6. EIGRP Terminology Neighbor TableāIP Next Hop Interface Router Note: A feasible successor is a backup route and stored in the Topology table Topology TableāIP Destination 1 Successor Destination 1 Feasible Successor Routing TableāIP Destination 1 Successor
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10. Configuring EIGRP for IP 172.16.10.0 10.110.1.0 192.168.0.0 AS=10 Router(config)# router eigrp 10 Router(config-router)# network 10.0.0.0 Router(config-router)# network 172.16.0.0 192.168.0.0 A C B Enable EIGRP Assign networks If you use the same AS number for EIGRP as IGRP, EIGRP will automatically redistribute IGRP into EIGRP
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19. Configuring Single Area OSPF Router(config-router)# network address mask area area-id Assigns networks to a specific OSPF area Router(config)# router ospf process-id Defines OSPF as the IP routing protocol Note: The process ID is locally significant and is needed to identify a unique instance of an OSPF database
20. OSPF Example hostname R3 router ospf 10 network 10.1.2.3 0.0.0.0 area 0 network 10.1.3.1 0.0.0.0 area 0 hostname R2 router ospf 20 network 10.0.0.0 0.255.255.255 area 0 hostname R1 router ospf 30 network 10.1.0.0 0.0.255.255 area 0 network 10.5.5.1 0.0.0.0 area 0 R3 R2 R1 10.1.2.0 10.1.1.0 10.5.5.0 Area 0 10.1.3.0
21. Verifying the OSPF Configuration Router# show ip ospf interface Displays area-ID and adjacency information Router# show ip protocols Verifies that OSPF is configured Router# show ip route Displays all the routes learned by the router Router# show ip ospf neighbor Displays OSPF-neighbor information on a per-interface basis
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Editor's Notes
Enhanced Interior Gateway Routing Protocol (EIGRP) is a proprietary Cisco protocol that runs on Cisco routers and internal route processors found in the Cisco Distribution and Core layer switches. In this section, youāll see the many features of EIGRP and describe how it works, with particular focus on the unique way it discovers, selects, and advertises routes. There are a number of powerful features that make EIGRP a real stand out from IGRP and other protocols. The main ones are listed here: Support for IP, IPX, and AppleTalk via protocol-dependent modules Efficient neighbor discovery Communication via Reliable Transport Protocol (RTP) Best path selection via Diffusing update algorithm (DUAL)
Enhanced IGRP (EIGRP) is a classless, enhanced distance-vector protocol that gives us a real edge over another Cisco proprietary protocol, Interior Gateway Routing Protocol (IGRP). Thatās basically why itās called Enhanced IGRP. Like IGRP, EIGRP uses the concept of an autonomous system to describe the set of contiguous routers that run the same routing protocol and share routing information. But unlike IGRP, EIGRP includes the subnet mask in its route updates. And as you now know, the advertisement of subnet information allows us to use VLSM and summarization when designing our networks!
EIGRP doesnāt send link-state packets as OSPF does; instead, it sends traditional distance-vector updates containing information about networks plus the cost of reaching them from the perspective of the advertising router. And EIGRP has link-state characteristics as wellāit synchronizes routing tables between neighbors at startup, and then sends specific updates only when topology changes occur.
The neighborship table (usually referred to as the neighbor table) records information about routers with whom neighborship relationships have been formed. The topology table stores the route advertisements about every route in the internetwork received from each neighbor. The route table stores the routes that are currently used to make routing decision. There would be separate copies of each of these tables for each protocol that is actively being supported by EIGRP, whether itās IP, IPX, or AppleTalk.
The neighbor table and topology table are held in ram and are maintained through the use of hello and update packets.
Successor route is used by EIGRP to forward traffic to a destination A successor routes may be backed up by a feasible successor route Successor routes are stored in both the topology table and the routing table
Like IGRP, EIGRP uses only bandwidth and delay of the line to determine the best path to a remote network by default. Cisco sometimes likes to call these path bandwidth value and cumulative line delayāgo figure.
To start an EIGRP session on a router, use the router eigrp command followed by the autonomous system number of your network. You then enter the network numbers connected to the router using the network command followed by the network number.
