Chapter 24. Implementing EIGRP for IPv6
This chapter covers the following exam topics:
2.0 Routing Technologies
2.7 Configure, verify, and troubleshoot EIGRP for IPv6 (excluding authentication, filtering, manual summarization, redistribution, stub)
When creating Enhanced Interior Gateway Routing Protocol (EIGRP) for IPv6, Cisco made the new EIGRP for IPv6 as much like EIGRP for IPv4 as possible. How close are they? Incredibly close, even closer than the IPv4 and IPv6 versions of the Open Shortest Path First (OSPF) protocol. With EIGRP, the only noticeable difference is the configuration, which enables EIGRP for IPv6 directly on the interfaces and, of course, the use of IPv6 addresses and prefixes. However, the old and new EIGRP protocols are practically twins when it comes to the concepts, show commands, and troubleshooting steps.
This chapter has two major sections. The first major section shows the EIGRP for IPv6 configuration options for EIGRP for IPv6 classic mode, comparing those steps with the classic mode configuration of EIGRP for IPv4. The second major section shows how to verify EIGRP for IPv6 while giving some troubleshooting tips.
“Do I Know This Already?” Quiz
Take the quiz (either here, or use the PCPT software) if you want to use the score to help you decide how much time to spend on this chapter. The answers are at the bottom of the page following the quiz, and the explanations are in DVD Appendix C and in the PCPT software.
1. An enterprise uses a dual-stack model of deployment for IPv4 and IPv6, using EIGRP as the routing protocol for both. Router R1 has IPv4 and IPv6 addresses on its G0/0 and S0/0/0 interfaces only, with EIGRP for IPv4 and EIGRP for IPv6 enabled on both interfaces. Which of the following answers is a valid way to configure R1 so that it enables EIGRP for IPv6 on the exact same interfaces as EIGRP for IPv4 in this case?
a. Adding the dual-stack all-interfaces router subcommand for EIGRP for IPv6
b. Adding the dual-stack interface subcommand to interfaces G0/0 and S0/0/0
c. Adding the ipv6 eigrp asn interface subcommand to interfaces G0/0 and S0/0/0
d. Adding the dual-stack all-interfaces router subcommand for EIGRP for IPv4
2. Which of the following configuration settings does not have a separate IPv4/EIGRP for IPv4 and IPv6/EIGRP for IPv6 setting, instead using one setting that both EIGRP for IPv4 and EIGRP for IPv6 use?
a. Interface bandwidth
b. Hello timer
c. Variance
d. Maximum paths
3. An enterprise uses a dual-stack model of deployment for IPv4 and IPv6, using EIGRP as the routing protocol for both. Router R1 has IPv4 and IPv6 addresses on its G0/0 and S0/0/0 interfaces only, with EIGRP for IPv4 and EIGRP for IPv6 enabled on both interfaces and the router ID explicitly set for both protocols. Comparing the EIGRP for IPv4 and EIGRP for IPv6 configuration, which of the following statements is true?
a. The EIGRP for IPv6 configuration uses the router eigrp asn global command.
b. Both protocols use the router-id router-id router subcommand.
c. Both protocols use the network network-number router subcommand.
d. The EIGRP for IPv6 configuration uses the ipv6 eigrp asn interface subcommand.
4. Three redundant IPv6 routes exist on R1 to reach IPv6 subnet 9 (2009:9:9:9::/64), a subnet connected to Router R9’s G0/0 interface. R1’s current successor route uses R2 as the next hop, with feasible successor routes through Routers R3 and R4. Then, another engineer makes changes to the configuration in the network, resulting in R1 having no routes to reach subnet 9. Which of the answers lists one configuration that would result in R1 having no routes at all to subnet 9?
a. Make R9’s G0/0 interface passive.
b. Change R2’s EIGRP ASN to some other number, but otherwise keep the same configuration.
c. Change the Hello timers on all of R1’s interfaces from 5 to 4.
d. Change R1’s EIGRP ASN to some other number, but otherwise keep the same configuration.
5. R1 and R2 are routers that connect to the same VLAN. Which of the answers list an item that can prevent the two routers from becoming EIGRP for IPv6 neighbors? (Choose two answers.)
a. Mismatched Hello timers
b. Mismatched ASNs
c. IPv6 addresses in different subnets
d. Using the same router ID
e. One passive router interface (used on this link)
6. The output of the show ipv6 eigrp neighbors command from R2 lists one neighbor. Which of the following answers is correct about the meaning of the output of the command in this example?
