Cisco Switching/Routing :: 3750v2 DHCP Snooping Not Working Dropping Packets
Jan 9, 2013
I recently installed DHCP snooping on a 3750v2 switch (Version 12.2(55)SE4) and configured the uplink(Po2) as a trusted port. The problem is that clients cannot receive an IP address. When I disable DHCP snooping it is working properly. DHCP snooping is configured correctly but I don't have an idea how to resolve it. [code]I tested the solution on the same kind of hardware switch and firmware and it worked out fine. What is causing the clients not to receive an IP address from the DHCP server?
I have a problem at a place where 5 ME3400 switches are connected in a straight line. I can't do much about the topology of that place, but the problem is they are all DHCP Snooping, but uni cast replies from the dhcp server further up the hierarchy gets eaten by the first switch! I can't really see why it not only inspects in and whines about it not being for itself - it then drops the message.
What have we done wrong (apart from the actual layout of that place, which I can't really change)?
Sep 28 13:49:29: DHCP_SNOOPING: received new DHCP packet from input interface (GigabitEthernet0/1) Sep 28 13:49:29: DHCP_SNOOPING: process new DHCP packet, message type: DHCPOFFER, input interface: Gi0/1, MAC da: 7444.012d.debd, MAC sa: 0013.1a4a.65c7, IP da: XX.YY.186.7, IP sa: XX.YY.186.1, DHCP ciaddr: 0.0.0.0, DHCP yiaddr: XX.YY.186.7, DHCP siaddr: 0.0.0.0, DHCP giaddr: 0.0.0.0, DHCP chaddr: 7444.012d.debd Sep 28 13:49:29: DHCP_SNOOPING: binary dump of option 82, length: 20 data: [Code] ......
It really should just send it on, as with any uni cast not on the switch itself - it should go out Gi0/2 really. Why isn't it?
All the trunks are trusted, DAI is on (I've tried shutting it off, as well), port-security is used but it's actually not dying on the switch having the client computer, but the first one in the chain with dhcp snooping.
I have a problem with high CPU load by DHCP Snooping process on Catalyst 6506 (WS-SUP720-3B, soft: s72033-ipservices_wan-mz.122-18.SXF11.bin). I have it enabled on 15 VLANS, in which there are subscriber devices residing, and sending DHCP requests through Cisco to DHCP server (Cisco acts as DHCP relay, and it's collecting the snooping database, I also use DAI).
Snooping database contains 6962 bindings now.
CPU load goes high only sometimes, and I don't have a clue, why it's going so high. It can load as high as 45-47% of CPU, like this:
When the load is high, the command: show ip dhcp snooping statistics is showing, that the overall quantity of Packets Processed by DHCP Snooping is increasing rapidly. In normal situations, it's like 10-20 packets per second, but when the load is high, it's 1000-10000 pps.
But when I look at SPAN from my subscriber's VLANS, I don't really see any flood of DHCP requests, or something like that - everything looks as usual. Maybe, some of subscriber's devices are sending incorrect DHCP requests, that are causing packets to loop inside RP, or something like that? How can I detect that thing?
Also I thought, that if I enable the ip dhcp snooping trust mode on all of the Catalyst interfaces, the DHCP snooping will not process the subscribers DHCP packets, and I can, by exclusion of interfaces from one to one, detect, from which interface the problem is originating. But this seems to be incorrect, I turned the ip dhcsp snooping trust on all interfaces, and I still get spikes of CPU load by DHCP snooping process. Why it's still examining packets, even on trusted interfaces, is it ok?
And one more question - if I disable the ip dhcp snooping globally, will it clear all my existing bindings in snooping database?
I have attempted to implement DHCP snooping and have been having some strange issues. I have 5 3560s taht I use for my edge and when I attempt to implement on all five, the VLAN that houses my voice data appears to no longer be able to recieve DHCP lease renewals so after the 24 expiration all of my phones lose their configs. Once I roll back the changes the voice VLAN comes back. The other VLANs seem to function correctly as theya re able to renew their DHCP addresses.
The 3560s tie into each other using GIG Ports 1 & 2 and the top and bottom switches tie into our core switch, a 4507. The config that I use is below, failry simple and straightforward.
