Chapter 9
What is a stub router
- A stub indicates that the networks in a design have only one way out to reach all other networks, which means that instead of creating multiple static routes, we can just use a single default route. Example: LA#config t LA(config)#ip route 0.0.0.0 0.0.0.0 172.16.10.5
Advanced distance vector
- Advanced distance-vector protocols use aspects of both distance-vector and link-state protocols, and EIGRP is a great example. EIGRP may act like a link-state routing protocol because it uses a Hello protocol to discover neighbors and form neighbor relationships and because only partial updates are sent when a change occurs. However, EIGRP is still based on the key distance-vector routing protocol principle that information about the rest of the network is learned from directly connected neighbors.
What is dynamic routing
- Dynamic routing is when protocols are used to find networks and update routing tables on routers.
Link state
- In link-state protocols, also called shortest-path-first (SPF) protocols, the routers each create three separate tables. One of these tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the routing table. Link-state routers know more about the internetwork than any distance-vector routing protocol ever could. OSPF is an IP routing protocol that's completely link-state. Link-state routing tables are not exchanged periodically. Instead, triggered updates containing only specific link-state information are sent. Periodic keepalives that are small and efficient, in the form of hello messages, are exchanged between directly connected neighbors to establish and maintain neighbor relationships.
What type of routing protocols are used in internetworks
- Interior gateway protocols (IGPs) and exterior gateway protocols (EGPs)
What is Interior gateway protocols
- Interior gateway protocols are used to exchange routing information with routers in the same autonomous system (AS). An AS is either a single network or a collection of networks under a common administrative domain, which basically means that all routers sharing the same routing-table information are in the same AS.
What is an Administrative Distances
- Is used to rate the trustworthiness of routing information received on a router from a neighbor router. An administrative distance is an integer from 0 to 255, where 0 is the most trusted and 255 means no traffic will be passed. - If one of the advertised routers has a lower AD than the other, then the route with the lowest AD will be chosen and placed in the routing table. - If both advertised routes to the same network have the same AD, then routing protocol metrics like hop count and/or bandwidth of the lines will be used to find the best path to the remote network. - The advertised route with the lowest metric will be placed in the routing table, but if both advertised routes have the same AD as well as the same metric, then the routing protocol will load-balance to the remote network, meaning the protocol will send data down each link.
Notes
- Mac addresses are always local on the LAN and never go through and past a router. - To see which packet switching method your router interface is using, use the command show ip interface - Remember that RIP uses the classful address when configuring the network address. - If a router receives a routing update that contains a higher-cost path to a network that's already in its routing table, the update will be ignored.
Distance vector
- The distance-vector protocols in use today find the best path to a remote network by judging distance. In RIP routing, each instance where a packet goes through a router is called a hop, and the route with the least number of hops to the network will be chosen as the best one. The vector indicates the direction to the remote network. RIP is a distance-vector routing protocol and periodically sends out the entire routing table to directly connected neighbors
How to stop RIP from propagating
- The passive-interface command prevents RIP update broadcast from being sent out of a specified interface but still allows that same interface to receive RIP updates. - Here's an example of how to configure a passive-interface on the Corp router's Fa0/1 interface, which we will pretend is connected to a LAN that we don't want RIP on. Example: Corp#config t Corp(config)#route rip Corp(config-router)#passive-interface FastEthernet 0/1 - This command will stop RIP updates from being propagated out of FastEthernet interface 0/1, but it can still receive RIP updates.
Cisco Express Forwarding (CEF)
- This is Cisco's newer creation, and it's the default packet-forwarding method used on all the latest Cisco routers. CEF makes many different cahce tables to help improve performance and is changed triggered, not packet triggered. This means that when the network topology changes, the cache changes along with it.
Process switching
- This process is not extremely complex and involves looking up every destination in the routing table and finding the exit interface for every packet.
Fast switching
- This solution was created to make the slow performance of process switching faster and more efficient. Fast switching uses a cache to store the most recently used destinations so that lookups are not required for every packet. By caching the exit interface of the destination device, as well as the layer 2 header, performance was dramatically improved.
What is Exterior gateway protocols
- are used to communicate between ASs. An example of EGP is Border Gateway Protocol (BGP).
