[j-nsp] weird MTU size on "show interface"

[Felix Schueren]

On 01.10.10 07:26, Michel de Nostredame wrote:
> Hi,
> 
> I was checking my EX4200 trying to resolve a strange connection
> problem with my vendor through a Metro Ethernet.
> During that time I found another weird situation (it is not related to
> the metroEthernet connection).
> 
> I setup two topology to test
> 
> EX4200.ae0 ===(LACP,trunk)=== ae0.M10
> 
> On above setup, the interface link-level MTU on EX4200 side (interface
> ae0) shows MTU 1514. But on M10 the interface link-level MTU shows
> 1518.
> The 1518 is what I expect to have as a VLAN trunk interface should be.
> 
the EXes do their (routed) vlans like most switches - in a weird way :)

I think this is a display bug - I see the same values (using 9.6) of
EX1514, MX1518 in a similiar setup.

I just tested this, and if I put an EX port in "family inet" mode, then
the display is correct, if I use "family ethernet-switching", then it's
incorrect but works anyway. The "interface vlan" shows an MTU of 1518,
and all my physical ports (ae or no) show 1514 yet do pass 1500 byte
frames correctly, regardless of whether I use vlan-tagging or pure
access ports. The displayed MTU is 1514 without vlan-tagging, and it
stays 1514 even with vlan-tagging.

Kind regards,

Felix

-- 
Felix Schüren
Head of Network

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