HTTP Status Code Definitions

Each Status-Code is described below, including a description of which method(s) it can follow and any metainformation required in the response.

Informational HTTP 1xx

This class of status code indicates a provisional response, consisting only of the Status-Line and optional headers, and is terminated by an empty line. There are no required headers for this class of status code. Since HTTP/1.0 did not define any 1xx status codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client except under experimental conditions.
A client MUST be prepared to accept one or more 1xx status responses prior to a regular response, even if the client does not expect a 100 (Continue) status message. Unexpected 1xx status responses MAY be ignored by a user agent.
Proxies MUST forward 1xx responses, unless the connection between the proxy and its client has been closed, or unless the proxy itself requested the generation of the 1xx response. (For example, if a proxy adds an "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding 100 (Continue) response(s).)

HTTP 100 Continue

The client SHOULD continue with its request. This interim response is used to inform the client that the initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server MUST send a final response after the request has been completed.

HTTP 101 Switching Protocols

The server understands and is willing to comply with the client’s request, via the Upgrade message header field, for a change in the application protocol being used on this connection. The server will switch protocols to those defined by the response’s Upgrade header field immediately after the empty line which terminates the 101 response.
The protocol SHOULD be switched only when it is advantageous to do so. For example, switching to a newer version of HTTP is advantageous over older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use such features.

Successful HTTP 2xx

This class of status code indicates that the client’s request was successfully received, understood and accepted.

HTTP 200 OK

The request has succeeded. The information returned with the response is dependent on the method used in the request, for example:
GET an entity corresponding to the requested resource is sent in the response;
HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the end server.

HTTP 201 Created

The request has been fulfilled and resulted in a new resource being created. The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field. The response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. The origin server MUST create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server SHOULD respond with 202 (Accepted) response instead.
A 201 response MAY contain an ETag response header field indicating the current value of the entity tag for the requested variant just created.

HTTP 202 Accepted

The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status code from an asynchronous operation such as this.
The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent’s connection to the server persist until the process is completed. The entity returned with this response SHOULD include an indication of the request’s current status and either a pointer to a status monitor or some estimate of when the user can expect the request to be fulfilled.

HTTP 203 Non-Authoritative Information

The returned metainformation in the entity-header is not the definitive set as available from the origin server, but is gathered from a local or a third-party copy. The set presented MAY be a subset or superset of the original version. For example, including local annotation information about the resource might result in a superset of the metainformation known by the origin server. Use of this response code is not required and is only appropriate when the response would otherwise be 200 (OK).

HTTP 204 No Content

The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation. The response MAY include new or updated metainformation in the form of entity-headers, which if present SHOULD be associated with the requested variant.
If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without causing a change to the user agent’s active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent’s active view.
The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.

HTTP 205 Reset Content

The server has fulfilled the request and the user agent SHOULD reset the document view which caused the request to be sent. This response is primarily intended to allow input for actions to take place via user input, followed by a clearing of the form in which the input is given so that the user can easily initiate another input action. The response MUST NOT include an entity.

HTTP 206 Partial Content

The server has fulfilled the partial GET request for the resource. The request MUST have included a Range header field indicating the desired range, and MAY have included an If-Range header field to make the request conditional.
The response MUST include the following header fields:

  • Either a Content-Range header field indicating the range included with this response, or a multipart/byteranges, Content-Type including Content-Range fields for each part. If a Content-Length header field is present in the response, its value MUST match the actual number of OCTETs transmitted in the message-body.
  • Date
  • ETag and/or Content-Location, if the header would have been sent in a 200 response to the same request
  • Expires, Cache-Control, and/or Vary, if the field-value might differ from that sent in any previous response for the same variant

If the 206 response is the result of an If-Range request that used a strong cache validator, the response SHOULD NOT include other entity-headers. If the response is the result of an If-Range request that used a weak validator, the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. Otherwise, the response MUST include all of the entity-headers that would have been returned with a 200 (OK) response to the same request.
A cache MUST NOT combine a 206 response with other previously cached content if the ETag or Last-Modified headers do not match exactly.
A cache that does not support the Range and Content-Range headers MUST NOT cache 206 (Partial) responses.

Redirection HTTP 3xx

This class of status code indicates that further action needs to be taken by the user agent in order to fulfil the request. The action required MAY be carried out by the user agent without interaction with the user if and only if the method used in the second request is GET or HEAD. A client SHOULD detect infinite redirection loops, since such loops generate network traffic for each redirection.
Note: previous versions of this specification recommended a maximum of five redirections. Content developers should be aware that there might be clients that implement such a fixed limitation.