R2# show ipv6 eigrp neighbors
EIGRP-IPv6 Neighbors for AS(1)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 Link-local address: Gi0/0 11 06:46:11 1 100 0 30
FE80::FF:FE22.2222
a. The neighbor’s link-local address on its common link must be FE80::FF:FE22:2222.
b. The neighbor’s EIGRP for IPv6 router ID must be FE80::FF:FE22:2222.
c. R2’s link-local address on its common link must be FE80::FF:FE22:2222.
d. R2’s EIGRP for IPv6 router ID must be FE80::FF:FE22:2222.
Answers to the “Do I Know This Already?” quiz:
Foundation Topics
EIGRP for IPv6 Configuration
Internally, EIGRP for IPv6 behaves much like its IPv4 counterpart, EIGRP. Once enabled on all routers in an internetwork, the routers exchange EIGRP messages. Those messages allow the routers to discover neighbors, form neighbor relationships, advertise subnets along with their metric components, and calculate metrics for competing routes using the same old calculation. EIGRP for IPv6 also uses the same successor and feasible successor (FS) logic, and Diffusing Update Algorithm (DUAL) processing when no FS exists.
Differences do exist, of course, with the most obvious being that EIGRP for IPv6 advertises IPv6 prefixes, not IPv4 subnets. The messages flow in IPv6 packets, many going to IPv6 multicast address FF02::A. But most of the big ideas mirror EIGRP for IPv4.
As for configuration, EIGRP for IPv6 configuration looks much like the OSPFv3 configuration just discussed in Chapter 23. The EIGRP for IPv6 routing protocol process must be created, and then must be enabled on various interfaces using an interface subcommand. The rest of the EIGRP for IPv6 configuration is optional, to change some default setting, with changes to what happens between neighbors, what metric is calculated, and so on.
Note
This chapter shows one of two styles of EIGRP for IPv6 configuration called classic mode (also called autonomous system mode). EIGRP classic mode has existed since EIGRP for IPv6 first became available. The more involved EIGRP named mode, which uses address families, can be used as well but is not included in this book.
This first section first works through the most common EIGRP for IPv6 configuration commands, followed by a look at the various other commands used to change some small feature.
EIGRP for IPv6 Configuration Basics
EIGRP for IPv6 configuration works much like OSPFv3. That is, the commands create the EIGRP for IPv6 process in one part of the configuration, with interface subcommands enabling the routing protocol on the interface. Figure 24-1 shows the fundamentals of this core configuration for IPv6.
If you remember EIGRP for IPv4 configuration, you will quickly see one key difference between the configuration in Figure 24-1 and what you know about EIGRP for IPv4. The example in the figure does not use any EIGRP network commands at all because EIGRP for IPv6 does not even support the network command. Instead, it uses the ipv6 eigrp asn interface subcommand. This process works like the OSPFv3 configuration from the preceding chapter, just with a slightly different command for EIGRP for IPv6.
The rest of the EIGRP for IPv6 configuration commands work either exactly like the EIGRP for IPv4 commands or very similarly to them. To show the similarities, Table 24-2 lists the EIGRP for IPv4 configuration options introduced in Chapter 10, “Implementing EIGRP for IPv4,” making comparisons to the similar configuration options in EIGRP for IPv6.
EIGRP for IPv6 Configuration Example
To show EIGRP for IPv6 configuration in context, the next several pages show an example using the internetwork from Figure 24-2. The figure shows the IPv6 subnets. It also shows the last quartet of each router’s interface IPv6 address as ::X, where X is the router number, to make it more obvious as to which router uses which address.
Note that Figure 24-2 mimics Figure 10-3, a figure used in several EIGRP for IPv4 examples in Chapter 10. Figure 24-2 uses the exact same interface types and numbers and router names. In fact, it uses a similar subnet numbering pattern. For instance, think of the four LAN-based IPv6 subnets as subnets 1, 2, 3, and 33, based on the last quartet values. Those same subnets in the examples in Chapter 10, based on the third octet of the IPv4 subnet numbers, are also 1, 2, 3, and 33, respectively.
