System information

The Network Layer
Book Title
13-292
When a VINES server receives a packet, it checks whether the packet is destined for another server
or if it’s a broadcast. If the current server is the destination, the server handles the request
appropriately. If another server is the destination, the current server either forwards the packet
directly (if the server is a neighbor) or routes it to the next server in line. If the packet is a broadcast,
the current server checks whether the packet came from the least-cost path. If it did not, the packet
is discarded. If it did, the packet is forwarded on all interfaces except the one on which it was
received. This approach helps diminish the number of broadcast storms, a common problem in other
network environments. The VINES routing algorithm is shown in Figure 13-4.
Figure 13-4 The VINES Routing Algorithm
The VIP packet format is shown in Figure 13-5.
Figure 13-5 The VIP Packet Format
The fields of a VIP packet are as follows:
• Checksum—Used to detect packet corruption.
• Packet length—Indicates the length of the entire VIP packet.
Check destination
VIP address
Look up source
VIP address
Packet received on
least cost path?
Destined for
neighbor
Find next
hop in
routing
table
Send to
neighbor
Send to
next hop
Discard
packet
Pass to transport
layer for further
processing
END
Pass to transport
layer, decrement
hop count, and
resend on all interfaces
except the one on
which the packet came
Packet destined
for this server
Broadcast
address
Neither this server
nor broadcast
No
No
Yes
Yes
Check-
sum
2 2 2 2 Variable11 4 4
Packet
length
Trans-
port
control
Protocol
type
Destination
network
number
Destination
subnetwork
number
Source
network
number
Data
Source
subnetwork
number
Field
length,
in bytes