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Modification of the interface MTU

Nils Kroll

Hi all!

Quick question regarding XGS 126: MTU is a property of the physical interface. If I want to reduce the MTU for a VLAN I have to do it on the physical interface.

By adjusting MTU value I seem to lose the VLAN interface and the associated dependencies e.g. firewall rules.

Is there a way to prevent this?

Thank you for your input! nk



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  • 0 in reply to Vivek Jagad

    Hi Vivek!

    The MSS adjustment solves the problem only for TCP connections. I will propose this to the customer but I don't expect him to agree to the solution.

    Background: It is a network in an industrial facility where the PRP protocol is used. There is a valid network layout in which connections to "single attached nodes" are established. When using PRP the packet is lengthened by a 6Byte trailer by a PRP switch. Neither the endpoints nor the firewall are involved. Packets with max payload can therefore exceed the MTU of the recipient. The requirement is that at least routed connections can be established without interface configuration at the endpoints. This should be transport layer independent.

  • 0 in reply to Nils Kroll

    As of now this can be consider a workaround or a probable solution. What are your customer's expectation as a solution then ?

    Thanks & Regards,
    _______________________________________________________________

    Vivek Jagad | Team Lead, Global Support & Services 


    Sophos Community | Product Documentation | Sophos Techvids | SMS
    If a post solves your question please use the 'Verify Answer' button.

  • 0 in reply to Vivek Jagad

    Hi!

    This is a short-term workaround (MSS config). Previously we used UTM instead of XG with reduced MTU but we missed that detail when switching to XGS. The goal is therefore a reduced MTU again.

    I had hoped that there is a way to correct the MTU without serious effects.. I will reduce the MTU in any case and restore the lost configuration.

    Thanks for your support!

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