Configuring access control lists
115
IPLink Software Configuration Guide
10 • IP context overview
ers maintain only the best route (the route with the lowest metric value) to a destination. After updating its
routing table, the router immediately begins transmitting routing updates to inform other network routers of
the change. These updates are sent independently of the regularly scheduled updates that RIP routers send.
RIP uses a single routing metric (hop count) to measure the distance between the source and a destination net-
work. Each hop in a path from source to destination is assigned a hop-count value, which is typically 1. When
a router receives a routing update that contains a new or changed destination-network entry, the router adds
one to the metric value indicated in the update and enters the network in the routing table. The IP address of
the sender is used as the next hop.
RIP prevents routing loops from continuing indefinitely by implementing a limit on the number of hops
allowed in a path from the source to a destination. The maximum number of hops in a path is 15. If a router
receives a routing update that contains a new or changed entry, and if increasing the metric value by one causes
the metric to be infinity (i.e. 16), the network destination is considered unreachable.
For information and examples on how to configure Routing Information Protocol (RIP) refer to chapter 18,
“RIP configuration”
on page 201.
Configuring access control lists
Packet filtering helps to control packet movement through the network. Such control can help to limit net-
work traffic and to restrict network use by certain users or devices. To permit or deny packets from crossing
specified interfaces, IPLink software provides access control lists.
An access control list is a sequential collection of permit and deny conditions that apply to packets on a certain
interface. Access control lists can be configured for all routed network protocols (IP, ICMP, TCP, UDP, and
SCTP) to filter the packets of those protocols as the packets pass through an IPLink. IPLink software tests
packets against the conditions in an access list one by one. The first match determines whether IPLink software
accepts or rejects the packet. Because IPLink software stops testing conditions after the first match, the order of
the conditions is critical. If no conditions match, the software rejects the address.
For information and examples on how configure access control lists, refer to chapter 19,
“Access control list
configuration”
on page 211.
Configuring quality of service (QoS)
In IPLink software, the link scheduler enables the definition of QoS profiles for network traffic on a certain
interface, as shown in
figure 17
on page 111. QoS refers to the ability of a network to provide improved service
to selected network traffic over various underlying technologies including Frame Relay, Ethernet and 802.x
type networks, and IP-routed networks. In particular, QoS features provide improved and more predictable
network service by providing the following services:
•
Supporting dedicated bandwidth
•
Improving loss characteristics
•
Avoiding and managing network congestion
•
Shaping network traffic
•
Setting traffic priorities across the network