Redistribution is important, because if you want to use EIGRP and donāt have all Cisco router, you need to configure redistribution commands. If you are using IGRP and want to migrate to EIGRP (yes, you should do this), configure EIGRP with the same AS number and EIGRP automatically redistributed IGRP into EIGRP routes. These routes show up as external routes with an AS of 170.
RIPv1 and RIPv2 use the same metric (hop count) and would find the 56K link the best path to the remote network. EIGRP and IGRP use the same metric as well (bandwidth and delay of the line) and would use the path through the LAN interfaces, not the serial T1ās.
Show ip route: Shows the entire routing table show ip route eigrp: Shows only EIGRP entries in the routing table show ip eigrp neighbors: Shows all EIGRP neighbors. show ip eigrp topology: Shows entries in the EIGRP topology table. Which EIGRP show command will provide you with the IP addresses of the devices with which the router has established an adjacency, as well as the transmit and queue counts for the adjacent routers? Which command will display all the EIGRP feasible successor routes known to a router?
The show ip route command, or the show ip route eigrp command, will show you the routing table the routes found by DUAL. -D is for āDualā -[90/2172] is the administrative distance and cost of the route. The cost of the route is a composite metric comprised from the bandwidth and delay of the line
Open Shortest Path First (OSPF) is an open standards routing protocol thatās been implemented by a wide variety of network vendors, including Cisco. If you have multiple routers, and not all of them are Cisco (what!) then you canāt use EIGRP now can you? So your remaining options are basically RIP, RIPv2 or OSPF. If itās a large network, then really, your only options are OSPF, or something called route redistributionāa translation service between routing protocols. OSPF converges quickly, although perhaps not as quickly as EIGRP, and it supports multiple, equal-cost routes to the same destination. But unlike EIGRP, it only supports IP routing.
OSPF is supposed to be designed in a hierarchical fashion, which basically means that you can separate the larger internetwork into smaller Internetworks called areas.
This slides represents some important Link State characteristics, compared to distance vector.
Notice how each router connects to the backboneācalled area 0, or the backbone area. OSPF must have an area 0, and all routers should connect to this area if at all possible, but routers that connect other areas within an AS together are called Area Boundary Routers (ABRs). Still, at least one interface must be in area 0. OSPF runs inside an autonomous system, but can also connect multiple autonomous systems together. The router that connects these ASās together is called an Autonomous System Boundary Router (ASBR). Area 0 is called the backbone area Hierarchical OSPF networks do not require multiple areas You must have an area 0 Multiple OSPF areas must connect to area 0
Configuring basic OSPF isnāt as simple as RIP, IGRP and EIGRP, and it can get can really complex once the many options that are allowed within OSPF are factored in. These two elements are the basic elements of OSPF configuration: -Enabling OSPF -Configuring OSPF areas The easiest, and also least scalable way to configure OSPF is to just use a single area. Doing this requires a minimum of two commands as shown in the next slide. The command you use to activate the OSPF routing process is: Lab_A(config)# router ospf ? <1-65535> A value in the range 1ā 65535 identifies the OSPF Process ID. Process IDās can be assigned any number from 0 to 65535 Areaās can be any number up to 2.4 billion
There are various ways to configure OSPF. The configuration of R3 shows how the 0.0.0.0 wildcard is used to place each interface individually into area 0 R2 show how two interface can be configured into area 0 with one wildcard network statement of 0.255.255.255 R3 shows the wildcards of 0.0.255.255 and 0.0.0.0 It doesnāt matter how you configure the network statements, the results are the same. Remember, the process ID is irrelevant and can be the same on each router, or different on each router, as they are in this example.
There are several ways to verify proper OSPF configuration and operation, and this slides shows some basic verification commands that you will use in the next hands-on labs.
Neighbors Neighbors are two or more routers that have an interface on a common network, such as two routers connected on a point-to-point serial link. Adjacency An adjacency is a relationship between two OSPF routers that permits the direct exchange of route updates. OSPF is really picky about sharing routing information, unlike EIGRP that directly shares routes with all of its neighbors. Instead, OSPF directly shares routes only with neighbors that have also established adjacencies. Link State Advertisement A Link State Advertisement (LSA) is an OSPF data packet containing link-state and routing information thatās shared among OSPF routers.
