Static Routing: Configuration, Advantages, and Uses

• Routers can learn about remote networks manually using static routes or dynamically using a dynamic routing protocol

Why use Static Routing

• Static routing offers advantages such as better security, as static routes are not advertised, and reduced bandwidth use, requiring no CPU cycles for communication
• Static routes have a known path for sending data

Static Routing Disadvantages

• Static routing can be time-consuming to configure and maintain initially
• Configuration is prone to errors, particularly in large networks
• Maintaining changing route information requires administrator intervention
• It does not scale well with growing networks
• Proper implementation demands complete knowledge of the entire network

Primary Uses of Static Routing

• Routing table maintenance is easier in smaller networks with little growth expectation
• Used for routing to and from stub networks (networks accessed by a single route with no other neighbors)
• A single default route represents a path to any network without a specific match in the routing table
• Default routes send traffic to any destination beyond the next upstream router

Default Static Route

• A default static route matches all packets and identifies the gateway IP address where the router sends packets without learned or static routes
• A default static route is a static route with "0.0.0.0/0" as the IPv4 destination address

Floating Static Routes

• These routes are static routes that act as a backup for primary static or dynamic routes if a link fails

Types of Static Routes

• Next-hop Route: Only the next-hop IP address is specified
• Directly Connected Static Route: Only the router exit interface is specified
• Fully Specified Static Route: Includes both the next-hop IP address and exit interface

IPv6 Static Routes

• Next-hop IPv6 Route: Only the next-hop IPv6 address is specified
• Directly Connected Static IPv6 Route: Only the router exit interface is specified
• Fully Specified Static IPv6 Route: The next-hop IPv6 address and exit interface are specified

Floating Static Routes with Admin Distance

• These are static routes with a higher administrative distance than other static or dynamic routes, making them less preferred
• Increasing the administrative distance of a static route can make it less desirable than other routes
• These routes are not used when a route with a better administrative distance is active but can take over if the preferred route fails

Testing Floating Static Routes

• Use the "show ip route" command to check that routing table uses the default static route
• Use "traceroute" to follow traffic flow via the primary route
• Disconnect the primary link or shut down the primary exit interface
• Verify the routing table is using the floating static route using the "show ip route" command

Common IOS Troubleshooting Commands

• ping
• traceroute
• show ip route
• show ip interface brief
• show cdp neighbors detail

Features of EIGRP

• Diffusing Update Algorithm (DUAL) at its core guarantees loop-free and backup paths
• DUAL enables EIGRP to store backup routes and quickly adapt to alternate routes
• EIGRP establishes relationships with directly connected routers also running EIGRP
• Neighbor adjacencies are used to track the status of these neighbors

Reliable Transport Protocol (RTP)

• RTP provides delivery of EIGRP packets to neighbors, facilitating DUAL

Partial and Bounded Updates

• EIGRP sends only partial updates (information about route changes) and these updates are bounded (sent only to affected routers)

Load Balancing

• EIGRP supports equal and unequal cost load balancing, allowing traffic distribution

EIGRP Routing

• EIGRP can route multiple protocols, including IPv4 and IPv6, using Protocol-Dependent Modules (PDMs)
• When a router detects a new neighbor, it records the neighbor's address and interface in the neighbor table
• EIGRP maintains a topology table containing all destinations advertised by neighboring routers

EIGRP Packet Types

• Hello packets are used for neighbor discovery and adjacency maintenance (sent unreliably via multicast)
• Update packets send routing information (sent reliably via unicast or multicast)
• Acknowledgment packets acknowledge reliable EIGRP messages (sent unreliably via unicast)
• Query packets request routes from neighbors (sent reliably via unicast or multicast)
• Reply packets respond to queries (sent reliably via unicast)

Packet Timing:

• Default Hello Interval, Multi-point Frame Relay: 60 seconds, Hold Time: 180 seconds
• Default Hello Interval, T1, Ethernet (Greater than 1.544Mb/s): 5 seconds, Hold Time: 15 seconds

EIGRP Updates

• Sends partial updates which only contains information about route changes
• Sends bounded updates which is only sent to routers affected by the change
• EIGRP sends Acknowledgement (ACK) packets when reliable delivery is used.
• An EIGRP acknowledgment is an EIGRP Hello packet without any data.

