How to change the DHCP relay/helper on H3C S5800 Series switch ?

[Server-Support]

Can anyone here assist me in what command should I use to change the DHCP relay (helper) setting on H3C S5800 Series switch on the below VLAN:

10.1.2.0/24 - Workstation level 1
10.1.3.0/24 - Wireless LAN level 1
10.1.4.0/24 - Workstation level 2
10.1.5.0/24 - Wireless LAN level 2

Old DHCP server IP: 10.1.3.2
New DHCP server IP: 10.1.3.196

I've gone through: https://h20566.www2.hpe.com/portal/site/hpsc/template.PAGE/public/kb/search/?sp4ts.oid=4179963&spf_p.tpst=kbSearchMain&spf_p.pbp_kbSearchMain_myAction=withResults&javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken#searchResultHead

but still not sure how to do it and what could be the impact for the production network traffic flow.

Does it requires switch restart or reboot ?

[EricAtHP · Accepted solution]

Assuming that DHCP is/was working with the old server, all you need to do is add the new server to the existing relay server group:

From the system prompt:

[HP-5800]dhcp relay server-group <your group id> ip 10.1.3.196

Then remove the old server:

[HP-5800]undo dhcp relay server-group <your group id> ip 10.1.3.2

For a configuration from scratch:

[HP-5800]dhcp enable

[HP-5800]dhcp relay server-group 1 ip 10.1.3.196

[HP-5800]interface vlan 1

[HP-5800-Vlan-interface1]dhcp relay server-select 1

[HP-5800-Vlan-interface1]dhcp select relay

Use the "display dhcp relay all" command to view the existing configuration.

[Server-Support]

Hi Eric,

Thanks for the reply. So is there any connectivity outage or switch reboot after updating the dhcp relay ?

[EricAtHP]

No reboot required and no connectivity loss.

The way dhcp realy works is that when the switch receives a DHCP broadcast, it turns it into a unicast and forwards it to all of the configured dhcp servers. All of the servers reply and the switch forwards all of the replies to the requesting client. The client then chooses one of the responses. Usually the one that offers the address the client is already using or the first response if it is the first time on the network.

That is why I recommended configuring the new server first and then removing the old server. You could add a step and test with a new client. If the client gets an address from the new server, then you are good to go. You may have to use a packet capture utility on the client to validate that it is getting offers from both dhcp servers. 

[Server-Support]

Many thanks for assisting me in this old legacy H3C S5800 Series switch. I didn't realize it that I can find someone who can assist me in this forum.

[Server-Support]

Hi Eric,

May I know hwere to get the value of GroupID ?

[EricAtHP]

It would have been configured by whoever did the initial config. Do a "display current" to view the config and look for it in the output.

[manuel.bitzi]

Hi Albert

The 5800 is a state of the art switch and still under development. There will be bigger announcements in the next months. Don't worry you are on the right track.

br

Manuel

[Server-Support]

Many thanks for the reply Manuel.

It is hard to find a Good online resource for H3C apart from this great forum. Because most environment uses Cisco or Juniper switches but not H3C.

So it seems that HP Procurve switch and H3C is almost similar in terms of command syntax.

[manuel.bitzi]

Hi Albert

The H3C 5800 is the same device as the HP 5800. You can change the brand if you want. Here you will find a lot of ressources:

http://h20565.www2.hp.com/portal/site/hpsc/public/psi/home/?sp4ts.oid=4177501&ac.admitted=1429510758745.876444892.492883150#manuals

br

Manuel

[Server-Support]

Hi Eric,

I can now login to the switch after getting the correct credentials, so this is the result of the current configuration:

<CORE-SWITCH01>
<CORE-SWITCH01>display dhcp relay all
    Interface name                                  Server-group
    Vlan-interface4                                       1
    Vlan-interface5                                       1
    Vlan-interface8                                       1
    Vlan-interface18                                      1
    Vlan-interface61                                      1
<CORE-SWITCH01>

[Server-Support]

Which means the command would be:

<CORE-SWITCH01>dhcp relay server-group 1 ip 10.1.3.196

Then remove the old server:

<CORE-SWITCH01>undo dhcp relay server-group 1 ip 10.1.3.2

Would that be correct two lines that I can execute or is that wrong ?

[Server-Support]

The full configuration dump can be located in the attached text file for more information.

The below code is just the snippet of the first few lines of the display running-config command:

******************************************************************************
* Copyright (c) 2004-2011 Hangzhou H3C Tech. Co., Ltd. All rights reserved.  *
* Without the owner's prior written consent,                                 *
* no decompiling or reverse-engineering shall be allowed.                    *
******************************************************************************

User interface aux0 is available.

Please press ENTER.

Login authentication

<CORE-SWITCH01>display current-configuration
#
 version 5.20, Release 1211
#
 sysname CORE-SWITCH01
#
 clock timezone #Web#10#02 add 10:00:00
#
 super password level 3 cipher ISqbSaL!#%&#@!!!
#
 dhcp relay server-group 1 ip 10.1.3.2
#
 irf domain 2
 irf mac-address persistent timer
 irf auto-update enable
 undo irf link-delay
 irf member 1 priority 32
 irf member 2 priority 31
#
 domain default enable system

.......

skip few hundred lines

.......

