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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Processing of the DS field in the presence of <strong>IP</strong>Sec tunnels then works as<br />

follows:<br />

1. The node where the <strong>IP</strong>Sec tunnel begins encapsulates the incoming <strong>IP</strong><br />

packets with an outer <strong>IP</strong> header <strong>and</strong> sets the DS field of the outer header<br />

accordingly to the SLA in the local DS domain.<br />

2. The secured packet travels through the DS network, <strong>and</strong> intermediate nodes<br />

modify the DS field in the outer <strong>IP</strong> header, as appropriate.<br />

3. If a packet reaches the end of an <strong>IP</strong>Sec tunnel, the outer <strong>IP</strong> header is stripped<br />

off by the tunnel end node <strong>and</strong> the packet is forwarded using the information<br />

contained in the inner (original) <strong>IP</strong> header.<br />

4. If the DS domain of the original datagram is different from the DS domain<br />

where the <strong>IP</strong>Sec tunnel ends, the tunnel end node must modify the DS field of<br />

the inner header to match the SLA in its domain. The tunnel end node then<br />

effectively acts as a DS ingress node.<br />

5. As the packet travels in the DS network on the other side of the <strong>IP</strong>Sec tunnel,<br />

intermediate nodes use the original <strong>IP</strong> header to modify the DS field.<br />

8.4 RFCs relevant to this chapter<br />

The following RFCs provide detailed information about the connection protocols<br />

<strong>and</strong> architectures presented throughout this chapter:<br />

► RFC 1349 – Type of Service in the Internet Protocol Suite (July 1992)<br />

► RFC 1633 – Integrated Services in the Internet Architecture: An <strong>Overview</strong><br />

(June 1994)<br />

► RFC 4495 – A Resource Reservation Protocol (RSVP) Extension for the<br />

Reduction of B<strong>and</strong>width of a Reservation Flow (May 2006)<br />

► RFC 2206 – RSVP Management Information Base Using SMIv2<br />

(September 1997)<br />

► RFC 2207 – RSVP Extensions for <strong>IP</strong>SEC Data Flows (September 1997)<br />

► RFC 2208 – Resource Reservation Protocol (RSVP) – Version 1 Applicability<br />

Statement (September 1997)<br />

► RFC 2209 – Resource Reservation Protocol (RSVP) – Version 1 Message<br />

Processing Rules (September 1997)<br />

► RFC 2210 – The Use of RSVP with IETF Integrated Services<br />

(September 1997)<br />

► RFC 2211 – Specification of the Controlled Load Network Element Service<br />

(September 1997)<br />

Chapter 8. Quality of service 325

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