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Community Member

Cisco 7606 fragmentation question

Hi All,

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

Thanks in advance.

Regards,

Sarah

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Cisco 7606 fragmentation question

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.

4 REPLIES
Cisco Employee

Re: Cisco 7606 fragmentation question

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.

Community Member

Re: Cisco 7606 fragmentation question

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

Cisco Employee

Re: Cisco 7606 fragmentation question

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

Community Member

Re: Cisco 7606 fragmentation question

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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