subnetting in windows server 2003

[vubinhlunel]

in windows server 2003, the RIP and OSPF do have the “disable subnet
summarization†option for the classless purpose but when I use the subnet of
the network 172.16.1.0/24 I still see the broadcasting address 172.16.255.255
via the gateway 172.16.1.1 of the network 172.16.0.0 in the “routing tableâ€.

does this have impacts on the network of 172.16.2.0/24, 172.16.3.0/24… when
it broadcast.

 

[Ben Voigt [C++ MVP]]

in windows server 2003, the RIP and OSPF do have the "disable subnet
summarization" option for the classless purpose but when I use the
subnet of the network 172.16.1.0/24 I still see the broadcasting
address 172.16.255.255 via the gateway 172.16.1.1 of the network
172.16.0.0 in the "routing table".

does this have impacts on the network of 172.16.2.0/24,
172.16.3.0/24. when it broadcast.

RIP and OSPF don't necessarily use the same routing table that the kernel
uses for routing decisions (usually a subset but could be completely
independent).

Plus, I don't think "summarization" has anything to do with CIDR. At least
not in the way you think it does when you say "for the classless purpose".

 

[vubinhlunel]

Dear Ben Voigt,

sorry i was unclear in my question.

i mean that i have 1 network 192.168.0.0/24 and the broadcast address for
this network is then 192.168.0.255. this is normal.

then i have another network at another side of the router (Windows Server
2003) who is 172.16.1.0/24 but the broadcast address appears in the routing
table for this network is 172.16.255.255 and i think that this address is the
broadcast address of 172.16.0.0/16. isn't it?

on some Cisco's routers there is something called "auto-summary" and this
text is from Cisco:

EIGRP automatically summarizes routes at the classful boundary. This is the
boundary where the network address ends, as defined by class-based
addressing. This means that even though Router is connected only to the
subnet 172.16.1.0, it will advertise that it is connected to the entire Class
B network, 172.16.0.0.

then the problem is that if i have another router that isn't directly
connected to the first router and routes a network of 172.16.2.0/24.

then when the first router learns about the network 172.16.2.0/24 from a
routing protocol (RIP or OSPF). it then will not route for this network
because it assumes that " I directly connect to this network because i have
the broadcast address of 172.16.255.255" !

in other word, my question is " does the router see the 172.168.1.0/24 on
the classfull or classless " ?

if classless, why broadcast address is 172.16.255.255. but not 172.168.0.255 ?

 

[vubinhlunel]

sorry i've made some mistakes.

Dear Ben Voigt,

sorry i was unclear in my question.

i mean that i have 1 network 192.168.0.0/24 and the broadcast address for
this network is then 192.168.0.255. this is normal.

then i have another network at another side of the router (Windows Server
2003) who is 172.16.1.0/24 but the broadcast address appears in the routing
table for this network is 172.16.255.255 and i think that this address is the
broadcast address of 172.16.0.0/16. isn't it?

on some Cisco's routers there is something called "auto-summary" and this
text is from Cisco:

EIGRP automatically summarizes routes at the classful boundary. This is the
boundary where the network address ends, as defined by class-based
addressing. This means that even though Router is connected only to the
subnet 172.16.1.0, it will advertise that it is connected to the entire Class
B network, 172.16.0.0.

then the problem is that if i have another router that isn't directly
connected to the first router and routes a network of 172.16.2.0/24.

then when the first router learns about the network 172.16.2.0/24 from a
routing protocol (RIP or OSPF). it then will not route for this network
because it assumes that " I directly connect to this network because i have
the broadcast address of 172.16.255.255" !

in other word, my question is " does the router see the 172.16.1.0/24 on the
classfull or classless " ?

if classless, why broadcast address is 172.16.255.255. but not 172.16.1.255 ?

 

[Ben Voigt [C++ MVP]]

Dear Ben Voigt,

sorry i was unclear in my question.

i mean that i have 1 network 192.168.0.0/24 and the broadcast address
for this network is then 192.168.0.255. this is normal.

then i have another network at another side of the router (Windows
Server 2003) who is 172.16.1.0/24 but the broadcast address appears
in the routing table for this network is 172.16.255.255 and i think
that this address is the broadcast address of 172.16.0.0/16. isn't it?

Yes it is. And this indicates a misconfiguration in the local IP address of
the interface. RIP/OSPF/other router table sharing protocols are not
involved.

on some Cisco's routers there is something called "auto-summary" and
this text is from Cisco:

EIGRP automatically summarizes routes at the classful boundary. This
is the boundary where the network address ends, as defined by
class-based addressing. This means that even though Router is
connected only to the subnet 172.16.1.0, it will advertise that it is
connected to the entire Class B network, 172.16.0.0.

That would be a useless implementation of summarization.

More typically, if a router has:

10.0.2.0/24 connected through eth0, next hop 192.168.1.2
10.0.3.0/24 connected through eth0, next hop 192.168.1.3

a trunk on eth1

Then instead of publishing each route through OSPF exchanges over eth1, it
should send just one route, "I am the next hop for 10.0.2.0/23"

then the problem is that if i have another router that isn't directly
connected to the first router and routes a network of 172.16.2.0/24.

then when the first router learns about the network 172.16.2.0/24
from a routing protocol (RIP or OSPF). it then will not route for
this network because it assumes that " I directly connect to this
network because i have the broadcast address of 172.16.255.255" !

in other word, my question is " does the router see the
172.168.1.0/24 on
the classfull or classless " ?

if classless, why broadcast address is 172.16.255.255. but not
172.168.0.255 ?

Because the IP address on the router interface is configured with the wrong
subnet mask?

 

[vubinhlunel]

Yes it is. And this indicates a misconfiguration in the local IP address of
the interface. RIP/OSPF/other router table sharing protocols are not
involved.


That would be a useless implementation of summarization.

More typically, if a router has:

10.0.2.0/24 connected through eth0, next hop 192.168.1.2
10.0.3.0/24 connected through eth0, next hop 192.168.1.3

a trunk on eth1

Then instead of publishing each route through OSPF exchanges over eth1, it
should send just one route, "I am the next hop for 10.0.2.0/23"


Because the IP address on the router interface is configured with the wrong
subnet mask?

no they are correct. i have an interface with IP address 192.168.0.2
mask-255.255.255.0 then another is 172.16.1.1 mask-255.255.255.0 (subnetted
from class B-->classless).

but the routing table is like this.

destination network mask gateway interface
0.0.0.0 0.0.0.0 192.168.0.254 externe
127.0.0.0 255.0.0.0 127.0.0.1 loopback
127.0.0.1 255.255.255.255 127.0.0.1 loopback
172.16.1.0 255.255.255.0 172.16.1.1 interne
172.16.1.1 255.255.255.255 127.0.0.1 loopback
172.16.255.255 255.255.255.255 172.16.1.1 interne
192.168.0.0 255.255.255.0 192.168.0.2 externe
192.168.0.2 255.255.255.255 127.0.0.1 loopback
192.168.0.255 255.255.255.255 192168.0.2 externe
244.0.0.0 244.0.0.0 192.168.0.2 externe
244.0.0.0 244.0.0.0 172.16.1.1 interne
255.255.255.255 255.255.255.255 192.168.0.2 externe
255.255.255.255 255.255.255.255 172.16.1.1 interne

if you have a Windows Server 2003. try to subnet a class-based like A,B or
C. you'll see that the broadcast address will be the classfull address.

thank for your helps.

vubinhlunel