IP CEF

[dj214]

Hello All:

This is kind of a followup of a post I made last week. I have 3 T's that I load balanced using IP CEF on my side ...just needed it outbound. Worked like a charm....load wise. All traffic appears spread evenly across the 3 t's.

What I have noticed is that the out band transfer rate dropped when I added a second line and even more so when I added the third....This was smtp traffic that was using the line(s) when this was noted.

Any reason why this would happen? Doesn't make sense. As soon as I shutodwn the 2 additional interfaces, rate increased again. Any help would be appreciated.

Thx

[Richard Burts]

You do not mention whether you used ip cef for per destination or for per packet balancing. But from your comment that traffic was spread evenly ocross 3 T1s I am assuming that you were using per packet balancing.

One factor that should be considered when trying to balance per packet is the potential impact of out of order packets. This frequently is aplication dependent but there are a number of applications that expect to receive packets in the same order that they were originated and suffer when packets are out of order. Some of them will discard all out of order packets and request retransmission from the "missing" packet, even after the missing packet shows up. I had a colleague who had this experience, he was supporting a customer who complained about the performance of a particular application. He enabled load sharing (per packet) over a second link, and saw performance of the application drop dramatically.

Using cef to balance per destination may not give quite the equally balanced results that per packet does, but per destination does not suffer from the out of order issue and in some cases may provide much better performance. I wonder if you are in one of those situations.

HTH

Rick

[dj214]

Rick:

I'm doing per packet since our ISP doesn't support CEF on his end. Must be out of order packets causing the issue. Lesson learned.

Thanks for your help.

[Richard Burts]

You can use CEF on your router even if the ISP does not support CEF. In general you will optimize performance of your router if you use CEF.

If you do enable CEF, then there is a decision about whether to do load sharing per destination or per packet. In most cases per destination is a better choice.

HTH

Rick

[nathan.deane]

Hi,

May i just ask what CPE you are using to perform Per - Packet load balancing becuase i am having teh same situaion with 2 x ADSl lines.

The Feature navigator says that only the 10000 and 12000 can have this functionality ?!?!

Thanks

Nathan

[thisisshanky]

Nathan,

Try the command ip load-sharing per-packet under the interface. Is the adsl on a wic-1adsl or is it via ethernet and external adsl modem ?

PS: Per-destination is a better choice, than per-packet.

[nathan.deane]

Agreed, Per Packet would be better but becuase all traffic is internet bound (no static point of ref) this is not possible.

the ADSl is to be used on a WIC, i will try that command.

Thanks

Nathan

[nathan.deane]

I meant to write "Agreed, Per Destination would be better"

;)

[renan]

I am trying to configure 2 T1's on seperate networks (same provider) to load balance on my 2610 router. The first T is configured as follows:

67.107.215.52/30

WAN port: 67.107.215.54

The second is configured as follows:

65.105.176.88/30

WAN Port: 65.105.176.90

How do I configure the IP routes to send traffic out so that it is load balanced? Note that I am new at this and all help is appreciated. Thanks.

[Richard Burts]

If you configure this:

ip route 0.0.0.0 0.0.0.0 67.107.215.53

ip route 0.0.0.0 0.0.0.0 65.105.176.89

then your router will load share over both T1 links.

HTH

Rick