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New Member

DHCP Relay on ACE module

Hi

We've configured DHCP relaying on 4 different contexts (we are PXE booting the machines to do initial setup).

It seemed to be working when we did the initially setup. Now we needed to add some new servers to the VLAN and have noticed a strange behaviour with the DHCP relaying agent. It seems to add a static arp entry for the first DHCP request. This has the unfortunate effect that subsequent DHCP offers for the same IP address never make it into the arp table on the context:

Admin/context33# sh arp | inc STATIC
192.168.33.211    00.21.5a.4a.6a.32  vlan33  STATIC     459       _         up
192.168.33.212    00.21.5a.4a.0a.dc  vlan33  STATIC     437       _         up

Can we somehow disable this feature/bug? It's really annoying having to clear does arp entries everytime we have to add a new server.

/Bjoern

PS We are running A2(1.6a) and A2(1.3)

6 REPLIES
Silver

Re: DHCP Relay on ACE module

Are those entries DHCP servers or clients?

Why do you have to delete them? Does the MAC change for an IP address?

New Member

Re: DHCP Relay on ACE module

koltlpeter wrote:

Are those entries DHCP servers or clients?

Why do you have to delete them? Does the MAC change for an IP address?

DHCP clients.

We need to PXE bootstrap servers during the initial setup/installation. After the server is installed (OS) we configure it with a static ip address outside the DHCP scope and let it run.

The problem arises when we have to build a new server after the initial DHCPOFFER (from the first server) has expired. If the new server is offered the same ip address as the first server, but the ACE still has an arp entry for the first server.

Hope that clarifies it a little

/Bjoern

Silver

Re: DHCP Relay on ACE module

Have you tried to tune the ARP values with arp learned-interval or arp interval commands?

New Member

Re: DHCP Relay on ACE module

Hmmmm wouldn't that only have an effect on dynamic ARP?

I'm more wondering if this is some kind of buggy implementation of DHCP snooping.

Cisco Employee

Re: DHCP Relay on ACE module

I don't recall the DHCP code adding static arp entry.

Are you sure those static entry are not simply in your configuration ?

Gilles.

New Member

Re: DHCP Relay on ACE module

Pretty sure:

Admin/context33# sh arp | inc STATIC

192.168.33.211    00.21.5a.4a.6a.32  vlan33  STATIC     459        _         up
192.168.33.212    00.21.5a.4a.0a.dc  vlan33  STATIC      437       _         up
Admin/context33# sh run | inc arp
Generating configuration....
Admin/context33#

/Bjoern

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