civic00typer
Gawd
- Joined
- Dec 5, 2003
- Messages
- 517
I am currently setting up an independent network for my SAN traffic. One of the recommendations from the manufacturer was to enable jumbo frames. On the 3750G it appears as though this must be done globally. I entered into priv exec mode and entered "system mtu jumbo 9000." After that I reloaded the switch and checked the MTU on my interfaces with "show interface gi 1/0/1." Further, the instructions indicated that I need to enable an individual VLAN to use Jumbo Frames (doesn't make sense according to the show interface command). Back into priv exex mode I entered VLAN 500 and then mtu 9000. I saved and reloaded the configuration.
After the reload I checked the configuration. Show interface VLAN 500 incidated the MTU was 1500, show interface GI1/0/1 (assigned to VLAN 500) indicated the MTU was 9000, and finally show vlan indicated the MTU was set at 9000.
"show vlan"
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 0 0
500 enet 100500 9000 - - - - - 0 0
"show interface vlan 500"
Vlan500 is up, line protocol is up
Hardware is EtherSVI, address is 0024.98af.5d41 (bia 0024.98af.5d41)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
"show run interface Gi1/0/1"
interface GigabitEthernet1/0/1
description BAMBINO 1 - 1
switchport access vlan 500
switchport mode access
flowcontrol receive desired
end
"show interface Gi1/0/1"
GigabitEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0024.98af.5d01 (bia 0024.98af.5d01)
Description: BAMBINO 1 - 1
MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec,
"show system mtu"
System MTU size is 1500 bytes
System Jumbo MTU size is 9000 bytes
Routing MTU size is 1500 bytes
What is going on here? Did I miss something? Why do I need to change the MTU on a VLAN if the global MTU setting applies to every interface? What is the explanation for the above results?
After the reload I checked the configuration. Show interface VLAN 500 incidated the MTU was 1500, show interface GI1/0/1 (assigned to VLAN 500) indicated the MTU was 9000, and finally show vlan indicated the MTU was set at 9000.
"show vlan"
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 0 0
500 enet 100500 9000 - - - - - 0 0
"show interface vlan 500"
Vlan500 is up, line protocol is up
Hardware is EtherSVI, address is 0024.98af.5d41 (bia 0024.98af.5d41)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
"show run interface Gi1/0/1"
interface GigabitEthernet1/0/1
description BAMBINO 1 - 1
switchport access vlan 500
switchport mode access
flowcontrol receive desired
end
"show interface Gi1/0/1"
GigabitEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0024.98af.5d01 (bia 0024.98af.5d01)
Description: BAMBINO 1 - 1
MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec,
"show system mtu"
System MTU size is 1500 bytes
System Jumbo MTU size is 9000 bytes
Routing MTU size is 1500 bytes
What is going on here? Did I miss something? Why do I need to change the MTU on a VLAN if the global MTU setting applies to every interface? What is the explanation for the above results?