Solved: Re: router as dhcp server,

sarahr202 · ‎10-14-2012

Hi everybody

I am reading about how to configure cisco router as dhcp server and troublshoot any issue related to it

I performed this lab as shown below:

R1--f0/0-199.199.19.0--R2---198.198.198.0----R4

R1 is configured as dhcp client

R2 is dhcp relay agent

R4 is dhcp server.

R1 f0/0 mac address: c000.211c.0000

Below is dhcp ack sent by R4( dhcp server) to R2( relay agent):

No. Time Source Destination Protocol Length Info
760 2618.315000 198.198.198.4 199.199.199.2 DHCP 342 DHCP ACK - Transaction ID 0x1208

Frame 760: 342 bytes on wire (2736 bits), 342 bytes captured (2736 bits)
Ethernet II, Src: c0:03:21:1c:00:00 (c0:03:21:1c:00:00), Dst: c0:01:21:1c:00:10 (c0:01:21:1c:00:10)
Internet Protocol Version 4, Src: 198.198.198.4 (198.198.198.4), Dst: 199.199.199.2 (199.199.199.2)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)
Bootstrap Protocol
    Message type: Boot Reply (2)
    Hardware type: Ethernet
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x00001208
    Seconds elapsed: 0
    Bootp flags: 0x8000 (Broadcast)
    Client IP address: 0.0.0.0 (0.0.0.0)
    Your (client) IP address: 199.199.199.1 (199.199.199.1)
    Next server IP address: 0.0.0.0 (0.0.0.0)
    Relay agent IP address: 199.199.199.2 (199.199.199.2)
    Client MAC address: c0:00:21:1c:00:00 (c0:00:21:1c:00:00)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (t=53,l=1) DHCP Message Type = DHCP ACK
    Option: (t=54,l=4) DHCP Server Identifier = 198.198.198.4
    Option: (t=51,l=4) IP Address Lease Time = 1 day
    Option: (t=58,l=4) Renewal Time Value = 12 hours
    Option: (t=59,l=4) Rebinding Time Value = 21 hours
    Option: (t=12,l=13) Host Name = "R1.lab.local."
    Option: (t=1,l=4) Subnet Mask = 255.255.255.0
    End Option
    Padding

Above we can see R1 f0/0 is being assigned 199.199.199.1. Lets confirm it.

R1#show ip int brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 199.199.199.1 YES DHCP up up

Now When I check the dhcp binding at R4, I should have found 199.199.199.1----> c0:00:21:1c:00:00 ( R1 f0/0 mac address)

However, I found something completely different:

R4#show ip dhcp binding

Bindings from all pools not associated with VRF:

IP address Client-ID/ Lease expiration Type

Hardware address/

User name

199.199.199.1 0063.6973.636f.2d63. Mar 02 2002 12:57 AM Automatic

3030.302e.3231.3163.

2e30.3030.302d.4661.

302f.30

None of the highlighted mac address matches the R1 f0/0 mac c0:00:21:1c:00:00

What is the issue here?

why do we have more than one mac bind to 199.199.199.1?

Where do these mac addresses come from?

thanks and have a great day.

singhaam007 · ‎10-14-2012

Hello Sarah,

please try this command

R4#show ip dhcp binding 199.199.199.1 and see what is the output.

thanks

View solution in original post

singhaam007 · ‎10-14-2012

hello Sarah,

its look like its default server automatic behaviour.

if you do

# debug ip dhcp server packets

it will show you in loggs that 0063.6973.636f.2d63.3030.302e.3266.6130.2e30.3030.302d.4661.302f.30 is one mca adress

R2#
*Oct 24 16:44:19.015: DHCPD: Sending notification of DISCOVER:
*Oct 24 16:44:19.015: DHCPD: htype 1 chaddr 0018.b9cd.bef0
*Oct 24 16:44:19.015: DHCPD: remote id 020a0000ac10170200000000
*Oct 24 16:44:19.015: DHCPD: circuit id 00000000
4 - 15 CCNP: Building Scalable Internetworks v5.0 - Lab 5-5 Copyright 2006, Cisco Systems, Inc
*Oct 24 16:44:19.015: DHCPD: DHCPDISCOVER received from client
0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30 on
interface FastEthernet0/0.
*Oct 24 16:44:19.015: DHCPD: Seeing if there is an internally specified pool
class:
*Oct 24 16:44:19.015: DHCPD: htype 1 chaddr 0018.b9cd.bef0

so in end you will get similar answer.

R2# show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type
Hardware address/
User name
172.16.23.101 0063.6973.636f.2d30. Oct 25 2006 10:20 PM Automatic
3031.382e.6239.6364.
2e62.6566.302d.4661.
302f.30

you can try manual binding if you want hope fully this will bit diffrent.

thanks

View solution in original post

cadet alain · ‎10-15-2012

Hi Sarah,

this string is not the MAC address but the client-identifier.

