Dynamic ARP Inspection (DAI)

Can someone point me to step-by-step configuration guide of how to enable DAI on Cisco Catalyst 6500 Series Switches.
Thanks

HI d.pennington,
SG200 is L2 switch only. so this mean switch not support dhcp snooping. Switch support IGMP snooping, Switch support dynamic arp table. You can management switch with web page GUI only (CLI) not supported.
Thanks,
Moh

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Do sg200-50 support dhcp snooping or dynamic arp inspection (DAI) ?

do the sg200-50 switches support:
dhcp snooping
dynamic arp inspection
?? thanks

HI d.pennington,
SG200 is L2 switch only. so this mean switch not support dhcp snooping. Switch support IGMP snooping, Switch support dynamic arp table. You can management switch with web page GUI only (CLI) not supported.
Thanks,
Moh

Dynamic ARP Inspections on Wifi Routers?

Is Dynamic ARP inspection possible to be done on wifi routers? I'm asking because I can't find any model with that feature. I would especially be interested in some cheaper models for home or small business use (maybe Linksys).

You could be better served posting this on the SOHO forum. Speaking to enterprise gear like the cisco WLC yes.
DAI for Wireless Access
The WLC protects against MIM attacks by performing a similar function as DAI on the WLC itself. DAI should not be enabled on the access switch for those VLANs connecting directly to the WLCs because the WLC uses GARP to support Layer 3 client roaming.
It is possible to enable DAI for each VLAN configured on a trunk between a FlexConnect and access point. Therefore, DAI is useful in wireless deployments where multiple SSIDs/VLANs exist on an FlexConnect. However, in an FlexConnect WLC deployment, there are two topologies that impact the effectiveness of the DAI feature. Both topologies assume that the attacker is associated to a FlexConnect WLC and is Layer 2-adjacent to the targets:
http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob73dg/emob73/ch4_Secu.html#pgfId-1019449

Help understanding DHCP Snooping and Dynamic ARP Inspection

Please help me to understand DHCP Snooping and Dynamic ARP Inspection.

HI Ezra,
In simple words:
DHCP Snooping is a feature which is available on switches. This feature is used to prevent rogue dhcp server attacks.
In the diagram, a valid dhcp server is connected to the network. The computers are suppose to receive dynamic ip addresses from the valid server. An attacker implants a rogue dhcp server on the network as shown in the diagram. The following steps are followed for a client to receive an ip address from a dhcp server.
When a client (computer) is connected to the switch and is configured to receive a dynamic ip address from a dhcp server, the dhcp service on the client, sends out a DHCP Discover packet, searching for servers on the network. This packet is broadcast in nature. DHCP servers on the network, would respond to the DHCP Discover packet sent from the client. In the example, both the DHCP servers would respond to the DHCP discover packet. The client would process the first packet it receives. If the response send by the rogue dhcp server reaches the client first, then the computer would have an ip address provided by the rogue dhcp server.
To prevent this, dhcp snooping is configured on the port on which the valid dhcp server is connected to. After the configuration is performed, no other ports on the switch would be able to respond to DHCP Discover packets from the clients. So even through the attacker has set up a rogue dhcp server, the port on the switch to which the attacker has connected would not be allowed to respond to DHCP discover packets. Thus dhcp snooping thwarts the attempt from the attacker in setting up a rogue dhcp server.
DAI:
Please read the expalined version from here: http://ciscocertstudyblog.blogspot.de/2010/06/ciscoblogpics.html
More about DHCP snooping and DAI: Please read this attached document with some detailed explanation.
Hope it helps.
Regards
Please use rating system and mark athe question answered it may help others.

