Cisco SG300 Switch, Layer 3 Mode, ARP Table Overflow Errors

[smatson3615]

I have two locations, A and B which are connected via point to point  switched Ethernet (flat layer 2 handoff).  Location A is our main  location that houses DNS, DHCP, Active Directory, Exchange, Network  Shares, etc.  Location A has it’s own firewall and T1 for Internet.   Location B has no servers however it has its own T1 and firewall for  Internet.  Clients at location B obtain IP’s via DHCP and access all  servers at location A through the point to point switched Ethernet.   I’ve attached a rough drawing of my network.
Location B has a Cisco  SG300 with a Cisco SG200 connected to it via a crossover cable.  The  point to point switched Ethernet and the firewall for the T1 at location  B are connected to the SG300.  VLAN10 is configured on the SG300 to  allow clients at location B to obtain a 152.x IP address (instead of the  151.x used at location A) and to send traffic to location A .  DHCP  relay is enabled and there is a static route for internet traffic to go  to the firewall at location B.  The SG300 is the default gateway for all  clients at location B.

I’ve been having  an issue with some  laptops that travel between location A and B not being able to connect  at location B.  It seems like after they return from location A to B  that they are able to obtain an IP through DHCP (I can see the lease on  the server at location A) however they are not able to connect to  Exchange, Active Directory, Network shares, Internet, etc at location A.   Running an ipconfig on the laptops give an unable to reach DNS error.   From the laptops that won’t connect I’m unable to ping the SG300 or any  servers at location B.  I am able to ping other clients connected to  the network at location B.

Initially rebooting the SG300 at  location B was the only way to allow the laptops to connect however the  next day there would be other laptops, or the same ones, that were  unable to connect.  I noticed that the following error in the Flash  Memory log of the SG300 throughout the day:  %ARP-E-ARPTBL: ARP Table  Overflow   This prompted me to lower the ARP Entry Age Out from the  default of 60000 seconds to 300 seconds.  Since I’ve  done that it’ s  been a week and there have been no laptop connection issues however I  continue to receive the same error: %ARP-E-ARPTBL: ARP Table Overflow  throughout the day.  I fear that I will experience the same issues in  the future if I cannot identify why I am receiving the ARP errors.  Any  suggestions.  My config or the SG300 attached  Thanks in advance!!!

[Tom Watts]

Hi Scott, this condition may be caused by a device such as a name server using a wrong gateway which in turn may not be able to identify packets which are local and which are not local.

I believe the root of the problem is going to be somewhere along these lines.

I suspect, depending how frequently you see the error (hopefully very often) you may be able to disconnect things 1 at a time until you no longer see the problems, this will help isolate where and what could be causing.

-Tom
Please mark answered for helpful posts

[ripruitt · Accepted solution]

Scott,

I recommend checking the TCAM Allocation Settings, under the Administration tab.

You can have a total of 510 (?) entires max on the SG300 switches. Do note that the ACLs are counted against this total number. The most IP entries can not exceed 484 total.

New Settings

You must save your current  configuration before changing the TCAM Allocation  Settings.

The new TCAM Allocation Settings must follow the rules  below.

1. For Max Number of IPv4 Static Routes: New value must be  greater than or equal to the current used

2. For Max Number of IP Interfaces: New value must be  greater than or equal to the current used

3. New Max Number of IPv4 Static Routes + 2*Max Number of  IP Interfaces + Max Number of IP Host <= 484 which is 510 (Total) - 26 (Used  Non-IP)

Max Number of IPv4 Static Routes: (Range: 1 - 32, Default:  32) Max Number of IP Interfaces: (Range: 2 - 32, Default:  32) Max Number of IP Hosts: (Range: 2 - 100, Default:  100) Available Non IP Entries After  Apply: 0

I hope that this is some help, if not feel free to call us here at Cisco Small Business Support for farther assistance. The number is 1(866)606-1866.

Richard Pruitt

[smatson3615]

A screen shot of my Routing Resources screen is below.  If I up the maximum entries higher than the default of 128 will that resolve the issue or would raising that value have consequences?

[melbeckman · Accepted solution]

i had the same problem and increasing the entry count to 288 solved it for me. The weird thing is that there seems to be a really low number of total ARP entries supporred by this switch. i had one routed interface on a /24 where every IP was in use, and that overflowed the table. my total usage was 266 entries, counting a few arps from other interfaces. i tried to increase the table to 300 but that yielded an nodescriptive error message. perhaps the count must be divisible by 8 or something (as 288 is).

I'm really surprised at this limitation.

[smatson3615]

Thanks Mel.  I'm surprised and disappointment by this limitation as well.  I increased the entry count to 288 so hopefully i won't receive any more errors.

[Josh6604]

WOW....same here!! Now my devices can get ip form server DHCP!!!!!!!!!!!! Thank You very much!! By the way, to modifed the count got to ADMINITRATION tab - Routing Resources - Maximium entries - user define.

Great solution!