ARP cache needs clearing constantly

I help manage a WISP network which has a Cisco 3750 at its core and a couple of Cisco 7200 routers to two separate ISPs. We have configured public and private VLANs. The infrastructure is based on point to multipoint links with cisco SG300 switches at each main location. I have a problem where devices are not contactable until the ARP cache on the router is cleared or they are pinged from a device on the local LAN. It seems that as soon as the switch times out the address from the CAM tables, it will not respond until the ARP cache is cleared. A simple example is this.
router 10.201.1.1 --- Core switch --- switch 10.201.2.254 --- AP 10.201.2.55 --- CP 10.201.2.37 --- Customer x.x.102.37
All devices remain active up to the AP. The CP and customer will drop off the network randomly. I would expect the traffic to refresh the CAM table as per normal. The ARP cache on the router shows the exact same information before and after clearing so there is no spoofing or eroneous info there. This is not an isolated case, it is exactly the same across all of the other devices in the setup.
This has only become apparant since moving the devices to being managed in VLAN 201. prior to that, the client had everything (over 3000) devices in VLAN 1 with public IPs along side Private. Obviously a problem.
Anyone seen this sort of problem and able to offer any tips, ideas or suggestions? I am all out of ideas.
Thanks.
Marty

Just to add to this. I have read a lot of information about HSRP and having to synce CAM and ARP tables. I am not using HSRP and in this case, the second 7200 router is connected to a different ISP and operates completely separately.
In light of the information on HSRP. I have reduced the ARP timer for the two VLANs to 240 seconds, which being less than the CAM timer of 300 seconds means that the CAM table always remains up to date. I see this as a work around because it will obviously lead to a large amount of ARP traffic but it does seem to fix this problem. I am not sure why when the CAM table loses the MAC address, fresh traffic doesn't reach the switch and trigger the update of the CAM table. It seems like the traffic is not being sent to the right place.

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Does arp cache clear when i/f unplugged

Hi,
Does IOS automatically clear the arp cache, fast-switching cache and route cache for all IP addresses in a particular subnet if the router interface on that subnet is unplugged, or do I need to do,
clear arp interface <type> <number>
and
clear arp-cache
as is shown at,
http://www.cisco.com/en/US/docs/ios/12_4/ip_addr/configuration/guide/ipb_arp_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1096656
Thanks, MH

MH
If you unplug the router interface and if the router interface then goes to line protocol down, then the ARP cache entries associated with that interface should be cleared.
HTH
Rick

Clear arp-cache to ping

I have an SMS server on my network that is unreachable from vlans other that its own. This happened after we pushed out tumbleweed via SMS. Now, in order to ping the server I must issue a clear arp-cache in the core switch, this only last for about 1 min and then the SMS server is unreachable again. Any help would be great.

Thanks Dabels,
I have had this problem as well, it turned out to be a pix.
Proxy-arp is enabled by default on all interfaces and its not apparent in the config when its on or off. Its configured as a sysopt and therefore, it often gets overlooked.
Agree with everything you say, check the mac in the arp table of the server when your pings are failing, then trace the MAC you find there which corresponds to the ip address of the router.
Or check the arp entry in the router (again when its failing) and verify the MAC is the SMS server, it may just turn out to be a router or a pix or even....another server which is routing between a pair of NIC's, such as a unix box or a windows server.
Let us know how you get on.
Cheers
Shaun

What is a ARP cache and how do I clear this cache?

Each time I try to repair my internet connection it states, "unable to complete the repair because it was unable to clear the ARP cache. I do not know or am unable to find in any help file where or what this cache is. Assistance with this would be appreciated greatly. thank you

See:
* http://www.mydigitallife.info/2007/06/20/clear-delete-and-refresh-arp-cache-entry/

Internet keeps going in and out - "unable to clear ARP Cache"

I recently upgraded my WRT54GS firmware to ver. 4.whatever the most recent is. I also secured the wireless router using the WPE key. My internet connection on one of my wireless laptops will cut out for about 30 + minutes and when I try to reconnect to the network it says unable to clear the arp cache. This same laptop had no problems when the network was unsecured and the firmware was ver 2. whatever.
Any help would be appreciated as this laptop is used to work from home two days a week.

Hi...Try out a couple of commands from the command prompt:
"netsh interface ip delete arpcache"
"arp -d "
If that doesn't work. reboot.
let me know if this works for u...

ARP cache and nameserver resolution.

Short question - I have a web site name that's not resolving correctly. Comcast says I must have an old resolution on my local cache and I need to clear it so the name will re-resolve. but comcast hates Macs.
How to you clear ARP Cache on a Mac.
(see my other post for the long question.

Well, I can only assume that cleared the cache. Didn't solve my name resolution problem though, but now I know it's not me...