HTTP 300 Multiple Choices

The requested resource corresponds to any one of a set of representations, each with its own specific location and agent- driven negotiation information is being provided so that the user (or user agent) can select a preferred representation and redirect its request to that location.
Unless it was a HEAD request, the response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content- Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.
If the server has a preferred choice of representation, it SHOULD include the specific URI for that representation in the Location field; user agents MAY use the Location field value for automatic redirection. This response is cacheable unless indicated otherwise.

HTTP 301 Moved Permanently

The requested resource has been assigned a new permanent URI and any future references to this resource SHOULD use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the Request-URI to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise.
The new permanent URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
If the 301 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
Note: When automatically redirecting a POST request after receiving a 301 status code, some existing HTTP/1.0 user agents will erroneously change it into a GET request.

HTTP 302 Found

The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
If the 302 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
Note: RFC 1945 and RFC 2068 specify that the client is not allowed to change the method on the redirected request.  However, most existing user agent implementations treat 302 as if it were a 303 response, performing a GET on the Location field-value regardless of the original request method. The status codes 303 and 307 have been added for servers that wish to make unambiguously clear which kind of reaction is expected of the client.

HTTP 303 See Other

The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.
The different URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
Note: Many pre-HTTP/1.1 user agents do not understand the 303 status. When interoperability with such clients is a concern, the 302 status code may be used instead, since most user agents react to a 302 response as described here for 303.

HTTP 304 Not Modified

If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields.
The response MUST include the following header fields:

  • Date, unless its omission is required

If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without one, caches will operate correctly.

  • ETag and/or Content-Location, if the header would have been sent in a 200 response to the same request
  • Expires, Cache-Control, and/or Vary, if the field-value might differ from that sent in any previous response for the same variant

If the conditional GET used a strong cache validator, the response SHOULD NOT include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.
If a 304 response indicates an entity not currently cached, then the cache MUST disregard the response and repeat the request without the conditional.
If a cache uses a received 304 response to update a cache entry, the cache MUST update the entry to reflect any new field values given in the response.

HTTP 305 Use Proxy

The requested resource MUST be accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 responses MUST only be generated by origin servers.
Note: RFC 2068 was not clear that 305 was intended to redirect a single request, and to be generated by origin servers only.  Not observing these limitations has significant security consequences.

HTTP 306 (Unused)

The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.

HTTP 307 Temporary Redirect

The requested resource resides temporarily under a different URI. Since the redirection MAY be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s), since many pre-HTTP/1.1 user agents do not understand the 307 status. Therefore, the note SHOULD contain the information necessary for a user to repeat the original request on the new URI.
If the 307 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.

Client Error HTTP 4xx

The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents SHOULD display any included entity to the user.
If the client is sending data, a server implementation using TCP SHOULD be careful to ensure that the client acknowledges receipt of the packet(s) containing the response, before the server closes the input connection. If the client continues sending data to the server after the close, the server’s TCP stack will send a reset packet to the client, which may erase the client’s unacknowledged input buffers before they can be read and interpreted by the HTTP application.

HTTP 400 Bad Request

The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.

HTTP 401 Unauthorized

The request requires user authentication. The response MUST include a WWW-Authenticate header field containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field. If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication".

HTTP 402 Payment Required

This code is reserved for future use.

HTTP 403 Forbidden

The server understood the request, but is refusing to fulfil it. Authorization will not help and the request SHOULD NOT be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it SHOULD describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client, the status code 404 (Not Found) can be used instead.

HTTP 404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.

HTTP 405 Method Not Allowed

The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.

HTTP 406 Not Acceptable

The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.
Unless it was a HEAD request, the response SHOULD include an entity containing a list of available entity characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.
Note: HTTP/1.1 servers are allowed to return responses which are not acceptable according to the accept headers sent in the request. In some cases, this may even be preferable to sending a 406 response. User agents are encouraged to inspect the headers of an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD temporarily stop receipt of more data and query the user for a decision on further actions.

HTTP 407 Proxy Authentication Required

This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy. The proxy MUST return a Proxy-Authenticate header field containing a challenge applicable to the proxy for the requested resource. The client MAY repeat the request with a suitable Proxy-Authorization header field. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication".

HTTP 408 Request Timeout

The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.

HTTP 409 Conflict

The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response body SHOULD include enough information for the user to recognize the source of the conflict. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might use the 409 response to indicate that it can’t complete the request. In this case, the response entity would likely contain a list of the differences between the two versions in a format defined by the response Content-Type.

HTTP 410 Gone

The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent. Clients with link editing capabilities SHOULD delete references to the Request-URI after user approval. If the server does not know, or has no facility to determine, whether or not the condition is permanent, the status code 404 (Not Found) SHOULD be used instead. This response is cacheable unless indicated otherwise.
The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server’s site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time — that is left to the discretion of the server owner.