Why does it matter that the internetwork used for this chapter mirrors the one used in Chapter 10? Not only are the EIGRP configuration commands similar but also the show command output. The show commands in this chapter, by using the exact same network topology, list almost the exact same output for EIGRP for IPv6 as they did for EIGRP for IPv4.
For this specific example, Example 24-1 begins by listing the additional IPv6 configuration required on R1 to make it a dual-stack router, including EIGRP for IPv6 configuration. The highlighted lines are the EIGRP for IPv6–specific configuration commands, while the rest of the configuration adds IPv6 routing and addressing.
Example 24-1 IPv6 and EIGRP for IPv6 Configuration on Router R1
ipv6 unicast-routing
!
ipv6 router eigrp 1
eigrp router-id 1.1.1.1
!
interface GigabitEthernet0/0
ipv6 address 2001:db8:1:1::1/64
ipv6 eigrp 1
!
interface serial 0/0/0
description link to R2
ipv6 address 2001:db8:1:5::1/64
ipv6 eigrp 1
!
interface serial 0/0/1
description link to R3
ipv6 address 2001:db8:1:4::1/64
ipv6 eigrp 1
With this first example, take a few moments to review the configuration thoroughly. All the routers need to use the same EIGRP for IPv6 autonomous system number (ASN), as configured on the ipv6 router eigrp asn global command. Just after this command, R1 explicitly sets its EIGRP router ID (RID) using the eigrp router-id command. Note that EIGRP for IPv6 also uses a 32-bit RID, as does OSPFv3, with the same exact rules for how a router picks the value.
The rest of the configuration simply enables EIGRP for IPv6 on each interface by referring to the correct EIGRP for IPv6 process, by ASN, using the ipv6 eigrp asn interface subcommand.
Example 24-2 shows the configuration on a second router (R2). Note that it also uses ASN 1 because it must match the ASN used by Router R1. Otherwise, these two routers will not become neighbors. Also, note that R2 sets its RID to 2.2.2.2.
Example 24-2 EIGRP for IPv6 Configuration on R2
ipv6 unicast-routing
!
ipv6 router eigrp 1
eigrp router-id 2.2.2.2
!
interface GigabitEthernet0/0
ipv6 address 2001:db8:1:2::2/64
ipv6 eigrp 1
!
interface serial 0/0/0
description link to R3
ipv6 address 2001:db8:1:6::2/64
ipv6 eigrp 1
!
interface serial 0/0/1
description link to R1
ipv6 address 2001:db8:1:5::2/64
ipv6 eigrp 1
!
interface serial 0/1/0
description link to R4
ipv6 address 2001:db8:1:8::2/64
ipv6 eigrp 1
Note
IOS allows the EIGRP for IPv6 routing process to be disabled, and then reenabled, using the shutdown and no shutdown commands in EIGRP configuration mode. While enabled by default at later IOS versions, note that earlier IOS versions defaulted to a disabled state, requiring the configuration of a no shutdown command in EIGRP configuration mode before EIGRP for IPv6 would work.
Other EIGRP for IPv6 Configuration Settings
Examples 24-1 and 24-2 showed the basics for EIGRP for IPv6 configuration. The next few pages discuss a few configuration options in comparison to EIGRP for IPv4.
Setting Bandwidth and Delay to Influence EIGRP for IPv6 Route Selection
By default, EIGRP for IPv6 uses the exact same settings as EIGRP for IPv4 when calculating the metrics for each route. And to be extra clear, the settings are not similar or simply using the same command syntax. EIGRP for IPv6 uses the exact same settings as EIGRP for IPv4, specifically the interface bandwidth and delay settings, as configured with the bandwidth and delay interface subcommands. A change to these values impacts both EIGRP for IPv4’s calculation of metrics and EIGRP for IPv6’s calculation.
EIGRP for IPv6 also uses the exact same formula as EIGRP for IPv4 to calculate the metric for a route. As a result, in some conditions, the EIGRP for IPv4 metric for a route to an IPv4 subnet will be the same metric as the EIGRP for IPv6 route from the same router to IPv6 subnet in the same location.
