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DHCP Service

hi experts,

i have a 3750G used for a branch office which is connected via MetroE to our main 6509. when i plugged my laptop in one of the ports in the 3750G i can't get an IP address via DHCP. i've already put the 'ip helper-address <dhcp server address>' in the interface vlan. now, i used the 'ip dhcp' service on the switch (which is non-standard and temporary config). i can ping and trace the dhcp server from the 3750G. not sure what i'm missing here. below is the config:

interface Vlan124

description subnet 172.25.124.0/24 access

ip address 172.25.124.253 255.255.255.0

ip helper-address 172.25.22.10

ip helper-address 172.25.22.20

no ip proxy-arp

ip pim sparse-dense-mode

ip dhcp pool Temp_Subnet_124

network 172.25.124.0 255.255.255.0

default-router 172.25.124.253

dns-server 128.x.x.x 128.137.1.3

netbios-name-server 128.x.x.x 128.x.x.x

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Re: DHCP Service

John

In a previous post you said:"when i made a ping from source int vlan 124, i got an error which says interface is not enabled. i did a show ip int bri on this switch and saw that int vlan 124 protocol is down."

I believe that this is your problem. I do not believe that you have an OSPF problem. If you resolve the problem with VLAN124 I believe that your routing will work. (note that IOS will not advertise the subnet of an interface that is not up/up)

Do you have an active device plugged into a port in VLAN124?

HTH

Rick

9 REPLIES
Hall of Fame Super Silver

Re: DHCP Service

Hello John,

check if there are any forward protocols in global config of the C3750G

sh run | inc forward

eventually you may need to add one for bootp protocol to restore default behaviour.

Hope to help

Giuseppe

Re: DHCP Service

when i made a ping from source int vlan 124, i got an error which says interface is not enabled. i did a show ip int bri on this switch and saw that int vlan 124 protocol is down. i've checked ospf network statements and can see the other main switch as its neighbors (also checked on main switch, both have ospf configured). i did a no shut but no avail. how can i enable this (can re-creating the int vlan help)?

Vlan124 172.25.124.253 YES NVRAM up down

Re: DHCP Service

Do you have vl124 in the vl db or otherwise have created the vl on the sw in question?

Jimmy

Re: DHCP Service

yes. i've created the vlan 124 database and then the int vlan 124.

vlan 124

name 172.25.124.0/24

from this switch, i can see all ospf route towards ds-main switch and sees as its ospf neighbor.

the ds-main switch sees the other route (loopback 172.25.0.124) using show ip route except for the ip address of this vlan 124 interface (172.25.124.253):

ds-main#sh ip ro 172.25.124.253

% Subnet not in table

ds-main#sh ip ro 172.25.0.124

Routing entry for 172.25.0.124/32

Known via "ospf 10", distance 110, metric 2, type intra area

Last update from 172.25.250.41 on GigabitEthernet2/13, 00:29:07 ago

Routing Descriptor Blocks:

* 172.25.250.41, from 172.25.0.124, 00:29:07 ago, via GigabitEthernet2/13

Route metric is 2, traffic share count is 1

i've tried re-creating the vlan database and the int vlan, shut and no shut the interface and also clear ospf process and the routing table but no avail. could this be a bug in the IOS?

Re: DHCP Service

John,

Please post the configuration regarding OSPF. I'd love to use "sh ip ospf interface brief" to re-check on Sw3750. Do you see Vlan124 there?

Please let me see your "show ip protocol" on Sw3750.

HTH,

Toshi

Hall of Fame Super Gold

Re: DHCP Service

John

In a previous post you said:"when i made a ping from source int vlan 124, i got an error which says interface is not enabled. i did a show ip int bri on this switch and saw that int vlan 124 protocol is down."

I believe that this is your problem. I do not believe that you have an OSPF problem. If you resolve the problem with VLAN124 I believe that your routing will work. (note that IOS will not advertise the subnet of an interface that is not up/up)

Do you have an active device plugged into a port in VLAN124?

HTH

Rick

Re: DHCP Service

thanks rick! int vlan was up/up when i connected my laptop and vlan was advertised/routing properly in ospf.

Hall of Fame Super Gold

Re: DHCP Service

John

I am glad that you got your problem resolved and that my suggestion was helpful. Thank you for posting to the forum and indicating that the problem is solved and what the solution was. Thank you for using the rating system to indicate that the problem was solved (and thanks for the rating). It makes the forum more useful when people can read about a problem and can know that they will read about the solution to the problem.

HTH

Rick

Re: DHCP Service

Had a feeling either the vlan wasnt created or nothing was plugged in.

Thanks for the update!

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