ip helper-address issue

[148west]

hi all

i have 3550 switch. i have created 2 voice vlans and ther interfaces (20 and 30). i have entered ip helper-address in both the interfaces also setup port accordingly. now when i connect my phone to vlan 20, i get ip address and it registers fine. with vlan30 its not getting any ip address. as soon as i change that same port to vlan 20 i get the ip address. any input on this would be helpful

interface Vlan20
ip address 172.120.20.1 255.255.255.0
ip helper-address 192.168.1.10
!
interface Vlan30
ip address 172.130.30.1 255.255.255.0
ip helper-address 192.168.1.10

3550#ping
Protocol [ip]:
Target IP address: 192.168.1.10
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 172.120.20.1
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.10, timeout is 2 seconds:
Packet sent with a source address of 172.120.20.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/4/16 ms

3550#ping  
Protocol [ip]:
Target IP address: 192.168.1.10
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 172.130.30.1
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.10, timeout is 2 seconds:
Packet sent with a source address of 172.130.30.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

[Roman Rodichev]

did you double check the DCHP scope on your DHCP server? Is it windows dhcp? if so, run wireshark on it and capture packets from 172.130.30.1 when phone tries to get an IP. See if you are getting DHCP requests.

[148west]

thanks for replying.

i have checked the scope its fine. on phone when i checked the dhcp ip address there is nothing there, also dhcp is enabled on phone.

[Roman Rodichev]

do

debug ip udp

and check if you see UDP forwarding to helper when phone requests IP

(don't forget to "term mon")

[148west]

hi

here is the output

000045: 01:23:25: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=329
000046: 01:23:25: UDP: sent src=172.130.30.1(67), dst=192.168.1.10(67), length=329
3550#
000047: 01:23:29: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=329
000048: 01:23:29: UDP: sent src=172.130.30.1(67), dst=192.168.1.10(67), length=329
3550#
000049: 01:23:37: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=329
000050: 01:23:37: UDP: sent src=172.130.30.1(67), dst=192.168.1.10(67), length=329
3550#
000051: 01:23:53: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=329
000052: 01:23:53: UDP: sent src=172.130.30.1(67), dst=192.168.1.10(67), length=329

[Roman Rodichev]

there are no responses back from the DHCP server.

If you try this same with the working scope, do you see return packets in UDP debug?

[148west]

yes

here is the output

3550#
000090: 01:26:43: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=328
000091: 01:26:43: UDP: sent src=172.120.20.1(67), dst=192.168.1.10(67), length=328
000092: 01:26:43: UDP: rcvd src=192.168.1.10(67), dst=172.120.20.1(67), length=308
000093: 01:26:43: UDP: sent src=0.0.0.0(67), dst=255.255.255.255(68), length=308
000094: 01:26:43: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=556
000095: 01:26:43: UDP: sent src=172.120.20.1(67), dst=192.168.1.10(67), length=556
000096: 01:26:43: UDP: rcvd src=192.168.1.10(67), dst=172.120.20.1(67), length=308
000097: 01:26:43: UDP: sent src=0.0.0.0(67), dst=255.255.255.255(68), length=308

[Roman Rodichev · Accepted solution]

So that clearly tells you that the problem is definitely, without a doubt, on the DHCP server configuration.

[148west]

thanks Roman for your input. i am using cucm as my dhcp server. let me go ahead and restart the dhcp monitor service.

thank you

[148west]

yep, resetting the dhcp services resolve the issue.

000221: 01:43:22: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=328
000222: 01:43:22: UDP: sent src=172.130.30.1(67), dst=192.168.1.10(67), length=328
000223: 01:43:22: UDP: rcvd src=192.168.1.10(67), dst=172.130.30.1(67), length=308
000224: 01:43:22: UDP: sent src=0.0.0.0(67), dst=255.255.255.255(68), length=308
000225: 01:43:22: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=556
000226: 01:43:22: UDP: sent src=172.130.30.1(67), dst=192.168.1.10(67), length=556
000227: 01:43:22: UDP: rcvd src=192.168.1.10(67), dst=172.130.30.1(67), length=308
000228: 01:43:22: UDP: sent src=0.0.0.0(67), dst=255.255.255.255(68), length=308

thanks

[Roman Rodichev]

That's great!