Internet Exchanges supporting jumbo frames?

Nick Hilliard nick at foobar.org
Wed Mar 9 18:18:35 UTC 2016


Mikael Abrahamsson wrote:
> I have many times ping:ed with 10000 byte packets on a device that has
> "ip mtu 9000" configured on it, so it sends out two fragments, one being
> 9000, the other one around 1100 bytes, only to get back a stream of
> fragments, none of them larger than 1500 bytes.

here's some data on INEX from a server interface with 9000 mtu.  fping
has 40 bytes overhead:

> # wc -l ixp-router-addresses.txt
>       85 ixp-router-addresses.txt
> # fping -b 1460 < ixp-router-addresses.txt | grep -c unreachable
> 0
> # fping -b 1500 < ixp-router-addresses.txt | grep -c unreachable
> 10
> # fping -b 5000 < ixp-router-addresses.txt | grep -c unreachable
> 11
> # fping -b 8960 < ixp-router-addresses.txt | grep -c unreachable
> 12

Out of interest, there were 5 different vendors in the output, according
to the MAC addresses returned.Some of this may be caused by
inappropriate icmp filtering on the routers, but the point is that it
would be unwise to depend on routers doing the right thing here. If
you're going to have a jumbo mtu vlan at an IXP, the VLAN needs to be a
hard specification, not an aspiration with any variance.

Nick




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