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Chapter 13 Policy and Static Routes
ZyWALL USG 50 User’s Guide
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C
HAPTER
14
Routing Protocols
14.1
Routing Protocols Overview
Routing protocols give the ZyWALL routing information about the network from
other routers. The ZyWALL stores this routing information in the routing table it
uses to make routing decisions. In turn, the ZyWALL can also use routing
protocols to propagate routing information to other routers. See
Section 6.6 on
page 105
for related information on the RIP and OSPF screens.
Routing protocols are usually only used in networks using multiple routers like
campuses or large enterprises.
14.1.1
What You Can Do in this Chapter
Use the
RIP
screen (see
Section 14.2 on page 298
) to configure the ZyWALL to
use RIP to receive and/or send routing information.
Use the
OSPF
screen (see
Section 14.3 on page 299
) to configure general OSPF
settings and manage OSPF areas.
Use the
OSPF Area Add/Edit
screen (see
Section 14.3.2 on page 306
) to
create or edit an OSPF area.
14.1.2
What You Need to Know
The ZyWALL supports two standards, RIP and OSPF, for routing protocols. RIP and
OSPF are compared here and discussed further in the rest of the chapter.
Finding Out More
See
Section 14.4 on page 308
for background information on routing protocols.
Table 81
RIP vs. OSPF
RIP
OSPF
Network Size
Small (with up to 15 routers)
Large
Metric
Hop count
Bandwidth, hop count, throughput,
round trip time and reliability.
Convergence
Slow
Fast
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14.2
The RIP Screen
RIP (Routing Information Protocol, RFC 1058 and RFC 1389) allows a device to
exchange routing information with other routers. RIP is a vector-space routing
protocol, and, like most such protocols, it uses hop count to decide which route is
the shortest. Unfortunately, it also broadcasts its routes asynchronously to the
network and converges slowly. Therefore, RIP is more suitable for small networks
(up to 15 routers).
In the ZyWALL, you can configure two sets of RIP settings before you can use it
in an interface.
First, the
Authentication
field specifies how to verify that the routing
information that is received is the same routing information that is sent. This is
discussed in more detail in
Authentication Types on page 309
.
Second, the ZyWALL can also
redistribute
routing information from non-RIP
networks, specifically OSPF networks and static routes, to the RIP network.
Costs might be calculated differently, however, so you use the
Metric
field to
specify the cost in RIP terms.
RIP uses UDP port 520.
Use the
RIP
screen to specify the authentication method and maintain the policies
for redistribution.
Click
Configuration > Network
>
Routing >
RIP
to open the following screen.
Figure 180
Configuration > Network > Routing > RIP
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The following table describes the labels in this screen.
14.3
The OSPF Screen
OSPF (Open Shortest Path First, RFC 2328) is a link-state protocol designed to
distribute routing information within a group of networks, called an Autonomous
Table 82
Configuration > Network > Routing Protocol > RIP
LABEL
DESCRIPTION
Authentication
Authentication
Select the authentication method used in the RIP network. This
authentication protects the integrity, but not the confidentiality, of
routing updates.
None
uses no authentication.
Text
uses a plain text password that is sent over the network (not
very secure).
MD5
uses an MD5 password and authentication ID (most secure).
Text
Authentication
Key
This field is available if the
Authentication
is
Text
. Type the
password for text authentication. The key can consist of alphanumeric
characters and the underscore, and it can be up to 8 characters long.
MD5
Authentication
ID
This field is available if the
Authentication
is
MD5
. Type the ID for
MD5 authentication. The ID can be between 1 and 255.
MD5
Authentication
Key
This field is available if the
Authentication
is
MD5
. Type the
password for MD5 authentication. The password can consist of
alphanumeric characters and the underscore, and it can be up to 16
characters long.
Redistribute
Active OSPF
Select this to use RIP to advertise routes that were learned through
OSPF.
Metric
Type the cost for routes provided by OSPF. The metric represents the
“cost” of transmission for routing purposes. RIP routing uses hop
count as the measurement of cost, with 1 usually used for directly
connected networks. The number does not have to be precise, but it
must be between 0 and 16. In practice, 2 or 3 is usually used.
Active Static
Route
Select this to use RIP to advertise routes that were learned through
the static route configuration.
Metric
Type the cost for routes provided by the static route configuration.
The metric represents the “cost” of transmission for routing purposes.
RIP routing uses hop count as the measurement of cost, with 1
usually used for directly connected networks. The number does not
have to be precise, but it must be between 0 and 16. In practice, 2 or
3 is usually used.
Apply
Click this button to save your changes to the ZyWALL.
Reset
Click this button to return the screen to its last-saved settings.
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System (AS). OSPF offers some advantages over vector-space routing protocols
like RIP.
OSPF supports variable-length subnet masks, which can be set up to use
available IP addresses more efficiently.
OSPF filters and summarizes routing information, which reduces the size of
routing tables throughout the network.
OSPF responds to changes in the network, such as the loss of a router, more
quickly.
OSPF considers several factors, including bandwidth, hop count, throughput,
round trip time, and reliability, when it calculates the shortest path.
OSPF converges more quickly than RIP.
Naturally, OSPF is also more complicated than RIP, so OSPF is usually more
suitable for large networks.
OSPF uses IP protocol 89.
OSPF Areas
An OSPF Autonomous System (AS) is divided into one or more areas. Each area
represents a group of adjacent networks and is identified by a 32-bit ID. In OSPF,
this number may be expressed as an integer or as an IP address.
There are several types of areas.
The backbone is the transit area that routes packets between other areas. All
other areas are connected to the backbone.
A normal area is a group of adjacent networks. A normal area has routing
information about the OSPF AS, any networks outside the OSPF AS to which it is
directly connected, and any networks outside the OSPF AS that provide routing
information to any area in the OSPF AS.
A stub area has routing information about the OSPF AS. It does not have any
routing information about any networks outside the OSPF AS, including
networks to which it is directly connected. It relies on a default route to send
information outside the OSPF AS.
A Not So Stubby Area (NSSA, RFC 1587) has routing information about the
OSPF AS and networks outside the OSPF AS to which the NSSA is directly
connected. It does not have any routing information about other networks
outside the OSPF AS.

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