Now, we're coming to the area that you can turn ON and OFF by navigating to System | Settings on the NetScaler.
Let's start with the ones that are enabled by default. The fact that they are enabled by default also means they play along well for the most part with most deployments.
Fast Ramp is a performance friend. Traditional (read RFC-based) TCP follows a very conservative approach to increasing window sizes; while this made perfect sense in the days of unreliable pipes, it stems the TCP connection from quickly reaching its top speed. Especially in the context of the NetScaler, which will sit closer to or at least have very solid connections to the Server, Fast Ramp works great and is one of those features that rarely has to be touched.
Even though it's enabled by default, the Edge Configuration mode only impacts very specific use cases. Notably, Link Load Balancing and Cache Redirection. It's called edge mode because it's sitting literally at the edge of the network learning services that are not even part of your infrastructure, purely with the goal of load balancing. There are two desired behaviors for such deployments:
Remember though, this is only when cache redirection or link load balancing are in use, not system wide.
As we discussed in the IP review section, SNIPs are the recommended way to configure IPs for the purpose of NetScaler to Server conversations. This mode, abbreviated as USNIP, simply enables your SNIPs to be used.
The Layer 3 mode is enabled by default. If you need the NetScaler to forward packets to an IP not owned by it, you need this mode. When enabled, NetScaler will behave like a router, looking at the routes it has learned or that has been configured with to forward packets. Disabling it will mean anything the NetScaler receives that doesn't have the destination IP as one of its IPs will be dropped. Situations where you would turn this off would be to prevent Servers in the backend from talking to each other or if you want routing to be entirely handled by a separate device (such as a router or firewall).
Path MTU Discovery, or PMTUD as it's known, is a pretty well-known networking technique that uses ICMP to learn what the lowest MTU along the path is. This way fragmentation is avoided and that is always a good thing. Fragmentation is inefficient, it costs performance at multiple points in the network, and then needs reassembly at end points.
First, let's get the advertisements out of the way—SRADV
, DRADV
, IRADV
, SRADV6
, and DRADV6
.
When you enable dynamic routing on the NetScaler, you do so to have it participate in routing and learn routes from other routers in its neighborhood. You then also have the ability to have it advertise the routes it knows. This is when you choose to enable the respective advertisement.
Next, there are a couple of RISE-related enhancements. These are RISE_APBR
and RISE_RHI
. First let's begin by understanding what RISE is. Remote Integrated Services Engine is a Cisco technology, which allows the NetScaler when used with the Cisco Nexus series of appliances, provides a tight integration between the two products and this enables some configuration automation and in turn easier management.
Here is a quote from the Cisco Whitepaper. Reference: http://www.cisco.com/c/dam/en/us/products/collateral/switches/nexus-7000-series-switches/white-paper-c11-731370.pdf:
"Each device can retrieve and program the hardware and software tables of the other (for example, the forwarding tables, routing tables, and access control lists [ACLs])."
The two RISE modes represent two of the fundamental use cases of this integration:
Let's now get to the modes that we are most concerned with while troubleshooting:
If it's purely for Client IP logging purposes that you are turning on USIP, consider Client IP Insertion or Web logging instead. The latter is especially designed for high performance logging. Another point to bear in mind while enabling USIP is that it reduces the reusability of a connection on the Server side. Why is that? Because when the NetScaler tries to look for a connection in its reuse pool, it looks for something that matches among other things, the source IP. Whereas, by default, you have a lot of matches given the SNIP remains somewhat a constant; with USIP, this gets chopped up into several small pools of connections.
A common question is what happens if both USNIP (which we discussed earlier) and USIP are enabled? USIP always overrides USNIP. Also, USIP can be enabled either at the Global level or at the service level. The service level setting takes precedence over the Global level setting.
Connection: close
header, which would have otherwise signified the end of the conversation and caused the client to close the connection and insert a replacement header of its own Connection: Keep-Alive
. The result is that the client doesn't need to re-establish newer connections for other requests on the page it's trying to load. The technique, as such, is perfectly valid and most browsers support it, however you might run into cases where the browser (by behavior) doesn't load the page until it receives the Connection: close
header. This once manifested for me as a certain browser not redirecting me on seeing a HTTP 302 for 180 seconds! Such situations would require you to leave this mode disabled.3.15.25.186