Neighbor Two routers that have an interface on a common network Usually discovered by helloās but can also be configured administratively Adjacency Relationship formed between selected neighbors in which routing information is exchanged. Not all neighbors are adjacent Only Broadcast and Non-Broadcast network types have Designated and Backup Designated Routers!!!
Each router that is participating in OSPF needs to be uniquely identified. The method of identification that OSPF uses is Router IDs (RID). 32 bits that uniquely identifies an OSPF router Highest IP address in router is RouterID Overridden by Loopback interface if present Even if Loopback address has lower value Recommended to use loopback interface Easier to manipulate this number Always up Interface loopback 0 Ip address 10.1.1.1 255.255.255.0 You can also Statically assign the Router ID in the OSPF router configuration mode: (config)# router ospf 1 (config-router)# router-id Do NOT use same loopback address on different routers
The following outlines the process OSPF takes and rules that are followed when electing a Designated Router: Routers elect a DR and BDR per network All routers set by default to priority 1 (0-255) Priority of zero (0) means router can not be elected as a DR Router with highest priority wins BDR (1 ā 255), if no other router has a higher priority the BDR will then become the DR RouterID breaks tie, Router ID is either the Highest Loopback or Highest Configured IP address on any given active interface If DR fails, BDR promoted to DR and a new BDR is elected Existing DR will not be overthrown if ābetterā router is turned on after initial election DRs and BDRs listen to multicast traffic on both multicast address 224.0.0.5 and 224.0.0.6 224.0.0.6 is exclusively listed to by DRs
Configuring loopback interfaces when using the OSPF routing protocol is important and Cisco suggests using them whenever you configure OSPF on a router. Loopback interfaces are logical interfaces, which means they are not real router interfaces. They can be used for diagnostic purposes as well as OSPF configuration. The reason you want to configure a loopback interface on a router is because if you donāt, the highest IP address on a router will become that routers Router ID (RID). The RID is used to advertise the routes as well as elect the designated router (DR) and backup designated router (BDR).
Sometimes it is desirable for a router to be configured so that it is not eligible to become the DR or BDR. You can do this by setting the OSPF priority to zero with the ip ospf priority priority# interface subcommand. Router(config-if)# ip ospf priority {0 ā 255} Change the priority of a router on an interface 0 means to not participate in election 1 is default, 255 is highest priority
First, what is the RID of each router? Which router is the default DR for the 172.16.1.0 LAN? There are three options that will ensure that R2 will be the DR for the LAN segment 172.16.1.0/24: Configure the priority value of the Fa0/0 interface of the R2 router to a higher value than any other interface on the Ethernet network Configure a loopback interface on the R2 with an IP address higher than any IP address on the other routers Change the priority value of the Fa0/0 interface of R1 and R3 to zero
This slides introduces the wildcards used in OSPF. These wildcards will also be used in access-list configurations. A 0 octet in the wildcard mask indicates that the corresponding octet in the network must match exactly. On the other hand, a 255 indicates that you donāt care what the corresponding octet is in the network number. A network and wildcard mask combination of 1.1.1.1 0.0.0.0 would match 1.1.1.1 only, and nothing else. This is really useful if you want to activate OSPF on a specific interface in a very clear and simple way. If you insist on matching a range of networks, the network and wildcard mask combination of 1.1.0.0 0.0.255.255 would match anything in the range 1.1.0.0ā1.1.255.255. Because of this, itās simpler and safer to stick to using wildcard masks of 0.0.0.0 and identify each OSPF interface individually.
This slides shows how to find a wildcard that can be used to configure a subnet in an octet.
You need to understand wildcard configuration. Configure the Lab_B router using wildcards: Router ospf 1 Network 192.168.40.1 0.0.0.0 area 0 Network 192.168.10.8 0.0.0.3 area 0 Network 192.168.10.4 0.0.0.3 area 0 NOTE: to remove a bad entry, use the following example: Router(config)#router ospf 1 Router(config-router)#no network 192.168.10.4 0.0.0.4 area 0 Router(config-router)#network 192.168.10.4 0.0.0.3 area 0
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