Limitations To The Header Insertion And Encryption Features - Cisco ASR 5000 Series Administration Manual

Enhanced Charging Service Overview
ECS can perform Header Enrichment to IP fragmented packets when all the fragments are received before the
reassembly timeout. If the packet size after Header Enrichment exceeds the MSS of the session, the reassembled packet
gets segmented, the multiple segments are forwarded.

Limitations to the Header Insertion and Encryption Features

This section lists known limitations to insertion and encryption of x-header fields in HTTP and WSP headers.
The following are limitations to insertion and encryption of x-header fields in HTTP headers.
Limitations in StarOS 14.0 and later releases:
 Header insertion does not occur for packets with incomplete HTTP headers.
 If a flow has x-header insertion and later some IP fragments are received for which reassembly fails, sequence
space of that segment will be mismatched.
 ECS does not support applying more than one modifying action on an inbound packet before sending it on the
outbound interface. For example, if header insertion is applied on a packet, then the same packet is not allowed
to be modified for NAT/ALG and MSS insertion.
 Header enrichment works only for the first request of a packet with concatenated requests, when the packets are
buffered at DCCA. There are no limitations on header enrichment for single GET or pipelined GET requests.
 Header enrichment works for packets at DCCA only when the packets pending of header insertion is buffered.
 Receive window will not be considered during header enrichment. That is, after header enrichment if packet
exceeds receive window, ECS will not truncate the packet.
 The maximum bytes per request after header enrichment is 2400 bytes. If concatenated requests exist, a
maximum of 2400 bytes after header enrichment can be inserted.
If due to header insertion, the packet size exceeds this limit, the behavior is unpredictable.
 Only those x-header fields in header portion of application protocol that begin with "x-" are parsed at HTTP
analyzer. In URL and data portion of HTTP any field can be parsed.
Limitations in StarOS 12.3 and earlier releases:
 The packet size is assumed to be less than "Internal MED MTU size, the size of header fields inserted". If the
total length of packet exceeds the internal MTU size, header insertion will not occur after the addition of fields.
 Header insertion occurs for both HTTP GET and POST requests. However, for POST requests, the resulting
packet size will likely be larger than for GET requests due to the message body contained in the request. If the
previous limitation applies, then POST request will suffer a bigger limit due to this.
 Header insertion does not occur for retransmitted packets.
 Header insertion does not occur for packets with incomplete HTTP headers.
 Header insertion does not occur for TCP OOO and IP fragmented packets.
 If a flow has x-header insertion and later some IP fragments are received for which reassembly fails, sequence
space of that segment will be mismatched.
 ECS does not support applying more than one modifying action on an inbound packet before sending it on the
outbound interface. For example, if header insertion is applied on a packet, then the same packet is not allowed
to be modified for NAT/ALG and MSS insertion.
 If a packet is buffered by ICAP, header insertion will not occur for that packet.
 Receive window will not be considered during header enrichment. That is, after header enrichment if packet
exceeds receive window, ECS will not truncate the packet.
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