Smaller than a /24 for BGP?

Sun Jan 29 07:06:12 UTC 2023

William Herrin wrote:

>>      The easiest way for applications know all the addresses of the
>>      destination is to use DNS. With DNS reverse, followed by forward,
>>      lookup, applications can get a list of all the addresses of the
>>      destination from an address of the destination.
> 
> The DNS provides no such guarantee.

Guarantee for what?

Remember that we have been enjoying secure confirmation that
certain IP address belongs to certain hostname by DNS reverse
look up without any guarantee.

 > Moreover, the DNS does guarantee
 > its information to be correct until the TTL expires, making it
 > unsuitable for communicating address information which may change
 > sooner.

I'm afraid you know very little about DNS operation. See rfc1034:

    If a change can be anticipated, the TTL can be reduced prior
    to the change to minimize inconsistency during the change,
    and then increased back to its former value following the
    change.

which is the way to operate DNS when host addresses are changing,
for example, by multihoming configuration changes.

In addition, when a dual homed site with end to end multihoming
changes one of its ISP, it is a good idea to offer all the three
addresses by DNS during the change. Make before break.

>>      With TCP, applications must be able to pass multiple addresses to
>>      transport layer (e.g. BSD socket).
>>
>> which implies addresses are supplied from applications by
>> DNS look up.
> 
> Which is a bit of hand-waving since the protocol can't do anything
> with that information regardless of whether you expand the API to
> provide it.

Read my draft, which explains how TCP should be modified.

						Masataka Ohta