12-30-2015 06:47 AM - edited 03-08-2019 03:15 AM
Hello,
We are facing an issue while configuring DHCP snooping.
We are configuring DHCP snooping on "Access SW" C2960X Software (C2960X-UNIVERSALK9-M), Version 15.0(2), we have multiple VLANs in our network. And for some VLAN we
have configure DHCP on "Dist. SW"Catalyst 4500 L3 Switch Software (cat4500e-UNIVERSALK9-M), Version 03.04.00.SG RELEASE SOFTWARE (fc3) and for remaining VLANs we have configured
DHCP on freeBSD.
When we enable DHCP snooping everything working fine for those vlans which are getting DHCP ip from freeBSD, but for vlans which have DHCP on Dist. SW client are unable to get IP.
VLAN2: DHCP on freeBSD // working fine
VLAN3: DHCP on Dist. SW // not working
VLAN4: DHCP on freeBSD //working fine
Access-SW#sh ip dhcp snooping
Switch DHCP snooping is enabled
DHCP snooping is configured on following VLANs:
2,3,4
DHCP snooping is operational on following VLANs:
2,3,4
DHCP snooping is configured on the following L3 Interfaces:
Insertion of option 82 is enabled
circuit-id default format: vlan-mod-port
remote-id: xxx.xxxx.xxxx (MAC)
Option 82 on untrusted port is not allowed
Verification of hwaddr field is enabled
Verification of giaddr field is enabled
DHCP snooping trust/rate is configured on the following Interfaces:
Interface Trusted Allow option Rate limit (pps)
----------------------- ------- ------------ ----------------
GigabitEthernet1/0/24 yes yes unlimited
VALN3 clients are unable to get DHCP IP. Only able ot get IP when we disable IP DHCP snooping
Can anyone help me to figure it out what is the issue.
snooping is only enable on Access SW.
Regards,
Solved! Go to Solution.
12-30-2015 11:36 AM
Hello
so you have enabled dhcp snooping on a switch that is actually an active dhcp server?
To be honest I have never come across this it defeats the objective of snooping as you dhcp server isnt residing on a actual physical interface
I need to test this myself but have you tried trusting the svi of vlan 3 ?
res
paul
12-30-2015 09:55 PM
Hi,
in Access SW
Put in global config. : no ip dhcp snooping information option
---- by default switch adds option 82 in DHCP packet.
there is a complete discussion on following link:
https://learningnetwork.cisco.com/thread/63215
12-30-2015 06:57 AM
Hello
Have you trusted the trunks between these switches
res
Paul
12-30-2015 11:04 AM
Thanks for the reply paul,
The freeBSD DHCP server and Catalyst 4500 L3 Switch both are connected with a CISCO 2960 switch on which DHCP snooping is not enabled. This switch is further connected with another CISCO 2960 switch which is at my access layer and client are connected with that switch. The trunk link between switches is a trusted interface at the client end switch where DHCP snooping is enabled as shown in the config earlier.
DHCP snooping trust/rate is configured on the following Interfaces:
Interface Trusted Allow option Rate limit (pps)
----------------------- ------- ------------ ----------------
GigabitEthernet1/0/24 yes yes unlimited ( Trunk link)
DHCP snooping is enabled only at the client end switch.
I further attached a diagram of my topology please see the attachment.
12-30-2015 11:36 AM
Hello
so you have enabled dhcp snooping on a switch that is actually an active dhcp server?
To be honest I have never come across this it defeats the objective of snooping as you dhcp server isnt residing on a actual physical interface
I need to test this myself but have you tried trusting the svi of vlan 3 ?
res
paul
12-30-2015 11:53 AM
Hello ,
DHCP snooping is not enabled on a CISCO 4500 MLS which is also acting as a DHCP server for management VLAN.
DHCP is only enabled on the access layer switch.
12-30-2015 09:55 PM
Hi,
in Access SW
Put in global config. : no ip dhcp snooping information option
---- by default switch adds option 82 in DHCP packet.
there is a complete discussion on following link:
https://learningnetwork.cisco.com/thread/63215
12-30-2015 10:07 PM
Thanks Zohaib Khan for the reply
This command works for me
In global config. : no ip dhcp snooping information option
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