Re: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)

[Bob Briscoe <[e-mail]>]

Rod,

On 14/03/2020 22:18, Rodney W. Grimes wrote:
> Bob,
> 	Questions and comments in line.
>
>
>> Finding the best max packet size is an area where neither IPv4 nor IPv6
>> has ever found a good solution. Getting a tunnel to fragment and
>> reassemble is indeed painfully sub-optimal, but all the other solutions
>> have their own problems. It is possible the sub-optimality is often
>> going on under-the-covers, just because it works. I do know that, for
>> IPv4, the Don't Fragment (DF) flag is often ignored by tunnels, as a
>> preferable alternative to just ditching the traffic.
>
> What do you base your "know" on?
> Can you please site an implementaiton?

Here's a selection of implementations that allow you to configure 
clearing the DF flag in order to allow fragmentation prior to encapsulation:

  * Cisco IOS:
    https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dplane/configuration/15-mt/sec-ipsec-data-plane-15-mt-book/sec-df-bit-ovride.html
  * Juniper JunOS:
    https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/clear-dont-fragment-bit-edit-interfaces.html
  * Huawei:
    https://support.huawei.com/enterprise/en/doc/EDOC1100034238/a1bd518c/optional-configuring-the-df-flag-bit-for-gre-packets
  * Ericsson Redback:
    http://rbman.ito.expert/en_lzn7830011_1_r4a/3_19082-CRA1191170_1-V1Uen.G.html#CHAPTER1.59
  * Linux: iptables -t mangle -A PREROUTING -j DF --clear

While searching, I also found clear-df by accident in a firewall manual 
(not even doing any tunnelling)

And I even discovered "clear-df" in an (expired) individual Internet 
Draft from Ericsson for the Yang data model of an IPv4 tunnel:
draft-liu-intarea-ipipv4-tunnel-yang-02

Note, these are not to be confused with suppressing propagation of DF=1 
from the arriving IP header to the outer (so that a downstream router 
within the tunnel is allowed to fragment). In Linux, that would be: 
iptables -t mangle -A POSTROUTING -j DF --clear

So yes, I know this is often done, but I don't know how often.



Bob

-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/