
____________________________________________________ DS34T101, DS34T102, DS34T104, DS34T108
101 of 366
10.6.13.5 Known Ethertypes
The block considers the following Ethertypes as known Ethertypes:
IPv4 (0x800)
IPv6 (0x86DD)
MPLS unicast (0x8847)
MPLS multicast (0x8848)
ARP (0x806)
10.6.13.6 Received OAM Time-Stamping
For any received packet forwarded to the CPU (ETH CPU path) the third dword of the buffer descriptor holds the
timestamp as latched by the block as the packet was received. This timestamp can be used by the CPU for
network delays measurements. The timestamp is 1
10.6.13.7 Neighbor Discovery (RFC 2461)
Where IPv4 has ARP, IPv6 has NDP, the neighbor discovery protocol. For the purposes of this discussion, NDP
and ARP are very similar: one node sends out a request packet (called a neighbor solicitation in NDP), and the
node it was looking for sends back a reply (neighbor advertisement) giving its link-layer address. NDP is part of
ICMPv6, unlike ARP, which doesn't run over IP. NDP also uses multicast rather than broadcast packets.
For NDP (ICMPv6) packets to be forwarded to the CPU,
Discard_switch_4 must be cleared.
10.6.13.8 Packet Payload Length Sanity Check
The packet classifier performs a sanity check between the payload length of the received packet and the
AAL1/SAToP/CESoPSN bundle’s configuration. Discarding packets that fail the sanity check can be disabled per
10.6.14 Packet Trailer Support
There are Ethernet switch chips that in some of their modes transmit packets with a trailer and expect the incoming
packets to have a trailer. A trailer is an addition of several bytes at the end of the packet that helps the switch to
decide about the incoming packet destination and to tag out-going packets.
When the device operates opposite such a switch, the trailer is supported in the following manner:
Transmitted packets: A 1 to 12 byte trailer is added to all transmitted packets. The trailer contents that are
stored in the packet buffer (immediately after the buffer descriptor starting from offset 0x8) may be varied
per packet.
Received packets: The trailer content is ignored. It is removed from packets destined to the payload-type
machines and not transferred with packets destined to CPU.
The structure of packets with trailer is illustrated in
Figure 10-62.