Worried about need to constantly repair disk permissions

Here is my analysis and conclusions as to why I need to constantly repair disk permissions:
I recently got the top-o'-the-line iMac (see info below) which shipped with Lion but since I wanted Snow Leopard (just because I have a few PowerPC games that I can't live without) I reformatted the hard drive - into 1 partition from the 2 that Lion had - and installed Snow Leopard and went back to business as usual....only with one **** great and fast computer. BTW, as far as I know this computer is exactly the same computer that shipped with Snow Leopard prior to Lion's introduction. I swore that I would never get another desktop computer because this one would last me forever. My only hesitation now is because the need to constantly repair permissions means something is not right. On the one hand I could just keep on repairing (daily?) the permissions for the next 20 years, or.... what? Is it possible (or should I be asking Apple itself instead of in this forum) that there is some other difference between the Snow Leopard and the Lion versions of this iMac - is this what "firmware" is all about? - that produces this constant need to repair permissions? If that's the case, would Apple give me a Snow Leopard-friendly logic board (and/or install the correct firmware) in exchange for the Lion logic board - or am I just going to have to live with having to perform this permissions-update function? Or is having to repair disk permissions not a big deal or something worrying about? Any ideas would be appreciated - thanks!
Hardware Overview:
Model Name:          iMac
Model Identifier:          iMac12,2
Processor Name:          Intel Core i7
Processor Speed:          3.4 GHz
Number Of Processors:          1
Total Number Of Cores:          4
L2 Cache (per core):          256 KB
L3 Cache:          8 MB
Memory:          12 GB
Boot ROM Version:          IM121.0047.B0A
SMC Version (system):          1.72f2
Hardware UUID:          B9D5A82D-6205-5FDD-BE77-46CC72811374

You do not need to repair permissions unless there's a specific problem.
For your info;
http://support.apple.com/kb/TS1448

ARP cache poison

i hope that this is the correct forum, apologies if it is not.
I constantly get a Norton "vulnerability blocked" notification because of ARP cache poison. I am assuming that this is a function of my OS, if not I will contact Symantec. Does anyone know how to get rid of this annoyance short of disabling Norton?

Remove Norton. It's a known troublemaker on Macs and there's very little for it to find - no viruses and only a few easy-to-avoid trojans. See my [Mac Virus guide|http://www.reedcorner.net/thomas/guides/macvirus> for more information.
If you're worried about your security on the network against hackers, make sure your machine is hidden behind a router. If you're using a wireless network, you're already hidden behind a router, but make sure you're using WPA encryption on that network with a good password.

ARP cache

Hi !
My MacBook (466) kernel said (console):
"could not enable ARP cache poisoning detection..."
Do you know what the reason is and how to solve it ?
Best regards;
lachala

No it isn't the same and each are cleared independently. The arp cache is a layer3 database and used for a completely different purpose than the mac-address-table albeit complimentary. The arp cache provides the sending ip host with the mac address of the destination host and the sender builds the l2 frame with this info. Then when the frame gets to the switch, the switch benefits by having the mac address in the mac-address-table table so that it knows which specif port to forward the frame to instead of sending it out all ports the way a hub would.
HTH pls rate!

ARP Cache Poison behavior by Apple TV

Norton Anti-Virus reports blocking an ARP Cache Poison attack against my home network. The reported source of the attack is the MAC number of the Apple TV on the network.
Whether Norton is "reliable" is apparently contentious in the support community. Several authors suggest, with authority, disabling Norton or the particular attack profile.
Whether that makes sense depends on what the Apple TV is innocently doing to be profiled as a network attack.
Even when supposedly "asleep" the Apple TV is doing something that meets the profile of an ARP Cache Poison attack. It did it every 30 minutes today, nine times yesterday, about 30 times day before and etc.
And if it is a design feature of the device, why is the device still performing despite having the activity continously blocked? What is the purpose of this attack-like activity, assuming it is not an attack? If it is an attack, how does one erase the programming initiating the attacks and still have an Apple TV?

