The CSS limit is in terms of packets...
501-1(config)# spanning-packets ?
Integer value(Range: 1-20)
501-1(config)# spanning-packets
We can hold max 20 packets per connection.
So, if you are doing L7 loadbalancing and are looking for a cookie, it better be in the first 20 packets.
ACE has a limit in buffers per connection and a limit of header size.
They are controller with a parameter-map
switch/User2(config-parammap-http)# set header-maxparse-length ?
<1-65535> Enter max-parse length for header
G.