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Cisco originally created EIGRP to advertise routes for IPv4, IPX, and AppleTalk. This
original EIGRP architecture easily allowed for yet another Layer 3 protocol, IPv6, to be
added. As a result, Cisco did not have to change EIGRP significantly to support IPv6, so
many similarities exist between the IPv4 and IPv6 versions of EIGRP.
Note: Many documents, including this chapter, refer to the IPv6 version of EIGRP as
EIGRP for IPv6. However, some documents at www.cisco.com also refer to this protocol
as EIGRPv6, not because it is the sixth version of the protocol, but because it implies a
relationship with IPv6.
As with the previous section “RIP Next Generation (RIPng),” this section begins with a
discussion of the similarities and differences between the IPv4 and IPv6 versions of
EIGRP. The remaining coverage of EIGRP focuses on the changes to EIGRP configuration
and verification in support of IPv6.
EIGRP for IPv4 and IPv6–Theory and Comparisons
For the most part, EIGRP for IPv4 and for IPv6 have many similarities. The following list
outlines some of the key differences:
■ EIGRP for IPv6 advertises IPv6 prefixes/lengths, rather than IPv4 subnet/mask information.
■ EIGRP for IPv6 uses the neighbor’s link local address as the next-hop IP address;
EIGRP for IPv4 has no equivalent concept.
■ EIGRP for IPv6 encapsulates its messages in IPv6 packets, rather than IPv4 packets.
■ Like RIPng and OSPFv3, EIGRP for IPv6 authentication relies on IPv6’s built-in authentication
and privacy features.
■ EIGRP for IPv4 defaults to use automatic route summarization at the boundaries of
classful IPv4 networks; IPv6 has no concept of classful networks, so EIGRP for IPv6
cannot perform any automatic summarization.
■ EIGRP for IPv6 does not require neighbors to be in the same IPv6 subnet as a requirement
to become neighbors.
Other than these differences, most of the details of EIGRP for IPv6 works like EIGRP for
IPv4. For reference, Table 17-5 compares the features of each.
Key
Topic
Table 17-5 Comparing EIGRP for IPv4 and IPv6
Feature EIGRP for
IPv4
EIGRP for IPv6
Advertises routes for... IPv4 IPv6
Layer 3 protocol for EIGRP messages IPv4 IPv6
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Table 17-5 Comparing EIGRP for IPv4 and IPv6
Feature EIGRP for
IPv4
EIGRP for IPv6
Layer 3 header protocol type 88 88
UDP Port N/A N/A
Uses Successor, Feasible Successor logic Yes Yes
Uses Dual Yes Yes
Supports VLSM Yes Yes
Can perform automatic summarization Yes N/A
Uses triggered updates Yes Yes
Uses composite metric, default using bandwidth and
delay
Yes Yes
Metric meaning infinity 232 – 1 232 – 1
Supports route tags Yes Yes
Multicast Update destination 224.0.0.10 FF02::10
Authentication EIGRP-specific Uses IPv6
AH/ESP
Configuring EIGRP for IPv6
EIGRP for IPv6 follows the same basic configuration style as for RIPng, plus a few additional
steps, as follows:
Step 1. Enable IPv6 routing with the ipv6 unicast-routing global command.
Step 2. Enable EIGRP using the ipv6 router eigrp {1 – 65535} global configuration
command.
Step 3. Enable IPv6 on the interface, typically with one of these two methods:
Configure an IPv6 unicast address on each interface, using the ipv6
address address/prefix-length [eui-64] interface command.
Configure the ipv6 enable command, which enables IPv6 and causes the
router to derive its link local address.
Step 4. Enable EIGRP on the interface with the ipv6 eigrp asn interface subcommand
(where the name matches the ipv6 router eigrp asn global configuration
command).
Step 5. Enable EIGRP for IPv6 with a no shutdown command while in EIGRP configuration
mode.
Step 6. If no EIGRP router ID has been automatically chosen, due to not having at
least one working interface with an IPv4 address, configure an EIGRP router
ID with the eigrp router-id rid command in EIGRP configuration mode.
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Note: For a complete discussion of options for enabling IPv6 on an interface, as mentioned
at Step 3, refer to Chapter 16’s Table 16-11.
The first four steps essentially mirror the four steps in the RIPng configuration process previously
listed in this chapter. The same interdependencies exist for EIGRP for IPv6 as well;
in particular, the command at Step 2 works only if Step 1’s command has been configured,
and the command at Step 4 fails if the command at Step 3 has not yet been completed.
EIGRP for IPv6 requires Steps 5 and 6, whereas RIPng does not need equivalent steps.