HTTP 411 Length Required

The server refuses to accept the request without a defined Content- Length. The client MAY repeat the request if it adds a valid Content-Length header field containing the length of the message-body in the request message.

HTTP Precondition Failed

The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This response code allows the client to place preconditions on the current resource metainformation (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.

HTTP 413 Request Entity Too Large

The server is refusing to process a request because the request entity is larger than the server is willing or able to process. The server MAY close the connection to prevent the client from continuing the request.
If the condition is temporary, the server SHOULD include a Retry- After header field to indicate that it is temporary and after what time the client MAY try again.

HTTP 414 Request-URI Too Long

The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present in some servers using fixed-length buffers for reading or manipulating the Request-URI.

HTTP 415 Unsupported Media Type

The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.

HTTP 416 Requested Range Not Satisfiable

A server SHOULD return a response with this status code if a request included a Range request-header field, and none of the range-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range request-header field. (For byte-ranges, this means that the first- byte-pos of all of the byte-range-spec values were greater than the current length of the selected resource.)
When this status code is returned for a byte-range request, the response SHOULD include a Content-Range entity-header field specifying the current length of the selected resource. This response MUST NOT use the multipart/byteranges content- type.

HTTP 417 Expectation Failed

The expectation given in an Expect request-header field could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.

Server Error HTTP 5xx

Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable of performing the request. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. User agents SHOULD display any included entity to the user. These response codes are applicable to any request method.

HTTP 500 Internal Server Error

The server encountered an unexpected condition which prevented it from fulfilling the request.

HTTP 501 Not Implemented

The server does not support the functionality required to fulfil the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.

HTTP 502 Bad Gateway

The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfil the request.

HTTP 503 Service Unavailable

The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the delay MAY be indicated in a Retry-After header. If no Retry-After is given, the client SHOULD handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply that a server must use it when becoming overloaded. Some servers may wish to simply refuse the connection.

HTTP 504 Gateway Timeout

The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.
Note: Note to implementors: some deployed proxies are known to return 400 or 500 when DNS lookups time out.

HTTP 505 HTTP Version Not Supported

The server does not support, or refuses to support, the HTTP protocol version that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client, other than with this error message. The response SHOULD contain an entity describing why that version is not supported and what other protocols are supported by that server.

Performance bottleneck symptoms

CPU Bottleneck Symptoms:

Symptoms for CPU bottlenecks include the following,
The Processor(_Total)\% Processor Time(measures the total utilization of your processor by all running processes) will be high. If the server typically runs at around 70% or 80% processor utilization then this is normally a good sign and means your machine is handling its load effectively and not underutilized. Average processor utilization of around 20% or 30% on the other hand suggests that your machine is underutilized and may be a good candidate for server consolidation using Virtual Server or VMWare.
Further to breakdown this %processor Time, monitor the counters – Processor(_Total)\% Privileged Time and Processor(_Total)\% User Time, which respectively show processor utilization for kernel- and user-mode processes on your machine. If kernel mode utilization is high, your machine is likely underpowered as it’s too busy handling basic OS housekeeping functions to be able to effectively run other applications. And if user mode utilization is high, it may be you have your server running too many specific roles and you should either beef hardware up by adding another processor or migrate an application or role to another box. The System\Processor Queue Length(indication of how many threads are waiting for execution) consistently greater than 2 or more for a single processor CPU is a clear indication of processor bottleneck . Also look at other counters like ASP\Requests Queued or ASP.NET\Requests Queued as well.

Tips to find out Application server bottlenecks:

  1. A high increase in application server processing time when the load is increased.
  2. One or more page components take more time when the same request db call is taking less execution time.
  3. The Static files are having less response time whereas the dynamic contents (servlets, jsp, etc) take more time.
  4. Network delay is negligible.
  5. Home Page gets displayed in few seconds even during the stress period(as it is fetched from the web server).
  6. Hits/sec & Throughput remains less.
  7. If the CPU/ Memory/Disk of the App server has any bottleneck symptoms.
  8. If the HTTP / HTTPS connections established doesn’t increase proportionally with the load.
  9. If the new connections established is very higher & the reused connections are very less.

Tips to find out Web server bottlenecks:

  1. Increased ‘Server Time’ breakup
  2. One or more page components of transaction takes more time where in the DB query is having less execution time.
  3. The static files are having high response time than the dynamic contents (servlets, jsp, etc)
  4. Network delay is negligible.
  5. Home Page takes more time for display.
  6. Hits/sec in the web server is very less.
  7. If the CPU/ Memory/Disk of the web server has any bottleneck symptoms.

