Hi
I just see that the mtu in lo is different from standard eth 1500
Any meaning of it?
eg:
Standard eth 1500
in linux. lo mtu 16436
in solaris. lo mtu is 8232
How about cisco / juniper loopback?
Thank you so much
I think that the MTU on LO is pretty irrelevant in general.
If it does matter, larger is probably better.
Owen
Hi
I just see that the mtu in lo is different from standard eth 1500
Any meaning of it?
You transfer huge amounts of data on loopbacks similar to sockets. Supporting large MTU's is appropriate, and given the virtual nature of loopbacks, is probably generally designed to handle the buffers that transfer the data.
How about cisco / juniper loopback?
Thank you so much
Juniper M120: Type: Loopback, MTU: Unlimited
Cisco 7206 12.2SRE: MTU 1514 bytes, BW 8000000 Kbit/sec, DLY 5000 usec,
Jack
Jack brings up a good point. MTU is basically pointless since packets never traverse any real interface.......
So in theory the size can be anything...
Not quite. You hit packet length field limits. IPv4 packets can't be
larger than 65535, and IPv6 packets also can't be larger than 65 576
(40 byte IPv6 header + 2^16 payload), unless the jumbograms and the
jumbo payload extension header is supported. Last time I checked, by
setting the loopback MTU > 65 576, Linux, for example, doesn't support
the jumbo payload extension header (or if it does, I didn't spend
enough time finding out how to switch it on - a very large MTU didn't
trigger it).
That being said, with a 64K MTU on loopback, you can legitimately claim
to get >10Gbps at home, as long as you don't mention how you're doing
it 
Regards,
Mark.
Thanks for the 411 Mark!
Again, this NANOG list is such a valuable source of info and knowledge!
I know in more recent Cisco IOS software (12.4.24T or later I think)
the MTU of a GRE interface is that of the largest memory block on the
box. I wouldn't be surprised if this is the same for loopbacks since
they are a software concept. The logic behind this is that the
largest frame the software interface can handle would be equal to the
largest chunk of memory to put that frame in.