arp between two l2 switch ?

[MrBeginner]

Hi ,

Please let me know arp can between two switch ? The server 1 and server 2 are same network and same vlan.server 1 connected to switch 1 . server 2 connected to switch 2 . switch 1 and switch 2 are connected using trunk. can i see macaddress of server1 in arp table of switch 2 and switch ?  the server2 only can see the mac address of server1 ?

[MHM Cisco World]

switch is L2 not L3 so it dont have ARP table and both server in same VLAN.
instead 
show mac-address 
then check which port connect server to SW, the mac-address with this Port is Mac of server.
NOTE:- server connect to other SW is see via trunk port interconnect both SW

[NetworkDave]

Hello MrBeginner,

Both Servers will have each others IP & MAC addresses in their ARP tables. Neither Switch will have an entry in its ARP Table for the Servers. Both Switches will have have an entry in their MAC tables for the Servers. When the switches receive ARP messages that do not contain an IP address belonging to them, the switches update their MAC table and forwarded the ARP messages.

Here are two links to excellent videos that explain the process:
----------------------------------------------------------------
Packet Traveling - How Packets Move Through a Network 26:46
https://www.youtube.com/watch?v=rYodcvhh7b8

Updated version
How Data moves through the Internet - Networking Fundamentals 14:38
https://www.youtube.com/watch?v=YJGGYKAV4pA

---------------------------------------------------------------

Remember to mark helpful posts and mark the correct answer as a solution, because that helps other users with similar questions.

[Richard Burts]

MHM says "switch is L2 not L3 so it dont have ARP table" This is a common misunderstanding. If a L2 switch has an IP configured on a vlan interface for management purposes then the switch DOES have an arp table. The arp table is not used by the switch for forwarding traffic from connected devices, but the arp table is used by the management IP for management traffic.

The original poster asks " can i see macaddress of server1 in arp table of switch 2" The answer is that if switch 2 management interface has attempted to communicate with server 1 then the mac address of server 1 would be in switch 2 arp table. But that would be an unusual situation, and so for practical purposes the answer is that no the mac of server 1 would not be seen in the arp table of switch 2.

[MrBeginner]

Hi @Richard Burts ,

let me know what kind of saturation cannot get arp address in end device like server 1 and 2,if l2 switch don't have the arp table and l2 switch have forwarding table ?

All L2 switch don't have arp table and they only have forwarding table including vswitch of vmware ?

[MHM Cisco World]

can you more elaborate ?

[Richard Burts]

I do not understand the most recent post of the original poster. I do not understand this part "let me know what kind of saturation cannot get arp address in end device like server 1 and 2" If server 1 and server 2 are in the same vlan/same subnet then each device will have in its arp table an entry to the other device. This is independent of any arp table that the switch might have.

I also do not understand this par "if l2 switch don't have the arp table and l2 switch have forwarding table" But let me attempt to clarify some things about L2 Switch: any arp table is about IP addresses and their associated mac address. In  L2 switch the arp table is used for the management IP address that might be configured. It has nothing to do with frame forwarding that the switch is doing. The forwarding table of the L2 switch is about the mac address of connected devices and has nothing to do with IP addresses of any device.

The original poster also says "All L2 switch don't have arp table" and I repeat part of my previous response: a switch will have an arp table if the switch is configured with an IP address for a management interface.

[Joseph W. Doherty]

Just to add a bit to the information Rick posted, when he mentions a L2 switch with an IP configured, he is referring to a class of switches that are manageable, some of which actually might also not support VLAN interfaces (or VLANs) (although as OP mentions using a trunk, that would be a VLAN capable switch).  Switches that don't support any kind of management, would not have an ARP table.

Basically, as Rick also explains, the ARP table, if in a switch, is for the switch acting as another host on the network, it has nothing to do with its L2 "switching" support. 

[MrBeginner]

Hi ,

please see below diagram.My problem is Server1 cannot communicate to to client 1,2. But server 1 can communicate the rest servers and clients. The client 1,2 cannot communicate to server1 but can communicate to the rest servers.I don't see the client 1,2 address in ARP table of server 1 . If i add static arp of client 1 and 2 on server1, they can communicate each other.

So i want to know what kind of saturation can block arp  ? what kind of security feature on switch can block arp request or arp ack ?

 

[MHM Cisco World]

the issue link interconnect both SW 
do show interface swithport 
are you see same in both side ?

[MrBeginner]

Hi @MHM Cisco World ,

If it is the issue link interconnect both SW, it will impact to other interconnectivity between Server1 to clients 3,4 ,server 2 to all clients,Server 3 to all clients because all are same network and single VLAN. This is the reason i would like to know who block the arp ?

[MHM Cisco World]

this make me stop if the server connect to Client and not connect to other Client then we must check 
first you mention that you use VM Server ? from SW connect to Server, ping each server, 
check the MAC and arp table (here you will see arp table even if it L2 because the SW is initiate the traffic)
if each port show MAC address of Server connect to it 
then do other test 
remove the Client that SW can connect and see other two Client if any one now can connect to Server 

for you Q about ARP, Yes some protocol like DAI have limit ARP pass through Link, and for trunk it prefer to increase it. 

[NetworkDave]

MrBeginner,

As you provide more specific information the picture gets just a little clearer.

You need to check Port-Security and Access Control Lists (ACLs) on both switches.

Please provide the model of the two switches and their running-config.

---------------------------------------------------------------

Remember to mark helpful posts and mark the correct answer as a solution, because that helps other users with similar questions.

[Joseph W. Doherty]

Ah, what you describe is "abnormal".  I.e. by default, in the same L2 domain, all your clients and servers should be able to intercommunicate.

Very, very interesting that you note statically (and only - i.e. no changes to clients 1 and 2) adding ARP entries for clients 1 and 2, on server 1, allow intercommunication.

I would think it unlikely that saturation would block just ARP between server 1 with clients 1 and/or 2.  Besides a possible issue, like a security issue (as mentioned by other posters), or perhaps some form of PVLAN, I'm wondering if it might be something as simple as misconfigured network mask on server 1 or clients 1 and 2.  I.e. besides all the server physically being on the same L2 domain, are they all logically configured within the same IP network?

It's also possible you've bumped into some form of exotic bug are a malfunction due to very long uptime (very rare, but I've seen Cisco device partially start to work "wrong" - cured by a reboot [maybe sunspots - laugh] - and after reboot, problem doesn't reappear).

If this is a "new" issue/problem, when no changes were made to devices, a reboot is a good thing to try.  If a new network, where it never has worked, get a second set of eyes to review device configs.