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Cisco 7606 fragmentation question

Answered Question
Apr 26th, 2006
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Hi All,


Does Cisco 7606 support jumbo packet fragmentation? If yes, how do I configure it?


Thanks in advance.


Regards,

Sarah

Correct Answer by Bobby Thekkekandam about 11 years 3 months ago

Hi Sarah,


We do support it, but with a caveat. When jumbo packets need fragmentation, such as going from a jumbo enabled vlan to non-jumbo enabled vlan, these packets get punted to the MSFC/RP and are process switched. So if there is a large amount of traffic that needs to be fragmented, you could run into a high CPU situation.


More on Jumbo Frame Support here.

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/swcg/intrface.htm#wp1041111


HTH,


Bobby


*Please rate helpful posts.



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Correct Answer
Bobby Thekkekandam Wed, 04/26/2006 - 07:45
User Badges:
  • Cisco Employee,

Hi Sarah,


We do support it, but with a caveat. When jumbo packets need fragmentation, such as going from a jumbo enabled vlan to non-jumbo enabled vlan, these packets get punted to the MSFC/RP and are process switched. So if there is a large amount of traffic that needs to be fragmented, you could run into a high CPU situation.


More on Jumbo Frame Support here.

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/swcg/intrface.htm#wp1041111


HTH,


Bobby


*Please rate helpful posts.



sarah12345 Wed, 04/26/2006 - 08:49
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Hi Bobby,


Thanks a lot for the info.


I am using 3 GigE ports. One port (g2/13) is sending traffic. Two ports (g1/11 and g1/12) are using LACP, so they are in the same channel-group. All three ports have the same VLAN enabled.


After setting the MTU, I still cann't have Cisco to fragment the packets correctly. Did I miss configuing something?


I configured the following:

system jumbomtu 2000


interface Port-channel2

...

mtu 2000

end


interface GigabitEthernet1/11

...

mtu 2000

end


interface GigabitEthernet1/12

...

mtu 2000

end


interface GigabitEthernet2/13

...

mtu 2000

end


Thanks and Regards,

Sarah




Bobby Thekkekandam Wed, 04/26/2006 - 09:00
User Badges:
  • Cisco Employee,

Hi Sarah,


IP fragmentation is only going to happen when routing from a jumbo-enabled vlan to a non-jumbo-enabled vlan. Within devices in the same VLAN, fragmentation is not possible, so all devices in the VLAN must be configured for the same jumbo MTU.


Which is the case here?


thanks,


Bobby

sarah12345 Wed, 04/26/2006 - 09:17
User Badges:

Hi Bobby,


Now I get it. In my case, all 3 ports are in the same VLAN. So I guess no fragmentation will happen. Cisco will just foward it along to the egress ports.


Thanks a lot for your help. I really appreciate it!


Regards,

Sarah

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