Глава №2. Резюме

In this chapter, you learned about Cisco’s EIGRP, an advanced distance vector routing protocol. The chapter focused on the following topics:

• Features of EIGRP, including fast convergence, use of partial updates, multiple network layer support,

use of multicast and unicast, VLSM support, seamless connectivity across all data link layer protocols and topologies, and sophisticated metrics.

• EIGRP’s underlying processes and technologies—neighbor discovery/recovery mechanism, RTP, DUAL

finite-state machine, and protocol-dependent modules.

• EIGRP’s tables—neighbor table (containing all routers with which it has a neighbor relationship),

topology table (containing all routes from all neighbors), and routing table (containing the best routes to each destination and used for forwarding packets).

• EIGRP terminology
• The advertised distance (the metric for an EIGRP neighbor router to reach the destination,

which is the metric between the next-hop router and the destination), the feasible distance (the sum of the AD from the next-hop neighbor plus the cost between the local router and the next-hop router), the successor (a neighboring router that has a least-cost loop-free path to a destination, the lowest FD), and the feasible successor (a neighboring router that has a loop-free backup path to a destination).

• Passive routes, those not undergoing recomputation; active routes, those undergoing

recomputation. Passive is the operational, stable state.

• The five EIGRP packet types: hello, update, query, reply, and acknowledgment. Updates, queries, and

replies are sent reliably.

• EIGRP initial route discovery process, started by a router sending hello packets. Neighboring routers

reply with update packets, which populate the router’s topology table. The router chooses the successor routes and offers them to the routing table.

• The DUAL process including selecting FSs. To qualify as an FS, a next-hop router must have an AD

less than the FD of the current successor route for the particular network, to ensure a loop-free network.

• The EIGRP metric calculation, which defaults to bandwidth (the slowest bandwidth between the

source and destination) plus delay (the cumulative interface delay along the path).

• Planning EIGRP implementations, including the IP addressing, network topology, and EIGRP traffic

engineering. The list of tasks for each router in the network includes enabling the EIGRP routing protocol (with the correct autonomous system number), configuring the proper network statements, and optionally configuring the metric to appropriate interfaces.

• Basic EIGRP configuration commands
  • router eigrp autonomous-system-number global configuration command
  • network network-number [wildcard-mask] interface configuration command
  • bandwidth kilobits interface configuration command

• Commands for verifying EIGRP operation
  • show ip eigrp neighbors
  • show ip route
  • show ip route eigrp
  • show ip protocols
  • show ip eigrp interfaces
  • show ip eigrp topology
  • show ip eigrp traffic
  • debug eigrp packets
  • debug ip eigrp
  • debug ip eigrp summary
  • debug eigrp neighbors

• Using the passive-interface type number [default] router configuration command to prevent a routing protocol’s routing updates from being sent through the specified router interface. With EIGRP, hello messages are not sent out of the specified interface, so neighborships are not formed on that interface. However, the router will still advertise the network to its EIGRP neighbors.
• Creating a statically configured default route with the ip route 0.0.0.0 0.0.0.0 next-hop | interface global configuration command. Alternatively, any major network residing in the local routing table can become an EIGRP default route when used in the ip default-network network-numberglobal configuration command.
• EIGRP summarization: EIGRP automatically summarizes on the major network boundary by default (in some IOS versions). To turn off automatic summarization, use the no auto-summary router configuration command. Use the ip summary-address eigrp as-number address mask [admin-distance] interface configuration command to manually create a summary route at an arbitrary bit boundary, as long as a more specific route exists in the routing table.

• EIGRP over Frame Relay, including:
  • An overview of Frame Relay, where PVCs are created by an SP and are identified by DLCIs, locally significant numbers between the router and the Frame Relay switch.
  • EIGRP over a physical interface using Inverse ARP dynamic mapping, the default
  • EIGRP over the physical interface using static maps with the frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco] [payload-compress {packet-by-packet | frf9 stac}] interface configuration command.
  • Configuring subinterfaces with the interface serial number.subinterface-number {point-to-point | multipoint} command.
  • Frame Relay multipoint subinterfaces, on which the IP address-to-DLCI mapping is done by either specifying the local DLCI value (using the frame-relay interface-dlci dlci command) and relying on Inverse ARP, or using manual IP address-to-DLCI mapping.
  • Frame Relay point-to-point subinterfaces, on which the IP address-to-DLCI mapping is done by specifying the local DLCI value.
  • Split horizon, which is disabled by default on most interfaces. Split horizon is enabled by default on Frame Relay multipoint interfaces. It can be disabled with the no ip split-horizon eigrp as-number command.
  • The neighbor {ip-address | ipv6-address} interface-type interface-number router configuration command, used to define a neighboring EIGRP router. Instead of using multicast packets, EIGRP exchanges routing information with the specified neighbor using unicast packets.

