CCNA 2 Chapter 3: Dynamic Routing

IPv6 Routing Table Entries

Components of the IPv6 routing table are very similar to the IPv4 routing table (directly connected interfaces, static routes, and dynamically learned routes). IPv6 is classless by design, all routes are effectively level 1 ultimate routes. There is no level 1 parent of level 2 child routes.

Static Routing Uses

Networks typically use a combination of both static and dynamic routing. Static routing has several primary uses: Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. Routing to and from a stub network. A network with only one default route out and no knowledge of any remote networks. Accessing a single default router. This is used to represent a path to any network that does not have a match in the routing table.

Dynamic Routing Protocols Components

Routing Protocols are used to facilitate the exchange of routing information between routers. The purpose of dynamic routing protocols includes: Discovery of remote networks Maintaining up-to-date routing information Choosing the best path to destination networks Ability to find a new best path if the current path is no longer available

Routing Table Entries

U Up—Route is valid G Gateway—Route is to a gateway router rather than to a directly connected network or host H Host name—Route is to a host rather than to a network, where the destination address is a complete address R Reject—Set by ARP when an entry expires (for example, the IP address could not be resolved into a MAC address) D Dynamic—Route added by a route redirect or RIP (if routed is enabled) M Modified—Route modified by a route redirect C Cloning—A new route is cloned from this entry when it is used L Link—Link-level information, such as the Ethernet MAC address, is present S Static—Route added with the route command

Verify RIP Routing

Verify RIP settings show ip protocols Verify RIP Routes show ip route | begin gateway

Static Routing Advantages and Disadvantages

Advantages Easy to implement in a small network. Very secure. No advertisements are sent, unlike with dynamic routing protocols. It is very predictable, as the route to the destination is always the same. No routing algorithm or update mechanisms are required. Therefore, extra resources (CPU and memory) are not required Disadvantages Suitable for simple topologies or for special purposes such as a default static route. Configuration complexity increases dramatically as the network grows. Managing the static configurations in large networks can become time consuming. If a link fails, a static route cannot reroute traffic. Therefore, manual intervention is required to re-route traffic.

Dynamic Routing Advantages & Disadvantages

Advantages Suitable in all topologies where multiple routers are required. Generally independent of the network size Automatically adapts topology to reroute traffic if possible. Disadvantages Can be more complex to initially implement. Less secure due to the broadcast and multicast routing updates. Additional configuration settings such as passive interfaces and routing protocol authentication are required to increase security. Route depends on the current topology. Requires additional resources such as CPU, memory, and link bandwidth.

IPv6 Routing Table Structure

Directly attached network routes These typically have 64-bit prefixes and identify adjacent links (network segments connected to the local segment via one router). Remote network routes These have varying prefixes and identify remote links (network segments connected to the local segment via several routers). Host routes These have 128-bit prefixes and identify a specific IPv6 node. Default route This uses the network prefix ::/0 and is used to forward packets when a network or host route cannot be determined.

Dynamic Routing Protocol Evolution

Dynamic routing protocols have been used in networks since the late 1980s. Newer versions support the communication based on IPv6.

Route Lookup Process

If the best match is a level 1 ultimate route, then this route is used to forward the packet. If the best match is a level 1 parent route, proceed to the next step. The router examines child routes (the subnet routes) of the parent route for a best match. If there is a match with a level 2 child route, that subnet is used to forward the packet. If there is not a match with any of the level 2 child routes, proceed to the next step. The router continues searching level 1 supernet routes in the routing table for a match, including the default route, if there is one. If there is now a lesser match with a level 1 supernet or default routes, the router uses that route to forward the packet. If there is not a match with any route in the routing table, the router drops the packet.

Dynamic Routing Protocols Components (cont.)

Main components of dynamic routing protocols include: Data structures - Routing protocols typically use tables or databases for its operations. This information is kept in RAM. Routing protocol messages - Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network. Algorithm - Routing protocols use algorithms for facilitating routing information for best path determination.

Dynamic Routing Protocols Components (cont.)

Main components of dynamic routing protocols include: Data structures - Routing protocols typically use tables or databases for its operations. This information is kept in RAM. Routing protocol messages - Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network. Algorithm - Routing protocols use algorithms for facilitating routing information for best path determination.

Configuring Passive Interfaces

R1(config)#router rip R1(config-router)#version 2 R1(config-router)#no auto-summary R1(config-router)#network 192.168.12.0 R1(config-router)#network 192.168.10.0

Router RIP Configuration Mode

Router1(config)#router rip Router1(config-router)# network 192.168.1.244 Router1(config-router)# network 192.168.1.248

Disable Auto Summarization

Similarly to RIPv1, RIPv2 automatically summarizes networks at major network boundaries by default. To modify the default RIPv2 behavior of automatic summarization, use the no auto-summary router configuration mode command. This command has no effect when using RIPv1. When automatic summarization has been disabled, RIPv2 no longer summarizes networks to their classful address at boundary routers. RIPv2 now includes all subnets and their appropriate masks in its routing updates. The show ip protocols now states that automatic network summarization is not in effect.

Directly Connected Entries

show ipv6 route

Remote IPv6 Network Entries

show ipv6 route