Slow network performance using Secondary IP addresses

[joch2joch]

Hi,

Please view the attached diagram.

I'm encountering a weird problem here. My router's LAN interface has 2 segments configured (x.x.x.x and y.y.y.y). The X segment is the primary, while the Y segment is secondary.

When my clients are using x.x.x.x addresses to access the mail server, there are no issues. However, when my clients are using y.y.y.y addresses, the performance slows down DRAMATICALLY. For example, downloading of email attachments, file copying and etc are visibly slower.

How can I approach this problem? What tools, or show commands can I use to monitor what's going on?

Thanks for the advice!

Joseph

[Kevin Dorrell]

Your diagram shows the situation before the change, i.e. the client and the server talk to each other directly. If I understand you correctly, you are saying that if you change the client ip address to y.y.y.y, and its default gateway to y.y.y.1, then the performance goes down. In this case, the traffic between the client and the server is going through the router (assuming all the netmasks are set correctly).

Check that the link between the router and the switch is working correctly. In particular, check the duplex on each side of that link. It should be auto-vs-auto, full-vs-full, or half-vs-half. It should never be auto-vs-full.

Kevin Dorrell

Luxembourg

[joch2joch]

Hi Kevin,

The speed and duplex settings are matching at both ends...otherwise the problem would have happened in the original IP configuration too.

Weird problemo! :)

Thanks!

Joe

[Kevin Dorrell]

Joe,

In the original configuration, the client and the server are on the same IP network x.x.x.0/24, so the traffic goes nowhere near the router. That is why it is fast.

When you move one of them to a different IP subnet, the traffic has to go through the router, even if the two ip subnets are on the same physical network. That is why I am suggesting that the slowdown is something to do with the link between the router and the switch. It could be the router running out of steam, but it takes a lot to upset a 7604; my bet would be on the router-switch link.

Kevin Dorrell

Luxembourg

[joch2joch]

Ooops...ya, u r right...but the router-switch duplex and speed matches.

Weird problemo

Joe

[Harold Ritter]

This sounds like a problem with the switching path used on the router. Is cef enabled on this interface. If you do a "show interface switching" you should be able to see what switching path is used.

Hope this helps,

[joch2joch]

Hello hritter,

Yea, CEF is enabled on the interface. Btw...HSRP is also running...if that means anything.

I've updated the diagram for a better picture. I've even included the configs of the particular interfaces.

Really appreciate all the advice given thus far!

Happy Holidays!

Joe