Dynamic ARP inspection rate limit issues with Windows Vista Systems

Good Day to everybody.
I had implemented DHCP Snooping & Dynamic ARP inspection feature to mitigate ARP spoofing attacks to one of customer location where we have mix of Windows vista & XP systems. By default DAI feature rate limit ARP packets on un-trusted ports to 15 Packets per second. With this value I was facing some issue to access file shares where port will go in error-disabled state due to ARP broadcast from system was crossing 15 PPS limit of DAI. For the same, I had increased the DAI limit to 64 & after that we had not facing this problem from windows XP systems, but windows vista systems are still giving problem. Also this probem is very random in nature & not all the windows Vista system will face same issue even though they are accessing same file share & are configured with same DAI rate limit.
That's why I am not able to figure out baseline values for DAI rate limits. I had already search microsoft documentation for limiting this ARP broadcast from Windows Vista system, but no luck.
Is there any way to find out correct settings for this DAI packet rate limiting in Windows Vista enviorement ?

Hello bensyseng,
check out this thread.
As topmahof said already it could correlate with a wrong Intel driver.
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Sg200-50 support dhcp snooping and dynamic arp inspection?

do the sg200-50 switches support:
dhcp snooping
dynamic arp inspection
?? thanks

HI d.pennington,
SG200 is L2 switch only. so this mean switch not support dhcp snooping. Switch support IGMP snooping, Switch support dynamic arp table. You can management switch with web page GUI only (CLI) not supported.
Thanks,
Moh

Jumbo frame caveat on 3750 - dynamic arp inspection

i want to enable jumbo frame on a stacked 3750 running 12.2.25(SEB2).
any caveats - the only caveat i found is dynamic arp inspection.

Hello,
There is no know problem with Jumbo/Giant frame support on 3750 platform other than the bug you reported.
I have verified that Jumbo/Giant frame support works on 12.2(25)SED in stack configuration.
Facts
- The 12.2(25)SEB2 release has been deferred. Cisco advises you to upgrade to to (at least) 12.2(25)SEB3.
http://www.cisco.com/cgi-bin/Software/Iosplanner/Planner-tool/printdefer.pl?platform=CAT3750&majorRel=12.2&release=12.2.25-SEB2&data_from=&file=12.2.25-SEB2.CAT3750.c.html
- Jumbo/Giant frame support
http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#3750
HTH

How config dynamic arp inspection for 300 or 500 series ?

Hi Cisco Expert ,
How config dynamic arp inspection for 300 or 500 series ? Do you have clearly document for this solution ? Could you please to share ?
i find in admin guide it's no simple to do
Thank you for kindly support.

Hi Siriphan, using the command line is the easiest way to deal with this.
You need to understand the difference between trusted and untrusted interfaces. The untrusted interfaces are the ports that will be inspected and if not specified within the arp entry list then will get dropped.
Any port you do not want arp inspection to be a part of, you need to trust that port.
Below is how to make a port trusted.
configure terminal
interface fe1
ip arp inspection trust
Once you establish the trusted ports, you can build your arp list.
configure terminal
ip ap inspection list create ARP_INSPECTION (the word after the create can be anything you want)
ip 192.168.100.3 mac-address 64:31:50:1c:50:a1
This is the example of adding 1 entry to your arp list. You can add128 of these entries. These IP/mac binds are the devices that are "safe" from being dropped.
Lastly, you need to enable the arp inspection globally. You DO NOT want to toggle the arp inspection without establishing your interfaces or bind list. If you do not establish your trust interfaces and list first, you will lock down any connection through the switch and essentially brick it.
To toggle the global arp inspection
configure terminal
ip arp inspection
Once you're done, save your running config to the start up config.
-Tom
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Ip arp inspection limit rate

Hi we have configured arp packet limit is 60 packets per second but we are receiving more than 60 arp packets on port and result in to port went to error disable mode.
config t
int G1/0/1
ip arp inspection limit rate 60
Can somone know what is reason behind more than 60 arp packets within one second on user port

I believe you also need to enable dynamic arp inspection globally for the vlan that you want to limit on, or this command doesn't work. It's like putting in all of the commands for port security; they don't do anything unless you enable port security on the port.
HTH,
John
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Arp inspection not working on ASA

Folks,
I configured a transparent firewall on ASA. I have arp inspection enabled, with dynamic mac learning and dynamic arp. I am able to ping through the transparent firewall using 2 routers with the same mac-address. The firewall shows me that it is learning both the mac-addresses and also forwarding packets, can someone help me understand why this is happening?

