In message <u6820o$37si7$1@dont-email.me>, at 21:17:12 on Mon, 12 Jun
2023, Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>Roland Perry <roland@perry.uk> wrote:
>> In message <kejfgdFoqj7U1@mid.individual.net>, at 15:26:20 on Sat, 10
>> Jun 2023, Rupert Moss-Eccardt <nin@moss-eccardt.com> remarked:
>>> On 10 Jun 2023 07:43, Roland Perry wrote:
>>>> In message <u5uvnt$1sqk7$1@dont-email.me>, at 10:43:09 on Fri, 9 Jun
>>>> 2023, Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>>>>
>>>>>>>>
>>>>>>>> Classic telephone exchanges and IP datacentres are about as differently
>>>>>>>> architected as it's possible to be. Circuit switching versus packet
>>>>>>>> switching.
>>>>>>>
>>>>>>> Irrelevant; routing (or routeing) - the decisions about where to
>>>>>>>direct a
>>>>>>> packet or a call - is analogous is each.
>>>>>>
>>>>>> The methodologies are utterly different.
>>>>>
>>>>> No, they're very similar - given a destination which connection
>>>>> should I send it down? There are differences in implementation -
>>>>> call setup versus packet-by-packet decisions, how to handle
>>>>> congestion - but the basic idea is the same.
>>>>
>>>> No, they are completely different. Circuit switching uses protocols
>>>> which essentially follow pre-programmed legs in a relatively sparse hub
>>>> and spoke network, whereas IP uses BGP, which is much more dynamic and
>>>> multi-transit-provider.
>>>
>>> Things have moved on and so a PVC is now probably over a packet-switch
>>> underlay. So the argument is a little pointless.
>>
>> Unless those packets were IP, routed by BGP, there would still be
>> architectural differences.
>
>You’re still conflating the forwarding of IP packets with the method of
>populating the routing table that is used to decide where to forward them.

There isn't one routing table (let alone one fairly static routing
table), that's the whole point. Each router with a packet to deliver has
its own individual routing table, based on information it's been
recently sent from all the routers it's peering with.

Think of it a bit like a hypothetical gantry where the southbound M1
approaches the M25, saying "Gatwick Airport 1hr 45 mins via Leatherhead;
1hr 38mins via Dartford".

{That's real data just now}
--
Roland Perry