AIX 5L Configuring TCP/IP (Unit 06): Dynamic Routing

Unit Objectives
Describe the concept of dynamic routing
Define an autonomous system
Discuss the routing protocols for interior and exterior gateways
Configure the routed and gated daemons

Dynamic Routing
AIX provides two daemons: routed and gated
Daemons operate in active and passive mode
Protocols supported include: RIP, RIP v2, OSPF and BGP
Interior and exterior gateways

Active – Broadcast routing information
Passive – Listen for routing information

Autonomous Systems
Definition – All systems under the same administrative control

Local Net 2
Interior Gateway
Local Net 1 –>Exterior Gateway Autonomous System –> Exterior Gateway –> Autosys
Interior Gateway
Local Net3

Route on summarized information outside your own autonomous system.
Exterior Gateway summarizes information

Routing Information Protocol (RIP)
Distance Vector Protocol – Selects the smallest number of hops between systems
Note: This may not be the best route if it happens to be on a slow route such as a modem.

How RIP Updates Work
They periodically broadcast routing information.
Limit of 15 hops for RIP
Propagation Delays – How long it takes for all the routing information to propagate to the other systems.

RIP Features
Metric is only hop count
Maximum hop count 15 hops
Suitable for small/medium internetworks
Routers broadcast updates on UDP
– Send message on startup to solicit routing tables
– Advertise tables every 30 seconds
– Send triggered updateds for topology changes

How RIP Handles Multiple Paths to the Same Network
RIP will choose the shortest number of hops even if it is not the fastest route.

RIP Version 2
Authentication – password sent in RIP messages
Route Tag – indicate internal versus external routes
Subnet Mask – provide subnet mask for destinations
Next Hop – allows advertisement of route via another router
Multicasting – multicast address ( for RIP
Supported only by gated

Configuring the routed Daemon
Identify known networks in the /etc/networks file (optional)
Identify any known gateways not directly connected to your network in the /etc/gateways file (optional)
Uncomment the line in the /etc/rc.tcpip file that starts the routed daemon adding any of the following options as needed:
startsrc -s routed -a “-q”
-s for active (gateway)
-q for passive (host)
-t for turning on tracing
-d for turning on debugging
-g for gateway
Run the script or
startsrc -s routed (Start the routed deamon)
startsrc -s routed -a “-q” (-a=arguments, -q=passive)
startsrc -s routed -a “-s” (-a=arguments, -s=active)

Note: You can not run routed and gated at the same time because they will conflict with each other.

Eight Statement Classes
1. Directive
2. Trace
3. Options
4. Interface
5. Definition
6. Protocol
7. Route
8. Control

Classes 1 and 2 can appear in any order in the configuration file.
The rest must appear in the above order.

gdc Command
Could use startsrc -s gated
gdc Provides an operational user interface for gated

gdc [-q] [-n] [-c coresize] [-f filesize] [-m datasize] [-s stacksize] [-t seconds] Subcommands

startsrc -s gated

Configuring RIP Using the gated Daemon
Example of a Simple RIP Running in Quiet Mode:
traceoptions all;
tracefile “/var/tmp/rip.quiet.trace” replace size 50k files 4;
rip yes {

Example of a Simple RIP Supplier
rip yes {

Open Shortest Path First (OSPF)
Interior gateway protocol
Link state routing protocol

All nodes have a copy of the network map.

Configuring OSPF Using the gated Daemon
interfaces {
interfaces {
rip no;
ospf yes;
area {
authtype none;
networks { mask mask

OSPF Areas
Area A Backbone Area C
Backbone has over lapping networks with Area A and Area C

Unit Summary
In active mode a host can send and receive routing information. In passive mode it only receives it.
An autonomous system is a group of networks under one administrative authority.
Interior gateways are routers within an autonomous system
Exterior gateways are routers that connect autonomouse systems together
RIP and OSPF are used on interior gateways and BPG on exterior ones.

Exercise 6 – Dynamic Routing
lssrc -s routed (see if the routed daemon is running)
lssrc -s gated

smitty – Communications Applications – TCP/IP – Further Configuration – Static Routes –
Flush Routing Table

netstat -r (verify clean routing table)

Switch to Ethernet Gateway
lssrc -s routed
lssrc -s gated
smitty tcpip – Further Communications …..
Flush Routing Table
netstat -r

startsrc -s routed -a “-s” (broadcast routing information)

Switch to Local Client
startsrc -s routed -a “-q” (listen only)
netstat -rn (view new indirect route created dynamically)
ping sys4

Switch to sys4
netstat -r
route -f (flush routing table)
startsrc -s routed -a “-q”
netstat -r
ping sys2
lssrc -s routed

Note: broadcast every half minute

netstat -in
rmdev -d -l en1 (remove it from the odm database)

Clean up environment from exercise
stopsrc -s routed
route -f
smitty tcpip
Further Configuration – Static Routes – Add a Static Route – default

Switch to the router
Follow same proceedure as above.

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