4 of the 5 switches feed our general office vlans for voice and data however the 5th switch is there for expansion and not in use. As such I have left the config changes in place on it and have tied myself and a colleague into it and have been operating fine for over a week now. So the config that I use seems sound in theory and should work on the other 4 switches with no issue.
I am working in a environment that is classed as collapssed Layer 3 environment. We have a core 6500 with routed links to 3560's which are access switches.
We have layer 3 vlans on the access switches, one for data one for voice.On the layer 3 vlans we have ip helper addresses that are used for DHCP. The DHCP servers are located on the 6500.
I recently had a incident where someone plugged a netgear router into a desk point because they thought they could use it for a switch. This router then started to dish out IP addresses to people in the morning for those who came in and docked their laptops. 99% of people weren't affected because they have desktop PC's are their leases hadn't expired.
Now we have bpduguard, bpdufilter to prevent people from plugging in switches that send out BPDU's. However this doesn't prevent the above senario where someone plugs a router or a 'dumb' switch that doesn't send BPDU's.Because of the above senario I started looking at DHCP Snooping, but I am unsure on a couple of things.
With the topology of our network I understand that I don't need to configure IP DHCP Snooping Trust on the L3 uplinks to our core switch. From what I understand I just need to enable IP DHCP Snooping globaly and then on the VLAN's on the access switch (because of the L3 topology VLAN's are local to the access switches). Only if I had L2 uplinks to the core would I need to configure IP DHCP Snooping Trust on the trunk links.
I am trying to understand the basics of DHCP snooping. I have a just a 3560 switch and a laptop ( to get a DHCP address) and my DSL router which has a DHCP server running. On the switch I have enabled "IP DHCP Snooping" and "IP DHCP Snooping VLAN 1" plugged the laptop and DSL router in and the laptop gets and IP address, should it?
I thought all ports were untrusted by default so the DHCP server should be blocked at offering IP addresses? If I wanted the DHCP server to be allowed to offer IP's I thought I should need to trust the port.
I have a new catalyst 2960,and i want to enable DHCP SNOOPING,but,it doesn't work,the server is stilling offert addresses IP and it's not connected in a trusted port,the schema is very simple:1 switch catalyst 2960 PST-S,1 server dhcp and 1 pc client,the PC and the server are in VLAN 10,DHCP SNOOPING is enabled in all ports and no port is trusted,but the client get addresse IP after retyping ipconfig /release and ipconfig /renew in dos commande.the configuration and the version of the switch are in the file attached.I tested the same configuration in a catalyst C3560-24PS and DHCP SNOOPING work normally,i tested in other catalyst 2960-PST-S,but the same probléme:DHCP SNOOPING without effect,the commands typed is:
I got some problem with enabling dhcp snooping on 4500 (cat4500e-lanbasek9-mz.122-54.SG.bin) the topology is as below: dhcp snooping enabled only on CORE (with interface trusted to dhcp server)the problem is that I put these 2 commands
ip dhcp snooping ip dhcp snooping vlan 1
but it is not enabled on any vlan
SW-CORE#sh ip dhcp snooping Switch DHCP snooping is enabled DHCP snooping is configured on following VLANs: none DHCP snooping is operational on following VLANs:
On B1 if I turn it on there is a "1" in the section " DHCP snooping is configured on following VLANs:" but on core no.As you can see I did put the trusted on the interface in the direction to the dhcp.First I thought it can be a problem with option 82, I've read a lot about the issues with that, but the problem would be explicable if the client did receive IP address, but it does.
Just spoke to the TAC and didn't get the information needed. When configuring ip dhcp snooping database I am adding this to my configuration:ip dhcp snooping database scp://email@example.com/home/dhcpsec/switch1.dhcp.database.txt..I assumed that to do this I would either specify the password on the command line, similar to the way its done when using ftp/http, or that I would need to create a public/private key.I have enabled scp and can manually copy a file from the switch to the linux server. So I believe I have all the aaa commands correct. Cisco WS-C3560G-24PS System image file is "flash:/c3560-ipservicesk9-mz.122-55.SE.bin".
