From: Matt White (mwhite23@gmail.com)
Date: Sat Jul 16 2005 - 00:55:35 GMT-3
Funny you should ask. I just spent well over an hour messing with
this, and it eventually took a reboot of a 6509 with a FlexWAN/HSSI
to get DHCP to work again on a network, even after removing all the
relevant commands... I guess this is one feature that needs some more
testing on mine (and apparently others') part.
14533
On Jul 15, 2005, at 2:42 PM, gladston@br.ibm.com wrote:
> Have you succesfully configured DHCP Snooping when helper address
> is used on local router?
>
> It is not working for me.
> Without snooping, R7 gets its address from R3 (dhcp server).
> After snooping is configured on CAT1, R3 does not receive the request.
>
> r7(client)----CAT1(0/6)----R6---serial----R3
>
> This is the config used:
>
> CAT1
> ip dhcp snooping vlan 10
> ip dhcp snooping
> !
> interface FastEthernet0/6
> desc **R6** ***path to R3 ***
> ip dhcp snooping trust
>
> R6 is acting as relay agent. It is receiving the request from R7:
>
> R6
> *Jul 15 17:27:25: IP: s=0.0.0.0 (FastEthernet4/0),
> d=255.255.255.255, len 322, rcvd 2
> *Jul 15 17:27:25: UDP src=68, dst=67
>
> This is the result on R3 with snooping on CAT1:
>
> (nothing -- DHCPDISCOVER is not received)
>
> If snooping is disabled, R3 works fine:
>
> Rack2R3#
> *Mar 1 06:57:07: DHCPD: DHCPDISCOVER received from client
> 0100.000c.3bd6.a9 through relay 148.5.46.6.
>
> *Mar 1 06:57:09: DHCPD: Sending DHCPOFFER to client 0100.000c.
> 3bd6.a9 (148.5.46.106).
> *Mar 1 06:57:09: DHCPD: unicasting BOOTREPLY for client
> 0000.0c3b.d6a9 to relay 148.5.46.6.
> *Mar 1 06:57:09: DHCPD: DHCPREQUEST received from client 0100.000c.
> 3bd6.a9.
> *Mar 1 06:57:09: DHCPD: Sending DHCPACK to client 0100.000c.
> 3bd6.a9 (148.5.46.106).
> *Mar 1 06:57:09: DHCPD: unicasting BOOTREPLY for client
> 0000.0c3b.d6a9 to relay 148.5.46.6.
>
>
> It seems there is something on the DHCP request when snooping are
> enabled that makes R6 do not relay the packet to R3.
>
>
> Other monitor commands are here:
>
> Rack2CAT1#sh ip dhc snoo
> Switch DHCP snooping is enabled
> DHCP snooping is configured on following VLANs:
> 10
> Insertion of option 82 is enabled
> Interface Trusted Rate limit (pps)
> ------------------------ ------- ----------------
> FastEthernet0/2 yes unlimited
> FastEthernet0/4 yes unlimited
> FastEthernet0/6 yes unlimited
>
>
> Rack2CAT1#sh deb
> DHCP Snooping event debugging is on
> 05:48:44: DHCPSN: Found ingress pkt on Fa0/7 VLAN 10
> 05:48:44: DHCP_SNOOPING: add relay information option.
> 05:48:44: DHCP_SNOOPING: binary dump of relay info option, length:
> 20 data:
> 0x52 0x12 0x1 0x6 0x0 0x4 0x0 0xA 0x0 0x6 0x2 0x8 0x0 0x6 0x0 0xB
> 0xFD 0xC7 0xC1 0x80
>
> 05:48:47: DHCPSN: Found ingress pkt on Fa0/7 VLAN 10
> 05:48:47: DHCP_SNOOPING: add relay information option.
> 05:48:47: DHCP_SNOOPING: binary dump of relay info option, length:
> 20 data:
> 0x52 0x12 0x1 0x6 0x0 0x4 0x0 0xA 0x0 0x6 0x2 0x8 0x0 0x6 0x0 0xB
> 0xFD 0xC7 0xC1 0x80
>
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