Frame Relay Monitoring and Troubleshooting

Frame Relay Monitoring and Troubleshooting

Frame Relay Monitoring and Troubleshooting

The following list summarizes the commands to use for viewing specific Frame Relay information on the router.

If you want to view . . .	Use . . .
DLCI numbers	show run show frame pvc
Frame Relay encapsulation method	show int show run
LMI information and traffic statistics	show frame lmi show int
Interface configuration (DCE or DTE)	show frame pvc show int
Global traffic statistics	show frame traffic
Addresses and associated DLCIs	show frame map

Note: Output for the show interfaces command shows an entry for DLCI followed by a number. This information is not the DLCI number associated with the interface.

As you troubleshoot Frame Relay, keep in mind the following tips:

• All routers at all locations must be configured to use the same frame relay encapsulation method.
• When using all Cisco routers, you can use the default Frame Relay encapsulation type (cisco). When using routers of multiple vendors, use the ietf encapsulation type.
• Frame Relay routers must know the DLCI number that is used to reach remote routers.
• Use inverse arp to dynamically discover DLCI numbers.
• Use static mappings to associate DLCI numbers with IP addresses manually.
• When configuring subinterfaces, do not set an IP address on the main interface. Instead, set IP addresses on each subinterface.
• For a point-to-point subinterface, or a multipoint subinterface with dynamic addressing, you must manually assign a DLCI to the subinterface.
• By default, Cisco routers autosense the LMI type and configure themselves accordingly. You only need to set the LMI type if autosensing does not work or if you want to manually assign it.

Shown here is sample output from the show frame-relay pvc command.

PVC Statistics for interface Serial5/1 (Frame Relay DTE)

DLCI = 55, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial5/1.1

   input pkts 64589   output pkts 3865     in bytes 15400

   out bytes 33896    dropped pkts 66      in FECN pkts 12

   in BECN pkts 15    out FECN pkts 0      out BECN pkts 0

   in DE pkts 5       out DE pkts 1

   out bcast pkts 15  out bcast bytes 128

pvc create time 00:35:11, last time pvc status changed 00:00:22

The following table describes major components of the output.

Entry	Description
DLCI = 55	Lists the DLCI number assigned to the PVC.
DLCI USAGE	Identifies the role of the router on the virtual circuit. For DTE frame relay devices, the usage will be LOCAL. For DCE devices, the usage will be SWITCHED.
PVC STATUS	Reports the PVC status as reported from the DCE through the LMI protocol. When you connect the DTE to the circuit, the LMI protocol communicates the PVC status as sent from the DCE device. The status will be one of the following: ACTIVE indicates the PVC is configured, is operational, and can transmit packets. LMI is active. INACTIVE indicates that the PVC has been configured, but has not received an active state from the DCE. This status identifies the PVC as down. The interface line status is also down. STATIC indicates that LMI has been disabled. A configuration exists, but status information cannot be received from the DCE because LMI has been disabled. DELETED indicates that the PVC has been configured, but that the LMI protocol has not reported status information.
FECN/BECN pkts	Identifies the number of packets received (in) or sent (out) that had the FECN or BECN bit set. Both flags identify that network congestion exists. Receiving devices use these flags to decide what to do about the congestion, such as slowing down or implementing a flow control mechanism. On a DTE device: in FECN pkts are packets sent from the DCE to the destination DTE device to indicate that congestion has occurred. A DTE that receives a FECN packet might slow its rate of data request, or it might implement flow control to detect and recover from lost packets. in BECN pkts are packets sent from the DCE to the sending DTE device to indicate that congestion has occurred. A DTE that receives a BECN packet might slow down its transmission rate. out FECN pkts and out BECN pkts are packets sent from the DTE. On a DTE device, these values have little meaning as the DTE is typically the terminating point in the circuit.
DE pkts	Identifies the number of packets sent or received that had the Discard Eligibility (DE) bit set. The DE bit is used to identify packets with a lower priority that could be dropped if necessary.

Routing Administrative Distances

Routing Administrative Distances

The administrative distance is a number assigned to a source of routing information (such as a static route or a specific routing protocol). The router uses these values to select the source of information to use when multiple routes to a destination exist. A smaller number indicates a more trusted route. The following table shows the default administrative values for a Cisco router.

Route Source	Administrative Distance
Connected interface	0
Static route	1
EIGRP summary route	5
EIGRP internal route	90
IGRP	100
OSPF	110
RIP	120
EIGRP external route	170

Note: You can modify how routes are selected by modifying the administrative distance associated with a source.

