04-12-2022 03:14 AM
I'm trying to use the DHCP relay feature, with no success.
I've already tried on a SG300, on a SG350X and now on a CBS350, so clearly I'm letting something pass.
Today I have the CBS350 in my lab. It's connected to the network (port 2, connected to another switch) and I have a cable directly connected from my computer to it (port 47).
I'm doing everything through the web interface, as I'm not a network expert.
That's what I'm doing:
- I create a new VLAN (103);
- I add the port 47 to VLAN 103;
- change port 2 to trunk;
- enable DHCP relay and add the DHCP server (snooping and option 82 are disabled);
The DHCP server has two scopes: the regular one (xxx.xxx.93.0/24) and the new one (xxx.xxx.103.0/24);
Then, when I try to get a new IP, I get a "time out" message:
"An error occurred while renewing interface Ethernet 2 : unable to contact your DHCP server. Request has timed out."
I've tried all tutorials from internet
I've also tried some from Cisco:
https://www.cisco.com/c/en/us/td/docs/switches/lan/csbms/CBS_250_350/CLI/cbs-350-cli-/dhcp-relay-commands.html
https://www.cisco.com/c/en/us/support/docs/smb/switches/cisco-350-series-managed-switches/smb5406-configure-dynamic-host-configuration-protocol-dhcp-snooping.html
Any help would be appreciated.
04-12-2022 04:37 AM
can you post show run (from console to look)
where is your DHCP Server ? what IP address ?
04-12-2022 04:42 AM
Hi, here is the "show run" output:
config-file-header switchf27fed v3.1.1.7 / RCBS3.1_930_871_081 CLI v1.0 file SSD indicator encrypted @ ssd-control-start ssd config ssd file passphrase control unrestricted no ssd file integrity control ssd-control-end cb0a3fdb1f3a1af4e4430033719968c0 ! ! unit-type-control-start unit-type unit 1 network gi uplink te unit-type unit 2 network gi uplink te unit-type unit 3 network gi uplink te unit-type unit 4 network gi uplink te unit-type-control-end ! vlan database vlan 103 exit voice vlan oui-table add 0001e3 Siemens_AG_phone voice vlan oui-table add 00036b Cisco_phone voice vlan oui-table add 00096e Avaya voice vlan oui-table add 000fe2 H3C_Aolynk voice vlan oui-table add 0060b9 Philips_and_NEC_AG_phone voice vlan oui-table add 00d01e Pingtel_phone voice vlan oui-table add 00e075 Polycom/Veritel_phone voice vlan oui-table add 00e0bb 3Com_phone ip dhcp relay address 192.168.93.3 ip dhcp relay enable bonjour interface range vlan 1 hostname switchf27fed username hi_there_:) password encrypted RWZYpw== privilege 15 ip ssh server ! interface vlan 103 name Servers ip address dhcp ip dhcp relay enable ! interface GigabitEthernet1/0/2 ip dhcp snooping trust switchport mode trunk ! interface GigabitEthernet1/0/47 ip dhcp snooping trust switchport access vlan 103 ! exit
04-12-2022 04:38 AM
You did not say where the DHCP server is.
If the DHCP server is connected in the other switch you did right putting the port 2 as trunk. However, unless the DHCP is on the vlan 103 on the other switch, DHCP requests will not get to them.
Also, the port 2 is connect to which port on the other switch? Does that port is in trunk as well?
If DHCP server is in a different vlan, you need to do inter-vlan routing in order your computer reach the DHCP server.
04-12-2022 04:50 AM
Hi Flavio.
Are you from Brazil?
The DHCP server is in our "regular" network (93.0).
The diagram would be something like this:
DHCP <-> switch <-> switch in lab <-> my computer
Just my lab's switch has a trunk port.
The other switch has no VLAN configured on it.
@Flavio Miranda wrote:If DHCP server is in a different vlan, you need to do inter-vlan routing in order your computer reach the DHCP server.
The DHCP servers is on VLAN1.
04-12-2022 04:53 AM
Yeah, Brazil. You?
DHCP <-> switch <-> switch in lab <-> my computer
Well, in this case, either you create the vlan 103 on the switch, put the DHCP server port on this vlan 103 or you need to do inter-vlan routing.
04-12-2022 04:58 AM - edited 04-12-2022 05:01 AM
Yeah, Brazil. You?
Me too
DHCP <-> switch <-> switch in lab <-> my computerWell, in this case, either you create the vlan 103 on the switch, put the DHCP server port on this vlan 103 or you need to do inter-vlan routing.
OK. But this is not DHCP relay, right?
Don't we "have" DHCP relay, exactly to avoid having one DHCP server on each VLAN?
04-12-2022 05:05 AM
Oh yeah, sorry. You not just trying to make it work right, you want to test DHCP relay.
Well, did you followed a guide like this and did not work?
04-12-2022 05:20 AM - edited 04-12-2022 05:20 AM
@Flavio Miranda wrote:Oh yeah, sorry. You not just trying to make it work right, you want to test DHCP relay.
Well, did you followed a guide like this and did not work?
That's exactly what I did.
Maybe the problem is that I have more than one switch between the DHCP server and my computer.
04-12-2022 08:51 AM
interface vlan 103 name Servers ip address dhcp ip dhcp relay enable
OK, the Broadcast will convert to unicast and send to DHCP server BUT it need IP source and I see the SVI ip address also assign IP form DHCP.
first check if the SVI have IP address and it better to manually add the IP address for SVI.
04-13-2022 07:58 AM
Hi MHM,
The switch gets an IP from DHCP indeed.
So if I understood, I need to a fixed IP on my switch to have DHCP relay working?
04-13-2022 08:44 AM
Yes, try set ip then check dhcp
relay
04-14-2022 12:45 AM
Thanks for your suggestion, but unfortunately setting a static IP on SVI did not work.
At first, I put a static IP on SVI VLAN 1. All good. All working.
After that, I put a static IP on SVI VLAN 103. Then I lost access to the switch using its hostname. I had to use its static IP (from VLAN 1) to access it.
And the worst is, I lost the DHCP relay configuration menu in options. I need to factory reset it to get the menu back.
Does it matter, having another switch between the DHCP server and the switch I'm trying to configure?
04-14-2022 03:11 PM
can you share
show ip route
for this switch.
04-18-2022 11:34 PM
Hi MHM,
This is the "show ip route" output:
Maximum Parallel Paths: 1 (1 after reset) IP Forwarding: enabled Codes: > - best, C - connected, S - static, R - RIP C 192.168.93.0/24 is directly connected, vlan 1 C 192.168.103.0/24 is directly connected, vlan 103
Maybe I have something wrong in DHCP server, because the switch gets an IP from the DHCP server for network 93.0. Just network 103.0 is not working.
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