How to avoid multiple DHCP request forward to all Servers?

[Thomas Markwalder]

On 4/7/17 5:13 AM, Simon Hobson wrote:
> priyankrathi <priyankrathi731 at gmail.com> wrote:
>
>> While observing the packet capture, I found that both the relay agent is
>> forwarding the request received from Client1 the server multiple times.
>> Similarly, the request from Client2 is also forwarded to the server multiple
>> times. 
>> My assumption is when a request comes on from Client1 from R:eth1 it
>> forwards the packet from R:eth3. As the same time, the second relay which is
>> running on R:eth2 and R:eth3 also listens to the packets and try again
>> forward it to the server. Request from any for the client gets looped
>> between both the relay agents and forwarded multiple times to server.
>> Basically, both relay agent starts flooding the network unless the max hop
>> count of the packet becomes zero.
> Yes, that would probably be the case. Bear in mind that you do NOT need to run multiple relay agents for this, it gains you nothing in terms of functionality, but creates more work and problems like the one you've found.
>
> So I'll repeat the question : what is it that you are trying to achieve that makes you think you need this setup ?
>
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As of 4.3.5, dhcrelay supports two new command line options which allow
you to specify interfaces as upstream or downstream only.  This can be
effective in eliminating reflections:

       -iu ifname
              Specifies an upstream network interface: an interface from
which
              replies  from  servers  and other relay agents will be
accepted.
              Multiple interfaces may be specified by using more than
one  -iu
              option.  This argument is intended  to  be used in conjunction
              with one or more -i or -id arguments.

       -id ifname
              Specifies a downstream  network  interface:  an 
interface  from
              which  requests  from  clients  and  other  relay agents
will be
              accepted.  Multiple interfaces may be specified  by 
using  more
              than  one  -id  option.  This argument is intended to be
used in
              conjunction with one or more -i or -iu arguments.