Cisco Switching/Routing :: C3550 Is DHCP Snooping Needed For Port Sec To Work
Oct 8, 2012
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'm trying to configure my C3550 with fast ethernet port 0/48 assigned to vlan 2 in static access mode and SVI vlan 2 configured as dhcp client.
But I see command ip address dhcp is not available on interface vlan 2:
Cat3550(config-if)#ip ad Cat3550(config-if)#ip address ? A.B.C.D IP address Cat3550(config-if)#ip address
Could it be a problem related to the version running on the equipment (see below the output of sh version command not sure of what EA1 stands for)? I read here [URL] that this command was introduced in version 12.1(2)T
If it is a version problem is there any possibility to download upgraded version for free?
Cat3550>sh ve Cisco Internetwork Operating System Software IOS (tm) C3550 Software (C3550-I5Q3L2-M), Version 12.1(20)EA1, RELEASE
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:
[Code]...
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.
I am trying to find a command for dhcp snooping rate-limiting on a CatOS. The PFC card is PFC. PFC3B is said to support that command. But there seems no this command.
-6k> (enable) sh ver
WS-C6509-E Software, Version NmpSW: 8.4(5) Copyright (c) 1995-2005 by Cisco Systems NMP S/W compiled on Aug 3 2005, 13:26:46
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?
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://dhcpsec@192.168.1.50/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 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?
I am trying to configure a loop back interface like so: [URL], on the following device:
C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(50)SE, RELEASE SOFTWARE (fc1on port gig0/1 which is using a 1000Base-SX adapter. This is for troubleshooting purposes and it does not appear to be a feasible option. Is there another way to accomplish in the IOS?
I need to apply DHCP snooping on 4500 series switches working as L2 in my Network. We have external DHCL Server in another location connected with 6500 series switch.
Running EIGRP Configured Voice & Data Vlan both DHCP Server -------- 6509 switch<----------------------------------->6509 Switch -------- 4500 switch ----------------------------------------------------------Ip Phones. (ving Redundant) (ving Redundant)
I need to know whether the configuration which I mentioned in scenario is enough for apply DHCP snooping in my network.
I am setting up an ASA5515 to replace an existing Linux based firewall. Unfortunately the ASA5515 does not support source based routing.I have two internet connections currently used for specific connections - the second connection is NOT a failover connection.I have the default route to Internet connection 1.I want to route smtp out the second Internet connection.The routers connecting to the internet are a 877 and an 878The options I am considering is a layer 3 switch between the firewall and the routers to enable source based routing or replacing the 2 routers with a single router and the appropriate wic interfaces.
I have purchased these two switches from ebay as a test lab, I plan to connect them up via a gigastack modulecable and enable ip routing on the c3550 and vlans to talk to each other.
I'm very much a procurve person and really need to get into the cisco switching.I will want to trunklacp between the switches - whats the process is setting that up on cisco switches?
i have a Ws-C3550-24-Emi switch and i need to upgrade its flash memory to 32Mb. I couldn't find any documents in cisco website about the memory upgrade guideline. Possible to upgrade this switch to 32Mb? If so, what's the max of memory i can upgrade? and the part number for this type of memory?
Here iis a diagram of my current lab where I am using IP SLA to automatically switch from ISP 1 to ISP 2 should the connection go down (and vice versa)
My switches are C3550 Layer 3 switches. Both ISP's do work so connectivity is not the problem.
If I shutdown the fa0/19 port on SW1 the SLA kicks in and changes my defualt route out 10.0.1.0 without a problem. And when I do a no shut it comes back to tge 192.168.10.0 netowrk just as we would expect. No problem there.
When I disconnect the ISP 1 cell phone the SLA does switch the defualt route to the 10.0.1.0 netowrk. Okay, just fine so far. Here isthe problem, when i reconnect the cell phone the SLA does not come back to the 192.168.10.0 netowrk without first having to delete the SLA and then recresting it (both switches).
We have two switches; a WS-C3550-48 and a WS-C3548-XL connected via fiber uplink ports. Both switches are on the same subnet 192.168.1.0 /24. I would like to change the subnet of the second switch, WS-C3548-XL, to be on 192.168.2.0 /24. Would it be possible to assign 192.168.2.x IP addresses to both uplink ports to achive this?
Or would I need to create a separate VLAN and assign both GigabitEthernet0/1 uplink ports to this VLAN?
I notice that my Cisco switches have 2 fiber GBIC ports on them each and while i have been around networking for quite some time i have never dug that much into fiber. So after some quick googlefu i learned that there is lots of different types and compatibility problems.
The 2 switches i would like to connect are a WS-C3550-12T and a WS-C3550-48-EM.From what i have read these are 1000-base-fx?
I want to implement port-based and MAC-based in these two switches: 2960 & 3560 (both of them have this IOS version: 12.2(55)SE1). And I haven't found a way to implement both of them at the same time. This is what I got:
ip dhcp use subscriber-id client-id ip dhcp subscriber-id interface-name ip dhcp excluded-address 192.168.0.0 192.168.0.2 ip dhcp excluded-address 192.168.0.251 192.168.0.255
[code]....
With this configuration I can use port-based, but not MAC based. If I remove the first two lines and change the last line for this one:
address 192.168.0.7 client-id 0112.ae1d.af58.60
Then, the computer with that MAC address got the correct IP, but then the port-based doesn't work. Also, I got this line in the interface what I want to use MAC-based:
On a 4500 switch port , defined as access vlan 10, if the user connects his own dhcp server ( instead of the normal pc that should be connected ), will it cause issues with my existing network. the existing network is all static ip. In above case, will the dhcp server start looking out and assign dhcp ip's , if a user unknowingly removes his static ip and changes to obtain ip via dhcp option on the lan properties.
I am upgrading from 3750-E IOS 12.2 to 3750-X IOS 15.0
I have a dhcp pool set up to give out an ip address based on the Physical port of the switch. I also have it configured to give out "reserved only" addresses.
The configuration works when i plug a dhcp device in the 3750E. (IOS12.2) The configuration does not work when i use the same config on 3750X (IOS15)
When i debug dhcp, i see the DHCP discover message come in, but no offers or anykind of response from the 3750X.
If i remove the "reserved only" line the switch gives out IPs, but of ocurse not the ones i want. I did that to prove both the client and the switch can give out an IP.
So i have a feeling the subscriber-id client-id interface name mapping is not right, or not created.
Here is a snippet of config.
! no ip dhcp use vrf connected ip dhcp use subscriber-id client-id ip dhcp subscriber-id interface-name
On a 4500 switch port , defined as access vlan 10, if the user connects his own dhcp server ( instead of the normal pc that should be connected ), will it cause issues with my existing network. the existing network is all static ip. In above case, will the dhcp server start looking out and assign dhcp ip's , if a user unknowingly removes his static ip and changes to obtain ip via dhcp option on the lan properties.
