From: Marvin Greenlee (marvin@ipexpert.com)
Date: Mon Jul 09 2007 - 22:27:42 ART
You're not quite seeing what you think you are seeing.
Example for DHCP configured:
R1(config-if)#ip add dhcp
R1(config-if)#
*Jul 9 21:32:27.884: IP: s=0.0.0.0 (local), d=255.255.255.255
(FastEthernet0/0), len 604, sending broad/multicast
*Jul 9 21:32:27.884: UDP src=68, dst=67
Your output shows "rcvd", not "sending". Note also that the source 0.0.0.0
is "Eth1/0", where if it was sending the source is local, and the dest is
the local interface.
Without an address configured, IP isn't processed for the interface
(including incoming). Enabling IP on the interface by adding an address
will cause the router to process incoming traffic on that interface.
Marvin Greenlee, CCIE #12237 (R&S, SP, Sec)
Senior Technical Instructor - IPexpert, Inc.
A Cisco Learning Partner - We Accept Learning Credits!
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
Mailto: mgreenlee@ipexpert.com
IPexpert - The Global Leader in Self-Study, Classroom-Based, Video
Class-On-Demand and Audio Certification Training Tools for the Cisco CCIE
R&S Lab, CCIE Security Lab, CCIE Service Provider Lab, CCIE Voice Lab and
CCIE Storage Lab Certifications.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Antonio Soares
Sent: Monday, July 09, 2007 8:52 PM
To: ccielab@groupstudy.com
Subject: Router sends DHCP Discover messages as soon as i assign it an IP
Hello group,
Noticed a strange thing and don't know how to explain it. A few seconds
after i assign an IP address to an interface, i see the router sending DHCP
Discover messages:
+++++++++++++++++++++++++++++++
R1#sh clock
*00:23:34.213 UTC Mon Mar 1 1993
R1#
R1#
R1#deb ip pa de
IP packet debugging is on (detailed)
R1#
R1#
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#
R1(config)#int e1/0
R1(config-if)#
R1(config-if)#no shut
R1(config-if)#
*Mar 1 00:23:48.998: %LINK-3-UPDOWN: Interface Ethernet1/0, changed state
to up
*Mar 1 00:23:49.999: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Ethernet1/0, changed state to up
R1(config-if)#
R1(config-if)#ip add 1.1.1.1 255.255.255.0
R1(config-if)#
R1(config-if)#
R1(config-if)#
*Mar 1 00:24:51.728: IP: s=0.0.0.0 (Ethernet1/0), d=255.255.255.255, len
576, rcvd 2
*Mar 1 00:24:51.728: UDP src=68, dst=67
R1(config-if)#
*Mar 1 00:24:55.727: IP: s=0.0.0.0 (Ethernet1/0), d=255.255.255.255, len
576, rcvd 2
*Mar 1 00:24:55.731: UDP src=68, dst=67
R1(config-if)#
*Mar 1 00:25:03.728: IP: s=0.0.0.0 (Ethernet1/0), d=255.255.255.255, len
576, rcvd 2
*Mar 1 00:25:03.728: UDP src=68, dst=67
R1(config-if)#
*Mar 1 00:25:19.730: IP: s=0.0.0.0 (Ethernet1/0), d=255.255.255.255, len
576, rcvd 2
*Mar 1 00:25:19.730: UDP src=68, dst=67
R1(config-if)#
R1(config-if)#
R1(config-if)#do u all
All possible debugging has been turned off
R1(config-if)#
+++++++++++++++++++++++++++++++
How to explain this ? This is exactly what we get when we configure "ip add
dhcp". Got the same bahaviour on 12.3 and 12.4 releases.
Thanks,
Antonio
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:40 ART