[c-nsp] MTU Issue on QinQ Eth link with MPLS

mb2 at os.datafx.com.au mb2 at os.datafx.com.au
Wed Jan 9 16:19:05 EST 2008


Quoting Masood Ahmad Shah <masood at nexlinx.net.pk>:

> Well, interesting.. sometimes Cisco guys forget to import some cool
> features; I don't know why but it has been seen on some occasion. Better you
> down grade to the release which support baby giants....
>
> For those switches that support up to 1530 bytes, the default MTU value is
> 1500. If you want to change this, use the global configuration command that
> is available for versions of software above 12.1(6)EA2. Here is sample
> configuration and verification:
>
>
> This URL might help...
>
> http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration
> _example09186a008010edab.shtml
>

Hi,

I now have the QinQ link connected to C2950G-24-EI's (Both supporting 
baby giants), and made the following changes:

Both 2950's:
system mtu 1530

7200's:

interface FastEthernet0/0.15
tag-switching mtu 1530

interface FastEthernet3/0.15
mpls mtu 1530

Running MPLS over the link, access to https(And other sites 
historically affected by mtu) was successful from "standard" Internet 
Tail, but VRF traffic was still affected by mtu(i.e. Could ping/resolve 
Internet Addresses, but could not visit majority of WebSites) - 
Switching back to our ATM link resolved the problem?






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