MTU Size Issue on Cisco 3560 Switch

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Oct 23rd, 2007
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Could anybody tell me how to change MTU Size on a Cisco 3560 Switch.i mean to say whether it is to be changed on FastEthernet Interfaces or on VLAN 1 or on Global Configuration Mode and with which Command to change it.

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Overall Rating: 4 (2 ratings)
ankbhasi Tue, 10/23/2007 - 07:18
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Hi Susheel,

switch(config)#system mtu 1500

Switch(config)#system mtu ?

<1500-1998> MTU size in bytes

jumbo Set Jumbo MTU value for GigabitEthernet or TenGigabitEthernet interfaces

routing Set the Routing MTU for the system



*Pls rate all helpfull post

Collin Clark Tue, 10/23/2007 - 08:25
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You'll have to reload the switch once you enter the command too!

susheel.p Wed, 10/24/2007 - 05:33
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i have been able to change the MTU size on the Switch now with the command mentioned by you.

bvsnarayana03 Wed, 10/24/2007 - 02:03
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let it be default. there are no problems observed with default mtu. dont change without any specific reasons.

Collin Clark Wed, 10/24/2007 - 05:00
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What problems have you seen changing it?

Kevin Dorrell Wed, 10/24/2007 - 05:19
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If you are running OSPF on any of the VLAN interfaces you might get a problem forming adjacencies due to the MTU mismatch. But there is a way of telling the neighbors to ignore the MTU mismatch.

Kevin Dorrell


susheel.p Wed, 10/24/2007 - 05:38
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I am using MPLS on my Routers and the MTU size i have set on my Router Interfaces is 1524.

When i do a normal ping from Customer's one site to another (where my Traffic has to pass through this Switch VLAN)i get a reply , but when a Ping with a Byte Size of 1500 or more the Packets get completely dropped.

I think due to MTU Mistach bet. Switch and Router the Packets r getting droped,that is why i was trying to change it.

could the Packets get dropped because of this reason.Please suggest.

guruprasadr Thu, 10/25/2007 - 23:50
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HI Susheel, [PLS RATE if HELPS]

In a better care the MTU in MPLS Routers can be defined to "1400" only.

By this we can avoid Packet Drops. If your customer sites are connected via MPLS VPN network means both the ends should have the same MTU Size defined.

Also, check with your service provider whether they have defined some MTU Size definitions.


Best Regards,

Guru Prasad R


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