OSPF "bad hello packet"

[James A. Crippen]

On Sat, 6 Jan 2001, Ondrej Feela Filip wrote:

> On Fri, 5 Jan 2001, James A. Crippen wrote:
> 
> > I'm getting "bad hello packet from 10.1.1.23 received: bad netmask
> > 255.255.255.0" even though there's really nothing wrong with this netmask
> > (I'm using 10.1.1.0/24 and 10.2.2.0/24 for some testing).
> 
> Are you sure, that all interfaces connected to network 10.1.1.0/24 have
> the same netmask?

Yes, see below.
 
> > Is there any reason why ospf thinks this is a bad netmask?  Should I just
> > ignore it?
> 
> Probably 10.1.1.23 has a different netmask than the router running BIRD.

Both are bird routers.  They're both connected to an isolated network on
one 100Mbps hub.  The network looks like this:

                10.2.2.0/24 -----+-----
                                 |10.2.2.23
                                 B
                        10.1.1.23|10.10.10.23
  10.1.1.0/24 ----------+--------+---------+------------ 10.10.10.0/24
               10.1.1.42|                  |10.1.1.1
                        A                  C
           12.17.190.232|                  |12.17.190.220
  12.17.190.224/28 -----+--------+---------+------------ 12.17.190.208/28
                    12.17.190.225|12.17.190.209
                                 D
                                 |12.17.190.161
                                 |
                                \|/
                                 V
                           The Internet

(I apologize for the horrible ASCII art.)  Basically 12.17.190.224/28 and
12.17.190.208/28 are subnets on the same ethernet segment.  /D/ is the
primary router between them, as well as the default gateway to the rest of
the Internet.  /A/ and /C/ are connected to this ethernet segment but on
different subnets, /A/ on 12.17.190.224/28 and /C/ on 12.17.190.208/28.  
Neither /A/ nor /C/ communicate routing information to /D/, thus all the
10 networks are invisible to the Internet.  Both /A/ and /C/ are connected
to another ethernet segment which is also connected to /B/.  /A/, /B/, and
/C/ all have interfaces on 10.1.1.0/24.  /B/ also has another interface on
the same ethernet segment but on a different subnet, 10.10.10.0/24.  This
is just a stub so I can watch another route propagate.  /B/ is connected
to yet another segment, this having only the 10.2.2.0/24 subnet on it, and
/B/ is the only connected router.

BTW, /A/ does not run any routing protocols.  It's my workstation which is
connected to the two ethernet segments so I can see the network traffic.

With that, I'm seeing the "Bad OSPF hello packet from 10.1.1.23