Network Bulls
www.networkbulls.com
Best Institute for CCNA CCNP CCSP CCIP CCIE Training in India
M-44, Old Dlf, Sector-14 Gurgaon, Haryana, India
Call: +91-9654672192
As an advanced distance vector routing protocol, EIGRP scales well with a growing network.
However, this scalability introduces complexity in design, configuration, and maintenance. This
section introduces some of the common issues surrounding an EIGRP network and a flowchart
approach to troubleshooting these issues.
Components of Troubleshooting EIGRP
When troubleshooting any network protocol, it is important to follow a defined flow or
methodology. The main aspect of troubleshooting routing protocols involves ensuring that
communication exists between the routers. The following sections describe the basic components
of troubleshooting a network that is running EIGRP. Figure 5-8 shows an example of the flow used
for diagnosing EIGRP problems.
Figure 5-8 EIGRP Troubleshooting
The major components of EIGRP troubleshooting include the following items:
■ EIGRP neighbor relationships
■ EIGRP routes in the routing table
■ EIGRP authentication
Troubleshooting EIGRP Neighbor Relationships
The first step in the flow is to troubleshoot neighbor relationships. Figure 5-9 shows the steps for
troubleshooting these issues.
Troubleshoot
EIGRP Neighbor
Relationships
Troubleshoot
EIGRP Routing
Table Issues
Troubleshoot
EIGRP
Authentication
Troubleshooting EIGRP 193
Figure 5-9 Troubleshooting EIGRP Neighbor Issues
Example 5-9 shows output from the show ip eigrp neighbors command, which indicates that a
successful neighbor relationship exists with two routers.
For EIGRP routers to form a neighbor relationship, both routers must share a directly connected
IP subnet. A log message that displays that EIGRP neighbors are “not on common subnet”
indicates that an improper IP address exists on one of the two EIGRP neighbor interfaces. Use the
show interface interface command to verify the IP addresses.
Example 5-9 Confirming EIGRP Neighbor Relationships
RouterX# show ip eigrp neighbors
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 10.23.23.2 Se0/0/1 13 00:02:26 29 2280 0 15
0 10.140.1.1 Se0/0/0 10 00:28:26 24 2280 0 25
Troubleshoot
EIGRP Neighbor
Relationships
Troubleshoot
EIGRP Routing
Table Issues
Troubleshoot
EIGRP
Authentication
Are all
interface statuses
up/up?
Are you
receiving “Not on
common subnet”
error?
Are all
required EIGRP
neighbors
configured?
Does
all required
hello packet
information match
neighbor?
194 Chapter 5: Implementing EIGRP
In the output in Example 5-10, the interface address is 10.2.2.3/24.
The network command that is configured under the EIGRP routing process indicates which router
interfaces will participate in EIGRP. The “Routing for Networks” section of the show ip protocols
command indicates that the networks have been configured; any interfaces in those networks
participate in EIGRP. In the output of Example 5-11, EIGRP is running on any interfaces that have
an IP address on the 10.0.0.0 and 192.168.1.0 networks.
The show ip eigrp interfaces command can quickly indicate on which interfaces EIGRP is
enabled and show how many neighbors can be found on each interface. In the output in
Example 5-10 Confirming EIGRP Neighbor IP Address
RouterX# show ip interface fa0/0
FastEthernet0/0 is up, line protocol is up
Internet address is 10.2.2.3/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Example 5-11 Confirming Router Interface Participation in EIGRP Routing
RouterX# show ip protocols
Routing Protocol is “eigrp 100”
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 100
--output omitted --
Maximum path: 4
Routing for Networks:
10.0.0.0
192.168.1.0
Routing Information Sources:
Gateway Distance Last Update
(this router) 90 00:01:08
10.140.1.1 90 00:01:08
Distance: internal 90 external 170
Troubleshooting EIGRP 195
Example 5-12, no peers currently exist on the FastEthernet 0/0 interface, and one peer exists on
the Serial 0/0/0 interface.
EIGRP routers create a neighbor relationship by exchanging hello packets. Certain fields in the
hello packets must match before an EIGRP neighbor relationship is established:
■ EIGRP autonomous system (AS) number
■ EIGRP K values
You can use the debug eigrp packets command to troubleshoot when hello packet information
does not match. In Example 5-13, a K value mismatch exists.
Troubleshooting EIGRP Routing Tables
If the neighbor relationships are established, routes can be exchanged. If they are not being
exchanged, the next step is to troubleshoot EIGRP routing table issues. Figure 5-10 shows the
steps involved in troubleshooting these problems.