For some reason it will not take the shun command...I've tried every combanation I could think of but it will always fail.. I'm guessing there is a bug or that its just not allowed in transparent mode..
You have to use the vlan before the number or it says invalid host.. when I do specify the vlan 2 it take it and then comes back with "Invalid vlan (2) shun failed

ARP Inspection issue

3 switches in the same broadcast domain (transparent mode), approx 200 vlans. Trunk links between switches allow all vlans 1-4096
I setup arp inspection for 1 particular vlan to troubleshoot an arp server issue, possibly an unintentionally arp MITM. Setup as follows:
ip arp inspection vlan 100
arp access-list DAI
permit ip any mac any
ip arp inspection filter DAI vlan 100
ip arp inspection vlan 100 logging acl-match matchlog
Once enabled some of the servers in each switch on vlan100 went into error disable mode and the Port channel between switches went into error disabled status, once I removed "no ip inspection vlan 100" and shut/no shut on the Port channel the Port channel came back up and I had to wade through and shut/no shut on all the error disabled server ports everything was back to normal.
Am I right saying the problem was caused by not setting the Port Channels between switches to "arp inspection trust" and should I just leave all the server ports to untrusted (default). i.e for all inter switch links
conf t
int Po200
ip arp inspection trust
end
then leave everything else is? Would this make the problem go away. I can't try now as Production kit, don't really have an ideal UAT lab as such yet.

Hello stephendrkw,
I believe you are right about the port channel causing the outage.
Typically all host ports would be configured as untrusted and all switchports connected to other switches would be trusted. Configuring a port as untrusted when it should be trusted, can cause an outage.
If you suspect a MITM attack, you can go to a pc that you think may be sending the ip traffic to the wrong mac and at the command prompt, type "arp -a 192.168.1.1" and verify it has the correct mac address mapped to the ip address. If it has the wrong mac, you can login to the switch then "show mac address-table address xxxx.xxxx.xxxx to locate the source of the MITM attack.
On the switch side, you can type "show arp | i 192.168.1.1" and "show arp | i "mac address" to verify what mac is binded to the ip address.
Hope this helps....

Unknown router granted dynamic ARP, now what?

I have discovered that the Cisco ASA5505 we are using for a firewall is granting a dynamic arp to an SMC router on the outside interface which has access to the internet. The IP address is not that of the single IP granted for the outside interface to the internet, but it is in the range under the net mask (8 addresses).
I tried using a non-MAC exempt rule in the AAA section to block this, but this doesn't seem to be a good solution.
Is the router coming in from the outside? Has the outside interface been breached? Apparently the ASA5505 doesn't think the router is violating an access rules.
The dynamic ARP appeared over the week end, when the normal equipment was shut down, but the firewall left running. Too bad the ARP table doesn't time stamp when this occurred.
The unknown router has the same MAC address that was found during the middle of last week. This appearance just started at the middle of last week.
I do not know what router this is, so I now have concern.
What steps should I take to track this down? (I am not an experienced seasoned security IP person)

Dear PK:
I did some reading on my own regarding "Gratuitous ARP" and understand that now, but am having problems discovering how the ASA5505 learned the ARP, since apparently the "show mac" command is not available under the ASA 5505 software (I am using the CLI window)
The available show commands are "show arp" and "show IP" which is close but doesn't give me what I need.
It could be that the connection on the other end of my dedicated IP (1 address) is changing or stopping and starting and then sending the Grat arp, as this seems most reasonable, but I would like to confirm that this is so.
It also doesn't help that last week Columbia University in New York scanned our block of addresses and attempted to sit upon both the http and telnet ports. Their laboratory is set up to scan banks of IP numbers and find misconfigured routers or security appliances.
Randall

ARP Inspection on SF-300-24 switch?