i have a strange problem in my campus network.im trying to run port security on my access switches which they are 3550 with ios c3550-ipservicesk9-mz.122-52.SE when i run the port security with Sticky option, even i put 1000 mac address for just learning on the port but when i issue the switchport port-security command every pc connected to that port loses its connection with network UNTIL i enable dhcp snooping!!! all my client are getting they ip address from DHCP server but strange thing is that how on earth i have to enable DHCP snooping to port security work properly? also when i check the configuration under the interface when dhcp snooping is not yet enabled switch doesnt add any mac address under the interface so no one can work until i enable snooping and then switch adds mac addresses under the interface configuration.is this Bug on this version of IOS?[code]
we've an infrastructure were the Access is based on Cat3750G Stacks connected to both Cores using L3 connections.On the Access Switches are implemented the following features DHCP Snooping, IP Source Guard and Dynamic ARP Inspection and all is working fine since years...the DHCP Servers are on a dedicated stack which act as a SFarm.
On the Access Switches the port configuration is the following:the Uplink Ports to both of the Cores are configured in TRUST for DHCP Snooping and ARP Inspection the Access Ports, where the end-device are connected, are UNTRUST for DHCP and ARP Inspection with IP Source Guard Active Right now I've to add a new L2 switch on one of the Access Port and I'm wondering if this is possible since I've to keep on the Stack Access Ports all the security feature active and I've also to implement DHCP Snooping on the new L2 switch to avoid rouge DHCP Server...
I suppose that the uplink to the L2 switch on the Stack Access Switch should be left as it is connected to an end device...but the uplink port on the L2 switch should be set up as TRUST...isn'it? Keeping in mind that I want to implement DHCP Snooping also on this L2 switch to avoid that Rogue DHCP Servers will impact the end-device connected to this L2 switch...is this scenario possible??? or I can't do that and should leave DHCP Snooping only on the Access Stack.
I have a problem with DHCP. I have two 2960 connected with a port channel on ports 47 and 48 as trunk with native vlan 10. I only have this one vlan. In port 1 of sw 1, I have a C800 as DHCP server.
I have an AP autonomous with single ssid on vlan 10. When I connect the AP to sw1, I receive dhcp with no problems.When I connect the AP to sw 2, I’m not getting IP by DHCP.I have DHCP snooping working on vlan 10 on both devices.
The ports where I connect the AP are access ports on vlan 10 config as trusted.The trunk ports are also configured as trusted.The port 1 of ws 1 that goes to the C800 is also configured as trusted.
figure out why I’m not getting IP by DHCP when I connect the AP to the SW 2.The only I notice is that when I connect the AP to sw 2, I get on SW 1 the message of packet drop by option 82, but even after configuring ip dhcp snooping information option allow-untrusted on both switches, the problem persists.
I've configured ip dhcp snooping on several vlans I want to monitor and the binding table doesn't seem to be building.eature DHCP is on, global ip dhcp snooping is enabled, VLAN snooping is enabled on the vlan's I want to monitor and my trusted interfaces are also configured. Alas no binding entries in the table! 7K is running 4.2(6).
We have a DHCP SERVER implemented in a cisco router 2610.This router is connected to a switch cisco 2960 configured as DHCP SNOOPING. At the switch appear the next log message: [code] The ip address: 10.100.200.1 belongs to DHCP SERVER configured at router cisco 2610. What to do so these log messages does not appear any more? Do I need to do some configuration changes at some switch or router?
We have a customer who uses about 20 x c2960's switches for access layer and 2 x c3560e for distribution layer. C2960's uses C2960-LANLITEK9-M , Version 12.2(58)SE1. Everything was working fine. Now we got information, that sometimes there are problems with connectivity. Customer tries to reach internet.
SW11#sh int fa0/18 FastEthernet0/18 is up, line protocol is up (connected) Hardware is Fast Ethernet, address is e8ba.806a.4412 (bia e8ba.806a.4412)
We have a remote site that is using 3750X switches as layer 2 switches back to our home site. The uplink port is showing dropped packets but the utilization on the link is never about 10%. We have a 100Mb circuit to this site. Our speed tests and iperf tests are not showing any issues that we can see. However the port is still droping packets. It is not dropping at a high rate but they are dropping.