• EIGRP over MPLS, including
  • MPLS, which uses labels assigned to each packet at the edge of the network; MPLS nodes use the label to determine where to send the packet.
  • A Layer 2 MPLS VPN, which provides a Layer 2 service across the backbone, where customer routers are connected together on the same IP subnet. A type of AToM, called EoMPLS may be used. Customer routers may also be connected to MPLS edge routers via VLAN subinterfaces; different subinterfaces in the PE routers are used to connect to different VLANs.
  • A Layer 3 MPLS VPN, which provides a Layer 3 service across the backbone, where customer routers are connected to ISP edge routers, and on each side, a separate IP subnet is used. The CE routers see the PE routers as another customer router in the path. PE routers maintain separate routing tables for each customer.
• EIGRP load-balancing, including
  • EIGRP equal-cost load balancing that distributes traffic over all interfaces with the same metric for the destination address.
  • The maximum-paths maximum-path router configuration command, to specify up to 16 equally good routes be kept in the routing table. Set maximum-path to 1 to disable load

balancing.

• • EIGRP unequal-cost load balancing, across routes with different metrics, using the variance multiplier router configuration command and the traffic-share [balanced | min across-interfaces] router configuration command.
• EIGRP operation in WAN environments
  • By default, EIGRP uses up to 50 percent of the bandwidth declared on an interface or subinterface. EIGRP uses the bandwidth of the link set by the bandwidth command, or the link’s default bandwidth if none is configured, when calculating how much bandwidth to use. Theip bandwidth-percent eigrp as-number percent interface configuration command changes the percentage.
  • Configuring multipoint interfaces: Configure the bandwidth to represent the minimum CIR times the number of circuits. For a small number of very low-speed circuits, define the interfaces as point-to-point so that their bandwidth can be set to match the provisioned CIR.

• Configuring, verifying, and troubleshooting EIGRP MD5 authentication, including the following

commands

• • ip authentication mode eigrp autonomous-system md5 interface configuration command
  • key chain name-of-chain global configuration command
  • key key-id key-chain configuration command
  • key-string key key-chain-key configuration command
  • accept-lifetime start-time {infinite | end-time | duration seconds} key-chain-key configuration command
  • send-lifetime start-time {infinite | end-time | duration seconds} key-chain-key configuration command
  • ip authentication key-chain eigrp autonomous-system name-of-chain interface configuration command
  • show ip eigrp neighbors
  • show ip route
  • show key chain
  • debug eigrp packets

• EIGRP scalability factors, including the amount of information exchanged, the number of routers, the depth of the topology, and the number of alternative paths through the network.
• The SIA state: If an EIGRP router does not receive a reply to all the outstanding queries within 3 minutes (the default time) it goes into SIA state, and the router resets the neighbor relationships for the neighbors that failed to reply. Reasons for going into SIA include: router is too busy, the link between the routers is not good, or the link has a unidirectional failure.
• The Active Process Enhancement feature that adds SIA-Query and SIA-Reply to ensure that only appropriate neighbor relationships are reset.

• Limiting the query range to help reduce SIAs, which can be accomplished by
  • Only announcing default routes to remote routers, which are configured to announce only their directly connected networks.
  • Configuring route summarization using the ip summary-address eigrp command on the outbound interfaces of the appropriate routers
  • Route and interface packet filtering.
  • Configuring the remote routers as stub EIGRP routers so that they will not be queried, using the eigrp stub [receive-only | connected |static | summary | redistributed] router configuration command.
  • Using both EIGRP route summarization and EIGRP stub features is recommended, to provide the best scalability.

• Graceful shutdown, which broadcasts a goodbye message (in a hello packet, with all K values set to 255) when an EIGRP routing process is shut down, to inform neighbors.