Overview

A router is a device that has multiple network interfaces and transfers Internet Protocol (IP) packets from one network or subnet to another within an internetwork. (In many IP-related documents, this device is also referred to as a "gateway." The term "router" is used in this chapter.) The gated daemon updates routing tables in internetwork routers. Developed at Cornell University, gated handles the RIP, EGP, BGP, and OSPF routing protocols and the Router Discovery Protocol (RDP), or any combination of these protocols.

Routing protocols are designed to find a path between network nodes. If multiple paths exist for a given protocol, the shorter paths are usually chosen. Each protocol has a cost or a metric that it applies to each path. In most cases, the lower the cost or metric for a given path, the more likely a protocol will choose it.

When started, gated reads the kernel routing table on the local machine. gated maintains a complete routing table in the user space, and keeps the kernel routing table (in the kernel space) synchronized with this table.

In large local networks, there are often multiple paths to other parts of the local network. gated can be used to maintain near optimal routing to the other parts of the local network, and to recover from link failures in paths.

Advantages

Using gated offers these advantages:

Dynamic routing eliminates the need to reset routes manually. When network failures occur, routes are automatically re-routed.
Dynamic routing makes it easier to add and administer nodes.
Dynamic routing lowers the cost of operating complex internet systems.
gated translates among several protocols, passing information within or between IP routing domains or autonomous systems. "Autonomous system" is used here to refer to a group of connected nodes and routers in the same administrative domain that are exchanging routing information via a common routing protocol.
gated gives the system administrator flexibility in setting up and controlling network routing. For example, gated can listen to network traffic at specified routers, determine available routes, and update local routing tables accordingly.

When to Use gated

gated is most often used in large networks, or small networks connected to larger wide-area networks.

gated should be run on routers (gateways) so its routing information can be sent to other routers. gated supports many routing protocols that allow routers to build and maintain dynamic routing tables and also RDP as a client with a replacement for rdpd. However, gated also supports RIP (Routing Information Protocol), which can run on end systems (systems with only one network interface) as well as routers.




	NOTE: `gated` also supports RDP as a client. RDP will replace `rdpd`.

gated is useful in topologies with multiple routers and multiple paths between parts of the network. gated allows the routers to exchange routing information and dynamically change routing information to reflect topology changes and maintain optimal routing paths.

Alternatively, you may configure IP routes manually with the route (1M) command. For end systems in subnets with only one router (gateway) to the rest of the internet, manually configuring a default route is usually more efficient than running gated. Type man 1M route at the HP-UX prompt.

When connected to wide-area networks, gated can be used to inject local routing information into the wide-area network's routing table.

Protocols

For routing purposes, networks and gateways are logically grouped into autonomous systems. An autonomous system (AS) is a set of networks and gateways that is administered by a single entity. Companies and organizations that wish to connect to the Internet and form an AS must obtain a unique AS number from the Internet Assigned Numbers Authority (IANA).

An interior gateway protocol is used to distribute routing information within the autonomous system. An exterior gateway protocol is used to distribute general routing information about an autonomous system to other autonomous systems.

Dividing networks into autonomous systems keeps route changes inside the autonomous system from affecting other autonomous systems. When routes change within an autonomous system, the new information need not be propagated outside the autonomous system if it is irrelevant to gateways outside the autonomous system.

gated supports the following interior gateway protocols, as defined in IETF RFCs:

RIP (Routing Information Protocol) is a common routing protocol used within an autonomous system. A de facto industry standard, it is also used by routed, a service distributed by Berkeley. RIP is not intended for use in WAN applications. There are currently two versions of RIP implementations: version 1, as defined in RFC 1058, and version 2, as defined in RFC 1388. gated supports all version 1 features and most of the features of version 2. The following version 2 features are not supported: RIP management information base (MIB) route tag, and route aggregation. (Note that authentication is now supported, with gated version 3.5.)
OSPF (Open Shortest Path First), like RIP, is a routing protocol that allows routing information to be distributed between routers in an autonomous system. Each router on the network transmits a packet that describes its local links to all other routers. The distributed database is then built from the collected descriptions. If a link fails, updated information floods the network, allowing all routers to recalculate their routing tables at the same time. OSPF is more suitable than RIP for routing in complex networks with many routers. gated 3.0 supports most of the features of OSPF version 2, as described in RFC 1247. The following version 2 feature is not supported: IP type of service (TOS) routing. Equal cost multipath routes are limited to one hop per destination, because the HP-UX kernel supports only one gateway per route.
HELLO was designed to work with routers called "Fuzzballs." Most installations use RIP or OSPF instead of HELLO. The HELLO protocol is no longer supported on HP-UX. RIP/OSPF can be used per requirements as they are internal routing protocols.




	NOTE: Do not mix RIP and OSPF protocols within a single network, because the routing information might conflict.

Table 8-1 “Comparison of RIP and OSPF Protocols” compares the advantages and disadvantages of the RIP and OSPF protocols.

Table 8-1 Comparison of RIP and OSPF Protocols

RIP	OSPF
Advantage: RIP is easy to configure.	Disadvantage: OSPF is complicated to configure and requires network design and planning.
Advantage: An end system (a system with only one network interface) can run RIP in passive mode to listen for routing information without supplying any.	Disadvantage: OSPF does not have a passive mode.
Disadvantage: RIP may be slow to adjust for link failures.	Advantage: OSPF is quick to adjust for link failures.
Disadvantage: RIP generates more protocol traffic than OSPF, because it propagates routing information by periodically transmitting the entire routing table to neighbor routers.	Advantage: OSPF generates less protocol traffic than RIP, because each router transmits only information about its links instead of the whole routing table, and because OSPF allows you to divide an autonomous system into areas, each with a designated router that exchanges inter-area routing information with other routers. Intra-area routing information is isolated to a single area.
Disadvantage: RIP is not well suited to large networks, because RIP packet size increases as the number of networks increases.	Advantage: OSPF works well in large networks.

gated supports the following exterior gateway protocols:

EGP (External Gateway Protocol) is known as a "reachability" protocol primarily because it permits a node on the NSFNET backbone to exchange information with other backbone nodes about whether a destination can be reached. Use EGP to communicate routing information between autonomous systems. The EGP protocol will be obsoleted in a future release of HP-UX. Use BGP instead of the EGP protocol. BGP offers more flexibility and requires less bandwidth than EGP
BGP (Border Gateway Protocol) is intended as a replacement for EGP. BGP uses path attributes to select routes. One of the attributes that BGP can pass is the sequence of autonomous systems that must be traversed to reach a destination. gated supports BGP versions 2, 3, and 4, as described in RFCs 1163 and 1267.

gated also supports the Router Discovery Protocol (RDP), which is neither an interior nor exterior gateway protocol. It is used to inform hosts of the existence of routers they can send packets to. It is used instead of, or in addition to, a statically configured default router. Router Discovery is made up of two parts: a server part that runs on routers, and a client part that runs on hosts.

Overview

Technical documentation

» Table of Contents

» Index

Advantages

When to Use gated

Protocols