I am trying to block all dhcp packets through 2960S lan base IOS. But when i set no trust interface for dhcp snooping, the dhcp packet source port will be err-disabled. Is there any other solution to block any DHCP packet through switch without interface or other service outage?Is possible to block DHCP packet through specific VLAN?
I faced with issue on ME3800. [code] With that configuration there is no problem with DHCP Relay packets.But if I add on interface #xconnect 82.199.1 19.1 77 encapsulation mpls it will stop forward DHCP relay packets immediately. All other traffic transfers without problem.
I have a switch that I have configured for jumbo packets, but they don't seem to be functioning. I have set system mtu jumbo 9000. The hosts are connected via 2x EtherChannel links. The hosts are jumbo frame enabled, and can ping their own local address using jumbo packets & do-not-fragment flags on the pings. They cannot, however, ping each other or the switch that way - it always says that the packet requires fragmentation. I know the attached machines (they're all VMs) and virtual switches support jumbos because I can ping within the virtual interfaces of the VMs. It's just traffic that goes over the switch that fragments.The switch is a WS-2960G-48TC. Here are the various outputs, with a section of config at the end.
hrnacancwtdevs3#show system mtu System MTU size is 1500 bytes System Jumbo MTU size is 9000 bytes System Alternate MTU size is 1500 bytes Routing MTU size is 1500 bytes
In a lab environment, I have a stack of two 3750v2-48ts switches. I upgraded the stack from 15.0(1)SE2 to 15.0(1)SE3 using archive download-sw.
Switch 1 in the stack reloaded and came back with the new image.
Switch 2 appears to be dead. No console out put. When power is applied, the SYST LED blinks 22 times, then stops. I've held in the mode button for up to 60 seconds, held in mode while applying power, removed the stack cables and repeated...there's not a whole lot else I can think of to do at this point.
I've been reading the documentation for the new 3750v2 switch, and I'm wondering is the IPBase license supports FULL OSPF. The product sheet notes that it supports OSPF in the IPBase license, but then further down the page it notes that for advanced routing functions (EIGRP,OSPF) you need the IPServices license. Are there any limitations to the OSPF process on a 3750v2 with the IPBase license?
According to documentation Cisco RPS 675 should have support for Cisco 3750v2 switch(WS-C3750V2-48PS).What kind of cable should be used to connect them?Cisco RPS has 16 pins and 3750v2 has 22 pins.I could not find that type of cable,
My old switch software version is c3750-ipbase-mz.122-35.SE5 and model number is WS-C3750-48TS-S and my new switch Software version is c3750-ipservicesk9-mz.122-50.SE5.bin and model number is WS-C3750V2 . I want a compatible (prefer same) version of IOS which works on both the switches as both the switch will be in a stack..
A new Cisco 3750V2 (WS-C3750V2-48PS-S) running IOS 'c3750-ipbasek9-mz.122-50.SE5.bin' waspurchased to add to a stack of 3 Cisco 3750 (WS- C3750- 48PS-S) switches. The IOS on the stacked switches is 'c3750-ipbase-mz.122-25.SEB4.bin'.I loaded this IOS on to the new Cisco 3750V2 and deleted its original IOS. Boot up failed with error 'hardware not supported by firmware'. I am now trying to follow the recovery procedure but the I can only initialise the flash (flash_init) and there is no 'boot_helper' command to load the boot helper files. There is no option to rum 'copy xmodem' so I cannot upload the original IOS image via xmodem on hyperterminal.
So I have a 2600 that I have configured three sub interfaces on. FA0.0.1 is set for DHCP and supports VLAN 1. FA 0/0.2 for Voice, FA 0/0.3 for Data. I have this router interface plugged into FA 0/24 on my 3550 and the 3550 is configured as a dot1Q trunk (I have attached configs for RTR and SW).I have most ports configured as access VLAN 1 which is where i have my ISP connection plugged FA0/1 on the 3550. When I connect the service provider link FA0/0.1 never picks up an address. If I take my internal DHCP server and connect it to FA0/1 of the 3550 it snags an address almost immediately.In my mind this validates that my config is fine. I also took the same cable from the service provider cable modem and connected it to my laptop and the laptop is pulling DHCP.