Re: DHCP on sub-interface with second-dot1q vlans

MYazdian · ‎04-10-2024

Hello all,

I have to provide IP for many clinets which each of them has to have individual VLAN ID. I am using q in q to provide ctag vlan under svlan.

the configuration on my router is like below:

ip dhcp pool SVL-200
network 10.225.0.0 255.255.255.0
default-router 10.225.0.1
dns-server 8.8.4.4 4.2.2.4

interface FastEthernet0/1.200
encapsulation dot1Q 200 second-dot1q 50-100
ip address 10.225.0.1 255.255.255.0

When I run the command "show ip dhcp binding" on the router, I can see the customers' mac addresses in the DHCP database and router has offered the IP. However, just one of the clients can acquire the IP, and I can ping it from the router!!! While the router stated that it has assigned IP addresses to clients, I am unable to view the IP addresses on every single client except one of them

I believe this problem is connected to assigning one DHCP Pool and one IP Network to many vlans (50-100). Because when I build many sub-interfaces and assign a single second-dot1q vlan to each of them, the problem appears to be resolved. However, I cannot have several DHCP pools and networks for each VLAN, and I must have a single IP network (10.225.0.0/24) on my DHCP POOL for all vlans (50-100).

Please let me know if anyone has a similar experience, especially those who work for service providers.

Thanks in advance

balaji.bandi · ‎04-10-2024

what is the use case here to provide connection to clients ? how is your network looks like ?

refer some use case and limitation :

https://www.cisco.com/en/US/docs/ios/lanswitch/configuration/guide/lsw_ieee_802.1q.html

BB

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MYazdian · ‎04-10-2024

Hello Balaji,

Thanks for reply.

This is the internet service provider solution same as DSLAM on Cisco document which ou attached. But have problem to ip assigmnet for each customer that has their own vlan!
I am not sure if we can add DHCP on the subinterface which has multiple second-dot1q vlan tag on it!

I am looking forward to find a solution for IP assigmnet

Thank You

balaji.bandi · ‎04-11-2024

What hardware model and IOS code running, as i remember correctly this was way back my deployment - now days there are many other ways to deploy this in the new architecture.

still i am not sure how your setup looks like - where the clients terminating. ?

how is your authentication with Radius ? check the radius integration with DHCP.

If you are using PPPoE then client need to get single IP

check latest deployment guide :

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/bbdsl/configuration/xe-16-8/bba-xe-16-8-book/bba-rmtid-dsl-xe.html

BB

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MHM Cisco World · ‎04-10-2024

Share

Debug ip dhcp server packets <-

Share this

MHM

MYazdian · ‎04-10-2024

Hi,

I have enabled debug ip dhcp server on my router. but, nothing show up during dhcp handshake process.

there is dhcp binding

R1#show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type
Hardware address/
User name

10.225.0.29 0110.b36f.485f.39 Jan 04 2006 06:32 PM Automatic
10.225.0.30 0110.b36f.5adb.37 Jan 05 2006 06:26 PM Automatic

mac address 0110.b36f.485f.39 is belongs to VLAN 50
mac address 0110.b36f.5adb.37 is belongs to VLAN 55

But I just can ping this clinet "0110.b36f.5adb.37" and other client on VLAN 50 is not pingable and when I check the client computer interface there is no any IPI and client getting APIPA IP!

MHM Cisco World · ‎04-10-2024

Debup ip udp

!