#
interface Ten-GigabitEthernet1/0/27
#
interface Ten-GigabitEthernet1/0/28
#
interface Ten-GigabitEthernet2/0/27
#
interface Ten-GigabitEthernet2/0/28
#
ospf 100 router-id 10.1.1.3
 silent-interface Vlan-interface2
 silent-interface Vlan-interface4
 silent-interface Vlan-interface5
 silent-interface Vlan-interface6
 silent-interface Vlan-interface8
 silent-interface Vlan-interface18
 area 0.0.0.0
  network 10.1.0.0 0.0.255.255
#
 dhcp enable
#
 ntp-service source-interface Vlan-interface2
 ntp-service unicast-server 10.1.3.26
#
 ssh server enable
#
 undo arp check enable
#
 load xml-configuration
#
 load tr069-configuration
#
user-interface aux 0 1
 authentication-mode scheme
user-interface vty 0 15
 authentication-mode scheme
#
irf-port 1/2
 port group interface Ten-GigabitEthernet1/0/27 mode enhanced
 port group interface Ten-GigabitEthernet1/0/28 mode enhanced
#
irf-port 2/1
 port group interface Ten-GigabitEthernet2/0/27 mode enhanced
 port group interface Ten-GigabitEthernet2/0/28 mode enhanced
#
return
<CORE-SWITCH01>

[EricAtHP]

You got it.

Good luck!

[Server-Support]

Hi Eric,

Since my H3C switch is configured as stacked and I only connected to the Switch #1 on COM1 serial port, do I need to do the same thing on the second switch for changing the DHCP relay setting ?

or that two lines of command is enough ?

[EricAtHP]

No, in IRF, both switches are logically one switch. Technically, the management processes of one switch is managing the whole stack.

In fact, if you want to play a little, keep the serial console session up that you have right now and then connect a second serial console to the other switch and connect. You will see a message indicating that you connected on the first connection and have exactly the same context.

[Server-Support]

Many thanks Eric.

Hopefully tomorrow over the weekend I can implement the changes on the DHCP relay without any issue or outage caused from the Putty session remotely.

[Server-Support]

Hi Eric,

Somehow I also amanged to found the IP address for the Web Management Platform for this H3C S5800 switch, therefore I can open it from old Windows Server with IE8 and go to Network | DHCP | DHCP Relay tab

is there any difference making the changes from the web console above compare with the COM1 serial port ?

I assume that in the IRF mode this change should only be done once either way (Web GUI or Putty COnsole).

[EricAtHP]

There is no difference between the web and CLI. That said, I have never used the web interface on that switch. You will find that many of the configuration options that are availble in the CLI don't exist in the web interface.

[jbutler1946]

     Looking for some additional help with the DHCP Relay on an HP A7510 Switch.  I had a relay group pointing to an older dhcp server. I changed the relay group on vlan 20 to relay group 3 (New 2012 DHCP Servers, and for testing purposes I even made relay group 4 (Single DHCP Server). Vlan20 was using the old server on relay group 2, after changing the server-group 3 devices are still pulling fron the old dhcp server group. I tried removing server group 2 completely and even rebooted the switch. No matter what I do vlan 20 will not use the new DHCP server. Maybe I'm missing something. See DHCP relay info below.

Thank You in advance for the help.

dhcp relay server-group 3 ip 10.2.50.7
dhcp relay server-group 3 ip 10.2.50.8
dhcp relay server-group 3 ip 10.2.50.248
dhcp relay server-group 4 ip 10.2.50.8

interface Vlan-interface2
ip address 10.2.1.1 255.255.0.0
#
interface Vlan-interface3
ip address 10.3.1.1 255.255.0.0
#
interface Vlan-interface5
ip address 10.5.0.2 255.255.255.252
#
interface Vlan-interface6
ip address 10.6.1.1 255.255.0.0
#
interface Vlan-interface20
ip address 10.20.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface30
ip address 10.31.1.1 255.255.0.0
#
interface Vlan-interface40
ip address 10.40.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface50
ip address 10.50.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface60
ip address 10.60.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface61
ip address 10.61.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface71
ip address 10.71.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface100
ip address 10.100.255.254 255.255.0.0
#
interface Vlan-interface200
ip address 10.200.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface220
ip address 10.220.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface230
ip address 10.230.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface240
ip address 10.240.255.254 255.255.0.0
#
interface Vlan-interface241
ip address 10.241.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 3
#
interface Vlan-interface250
ip address 10.250.255.254 255.255.0.0
#
interface Vlan-interface251
ip address 10.251.255.254 255.255.0.0
dhcp select relay
dhcp relay server-select 4
#
interface Vlan-interface601
ip address 172.16.1.254 255.255.255.0
#
interface Vlan-interface701
ip address 172.16.2.254 255.255.255.0