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VLan - High Re-transmission Rates

LittleJoe
Frequent Visitor

VLan - High Re-transmission Rates

When implementing vLan's on our network 2620's we are seeing high re-transmission rates between the workstations on all non default vlans and our servers that are located on the core 5412 default vlan.

 

I have attached sanitized versions of the config's.

 

I am pretty sure that it has to do with the vlan configuration but just can not place my finger on it.

 

Any toughts as to what it could be?

6 REPLIES
paulgear
Esteemed Contributor

Re: VLan - High Re-transmission Rates

Hi Little Joe,

In your sanitised config, is XXX.XXX the same in each IP address? If so, then you've got a problem in that you're running the same subnet on multiple VLANs. VLANs 141 & 241 should have different subnets allocated to them.

If you post your 'show ip route' output, you should see this more clearly.
Regards,
Paul
LittleJoe
Frequent Visitor

Re: VLan - High Re-transmission Rates

Paul,

 

Maybe I should have chosen better placeholders. The 141 vlan is xxx.xxx and 241 is xxx.yyy

 

show ip route is as follows:

xxx.xxx.141.0/24    1st             141  connected            1          0
xxx.yyy.141.0/24    1st-Voice  241  connected            1          0

paulgear
Esteemed Contributor

Re: VLan - High Re-transmission Rates

If that's the case, i can't see any obvious problems with your configuration (although that's no guarantee of anything ;-).

 

My guess is lower layer issues, such as cabling.  What do the error counters on the ports connected to your workstations say?

Regards,
Paul
LittleJoe
Frequent Visitor

Re: VLan - High Re-transmission Rates

I do not suspect that it is cabling since the issue only surfaces once we move a building or a floor to the vlanned network. If the floor is moved back to the "flat" network the retransmitted packets drop to near nothing.

 

I am stumpped...

paulgear
Esteemed Contributor

Re: VLan - High Re-transmission Rates

Do you run multiple routers on the same LAN?  If so, you may be running into the default Windows firewall setting which blocks ICMP redirects even from the default gateway.  I had a severe performance problem which i tracked down to Windows ignoring ICMP redirects, which instantly went away when i added a rule to allow them from the default gateway.

 

But all of this is just guessing without more detailed information.  Where and how are you detecting the retransmissions?  Can you reproduce it with flood pings or iperf?  Does it affect only one platform or one VLAN or one direction?  Are there certain things that are immune?

Regards,
Paul
Matcol
Frequent Advisor

Re: VLan - High Re-transmission Rates

Where are your hosts' default gateway addresses?

 

Should you have them on the 5412?

 

I personally would use the 5412 for inter-VLAN routing.

 

I wouldn't have IP addresses on 141 and 241 VLANs on your Layer2 switch.

 

Disable ip routing on the 2620 and use the 5412 instead - does the problem persist?