Example 5-12 Confirming EIGRP Status and Neighbors on an Interface
RouterX# show ip eigrp interfaces
IP-EIGRP interfaces for process 100
Xmit Queue Mean Pacing Time Multicast Pending
Int Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Fa0/0 0 0/0 0 0/1 0 0
Se0/0/0 1 0/0 38 10/380 552 0
NOTE EIGRP K values are used in the EIGRP best-path selection process and are discussed
in the Cisco CCNP curriculum.
Example 5-13 Verifying EIGRP Hello Packet Mismatches
RouterX# debug eigrp packets
Mismatched adjacency values
01:39:13: EIGRP: Received HELLO on Serial0/0 nbr 10.1.2.2
01:39:13:AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
01:39:13: K-value mismatch
196 Chapter 5: Implementing EIGRP
Figure 5-10 Troubleshooting EIGRP Routing Tables
EIGRP routes that appear with a “D” in the routing table indicate that they are intra-AS routes,
and those with “D EX” indicate that they are external AS routes. No EIGRP routes in the routing
table can indicate that a Layer 1 or 2 issue or an EIGRP neighbor problem exists.
In the output in Example 5-14, the 172.16.31.0/24 network is an intra-AS route, and 10.3.3.0/24
is a route that was redistributed into EIGRP.
Example 5-14 Confirming EIGRP Intra-AS and Redistributed Routes
RouterX# show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.31.0/24 [90/40640000] via 10.140.1.1, 00:01:09, Serial0/0/0
O 172.16.31.100/32 [110/1563] via 10.140.1.1, 00:26:55, Serial0/0/0
10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
C 10.23.23.0/24 is directly connected, Serial0/0/1
D EX 10.3.3.0/24 [170/40514560] via 10.23.23.2, 00:01:09, Serial0/0/1
C 10.2.2.0/24 is directly connected, FastEthernet0/0
Troubleshoot
EIGRP Neighbor
Relationships
Troubleshoot
EIGRP Routing
Table Issues
Troubleshoot
EIGRP
Authentication
Are all
required EIGRP
networks being
advertised?
Are there
any route filters
that block EIGRP
networks?
Are there
duplicate EIGRP
router IDs?
Is there
a discontiguous
network?
Troubleshooting EIGRP 197
The show ip eigrp topology command displays the EIGRP router ID. The EIGRP router ID comes
from the highest IP address assigned to a loopback interface. If no loopback interfaces are
configured, the highest IP address assigned to any other active interface is chosen as the router ID.
No two EIGRP routers can have the same EIGRP router ID. If they do, you will experience
problems exchanging routes between the two routers with equal router IDs.
In the output in Example 5-15, the router ID is 192.168.1.65.
EIGRP routes that are found in the topology table but not in the routing table can indicate an issue
that requires help from Cisco Technical Assistance Center (TAC) to diagnose the problem.
Route filtering enables routes to be filtered from an EIGRP routing advertisement as they come in
from a neighbor or as they are sent out to a neighbor. These filters can cause routes to be missing
from the routing table. The show ip protocols command shows whether any filter lists are applied
to EIGRP.
Example 5-15 Displaying EIGRP Router IDs
RouterX# show ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(192.168.1.65)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.1.1.0/24, 1 successors, FD is 40514560
via 10.140.1.1 (40514560/28160), Serial0/0/0
P 10.2.2.0/24, 1 successors, FD is 28160
via Connected, FastEthernet0/0
P 10.3.3.0/24, 1 successors, FD is 40514560
via 10.23.23.2 (40514560/28160), Serial0/0/1
P 10.23.23.0/24, 1 successors, FD is 40512000
via Connected, Serial0/0/1
P 192.168.1.64/28, 1 successors, FD is 128256
via Connected, Loopback0
P 192.168.1.0/24, 1 successors, FD is 40640000
via 10.23.23.2 (40640000/128256), Serial0/0/1
P 10.140.2.0/24, 2 successors, FD is 41024000
via 10.23.23.2 (41024000/40512000), Serial0/0/1
via 10.140.1.1 (41024000/40512000), Serial0/0/0
P 10.140.1.0/24, 1 successors, FD is 40512000
via Connected, Serial0/0/0
P 172.16.31.0/24, 1 successors, FD is 40640000
NOTE Filtering routing information is covered in the CCNP course materials.
198 Chapter 5: Implementing EIGRP
By default, EIGRP is classful and performs automatic network summarization. Automatic
network summarization causes connectivity issues in discontiguous networks. The show ip
protocols command confirms whether automatic network summarization is in effect.
In the sample output in Example 5-16, no filter lists are applied to EIGRP AS 100, and automatic
network summarization is in effect.