Routers can learn about routes to other networks using multiple routing protocols. In addition, there might be multiple paths between any two points. When making routing decisions, the router uses the following criteria for choosing between multiple routes:

1. If a router has learned of two routes to a single network through different routing protocols (such as RIP and OSPF), it will choose the route with the lowest administrative distance (OSPF in this example).
2. If a router has learned of two routes through the same protocol (for example two routes through EIGRP), the router will choose the route that has the best cost as defined by the routing metric (for EIGRP the link with the highest bandwidth and least delay will be used).

Routing Protocol Comparison

Routing Protocol Comparison

The following table compares various features of the routing protocols you will need to know for this course.

Characteristic	RIP	OSPF	EIGRP
Routing method	Distance vector	Link state	Balanced hybrid
Public standard	Yes	Yes	No
Metric	Hop count	Link cost	Bandwidth and delay
VLSM support Classless routing Sends mask in updates	Version 2 only	Yes	Yes
Route summarization	Automatic and manual, version 2 only	Manual only, and only between areas*	Automatic and manual
Convergence time	Slow	Fast	Faster than OSPF
Discovers neighbors before sending routing information	No	Yes	Yes
Sends full routing table at each update	Yes	No	No
Loop avoidance	Hold down timers, split horizon, poison reverse	Full network topology	Partial network topology
Memory and CPU requirements	Low	Can be high	Lower than OSPF
Uses areas in network design	No	Yes	No
Uses wildcards to define participating networks	No	Yes	Optional
Maintains multiple paths to the same network (load balancing support)	Yes, equal-cost only (version 2)	Yes, equal-cost only	Yes, both equal- and unequal-cost
Update address used	Version 1 uses broadcasts Version 2 uses multicasts to 224.0.0.9	Multicast to 224.0.0.5 for hello packets and updates to non-DR routers Multicast to 224.0.0.6 for sending updates to the DR	Multicast to 224.0.0.10 for hello packets Unicast for updates

*Note: Summarization with OSPF is only possible on area border routers (ABR) and autonomous system border routers (ASBR). This means that you need multiple areas before you can do route summarization with OSPF.

EIGRP Command List

EIGRP Command List

You configure EIGRP just the same as you would configure IGRP. The following table lists the applicable commands.

Command	Function
Router(config)#router eigrp number	Defines an EIGRP process. The number must match between routers for information to be shared.
Router(config-router)#network n.n.n.n Router(config-router)#network n.n.n.n w.w.w.w	Identifies a network that participates in the routing process. Networks can be specified with or without the wildcard mask. If you do not use a wildcard mask, the network address you add will be automatically truncated based on classful network boundaries. You must use a wildcard mask to identify VLSM subnets.
Router(config-router)#no auto-summary	Turn off automatic route summarization. With automatic route summarization, subnets are summarized based on classful boundaries when advertising routes on networks with a different class boundary. You must disable automatic summarization if you have a network address (such as 10.0.0.0) subnetted into smaller subnets and separated by a network with a different classful network address (such as 12.0.0.0).

Example
The following commands enable EIGRP on a router and define three networks that participate in the routing process.

Router(config)#router eigrp 2
Router(config-network)#network 172.16.1.0 0.0.0.255
Router(config-network)#network 172.16.2.0 0.0.0.255
Router(config-network)#network 172.16.3.0 0.0.0.255

Use the following commands to manage and monitor EIGRP.

Command	Features
show ip route	View EIGRP-learned routes.
show eigrp neighbors	View neighboring routers from which EIGRP routes can be learned. Lists the IP address of the connected router.
show eigrp interfaces	View the interfaces that are running EIGRP and the number of connected routers.

EIGRP Facts

EIGRP FactsEnhanced IGRP is a Cisco-proprietary balanced hybrid routing protocol that combines the best features of distance vector and link state routing. EIGRP:

• Sends the subnet mask in the routing update. It supports route summarization and VLSM.
• Supports automatic classful route summarization at major network boundaries (this is the default in EIGRP). Unlike IGRP and RIP, manual route summarization can also be configured on arbitrary network boundaries to reduce the routing table size.
• Is not susceptible to routing loops. Instead, EIGRP uses built-in loop avoidance techniques. Under certain conditions, EIGRP will use split horizon, but not hold downs or flush timers.
• Is scalable and does not have the 16 hop limitation of RIP.
• Uses hello packets to discover neighbor routers. Hello intervals on EIGRP routers do not need to match.
• Exchanges the full routing table at startup, and then partial routing updates thereafter.
• Uses unicasts or multicasts to 224.0.0.10 for routing updates. Hello packets always use the multicast address.
• Uses bandwidth, delay, reliability, and load for the route metric. The metric is expressed as the number of microseconds.
  • The degree to which each value is used to calculate the metric can be customized by modifying one of five K values.
  • By default, K1 and K3 are set to 1, while K2, K4, and K5 are set to 0. These settings mean that with the default configuration, only delay and bandwidth have an effect on the metric.
  • On serial links, a default bandwidth of 1544 is used. EIGRP does not detect the actual bandwidth on the link. You must manually configure bandwidth values for accurate metric calculations.
• Uses an autonomous system (AS) number to identify routers that are to share EIGRP information. The AS number on both routers must match.
• Maintains partial network topology information in addition to routes.
• Supports load balancing on equal-cost and unequal cost links. This means that EIGRP can keep multiple paths to a single network, even if they have a different cost. With IOS 12.4 and above, EIGRP supports up to 16 paths (earlier versions supported up to 6), with the default being 4 equal-cost paths.
• Minimizes network bandwidth usage for routing updates. During normal operation EIGRP transmits only hello packets across the network. EIGRP does not send periodic routing updates like RIP and IGRP. When change occurs, only routing table changes are propagated in EIGRP not the entire table.
• Requires less processing and memory than link state protocols.
• Converges more quickly than distance vector protocols. In some cases, convergence can be almost instantaneous because an EIGRP router stores backup routes for destinations. If no appropriate route or backup exists in the routing table, EIGRP will query neighbor routers to discover an alternate route. In this manner, EIGRP can quickly adapt to alternate routes when changes occur.
• Uses the DUAL link-state algorithm for calculating routes.
• Supports multiple protocols. EIGRP can exchange routes for IP, AppleTalk and IPX/SPX networks.
• Uses a neighbors table to keep track of neighbor routers. The neighbors table includes the following for each neighbor:
  • A hold time. Each hello packet includes a hold time that identifies how long the hello information is valid. If the hold time expires without receipt of a hello packet, the neighbor is assumed to be unreachable.
  • Round-trip timers that help the router identify cost values to reach the neighbor router.
• Uses a topology database to keep track of all known networks.
  • The topology table has a list of each destination network and all neighbor routers that reported routes to that network.
  • The best routes that will be used for routing packets are copied from the topology table into the routing table.
  • The topology table holds up to 16 known routes (previously up to 6 before IOS version 12.4).

To understand how EIGRP can provide load balancing and fast recovery for failed links, you need to understand the following concepts:

Term	Definition
Advertised Distance (AD)	The advertised distance (AD) is the cost to the destination network as reported by the neighbor router. The AD is also called the reported distance (RD).
Feasible Distance (FD)	The feasible distance (FD) is the lowest total cost to a destination network. The feasible distance is identified for each destination network, and is determined as follows: For each neighbor, a total cost to the network through the neighbor is calculated by adding the AD to the cost required to reach the neighbor router (the cost of the link used to reach the neighbor router). The router compares the total cost of all routes. The lowest total cost to the destination network is the feasible distance to the network. Note: Sometimes the total cost for each neighbor route is referred to as a feasible distance. However, the term more correctly identifies the lowest known cost to the network, not the total cost for each reported (possible) route.
Successor	A successor is the route to a destination network with the lowest total cost. When a new route is first learned, the total cost to the successor route is used as the feasible distance to that network. The successor route is copied from the topology table into the routing table. You can have multiple successor routes if multiple routes to the same network exist with the same lowest metric.
Feasible Successor	A feasible successor is an alternate route to a destination network. The total cost to the route through the feasible successor is higher than the total cost of successor routes. A route must meet the following condition to qualify as a feasible successor route: The advertised distance of the route through that neighbor must be less than the feasible distance used for that network (AD < FD). Be aware of the following regarding feasible successors: Satisfying the AD < FD condition ensures that the route is loop free. In other words, the router knows for sure that the route does not include itself in the path if the AD is lower than the FD. Note: Successor routes must also meet this condition. Feasible successor routes are kept in the topology table but are not copied to the routing table. Successor routes can also be classified as feasible successor routes. When all successor routes to a network are lost, the router can immediately begin to use the next best feasible successor route. This provides for rapid recovery in the event of a topology change.