EIGRP Data Portion

• The data portion of an EIGRP message is encapsulated in a packet
• Called type, length, value (TLV)
• The types of TLVs include EIGRP parameters, IP internal, and external routes

EIGRP Parameters

• Opcode: Indicates packet type: Update (1), Query (3), Reply (4), Hello (5)
• Autonomous System Number: ID for the EIGRP routing process

EIGRP Message parameters

• Includes the weights that EIGRP uses for its composite metric
• Bandwidth and delay weighted equally by default, K1 for bandwidth, K3 field for delay (both set to one (1). Other K values are set to zero (0)
• The Hold Time: the amount of time the EIGRP neighbor receiving this message should wait before considering the advertising router to be down.

EIGRP Metric Details

• Delay: Sum of delays in units of 10 microseconds from source to destination; 0xFFFFFFFF indicates unreachable route
• Bandwidth: Lowest configured bandwidth of any interface along the route
• Prefix Length: Specifies the number of network bits in the subnet mask
• Destination: The destination network address; this field is variable
• Enables the EIGRP Process: "router eigrp autonomous-system" command

Autonomous System Numbers

• The EIGRP autonomous system number is not associated with the Internet Assigned Numbers Authority (IANA)
• local regional Internet registry (RIR) assigns autonomous system numbers
• Autonomous system numbers were 16-bit numbers ranging from 0 to 65,535 and today, 32-bit autonomous system numbers are assigned increasing the number of available autonomous system numbers to over 4 billion.
• Internet Service Providers (ISPs), Internet backbone providers, and large institutions connecting to other entities require an autonomous system number.

Border Gateway Protocol (BGP)

• Often uses the Border Gateway Protocol (BGP), which does use the IANA autonomous system number in its configuration.

EIGRP Router ID

• The EIGRP router ID uniquely identifies each router in the EIGRP routing domain
• The router ID is used in both EIGRP and OSPF routing protocols
• Derived Router ID, first use the IPv4 address configured with the eigrp router-id configuration mode command
• Secondly, if the router ID is not configured, the router chooses the highest IPv4 address of any of its loopback interfaces
• Thirdly, if no loopback interfaces are configured, the router chooses the highest active IPv4 address of any of its physical interfaces.

Configuring EIGRP

• Enables EIGRP for the interfaces on subnets "router eigrp X" "network X.X.X.X"
• Use passive-interface command to prevent neighbor adjacencies, suppress unnecessary update traffic, and increase security controls
• Use the "show ip eigrp neighbors" command to view the neighbor table and verify that EIGRP has established an adjacency with its neighbors.

Show IP EIGRP Command

• The show ip protocols command displays the parameters and other information about the current state of any active IPv4 routing protocol processes configured on the router
• displays different types of output specific to each routing protocol

EIGRP Metric Weights

• The formula consists of values K1 to K5, known as EIGRP metric weights. K1 and K3 represent bandwidth and delay, respectively. K2 represents load, and K4 and K5 represent reliability
• By default, K1 and K3 are set to 1, and K2, K4, and K5 are set to 0. The result is that only the bandwidth and delay values are used in the computation of the default composite metric
• EIGRP for IPv4 and EIGRP for IPv6 use the same formula for the composite metric.

