[ntp:questions] (Software) timeserver for windows being broadcast-able incl. keys

Per Hedeland per at hedeland.org
Sat Mar 17 13:10:58 UTC 2007


In article <45FB2283.8000201 at cag.zko.hp.com> Tom Smith
<smith at cag.zko.hp.com> writes:
>Per Hedeland wrote:
>> In article <45FAAA30.2080401 at cag.zko.hp.com> Tom Smith
>> <smith at cag.zko.hp.com> writes:
>>> Erik wrote:
>>>> On 15 mrt, 17:21, Tom Smith <s... at cag.zko.hp.com> wrote:
>>>>>> broadcast 145.47.51.127 key 1
>>>>>> broadcast 145.47.51.255 key 1
>>>>>> broadcast 145.47.52.127 key 1
>>>>>> broadcast 145.47.53.127 key 1
>>>>> That's the right idea, but the second one above already
>>>>> includes the first.
>> 
>> How do you figure that? If (according to latest report) there are two
>> networks a) 145.47.51.0/25 and b) 145.47.51.128/25, the address
>> 145.47.51.255 doesn't "include" 145.47.51.127 in any way. 145.47.51.127
>> is the broadcast address for a), 145.47.51.255 is the broadcast address
>> for b) - and hosts on network a) will not see 145.47.51.255 as a
>> broadcast address - in fact they will just see it as a random address on
>> a remote network. A broadcast address is either 255.255.255.255 or one
>> where the network part matches exactly and the host part is all-ones.
>
>145.47.51.0/25 = *.0-127
>    broadcast 145.47.51.127 broadcasts to all of them
>145.47.51.128/25 = = *.128-255
>    broadcast 145.47.51.255 broadcasts to all of them
>
>145.47.51.0/24 - *.0-255
>    broadcast 145.47.51.255 broadcasts to all of them

Yes of course - but the 2 x /25 and the 1 x /24 are two different cases,
and according to the OP /25 was used here.

>Whether it would "work", depends on the next answer, which
>was:

No, regardless of whether the subnets are on the same wire, or whether
routers forward directed broadcasts, the hosts on 145.47.51.0/25 will
never see 145.47.51.255 as a broadcast address. For route advertisement
to remote networks, adjacent subnets can and should be aggregated -
i.e. the router that has both 145.47.51.0/25 and 145.47.51.128/25 can
advertise 145.47.51.0/24 - but that doesn't change the local broadcast
address on those networks, of course.

The remaining points seem to result from a similar misconception, so I
won't comment further on them.

--Per Hedeland
per at hedeland.org




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