First, at Step 5, IOS supports the ability to stop and start the EIGRP process with the
shutdown and no shutdown router mode subcommands. After initial configuration, the
EIGRP for IPv6 process starts in shutdown mode, so to make the process start, IOS requires
a no shutdown command.
Step 6 shows the other difference as compared to RIPng configuration, but this step may
or may not be needed. The EIGRP for IPv6 process must have a router ID (RID) before the
process works. EIGRP for IPv6 uses the same process as EIGRP for IPv4 for choosing the
RID. The EIGRP for IPv6 RID is indeed a 32-bit number, with two of the EIGRP RID decision
steps based on IPv4 configuration. The following list defines how EIGRP for IPv6
picks its RID, listed in the order of preference:
Step 1. Use the configured value (using the eigrp router-id a.b.c.d EIGRP subcommand
under the ipv6 router eigrp command).
Step 2. Use the highest IPv4 address on an up/up loopback interface.
Step 3. Use the highest IPv4 address on an up/up nonloopback interface.
Note that although most installations already have IPv4 addresses configured, it is possible
that the EIGRP for IPv6 process cannot derive a RID value. If the router has no working
interfaces that have IPv4 addresses, and the EIGRP for IPv6 RID is not explicitly
configured, then the EIGRP for IPv6 process simply does not work. So, the six-step configuration
process includes a mention of the EIGRP RID; more generally, it may be prudent
to configure a RID explicitly as a matter of habit.
After being enabled on an interface, EIGRP for IPv6 performs the same two basic tasks as
it does with EIGRP for IPv4: it discovers neighbors and advertises about connected subnets.
EIGRP for IPv6 uses the same set of neighbor checks as do routers using EIGRP for
IPv4, except that EIGRP for IPv6 does not require that neighboring IPv6 routers have IPv6
addresses in the same subnet. (See Table 2-4 in Chapter 2, “EIGRP Overview and Neighbor
Relationships,” for the list of neighbor validations performed by EIGRP for IPv4).
Also, as with EIGRP for IPv4, EIGRP for IPv6 advertises about any and all connected subnets
on the interface, with the exception of the link local addresses and the local routes
(the host routes for a router’s own interface IPv6 addresses).
Example 17-3 shows a sample configuration on Router R1 from Figure 17-1. All neighboring
routers must use the same ASN; ASN 9 will be used in this case.
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Example 17-3 Configuring EIGRP for IPv6 Routing and Routing Protocols on R1
R1# show running-config
! output is edited to remove lines not pertinent to this example
! Configuration step 1: enabling IPv6 routing
ipv6 unicast-routing
! Next, configuration steps 3 and 4, on 5 different interfaces
interface FastEthernet0/0.1
ipv6 address 2012::1/64
ipv6 eigrp 9
!
interface FastEthernet0/0.2
ipv6 address 2017::1/64
ipv6 eigrp 9
!
interface FastEthernet0/1.18
ipv6 address 2018::1/64
ipv6 eigrp 9
!
interface Serial0/0/0.3
ipv6 address 2013::1/64
ipv6 eigrp 9
!
interface Serial0/0/0.4
ipv6 address 2014::1/64
ipv6 eigrp 9
!
interface Serial0/0/0.5
ipv6 address 2015::1/64
ipv6 eigrp 9
!
! Configuration steps 2, 5, and 6
ipv6 router eigrp 9
no shutdown
router eigrp 10.10.34.3
Verifying EIGRP for IPv6
The EIGRP for IPv6 show commands generally list the same kinds of information as the
equivalent commands for EIGRP for IPv4, even more so than RIPng. In most cases, simply
use the same show ip... commands applicable with IPv4 and EIGRP, and substitute ipv6
instead of ip. Table 17-6 lists a cross-reference comparing the most popular EIGRP-related
commands for both versions. Note that the table assumes that the commands begin either
show ip or show ipv6 in all but the last row of the table.
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Example 17-4 shows a few sample show commands taken from Router R3 in the internetwork
shown in Figure 17-1. The explanatory comments are listed within the example in
this case.
Example 17-4 IPv6 EIGRP show Commands
! On R3, as when using RIPng, the next-hop address is the
! link-local address of the next router.
R3# show ipv6 route 2099::/64
Routing entry for 2099::/64
Known via “eigrp 9”, distance 90, metric 2174976, type internal
Route count is 2/2, share count 0
Routing paths:
FE80::22FF:FE22:2222, Serial0/0/0.2
Last updated 00:24:32 ago
FE80::11FF:FE11:1111, Serial0/0/0.1
Last updated 00:07:51 ago
! Note that the next command lists only EIGRP-learned routes. It lists
! two next-hops for 2099::64. Note the next-hop information lists
! link-local addresses.