Bandwidth and Delay

• The default K values can be changed with the metric weights router configuration mode command: “Router(config-router)# metric weights tos k1 k2 k3 k4 k5”
• Use the show interfaces command to verify bandwidth.
• Most serial bandwidths are set to 1,544 kb/s (default).
• Because both EIGRP and OSPF use bandwidth in default metric calculations, a correct value for bandwidth is very important to the accuracy of routing information.
• BW - Bandwidth of the interface (in Kilobits per second).
• DLY - Delay of the interface (microseconds).
• Reliability - Reliability of interface as a fraction of 255 (255/255 is 100% reliability).
• Txload, Rxload - transmit and receive load on the interface as a fraction of 255 (255/255 is completely saturated)

Delay and Media

• Delay is the measure of the time it takes for a packet to traverse a route. Ethernet has a delay of 1,000

DUAL

• Diffusing Update Algorithm (DUAL) provides loop-free paths, loop-free backup paths which can be used immediately, results in fast convergence and results in Minimum bandwidth usage with bounded updates.

Successor and Feasible Distance

• Successor is a neighboring router used for packet forwarding and the least-cost route to the destination network. The IP address of a successor is shown in a routing table entry right after the word via.
• Feasible Distance (FD) is the lowest calculated metric to reach the destination network and is listed in the routing table entry as the second number inside the brackets.
• Is the metric for the route.
• Successor Route is the best route for a destination and is used for forwarding traffic.
• Feasible Successor is a backup route that meets the Feasibility Condition and can be quickly activated if the primary route fails.
• Feasibility Condition (FC):The FC is met when a neighbor's Reported Distance to a network is less than the local router's Feasible Distance to the same destination network.

EIGRP Summarization

• Instead of sending three separate networks, R3 can summarize the 192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24 networks as a single route.
• Manually Summarized Routes: "R3 (config)# interface serial 0/0/0" "R3 (config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0" "R3 (config-if)# interface serial 0/0/1"
• "R3 (config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0"
• Route Protocol Default: Using a static route to 0.0.0.0/0 as a default route is not routing protocol dependent and EIGRP requires the use of the redistribute static command to include this static default route with its updates.

Verify EIGRP

• Use the show ip eigrp neighbors command to verify EIGRP neighbors.

Troubleshooting EIGRP

• EIGRP neighbor relationships might not form for a variety of reasons, including the following: Interface is down, Mismatched autonomous system numbers,or Incorrect network statement

Troubleshooting Mismatched K values

• Both routers must be using exactly the same K values if the network command is misconfigured, EIGRP may not be enabled on the proper interfaces
• Passive interface feature suppresses the sending and receiving of hello packets while still allowing the interface's network to be advertised.

Subnets and Authentication:

• The exchange of hello packets must be done on the same subnet; if it isn't, the hello packets are ignored
• If authentication is being used, the key ID and key string must match, and the key must be valid (if valid times have been configured).
• Access Control Lists (ACLs): EIGRP multicast address 224.0.0.10 may be denied by an access control list (ACL).
• Timers: Timers do not have to match; if they are not configured correctly, neighbor adjacencies could flap.
• Troubleshooting Incorrect Network Statement: network command is misconfigured, EIGRP may not be enabled on the proper interfaces causing hello packets to not be sent or and neighbor relationships will not be formed. To combat this the command show ip eigrp interfaces shows the interfaces participating in the EIGRP process.

Verifying Routes

• Better Source of Information: For an EIGRP-learned route to be installed in the routing table, it must be the most trusted routing source due to administrative distance (AD). EIGRP's AD is 90 for internally learned routes and 170 for externally learned routes.
• Split Horizon (Cont.) In interface configuration mode a “no ip split-horizon” command will disable split horizon on an interface.

Understanding EIGRP

• The best route (based on the lowest feasible distance [FD] metric) for a specific network in the EIGRP topology table becomes a candidate to be injected into the router's routing table and is known as the successor (best) route and is then advertised to neighboring routers.
• In the brackets after the next-hop IP address is the FD followed by the reported distance (RD) Feasible distance is The RD plus the metric to reach the neighbor at the next-hop address that is advertising the RD and the reported distance is The distance from the neighbor at the next-hop address to the destination network. EIGRP supports variable-length subnet masking (VLSM). In Cisco IOS versions before 15.0, EIGRP automatically performed route summarization on classful network boundaries.

