Strange issue with "ip helper-address" feature.

Answered Question
Sep 29th, 2010

Hi all,

I've found a strange problem when trying to set up the following scenario and need some expertise:

scenario1.JPG

Once everything is set, the phone is not getting an IP address from the DHCP server. Pings from a PC to SVI 71 or even DHCP Server with a static address, work fine (as expected) . Further investigations, by enabling dhcp snooping on L3 Switch for Vlan 71, reveal that the DHCP Discover packet is actually being received by the L3Switch, as shown. So, no problem here.

dhcpsnooping.JPG

But, a "debug ip packet detail 101" (ACL 101) shows that the packet is being unicasted, but the source address is 0.0.0.0 instead of

SVI IP address of vlan 71.

debugippacket.JPG

Of course, the DHCP server never receives these packets (I assume L3Switch itself drops them).

No more investigations have been made, since I have tested the scenario in lab with a CAT3560 as L3 Switch and everything is fine, and source ip address for unicast broadcasts leaving the L3switch is 10.70.1.1 (as usual)

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Some details for L3Switch in real environment are:

WS-C4510R-E with double WS-X45-SUP6-E  (version 12.2 (40) SG of cat4500e-IPBASEK9-M)

If more details are needed, just ask. Any idea?

Regards

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 6 years 3 months ago

Hello Pablo,

this looks like to be a software bug on the C4510R-E, an IOS upgrade to a more recent IOS version might solve this issue.

searching with the bug toolkit may be of help too

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Wed, 09/29/2010 - 12:52

Hello Pablo,

this looks like to be a software bug on the C4510R-E, an IOS upgrade to a more recent IOS version might solve this issue.

searching with the bug toolkit may be of help too

Hope to help

Giuseppe

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