R3# show ipv6 route eigrp
IPv6 Routing Table - Default - 19 entries
Table 17-6 Comparing EIGRP Verification Commands: show ip and show ipv6...
Function show ip... show ipv6...
All routes ... route ... route
All EIGRP learned routes ... route eigrp ... route eigrp
Details on the routes for a specific
prefix
... route subnet mask ... route prefix/length
Interfaces on which EIGRP is
enabled, plus metric weights,
variance, redistribution, maxpaths,
admin distance
... protocols ... protocols
List of routing information
sources
... protocols
... eigrp neighbors
... eigrp neighbors
Hello interval ... eigrp interfaces detail ... eigrp interfaces detail
EIGRP database ... eigrp topology [all-links] ... eigrp topology [all-links]
Debug that displays sent and received
Updates
debug ip eigrp notifications
debug ipv6 eigrp notifications
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Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, M - MIPv6, R - RIP, I1 - ISIS L1
I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary, D - EIGRP
EX - EIGRP external
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
D 2005::/64 [90/2684416]
via FE80::11FF:FE11:1111, Serial0/0/0.1
via FE80::22FF:FE22:2222, Serial0/0/0.2
D 2012::/64 [90/2172416]
via FE80::22FF:FE22:2222, Serial0/0/0.2
via FE80::11FF:FE11:1111, Serial0/0/0.1
D 2014::/64 [90/2681856]
via FE80::11FF:FE11:1111, Serial0/0/0.1
D 2015::/64 [90/2681856]
via FE80::11FF:FE11:1111, Serial0/0/0.1
! lines omitted for brevity...
D 2099::/64 [90/2174976]
via FE80::22FF:FE22:2222, Serial0/0/0.2
via FE80::11FF:FE11:1111, Serial0/0/0.1
! show ipv6 protocols displays less info than its IPv4 cousin.
R3# show ipv6 protocols
IPv6 Routing Protocol is “eigrp 9”
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Interfaces:
FastEthernet0/0
Serial0/0/0.1
Serial0/0/0.2
Redistribution:
None
Maximum path: 16
Distance: internal 90 external 170
! This command lists the equivalent of the information in the
! show ip protocols commands’ “Routing Information Sources” heading.
! Note the link local addresses are listed.
R3# show ipv6 eigrp neighbors
IPv6-EIGRP neighbors for process 9
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 Link-local address: Se0/0/0.2 14 01:50:51 3 200 0 82
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FE80::22FF:FE22:2222
0 Link-local address: Se0/0/0.1 13 01:50:52 14 200 0 90
FE80::11FF:FE11:1111
! The next command lists the EIGRP topology database, including
! feasible distance calculations, reported distance, and listing
! all successor and feasible successor routes.
R3# show ipv6 eigrp topology
IPv6-EIGRP Topology Table for AS(9)/ID(10.10.34.3)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 2005::/64, 2 successors, FD is 2684416
via FE80::11FF:FE11:1111 (2684416/2172416), Serial0/0/0.1
via FE80::22FF:FE22:2222 (2684416/2172416), Serial0/0/0.2
P 2012::/64, 2 successors, FD is 2172416
via FE80::11FF:FE11:1111 (2172416/28160), Serial0/0/0.1
via FE80::22FF:FE22:2222 (2172416/28160), Serial0/0/0.2
P 2013::/64, 1 successors, FD is 2169856
via Connected, Serial0/0/0.1
! lines omitted for brevity
P 2099::/64, 2 successors, FD is 2174976
via FE80::11FF:FE11:1111 (2174976/30720), Serial0/0/0.1
via FE80::22FF:FE22:2222 (2174976/30720), Serial0/0/0.2
! Finally, the link-local address of neighbor R1 is identified.
R3# show cdp entry R1
————————————-
Device ID: R1
Entry address(es):
IP address: 10.10.13.1
IPv6 address: 2013::1 (global unicast)
IPv6 address: FE80::11FF:FE11:1111 (link-local)
Platform: Cisco 1841, Capabilities: Router Switch IGMP
Interface: Serial0/0/0.1, Port ID (outgoing port): Serial0/0/0.3
! lines omitted for brevity
The most notable fact listed in the example is that the output confirms that little difference
exists with the show commands for EIGRP for IPv4 versus IPv6. The main differences
relate to the show ip protocols/show ipv6 protocols commands and that EIGRP for
IPv6 uses a link-local IP address for the next hop of each route.
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