Re: [IPsec] I-D Action: draft-ietf-ipsecme-ikev2-fragmentation-03.txt

["Valery Smyslov" <[e-mail]>]

>> Sorry, I wasn't very clear. By "isn't very useful" I meant that it is
>> not useful
>> for the usual PMTU discovery goal in TCP - to find _maximum_ IP datagram
>> size that is not fragmented by IP level. In IKE its the goal is 
>> different -
>> to find _some_reasonable_ IP datagram size that is not fragmented by IP.
>>
>> If we have the size that is guaranteed to not be fragmented,
>> no PMTU discovery will be needed. As far as I understand, for IPv6
>> it is 1280 bytes. But as far as I know, there's no such value for IPv4.
>> If we mandate (or recommend) using really small value e.g. 128 bytes,
>> than the perfomance will suffer badly, so it it not a good option.
>> I'm especially worring about network I'm not familiar with -
>> mobile networks or other constrained environments.
>> It would be great if some experts in such networks could clarify this.
>>
> I'm even more worried that if we use small fragments, reliability will 
> deteriorate. Because we do not have per-packet acknowledgement, and so if 
> any fragment is dropped, the whole message must be resent. This is 
> probably a greater risk in mobile networks.

Yes, a good point.