Inter VLAN Latency

Hello All,

I am experiencing latency issues with my VLANS.

Users on VLAN100 are experiencing occasional high latency to servers on VLAN300.


I feel as though its a configuration issue, but am not sure...i fee like packets are being routed incorrectly, but I am a newb and not sure how to diagnose this issue.

Diagram of Switch Layout
JAntkillerAsked:
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JAntkillerAuthor Commented:
Also to note, First time using VOIP as well (have around 30 phones connected, no QoS is configured yet). The only VOIP phones are connected to the Dell N1548P, and workstations connected to the Phone switch which hands out an IP on VLAN100.
asavenerCommented:
How are you measuring the latency?  How long does it last?

Some things to look at:

Run a traceroute during times of good performance and bad performance.  This can highlight routing issues.

Check port utilization during times of good performance and bad performance.  This can highlight congestion issues.
JAntkillerAuthor Commented:
Basically, i had users complain about the speed of one of their applications. When i began to ping that server from inside VLAN100 (server is on VLAN300), pings came back ranging  from 200-800ms.

As a temporary fix, i just put the server on VLAN100, but long term i want to find out what the  issue is.
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asavenerCommented:
I had another person in a similar situation, and it ended up being a bad port on the switch.

I suggest you test other machines on the same subnet, and see whether the issue is with that server, or with the entire subnet.
JustInCaseCommented:
From topology itself and your description I guess there could not be definite answer.
My guess is that you either have some network loop or wrong switch is root bridge (if topology is L2).
If there is a network loop CPU is overloaded, so check CPU usage on switches.
Lower STP priority on a switch that should be core of your network (again if that is L2 topology). Just notice that in this case there will be 30-50 seconds of downtime until STP reconverges.
Ian ArakelNetwork Lead: Data and SecurityCommented:
Hi JAntkiller,

Kindly confirm if the latency is faced for a specific server in vlan 300 from a specific server in vlan 100 or is it random.
Install ping plotter on your local workstation to ping a server in vlan 300 and configure the settings such that a notification is sent in case of any abrupt increase.
Verify the source based traceroute and corresponding vlan interfaces / port errors,CRC's and utilization to isolate the cause.
JAntkillerAuthor Commented:
Hi,


The latency issue is not related to a specific server.

And the tracert shows only 1 hop.
Ian ArakelNetwork Lead: Data and SecurityCommented:
Hi

Does the trace get completed?
asavenerCommented:
Are the servers still in the same VLAN?
JAntkillerAuthor Commented:
Negative all of the servers are on a sperate VLAN (for the time being however, i did put one of my servers on the vlan that is having issues, and that did solve the latency problem for the clients within that vlan.)
asavenerCommented:
OK, some things to check:

1) Is the router experiencing resource problems?  Check CPU utilization.
2) Is the router connected to a bad port?  Try changing the port(s) the router is using.  
3) Is that uplink over utilized?
4) Is there a rogue device on the affected subnet?  Check the ARP table on the router, and see if a lot of IP addresses have the same MAC address.  Try shutting down all but one device on the subnet and see if the problem continues.  Add back devices incrementally and test the connection, and see if you can find a device that causes the issue.

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JAntkillerAuthor Commented:
Thank you
JAntkillerAuthor Commented:
After more investigation, i found a few things out.

1. The Sonicwall is experiencing high CPU utilization during file transfers to different VLAN's
2. The Primary backbone switches (Dell 5524P's are L2 Switches)

Do i need a layer 3 switch?
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