0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30

is cisco-0018.b9cd.bad0.Fa0/0 in Hex.

You can change this behaviour with the command ip address dhcp client-id fastethernet0/0 and then you'll see the MAC

address of the interface as client-identifier.

Regards.

Alain

Don't forget to rate helpful posts.

View solution in original post

cadet alain · ‎10-15-2012

Hi,

http://www.asciitable.com/

63 in hex is 99 in decimal and the ascii code for decimal 99 is lower case c

69 in hex is 105 in decimal which is ascci code for lowercase i. and so on...

Regards.

Alain

Don't forget to rate helpful posts.

View solution in original post

cadet alain · ‎10-17-2012

Hi Sarah,

http://blog.ioshints.info/2007/08/default-dhcp-client-id.html

Regards.

Alain

Don't forget to rate helpful posts.

View solution in original post

singhaam007 · ‎10-14-2012

Hello Sarah,

please try this command

R4#show ip dhcp binding 199.199.199.1 and see what is the output.

thanks

sarahr202 · ‎10-14-2012

Hi Singh

I recreated the lab as shown below, still same result.

R1 f0/0----------f0/0--R2---------------------R3

R1 dhcp client

R2 dhcp relay agent

R3 dhcp server.

R3#show ip dhcp binding 199.199.199.1

IP address Client-ID/ Lease expiration Type

Hardware address/

User name

199.199.199.1 0063.6973.636f.2d63. Mar 02 2002 12:06 AM Automatic

3030.302e.3266.6130.

2e30.3030.302d.4661.

302f.30

R1#show int f0/0

FastEthernet0/0 is up, line protocol is up

Hardware is Gt96k FE, address is c000.2fa0.0000 (bia c000.2fa0.0000)

R1#show ip int brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 199.199.199.1 YES DHCP up up

Thanks

singhaam007 · ‎10-14-2012

hello Sarah,

its look like its default server automatic behaviour.

if you do

# debug ip dhcp server packets

it will show you in loggs that 0063.6973.636f.2d63.3030.302e.3266.6130.2e30.3030.302d.4661.302f.30 is one mca adress

R2#
*Oct 24 16:44:19.015: DHCPD: Sending notification of DISCOVER:
*Oct 24 16:44:19.015: DHCPD: htype 1 chaddr 0018.b9cd.bef0
*Oct 24 16:44:19.015: DHCPD: remote id 020a0000ac10170200000000
*Oct 24 16:44:19.015: DHCPD: circuit id 00000000
4 - 15 CCNP: Building Scalable Internetworks v5.0 - Lab 5-5 Copyright 2006, Cisco Systems, Inc
*Oct 24 16:44:19.015: DHCPD: DHCPDISCOVER received from client
0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30 on
interface FastEthernet0/0.
*Oct 24 16:44:19.015: DHCPD: Seeing if there is an internally specified pool
class:
*Oct 24 16:44:19.015: DHCPD: htype 1 chaddr 0018.b9cd.bef0

so in end you will get similar answer.

R2# show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type
Hardware address/
User name
172.16.23.101 0063.6973.636f.2d30. Oct 25 2006 10:20 PM Automatic
3031.382e.6239.6364.
2e62.6566.302d.4661.
302f.30

you can try manual binding if you want hope fully this will bit diffrent.

thanks

cadet alain · ‎10-15-2012

Hi Sarah,

this string is not the MAC address but the client-identifier.

0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30

is cisco-0018.b9cd.bad0.Fa0/0 in Hex.

You can change this behaviour with the command ip address dhcp client-id fastethernet0/0 and then you'll see the MAC

address of the interface as client-identifier.

Regards.

Alain

Don't forget to rate helpful posts.

sarahr202 · ‎10-15-2012

Thanks Alain

0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30

is cisco-0018.b9cd.bad0.Fa0/0 in Hex.

The highligted numbers are already in hex

How can we say

0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30

is cisco-0018.b9cd.bad0.Fa0/0 in Hex.?

cadet alain · ‎10-15-2012

Hi,

http://www.asciitable.com/

63 in hex is 99 in decimal and the ascii code for decimal 99 is lower case c

69 in hex is 105 in decimal which is ascci code for lowercase i. and so on...

Regards.

Alain

Don't forget to rate helpful posts.

sarahr202 · ‎10-16-2012

Hi Alain

0063.6973.636f.2d30.3031.382e.6239.6364.2e62.6566.302d.4661.302f.30

You are saying the above string is in hex, and its ASCI representation is:

cisco-0018.b9cd.bad0.Fa0/0

Is that correct?

But i thought mac address is written in hex.

thanks

cadet alain · ‎10-17-2012

Hi Sarah,

http://blog.ioshints.info/2007/08/default-dhcp-client-id.html

Regards.

Alain

Don't forget to rate helpful posts.

sarahr202 · ‎10-17-2012

thanks Alain. I got it. Nice link