Broadcast forwarding

[dukenukem]

Hi All,

I have previously asked about forwarding broadcasts and i got some answers. However i have a few problems.

This is my scenario :

I have 3 routers connected like this:

Router B---> Router A <--- Router C

[ [

[ [

ethernet ethernet

lets say that A router is the main one.

What must be configured on my router A ATM subinterfaces or anywhere else on it, to allow boradcast from Router Bs ethernet interface, to reach routers C ethernet interface.????

I am using ip helper addresses, and ip directed broadcast to send the bradcasts to the whole subnet on the interface.

Can u also please show each interface brief configuration??

Thanks,

George

[Richard Burts]

Your drawing is difficult to interpret. It is clear that A is in the middle between B and C. The drawing shows something about Ethernet but I can not tell what you meant it to show. The drawing does not have anything about ATM but your question mentions ATM subinterfaces. So I am a bit confused.

Since I do not really understand what you are asking let me review a few principles and if this does not answer your question perhaps you can clarify what you need.

If router B on one (or more) of its LAN interfaces receives UDP broadcasts that it wants to forward to some remote destination then you configure ip helper-address on the LAN interface on which the broadcasts are received. The helper-address identifies the destination to which the broadcast should be forwarded.

If router B configures helper-address and the destination is router C then there is nothing that needs to be configured on router A.

helper-address usually uses a unicast address as the destination to forward packets to. It is possible to specify a subnet broadcast address as the destination (for example ip helper-address 172.16.4.255 would be a subnet broadcast destination). This uses the feature of directed broadcast. If you do use a subnet broadcast address then there is something that needs to be configured on router C (and nothing is needed on router A). On router C on each interface which may be receiving the subnet broadcast you need to configure ip directed-broadcast.

I hope this explains what you need. If not please clarify your question.

HTH

Rick

[dukenukem]

Hi Rick,

thanks for the reply.

I understand what u say about the ip helper-address commands, but not very clear on the ip directed-broadcast command. In the example you describe to me, where should i configure this on Router C ? on the serial interface , or on the Ethernet interface ?

What i am trying to figure out from my question about boradcasts, is a problem we have at work for accessing shares on a win2000 server using UNC path (\\server\share) . In the "diagram" i showed in my posting, the server is located on the Ethernet of Router C.

PCs on Router B ethernet can access other shares on any machine on Router A ethernet and vice versa (from A to read any share on B)

Furthermore PCs on Router A ehternet can access the shares on machines on Router C ehternet and vice versa (from C to A)

Machines on Router C ethernet can access shares on PCs on Router A ethernet as well as machines on Router B ethernet.

The problem comes when trying to access UNC path from B Ethernet to C ethernet. Nohthing seems to work.

Both B to C ping with replies, both using names and IPs.

Any ideas as to what the problem is or any debugging commands i can use to trace the problem????

I hope u can help .

Thanks again,

George

[Richard Burts]

George

the directed-broadcast would go on the interface where the packet actually would become a broadcast (so on the Eternet and not on the serial). Enabling or disabling directed broadcasts is an interface level function so you need the command on any interface which you want to create the actual broadcast.

I am trying to understand the situation that you describe. Is this set of relationships true?:

PCs at B successfully share with A

PCs at A successfully share with B

PCs at C successfully share with A

PCs at A successfully share with B

PCs at C successfully share with B

but

PCs at B are not successful in share with C

If the above relationships are what you describe it would be very helpful to compare the configuration of B and C. Can you post the configs? If you can not post them for some reason could you email the configs to me (my email address is available through my forum profile).

HTH

Rick