Describe how MAC addresses are used during the routing process
A MAC (hardware) address will only be used on a local LAN. It will never pass a router's interface. A frame uses MAC (hardware) addresses to send a packet to either a host on the LAN or a router's interface (if the packet is destined for a remote network). As packets move from one router to another, the MAC addresses used will change, but normally the original source and destination IP addresses within the packet will not.
Understand administrative distance and its role in the selection of best route
Administrative distance (AD) is used to rate the trustworthiness of routing information received on a router from a neighbor router. Administrative distance is an integer from 0 to 255, where 0 is the most trusted and 255 means no traffic will be passed via this route. All routing protocols are assigned a default AD, but it can be changed at the CLI.
How advertise a Default Route Using RIP
Advertise my network to other routers in the AS as the default route to show them where to send packet destined for the Internet. Example: Corp(config)#ip route 0.0.0.0 0.0.0.0 fa0/0 Corp(config)#router rip Corp(config)#default-information originate
What command to use to check for dhcp conflicts
Corp#sh ip dhcp conflict - This command would tell us if we had two host with the same IP address. - Two detection methods are used to confirm this: • A ping from DHCP server to make sure no other host responds before handing out an address. • A gratuitous ARP from a host that receives a DHCP address from the server.
Differentiate distance-vector, link-state, and hybird routing protocols
Distance-vector routing protocols make routing decisions based on hop count (think RIP), while link-state routing protocols are able to consider multiple factors such as bandwidth available and building a topology table. Hybrid routing protocols exhibit characteristics of both types.
Cisco uses three types of packet-forwarding techniques
Following cards
Routing Protocols
Following cards
Default administrative distances
Route source Default AD Connected interface --> 0 Static route ------------> 1 External BGP ----------> 20 EIGRP -----------------> 90 OSPF ------------------> 110 RIP ---------------------> 120 External EIGRP --------> 170 Internal BGP -----------> 200 Unknown ---------------> 255 (this route will never be used)
Compare and contrast static and dynamic routing
Static routing creates no routing update traffic and creates less overhead on the router and network links, but it must be configured manually and does not have the ability to react to link outages. Dynamic routing creates routing update traffic and uses more overhead on the router and network links.
Configure static routes at the CLI
The command syntax to add a route is ip route [destination_network] [mask] [next-hop_address or exit interface] [administrative_distance] [permanent]
Differentiate the three types of routing
The three types of routing are static (in which routes are manually configured at the CLI), dymaic (in which the routers share routing information via a routing protocol), and default routing (in which a special route is configured for all traffic without a more specific destination network found in the table).
Create a default route
To add a default route, use the command syntax ip route 0.0.0.0 0.0.0.0 ip-address or exit interface type and number
List the information required by a router to successfully route packets
To be able to route packets, a router must know, at a minimum, the destination address, the location of neighboring routers through which it can reach remote networks, possible routes to all remote networks, the best route to each remote network, and how to maintain and verify routing information
Configure RIPv2 routing
To configure RIP routing, first you must be in global configuration mode and then you type the command router rip. Then you add all directly connected networks, making sure to use the classful address and the version 2 command and to disable auto-summarization with the no auto-summary command.
View and interpret the routing table of a router.
Use the show ip route command to view the routing table. Each route will be listed along with the source of the routing information. A C to the left of the route will indicate directly connected routes, and other letters next to the route can also indicate a particular routing protocol that provided the information, such as, for example, R for RIP.
Describe the basic IP routing process
You need to remember that the frame changes at each hop but that the packet is never changed or manipulated in any way until it reaches the destination device (the TTL field in the IP header is decremented for each hop, but that's it).
What is the command syntax to add a static route?
ip route [destination_network] [mask] [next-hop_address or exit interface] [administrative_distance] [permanent] Example: ip route 209.165.201.2 255.255.255.0 209.165.202.3 2
Static Routing Cons
• Must have a vault-tight knowledge of the internetwork and how each router is connected in order to configure routes correctly. • If you add a network to the internetwork, you have to tediously add a route to it on all router by hand. • It's not feasible to use it in most large network because maintaining it would be a full-time job in itself.
Static Routing Pros
• There is no overhead on the router CPU, which mean you could probably make do with a cheaper router than you would need for dynamic. • There is no bandwidth usage between routers, saving you money on WAN links as well as minimizing overhead on the router since you're not using a routing protocol • It adds security because you, the administrator, can be very exclusive and choose to allow routing access to certain network only.
