Level 3 BGP Advertisements

james machado hvgeekwtrvl at gmail.com
Thu Aug 30 14:48:32 CDT 2012


On Thu, Aug 30, 2012 at 11:50 AM, Blake Hudson <blake at ispn.net> wrote:
> Matt Addison wrote the following on 8/29/2012 6:08 PM:
>
>> Sent from my mobile device, so please excuse any horrible misspellings.
>>
>> On Aug 29, 2012, at 18:30, james machado <hvgeekwtrvl at gmail.com> wrote:
>>
>>> On Wed, Aug 29, 2012 at 1:55 PM, STARNES, CURTIS
>>> <Curtis.Starnes at granburyisd.org> wrote:
>>>>
>>>> Sorry for the top post...
>>>>
>>>> Not necessarily a Level 3 problem but;
>>>>
>>>> We are announcing our /19 network as one block via BGP through AT&T, not
>>>> broken up into smaller announcements.
>>>> Earlier in the year I started receiving complaints that some of our
>>>> client systems were having problems connecting to different web sites.
>>>> After much troubleshooting I noticed that in every instance the xlate in
>>>> our Cisco ASA for the client's IP last octet was either a 0 or 255.
>>>> Since I am announcing our network as a /19, the subnet mask is
>>>> 255.255.224.0, that would make our network address x.x.192.0 and the
>>>> broadcast x.x.223.255.
>>>> So somewhere the /24 boundary addresses were being dropped.
>>>>
>>>> Just curious if anyone else has seen this before.
>>>
>>> some OS's by M and others as well as some devices have IP stacks which
>>> will not send or receive unicast packets ending in 0 or 255.  have had
>>> casses where someone was doing subnets that included those in the DCHP
>>> scopes and the computers that received these addresses were black
>>> holes.
>>>
>>> james
>>
>> MSKB 281579 affects XP home and below. Good times anytime someone adds
>> a .0 or .255 into an IP pool.
>>
> It might be relevant to note that XP and below is simply respecting classful
> boundaries. This does not affect all .0 or .255 address, just class C
> addresses (192.0.0.0 through 223.255.255.255) that end with .0 or .255. If
> your IP range is 0.0.0.0 - 191.255.255.255 you are not affected (by this
> particular bug) by using .0 or .255 as the last octet unless the address is
> ALSO the last octet of the classful boundary for your subnet. In effect,
> these OS's simply enforce classful boundaries regardless of the subnet mask
> you have set. As the KB states, this "bug" affects supernets only. I'm not
> trying to defend MS (they can do that themselves), but your statement was
> misleading.

I can distinctly remember having the issue in 10/8 address space with
Win2k and WinXP

>
> We do, sometimes, use .0 and .255 addresses. Most clients work fine with
> them (including XP). However, I have personally seen a few networks where an
> administrator had blocked .0 and .255 addresses, causing problems for people
> on his network communicating to hosts that ended in .0 or .255. It has been
> years since I have seen an issue with a .0 or a .255 IP however. Given fears
> over IP shortages, even a couple percent of addresses wasted due to
> subnetting can be cause for adjusting network policy. I would not be
> surprised if folks who excluded .0 and .255 addresses from their assignable
> pools will re-evaluate that decision over the next few years.
>
> --Blake
>
>
>



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