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Ip Helper doesn't work?

I use a 3550 L2/L3 switch and I need to use a remote dhcp server.

I configured it on my router but it didn't work.

So I prepared a testing router with a very simple configuration but again I had problem. The request starts regulary, the router forward the request correctly, the dhcp server offers the ip address but the router answer back to the dhcp server that the his port 68 was unreachable.

Where I did wrong?

TIA.

Follows the configuration and some debug output.. test# sh ver test#sh ver

Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version

12.2(25)SEB4, RELEASE SOFTWARE (fc1) Copyright (c) 1986-2005 by Cisco Systems, Inc. Compiled Tue 30-Aug-05 17:35 by yenanh

ROM: Bootstrap program is C3550 boot loader ..

test#sh running-config Building configuration...

Current configuration : 2385 bytes ! version 12.2 no service pad service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname test ! enable secret ***************** enable password *************** ! no aaa new-model ip subnet-zero ip routing ! ! ! ! ! ! no file verify auto spanning-tree mode pvst spanning-tree extend system-id ! vlan internal allocation policy ascending ! ! interface FastEthernet0/1 no switchport ip address 172.28.48.254 255.255.255.0 ! interface FastEthernet0/2 no switchport ip address 172.28.33.254 255.255.255.0 ip helper-address 172.28.48.77 ! interface FastEthernet0/3 switchport mode dynamic desirable !

.....

snmp-server community cce RO ! control-plane ! ! line con 0 exec-timeout 0 0 line vty 0 4 password ********* login line vty 5 15 password ********* login ! ! end

test#

debug ip udp debug ip icmp

test#

17:42:20: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=308 17:42:20: UDP: sent src=172.28.33.254(67), dst=172.28.48.77(67), length=308 17:42:20: UDP: rcvd src=172.28.48.77(67), dst=172.28.33.254(68), length=308 17:42:20: ICMP: dst (172.28.33.254) port unreachable sent to 172.28.48.77 17:42:22: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=308 17:42:22: UDP: sent src=172.28.33.254(67), dst=172.28.48.77(67), length=308 17:42:22: UDP: rcvd src=172.28.48.77(67), dst=172.28.33.254(68), length=308 17:42:24: UDP: rcvd src=0.0.0.0(68), dst=255.255.255.255(67), length=308 17:42:24: UDP: sent src=172.28.33.254(67), dst=172.28.48.77(67), length=308 17:42:24: UDP: rcvd src=172.28.48.77(67), dst=172.28.33.254(68), length=308 17:42:24: ICMP: dst (172.28.33.254) port unreachable sent to 172.28.48.77
Reply to
root
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Try this: no service dhcp interface FastEthernet0/1 no ip directed-broadcast interface FastEthernet0/2 no ip directed-broadcast

Reply to
Make

Try this: no service dhcp interface FastEthernet0/1 no ip directed-broadcast interface FastEthernet0/2 no ip directed-broadcast

Reply to
Make
  1. Make sure your router is only forwarding DHCP requests to the DHCP server

! DHCP interface configuration template

int x/x ip helper-address exit

no ip forward-protocol udp tftp no ip forward-protocol udp domain no ip forward-protocol udp nameserver no ip forward-protocol udp time no ip forward-protocol udp netbios-ns no ip forward-protocol udp netbios-dgm no ip forward-protocol udp tacacs

  1. Make sure that the DHCP server is pingable from the router in question
Reply to
Merv

[Snip]

Looks like maybe your DHCP server is broken, or there is some NAT going on in the path or something.

See above, the router sends to the server with both source and destination port == 67 (bootps), but the server responds with destination port == 68 (bootpc), hence the port unreachable. The server should be using 67 as well.

Reply to
Martin Gallagher

what is the IOS version that is being used? post show version

Reply to
Merv

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