Be aware of the following regarding the EIGRP and routes:

• All known routes to a destination are kept in the topology table. Only successor routes are copied to the routing table.
• If the successor route goes down and there are no feasible successors, routes whose advertised distance is greater than the feasible distance for the route are not used because they might be routes that include loops.
• When the last feasible successor route to a network is lost, the router recalculates all routes for the lost neighbor. Instead of using other routes that are not feasible successor routes, it first communicates with neighbor routers. If necessary, the router recalculates the feasible distance for the route.
• A route whose AD is greater than the FD does not prove that a loop exists, only that a loop might exist. After the last feasible successor route is lost, a previously unacceptable route could be identified as a feasible successor route as long as its AD is less than the newly-calculated FD.
• By default, EIGRP uses equal-cost load balancing. To use unequal-cost load balancing, configure the variance value. The variance is a multiplier that identifies the degree to which alternate paths can be used.
  • The variance value ranges from 1 to 255.
  • The default variance is 1, meaning that only routes that match the best route can be used.
  • Setting the variance to 2 allows alternate routes to be used whose total costs are within a factor of 2 (double or less) of the best cost route.
  • Only feasible successor routes can be used. This means that a route whose AD is greater than the FD cannot be used as an alternate route, even if its total cost is within the variance amount.

For an EIGRP router to share information with a neighbor, the following conditions must be met:

• Both routers are on the same subnet with the same subnet mask.
• If used, authentication checks must pass.
• Both routers must be configured with the same AS number.
• Metric weight values (K values) must match on both routers.

OSPF Command List

OSPF Command List

OSPF is fairly simple, with only a few variations from the RIP and IGRP configuration steps you have previously use. Configuration is as simple as defining the OSPF process using the router ospf command, and then identifying the networks that will participate in OSPF routing. The following table lists the commands and details for configuring OSPF.

Command	Purpose
Router(config)#router ospf process-id	Use to enter configuration mode for OSPF. The process ID identifies a separate routing process on the router. Note: Process IDs do not need to match between routers (in other words, two routers configured with different process IDs might still share OSPF information).
Router(config-router)#network a.b.c.d w.w.w.w area number	Identifies networks that participate in OSPF routing. a.b.c.d is the network address. This can be a subnetted, classless network. w.w.w.w is the wildcard mask. The wildcard mask identifies the subnet address. number is the area number in the OSPF topology. The area number must match between routers.
Router(config-router)#router-id a.b.c.d	Configures the router ID for the OSPF process. The router ID is used to identify the DR/BDR if two routers have matching priority values.
Router(config)#interface ethernet0/1 Router(config-if)#ip ospf priority <0-255>	Sets the OSPF priority number for an interface. The priority number is used in the DR/BDR election process. The router with the highest priority becomes the DR. Configure a value of 0 to ensure that a router never becomes the DR or BDR. Note: The priority is set on an interface, and applies to the DR/BDR election process on that interface.
Router(config)#interface loopback0 Router(config-if)#ip address a.b.c.d m.m.m.m	Sets an IP address for a loopback interface. The IP address is used as the router ID and is used to determine the DR and BDR if two routers have the same priority value.

Example
The following graphic shows a sample network with two OSPF areas.

Use the following commands to configure OSPF on each router:

Router	Configuration
SFO	router ospf 1 network 10.1.0.0 0.0.15.255 area 0 network 10.1.16.0 0.0.15.255 area 1 network 10.1.32.0 0.0.15.255 area 1
LAX	router ospf 2 network 10.1.16.1 0.0.0.0 area 1 network 10.2.0.1 0.0.0.0 area 1
PHX	router ospf 1 network 10.1.32.0 0.0.15.255 area 1 network 10.3.0.0 0.0.255.255 area 1

Notice the following in the configuration:

• The process ID on each router does not have to match. OSPF uses areas to identify sharing of routes, not the process ID.
• You can use the subnet address with the appropriate wildcard mask (as in 10.1.16.0 0.0.15.255), or you can use the IP address of the router interface with a mask of 0.0.0.0.
• The network command identifies the subnet, wildcard mask, and the OSPF area of the subnet. A subnet can only be in one area.