For instance, in Figure 24-3, all the routers are dual-stack routers, with EIGRP for IPv4 and EIGRP for IPv6 enabled on all the interfaces in the design. Subnet 10.1.33.0/24 has been noted in the upper right, in the same location as IPv6 subnet 33 (2001:DB8:1:33::/64). R1’s EIGRP for IPv4 and EIGRP for IPv6 processes will calculate the same exact metric for these routes based on the same collection of interface bandwidth and delay settings.
Example 24-3 shows the IPv4 and IPv6 routes on R1 for the subnets shown in Figure 24-3. Note the highlighted metrics in all cases are 2,684,416.
Example 24-3 Identical Metrics for IPv4 and IPv6 Routes with EIGRP for IPv4 and EIGRP for IPv6
R1# show ip route | section 10.1.33.0
D 10.1.33.0/24 [90/2684416] via 10.1.5.2, 00:02:23, Serial0/0/0
[90/2684416] via 10.1.4.3, 00:02:23, Serial0/0/1
R1# show ipv6 route | section 2001:DB8:1:33::/64
D 2001:DB8:1:33::/64 [90/2684416]
via FE80::FF:FE00:3, Serial0/0/1
via FE80::FF:FE00:2, Serial0/0/0
Note that both commands list two equal-cost routes on R1, for subnet 33, but the format of the output differs a little. The format of the show ip route command puts the destination subnet on the same first line as the first route’s forwarding instructions. The show ipv6 route command lists the destination prefix on the first line, with each route’s forwarding instructions on the second and third lines, respectively.
EIGRP Load Balancing
EIGRP for IPv6 and EIGRP for IPv4 use the exact same concepts, with the exact same configuration command syntax, for equal-cost and unequal-cost load balancing. However, EIGRP for IPv6 has its own configuration settings, made with the maximum-paths and variance commands inside EIGRP for IPv6 configuration mode. EIGRP for IPv4 has separate settings, using these same two commands, in EIGRP for IPv4 configuration mode.
For example, imagine that in a dual-stack network, the routers use EIGRP for IPv4 and EIGRP for IPv6. The network engineer would probably choose the same variance and maximum-paths settings for both routing protocols. However, for the sake of pointing out the differences, imagine the engineer chose different settings, like these:
EIGRP for IPv4: At most 2 routes, with variance 3 for unequal cost routes
EIGRP for IPv6: At most 5 routes, with variance 4 for unequal cost routes
Example 24-4 shows how to make these different settings for these two different routing processes. However, note that the commands happen to use the exact same syntax.
Example 24-4 Setting Load-Balancing Parameters per Routing Process
R1# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
! First, configure the settings for IPv4
R1(config)# router eigrp 10
R1(config-router)# maximum-paths 2
R1(config-router)# variance 3
! Next, configure the similar settings for IPv6
R1(config-router)# ipv6 router eigrp 11
R1(config-rtr)# maximum-paths 5
R1(config-rtr)# variance 4
R1(config-rtr)# ^Z
R1#
EIGRP Timers
EIGRP for IPv6 and EIGRP for IPv4 use the exact same concepts for the Hello and hold timers as does EIGRP for IPv4. To allow these values to be set differently for each routing process, IOS gives us slightly different syntax on the EIGRP for IPv6 and EIGRP for IPv4 commands, with the EIGRP for IPv6 commands using the keyword ipv6 rather than ip. Otherwise, the EIGRP for IPv6 syntax mirrors the EIGRP for IPv4 version of the commands.
Example 24-5 shows a sample that changes both the EIGRP for IPv4 and EIGRP for IPv6 Hello timer, just to show the different commands side by side. For EIGRP for IPv4, the Hello timer is set to 6 seconds, and for EIGRP for IPv6, it is set to 7 seconds.
Example 24-5 Setting the EIGRP for IPv4 and EIGRP for IPv6 Hello Timers
R1# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)# interface gigabitethernet0/1
R1(config-if)# ip hello-interval eigrp 10 6
R1(config-if)# ipv6 hello-interval eigrp 11 7
R1(config-rtr)# ^Z
R1#
The choices for the timer values are arbitrary, just to make it clear which command is for each routing protocol. In real networks, these settings will likely have the same values for both EIGRP for IPv4 and EIGRP for IPv6.
