dhcp

[r0me0]

• I have two c2951 routers connected to a 3945e router, and a c3560 connected to each router as a lab. I can't get a host that is connected to one of the c3560 to c2951 to get ipconfig from dhcp on 3945e. What do I have to do to get the host to get a ip address?

[MHM Cisco World]

share the config 

[Georg Pauwen]

Hello,

do you have an ip helper-address configured on the 2951 interface (the first layer 3 interface between the host and the 3945e) ?

[r0me0]

Hello Georg,

Yes gi0/1 ip-address 192.168.10.1 on the c2951 has IP-helper address 172.16.10.1 gi0/2 on 3945e. The c3560 switch is connected to gi0/1 c2951. The dhcp pool on 3945e has network 192.168.10.0 255.255.255.0

[Georg Pauwen]

Hello,

that sounds right. Can you post the running configs (sh run) of all three devices ?

[MHM Cisco World · Accepted solution]

The router with local dhcp server dont know path for retrun back dhcp offer.

Make sure that router local dhcp know all dhcp pool subnet.

In SW with ip helper are you sure you can ping router local dhcp server ?

[r0me0]

No, I can not ping for c3560 switch natasha to dhcp router david, but i can ping from c2951 router Anne to c3945e dhcp router david.

here is the attempt to ping.

Natasha Pinelands Security

User Access Verification

Password:
natasha>en
Password:
natasha#show cdp entry * proto
Protocol information for anne :
IP address: 192.168.10.1
IPv6 address: 2001:DB8:3C4D:14:CEEF:48FF:FE4B:3022 (global unicast)
IPv6 address: FE80::CEEF:48FF:FE4B:3022 (link-local)
natasha#192.168.10.1
Trying 192.168.10.1 ... Open
Anne ShopNatasha Security

User Access Verification

Password:
Password:
anne>en
Password:
anne#show cdp entry * proto
Protocol information for natasha :
IP address: 192.168.10.2
IPv6 address: 2001:DB8:3C4D:14:21C:B0FF:FED9:34C0 (global unicast)
IPv6 address: FE80::21C:B0FF:FED9:34C0 (link-local)
Protocol information for david :
IP address: 172.16.10.1
IPv6 address: 2001:DB8:3C4D:12:6273:5CFF:FE3D:4702 (global unicast)
IPv6 address: FE80::6273:5CFF:FE3D:4702 (link-local)
anne#ping 172.16.10.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.10.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
anne#exit

[Connection to 192.168.10.1 closed by foreign host]
natasha#ping 172.16.10.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.10.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
natasha#

[MHM Cisco World]

You use ip default gateway ,

Use defualt route 

Ip route 0.0.0.0 0.0.0.0 

Instead and double check you enable ip routing in SW.

[Richard Burts]

It might be helpful if we had some diagram showing the relationships in this environment. Without that can you tell me if I am correct in understanding this about the topology: you have a computer connected to some port on a 3560 switch, the 3560 switch is connected on some other port to a 2951 router interface, the 2951 is connected on some other interface to some interface on 3945? Assuming that this is correct then please provide these:

- What port on the 3560 switch is connected to the computer?

- please post the output of show interface status of the 3560 switch so that we can confirm the interface connecting to the computer and what vlan this is in.

- what port on the 3560 switch connects to the 2951 router? Please post the configuration of this port so that we can know whether this is an access port or a trunk port.

- what interface on 2951 router connects to the 3560 switch? Please post the configuration of this interface (including any subinterfaces that might be configured) so that we can identify any connected vlans and subnets, and verify whether there is ip helper-address for the vlan where the computer is connected, and verify whether there are any ACL or other filtering being done.

- what interface on 2951 router connects to the 3945 router. Is this interface a regular routed interface? Please post the configuration of this interface so that we can verify the subnet and host address and verify whether there are any ACL or other filtering being done.

- what interface on 3945 router connects to the 2951 router. Is this interface a regular routed interface? Please post the configuration of this interface so that we can verify the subnet and host address and verify whether there are any ACL or other filtering being done.

- Please post the configuration of the DHCP scope on the 3945 router for the network where the computer is being connected.

- Please post the output on the 3945 router of show ip route so that we can verify that the 3945 does have a route for the subnet where the computer is connected and a correct next hop address for that path.

[r0me0]

Hello Advisor,

thanks for helping me out with this issue. I added a static ipv6 route from the local dhcp router 3945e via gi0/2 with admin distance 150 to the 3560 switch ipv6 subnet address and that did it. So now the host connected to the switch is getting a ip-address from the dhcp pool