Why is is Express Cache Routing disabled globally by default?

[deschete]

I see that it can be enabled per interface, but why would a user not want to have Express Cache Routing enabled globally on the 1335?

Today during performance testing, we were able to push 90Mb between two 100Mb ports on separate VLANs.  We were only able to push 121Mb between the two Gigabit ports on separate VLANs, however.

Doing a little reading I noticed that Express Cache Routing is an option, and that it's disabled globally.  I have not yet enabled it and performed my testing again to see if performance increases, but since we're going to deploy soon, what would be the disadvantage to turning it on?

[Anonymous]

-Thanks for posting your question on the forum!

The NetVanta 1335 Series router possesses a full Layer 3 routing stack and is therefore considered a router that possesses switching capabilities. It supports the AOS firewall, VPN, Policy Based Routing (PBR), and other routing features. Any traffic processed by these features is sent to the CPU for processing. The NetVanta 1335 can act as a Layer 3 switch, when the routing features are not being used. The NetVanta 1335 has a 16-route express cache which is used to push forwarding routes for VLAN interfaces down into the switch fabric. The NetVanta 1335 does not possess a host cache; instead, any traffic must match a forwarding route for it to be hardware switched. If the traffic does not match a forwarding route in hardware, and the cache is full, the traffic is sent to the CPU for processing.

If you are using any routing features on the NetVanta 1335, you can enable FFE (fast forwarding engine) to help streamline the processing. However, keep in mind, that it is recommended that if you are using the route-cache on an interface in the NetVanta 1335 that you do not enable the AOS RapidRoute engine (FFE). In firmware release R10.4.0 or later, FFE is enabled by default and must be disabled using the "no ip ffe" command on the corresponding interface. For more information refer to the RapidRoute configuration guide, RapidRoute/ FFE in AOS.

Please do not hesitate to let us know if you have any further questions.

Thanks,

Noor

[deschete]

Today I did more testing with the 1335.  To provide more information, this device is not going to be used for GRE, NAT, or PBR.  I'm using it as a Layer 3 switch, I'm shaping traffic on one Layer 3 VLAN and I'm running BGP with a very small number of routes.

When I copy a file from a file server attached via the the first Gigabit Ethernet port to my PC on the second Gigabit Ethernet port, I can copy the file around 135Mb.  If I enable express cache routing globally and I repeat this test, I am able to copy the file around 400-600Mb.  If I enable and disable the command during the copy, I can watch the speed go up and down.

It sounds like, based on your post, that you're suggesting that I do NOT use express cache routing and that I enable FFE on each interface instead.  However, I see in the page linked that one of the conditions where you would want to disable FFE would be "If Layer 3 Switching is Enabled," which it is in this case with the 1335.

If FFE is enabled by default, then when I did the initial testing it was enabled - and the performance was not as high as Express Cache Routing.  In fact, it was 3-4 times faster with Express Cache Routing.  Is this abnormal and unexpected?

[deschete]

Here's a graph of the two interfaces, one has traffic coming in and it's going out the other on a second VLAN.  THe arrows point to the much slower part of the transmission when 'no ip route-cache express' is in place, and then notice the significant increase in bandwidth - this is when 'ip route-cache express' is issued.  The gap at 16:12 is when one file transfer ends and the next peak is when a new transfer was started.

[Anonymous · Accepted solution]

- I apologize for the confusion. I did want to clarify that FFE will only benefit the performance if one of the following features are in use:

• the firewall is on
• crypto is enabled (ip crypto ffe)
• top-talkers is enabled (which uses the firewall)
• netflow is enabled
• access-groups are enabled
• route-cache is disabled

The results do not surprise me as, based on the description you provided of your configuration, you are not using any features on the 1335 that will benefit the 1335's performance by enabling FFE. In your scenario, I would recommend disabling FFE and enabling express cache routing.

Please do not hesitate to let us know if you have any further questions.

Thanks,

Noor

ADTRAN Tech Support