Hey Jamison,
The consensus view is this: 1500 Bytes is the MTU of the internet, and
MTU1500 has so much inertia that you or me or all this mailing list
together could not change it.
The sages also tell us that PMTUd--path MTU discovery--does not work
with any reliability and thus does not work in reality. Things like NAT,
firewalls and deep packet inspectors routinely break ICMP of all kinds.
Most crushingly for an IX: there's no such thing as layer-2 MTU
discovery. In the same L2 domain, all routers need to use the same MTU,
or stuff will break (Jeremy pointed to one example of failing BGP
message exchange). If I set my router to MTU1500, and you set yours to
MTU9000, how would we ever know? This is a misconfiguration, so what
could coordinate those values on an IX?
Thus, we should all use MTU 1500.
We could have a separate VLAN that's MTU 9000 where all the routers
connected would set their interface to MTU 9000. The routers wouldn't
have any MTU breakage over that L2 domain. SIX does this, and it seems
the best and most rational way to allow MTU 9000 for those who want it.
Finally, views do differ, i'm sure others have opinions that do not
match mine.
Cheers,
Jonathan
Jonathan Stewart
Network Engineer
LES.NET - AS18451
Desk: 1-204-666-6191
Mobile: 1-204-990-2120
130 Portage Avenue E
Winnipeg, MB R3C 0A1
CANADA
On Fri., 2021-06-18 1:09 p.m., Jamison Masters wrote:
>
> Hi all,
>
> We are migrating our connections to 10G, and I’m wondering if I should
> request jumbo frames.
>
> I’m trying for due diligence, and apologize if this is a rudimentary
> question. Nanog searches do not have clear recommendations, or maybe
> I did not search enough.
>
> My experience with jumbo frames indicates to me that I should be safe
> with 9000 byte frames, but there could be PMTU discovery and
> fragmentation issues during transit or on the receiving side.
>
> Would you or would you not enable 9K frames with IXP and ISP
> connections? I just do not have enough experience in this regard, so
> I am thankful for any thoughts here.
>
> My inclination is to go with 9K frames, yet I do not want to deal with
> ancillary issues that I cannot anticipate, discern, or troubleshoot –
> especially during a cut.
>
> Any experience from the group is appreciated.
>
> Thank you,
>
> Jamison Masters
>
> Verus Corporation
>
> [log in to unmask]
>
>
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