Auto-Summarization

• In Cisco IOS version 15.0 and newer, auto summarization is turned off by default and the no auto-summary command is no longer needed

Identifying Packets

• EIGRP packets are identified using the well-known protocol ID 88 for both IPv4 and IPv6. When EIGRPv6 is enabled, the routers communicate with each other using the interface's IPv6 link-local address as the source. The destination address may be either a unicast link-local address or the multicast link-local address FF02::Α.

EIGRPv6 Packet Details

• EIGRP Packet: Hello, Acknowledgment, Query, Reply, and Update packets

Configuring IPv6

• There are two methods for configuring IPv6 for EIGRP on IOS and IOS XE routers which include Classic AS mode and Named mode. Classic mode is the original IOS method for enabling IPv6 on EIGRP and the routing process is configured using an autonomous system number.

Configuring EIGRPv6

• Step 1. Configure the EIGRPv6 process by using the global configuration command ipv6router eigrp as-number.
• Step 2. Assign the router ID by using the IPv6 address family command eigrp router-id id. The router ID should be manually assigned to ensure proper operation of the routing process. The default behavior for EIGRP is to locally assign a router ID based on the highest IPv4 loopback address or, if that is not available, the highest IPv4 address.
• Step 3. Enable the process on the interface by using the interface parameter command ipv6eigrp as-number.

Named Mode

• Named mode provides support for IPv4, IPv6, and virtual routing and forwarding (VRF), all within a single EIGRP instance
• Step 1. Configure the EIGRPv6 routing process in global configuration mode by using the command router eigrp process-name ( you specify a name instead of an autonomous system number).
• Step 2. Define the address family and autonomous system number (ASN) to the routing process by using the command address-family ipv6 autonomous-system as-number.
• Step 3. Assign the router ID by using the IPv6 address family command eigrp router-idrouter-id.
• IPv6 uses the same EIGRP verification commands.

IPv6 Routing

• There is no concept of classful or classless routing in IPv6, and therefore, autosummarization is not possible
• EIGRPv6 summarization for IPv6 is manually configured on a per-interface basis, using the same rules as for IPv4: The summary aggregate prefix is not advertised until a prefix matches it & More specific prefixes are suppressed. A Null0 route with an administrative distance of 5 is added to the routing table as a loop-prevention mechanism.
• Network summarization is configured at the interface level in classic mode using the command ipv6 summary-address eigrp as-number ipv6-prefix/prefix-length or in named mode with the command summary-address ipv6-prefix/prefix-length under af-interface. IPv6 Neighbor Issues:
• Neighbor issues are mostly the same
• To verify EIGRPv6 neighbors, use the show ipv6 eigrp neighborscommand (EIGRPv6 neighbors are identified by their link-local address)
• Verify an interface is up, and to do this you use the show ipv6 interface brief command

Commands to verify Neighbor summary

• To verify EIGRPv6 neighbors, use the show ipv6 eigrp neighborscommand (EIGRPv6 neighbors are identified by their link-local address)
• show ipv6 protocols command to verify the autonomous system number being used, the show ipv6 protocols command to verify the router interfaces participating in the EIGRPv6 autonomous system that are passive
• show ipv6 eigrp interfaces detailcommand to verify whether an interface is enabled for EIGRPv6 authentication
• show key chain command and the show ipv6 eigrp interfaces detail command to verify whether an interface is enabled for EIGRPv6 authentication.
• use show ipv6 eigrp interfaces and show ipv6 protocols, to verify the interfaces that are participating in the routing process ACLs:
• EIGRPv6 uses the IPv6 multicast address FF02::A to form neighbor adjacencies
• If an IPv6 access control list (ACL) is denying packets destined to the multicast address FF02::A, neighbor adjacencies do not form.