vIf the destination address does not equal the local VINES IP address or the
broadcast address, VINES IP checks its routing tables for the next hop. If the
hop count equals 0, VINES IP discards the packet. Otherwise, it decrements the
hop count by one and forwards the packet to the next hop.
If the destination VINES IP address is not in the routing table and the error bit in
the transport control field is set, VINES IP drops the packet and returns an ICP
Destination Unreachable message to the source. If the error bit in the transport
control field is not set, VINES IP discards the packet and does not return a
message to the source.
Table53. Vines IP Header Fields Summary
VINES IP Header Field # of Bytes Description
Checksum 2 Detects bit-error corruption of a packet.
Packet Length 2 Indicates the number of bytes in the packet
including the VINES IP header and data.
Transport Control 1 Consists of the following five subfields:
Class Determines the type of nodes to
which VINES IP broadcast packets
are sent.
Error If the error bit is set, an exception
notification packet is sent to the
transport layer protocol entity when
a packet cannot be routed to a
service or client node.
Metric Requests that the service node of
the destination client node return to
the source a routing cost from the
service node to the destination
client node.
RedirectIndicates whether the packet
contains an RTP message
specifying a better route to use.
Hop Count
Specifies the range a packet can
travel. The hop count can range
from 0x0 to 0xf.
Protocol Type 1 Specifies the VINES network layer protocol
of the packet as VINES IP,RTP, ICP,or
VINESARP.
Destination Network Number 4 A4-byte network number in the VINES IP
address of the destination.
Destination Subnetwork
Number 2 A2-byte subnetwork number in the VINES
IP address of the destination.
Source Network Number 4 A4-byte network number in the VINES IP
address of the source.
Source Subnetwork Number 2 A 2-byte subnetwork number in the VINES
IP address of the source.
Routing Update Protocol (RTP)
RTP gathers and distributes routing information that VINES IP uses to compute
routes throughout the network. RTP enables each router to periodically broadcast
routing tables to all of its neighbors. The router then determines the destination
neighbor it will use to route the packet.
Using VINES
Chapter5. Using VINES 235