EIGRP for IPv6 Verification and Troubleshooting
To the depth discussed in this book, EIGRP for IPv4 and EIGRP for IPv6 behave almost identically. Earlier, Table 24-2 listed the configuration commands, side by side, to show the similarities. This second major section of the chapter now looks at EIGRP for IPv6 verification and troubleshooting, with even more similarities between EIGRP for IPv6 and its older cousin EIGRP for IPv4.
So many similarities exist between EIGRP for IPv6 and EIGRP for IPv4 that you should just assume that they work the same, except for a few differences, as noted in the following list:
EIGRP for IPv6 advertises IPv6 prefixes, whereas EIGRP for IPv4 advertises IPv4 subnets.
EIGRP for IPv6 show commands use a keyword of ipv6, in the same position where EIGRP show commands use a keyword of ip.
EIGRP for IPv6 uses the same checklist for choosing whether to become neighbors, except EIGRP for IPv6 routers may become neighbors if they have IPv6 addresses in different subnets. (EIGRP for IPv4 neighbors must be in the same IPv4 subnet.)
EIGRP for IPv6 does not have an autosummary concept (while EIGRP for IPv4 does).
As you can see, the list of differences mentioned here is short. The similarities will become clearer through the many examples of show command output in the remainder of this chapter. To begin, Figure 24-4 reviews the EIGRP for IPv6 show commands discussed in this chapter. Note that all the commands in the figure use the same syntax as the EIGRP for IPv4 equivalent but with ip changed to ipv6.
Similar to the preceding chapter’s flow, this chapter’s second major section breaks the discussion down in the same general sequence as EIGRP for IPv6 does when bringing up the EIGRP for IPv6 process. This section first examines EIGRP for IPv6 interfaces, then neighbors, topology, and finally, IPv6 routes.
All the troubleshooting examples in the rest of this chapter use the example configuration from Routers R1, R2, R3, and R4, as shown in Figure 24-2.
EIGRP for IPv6 Interfaces
By enabling EIGRP for IPv6 on an interface, the router attempts to do two things:
1. Discover EIGRP for IPv6 neighbors off that interface
2. Advertise about the prefix connected to that interface
To make sure that EIGRP for IPv6 works correctly, an engineer should verify that EIGRP for IPv6 is enabled on the right interfaces. Or, from a troubleshooting perspective, one of the most common problems with EIGRP for IPv6 may be that a router did not enable EIGRP for IPv6 on an interface.
As was the case for EIGRP for IPv4, with EIGRP for IPv6, some commands list all interfaces on which EIGRP is enabled (including passive), some list all EIGRP interfaces but note which are passive, and some simply do not list the passive interfaces. Example 24-6 shows a sample that points out these differences, by first making R1’s G0/0 interface passive. It then lists output from the show ipv6 eigrp interfaces command, which omits G0/0, and then the show ipv6 protocols command, which includes G0/0, but noted as a passive interface.
Example 24-6 Verifying OSPFv3 Interfaces and Related Parameters
R1# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)# ipv6 router eigrp 1
R1(config-rtr)# passive-interface g0/0
R1(config-rtr)# ^Z
R1#
R1# show ipv6 eigrp interfaces
EIGRP-IPv6 Interfaces for AS(1)
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0/0/0 1 0/0 1 0/15 50 0
Se0/0/1 1 0/0 1 0/15 50 0
R1# show ipv6 protocols
IPv6 Routing Protocol is "connected"
IPv6 Routing Protocol is "eigrp 1"
EIGRP-IPv6 Protocol for AS(1)
Metric weight K1=1, K2=0, K3=1, K4=0, K5=0
NSF-aware route hold timer is 240
Router-ID: 1.1.1.1
Topology: 0 (base)
Active Timer: 3 min
Distance: internal 90 external 170
Maximum path: 16
Maximum hopcount 100
Maximum metric variance 1
Interfaces:
Serial0/0/0
Serial0/0/1
GigabitEthernet0/0 (passive)
Redistribution:
None
IPv6 Routing Protocol is "ND"
Note that the show ipv6 eigrp interfaces command lists many lines of output per interface. Also, like the show ipv6 protocols command, it lists all EIGRP-enabled interfaces, including passive interfaces.