Short answer: it is a false positive. I don't know exactly what causes it but I would guess Apple's Bonjour protocol, which is why you see something every 30 minutes. That's just a blind guess, but seems to fit.
Realize that a report of ARP poisoning wouldn't be likely on a private LAN, unless you got infected somehow. No known malware like this for iOS devices (and much harder to insert one on AppleTV versus an iPhone or iPad.) There are legitimate cases where ARP spoofing is used. And even Cisco has instances where they say to ignore that warning:
CSCsm25943—The meaning of the following error message on the controller is not clear. This message does not necessarily imply that any actual "ARP poisoning" is occurring. Rather, this message appears when a WLAN is configured for DHCP Required and a client (after associating to this WLAN) transmits an ARP message without first using DHCP. The client is unable to send or receive any data traffic until it performs DHCP through the controller.
DTL-1-ARP_POISON_DETECTED: STA [00:01:02:0e:54:c4, 0.0.0.0] ARP (op 1) received with
invalid SPA 192.168.1.152/TPA 192.168.0.206
Workaround: Perform the following steps:
• Verify that the client eventually does perform DHCP without undergoing an unacceptable outage. If the outage before performing DHCP is acceptable, then you can ignore this message.
I'm not saying that Norton's message is the same as Cisco's. Just that Cisco states that the meaning of why the message appears is not clear and sometimes is acceptable. And Cisco is the world leader in networking technology so if they don't always know why you get an ARP poisoning warning....
I won't go into the politics of "Norton bad" or whatever, but based on my experience (bias) with Norton in it's various forms for over 10 years, IMHO you can ignore this. Hopefully you can configure Norton to selectively ignore this. If not, you may have to use a different security program. Me personally, I do not recommend any "security suites" because they cause exactly this kind of additional headache. Just a "plain" antivirus program. Windows has a built-in firewall and most people will be using a hardware firewall at the office or home so the firewall in the "security suite" is extraneous.

ARP cache error

We have a SBS 2003 server running with a standard dual network configuration. One card for accessing the internet and the other card to connect the server to the local network.
We frequently lose our internet connection for an unknown reason (although the other card is fine and all client computers are still able to access the server -- they just loose internet access.)
We also receive the 'Clearing the ARP Cache' error message when trying to repair the connection.
However, instead of rebooting the server, we simply go into the Network Connections, locate the card that is for the internet connection, right-click and choose 'Disable', and then after it is disabled, right-click and choose 'Enable'.

Hi,
Before going further, would you please let me know if you have configured RRAS on your server? Based on your description, the problem can be caused if you are using RRAS as your basic firewall/NAT.
Please try the following suggestions to see if the problem can be resolved.
1. Firstly, we should make sure whether the network setting is correctly and properly configured. Please re-run CEICW Wizard on the SBS Server, it helps us automatically configure the network
settings, you can refer to this step-by-step article to finish the wizard:
How to configure Internet access in Windows Small Business Server 2003
http://support.microsoft.com/kb/825763/en-us
2. Please double check if you have correctly configured your DNS settings.
a. Leave the Default Gateway of the internal NIC blank on the SBS Server.
b. Configure both the internal NIC and the external NIC to use the internal DNS Service as the DNS Server.
c. On the DNS Server, create the DNS Forwarder to forward the external DNS resolution requests to the ISP's DNS
d. On the DNS Server, delete any public IP that is being registered in the local DNS.
3. Type "arp -d *" (without the quotation mark) from the command prompt. Then try repairing the network card again. If error still occurs, please turn to step 4.
4. Try turning off the "Routing and Remote Access" service, it can cause this problem.
a. Click Start->Run, type "services.msc", go and find "Routing & Remote Access", right click it and choose Properties.
b. Set start-up type to disabled and stop the service.
c. Then restart the computer which is mandatory in this case.
d. Try repairing the network card again, any luck?
If the problem persists, please help me gather the following information:
1. Does everything work normally before? If so, what changes have you made to the server/clients before the problem occurred?
2. Make sure that you uncheck "register this connections in DNS" check box from external NIC.
3. Confirm the connection binding order.
a. Please open Control Panel -> network connections.
b. Click Advanced -> Advanced settings
c. In the adapters and bindings tab, make sure that the internal adapter is on the top.
For your information:
A Description of the Repair Option on a Local Area Network or High-Speed Internet Connection
https://support.microsoft.com/kb/289256/en-us
Hope it helps.
Best Regards,
Andy Qi
Andy Qi
TechNet Community Support

Csm arp cache timeout issues

Hello all.
The arp cache timeout of the csm is normally 4 hours.
Now if we want to replace one of our servers we would need to wait 4 hours before the new servers mac address is learned if we keep the old ip-address.
I know we can manually flush one entry from the arp cache but is there a way for the csm to find out sooner if the mac address has changed?
I also know we can make the time shorter before the cache expires but what would be the consequences if we would put the timer to lets say 1000 seconds?
Would we then be flooding our network with arp requests all the time?
Finally I would expect that if an icmp request would fail because of the change of mac addres the csm would make an arp request to find out who has the ip I am trying to ping.
What is the procedure if the icmp request would fail?
Thank you.
Daniel Levi

I would not suggest using the manual method, since it is time consuming and also there is a good chance that the new ARP request may load the CSM. I would suggest that you wait for the arp cache timeout.

