topic Re: SDA client Can t obtain IP address from DHCP in Software-Defined Access (SD-Access)

SDA client Can t obtain IP address from DHCP

HAT — Mon, 28 Jun 2021 16:06:17 GMT

Hi All,

I m currently working on a SDA solution for my company . I have an IP phone currently connected to the fabric edge but struggling to obtain an IP address from the DHCP server sitting in the shared services area.

The underlay routing to the DHCP server within the relevant VN is working fine , the fabric edge has been configured with DHCP information option , dhcp snooping vlan XXX, dhcp snooping .

The vlan (1022) interface configuration also appears to be fine .

Although the phone successfully authenticates and get assigned to the correct Vlan ,it won t obtain an IP address from the DHCP server . What I m missing here ?

Any help would be much appreciated .

Thanks in advance

Re: SDA client Can t obtain IP address from DHCP

Scott Hodgdon — Mon, 28 Jun 2021 16:20:01 GMT

HAT,

When you define an IP Pool, you should have a DHCP server designated as part of that definition. When you add the IP Pool to the VN, it should create an IP Helper address on the SVI on the edge, and there should be a loopback on the Border with the same IP address as the SVI. Are you seeing these ?

Also, we use Option 82 for DHCP in SDA, so if your DHCP does not support this option then it will not work with fabric. Most modern DHCP servers support this option. The most commonly used DHCP server that we saw issues with in the past was Windows 2008, which does not support this option. Clients that upgraded from Windows 2008 to a newer version experience no problems.

Cheers,
Scott Hodgdon

Senior Technical Marketing Engineer

Enterprise Networking and Cloud Group

Re: SDA client Can t obtain IP address from DHCP

HAT — Mon, 28 Jun 2021 23:42:32 GMT

Hi Scott,

Thanks for the prompt answer . As seen below I can see the IP helper address on the SVI , the loopback on the border is also matching the SVI

SDA-EDGE-POC-2#sh run interface vlan 1022
Building configuration...

Current configuration : 331 bytes
!
interface Vlan1022
description Configured from Cisco DNA-Center
mac-address 0000.0c9f.xxxx
vrf forwarding Corporate_VN_POC
ip address 10.223.5.1 255.255.255.0
ip helper-address 172.28.251.10
no ip redirects
ip route-cache same-interface
no lisp mobility liveness test
lisp mobility 10_223_5_0-Corporate_VN_POC-IPV4
end

SDA-Border-POC#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
Vlan1 unassigned YES NVRAM up up
Vlan3003 unassigned YES unset down down
Vlan3013 10.223.255.1 YES NVRAM up up
Vlan3014 10.223.255.5 YES NVRAM up up
Vlan3015 10.223.255.9 YES NVRAM up up
Te1/1/4 10.223.253.66 YES NVRAM up up
LISP0 unassigned YES unset up up
LISP0.4097 10.223.254.1 YES unset up up
LISP0.4102 10.223.255.5 YES unset up up
LISP0.4103 10.223.255.9 YES unset up up
Loopback0 10.223.254.1 YES NVRAM up up
Loopback1021 10.223.2.1 YES manual up up
Loopback1022 10.223.5.1 YES manual up up
Loopback1023 10.223.4.1 YES manual up up
Loopback1024 10.223.0.1 YES manual up up
Tunnel0 10.223.254.1 YES unset up up

I m using a 3650 switch as a DHCP server , does that support Option 82 , if yes how would I configure it ?

Please find below the dhcp configuration for the relevant dhcp pool

ip dhcp pool Ipecs-PoC
network 10.223.5.0 255.255.255.0
domain-name mydomain.com
dns-server xx.xx.xx.xx
default-router 10.223.5.1
option 66 ip xx.xx.xx.xx
option 150 ip xx.xx.xx.xx
option 160 ascii http://xx.xx.xx.xx/PROVISIONING/
lease 0 8

Once again thanks for your assistance

HAT,

Re: SDA client Can t obtain IP address from DHCP

Scott Hodgdon — Thu, 01 Jul 2021 16:13:56 GMT

HAT,

Which version of IOS are you using on the 3650 ? I have never tried this with a switch, so I need to find the config if it exists.

Cheers,
Scott Hodgdon

Senior Technical Marketing Engineer

Enterprise Networking and Cloud Group

Re: SDA client Can t obtain IP address from DHCP

HAT — Mon, 12 Jul 2021 15:06:11 GMT

Hi Scott

My apologies , just seeing your latest post now . Please find below details of the switch I m using as DHCP server

Switch Ports Model SW Version SW Image Mode
------ ----- ----- ---------- ---------- ----
* 1 28 WS-C3650-24TD 16.3.6 CAT3K_CAA-UNIVERSALK9 INSTALL

Looking forward to hearing from you

Thanks

Re: SDA client Can t obtain IP address from DHCP

Scott Hodgdon — Mon, 12 Jul 2021 15:57:17 GMT

HAT,

I have never tried this, so hopefully it works for you. If not, I recommend an option 82 capable DHCP server on a computer instead of the router.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/xe-3s/dhcp-xe-3s-book/config-dhcp-server-xe.html#GUID-A89D6831-F21C-47BA-A3D5-531139B66AFC

Cheers,
Scott Hodgdon

Senior Technical Marketing Engineer

Enterprise Networking and Cloud Group