01-27-2007 02:52 AM
HI
Is it possibel to set MTU on Fastethernet ?
I was trying to change MTU on 7206 and i got this error
config-if)#ip mtu ?
<68-1500> MTU (bytes)
config-if)#mtu 1510
% Interface FastEthernet0/0 does not support user settable mtu.
01-28-2007 10:59 AM
The message means that the MTU cannot be configured for the datalink for the specific hardware in question.
If you are trying to set the MTU to support MPLS label stack,
1) If you have not configured MPLS MTU, then any 1500 bytes packet would be fragmented at 1492 and the resulting fragments would be assigned the labels. As the MPLS MTU defaults to the datalink MTU value.
2) Most ethernet hardware is supposed to switch 4 to 8 bytes more than the conventional 1500 bytes frame size. If this support is there in the hardware being used by you then, you can configure MPLS MTU to avoid fragmentation at 1492, and transmit the 1500 bytes packet. Hence supporting the dual label stack.
HTH-Cheers,
Swaroop
For further information on the MTU, as a reading reference, you can refer to RFC 3032 complete Section "3".
01-31-2007 10:37 PM
Thank you . The RFC was so useful
And know i want to aks you
1. MPLS MTU command , should be on the Edge-LSR interface connected to MPLS clou or on the interface connected to CE ?
2.On section 3.4 of the RFC it says that :
4. If the IP datagram has the "Don't Fragment" bit set in its IP
header:
a. the datagram MUST NOT be forwarded
b. Create an ICMP Destination Unreachable Message:
i. set its Code field [3] to "Fragmentation Required and DF
Set",
ii. set its Next-Hop MTU field [4] to the difference between
the Effective Maximum Frame Payload Size and the value
of N
c. If possible, transmit the ICMP Destination Unreachable
Message to the source of the of the discarded datagram.
How can i do this
If the source who set DF is client , it will be easy , but what if a webserver is setting DF ? and also do not support path Mtu discover ?
regards
02-02-2007 11:55 AM
Please note the range available. Your "1510" exceeds it.
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