OSPF Facts

OSPF Facts

The Open Shortest Path First (OSPF) routing protocol is a robust link state routing protocol well-suited for large networks. OSPF:

• Is a public (non-proprietary) routing protocol.
• Is considered a classless routing protocol because it does not assume the default subnet masks are used. It sends the subnet mask in the routing update and supports manual route summarization and VLSM. OSPF does not perform automatic route summarization.
• Is not susceptible to routing loops. Instead, OSPF uses built-in loop avoidance techniques. Mechanisms such as holddown timers, split horizon, or poison reverse are not needed.
• Is scalable and does not have the 16 hop limitation of RIP.
• Uses multicasts to share routing information (using 224.0.0.5 and 224.0.0.6).
• Uses link costs (bandwidth) as a metric for determining best routes. The Shortest Path First (SPF) algorithm (also called the Dijkstra SPF algorithm) is used to identify and select the optimal route.
• Supports load balancing over equal-cost paths. Up to 16 equal-cost paths can be used (the default is 4).
• Uses hello packets to discover neighbor routers.
• Shares routing information through Link State Advertisements (LSAs). LSAs contain small bits of information about routes. (Unadvertised links save on IP space, but they cannot be pinged because they won't appear in an OSPF routing table.)
• Under normal conditions, OSPF only sends out updated information rather than exchanging the entire routing table.
• Converges faster than a distance vector protocol. Following convergence sends updates when routes change or every 30 minutes.
• Can require additional processing power (and therefore increased system requirements). Good design can minimize this impact.
• Maintains a logical topographical map of the network in addition to maintaining routes to various networks.
• Uses areas to subdivide large networks. Routers within an area share information about the area. Routers on the edge of areas (called Area Border Routers (ABR)) share summarized information between areas.
  • The backbone is a specialized area connected to all other areas. It contains networks not held within another area, and distributes routing information between areas. You can think of the backbone as the "master" or "root" area. Its address is always 0.0.0.0. All OSPF networks must have a backbone area.
  • A stub area is an area with a single path in to and out of the area.

To help minimize traffic caused by routing updates, OSPF defines the following router roles:

Role	Description
Designated Router (DR)	On each subnet, a single OSPF router is elected as the designated router (DR). The DR is responsible for coordinating routing table updates for all routers on the subnet. Routing information is sent from other routers to the DR. The DR manages the changes and forwards any necessary information to other routers on the subnet.
Backup Designated Router (BDR)	On each subnet, a single OSPF router is identified as the backup designated router (BDR). The BDR becomes the DR if the DR becomes unavailable.
DROTHER	Any other router that is not a DR or a BDR is called a DROTHER. This is simply a term used to describe a non-DR or non-BDR router. It is not technically an OSPF router role.

Be aware of the following facts about the DR and BDR:

• Based on the network link type, a DR/BDR might not be used. A DR/BDR is used on broadcast networks (like Ethernet) where multiple routers exist on the same subnet. For point-to-point networks, a DR/BDR is not used. By default, the network type is identified based on the media type used. You can manually configure the network type if desired.
• If the network type uses a DR/BDR, a single DR and a single BDR is identified for each subnet.
• When routers first come on line, they exchange hello packets. Part of this process is used to elect (identify) the DR and the BDR.
• The following values are used to elect the DR and BDR:
  • The router with the highest OSPF priority becomes the DR. The priority value is a number between 0-255. By default, all routers have a priority of 1.
  • If two or more routers have the same highest priority value, the router with the highest router ID becomes the DR. The router ID is a 32-bit number expressed in A.B.C.D format. The router ID for a specific router is chosen in the following order:
    • For a specific OSPF process, you can manually configure a router ID. If a router ID has been configured, that value is used.
    • If no router ID has been manually configured, the system uses the highest IP address assigned to a loopback address.
    • If the router does not have a loopback address, the router ID is the highest IP address assigned to any interface in the up state.

    Note: Using a loopback address is preferred over using the interface IP address because it allows you to control which router becomes the DR, and because loopback interfaces never go down. If an interface address is used for the router ID, the router ID might change if that interface goes down.

  • In most cases, the BDR is the router with the next highest priority or router ID.
• Configuring a priority of 0 for a router means that the router will never become the DR or BDR.
• Once a DR has been elected, it remains the DR, even if another router with a higher priority or router ID comes on line. You must clear or reset the OSPF process to force a new election.
• If the DR goes down, the BDR automatically becomes the DR. When the original DR comes back on line, it will not automatically resume the DR role unless a reset is performed.

OSPF routers share route information only with adjacent neighbor routers. The following conditions must be met for two routers to become fully adjacent:

• Both routers must be on the same subnet and use the same subnet mask.
• Both routers must have the same hello and dead intervals configured.
  • The hello interval identifies how frequently neighbor routers exchange hello packets.
  • The dead interval identifies the amount of time to allow without an expected hello packet. If a periodic hello packet has not been received within the dead interval, the router assumes that its neighbor has gone offline.
• Both routers must use the same OSPF area.
• If authentication is required, both routers must pass the authentication requirements.
• The stub area flag (value) for each router must match.