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Secondary IP interface address and slow performance

Posted on 2007-08-03
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Last Modified: 2013-11-05
We have a location that has the need for about 500 ip host addresses.  Our primary ip network is 172.20.1.0   To accomodate the additional IP addresses, I added a secondary ip address on the Ethernet interface of 172.20.11.0   This works well except for the fact that communication speed between the .1 and .11 subnet is extremely poor.  Most of our servers are on the .1 subnet and some hosts on the .11 subnet have difficulty accessing applications on those servers because of the slow communication.  I did expect some performance degradation considering the fact that I am routing between 2 networks, but what we are experiencing seems excessive.  Copying files between hosts on the 2 different networks is many orders of magnitude slower than copying between hosts on the same network.  Our backup server is on the .1 network and backing up/restoring to the .11 network is extremely slow.  The router we are on happens to be a very OLD one (Cisco 3640) and that may play a role in causing this problem.

Are such network perfromance issues expected when using secondary ip addresses?  Is the problem with the old router?  Are there additional configuration changes I should make, such as using VLANS?

Any help would be appreciated.
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Question by:rayscue
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LVL 32

Expert Comment

by:harbor235
ID: 19625967
If you have a 3640 then the max throughput on the interface is 100M full duplex.
how much traffic is on the interface? is it configured properly? Are there any errors on
the interface? Is CEF enabled?

the max perfromance with CEF turned on is only 50,000-70,000 PPS without CEF its
4000 PPS.

Need more info

-harbor235
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by:harbor235
ID: 19626063
A 3640 can only do 50,000 - 70,000 PPS with CEF on, 4000PPS with it off, is CEF on?
(sh ip cef)

How much traffic is going through this interface since you added 500 hosts? thats a alot for a 3640. If it were another router there may not be an issue.

we need more info

-harbor235 ;}


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Expert Comment

by:harbor235
ID: 19626077
oops, thought i lost the first post , DOH !!!!

-harbor235 ;{
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Author Comment

by:rayscue
ID: 19626118
There would be quite a bit of traffic on the interface as there are 7 other subnets connected to this router.  This router is basically the hub of our network.  However, the Ethernet interface usually runs somewhere between 500-1000 PPS max.  I don't believe CEF is available on this router.  There aren't any errors being generated on the interface.

The interface is configured as follows:

interface FastEthernet0/0
 ip address 172.20.11.30 255.255.255.0 secondary
 ip address 172.20.1.30 255.255.255.0
 duplex auto
 speed auto
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LVL 32

Expert Comment

by:harbor235
ID: 19628284
What version of code are you running, CEF is definitely available.


-habor235 ;}
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Expert Comment

by:lrmoore
ID: 19628528
Is this 3640 interface .30 the default gateway for both networks?
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Accepted Solution

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harbor235 earned 375 total points
ID: 19628901

Is this an Ethernet or Fast Ethernet  interface? Could be alot for the router if it was a 10M interface with CEF off.  What happened when you entered "show ip cef" ? If it said CEF was not running try turning it on" ip cef" its worth a try to check it out?

lrmoore, If the GW was set incorrectly and proxy-arp was on, I don't think there would be a perfromance hit after the initial caching of the mac-address. What do you think?

-harbor235 ;}




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Author Comment

by:rayscue
ID: 19638106
harbor235

You're right about CEF.  It is available and it was set to off.  I have enabled it and will see if that makes any difference.  I should be able to determine that tonight when we do some backups over the network.

We set the default gateway to be .11.30 for the .11 hosts and .1.30 for the .1 hosts.
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Author Comment

by:rayscue
ID: 19661971
harbor235

After implementing CEF our throughput to the .11 subnet increased by about 50%-60%.  Although the throughput to servers on the .11 network is still considerably less than the throughput to servers on the .1 network, implementing CEF was a viable solution for us.  This along with a router upgrade later on should provide us the throughput we need.  Thanks for your help!
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