2 a root level domain name server
(example only, use your destination instead)
Use this format of ping to determine the MTU
for the path between your source and destinaton
When I try pinging with large MTUs in ONTAP, the latency increases as shown below, indicating that the ICMP is being fragmented by the intermediate nodes.
Also anyone have any idea why 65456 bytes is the ONTAP limit in this case?
And yes I know that I do not have Jumbo Frames configured on my 3050 below as I was just trying to get the ping syntax for "do not fragment" and had not set up the intermediate nodes yet.
--- 10.10.5.103 ping statistics ---
3 packets transmitted, 0 packets received, 100% packet loss
3050B> ping -s -v 10.10.5.103 65457
ping: wrote 10.10.5.103 65476 chars, error=Message too long
ping: wrote 10.10.5.103 65476 chars, error=Message too long
--- 10.10.5.103 ping statistics ---
2 packets transmitted, 0 packets received, 100% packet loss
3050B> ping -s -v 10.10.5.103 65456
65472 bytes from 10.10.5.103 (10.10.5.103): icmp_seq=0 ttl=127 time=12.577 ms
65472 bytes from 10.10.5.103 (10.10.5.103): icmp_seq=1 ttl=127 time=12.360 ms
65472 bytes from 10.10.5.103 (10.10.5.103): icmp_seq=2 ttl=127 time=12.223 ms
3050B> ping -s -v 10.10.5.103
64 bytes from 10.10.5.103 (10.10.5.103): icmp_seq=0 ttl=127 time=0.506 ms
64 bytes from 10.10.5.103 (10.10.5.103): icmp_seq=1 ttl=127 time=0.632 ms
64 bytes from 10.10.5.103 (10.10.5.103): icmp_seq=2 ttl=127 time=0.509 ms
3050B> ifconfig -a
e0a: flags=0x2d48867<UP,BROADCAST,RUNNING,MULTICAST,TCPCKSUM> mtu 1500
inet 10.10.211.7 netmask-or-prefix 0xffffff00 broadcast 10.10.211.255
partner inet 10.10.211.6 (not in use)
ether 00:a0:98:03:71:0a (auto-1000t-fd-up) flowcontrol full
e0b: flags=0xad48867<UP,BROADCAST,RUNNING,MULTICAST,TCPCKSUM> mtu 1500
ether 02:a0:98:03:71:0a (auto-1000t-fd-up) flowcontrol full
trunked jumbo
e0c: flags=0xad48867<UP,BROADCAST,RUNNING,MULTICAST,TCPCKSUM> mtu 1500
ether 02:a0:98:03:71:0a (auto-1000t-fd-up) flowcontrol full
trunked jumbo
e0d: flags=0x2508866<BROADCAST,RUNNING,MULTICAST,TCPCKSUM> mtu 1500
ether 00:a0:98:03:71:09 (auto-unknown-cfg_down) flowcontrol full
lo: flags=0x1948049<UP,LOOPBACK,RUNNING,MULTICAST,TCPCKSUM> mtu 8160
inet 127.0.0.1 netmask-or-prefix 0xff000000 broadcast 127.0.0.1
ether 00:00:00:00:00:00 (VIA Provider)
jumbo: flags=0x22d48863<UP,BROADCAST,RUNNING,MULTICAST,TCPCKSUM> mtu 1500
inet 10.10.211.207 netmask-or-prefix 0xffffff00 broadcast 10.10.211.255
partner jumbo (not in use)
ether 02:a0:98:03:71:0a (Enabled virtual interface)