Next, focus for a moment on troubleshooting related to EIGRP for IPv6 interfaces. As with OSPF, most troubleshooting revolves around the neighbor relationships. However, this short list describes two problems that can happen related to the interfaces:
The omission of an ipv6 eigrp asn interface subcommand on an interface that has no possible neighbors may go overlooked. This omission does not impact EIGRP for IPv6 neighbors. However, this omission means that EIGRP for IPv6 is not enabled on that interface, and therefore the router will not advertise about that connected subnet. This problem shows up as a missing route.
Making an interface passive to the EIGRP for IPv6 process, when a potential EIGRP for IPv6 neighbor is connected to that link, prevents the two routers from becoming neighbors. Note that the neighbor relationship fails with just one of the two routers having a passive interface.
For example, consider Router R4 in this chapter’s sample network. Its G0/0 interface connects to a LAN, with no other routers. Currently, R4’s configuration includes the ipv6 eigrp 1 interface subcommand on R4’s G0/0 interface. If instead that command were mistakenly missing (or if it were just removed as an experiment in lab), R4 would not advertise a route for the connected subnet (subnet 33, or 2001:DB8:1:33::/64).
Example 24-7 shows that specific example. To re-create the problem, though, before gathering the output in Example 24-7 on R4, the no ipv6 eigrp 1 command was issued on R4’s G0/0 interface, disabling EIGRP from that interface. Example 24-7 then shows R1 does not have a route to subnet 33 or EIGRP topology data.
Example 24-7 Missing Route to Subnet 33 on R1
R1# show ipv6 route 2001:DB8:1:33::
% Route not found
R1# show ipv6 eigrp topology | include 2001:DB8:1:33
R1#
EIGRP for IPv6 Neighbors
From one perspective, EIGRP neighbor relationships are simple. When two EIGRP for IPv6 routers sit on the same data link, they discover each other with EIGRP for IPv6 Hello messages. Those Hello messages list some parameters, and the neighbors check the Hello to determine whether the routers should become neighbors:
If the parameters match, each router adds the other router to their EIGRP for IPv6 neighbor table, as listed with the show ipv6 eigrp neighbors command.
If the parameters do not match, the routers do not become neighbors, do not add each other to their neighbor tables, and do not list each other in the output of the show ipv6 eigrp neighbors command.
From another perspective, troubleshooting EIGRP neighbor relationships means that you have to remember a lot of small details. The neighbors check lists of parameters that must match. At the same time, other problems can prevent the routers from becoming neighbors as well. Thankfully, EIGRP for IPv6 uses the same list as EIGRP for IPv4, with one noticeable difference: EIGRP for IPv6 does not require the neighbors to be in the same subnet.
Table 24-3 lists the items to consider when troubleshooting EIGRP neighbor relationships.
For instance, in the configuration example in this chapter, all four routers use EIGRP for IPv6 ASN 1. However, suppose that Router R2’s configuration had mistakenly used ASN 2, while the other three routers correctly used ASN 1. What would happen? R2 would have failed to form a neighbor relationship with any of the other routers.
Many EIGRP for IPv6 show commands mention the EIGRP for IPv6 ASN, but the show ipv6 protocols command shows the value in a couple of obvious places. Example 24-6, earlier, shows this.
As a troubleshooting strategy for the exam, note that every pair of EIGRP for IPv6 routers on the same link should become neighbors. So, when an exam question appears to point to some IPv6 routing problem, check the routers, count the EIGRP neighbor relationships, and make sure all the neighbor relationships exist. If any are missing, start troubleshooting EIGRP for IPv6 neighbor relationships based on Table 24-3.
To examine the neighbors, use the show ipv6 eigrp neighbors command. Because of the length of IPv6 addresses, this command lists two lines per neighbor rather than one line (as is the case with the EIGRP for IPv4 version of this command). The output in Example 24-8 shows this command’s output from Router R2, with highlights in two lines for a single neighbor (R3).
Example 24-8 R2’s EIGRP for IPv6 Neighbors
R2# show ipv6 eigrp neighbors
EIGRP-IPv6 Neighbors for AS(1)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
2 Link-local address: Se0/1/0 10 06:37:34 104 624 0 13
FE80::D68C:B5FF:FE6B:DB48
1 Link-local address: Se0/0/0 11 06:37:54 1 100 0 38
FE80::FF:FE00:3
0 Link-local address: Se0/0/1 11 06:46:11 1 100 0 30
FE80::FF:FE00:1
Take a moment to focus on the IPv6 address and interface listed in the highlighted two lines. The output, taken from Router R2, lists R3’s link-local address that sits on the other end of R2’s S0/0/0 interface. The listed S0/0/0 interface is R2’s interface. In summary, the details list the local router’s interface and the neighbor’s link-local address. So, to identify the EIGRP for IPv6 neighbor, you have to use that neighbor’s link-local address (and not their EIGRP for IPv6 RID).
