DHCP for PPP Link (revisited)

October 21, 2008 at 11:08 pm | Posted in IP Services | 1 Comment

Another caveat found today, in relation to the topic posted previously. https://enotepad.wordpress.com/2008/09/25/dhcp-for-ppp-link/

It is found when I do the WB Vol1 IP Services, Task 13.7 DHCP Proxy.

The Caveat:

When we specify DHCP server address, make sure that the IP address should be the source of the return “IP address offer” packet from the DHCP server. It is very relevant when the DHCP server has more than 1 path to the client.

If we specify one IP address, e.g. 155.1.67.6, while the return path from DHCP server exit another interface with IP address of 155.1.146.6, then the client will reject the offer, due to the “server not in approved list”.

 

R3#
 ip dhcp-server 155.1.67.6
 
*Mar  1 22:37:10.151: DHCP Offer Message   Offered Address: 155.1.23.2
*Mar  1 22:37:10.151: DHCP: Lease Seconds: 86400    Renewal secs:  43200    Rebind secs:   75600
*Mar  1 22:37:10.151: DHCP: Server ID Option: 155.1.146.6
*Mar  1 22:37:10.151: DHCP: offer received from 155.1.146.6
*Mar  1 22:37:10.151: DHCP: offer: server 155.1.146.6 not in approved list
R3#
ip dhcp-server 155.1.67.6
ip dhcp-server 155.1.146.6
*Mar  1 22:40:48.675: DHCP Offer Message   Offered Address: 155.1.23.2
*Mar  1 22:40:48.675: DHCP: Lease Seconds: 86400    Renewal secs:  43200    Rebind secs:   75600
*Mar  1 22:40:48.675: DHCP: Server ID Option: 155.1.146.6
*Mar  1 22:40:48.675: DHCP: offer received from 155.1.146.6
*Mar  1 22:40:48.675: DHCP: offer received in bad state: Requesting  punt
*Mar  1 22:40:48.863: DHCP: XID MATCH in dhcpc_for_us()
*Mar  1 22:40:48.863: DHCP: Received a BOOTREP pkt
*Mar  1 22:40:48.863: DHCP: Scan: Message type: DHCP Ack
*Mar  1 22:40:48.863: DHCP: Scan: Server ID Option: 155.1.146.6 = 9B019206
*Mar  1 22:40:48.863: DHCP: Scan: Lease Time: 86400
*Mar  1 22:40:48.863: DHCP: Scan: Renewal time: 43200
*Mar  1 22:40:48.867: DHCP: Scan: Rebind time: 75600
*Mar  1 22:40:48.867: DHCP: Scan: Subnet Address Option: 255.255.255.0
*Mar  1 22:40:48.867: DHCP: rcvd pkt source: 155.1.146.6,  destination:  155.1.23.3
*Mar  1 22:40:48.867:    UDP  sport: 43,  dport: 43,  length: 308
*Mar  1 22:40:48.867:    DHCP op: 2, htype: 1, hlen: 6, hops: 0
*Mar  1 22:40:48.867:    DHCP server identifier: 155.1.146.6
*Mar  1 22:40:48.867:         xid: 1DC0, secs: 0, flags: 0
*Mar  1 22:40:48.867:         client: 0.0.0.0, your: 155.1.23.2
*Mar  1 22:40:48.867:         srvr:   0.0.0.0, gw: 155.1.23.3
*Mar  1 22:40:48.867:         options block length: 60
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  1. […] Also see other related issue found at https://enotepad.wordpress.com/2008/10/21/dhcp-for-ppp-link-revisited/ […]


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