02-24-2012 06:59 AM - edited 03-07-2019 05:09 AM
I have a switch that I have configured for jumbo packets, but they don't seem to be functioning.
I have set system mtu jumbo 9000. The hosts are connected via 2x EtherChannel links. The hosts are jumbo frame enabled, and can ping their own local address using jumbo packets & do-not-fragment flags on the pings. They cannot, however, ping each other or the switch that way - it always says that the packet requires fragmentation.
I'm pretty stumped here. I know the attached machines (they're all VMs) and virtual switches support jumbos because I can ping within the virtual interfaces of the VMs. It's just traffic that goes over the switch that fragments.
The switch is a WS-2960G-48TC. Here are the various outputs, with a section of config at the end.
hrnacancwtdevs3#show system mtu
System MTU size is 1500 bytes
System Jumbo MTU size is 9000 bytes
System Alternate MTU size is 1500 bytes
Routing MTU size is 1500 bytes
hrnacancwtdevs3#
-----------------------------------------------------------------------------------------------------------------------------------------------
hrnacancwtdevs3#show vlan mtu
VLAN SVI_MTU MinMTU(port) MaxMTU(port) MTU_Mismatch
---- ------------- ---------------- --------------- ------------
1 1500 9000 9000 No
1002 - 9000 9000 No
1003 - 9000 9000 No
1004 - 9000 9000 No
1005 - 9000 9000 No
1100 1500 9000 9000 No
hrnacancwtdevs3#
-----------------------------------------------------------------------------------------------------------------------------------------------
(attempt to ping the local address on the switch itself with a large packet)
hrnacancwtdevs3#ping 10.7.100.1 source 10.7.100.1 size 2000 df-bit
Type escape sequence to abort.
Sending 5, 2000-byte ICMP Echos to 10.7.100.1, timeout is 2 seconds:
Packet sent with a source address of 10.7.100.1
Packet sent with the DF bit set
.....
Success rate is 0 percent (0/5)
hrnacancwtdevs3#
-----------------------------------------------------------------------------------------------------------------------------------------------
hrnacancwtdevs3#show interfaces mtu
Port Name MTU
Gi0/1 9000
Gi0/2 9000
Gi0/5 9000
Gi0/6 9000
Po1 SAN 1 9000
Po2 VMSRV3 9000
hrnacancwtdevs3#
-----------------------------------------------------------------------------------------------------------------------------------------------
(Interface config)
interface Port-channel1
description SAN 1
switchport access vlan 1100
switchport mode access
!
interface Port-channel2
description VMSRV3
switchport access vlan 1100
switchport mode access
!
interface GigabitEthernet0/1
switchport access vlan 1100
switchport mode access
channel-group 1 mode on
!
interface GigabitEthernet0/2
switchport access vlan 1100
switchport mode access
channel-group 1 mode on
!
interface GigabitEthernet0/5
switchport access vlan 1100
switchport mode access
channel-group 2 mode on
!
interface GigabitEthernet0/6
switchport access vlan 1100
switchport mode access
channel-group 2 mode on
!
interface Vlan1100
ip address 10.7.100.1 255.255.255.0
no ip route-cache
!
02-24-2012 08:23 AM
Hi,
After you configured the jumbo frame support did you reload the switch
For 2960/2970 see this link :-
2970(config)# system mtu jumbo 9000 2970(config)# exit 2970# reload
Regards
Alex
02-24-2012 08:25 AM
Hi Alex -
Yes, I've reloaded the switch a couple times. I even tried upgrading to the most recent firmware.
That guide was the one I initially followed when setting up jumbo frames.
02-24-2012 08:35 AM
Can you change the size to 1998 and test again?
According to the command reference guide:
The size of frames that can be received by the switch CPU is limited to 1998 bytes, regardless of the value entered with the
system mtu
command. Although forwarded or routed frames are usually not received by the CPU, some packets (for example, control traffic, SNMP, Telnet, and routing protocols) are sent to the CPU.
HTH
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