EIGRP for IPv6 Topology Database
If you keep the discussions to topics within the scope of this book, once EIGRP for IPv6 routers become neighbors, they should exchange all appropriate topology data. Outside the scope of this book, other router features can filter the topology data sent between routers. But for now, if the neighbor comes up, you can assume they exchange the topology data.
However, you should be ready to interpret the meaning of some of the topology data described by EIGRP for IPv6. Thankfully, the EIGRP for IPv6 topology data works just like it does for EIGRP for IPv4, other than one obvious difference: It lists IPv6 prefixes. The following list points out the concepts that remain identical between the two:
The metric components (bandwidth, delay, reliability, load)
The metric calculation
The idea of a successor route (the best route)
The idea of FS routes
The feasibility condition, in which the reported distance (the composite metric reported by the neighbor) is lower (better) than the local router’s metric
For example, Figure 24-5 shows an excerpt from the output of the show ipv6 eigrp topology command. This output shows R1’s topology data for subnet 3 (2001:DB8:1:3::/64), the subnet off R3’s G0/0 LAN interface. The left side shows the two details particular to IPv6: the IPv6 prefix/length and the next-hop router’s link-local address.
Note that while the left side shows the IPv6 prefix and IPv6 next-hop router address, the right side shows the exact same ideas as used with EIGRP for IPv4. In fact, this example mirrors an example back in Chapter 10, shown there as Figure 10-4. That chapter also showed topology data from R1’s database for the subnet off R3’s G0/0 LAN interface. However, that example was for EIGRP for IPv4 and for subnet 10.1.3.0/24. If you take the time to flip back to Figure 10-4, you will see the exact same information for all the data on the right based on the EIGRP for IPv4 topology database, but IPv4 information about the subnet, mask, and next-hop address on the left.
In short, study the Chapter 10 details about the metric components, the metric computed as a formula, the successor and FS, and so on. If you master those details for EIGRP for IPv4, you have mastered the equivalent for EIGRP for IPv6.
Example 24-9 shows the EIGRP topology table for one last insight into the internals of EIGRP for IPv6. The output shows R1’s detailed topology data for subnet 3 (2001:DB8:1:3::/64). Note that the first highlighted line lists the next-hop address and outgoing interface. It lists the composite metric—that is, the metric as calculated from the input of the various metric components—on the second highlighted line. The next two highlighted lines show the two metric components that impact the calculation (by default): bandwidth and delay. Finally, note that it mentions that EIGRP uses the minimum bandwidth (1544 Kbps) and the total delay (20,100).
Example 24-9 R2’s EIGRP for IPv6 Neighbors
R1# show ipv6 eigrp topology 2001:DB8:1:3::/64
EIGRP-IPv6 Topology Entry for AS(1)/ID(1.1.1.1) for 2001:DB8:1:3::/64
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2172416
Descriptor Blocks:
FE80::FF:FE00:3 (Serial0/0/1), from FE80::FF:FE00:3, Send flag is 0x0
Composite metric is (2172416/28160), route is Internal
Vector metric:
Minimum bandwidth is 1544 Kbit
Total delay is 20100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
Originating router is 3.3.3.3
FE80::FF:FE00:2 (Serial0/0/0), from FE80::FF:FE00:2, Send flag is 0x0
Composite metric is (2684416/2172416), route is Internal
Vector metric:
Minimum bandwidth is 1544 Kbit
Total delay is 40100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 2
EIGRP for IPv6 Routes
Verifying EIGRP for IPv6–learned routes is relatively easy as long as you realize that the code for EIGRP is D and not E. Example 24-10 shows R1’s entire IPv6 routing table, with six EIGRP-learned IPv6 routes.