Access-list 100 permit host 0.0.0.0 host 255.255.255.255

Debug ip packet 100

Run both above debug with debug ip dhcp server packet details

Share output

Note:-undebug all <<-do this to disable all debug we run for troubleshooting

MHM

MYazdian · ‎04-11-2024

Hi MHM,

there is screenshot from debug ip dhcp server packet detail

Jan 5 12:33:00.018: DHCPD: client's VPN is .
Jan 5 12:33:00.022: DHCPD: DHCPDISCOVER received from client 0110.b36f.485f.39 on interface FastEthernet0/1.200.
Jan 5 12:33:00.022: DHCPD: Allocate an address without class information (10.225.0.0)
Jan 5 12:33:00.022: DHCPD: Saving workspace (ID=0xAC00002E)
Jan 5 12:33:02.021: DHCPD: Reprocessing saved workspace (ID=0xAC00002E)
Jan 5 12:33:02.021: DHCPD: DHCPDISCOVER received from client 0110.b36f.485f.39 on interface FastEthernet0/1.200.
Jan 5 12:33:02.021: DHCPD: Sending DHCPOFFER to client 0110.b36f.485f.39 (10.225.0.31).
Jan 5 12:33:02.021: DHCPD: no option 125
Jan 5 12:33:02.021: DHCPD: creating ARP entry (10.225.0.31, 10b3.6f48.5f39, vrf default).
Jan 5 12:33:02.021: DHCPD: unicasting BOOTREPLY to client 10b3.6f48.5f39 (10.225.0.31).
Jan 5 12:33:02.021: DHCPD: removing ARP entry (10.225.0.31 vrf default).
Jan 5 12:33:09.193: DHCPD: client's VPN is .
Jan 5 12:33:09.193: DHCPD: DHCPDISCOVER received from client 0110.b36f.5adb.37 on interface FastEthernet0/1.200.
Jan 5 12:33:09.193: DHCPD: Allocate an address without class information (10.225.0.0)
Jan 5 12:33:09.197: DHCPD: Saving workspace (ID=0x7100002F)
Jan 5 12:33:11.197: DHCPD: Reprocessing saved workspace (ID=0x7100002F)
Jan 5 12:33:11.197: DHCPD: DHCPDISCOVER received from client 0110.b36f.5adb.37 on interface FastEthernet0/1.200.
Jan 5 12:33:11.197: DHCPD: Sending DHCPOFFER to client 0110.b36f.5adb.37 (10.225.0.32).
Jan 5 12:33:11.197: DHCPD: no option 125
Jan 5 12:33:11.197: DHCPD: creating ARP entry (10.225.0.32, 10b3.6f5a.db37, vrf default).
Jan 5 12:33:11.197: DHCPD: unicasting BOOTREPLY to client 10b3.6f5a.db37 (10.225.0.32).
Jan 5 12:33:11.197: DHCPD: removing ARP entry (10.225.0.32 vrf default).
Jan 5 12:33:11.237: DHCPD: client's VPN is .
Jan 5 12:33:11.237: DHCPD: DHCPREQUEST received from client 0110.b36f.5adb.37.
Jan 5 12:33:11.237: DHCPD: Can't find any hostname to update
Jan 5 12:33:11.237: DHCPD: Sending DHCPACK to client 0110.b36f.5adb.37 (10.225.0.32).
Jan 5 12:33:11.237: DHCPD: no option 125
Jan 5 12:33:11.237: DHCPD: creating ARP entry (10.225.0.32, 10b3.6f5a.db37, vrf default).
Jan 5 12:33:11.237: DHCPD: unicasting BOOTREPLY to client 10b3.6f5a.db37 (10.225.0.32).
Jan 5 12:33:25.065: DHCPD: client's VPN is .
Jan 5 12:33:25.065: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:33:25.065: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.
Jan 5 12:33:27.981: DHCPD: client's VPN is .
Jan 5 12:33:27.981: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:33:27.981: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.
Jan 5 12:33:29.081: DHCPD: client's VPN is .
Jan 5 12:33:29.081: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:33:29.081: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.
Jan 5 12:33:31.333: DHCPD: client's VPN is .
Jan 5 12:33:31.333: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:33:31.333: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.
Jan 5 12:33:32.925: DHCPD: client's VPN is .
Jan 5 12:33:32.925: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:33:32.925: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.
Jan 5 12:34:00.133: DHCPD: client's VPN is .
Jan 5 12:34:00.133: DHCPD: DHCPDISCOVER received from client 0110.b36f.485f.39 on interface FastEthernet0/1.200.
Jan 5 12:34:00.133: DHCPD: Sending DHCPOFFER to client 0110.b36f.485f.39 (10.225.0.31).
Jan 5 12:34:00.133: DHCPD: no option 125
Jan 5 12:34:00.133: DHCPD: creating ARP entry (10.225.0.31, 10b3.6f48.5f39, vrf default).
Jan 5 12:34:00.137: DHCPD: unicasting BOOTREPLY to client 10b3.6f48.5f39 (10.225.0.31).
Jan 5 12:34:00.137: DHCPD: removing ARP entry (10.225.0.31 vrf default).
Jan 5 12:35:00.229: DHCPD: client's VPN is .
Jan 5 12:35:00.229: DHCPD: DHCPDISCOVER received from client 0110.b36f.485f.39 on interface FastEthernet0/1.200.
Jan 5 12:35:00.229: DHCPD: Sending DHCPOFFER to client 0110.b36f.485f.39 (10.225.0.31).
Jan 5 12:35:00.229: DHCPD: no option 125
Jan 5 12:35:00.229: DHCPD: broadcasting BOOTREPLY to client 10b3.6f48.5f39.
Jan 5 12:36:00.373: DHCPD: client's VPN is .
Jan 5 12:36:00.377: DHCPD: DHCPDISCOVER received from client 0110.b36f.485f.39 on interface FastEthernet0/1.200.
Jan 5 12:36:00.377: DHCPD: Sending DHCPOFFER to client 0110.b36f.485f.39 (10.225.0.31).
Jan 5 12:36:00.377: DHCPD: no option 125
Jan 5 12:36:00.377: DHCPD: broadcasting BOOTREPLY to client 10b3.6f48.5f39.
Jan 5 12:36:01.925: DHCPD: client's VPN is .
Jan 5 12:36:01.925: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:36:01.925: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.
Jan 5 12:36:06.093: DHCPD: client's VPN is .
Jan 5 12:36:06.093: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:36:06.093: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.un
Jan 5 12:36:08.869: DHCPD: client's VPN is .
Jan 5 12:36:08.869: DHCPD: DHCPREQUEST received from client 01fc.4482.c77e.eb.
Jan 5 12:36:08.869: DHCPD: Finding a relay for client 01fc.4482.c77e.eb on interface FastEthernet0/0.debug all
All possible debugging has been turned off

MYazdian · ‎04-15-2024

Hi Guys,

nobody has any idea about dhcp-server and IP assignment on the interfaces on Cisco Router which has second-dot1q VLAN (500-600)

Thanks in advance

MHM Cisco World · ‎04-15-2024

Hi friend

I dont forget you'

The only why to make this work is config dhcp helper in SW user direct connect.

This make SW send unicast to dhcp and dhcp match the IP of helper with defualt-router under dhcp pool.

Otherwise I dont see away SW can know this broadcast is for which vlan.

Anyway and will do second review' and update you tonight

Thanks for waiting

MHM

MYazdian · ‎04-15-2024

Thank You MHM and really appreciate it