ACE - MAX PARSE LENGTH

[Dave Ng]

Hi,

Recently, we have tried to migrate one of the web services that is fronted by the Cisco ACE 4710 and we observed that some of the HTTP packets were dropped by the ACE 4710 as the maximum parse length (e.g. HTTP header) exceeded the default length of 4096 bytes.

We’ve resolved the issues by configuring a HTTP parameter to accept HTTP packets with parse length exceeding 4096 bytes.

Sample of configuration

!

parameter-map type http http_parameter_map

  case-insensitive

  persistence-rebalance

  set header-maxparse-length 8192

  set content-maxparse-length 9192

  length-exceed continue

!

Does anyone know what is the recommended parse length to be configured on the Cisco ACE 4710 and are there any security or performance implications to configure the load balancer to accept HTTP packets that exceed the maximum parse length?

[Kanwaljeet Singh]

Hi Dave,

By default the max parse length as you know is 4096. If ACE has to look in for a cookie or something else in header beyond that then you need to increase the parse length accordingly. Maximum you can set is 65535. If the traffic still gets dropped and you see increase in dropped counter due to max parse length exceeded, then you can configure length-exceed continue which i see you have already done.

Regards,

Kanwal

[Cesar Roque]

Hi Dave,

There is no really a recommended parse-length because it depends more in the application and how it behaves. If you increase the parse-length the ACE has to buffer more to look what it needs to take the loadbalance decission, so it could be a little bit slower.

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Cesar R
ANS Team