I'm having an issue where two PCs are responding to ARP requests "Who is 192.168.0.1".
The real 192.168.0.1 is on port 1 of the switch, and has a MAC address of 00:24:a5:c7:e0:a8. I can't seem to setup ARP Inspection properly as the rogue device continues to respond. Can somebody provide the proper steps? I've enabled DHCP Snooping, enabled ARP Inspection, enabled IP source guard, added FE1 as a trusted interface and all others untrusted, yet this continues to be an issue. Not sure what I'm doing wrong and can't find any documentation on the web to help out. I know where the offending piece of hardware is, unfortunately due to its location I can't fix it for several weeks so just looking to bandaid this for the time being.
Thanks for any help!
Ryan

Thanks for your reply. No, it does not seem to be working as intended. Please see my screen attachments.
I am still getting multiple responses to "WHO HAS 192.168.0.1" from the clients. Should just be from the trusted host on port 1.
Any other hints are appreciated. Thank you!

Why all packets dropped with %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs error msg for arp inspected vlans for DMZ and Backup

Hi,
We have got cisco 3759 switch where the followign line was configrued only
ip arp inspection vlan 6,100
And on those vlans no arp inspection trust was configrued. DMZ and backup servers were connected on that switch. Switch got restarted wihtin 5 minutes for the power outage and when the swithc came online it was denying all the packets coming through the vlan 100 adn 6 althought it was allowing packets before the power outage.
It took me 30 minutes to find out that arp inspection was enables which might cause the issue, but I am still unsue why it would block all packets for vlan 100 & 6.After taking out the command ' ip arp inspection vlan 6,100' all started working fine.
What is the reason the switch had this issue? Is there any resolution for this? thanks
FYI: The error messages-
0:48:32: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Gi1/0/1, vlan 6.([001e.0b5f.3a8c/220.233.31.177/0000.0000.0000/220.233.31.182/14:48:32 AEST Sun Feb 28 1993])
00:48:33: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Gi1/0/3, vlan 6.([000c.2915.1abe/220.233.31.184/0000.0000.0000/220.233.31.177/14:48:32 AEST Sun Feb 28 1993])
00:48:33: %SW_DAI-4-DHCP_SNOOPING_DENY: 2 Invalid ARPs (Req) on Gi1/0/1, vlan 6.([001e.0b5f.3a8c/220.233.31.177/0000.0000.0000/220.233.31.178/14:48:33 AEST Sun Feb 28 1993])
00:48:33: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Gi1/0/1, vlan 6.([001e.0b5f.3a8c/220.233.31.177/0000.0000.0000/220.233.31.184/14:48:33 AEST Sun Feb 28 1993])
Regards,
Arman

Code version:
System image file is "flash:c3750-ipservicesk9-mz.122-50.SE3/c3750-ipservicesk9-mz.122-50.SE3.bin"
I don’t have any etherchannel running from the switch. It is connected to vmware machines which are on DMZ.
rgds,
arman

Arp inspection limit

Can anyone help explain to me the way that arp inspection packet per second limiting works when enabling burst. For example, if my config is "ip arp inspection limit rate 25 burst 3", does the switch check every three seconds to see if arp packets were beyond the threshold every second of that interval? Is it simply checking every three seconds to see if the total arp packets are above 75 for the entire interval? Is it checking every three seconds or every second for the prior three second interval?
I am having a consistent issue with multiple devices in one building violating our arp packet per second limit. Is anyone else using a burst interval, and have you come across any client hardware that consistently violates the pps limit? What is your pps limit?

Initially we used the default settings, ie 15 pps, but since the migration of the park in Win7 we had problems (probably Windows network discovery):
% SW_DAI-4-PACKET_RATE_EXCEEDED: 16 packets received in 855 milliseconds on Fa0/1.
So we set the threshold at 64 pps with a burst of three seconds (ip arp inspection limit rate 64 burst interval 3)
Recently I had a user who exceeded the threshold:
% SW_DAI-4-PACKET_BURST_RATE_EXCEEDED: 279 packets received in 3 seconds on Fa0/35.
The message in the logs, suggests that if the threshold is exceeded per second, you can expect to see the value of 3 seconds. The threshold would be your value multiplied by the duration of the burst threshold (ie 64x3 = 192?). I'm not sure.

Dynamic ARP Inspection (DAI)

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