the Fragment Offset field and the Header Checksum field.
compatibility with IPsec AH and Traceroute.
This Internet-Draft will expire on July 17, 2010.
here to describe this form of address space.
main cause of the routing scaling problem.
prefixes.  This gives rise to the term Core-Edge Separation scheme.
encapsulation overhead, and regarding RFC 1191 Path MTU Discovery.
header so there is no overhead or worsening of PMTUD difficulties.
causes it to be forwarded it to a BR of the destination ISP network.
3.  Traceroute should work over the entire path.
otherwise be required in ITRs and ETRs which use encapsulation.
and ETRs for any practical map-encap system.
the destination host with the re-assembly task.
IPv4 headers are only forwarded to upgraded routers, or to an ETR.
expected to drop the packet without generating any ICMP message.
EAF provides only the 30 most significant bits of an ETR address.
common for routers to each use a /30 prefix.
bit 48 of the IPv4 header.
and secondly RFC 3514 which I discuss below.  The aims of the J.
proposed new uses of IPv4 header bits, and setting bit 48 to 1.
development of these proposals from ca. 1998 and 2002.
and straightforward PMTUD are very significant.
support it.  The details of this transition are for future work.
accepted by ITR for tunneling to an ETR.
are two reasons for these restrictions.
the types of packets it handles.
from the ETR, they may be fragmented en-route to the ETR.
result in the servers sending DF=0 packets of up to 1470 bytes long.
must be chosen with some care.
desirability of rejecting fewer fragmentable packets.
all links of ~9k bytes.
and so the better the total load can be shared amongst them.
conventional addresses or on the new kind of SPI address.
in the future.  For now, it will be assumed to be 1470 bytes.
The IPv4 header is defined in RFC 791 [RFC0791].
Figure 1: IPv4 header format.
to 63 and bits 80 to 95 are altered.
Figure 2: IPv4 header bits altered in EAF format.
most significant bits of the ETR address.
Figure 3: IPv4 header bits as used in EAF format.
in Figure 3 in an order TBD.
RFC 791 defines bit 48 as Flag Bit 0: "reserved, must be zero".
will have the bit set to 1."
has not been widely implemented.
usage of the abovementioned bits.
0  The packet's header bits conform to RFC 791 semantics.
to be included in an ICMP message.
As mentioned above, ITRs will drop all packets which are fragments.
will not check the header's integrity via any checksum facility.
possible bit error scenarios are discussed in Appendix 1.
ICMP message to the sending host.
the following functionality as well.
to include the packet, or part of it, in an ICMP message.
by an ITR have the MF flag and all Fragment Offset bits set to 0.
current state of the header, after bits 80 to 95 have been set to 0.
routers, and for the consequently different Header Checksum.
tunneled to an ETR, which ETR to tunnel them to etc.
sending host, including some number of bytes of the original packet.
The router sets bit 48 to 1.
according to the EAF format.
functionality so it recognises the EAF formatted packet.
towards the ETR address specified in bits 50 to 63 and 80 to 95.
This new forwarding functionality is described in the next section.
section if the EAF formatted packet cannot be forwarded.
the ITR sends the packet to, will decrement the packet's TTL.
ITR which is itself a router.
apart from those mentioned in this section.
change to the TTL bits.
destination address can proceed as usual.
hop MTU, and there being no path to forward the packet on.
ordinary IPv4 format - as described in a section above.
packet at the router where this MTU limit was exceeded.
PTB message addressed to the sending host [ITR-complexity].
a PTB message which will always be recognised by the sending host.
before reaching the router where the MTU limit was exceeded.
Therefore, PTB messages will only be generated for DF=1 packets.
the current router's next-hop MTU.
packet with such a destination address to that destination network.
which leads directly to that destination network.
upstream, to be forwarded to other ETRs.
network unreachable message as described above.
Ivip4 or any comparable core-edge separation system is deployed.
packets to destination hosts all over the world, where possible.
ordinary end-user networks and SPI end-user networks.
functioning as a provider network.
Edge - router) to the CE router, which itself functions as an ETR.
all links equal or exceed MinCoreMTU bytes.
provider network which houses ETRs.
to hosts in SPI end-user networks, via DITRs.
encapsulation with all its attendant complexities to handle PMTUD.
IPsec Authentication Header is unaffected by EAF.
RFC 3514, April 1 2003.
Bit errors are unlikely to go undetected by L2 protection mechanisms.
advertises a prefix which matches the destination address.
other fragments would be received.
a series of highly improbable - and unfortunate - events.
packet and generate an ICMP destination network unreachable message.
to bit 48 being set.
caused it to be presented to any upper layer protocol.
header into an ordinary IPv4 format, calculating a fresh checksum.
ETR, due to it failing to have the proper IP version bits.
that any serious negative consequences would arise.
instances.  The only exception which comes to mind are ping packets.
generation of a spurious ICMP Time Exceeded message.
and so the packet would be dropped.
such as the fast hybrid fast-push mapping distribution system.
which required extra bits to be sent with each traffic packet.
between ITRs and ETRs for purposes including testing reachability.
Routing Research Group's final recommendation.