Force mapping to a specific MAC address a multicast IP address in ARP cache table with netsh

Hi all,
I would like to know if there is any solution (netsh option, registry entry, whatever...) to force mapping a given MAC address to a multicast IP address (224.x.y.z) in my ARP cache table.
I am doing the following:
netsh.exe interface ip add neighbors "Ethernet" "224.224.xxx.yyy"
"00-80-EE-UU-VV-WW"
But the entry in the ARP table is substitued by the calculated multicast MAC@ corresponding to my multicast IP@ :
netsh.exe interface ip show neighbors "Ethernet"
Interface 12 : Ethernet
Internet Address
Physical Address Type
224.0.0.22
01-00-5e-XX-YY-ZZ
static
224.224.yyy.zzz
01-00-5e-UU-VV-WW
static
(For information, calculation of the Multicast MAC Address is described in RFC1112§6.4 -> The MAC@ equals 01-00-5e + the last 23 digits of the multicast MAC Address)
My problem is that I'm not using an Ethernet network but an AFDX (used on Airbus A380, Boeing 787 Dreamliner, by the NASA...). This network topology is a deterministic Ethernet. The network must know accurately where each network packet is going. Thus...
the multicast MAC@ cannot be accepted and packet destinated to that MAC@ are not going anywhere.
So, I must match accurately my multicast IP@ to my MAC@ (00-80...).
It used to work with Windows XP (which was not doing any "magical" MAC@ substitution on multicast IP@), but since Windows Vista, netsh is doing the substitution described above. Is there any way to disable this substitution or force my IP
to MAC mapping in ARP table? And of course, I'm not using XP anymore ;)... but a tablet with Windows 8.1.
Thanks for any help.
Cheers,
Olivier.

Hi,
The article you pointed me to is just an explanation of what I said in my original post : "Multicast MAC Address is described in RFC1112§6.4".
But, as I said in my original post, this is true ONLY for Ethernet network. And I am NOT on an Ethernet network.
So MAC address automatic calculation for my IP address done by Windows/netsh/arp is wrong in my case. The calculation Windows is doing is correct ONLY for Ethernet network. Since I am not on Ethernet, I don't want these calculations, and I'm looking for
a solution to disable them.
So, the underlying question is : "Is Microsoft/netsh/arp able to handle other network's type than Ethernet ?"
Thanks,
Olivier Dupré.

LR 5 "encountered error reading preview cache need to quit.

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In your Lightroom folder, which is by default installed in the My Pictures folder (Mac: Pictures) you will see a file with an extension of .lrdata. This is the previews file. Remove it.
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How to do crystal reports in bi-7 i need clear steps

how to do crystal reports in bi-7 i need clear steps

Hi,
Please read the following documents.
I am sure that this is going to help you in creating crystal reports.
Regards,
Subha
Pls grant me points if it is found useful
Use
The Reporting Agent allows you to precalculate BEx queries (as useful queries) for Crystal reports in the background. This is a device used to improve system performance when executing Crystal reports.
Prerequisites
·        In the BEx Query Designer, you have defined a useful query for Crystal Reports and determined variables for the required characteristics.
·        You may want to apply a filter when precalculating this useful query using a control query (see Parameter Filtering in the section below). In this case, you need to have created an additional suitable query in the BEx Query Designer.
The associate variable must have the type Changeable with Query Navigation. Other variables can have any type.
Procedure
       1.      Choose the REPORTING_AGENT transaction code.
       2.      Select Precalculating Crystal Reports Queries and choose Execute.
       3.      Navigate to the required query in the left-hand Reporting Agent Settings tree.
       4.      You have the following options for creating a new setting:
-         Choose New Setting from the context menu.
-         Choose Create New Setting.
The New Reporting Agent Setting dialog box appears.
       5.      Enter a technical name and a description.
The following information is displayed on the General tab page:
-         The functional area of the setting is Precalculation of Crystal Reports Queries.
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For more information and recommendations for choosing parameters in a straightforward example, see Parameterizing Crystal Reports Queries Setting.
Filtering Parameters
No Filters
When you do not want to use a control query to precalculate variables, choose No Filter.
You can combine this option with parameterization using Variables (see below).
Explicitly Using Query Result
If you want to use a control query when filtering, choose Explicitly Using Query Result. You can now make entries in the Control Query and Variants fields.
Specify the technical name of the control query. Input help is available. After you save your entries, the system updates the information according to your selections.
You only need to specify a variant when the control query contains input-ready mandatory variables. This does not happen very often, however.
You can combine this option with parameterization using Variables (see below).
Parameter Variants
After making your setting for filtering a parameter, you can process variant for the individual characteristic values of the variables set in the useful query.
Note: The variable screen only offers such variables when they have not already been filled by the control query. (This can also include variables of type Changeable with Query Navigation, as long as they arent filled by the query).
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A dialog box appears in which you can choose values for the SAP variables used in the useful query, in the Query Selection area. Input help is available for those InfoObjects for which SAP variables have been created.
Enter the required data.
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ARP cache needs clearing constantly

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