Cisco Switching/Routing :: ME 3400 - DHCP Snooping
Sep 27, 2012
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?
[core] -- [sw1] -- [sw2] -- [sw3] -- [sw4] -- [sw5]
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.
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Mar 2, 2013
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:
PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process
116 81471244 322596368 252 42.95% 43.48% 36.06% 0 DHCP Snooping
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?
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Oct 12, 2011
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.
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Apr 9, 2012
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.
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Jan 18, 2013
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.
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Apr 17, 2012
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:
-ip dhcp snnoping
-ip dhcp snooping vlan 10
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Nov 24, 2011
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.
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Nov 14, 2012
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
[Code] ......
Up time is 1183 days, 1 hour, 41 minutes
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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?
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Feb 10, 2011
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".
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Feb 14, 2012
does Cisco 2600 series switch support 802.1x and DHCP snooping?
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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]
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Sep 24, 2012
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.
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May 7, 2013
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.
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Sep 14, 2010
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).
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Sep 3, 2012
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?
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Sep 25, 2012
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.
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Sep 13, 2010
We purchased ME 3400 switch and trying to implement it. But its quite surprising in the ME3400 configuration guide that the switch does not support VTP. When I checked in Feature navigator under feature "VTP" i could see ME3400 supports VTP. But when i get into CLI of ME3400, i am not getting any option of configuring VTP. I could see in some sites VMPS is supported in ME3400.
I would like to confirm the following:
1. Does VTP support present in ME3400 or not? If not, what would be the reason that it is not included in ME3400.
2. If not what is the alternative.
Network is already running VTP of around 30 switches.
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May 13, 2012
We are using cisco ME 3400 E series switch. Which port we can use as CFM port ? We configured CFM in gig port.Is all the ports will act as CFM port or any separate CLI command is there for enable ?
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Dec 19, 2012
I`m searching about bandwidth control down and upstream with vlans, i found many options but no one works good, follow some examples i have found on the internet
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Feb 25, 2013
I have a Cisco switch 3400-ME, it's running IOS1.bin file. Now i want to change the running IOS to IOS0.bin.I entered 2 commands:
boot system flash:dir1/IOS0.bin
boot system flash:dir1/IOS1.bin
But when i show running config, it has no any boot system commands. when i relboot that switch?
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Aug 6, 2012
We just installed a Cisco ME-3400EG switch at one of our sites. A Cisco C3750X switch is connected to the 3400. When we run the command CDP NEIGHBORS, the 3400 shows no devices. We can access the 3750 via the 3400. Also, when we run CDP NEIGHBORS on the 3750 we do not see the 3400 (but other devices are displayed). How can we get CDP to display the devices on the 3400? We have already tryed CDP RUN.
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Nov 21, 2011
I useing Cisco861 : C861-universalk9-mz.124-24.T3.bin on my Cisco861 the command "ip pim dense-mode","ip igmp static-group "command does not exist,
router(config)# ip p?
port-map prefix-list
router(config)#
[Code]....
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Oct 10, 2012
What image i would need for my 2950 to enable DHCP snooping and DAI features (just for lab purpose)?
or are these features just available on the bigger modular switches (4500 and 6500)?
>sh ver
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(22)EA8a, RELEASE SOFTWARE (fc1)
[Code].....
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Nov 28, 2012
how to configure igmp snooping on a 3560.
I have a pure L2 switching network and 2 hosts on the same vlan that want to communicate a protocol between each other using multicast packets.
I wanted to configure ip snooping only on this vlan and create a multicast group limited to only these 2 host ir order to make sure that the multicast traffic is only between both of them.
Since both are sender and receiver I´m not quite sure on how to configure this. In theory I also need to set an IP Multicast Address on the switch to where the hosts will send their multicast packets.
This is basically the network:
HOST_A---|SWITCH_A|==|SWITCH_B|---HOST_B
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Oct 10, 2012
In the following topology
R1(f0/0)------------(f0/1)SW1(f0/2)------------R2
R1 is configured as host (no ip routing) with ip igmp join 239.10.10.10 on fa0/0 and R2 with ip pim sparse-mode on f0/0. SW1 is a Catalyst 3560 running IOS 12.2(25)SEE4 working at Layer 2 only in this topology (VLAN 1).
I configured SW1 for igmp snooping:
ip igmp snooping
ip igmp snooping vlan 1
Basically, I can see 'snooped' muticast group (via IGMP reports sent by R1)
SW1#sh ip igmp snooping group
Vlan Group Type Version Port List
----------------------------------------------------------------
1 224.0.1.40 igmp v2 Fa0/2
1 239.10.10.10 igmp v2 Fa0/1, Fa0/2
SW1#
SW1#
SW1#
[code]....
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Apr 29, 2011
an attacker have configured his PC with an static IP address but there is no such entry configured statically in switch, neither in DHCP snooping database.now when he want to generate traffic will switch block him? because there is no entry of his PC in the switch database.
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Jul 24, 2012
I have an issue with SRW2024P-K9-BR (SG300). Datasheet and configuration guide show me that is possible configure DHCP snooping in this switches, but web interface and console don't appear related menus/commands.
I'm using firmware version 1.1.2.0 and didn't found anything about this here.
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Jan 7, 2012
I am running DHCP snooping for VLAN 1 on below switch
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(22)EA4a, RELEASE SOFTWARE (fc1)
Model number: WS-C2950-24
Looks like below IOS does not support snooping.
Model number: WS-C2950-24
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(14)EA1a, RELEASE SOFTWARE (fc1)
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Sep 23, 2012
I've got a pair of Nexus 7010's running vPC. I am having a Multicast issue with a cluster of Linux servers that need to talk Multicast for cluster/high-availability operation. All the servers need to talk to a single multicast address and I am having trouble getting them to communicate. I believe I need to enable IP IGMP Snooping Querier on the N7K's and it needs to be enabled on the VLAN where the servers reside. How to enable IP IGMP Snooping Querier on a VLAN ?
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Nov 14, 2012
We have a 3750 acting as the core. By default IGMP snooping is enabled on cisco 3750 from the documents.but, when we see the ip mroute table on the switch, it doesnt show any output.
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Nov 24, 2011
Our switch model is "Cisco Catalyst Blade Switch 3020 for HP" We are building HA (High Availability) Databases infrastructure.Currently, there are two nodes(hosts- servers) and two above switch for HA.
Oracle said we need to turn off the IGMP Snooping in order to use the multicasting for their interconnect communication.So my question is:
Q1> Is there any way to use Multicasting without turning off IGMP Snooping on Switch side?
Q2> If 'yes', how can we configure the switch for Multicasting ?
Oracle uses 230.0.1.0 & 224.0.0.251 IPs with 42000 range port for Multicasting communication.
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Mar 22, 2012
I've been looking into IGMP snooping and have read that a L2 switch will forward multicast traffic to all ports connected to an interested receiver AND all mrouter ports. In a L2 'V' topology this results in all multicast traffic routed onto a VLAN being forwarded to the 2nd distribution switch. My question is how should a 6500 Sup720 deal with this unwanted multicast traffic? Both a Local SPAN of the RP and a Netdr capture suggest that this traffic is punted to the RP and ultimately dropped. Is this expected behavior or should the traffic be dropped in H/W?
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