DSL Network Design Question

Sun Aug 14 15:57:41 UTC 2005

On Sun, 14 Aug 2005, Roy Badami wrote:

>    Jon> Believe it or not, even not too old (12.1T) IOS versions have
>    Jon> issues forwarding packets to .255 addresses.
>
> Do you know what the issue is, and when it was fixed (or better, have
> a bug number I can lookup)?  I currently use .0 and .255 addresses on
> our corporate network, and have never _noticed_ any issues (though
> we're not currently running anything as old as 12.1T for IP).

We use a few subnets (usually /27 or so sized) which we have chopped up 
into /32s for lo0 interfaces on all our core routers.  One of these 
subnets includes a .255 which got assigned as x.y.z.255/32 to one of our 
routers, and so that router exports it into OSPF as a /32.  I found that 
anything on the other side of one of our T1 & DSL aggregation 7206's 
running 12.1T could not reach that .255 router.

In fact, that 7206 can't reach the .255 and if it tries to, it 
apparently assumes you meant to send a broadcast to any interface 
which happens to be in the same x.y.z/24 as x.y.z.255.  Pinging x.y.z.255 
results in replies from locally connected x.y.z/24 customers.

I don't know that it has been fixed.  We only run a little 12.1T in places 
where we needed an odd mix of features only available in 12.1T.  AFAIK, we 
could theoretically upgrade to 12.3M, but we tried it once early in 12.3 
and it didn't go well.  We ended up rolling back to 12.1T due to too many 
new bugs.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                | 
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