Wrong DHCP relay vlan on C1300

[VTH]

Hi,

so i've bought a c1300 to test the functionalities I need and I run into some problems.

I have a a access point on port 16 with 2 radios for vlan 1 Clients and vlan 4 guests. On my old Cisco and Dell Switches I made an Ip helper-adress on the vlan interface and everything got the correct IP address. On the C1300 the ip addresses are all over. Some Guests get Management or TelefonNetwork IP Addresses. Option 82 is activated. how can I solve this problem?

DHCP Server for clients are in the Server network vlan10 with ip 10.0.1.1 and 10.0.1.2. Client Scope is 10.0.0.0/24

DHCP Server for guest is 192.168.4.254 with scope 192.168.4.0/24

v4.1.6.54 / RLSB4.1.6_951_410_024
unit-type-control-start
unit-type unit 1 network gi uplink te
unit-type-control-end
!
spanning-tree mode rapid-pvst
spanning-tree priority 24576
spanning-tree vlan 4,10,30,70 priority 24576
vlan database
vlan 4,10,30,70
exit
voice vlan id 70
voice vlan cos 5 remark
voice vlan oui-table add 0001e3 Siemens_AG_phone
no lldp med network-policy voice auto
lldp med network-policy 1 voice vlan 70 vlan-type tagged up 5 dscp 46
ip dhcp relay address 10.0.1.1
ip dhcp relay address 10.0.1.2
ip dhcp relay address 10.0.3.254
ip dhcp relay address 10.0.7.254
ip dhcp relay address 192.168.4.254
ip dhcp relay enable
!
interface vlan 1
 name Client
 no ip address dhcp
 ip dhcp relay enable
!
interface vlan 4
 name External-WLAN
 ip dhcp relay enable
!
interface vlan 10
 name Server
 ip dhcp relay enable
!
interface vlan 30
 name Management
 ip address 10.0.3.13 255.255.255.0
 ip dhcp relay enable
!
interface vlan 70
 name TelefonNetzwerk
 ip address dhcp
 ip dhcp relay enable
!
interface GigabitEthernet1/0/16
description AP
spanning-tree bpduguard enable
switchport mode trunk
switchport trunk native vlan 30
power inline priority critical
!

[pieterh]

the dhcp server needs some mechanism to determine from which vlan to which helper a packet needs to be forwarded
normally the switch uses the vlan ip-address as source address to forward the packets
and the dhcp-server can respond to this vlan address

in this configuration the switch only has a ip-address for management in vlan30  and  for phones in vlan70

[pieterh]

Cisco Catalyst 1300 Switches Series CLI Guide - DHCP Relay Commands [Cisco Catalyst 1300 Series Switches] - Cisco

User Guidelines

The operational status of DHCP Relay on an interface is active if one of the following conditions exist:

• DHCP Relay is globally enabled, and there is an IP address defined on the interface.

Or

• DHCP Relay is globally enabled, there is no IP address defined on the interface, the interface is a VLAN, and option 82 is enabled.

[pieterh]

i see in your post mentioned that  option 82 is activated, but what is its configuration ?

[VTH]

So Option82 is in default. In the Admin Guide ist stated: "Whenever DHCP Relay is enabled on a VLAN without an IP address, Option 82 is inserted automatically. "

And I activated Option 82 aditionally with all default settings. What should its configuration for vlan be? I dont want to add IP addresses for every vlan. The switch should have an management vlan 30 IP address. The vlan 70 ip address was just a test and I would like to delete it.

[pieterh]

is this C1300 a replacement or extension to an existing network ?

[VTH]

its a replacement of a Dell N1524. The Dell switches use almost the same OS as the cisco and allow an ip helper-address on vlan interface to route dhcp traffic.

[pieterh]

Then the Cisco's default is different than Dells.

Try if changing change from hex to ASCII improves.

[KJK99]

@VTH 

I'm not sure how it worked on your DELL switch, but here's what the C1300 manual says.

For DHCP relay to be functional, an IP address must be configured on the VLAN or interface.

If you do not want to set up IP addresses on the VLANs of your C1300 switch, configure the DHCP relay on the device that does inter-VLAN routing.

[VTH]

---

@KJK99 wrote:

@VTH 

I'm not sure how it worked on your DELL switch, but here's what the C1300 manual says.

For DHCP relay to be functional, an IP address must be configured on the VLAN or interface.

If you do not want to set up IP addresses on the VLANs of your C1300 switch, configure the DHCP relay on the device that does inter-VLAN routing.

---

that doesnt make sense. the device that is handling inter-vlan routing is also the dhcp server -> the firewall. The switch needs the dhcp-relay option to send the dhcp broadcast to the firewall.

[VTH]

okay so I think I found the problem. I dont need Option 82 if the dhcp server is on the same vlan.

I just disabled dhcp relay von all vlans except vlan 1 where the dhcp server is on vlan 10. now my guest clients on vlan 4 get the correct ip address and my clients on vlan 1 get their ip from the relayed vlan 10 dhcp servers.

[KJK99]

Sounds like your network is misconfigured. Good luck!