Hardware Malfunctioning Symptoms:

  1. System\Context Switches/sec (measures how frequently the processor has to switch from user- to kernel-mode to handle a request from a thread running in user mode). If this counter suddenly starts increasing however, it may be an indicating of a malfunctioning device, especially if you are seeing a similar jump in the Processor(_Total)\Interrupts/sec counter on your machine.
  2. You may also want to check Processor(_Total)\% Privileged Time Counter and see if this counter shows a similar unexplained increase, as this may indicate problems with a device driver that is causing an additional hit on kernel mode processor utilization.
  3. If Processor(_Total)\Interrupts/sec does not correlate well with System\Context Switches/sec however, your sudden jump in context switches may instead mean that your application is hitting its scalability limit on your particular machine and you may need to scale out your application (for example by clustering) or possibly redesign how it handles user mode requests. In any case, it’s a good idea to monitor System\Context Switches/sec over a period of time to establish a baseline for this counter, and once you’ve done this then create a perfmon alert that will trigger when this counter deviates significantly from its observed mean value.

Memory Bottleneck Symptoms:

When it comes to the System memory, there are 3 things to monitor:

  1. Monitor Cache (Hits/Misses),
  2. Monitor Memory (Memory Available/sec, Process/Working Set),
  3. Monitor Paging (Pages Read/Sec, Pages Input/Sec, Page Faults/Sec, % Disk Processing)Memory\Available Bytes,

If this counter is greater than 10% of the actual RAM in your machine then you probably have more than enough RAM and don’t need to worry. The Memory\Pages/sec counter indicates the number of paging operations to disk during the measuring interval, and this is the primary counter to watch for indication of possible insufficient RAM to meet your server’s needs. You can monitor Process(instance)\Working Set for each process instance to determine which process is consuming larger and larger amounts of RAM. Process(instance)\Working Set measures the size of the working set for each process, which indicates the number of allocated pages the process can address without generating a page fault. A related counter is Memory\Cache Bytes, which measures the working set for the system i.e. the number of allocated pages kernel threads can address without generating a page fault. Finally, another corroborating indicator of insufficient RAM is Memory\Transition Faults/sec, which measures how often recently trimmed page on the standby list are re-referenced. If this counter slowly starts to rise over time then it could also indicating you’re reaching a point where you no longer have enough RAM for your server to function well.

Disk Bottleneck Symptoms:

A bottleneck from a disk can significantly impact response time for applications running on your system. Physical Disk (instance)\Disk Transfers/sec counter for each physical disk and if it goes above 25 disk I/Os per second then you’ve got poor response time for your disk. By tracking Physical Disk(instance)\% Idle Time, which measures the percent time that your hard disk is idle during the measurement interval, and if you see this counter fall below 20% then you’ve likely got read/write requests queuing up for your disk which is unable to service these requests in a timely fashion. In this case it’s time to upgrade your hardware to use faster disks or scale out your application to better handle the load. Look for the Physical Disk (instance)\Average Disk Queue length & Physical Disk (instance)\Current Disk Queue length parameters to get more details on the queued up requests.

Network Performance/Bottlenecks:

The first step in monitoring is to monitor the network performance, to make sure your network performance is good. There are some simple ways to do so. First monitor whether you are getting the same bandwidth which you are supposed to get. The easiest way to find out is to check the current bandwidth counter with your expected bandwidth. Also verify the rate at which the server sends and receives the data. Network performance depends on 2 factors, network cards and interfaces (Switches/Routers) configured on the servers.

Here are some of the counters to find network bottlenecks:

Network Interface: Current Bandwidth
This counter determines your current bandwidth of the network interface. Capture this counter value and correlate with bytes receives/sec, bytes send/sec and bytes total/sec.
If the bytes total should be at least half of your total bandwidth .If not so then we can confirm a network bottle neck

Network Interface: Bytes Total/sec:
To determine if your network connection is creating a bottleneck, compare the Network Interface: Bytes Total/sec counter to the total bandwidth of your network adapter card. To allow headroom for spikes in traffic, you should usually be using no more than 50 percent of capacity. If this number is very close to the capacity of the connection, and processor and memory use are moderate, then the connection may well be a problem. To determine the network utilization (throughput on a server’s network cards), you can check the following counters:

  1. Network\Bytes Received/sec
  2. Network\Bytes Sent/sec
  3. Network\Bytes Total/sec
  4. Network Current Bandwidth

If the total byte per second value is more than 50 percent of the total network utilization under average user/work load, then your server is having some problems under peak load conditions. Make sure you compare network counter values with Physical Disk\% Disk Time and Processor\% Processor Time utilization. If the disk time and processor time values are low but the network values are very high, there might be a problem with your network.
There are 2 ways to solve this problem:

  1. By optimizing the network card settings
  2. By adding an additional network card.