dhcp server functionality in cisco routers and switches

[sarahr202]

Hi everybody.

1) Is Ios- based dhcp server functionality only available in cisco routers? What about ios based multilayer switch? Can these switches provide dhcp server services ?

2)   Can  a router acting as dhcp relay agent insert option 82 ?

3) By default, IOS -based dhcp server drops dhcp message containing option 82,  this behavior can be changed using :

ip dhcp intformation trusted

What about if ios-based dhcp server receive option 82 with GIADD field set to zeros, will ios-based  dhcp server still drops the dhcp message though it is configured with"ip dhcp information trusted" ?

Thanks and have a great weekend.

[JohnTylerPearce · Accepted solution]

1) You can run an "IOS-based" dhcp server on Cisco routers and Cisco L3 switches.

2) Yes I believe it can

3) I dunno.

[sarahr202]

Hi JohnTylerPearce

I found some info with regard to " ip dhcp relay information trusted" command.

"If the relay agent inserts option 82 but does not  set the giaddr field in the DHCP packet, the DHCP server interface must  be configured as a trusted interface by using the

ip dhcp relay information trusted

global configuration command. This configuration prevents the server from dropping the DHCP message. "

The question is:  what is the default behavior of an ios-based dhcp server  if it receives a dhcp message with option 82 and GIADD is set to some ip say 199.199.199.1? Will it drop it? What do we need to do to make iops based dhcp server accepts such message?

thanks and havea great weekend

[smehrnia · Accepted solution]

hi,

as u already know dhcp uses giaddr field to distinguish where (which subnet) this packet is comming from, so it can assign an address from the respective pool. I remember once i read in an article; if the “giaddr” is missing or zero, then option 82 serves as refinement to the request, allowing the DHCP server to select a “sub-range” in the pool.

by the way a packet with giaddr is all good for ios dhcp.

by default; Cisco IOS dhcp server can use information provided by option 82 to allocate IP addresses. and its within the feature of dhcp class capability. this feature is enabled by default, and if not, re-enable it using: ip dhcp use class

plz Rate if it helped.

Soroush.

[sarahr202]

Thanks Soroush

by default; Cisco IOS dhcp server can use information provided by option  82 to allocate IP addresses. and its within the feature of dhcp class  capability. this feature is enabled by default, and if not, re-enable it  using:

ip dhcp use class

Well  what I understand from above is what cisco ios dhcp sever does with information provided by option 82.  The question  is :What is the default behavior if cisco ios dhcp server receives option 82? does it drop it? does it accept it?

thanks and have a great weekend.

[smehrnia · Accepted solution]

default; it accepts it as long as there is valid a giaddr field, its not zero!