Example 24-10 EIGRP for IPv6 Routes on R1
R1# show ipv6 route
IPv6 Routing Table - default - 13 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, R - RIP, I1 - ISIS L1, I2 - ISIS L2
IA - ISIS interarea, IS - ISIS summary, D - EIGRP, EX - EIGRP external
ND - Neighbor Discovery, l - LISP
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
C 2001:DB8:1:1::/64 [0/0]
via GigabitEthernet0/0, directly connected
L 2001:DB8:1:1::1/128 [0/0]
via GigabitEthernet0/0, receive
D 2001:DB8:1:2::/64 [90/2172416]
via FE80::FF:FE00:2, Serial0/0/0
D 2001:DB8:1:3::/64 [90/2172416]
via FE80::FF:FE00:3, Serial0/0/1
C 2001:DB8:1:4::/64 [0/0]
via Serial0/0/1, directly connected
L 2001:DB8:1:4::1/128 [0/0]
via Serial0/0/1, receive
C 2001:DB8:1:5::/64 [0/0]
via Serial0/0/0, directly connected
L 2001:DB8:1:5::1/128 [0/0]
via Serial0/0/0, receive
D 2001:DB8:1:6::/64 [90/2681856]
via FE80::FF:FE00:3, Serial0/0/1
via FE80::FF:FE00:2, Serial0/0/0
D 2001:DB8:1:7::/64 [90/2681856]
via FE80::FF:FE00:3, Serial0/0/1
D 2001:DB8:1:8::/64 [90/2681856]
via FE80::FF:FE00:2, Serial0/0/0
D 2001:DB8:1:33::/64 [90/2684416]
via FE80::FF:FE00:3, Serial0/0/1
via FE80::FF:FE00:2, Serial0/0/0
L FF00::/8 [0/0]
via Null0, receive
The pair of highlighted lines about halfway through the example describes the one route to IPv6 subnet 3 (2001:DB8:1:3::/64). Each route lists at least two lines, with the first line listing the prefix/length and, in brackets, the administrative distance and the metric (feasible distance). The second line lists the forwarding instructions for a route.
When a router has multiple routes to reach one IPv6 prefix, the output shows one line with the prefix and then one line for each route. The line for each route lists the forwarding instructions (neighbor’s link-local address and local router’s outgoing interface). The highlighted lines at the end of the example, for subnet 33, show one such example, with two routes, each with a different next-hop address and different outgoing interface.
As for troubleshooting IPv6 routes, again, most of the troubleshooting for routes begins with questions about neighbors. Thinking through a potential EIGRP for IPv6 problem actually follows the same logic as working through an OSPFv3 problem. Repeating some of the logic from the preceding chapter, when a router simply has no route to a given subnet—for instance, if R1 had no route at all for subnet 33—then do the following:
Step 1. Check the routers with interfaces directly connected to that IPv6 prefix. A router must have EIGRP for IPv6 enabled on that interface before EIGRP for IPv6 will advertise about the subnet.
Step 2. Check EIGRP for IPv6 neighbor relationships for all routers between the local router and the routers with an interface connected to IPv6 prefix X.
For instance, in Figure 24-2, if Router R4 did not have an ipv6 eigrp 1 command under its G0/0 interface, all the routers would have their correct EIGRP for IPv6 neighbor relationships, but R4 would not advertise about subnet 33.
If a router has a route but it appears to be the wrong (suboptimal) route, take these steps:
Step 1. Check for broken neighbor relationships over what should be the optimal path from the local router and prefix Y.
Step 2. Check the interface bandwidth and delay settings. Pay particular attention to the lowest bandwidth in the end-to-end route, because EIGRP ignores the faster bandwidths, using only the lowest (slowest) bandwidth in its metric calculation.
Chapter Review
One key to doing well on the exams is to perform repetitive spaced review sessions. Review this chapter’s material using either the tools in the book, DVD, or interactive tools for the same material found on the book’s companion website. Refer to the “Your Study Plan” element for more details. Table 24-4 outlines the key review elements and where you can find them. To better track your study progress, record when you completed these activities in the second column.
Review All the Key Topics
Key Terms You Should Know
Command References
Tables 24-6 and 24-7 list configuration and verification commands used in this chapter. As an easy review exercise, cover the left column in a table, read the right column, and try to recall the command without looking. Then repeat the exercise, covering the right column, and try to recall what the command does.
Table 24-6 Chapter 24 Configuration Command Reference
Table 24-7 Chapter 24 show Command Reference