Dynamic Routing Protocols & router password recovery

Dynamic Routing Protocols & router password recovery By admin 05 September 2008 at 11:00 pm and have

Dynamic Routing Protocols:

Dynamic routing helps the admin overcome the time-consuming process of configuring and maintaining static routes.
Routing protocols have been used since the early 80s.
Routing algorithms have been in use since 1969.
Some function(s) of Dynamic Routing Protocols:
Dynamically share information between routers.
Automatically update routing table when topology changes.
Determine best path to a destination.

The purpose of a dynamic routing protocol is to:
Discover remote networks.
Maintain up-to-date routing information.
Choose the best path to destination networks.
Find a new best path if the current path disappears.

Components of a routing protocol:
Data Structures – Some routing protocols use tables and/or databases for operations. This info is kept in RAM.
Algorithm – A procedure for accomplishing a certain task. Different protocols use different algorithms.
Routing protocol messages – These are messages for discovering neighbours and exchange of routing information.

Advantages of static routing:
Can backup multiple interfaces/networks on a router.
Easy to configure.
No extra resources (CPU/memory) are needed.
More secure.

Disadvantages of static routing:
Network changes require manual reconfiguration.
Config is error-prone, especially in large networks.
Admin intervention is required to maintain changing route info
Does not scale well in large topologies.
Requires complete knowledge of the whole network for proper implementation.

Advantages of Dynamic routing:
Admin has less work maintaining the config when adding or deleting networks.
Protocols automatically react to the topology changes.
Config is less error-prone.
More scalable, growing the network usually does not present a problem.

Disadvantages of Dynamic routing:
Router resources are used (CPU cycles, memory and link BW).
More admin knowledge is required for config, verification, and troubleshooting.

Classifying Routing Protocols:
Dynamic routing protocols are grouped according to characteristics.
Dynamic Routing Protocols.
Interior Gateway Protocols.
Distance Vector Protocols.
Link-State Protocols.
Exterior Gateway Protocols.

Autonomous System is a group of routers under the control of a single authority (eg. Company).

Interior Gateway Routing Protocols (IGP).
Used for routing inside an autonomous system and used to route within the individual networks themselves.
Example: RIP, EIGRP, OSPF.

Exterior Routing Protocols (EGP).
Used for routing between autonomous systems.
Example: BGPv4.

IGP: Comparison of Distance Vector and Link State routing protocols.
Distance vector.
Routes are advertised as vectors of distance and direction.
Incomplete view of network topology.
Generally, periodic updates.
Link State.
Complete view of network topology is created.
Updates are not periodic.

Classifying Routing Protocols:

Classful routing protocols.
Do NOT include subnet mask information in routing updates.
RIPv1, IGRP.

Classless routing protocols.
Do include subnet mask in routing updates. (support VLSM)
RIPv2, EIGRP, OSPF, IS-IS, BGP

Convergence is defined as when all routers’ routing tables are at a state of consistency (not identical but will know about the same networks).
Convergence time is the time it takes for all routers to converge. Faster is better! (RIP is a poor one can take up to 7.5min, OSPF a matter of seconds, EIGRP can converge the fastest, under a second).
Convergence properties include the speed of propagation of routing information and the calculation of optimal paths. Routing protocols can be rated based on the speed to convergence.
The faster the convergence, the better the routing protocol. Generally, RIP and IGRP are slow to converge, whereas EIGRP and OSPF are faster to converge.

Routing Protocols Metrics:

Metric – a value or unit of measure used by a routing protocol to determine which routes are better then others.
Metrics used in IP routing protocols:
Hop count – counts the number of routers a packet must traverse.
Bandwidth – path selection by preferring the path with the highest bandwidth.
Load – traffic utilization of a certain link.
Delay – time a packet takes to traverse a path.
Reliability – assesses the probability of a link failure, calculated frm the interface error count or previous link failures.
Cost – value determined either by the IOS or by the network admin to indicate preference for a route. Cost can represent a metric, a combination of metrics or a policy.

The Metric Field in the Routing Table: (1st number is the administrative distance, second number is the hop count in [120/1])
Metric used for each routing protocol.
RIP – hop count.
IGRP and EIGRP – Bandwidth and Delay (default), Load, Reliability.
IS-IS and OSPF – Cost, Bandwidth (Cisco’s implementation).

The metric associated with a certain route can be best viewed using the #show ip route command.

Load balancing:
This is the ability of a router to distribute packets among multiple same cost paths.
Load balancing across equal cost paths.

Administrative Distance of a route:

A metric is used to determine the best path to a destination.
When comparing routes using different protocols, the metrics are incompatible. E.g. hops vs. Bandwidth.
Administrative Distance (AD):
A numeric value specifying the preference of a particular routing source. I.E. the reliablility of the route information.

Identifying the Administrative Distance (AD) in a routing table.
It is the first number in the brackets in the routing table.
The lower the value the better – best = 0, worst = 255.
The lower the value the more trustworthy the route.
0 is directly connected to the router.
#show ip protocol.
If you see the word “distance” it usually means AD.

Dynamic Routing Protocols:

#show ip route
#show ip protocols.

Static Routes:
AD of a static route has a default value of 1 regardless of how it is configured.
You can verify AD values with #show ip protocols.
It is possible to change the AD of static routes

Directly connected routes:
Immediately appear in the routing table as soon as the interface is configured, enabled and operational.

Password Recovery:

Do a hard reboot (cold reboot) – i.e. turn power off/on.
In Hyperterminal, Hit Ctrl-Break key combination with 60s (hit a few times).
Router prompt should display rommon >(read only memory monitor mode).
Type:
rommon> confreg 0×2142     – to change config register.
rommon> i            - to reboot/initialize router.
router should reboot into setup mode (ctrl-C to bypass).
Type:
.R1(config)#config-register 0×2102    - to change back to default otherwise if you have to reboot again you will not be using th.
Then either 1) erase startup-config OR 2) copy it to RAM and change passwords (then save back to NVRAM).
In the real world.
Copy startup-config running-config.