Troubleshooting EIGRP Authentication
The last step in the flowchart in Figure 5-8 is to troubleshoot EIGRP authentication problems, if
configured. This is accomplished by verifying that EIGRP authentication is successful.
Example: Successful MD5 Authentication
The output of the debug eigrp packets command on Router X, shown in Example 5-17, illustrates
that Router X is receiving EIGRP packets with MD5 authentication and a key ID equal to 1 from
Router Y.
Example 5-16 Confirming EIGRP Automatic Network Summarization
RouterX# show ip protocols
Routing Protocol is “eigrp 100”
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 100
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is in effect
Automatic address summarization:
192.168.1.0/24 for FastEthernet0/0, Serial0/0/0, Serial0/0/1
Summarizing with metric 128256
10.0.0.0/8 for Loopback0
Summarizing with metric 28160
Maximum path: 4
Example 5-17 Confirming MD5 Authentication on Router X
RouterX# debug eigrp packets
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY, SIAREPLY)
*Jan 21 16:38:51.745: EIGRP: received packet with MD5 authentication, key id = 1
*Jan 21 16:38:51.745: EIGRP: Received HELLO on Serial0/0/1 nbr 192.168.1.102
*Jan 21 16:38:51.745: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ
un/rely 0/0
Troubleshooting EIGRP 199
Similarly, the output of the debug eigrp packets command on Router Y, shown in Example 5-18,
illustrates that Router Y is receiving EIGRP packets with MD5 authentication and a key ID equal
to 2 from Router X.
Example: Troubleshooting MD5 Authentication Problems
In the example, the key string for key 2 of Router X, the one that is used when EIGRP packets are
sent, is changed to be different from the key string that Router Y is expecting.
The output of the debug eigrp packets command on Router Y, shown in Example 5-19, illustrates
that Router Y is receiving EIGRP packets with MD5 authentication and a key ID equal to 2 from
Router X, but that an authentication mismatch exists. The EIGRP packets from Router X are
ignored, and the neighbor relationship is declared to be down. The output of the show ip eigrp
neighbors command should confirm that Router Y has no EIGRP neighbors.
Example 5-18 Confirming MD5 Authentication on Router Y
RouterY# debug eigrp packets
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY,
SIAREPLY)
RouterY#
*Jan 21 16:38:38.321: EIGRP: received packet with MD5 authentication, key id = 2
*Jan 21 16:38:38.321: EIGRP: Received HELLO on Serial0/0/1 nbr 192.168.1.101
*Jan 21 16:38:38.321: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ
un/rely 0/0
Example 5-19 MD5 Authentication Mismatch
RouterY# debug eigrp packets
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY, SIAREPLY)
RouterY#
*Jan 21 16:50:18.749: EIGRP: pkt key id = 2, authentication mismatch
*Jan 21 16:50:18.749: EIGRP: Serial0/0/1: ignored packet from 192.168.1.101, opc
ode = 5 (invalid authentication)
*Jan 21 16:50:18.749: EIGRP: Dropping peer, invalid authentication
*Jan 21 16:50:18.749: EIGRP: Sending HELLO on Serial0/0/1
*Jan 21 16:50:18.749: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
*Jan 21 16:50:18.753: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 192.168.1.101
(Serial0/0/1) is down: Auth failure
RouterY# show ip eigrp neighbors
IP-EIGRP neighbors for process 100
RouterY#
200 Chapter 5: Implementing EIGRP
The two routers keep trying to reestablish their neighbor relationship. Because of the different
keys that are used by each router in this scenario, Router X authenticates the hello messages that
are sent by Router Y using key 1. However, when Router X sends a hello message back to Router
Y using key 2, an authentication mismatch will occur. From the perspective of Router X, the
relationship appears to be up for a while, but then it times out, as illustrated by the messages that
were received on Router X, shown in Example 5-20. The output of the show ip eigrp neighbors
command on Router X also illustrates that Router X does have Router Y in its neighbor table for
a short time.
Summary of Troubleshooting EIGRP
The following summarizes the key points that were discussed in this section:
■ Troubleshooting EIGRP includes several aspects, such as resolving neighbor relationships,
routing table issues, and authentication problems.
■ Issues that can cause EIGRP neighbor problems include incorrect network commands and
hello packet information mismatches. Use the show ip eigrp neighbors command to help
troubleshoot these issues.
■ Missing EIGRP routes from the routing table can be because of route filtering or automatic
summarization in discontiguous networks. Use the show ip route command to help
troubleshoot these issues.
■ The debug eigrp packets command can help you troubleshoot MD5 authentication
problems.
No comments:
Post a Comment