Information Technology Reference
In-Depth Information
Periodically, all clients advertise both their network-layer and their Media Access Control (MAC)-layer
addresses with the equivalent of a hello packet. Hello packets indicate that the client is still operating
and network ready. The servers themselves send routing updates to other servers periodically. Routing
updates alert other routers to changes in node addresses and network topology.
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.
Figure13-4 The VINES Routing Algorithm
Packet destined
for this server
Neither this server
nor broadcast
Check destination
VIP address
Broadcast
address
Pass to transport
layer for further
processing
Destined for
neighbor?
No
Yes
Look up source
VIP address
Find next
hop in
routing
table
Send to
neighbor
No
Packet received on
least cost path?
Send to
next hop
Yes
Discard
packet
Pass to transport
layer, decrement
hop count, and
resend on all interfaces
except the one on
which the packet came
END
The VIP packet format is shown in Figure 13-5.
