DHCP snooping
According to the figure
If we deploy ip helper in the interface vlan10
And dhcp client at vlan 10 request and address from dhcp server at vlan 20 traffic will go to interface vlan 10 and then will take the giaddr 10.10.10.254 then traffic
Will go to the server at switch 2
The replay from dhcp server at switch 2 will come to Switch 1 and then it will remove giadd 10.10.10.254 then send the replay to client
If we put
Ip dhcp realy information option …….at switch 1
The relay switch 2 will put the option 82 in the request of the clinet to server then when reply come it will remove option 82 and send to the clinet
If we use dhcp snooping
The rely will remove old option 82 of the relay added before and put its new option 82 ( New dhcp snooping option) and put the giadd zero
To avoide these problem ( of giaddr zero )we can use
no ip dhcp snooping information option
That mean traffic will go to switch 2 without option 82 at and giaddr will still the same as before 10.10.10.254
So we should use the previous command Ip dhcp realy information option at switch 1 ??? that is the question or we can only use
no ip dhcp snooping information option
And if we put the
ip dhcp relay information trust-all ……………that mean the traffic will go to switch 2 with new option 82 giadd zero and pass it to DHCP sever
that mean trffic will go to switch 2 and server with giaddr zero
Kindly clarify and if I have wrong clarification kindly send me and if we have many switches 3 or 4 until clinet request go to server what is the best solution
Comments
kindly i need to arise my question to INE expert to answer my question
By default a layer2 switch inserts remote-id in dhcp requests. It requires dhcp snooping to be turned on, and the feature is disbaled with
no ip dhcp snooping information option
which will disable insertion of opt 82 globaly. Switch will not change giaddr address.
By default a layer 2 switch will frop packets with option 82 on untrusted ports. On trusted ports opt 82 is allowed. This check is only done if snooping is enabled. To enable opt 82 on untrusted ports (say when you have two or more layer 2 switches connected back to back) you need
ip dhcp snooping information option allow-untrusted
As far as relay agent goes (layer 3 device), you need
ip dhcp relay information trusted (per interface) or
ip dhcp relay information trust-all (globaly)
to process DHCP packets with giaddr=0 and opt 82 set (when you have layer 2 switch setting opt 82 before packets get to relay agent.
Finally, if relay agent gets packet with opt 82, it will overwrite it with its own opt 82. To change this you need
ip dhcp relay information policy keep
thanks JK
but if u have any reference documentation about that that is great
also if u have native configuration example fro dhcp snooping over multiple switches including layer 2 and layer 3
that is a great
thanks JK
but if u have any reference documentation about that that is great
also if u have native configuration example fro dhcp snooping over multiple switches including layer 2 and layer 3
that is a great