Cisco Switching/Routing :: Cat3750G / DHCP Snooping With IPSourceGuard And DAI On Access Port

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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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]

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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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Cisco Switching/Routing :: DHCP Snooping On 6506

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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Cisco Switching/Routing :: 3560 Implement DHCP Snooping

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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Cisco Switching/Routing :: 6500 IP DHCP Snooping Over L3 Links

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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Cisco Switching/Routing :: 3560 - Basics Of DHCP Snooping

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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Cisco Switching/Routing :: Dhcp Snooping Without Effect In Catalyst 2960-PST-S

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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Cisco Switching/Routing :: 4500 - Enabling DHCP Snooping On 1 VLan?

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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Cisco Switching/Routing :: WS C6509 E - DHCP Snooping Command On CatOS

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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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?

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Cisco Switching/Routing :: WS-C3560G-24PS Configuring Ip Dhcp Snooping Database With Scp

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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Cisco Switching/Routing :: Does 2600 Series Switch Support 802.1x And DHCP Snooping

Feb 14, 2012

does Cisco 2600 series switch support 802.1x and DHCP snooping?

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Cisco Switching/Routing :: 2960 - DHCP Snooping Multiple Switches AP Autonomous

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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Cisco Switching/Routing :: Nexus 7000 - Ip Dhcp Snooping Binding Table Is Empty?

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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Cisco Switching/Routing :: Router Is Connected To Switch 2960 Configured As DHCP SNOOPING

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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Cisco Switching/Routing :: Apply DHCP Snooping On 4500 Series Switches Working As L2 In Network

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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Cisco Switching/Routing :: 4500 DHCP Server On Access Port

Apr 24, 2011

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.

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Cisco Switching/Routing :: 4500 - Dhcp Server On Access Port

Dec 24, 2011

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.

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Cisco Switching/Routing :: 861 Do Not Use IGMP Snooping?

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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Cisco Switching/Routing :: Port / MAC Based DHCP For 2960 And 3560

Jan 3, 2012

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: 

ip dhcp server use subscriber-id client-id

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Cisco Switching/Routing :: P3750-E - Port Based DHCP IOS 15 Not Working

Apr 9, 2013

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

[Code]......

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Cisco LAN :: C2950 IOS For DHCP Snooping And DAI

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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Cisco Switching/Routing :: IGMP Snooping On 3560

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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Cisco Switching/Routing :: IGMP Snooping On The Cat3560?

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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Cisco Switching/Routing :: Configure 2960 8 Port Switch With DHCP Server?

Jun 24, 2012

I need to configure a Cisco 2960 switch as a DHCP server.    The current IP address will be on a different seed than the DHCP addresses.  i.e.
 
Switch IP = 10.1.2.3, GW = 10.1.2.1, Subnet = 255.255.255.0
DHCP addresses would be 192.168.1.1 - 200, GW=???? (10.1.2.3?) and subnet would be 255.255.255.0

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Cisco :: No Entry In DHCP Snooping Database?

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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Cisco Switches :: SRW2024P-K9-XX DHCP Snooping

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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Cisco WAN :: C2950 / IOS Support For DHCP Snooping

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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Cisco Switching / Routing :: C3560 - 48PS Port / Get Any Device To Talk To DHCP Server?

Sep 11, 2011

I have a c3560 that on Port 1 I can not get any device to talk to the DHCP server.Previously there was a client connected to this port however over the weekend he stated he lost connectivity.

In my troubleshooting I have connected that client to another port and now he is good to go...I connected my laptop and tried to connect to the network however I could not.I checked the logs and did not see anything that lead me to think it was having problems.

Is there another way to shut this down and hopefully start it back up without having to restart the entire switch?

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Cisco Switching/Routing :: 2960 - DHCP Server Port-Based Address Allocation

Nov 15, 2012

Does the 2960 switches with LAN-Lite support DHCP Server Port-Based Address Allocation?

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Cisco Switching/Routing :: Lose Lot Of Bandwidth Over Trunk Port (vs Access Port) 3750g

Feb 18, 2013

I have a 3750g connected to a "core" switch stack of 7 other 3750g's via 2 GigE ports in a trunk.  This is currently in a switchport mode access port- channel so only the default vlan data is sent over. Now we have a need due to physical location of these switches, to allow vlan20 (DMZ) from this 3750g to the switch stack.  I will configure a few ports on the switch stack for vlan20 and they need to be able to talk to the stand alone 3750g.To do this I will change the port channel on both endpoints to

-switchport trunk ecapsulation dot1q

-switchport mode dynamic desirable
 
also making the appropriate change on the interfaces belonging to this trunk.My question is, now that its a trunk port that carries multiple VLANs, how much is the bandwidth reduced on that 2gbps link?I have a very active VLAN (10) on the stand alone switch, but on the core I'm not going to be assigning VLAN 10 to any ports.  So does traffic from VLAN10 even come across the trunk (wasting bandwidth) if no ports on the core side are assigned to it?  I really just need vlan 1 and 20 (for now).

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Cisco Switching/Routing :: Nexus 7010 - IP IGMP Snooping Querier

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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